Marie Chédru
email: marie.chedru@unilasalle.fr

Catherine Delhoume

How does studying abroad affect engineering students' intercultural competence: A longitudinal case study

Keywords: Intercultural competence, engineering students, study abroad, cultural intelligence, longitudinal study ORCID

How does studying abroad affect engineering students' intercultural competence: A longitudinal case study

Marie Chédru, Catherine

Introduction

Engineers are increasingly exposed to cross-cultural cooperation. Whether as expatriates or members of multinational teams, engineers are expected to work effectively in intercultural environments [START_REF] Gash | Cultural Intelligence: Engineering Success For A Flat World[END_REF]. As a result, intercultural competence (IC), "the complex abilities that are required to perform effectively and appropriately when interacting with others who are linguistically and culturally different from oneself" (Fantini, 2009, p. 458), has become key to an engineer's success in today's global society [START_REF] Cti | Références et orientations de la Commission des titres d'ingénieur -Référentiel Critères majeurs d'accréditation -Version[END_REF][START_REF] Rico-García | Intercultural communication in engineering studies: a key competence in global labour markets[END_REF]. Helping engineering students develop their IC has thus taken on increased importance in engineering education [START_REF] Cti | Références et orientations de la Commission des titres d'ingénieur -Référentiel Critères majeurs d'accréditation -Version[END_REF][START_REF] Weisser | Former aux compétences interculturelles en école d'ingénieur[END_REF]. Study abroad is generally considered one of the most effective means for increasing IC (e.g. [START_REF] Deardorff | Identification and assessment of intercultural competence as a student outcome of internationalization[END_REF]. Foreign language acquisition and the development of intercultural communicative competence are regarded as the two major benefits of studying abroad [START_REF] Guo | Intercultural communicative competence, language proficiency, and study abroad[END_REF]. Through international academic mobility, students also improve their self-efficacy [START_REF] Cushner | Overseas Student Teaching: Affecting Personal, Professional, and Global Competencies in an Age of Globalization[END_REF][START_REF] Petersdotter | International experience makes a difference: Effects of studying abroad on students' self-efficacy[END_REF] and their tolerance of ambiguity [START_REF] Dewaele | Is multilingualism linked to a higher tolerance of ambiguity?[END_REF]. They demonstrate a greater intercultural awareness [START_REF] Anderson | Short-term study abroad and intercultural sensitivity: A pilot study[END_REF] and openness to cultural diversity, resulting in globally-minded individuals [START_REF] Clarke | Student Intercultural Proficiency From Study Abroad Programs[END_REF].

Even though study abroad programs have recently taken on increased importance in engineering education, engineering students have historically been underrepresented in such programs [START_REF] Davis | Impact of a Global Engineering Course on Student Cultural Intelligence and Cross-Cultural Communication[END_REF]. Therefore, research is still scarce about how a period of studying abroad influences the development of engineering students' IC [START_REF] Berka | The Role of Study Abroad Curricular Interventions in Engineering Students' Intercultural Competence Development[END_REF][START_REF] Chédru | The effect of study abroad and personality on cultural intelligence: A deeper understanding using the expanded model of cultural intelligence[END_REF][START_REF] Ortiz-Marcos | Assessment of Global Competence of Engineers for a Sustainable World. Evidence from TA VIE Project[END_REF]. To fill this gap, this study investigates the effect of a study abroad semester on the development of engineering students' IC. The objective is to examine whether there is a significant increase observed in students' IC after their study abroad semester compared to pre-departure.

2. Literature review 2.1. Intercultural competence: definition and assessment tools 2.1.1. Defining intercultural competence [START_REF] Trompenaars | Research Application: Toward a General Framework of Competence for Today's Global Village[END_REF] define IC as the "capability of successful communication and effective collaboration with people of other cultures through recognition of differences and respect for other points of view" (p. 443). Due to its complexity, countless frameworks were used to grasp the notion of IC. The terms used to refer to this concept vary by discipline and approach [START_REF] Deardorff | Assessing intercultural competence[END_REF]. For example, from a review of the literature on cross-cultural adaptability and intercultural relations (Van der Zee et al., 2013), [START_REF] Van Der Zee | The Multicultural Personality Questionnaire: Reliability and Validity of Self-and Other Ratings of Multicultural Effectiveness[END_REF] identified five personality dimensions that make up IC: cultural empathy, open-mindedness, social initiative, emotional stability, and flexibility. From another perspective, [START_REF] Earley | Cultural intelligence: individual interactions across cultures[END_REF] introduced the concept of cultural intelligence (CQ) based on contemporary theories of intelligence [START_REF] Ang | Cultural intelligence: Its measurement and effects on cultural judgment and decision making, cultural adaptation and task performance[END_REF]. CQ refers to an individual's capability to deal effectively in situations characterised by cultural diversity. It comprises four primary factors: metacognitive, cognitive, motivational, and behavioural CQ.

While cross-cultural adaptability and CQ both relate to IC, they, however, highlight different aspects of this construct. Thus, by attending to the different facets of IC, this study aims to gain a more comprehensive understanding of engineering students' IC development during their study abroad experience.

Assessment of intercultural competence

In their review of measures for assessing cross-cultural competence, Matsumoto and Hwang (2013, p. 867) identified the Multicultural Personality Questionnaire (MPQ) by [START_REF] Van Der Zee | The Multicultural Personality Questionnaire: Reliability and Validity of Self-and Other Ratings of Multicultural Effectiveness[END_REF] and the Cultural Intelligence Scale (CQS) by [START_REF] Ang | Cultural intelligence: Its measurement and effects on cultural judgment and decision making, cultural adaptation and task performance[END_REF] as two of the most promising instruments.

Multicultural personality and the Multicultural Personality Questionnaire

The Multicultural Personality Questionnaire (MPQ) assesses personality dimensions that are of relevance to intercultural success. It includes scales for cultural empathy, openmindedness, social initiative, emotional stability, and flexibility. Cultural empathy is defined as "the capacity to clearly project an interest in others as well as to obtain and to reflect a reasonably complete and accurate sense of another's thoughts, feelings, and/or experiences" [START_REF] Ruben | Assessing Communication Competency for Intercultural Adaptation[END_REF]cited in Van der Zee & Van Oudenhoven, 2001, p. 279). Open-mindedness refers to an "open and unprejudiced attitude toward cultural differences" (Van der Zee et al., 2013, p. 118). Social initiative is defined as the ability to take initiative and be active in social situations [START_REF] Van Oudenhoven | Predicting multicultural effectiveness of international students: the Multicultural Personality Questionnaire[END_REF]. Emotional stability reflects an ability to remain calm in new and stressful situations (Van der Zee et al., 2013). Flexibility refers to "interpreting novel situations as a positive challenge and adapting to these situations accordingly" [START_REF] Van Der Zee | The multicultural personality questionnaire: a multidimensional instrument of multicultural effectiveness[END_REF], 2001 cited in Van der Zee et al., 2013, p. 118). It can be regarded as the ability to deal with lack of control (Van der Zee & van Oudenhoven, 2013). Flexibility facilitates adaptation to a new intercultural situation, and is particularly important when individuals' expectations of the situation in the host country do not correspond to reality [START_REF] Van Oudenhoven | Predicting multicultural effectiveness of international students: the Multicultural Personality Questionnaire[END_REF]. [START_REF] Earley | Cultural intelligence: individual interactions across cultures[END_REF] conceptualised CQ as a multidimensional construct consisting of four primary factors: metacognitive, cognitive, motivational, and behavioural CQ. The Expanded Cultural Intelligence Scale (E-CQS) includes subdimensions for each of the four primary factors and is especially useful for focusing on specific CQ capabilities. [START_REF] Van Dyne | Sub-dimensions of the four factor model of cultural intelligence: Expanding the conceptualization and measurement of cultural intelligence[END_REF] reviewed psychometric evidence supporting the E-CQS and proposed that the next wave of CQ research should be guided by a deeper understanding of each of the four factors of CQ. It should facilitate more focused action steps for personal development plans aimed at improving CQ (Van Dyne et al., 2012, p. 308).

Cultural intelligence and the Expanded Cultural Intelligence Scale

Metacognitive CQ refers to "an individual's level of conscious cultural awareness and executive processing during cross-cultural interactions" [START_REF] Ang | Handbook of cultural intelligence: Theory, measurement, and applications[END_REF]cited in Van Dyne et al., 2012, p. 298). It comprises planning, awareness, and checking. Planning is defined as "strategizing before a culturally diverse encounter" (Van Dyne et al., 2012, p. 299), awareness as "knowing about cultural thinking and knowledge of self and others in real time" (Van Dyne et al., 2012, p. 299), and checking as "reviewing assumptions and adjusting mental maps when actual experiences differ from expectations" (Van Dyne et al., 2012, p. 299).

Cognitive CQ reflects "knowledge of the norms, practices and conventions in different cultures acquired from education and personal experiences" (Ang et al., 2007, p. 338). Cognitive CQ includes culture-general knowledge and context-specific knowledge. Culture-general knowledge corresponds to "declarative knowledge of the major elements that constitute the cultural environment" (Van Dyne et al., 2012, p. 299), and context-specific knowledge is defined as "declarative knowledge of how cultural universals are manifested in a specific domain and procedural knowledge of how to be effective in that domain" (Van Dyne et al., 2012, p. 299).

Motivational CQ reflects the "capability to direct attention and energy toward learning about and functioning in situations characterized by cultural differences" (Ang et al., 2007, p. 338). The three sub-dimensions of motivational CQ are intrinsic interest, extrinsic interest, and selfefficacy to adjust. Intrinsic interest is defined as "valuing culturally diverse experience in and of itself because it is inherently satisfying" [START_REF] Deci | Intrinsic Motivation[END_REF]cited in Van Dyne et al., 2012, p. 303), extrinsic interest as "valuing the tangible, personal benefits that can be derived from culturally diverse experiences" [START_REF] Ryan | Intrinsic and extrinsic motivations: Classic definitions and new directions[END_REF]cited in Van Dyne et al., 2012, p. 304), and self-efficacy to adjust as "having task-specific confidence in culturally diverse situations" (Van Dyne et al., 2012, p. 304).

Behavioural CQ reflects the "capability to exhibit appropriate verbal and non-verbal actions when interacting with people from different cultures" (Ang et al., 2007, p. 338). The three subdimensions of behavioural CQ are verbal behaviour, non-verbal behaviour, and speech acts. Verbal behaviour is defined as "flexibility in vocalization (e.g. accent, tone)" (Van Dyne et al., 2012, p. 305); non-verbal behaviour as "flexibility in communication that is conveyed via gestures, facial expressions, and body language, rather than through words" [START_REF] Knapp | Nonverbal communication in human interaction[END_REF]cited in Van Dyne et al., 2012, p. 305), and speech acts as flexibility in ways of communicating specific types of messages such as requests, invitations, apologies, gratitude or disagreement (Van Dyne et al., 2012, p. 305).

Van [START_REF] Van Dyne | Sub-dimensions of the four factor model of cultural intelligence: Expanding the conceptualization and measurement of cultural intelligence[END_REF] pointed out that, by definition, CQ dimensions are malleable abilities that can be improved through active engagement in education, travel, international missions, and other cross-cultural experiences.

Intercultural competence and engineering education

The accreditation bodies for engineering degrees describe the ability to work in an international and multicultural context as an essential element of engineering education [START_REF] Cti | Références et orientations de la Commission des titres d'ingénieur -Référentiel Critères majeurs d'accréditation -Version[END_REF]. Future engineers have to master one or more foreign languages and to demonstrate cultural openness. They have to adapt to international contexts and to cooperate on collective global issues (CTI, 2022, p. 21). In order to succeed within any multicultural environment, engineers have to develop IC. According to Grandin and Hedderich (2009, p. 364), engineers are expected to demonstrate: (i) open-mindedness and tolerance; (ii) knowledge of different cultures around the world; (iii) cultural awareness and acceptance of difference; (iv) multilingualism; (v) awareness of differences in terms of engineering cultures. Grandin and Hedderich (2009, p. 368) highlighted that the basic predispositions necessary for the successful development of IC are curiosity, openness and tolerance of ambiguity, as well as a willingness to interact with host country nationals. They argued that for engineers in particular, IC includes the ability to collaborate with people who define problems differently [START_REF] Downey | The Globally Competent Engineer: Working Effectively with People Who Define Problems Differently[END_REF] and use different technical and management approaches to solve those problems (Grandin & Hedderich, 2009, p. 368). According to [START_REF] Messelink | Intercultural competencies: What students in study and placement mobility should be learning[END_REF], educators should consider intercultural learning as a path towards greater employability.

Study abroad is an ideal program element to instil IC in students [START_REF] Deardorff | Identification and assessment of intercultural competence as a student outcome of internationalization[END_REF][START_REF] Vande Berg | Applying Theory and Research: The Evolution of Intercultural Competence in U.S. Study Abroad[END_REF]. However, integrating such an experience into engineering curricula has proven to be a major challenge. This is largely due to the very dense and content-demanding nature of the curriculum [START_REF] Lohmann | Defining, developing and assessing global competence in engineers[END_REF][START_REF] Maldonado | Building international experiences into an engineering curriculum -a design project-based approach[END_REF]. Short-term international experiences, such as project-based approaches, have therefore been designed to minimise their impact on already constrained schedules (e.g. [START_REF] Berger | Designing Short-Term Study Abroad Engineering Experiences to Achieve Global Competencies[END_REF][START_REF] Maldonado | Building international experiences into an engineering curriculum -a design project-based approach[END_REF]. For example, [START_REF] Maldonado | Building international experiences into an engineering curriculum -a design project-based approach[END_REF] argued that while immersed in a different culture and language for a short time period (i.e. 2 weeks), engineering students experienced the challenge of interacting with culturally diverse teams.

Therefore, although traditional longer-term study abroad experiences have significant impacts on participants, engineering students have long been underrepresented in such programs. As a result, only a few studies [START_REF] Berka | The Role of Study Abroad Curricular Interventions in Engineering Students' Intercultural Competence Development[END_REF][START_REF] Chédru | The effect of study abroad and personality on cultural intelligence: A deeper understanding using the expanded model of cultural intelligence[END_REF][START_REF] Shoemaker | Cultural Intelligence and Experiences in International Engineering Programs[END_REF] investigated the influence of international mobility on engineering students' IC. [START_REF] Shoemaker | Cultural Intelligence and Experiences in International Engineering Programs[END_REF] provided evidence that students' CQ scores were significantly higher after their return from international engineering programs, compared to their scores before they departed. Programs' duration ranged from three to eight weeks. Programs also varied depending on diverse characteristics: internship experiences, classes taught by homeuniversity faculty or by local faculty, presence or number of format cultural excursions built into each program etc. [START_REF] Shoemaker | Cultural Intelligence and Experiences in International Engineering Programs[END_REF].

Using the Intercultural Development Inventory (IDI) by [START_REF] Hammer | Measuring intercultural sensitivity: The intercultural development inventory[END_REF], [START_REF] Berka | The Role of Study Abroad Curricular Interventions in Engineering Students' Intercultural Competence Development[END_REF] investigated to what extent study abroad curricular interventions supported engineering students' development of IC. The one-year study abroad program consisted of a semester of coursework followed by a six-month internship in the host country. The threephases curricular interventions (pre-departure, during students' year abroad and after their return) aimed to help students fully immerse themselves in the target culture. Their results showed that while curricular interventions had a clear and positive impact on the intercultural development of engineering students, the changes in students' IC after the study abroad program were not statistically significant, contrary to their expectations [START_REF] Berka | The Role of Study Abroad Curricular Interventions in Engineering Students' Intercultural Competence Development[END_REF]. [START_REF] Chédru | The effect of study abroad and personality on cultural intelligence: A deeper understanding using the expanded model of cultural intelligence[END_REF] showed that after a study abroad semester, engineering students improved their IC. More specifically, ten out of the eleven sub-dimensions of E-CQS increased. Extrinsic interest was the only sub-dimension that remained stable [START_REF] Chédru | The effect of study abroad and personality on cultural intelligence: A deeper understanding using the expanded model of cultural intelligence[END_REF].

Hypotheses

Studying abroad implies the discovery of a new environment and usually a radical change in living conditions. While abroad, students have many opportunities to empathise with the feelings, thoughts, and behaviours of members from different cultural groups. Therefore, it is assumed that they will significantly improve their cultural empathy over this time period.

Research shows that students usually emphasise a broader open-mindedness as an outcome of their study abroad experience [START_REF] Gu | Learning and growing in a 'foreign' context: intercultural experiences of international students[END_REF][START_REF] Hadis | Why Are They Better Students When They Come Back? Determinants of Academic Focusing Gains in the Study Abroad Experience[END_REF][START_REF] Weibl | Cosmopolitan identity and personal growth as an outcome of international student mobility at selected New Zealand, British and Czech universities[END_REF]. They report their personal growth in terms of more respectful attitudes towards host culture and values. Through this experience they gain broadened life experiences and interests. This implies that a study abroad semester should lead to an increase in open-mindedness.

Individuals staying in a foreign country face the challenge of establishing new social relationships [START_REF] Zimmermann | Do we become a different person when hitting the road? Personality development of sojourners[END_REF]. [START_REF] Bochner | Friendship Patterns of Overseas Students: A Functional Model[END_REF] identified three distinct interpersonal networks in which international students are involved: the first one is monocultural, and consists of bonds between compatriots; the two others are bicultural and multicultural, and consist of bonds with host country students. As stays abroad offer many opportunities to make new social contacts, social initiative is expected to increase during this period.

In a new cultural environment, the usual ways of dealing with the problems of everyday life are not necessarily effective. This suggests that students abroad will meet many occasions to switch from one strategy to another, and thus increase their flexibility.

For some students, studying abroad is the first opportunity to leave their home country. Being immerged in a new environment and adapting to a new culture are perceived as stressful events by many individuals [START_REF] Leone | The crosscultural generalizability and validity of the Multicultural Personality Questionnaire[END_REF]. Higher levels of emotional stability have been associated with more effective management of acculturation stressors and better ability to cope with the challenges of mobility [START_REF] Andrews | Sending Your Teenagers Away: Controlled Stress Decreases Neurotic Vulnerability[END_REF]. Although emotional stability is seen as a core feature of the successful international immersion [START_REF] Leone | The crosscultural generalizability and validity of the Multicultural Personality Questionnaire[END_REF], it is also considered as a relatively stable personality dimension [START_REF] Mccrae | Perspectives de la théorie des cinq facteurs (TCF) : traits et culture[END_REF] which is not affected by an international experience (Bartel-Radic, 2014). It is therefore expected that emotional stability will not be significantly affected by a study abroad semester. Thus, we predict the following hypothesis: H1: A study abroad semester will lead to an increase in cultural empathy ( H1a), openmindedness (H1b), social initiative (H1c), and flexibility (H1d). Emotional stability will not significantly change after a study abroad semester (H1e).

Metacognitive CQ refers to the recognition and understanding of differences between cultures. As Şahin et al. (2014) pointed out, exposure to other cultures provides many opportunities to consciously examine one's own cultural assumptions and to engage in a reflective process before and during interactions. Each subdimension of students' metacognitive CQ (planning, awareness, and checking) should therefore increase after a study abroad semester.

After a semester abroad, students should have absorbed novel cultural facts, become more familiar with similarities and differences among cultures, and thus have improved both dimensions of their cognitive CQ: culture-general knowledge, and context-specific knowledge [START_REF] Chédru | The effect of study abroad and personality on cultural intelligence: A deeper understanding using the expanded model of cultural intelligence[END_REF].

Experiences abroad increase students' self-efficacy [START_REF] Petersdotter | International experience makes a difference: Effects of studying abroad on students' self-efficacy[END_REF] and their interest in other cultures [START_REF] Mohajeri Norris | How study abroad shapes global careers: Evidence from the United States[END_REF]. [START_REF] Crossman | International experience and graduate employability: Stakeholder perceptions on the connection[END_REF] showed that students perceived clear connections between international experience and graduate employability. International experience provides many opportunities for experiential learning and networking. It also contributes to the acquisition of additional languages and the development of soft skills [START_REF] Crossman | International experience and graduate employability: Stakeholder perceptions on the connection[END_REF]. Consequently, an increase in each subdimension of students' motivational CQ (intrinsic interest, extrinsic interest, and self-efficacy to adjust) should be observed after a study abroad semester [START_REF] Chédru | The effect of study abroad and personality on cultural intelligence: A deeper understanding using the expanded model of cultural intelligence[END_REF].

Living abroad for one semester should improve students' understanding of appropriate practices and behaviours in non-native settings, resulting in improvements in all three dimensions of behavioural CQ (verbal behaviour, non-verbal behaviour, and speech acts).

Consequently, we predict the following hypothesis: H2: A study abroad semester will enhance the three dimensions of metacognitive CQ, planning, awareness, and checking (H2a), the two dimensions of cognitive CQ, culture-general knowledge, and context-specific knowledge (H2b), the three dimensions of motivational CQ, intrinsic interest, extrinsic interest, and self-efficacy to adjust (H2c), and the three dimensions of behavioural CQ, verbal behaviour, non-verbal behaviour, and speech acts (H2d).

Method

GoLasalle semester abroad

The GoLaSalle semester program [START_REF] Delhoume | L'interculturalité à l'épreuve de l'intersubjectivité. Exemple du semestre GoLaSalle dans une université étrangère[END_REF]) is a partnership between the engineering school UniLaSalle (France) and Lasallian Universities across the world. The program allows engineering students to take part in a study semester in one of the partner Universities present in 6 different countries (the Philippines, Colombia, Mexico, Brazil, Costa Rica, and the United States). Students' participation in the GoLaSalle mobility program is compulsory. It takes place during the fifth semester of a five-year degree.

Participants

Instruments

The Multicultural Personality Questionnaire

The French version of the Multicultural Personality Questionnaire [START_REF] Faniko | Assessing Multicultural Effectiveness Among Young Swiss People[END_REF]Van der Zee et al., 2013) was administered. In total, the MPQ includes 37 items and consists of five factors. Items are introduced by the following question: "To what extent do the following statements apply to you?" Answers were recorded on a 5-point Likert-type scale ranging from 1 (totally not applicable) to 5 (completely applicable). Sample items from each of the five factors are the following: cultural empathy (7 items; α T1 = .82, α T2 = .84), "Notices when someone is in trouble"; open-mindedness (7 items; α T1 = .77, α T2 = .84), "Is interested by other cultures"; social initiative (8 items; α T1 = .83, α T2 = .80), "Easily approaches other people"; emotional stability (8 items; α T1 and T2 = .85), "Keeps calm when things don't go well"; and flexibility (7 items; α T1 = .86, α T2 = .84), "Wants to know exactly what will happen" (reverse-scored). All Cronbach's alphas were above the recommended threshold of .70 [START_REF] Nunnally | Psychometric theory[END_REF]. The subscales could therefore be regarded as reliable.

The Expanded Cultural Intelligence Scale (E-CQS)

Participants completed the 37-item French version of the Expanded Cultural Intelligence Scale [START_REF] Gagné-Deland | Élaboration et validation d'une version francophone de l'expanded cultural intelligence scale[END_REF][START_REF] Van Dyne | Sub-dimensions of the four factor model of cultural intelligence: Expanding the conceptualization and measurement of cultural intelligence[END_REF]. Answers were given on a 7-point Likert-type scale, ranging from 1 (strongly disagree) to 7 (strongly agree). Examples of items for each of the sub-dimensions are: planning (3 items; α T1 = .72, α T2 = .82), "I ask myself what I hope to accomplish before I meet with people from different cultures."; awareness (3 items; α T1 = .74, α T2 = .81), "I am conscious of how other people's culture influences their thoughts, feelings, and actions."; checking (3 items; α T1 = .73, α T2 = .76), "I double check the accuracy of my cultural knowledge during intercultural interactions"; culture-general knowledge (5 items; α T1 =.76, α T2 = .82), "I can describe similarities and differences in legal, economic, and political systems across cultures."; context-specific knowledge (5 items; α T1 and T2 = .87), "I can describe the ways that leadership styles differ across cultural settings."; intrinsic interest (3 items; α T1 = .83, α T2 = .86), "I thrive on the differences in cultures that are new to me."; extrinsic interest (3 items; α T1 = .68, α T2 = .75), "Given a choice, I value the tangible benefits (pay, promotion, perks) of an intercultural rather than a domestic role."; self-efficacy to adjust (3 items; α T1 = .81, α T2 = .86), "I am confident I can socialize with locals in a culture that is unfamiliar to me."; verbal behaviour (3 items; α T1 = .79, α T2 = .77), "I change my use of pause and silence to suit different cultural situations."; non-verbal behaviour (3 items; α T1 = .77, α T2 = .74), "I change my nonverbal behaviours (hand gestures, head movements) to fit the cultural situation."; and speech acts (3 items; α T1 and T2 = .88), "I vary the way I show gratitude (express appreciation, accept compliments) based on the cultural context.". All Cronbach's alphas were very close to or above the recommended threshold of .70 [START_REF] Nunnally | Psychometric theory[END_REF]. The subscales could therefore be regarded as reliable.

Procedure

As the GoLaSalle program takes place during the fifth semester of a five-year degree, participants completed all measures (MPQ, E-CQS) and demographic questions in May (T1), one to two months before the start of their semester abroad, and again in February (T2) of the following year, i.e. one to two months after their return. We made the questionnaires available online and asked the students to complete them in class so that any questions of clarification could be answered face to face. To respect the principles of the "Charte française de déontologie des métiers de la recherche", the students filled in a consent form which states that there are no right or wrong answers and that the answers are treated confidentially and anonymously.

Analysis

As the literature found mixed results regarding gender effects on the intent to study abroad [START_REF] Salisbury | To See the World or Stay at Home: Applying an Integrated Student Choice Model to Explore the Gender Gap in the Intent to Study Abroad[END_REF][START_REF] Tompkins | Gender Influences on Students' Study Abroad Participation and Intercultural Competence[END_REF], but also on MPQ [START_REF] Faniko | Assessing Multicultural Effectiveness Among Young Swiss People[END_REF][START_REF] Van Der Zee | Validation of the multicultural personality questionnaire in the context of personnel selection[END_REF][START_REF] Van Der Zee | The multicultural personality questionnaire: a multidimensional instrument of multicultural effectiveness[END_REF] and CQS dimensions [START_REF] Varela | The development of the global manager: An empirical study on the role of academic international sojourns[END_REF], separate paired-sample t-tests for men and women were conducted to investigate differences over time. When differences were statistically significant (p < .05), the effect size was calculated using eta squared ( 2 ). With  2 values around .01, the effect size was considered as small, around .06, it was considered as moderate, and large with values around or above .14 [START_REF] Cohen | Statistical Power Analysis for the Behavioral Sciences[END_REF].

Results

The results revealed significant changes over time for both MPQ (Table 1) and E-CQS dimensions (Table 2), for both men and women.

MPQ results

Gender differences

Before departure, independent-samples t-tests showed that women scored higher than men on: cultural empathy, t (289) = 2.00, p < .05, two-tailed,  2 = .01 (M = 3.95, SD = .62 and M = 3.81, SD = .60, for women and men, respectively); and open-mindedness, t (289) = 2.21, p < .05, two-tailed,  2 = .02 (M = 3.87, SD = .59 and M = 3.69, SD = .62, for women and men, respectively). Men (M = 3.14, SD = .74) scored higher than women (M = 2.66, SD = .83) on emotional stability, t (289) = 5.22, p < .001, two-tailed,  2 = .09.

Differences across time

Mean scores for cultural empathy, open-mindedness, and social initiative were significantly higher post-sojourn than pre-departure for women (Table 1). The magnitude of the difference in the means was small for cultural empathy ( 2 = .03), large for open-mindedness ( 2 = .17), and moderate for social initiative ( 2 = .10). Emotional stability increased over time for both men and women but without reaching a significant level. Contrary to our expectations, flexibility decreased over time for both men and women but the difference did not reach a significant level. The only personality factor to change significantly over time for men was open-mindedness, suggesting that men became more open-minded after their semester abroad. The eta squared statistics indicated that the magnitude of the difference in the means was large ( 2 = .17). As expected, a study abroad semester positively impacted openmindedness and had no significant impact on emotional stability. H1b and H1e were thus confirmed. The positive impact on cultural empathy and social initiative was confirmed for women only. H1a and H1c were thus partially confirmed. H1d could not be confirmed as flexibility did not exhibit a significant difference over time.

Men (n = 145)

Women

E-CQS results

Gender differences

Before departure, independent-samples t-tests showed that women (M = 5.56, SD = .90) scored higher than men (M = 5.36, SD = .92) on awareness, reaching almost a statistical significance: t (286) = 1.95, p = .05, two-tailed,  2 = .01. Women (M = 5.43, SD = 1.06) also scored higher than men (M = 5.20, SD = 1.15) on intrinsic interest, but with a p-value > .05: t (286) = 1.76, p = .08, two-tailed,  2 = .01.

Differences across time

Mean scores for each of the three dimensions of metacognitive CQ were significantly higher post-sojourn than pre-departure for women (Table 2). The magnitude of the difference in the means was moderate for planning ( 2 = .06) and checking ( 2 = .04), and small for awareness ( 2 = .03). For men, two of the three dimensions of metacognitive CQ increased over time (planning and checking), but without reaching a significant level. H2a was thus confirmed for women only.

In accordance with our expectations, the two dimensions of cognitive CQ increased over time for both men and women. The magnitude of the difference in the means for culture-general knowledge was moderate for men ( 2 = .04), and large for women ( 2 = .25). For culturespecific knowledge, the magnitude of the difference in the means was large for both men ( 2 = .17) and women ( 2 = .29). H2b was thus confirmed.

Mean scores for two of the three dimensions of motivational CQ were significantly higher post-sojourn than pre-departure for women. The magnitude of the difference in the means was small for intrinsic interest ( 2 = .03) and moderate for self-efficacy to adjust ( 2 = .06). Mean score for extrinsic interest increased over time for women, but without reaching a significant level. For men, two of the three dimensions of motivational CQ increased over time (intrinsic interest and self-efficacy to adjust), but without reaching a significant level. H2c was thus partially confirmed for women only.

The three dimensions of behavioural CQ increased over time for both men and women. The magnitude of the difference in the means for verbal behaviour was small for men ( 2 = .03), and moderate for women ( 2 = .04). For non-verbal behaviour, the magnitude of the difference in the means was moderate for both men and women ( 2 = .04). For speech acts, the magnitude of the difference in the means was moderate for men ( 2 = .04), and large for women ( 2 = .11). H2d was thus confirmed.

Men (n = 143)

Women

Discussion

Theoretical implications

The purpose of this study was to investigate whether and, if so, how a study abroad semester impacted engineering students' IC as measured by two instruments, MPQ and E-CQS. The participants in this study were 293 French engineering students (159 males and 134 females) who spent their fifth semester of a five-year degree in either the Philippines, Colombia, Mexico, Brazil, Costa Rica, or the United States.

For females, the MPQ results demonstrated a significant increase over time on three dimensions: open-mindedness, social initiative, and cultural empathy. As expected no significant effect was found for emotional stability and, against our expectations, flexibility showed no increase over time. For men, emotional stability remained stable as expected and out of the four other dimensions, the only one that increased significantly over time was openmindedness.

Our results suggest a gender effect on cultural empathy and open-mindedness (with women scoring higher than men before departure) and on emotional stability (with men scoring higher than women before departure). These findings are in accordance with the results of several authors [START_REF] Faniko | Assessing Multicultural Effectiveness Among Young Swiss People[END_REF][START_REF] Tompkins | Gender Influences on Students' Study Abroad Participation and Intercultural Competence[END_REF][START_REF] Van Der Zee | Validation of the multicultural personality questionnaire in the context of personnel selection[END_REF][START_REF] Van Der Zee | The multicultural personality questionnaire: a multidimensional instrument of multicultural effectiveness[END_REF].

Compared to their male counterparts, women seemed more able to use the experience abroad as a developmental tool. Women's results are consistent with the analysis made by [START_REF] Herfst | Intercultural Effectiveness Training in three Western immigrant countries: A cross-cultural evaluation of critical incidents[END_REF] which indicates that because of their social component, cultural empathy, open-mindedness and social initiative are more easily trainable than the dimensions of emotional stability and flexibility. As these authors argue, open-mindedness is a prerequisite for the expression of the two other dimensions: "Once one has opened one's mind to an intercultural encounter one subsequently may show social initiative or cultural empathy" (Herfst et al., 2008, p. 74). As our results show, women's levels of open-mindedness and cultural empathy before departure were higher than men's ones. These characteristics predisposed women to more favourable attitudes in an intercultural context and allowed them, as in a virtuous circle, to further strengthen open-mindedness, cultural empathy, and social initiative.

For men, open-mindedness increased significantly over time, but this is the only significant variation observed. Two hypotheses can be put forward to explain this result. First, the level of open-mindedness reached by the end of the sojourn may not yet have been sufficient to trigger the processes of social interaction and cultural empathy. Second, to see significant changes, the length of the sojourn for men may have had to be longer. Indeed, according to several studies, it takes four to six months to settle down and overcome the daily issues of work, life, and social communication [START_REF] Varela | Learning outcomes of study-abroad programs: A meta-analysis[END_REF][START_REF] Zimmermann | Do we become a different person when hitting the road? Personality development of sojourners[END_REF]. This adjustment period probably fluctuates depending on the initial levels of IC dimensions. The lower the initial levels of IC dimensions, the longer it takes to adjust in a new environment.

As expected, no significant effect was found over time for emotional stability. However, we note a slight increase (without reaching a significance level) suggesting that students felt more emotionally stable as the sojourn progressed. This is in line with the results obtained by [START_REF] Schartner | The effect of study abroad on intercultural competence: a longitudinal case study of international postgraduate students at a British university[END_REF] and [START_REF] Zimmermann | Do we become a different person when hitting the road? Personality development of sojourners[END_REF]. While adjustment difficulties are more important during the first four to six months abroad, they then decrease and remain stable.

The only decreasing dimension for both women and men, although to a lesser extent for men, is flexibility. Before going abroad, the participants scored rather low on flexibility suggesting they liked routine and fixed habits. While abroad, students face many challenges. They have to adapt to new local habits and rules. Instead of becoming more flexible while facing new situations, the semester abroad highlighted their intrinsic need for routine and certainty. In other words, this experience abroad confirmed that they like to stay in control of a situation.

For females, the E-CQS results demonstrated a significant increase over time on each dimension of metacognitive, cognitive, and behavioural CQ. They also showed an increase in each of the three dimensions of motivational CQ, even only one (extrinsic interest) did not reach a significant level. For men, each dimension of cognitive and behavioural CQ increased significantly over time, but contrary to our expectations, no significant effect was found for metacognitive and motivational CQ.

No significant gender effect is observed on the different E-CQS dimensions. Nevertheless, we note that women scored higher than men before departure on awareness and intrinsic interest.

Like [START_REF] Shoemaker | Cultural Intelligence and Experiences in International Engineering Programs[END_REF] and [START_REF] Chédru | The effect of study abroad and personality on cultural intelligence: A deeper understanding using the expanded model of cultural intelligence[END_REF], our results provide empirical evidence that study abroad has a significant effect on the development of engineering students' CQ. However, the results differ depending on gender: once again, the effect of the sojourn on CQ changes has been more profitable for women than for men. Actually, upon their return, women outperformed men on almost all CQ dimensions. When getting back, men improved their cognitive CQ. This means that their overall understanding of how cultures differ from one context to another has improved. They also refined their ability to behave suitably in different cultural contexts (behavioural CQ). Yet surprisingly, men did not improve their scores on metacognitive CQ after one semester abroad. This result suggests that, for example, the experience abroad did not help them realise that culture influences social interactions, people's thoughts, feelings or actions (awareness). Metacognitive CQ is probably the most difficult construct to conceive. It entails "slowing down long enough" to pay close attention to what is happening inside our own and other people's heads (Van Dyne et al., 2010, p. 136). Metacognitive CQ refers to our ability to "use our cultural knowledge to plan an appropriate strategy, accurately interpret what's going on in a cross-cultural situation, and check to see whether our expectations are accurate or whether our mental model of that particular person and/or culture should be revised" (Van Dyne et al., 2010, p. 136). This ability needs maturity and time for reflection. Students may have acquired such competence, but a lack of hindsight may have prevented them from realising it. To ensure that students are aware of what they are learning and achieving, authors suggest providing guidance and mentorship during the study abroad period (e.g. [START_REF] Berka | The Role of Study Abroad Curricular Interventions in Engineering Students' Intercultural Competence Development[END_REF]. Such interventions aim to support the development of students' IC.

Having a closer look at motivational CQ, we observe that extrinsic interest proved to be the dimension least impacted by the study abroad semester. Female students gained more confidence in their effectiveness in a cross-cultural encounter (self-efficacy to adjust), and the level of enjoyment they derived from culturally diverse situations (intrinsic interest) increased after the sojourn. However, neither male nor female students' interest in the tangible benefits they can derive from culturally diverse experiences (extrinsic interest) was affected by the study abroad experience. We note that the tangible benefits mentioned in the present subscale's items for extrinsic interest (e.g. status, promotion, perks, that would be gained by living or working in a different culture) could easily attract any employee who would consider expatriating. But for students who experience a study abroad semester in the middle of their curriculum, these advantages may not meet their current concerns. Thus, like [START_REF] Chédru | The effect of study abroad and personality on cultural intelligence: A deeper understanding using the expanded model of cultural intelligence[END_REF], we propose that the extrinsic interest items be changed to better address students' concerns. Advantages such as enhanced networking, career prospects, and employability, for example, could be highlighted in new items [START_REF] Chédru | The effect of study abroad and personality on cultural intelligence: A deeper understanding using the expanded model of cultural intelligence[END_REF].

With higher levels of openness and cultural empathy before departure, women were in a more favourable mindset than men to engage in the study abroad semester. In addition, although the difference was not statistically significant, women's intrinsic motivation before departure was also higher than that of men. Thus, if women's CQ increased more than men's CQ during the study abroad semester, it is probably due to favourable initial predispositions that made a difference.

Practical implications

This study demonstrates the importance of a study abroad semester in improving students' IC. Educators and administrators can use the results of this research to show that study abroad is a key contribution to preparing engineering students for culturally diverse assignments that await them upon graduation. Even if engineering curricula are dense, it is worth including a study abroad semester to give the students the opportunity to become culturally competent.

Before departure, our participants were prepared regarding academic and administrative aspects of their sojourn (curriculum and everyday life issues). However, more attention should be paid to the cultural aspects of this experience. Prior research has shown that students who receive pre-departure intercultural training report greater intercultural gains and a better adjustment [START_REF] Berka | The Role of Study Abroad Curricular Interventions in Engineering Students' Intercultural Competence Development[END_REF][START_REF] Engle | Assessing Language Acquisition and Intercultural Sensitivity Development in Relation to Study Abroad Program Design[END_REF][START_REF] Paras | Understanding how program factors influence intercultural learning in study abroad: The benefits of mixedmethod analysis[END_REF][START_REF] Young | The effects of cross-cultural communication education on international students' adjustment and adaptation[END_REF]. Formal instruction on culture shock [START_REF] Ward | The Psychology of Culture Shock[END_REF]) and local culture, information about the benefits students will gain from this experience and how it will increase their employability, should enhance their levels of intrinsic motivation and openness before departure which in turn should improve their intercultural efficiency.

Given the IC disparities observed between women and men prior to departure (women scored higher on cultural empathy, openness, awareness, and intrinsic interest while men scored higher on emotional stability), activities could be specifically designed to strengthen these abilities before departure. For example, stress management activities could be offered to those with low emotional stability, women in priority. Other activities (e.g. photo essays, analysis and comparison of similarities and differences between cultures, incentive to become a buddy for an international student on campus, etc.) could be offered to men in priority to improve their cultural empathy and openness. To increase men's interest in studying abroad, [START_REF] Tompkins | Gender Influences on Students' Study Abroad Participation and Intercultural Competence[END_REF] suggested recruiting men as study abroad ambassadors. As role models, the ambassadors would help male students become aware of the many benefits of studying abroad. As men outnumber women in most fields of study in engineering education, any strategy to motivate them to study abroad is of prime importance.

We noticed that our students had a fairly low level of flexibility. The flexibility score was the lowest among the five MPQ dimensions for men and one of the lowest (along with emotional stability) for women. In addition, we found that the semester abroad did not improve student's flexibility. This result is somewhat concerning. It is obvious that engineers need to be able to work in complex and uncertain environments. The ability of engineering students to be flexible and to tolerate ambiguity is an asset for their future assignments [START_REF] Grandin | Intercultural Competence in Engineering: Global Competence for Engineers[END_REF]. If the semester abroad experience did not increase student's flexibility, this means that measures should be taken much earlier in the curriculum to develop this ability [START_REF] Khan | Tolerance of ambiguity: A comparison between engineering and nonengineering students[END_REF]. [START_REF] Saarikoski | Developing tolerance for ambiguity and uncertainty by interdisciplinary intensive courses[END_REF] suggested, for example, the introduction of intensive interdisciplinary courses in engineering education to improve student's tolerance of ambiguity.

In-country mentorship and debriefing workshops post-sojourn are also recommended to help the students become aware of their achievements and translate their experience into useful competencies for their employability [START_REF] Berka | The Role of Study Abroad Curricular Interventions in Engineering Students' Intercultural Competence Development[END_REF][START_REF] Messelink | Intercultural competencies: What students in study and placement mobility should be learning[END_REF]. A starting point for this reflection is to ask the students to examine their own MPQ and E-CQS scores and to analyse how and why they have changed as a result of the stay abroad.

Limitations and future research

IC development is not uniform across dimensions and gender. While almost all women's IC dimensions gained from studying abroad, men's IC showed less malleability. Further research should explore why men did not benefit as much as women from this experience [START_REF] Salisbury | To See the World or Stay at Home: Applying an Integrated Student Choice Model to Explore the Gender Gap in the Intent to Study Abroad[END_REF]; this is particularly important given that men are often the majority in engineering education. One hypothesis is that openness, cultural empathy and intrinsic motivation seem to be key factors as predispositions necessary to further increase IC during an international sojourn. Thus, like some authors who investigated the moderating role of openness in the relationship between study abroad participation and CQ [START_REF] Chédru | The effect of study abroad and personality on cultural intelligence: A deeper understanding using the expanded model of cultural intelligence[END_REF][START_REF] Ramirez | Impact on intercultural competence when studying abroad and the moderating role of personality[END_REF], it would be interesting to extend this approach to other dimensions such as cultural empathy, intrinsic motivation or a combination of these dimensions.

One of the limitations of this study is the use of self-assessments to determine students' IC. Self-assessments may generate biased data, as students may feel compelled to report socially desirable outcomes of their international experience [START_REF] Ogden | Toward a research agenda for U.S. education abroad[END_REF]. Thus, as recommended by [START_REF] Ramsey | Exploring the Impact of Cross-Cultural Management Education on Cultural Intelligence, Student Satisfaction, and Commitment[END_REF], future research should include "multiple measurement methods" that seize both the perspectives of self and others, e.g. behavioural observations. Furthermore, our findings should be interpreted with caution because the observed changes could be due to maturation, i.e. "any naturally occurring growth or change in individuals" (Ogden, 2015, p. 10). To counter this limitation, future research should use a control group, i.e. compare differences in IC development with a group of students who stayed at home. Future studies should take into account participant's prior overseas experience to determine whether it moderates the level of IC development [START_REF] Mazzurco | Are Engineering Students Culturally Intelligent?: Preliminary Results from a Multiple Group Study[END_REF]. Further research is also needed to validate our findings with cohorts of students of different nationalities and from different engineering fields. Last, additional studies are required to assess how studying abroad impacts IC months and years after students return to their home country. In addition, it would be interesting to examine how studying abroad affects students' employability and career outcomes over the long run.

Findings from this study are very encouraging. They show the benefits of integrating a study abroad semester into the curriculum of engineers to enhance their IC. As engineers are more and more expected to work effectively in diverse cross-cultural settings, study abroad is a key contribution to the successful education of "global engineers".

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Marie

  Participants included 293 French engineering students. Males represented 54% (n = 159) and females 46% of the respondents (n = 134). All of them were studying agronomy. The average age was 19.6 years (SD = 0.8 years) pre-departure (T1) and 20.4 years (SD = 0.7 years) postsojourn (T2). The students sojourned in the Philippines (n = 85), Colombia (n = 75), Mexico (n = 71), Brazil (n = 26), Costa Rica (n = 22) and the United States (n = 14).

  Chédru is Associate Professor at UniLaSalle where she teaches Organizational Behavior. Member of InTerACT Research Unit UP 2018.C102 (Innovation Territoire Agriculture et Agroindustrie, Connaissance et Technologie), her research interests focus on Engineering Education. Catherine Delhoume is Associate Professor at UniLaSalle where she teaches sociology. Member of InTerACT Research Unit UP 2018.C102 (Innovation Territoire Agriculture et Agroindustrie, Connaissance et Technologie), her research interests focus on social acceptability of innovative projects in the rural world, transitions to more sustainable farming systems and interculturality.

Table 1 :

 1 Results of paired-sample t-tests on each of the 5 MPQ factors.

	(n = 133)

Table 2 :

 2 Results of paired-sample t-tests on each of the 11 E-CQS subdimensions.

	(n = 130)


Pierre Hornych

Diana Khairallah

Juliette Blanc

Jean- Michel Michel Piau

Mohsen Hosseingholian

Simon Pouget

Fréderic Savin

Alain Ducreau

Louis-Marie Cottineau

Frederic Savin

Monitoring of railway structures of the high speed line BPL with bituminous and granular sublayers

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Ballast deterioration, under dynamic loads, remains an important issue on high-speed tracks that can lead to high maintenance costs. Several studies have shown that these settlements are related to the high accelerations produced in the ballast by high-speed trains (Pita et al., 2004;[START_REF] Quezada | Mécanismes de tassement du ballast et sa variabilité[END_REF][START_REF] Saussine | Contributiona la modélisation de granulats tridimensionnels: application au ballast[END_REF][START_REF] Suiker | The mechanical behavior of ballasted railway tracks[END_REF].

The use of asphalt sublayers under the ballast has been identified as a possible solution for improving track structures. By interposing a semi-rigid layer of asphalt concrete (GB) between the ballast and the UGM layer, the behavior of the overall structure is greatly improved. This applies to both high-speed passenger and freight lines. The use of asphalt concrete (GB) in railway construction has emerged in different countries. Indeed, over the last decade 322 km of sub-ballast layers have been built for new projects in the Midwestern United States; mainly for heavy freight traffic [START_REF] Rose | Asphalt Railway Trackbeds : Recent Designs, Applications and Performances[END_REF].

In 2005, SNCF built a 3 Km long test section in the East HSL (LGV Est), linking Paris to Strasbourg, with a GB sublayer. The data retrieved from this first instrumented test indicated satisfactory performance of the experimental railway section [START_REF] Cardona | Use of a bituminous mixture layer in high-speed line trackbeds[END_REF][START_REF] Quezada | Mécanismes de tassement du ballast et sa variabilité[END_REF]. The presence of the asphalt sublayer has proven to reduce the aggressiveness of the loading applied by passing trains, leading to an increase of the structure durability.

In spring 2014, the project "Monitoring of HSL BPL" has been launched to instrument several sections of the new high-speed line (HSL) Bretagne-Pays de la Loire (BPL) (between Rennes and Le Mans, in the West of France). HSL BPL is the first large-scale application of the asphalt concrete sublayer technique in France (next to the East European HSL in its second phase), with varying subgrade conditions, and using higher performance asphalt materials. Data acquisition and analysis started at the end of 2016, when trains were first put into circulation (for a test phase). The line has officially initiated its operations in July 2017 with trains travelling at a speed of 320 Km/h.

Structure of HSL Bretagne-Pays de Loire

HSL BPL consists of 105 km of innovative track with an asphalt concrete (GB) sublayer under the ballast on its east route, and 77 km with a granular underlayment on its west route. An asphalt concrete (GB) of class 4 (GB4), according to French standard NF EN 13-108-1, has been used for this project. The unbound granular material (UGM) has a particle size 0/31.5 mm, and is of type A, according to French specifications. The innovative track structure, shown in Figure 2, includes the upper part of the earthworks (PST), which is treated with lime and hydraulic binders. The PST is surmounted by 15 cm of Unbound Granular layer (UGM) and a 12cm thick asphalt layer. The standard structure comprises a 37 cm thick granular sublayer in addition to a cement-treated subgrade layer. Four sections were instrumented (Figure 1): three sections with asphalt concrete underlayment and one with a standard granular structure [START_REF] Khairallah | Monitoring Of Railway Structure With Bituminous Underlayment[END_REF]. The objective of this instrumentation is to monitor the mechanical response of the different structures used on BPL HSL, by measuring accelerations, sub-ballast structure displacements, horizontal and vertical deformations and temperatures in different layers, and also water contents at the top of the subgrade.

Instrumentation: Sensors, Measurements and Acquisition system

The aim of the instrumentation is to monitor dynamic responses of the different structures, and thus to better understand the effect of different layers on dynamic response and track durability. The sensors were chosen and implemented by IFSTTAR. Accelerometers, weather stations, anchored displacement sensors, horizontal and vertical strain gauges, moisture probes and temperature sensors were used for the instrumentation of the sections.

Section 2 is instrumented with 6 vertical strain gages in the UGM layer, 16 accelerometers placed at different levels, 4 moisture content probes in the UGM, 2 temperature sensors, 2 anchored displacement sensors and a weather station. As for section 4, 6 vertical strain gages, 10 horizontal strain gages in the asphalt layer, 8 accelerometers, 4 moisture content probes, 3 temperature sensors, 2 anchored displacement sensors and a weather station monitor the track.

Accelerometers are installed to record the track's vertical dynamic behavior, with measurements at several levels: under the sleepers, at the top of the asphalt concrete layers and at the top of the granular layer. Anchored displacement sensors measure the structure's total vertical displacement under the ballast (GB + granular layer + subgrade for section with bituminous sublayer or UGM + subgrade for section with granular sublayer). Strain gages are installed at the base of the GB layer to measure longitudinal and transverse strains along with temperature sensors placed at the top and bottom of the layer. Moisture content probes quantify water content variations. Vertical strain gages monitor deformation levels of the unbound granular material (UGM). As a result, effects of seasonal moisture content variations can be inferred from the measured deformations.

A scheme of the implementation of accelerometers and anchored displacement sensors for section 2 (granular sublayer) and section 4 (asphalt sublayer) is presented in Figure 3.

Figure 3 -Sections 2 and 4: instrumentation layout for accelerometers and displacement sensors

At each section's level, two types of measurements are performed: "slow" measurements and "fast" measurements. Slow measurements involve temperature probes, water content probes, weather data and anchored displacement sensors. These measurements are recorded continuously every 5 minutes. Fast measurements include accelerometers, vertical and horizontal extensometers and anchored displacement sensors. Fast measurements are recorded under the passage of trains. They are triggered when the measured acceleration exceeds a certain threshold (threshold set for an accelerometer placed at the top of the first sublayer). The threshold is fixed at a very low value in order to record all train passages. The signal acquisition frequency is 2000 Hz [START_REF] Khairallah | Monitoring Of Railway Structure With Bituminous Underlayment[END_REF].

On each site, acquisition systems are installed in a weatherproof cabinet resistant to vibrations of trains with 320 km/h velocity. Cabinets are powered by a built-in system (solar panels + batteries) for uninterrupted year-round operation. Based on their performance and previous experience, acquisition systems based on the Pegase platform developed by IFSTTAR [START_REF] Cam | Improving wireless sensor behavior by means of generic strategies[END_REF] and produced by A3IP were chosen. Saved results on all sections are transferred continuously via 3G network (within few hours at most) to a remote server. Results are stored in a relational database, enabling fast-multi-criteria searches. Acquisition parameters can be configured remotely, through a web application. For each acquisition board, the slow and fast measurements can be visualized in real time.

Data acquisition carried out on BPL HSL is divided in two phases. The first phase, entitled "speed up phase", corresponds to a test phase of the track, before the start of commercial traffic. The passing train characteristics are known, with increasing speeds ranging from 160 to 352 km/h. The train is composed of 13 bogies. The second acquisition phase corresponds to the commercial traffic phase; where the average train speed is 320 km/h, and where different highspeed trains, with different bogie loads and characteristics pass on the track.

Data processing during the speed-up test phase

Before opening the BPL track to commercial traffic, a series of tests were performed on the track, at increasing speeds, between November 2016 and January 2017. These tests were performed with the same high speed train (HST), with known loads, and train speeds varying from 160 Km/h to 352 Km/h. Since the loads were always the same, responses obtained on different sections, and at different speeds, can be easily compared.

A train journey on the BPL railway track generates more than 50 data files that need to be treated and plotted. Scilab, a free numerically oriented programming language is used to automate signal processing.

Different routines and functions have been developed, using Scilab, to complete the following steps, leading to visualization of signals:

 Scale the measurements of the various sensors installed.  Calculate the speed of the passing HST train at this date.  Filter the recorded sensor signals using a low pass filter.  Select the desired sensor(s) to plot their signal(s).  Visualize the needed time signals.

These steps have been programmed with Scilab for all the sections. The section(s) to study can be selected at the beginning of the data processing program. It is possible to run multiple calculation functions, read data files, scale, filter, calculate velocities, process and plot graphs.

The test train is composed of 8 wagons, with 7 intermediate carrier bogies, with practically identical loads. To evaluate the response of the track to the train loads, it was decided to calculate the average signal, corresponding to these identical bogies. For each sensor signal thus filtered, the cumulative method of carrier bogies is then applied to the HST's seven carrying bogies as shown in Figure 4 on the displacement signal. The filtered signal of a displacement sensor is cut off to isolate the sequences in connection with the seven carrier bogies passage. For each sensor, a statistical treatment is then applied, to calculate the mean curve and the curves corresponding to +/-one standard deviation.

Figure 4 -Filtered displacement signal for a train passage -Train speed 320 km/h

Acceleration (as in Figure 5) and displacement (as in Figure 6) signals corresponding to the 7 carrier bogies of the train have been superimposed on the same graph, and represented as a function of distance (converting the time to distance, using the train velocity). The "average response" of the considered sensor has then been calculated point by point.

Comparison of the response of the structures with granular and asphalt sublayers

One of the objectives of the project on "Monitoring of the BPL High Speed Line" is to evaluate the behavior of the structures with asphalt sublayers, and to compare it with traditional structures with granular sublayers.

Since the behavior of bituminous materials is strongly dependent on temperature, it is important to note that during the three months of the speed up test phase (between November 2016 and January 2017), only small temperature variations were observed. Temperatures at the top of GB and UGM layer reached at maximum 10°C degrees in November and at minimum 2°C degrees during the coldest days in January. Therefore, temperature variations were neglected in the analysis of the results.

The objective is in particular to compare the maximum downward vertical accelerations generated by the passage of the trains, which have the most damaging effect for the ballast layer, as they reduce the apparent weight of the ballast grains and the inter-granular friction forces [START_REF] Chupin | Modélisation de la réponse dynamique d'une structure ferroviaire multicouche sous chargement roulant[END_REF]. To compare the response of the two sections, "maximum" positive accelerations (oriented downwards) and "minimum" negative accelerations (oriented upwards) are compared along with the maximum deflections of the track (oriented downwards). These values and the standard deviation are determined from the mean signals of the seven bogies obtained with the Scilab "averaging" procedure.

Figure 7 shows the maximum vertical deflection values measured on sections 2 (granular sublayer) and 4 (bituminous sublayer) as a function of train speed, during the speed up test phase. The displacements obtained on the two sections are very close, and of the order of 25 mm/100. These low and stable deflections are due to the high bearing capacity of the subgrade, which consists of cement treated soil on all the instrumented sections of the BPL line. The results also indicate no significant increase of deflections with speed. For the highest speed, reaching 352 Km/h, maximum deflection values do not exceed 27 mm/100, on both sections. Figure 8 presents a comparison between the average signals of the anchored displacement sensors on granular section 2 and asphalt section 4, for two trains passing at a speed of 320 Km/h. It can be seen that the shape of the displacement signals is somewhat different and smoother on the asphalt section (blue and red curves), rather than on the granular section (gray and yellow curves). The displacements on the asphalt section show a smaller decrease between the two peaks than on the granular section, where the drop between the two peaks is more important. The dashed lines represent the accelerometers of the granular section (2) and the full lines of the asphalt section (4). For all the sensors, and for both upward and downward accelerations, the maximum accelerations at the top of the asphalt concrete sublayer are by far lower than those measured at the top of the granular sublayer. In other terms, from the different curves presented above, it can be concluded that the presence of the asphalt layer in the structure leads to a significant reduction (almost by a factor of two) of the accelerations under the ballast. For the bituminous section, it can also be concluded that the accelerations between rails are lower than those measured under the outer rail. This reduction is not observed on the granular section.

Conclusion

In order to study the influence of the asphalt sublayer, and the dynamic responses of the various railway structures with asphalt concrete and granular sublayer, four different sections of the "Bretagne -Pays de la Loire" high-speed lane have been instrumented using accelerometers, strain gages, displacement sensors, temperature sensors and moisture probes. The acquisition system is fully remotely controllable and data are transmitted via 3G network.

Programed Scilab routines are used to automate data treatment; filter sensor measurements, calculate train velocities, plot sensor outputs, superimpose signals of individual train bogies and determine curve peaks.

In this paper, evolutions of track vertical accelerations and displacements, as a function of train speeds have been analyzed for two different instrumented track structures: a standard section with granular sublayer and an innovative section with asphalt concrete sublayer. It can be concluded that the presence of an asphalt layer in the structure reduces the acceleration levels under the ballast, which is beneficial for its stability. As for deflection levels, the asphalt concrete sublayer affects the shape of the deflection curves. Other studies are under way to analyse the very large database of results generated by the instrumentation of the BPL line, and in particular also the slow measurements (temperatures, moisture contents, settlements) and the strain gage measurements

Figure 1 -

 1 Figure 1 -HSL "Bretagne Pays de la Loire" lane

Figure 2 -

 2 Figure 2 -Structure of the different sections with and without asphalt concrete.

Figure 5 -

 5 Figure 5 -Superimposed acceleration signals of the seven carrier bogies, and average signal.

Figure 6 -

 6 Figure 6 -Superimposed displacement signals of the seven carrier bogies and average displacement signal

Figure 7 -

 7 Figure 7 -Variation of vertical deflections, in function of train speed, for the sections with bituminous and granular sublayer.

Figure 8 -

 8 Figure 8 -Average signals of anchored displacement sensors on granular section 2 and bituminous section 4 -Speed 320 km/h.

Figure 9 and

 9 Figure9and Figure10present respectively the minimum and maximum accelerations for the accelerometers installed between rails (Figure9) and under the outer rail (Figure10).

Figure 9 -

 9 Figure 9 -Comparison of maximum accelerations on the granular and bituminous sections, for accelerometers installed between rails.

Figure 10 -

 10 Figure 10 -Comparison of maximum accelerations on the granular and bituminous sections, for accelerometers installed under the outer rail.