1,721,288 research outputs found
Reinforced soil with geosynthetics - hands-on learning (PBL) using sand and paper
No full textAn elective module on geosynthetics was designed and made available to Civil Engineering students (5 years’ integrated masters). This paper reports a hands-on activity using sand and paper, adopted as part of a problem-based learning (PBL) model and the feedback collected in 2011/2012 using questionnaires. The model and its main features are briefly described, particularly the problem on soil reinforcement with geosynthetics. The students’ feedback and some of their outputs are presented to highlight how simple and relatively cheap activities can contribute to learning and create a positive impact on students. The success of the PBL approach is enhanced by managing expectations, as well as giving adequate support and feedback to students
Building with sand -simple outreach activities to promote GeoEngineering
No full textThis paper describes two sets of simple outreach activities, designated as “Building with sand”, promoted in Portugal or in the UK. The hands-on activities focused on reinforced soil, using sand and paper. The activities included: 1) 30 minutes’ sessions in a Geotechnical laboratory (UK) in which participants build small cylindrical samples of reinforced and unreinforced sand and compare their resistance; 2) 3 hours’ sessions where students are challenged to build and load small reinforced soil structures (Portugal). For the latter, in 2011/2012 pre- and post-activity questionnaires were used, focusing on the students’ learning and perceptions/opinions. The activity organised was clearly a success for both the learning and the impact on the students participating. The results from the questionnaires indicate that with this activity it was possible for students to grasp complex concepts on soil strength and soil reinforcement. For both sets of activities the required resources were limited, making them easily replicable. The activities are easily adaptable to different audiences, which can range from K-12 students to graduate students
Bearing capacity of reinforced soil under a strip footing: centrifuge tests
No full textGeosynthetics can be used to increase the bearing capacity of poor foundation soils and/or to reduce excessive settlements. This paper analyses the case of shallow foundations on reinforced soil using centrifuge tests, namely that of a strip footing on a horizontal ground reinforced with one layer of geosynthetic. The response of reinforced models was compared to that of a similar unreinforced model. The influence of the depth of the reinforcement layer was studied. Two different reinforcement materials were used: a geotextile and a geogrid. The ultimate bearing capacity, as well as the bearing capacity at particular settlement levels were analysed. The results indicate that using one layer of reinforcement contributes to in-creasing the ultimate bearing capacity, provided the reinforcement is adequately positioned. It is likely that the higher limit for the normalized depth of the reinforcement layer recommended in the literature may need to be reduced, when using only one layer of reinforcement. The improvement in bearing capacity at particular settlement levels is important as often the settlement, rather than the bearing capacity, controls design. The models tested exhibited reduced bearing capacity for normalised settlements of 5%B (B, width of the footing), while for smaller normalised settlements (2%B) the reinforcement layer included was effective, particularly when the reinforcement layer was placed nearer to the footing. The experimental data was compared to analytical estimates of the bearing capacity with proposals from the literature. The analytical estimates are optimistic, particularly for the geogrid
Challenges and benefits in implementing problem-based learning in an elective MSc course: Application of Geosynthetics in Civil Engineering
No full textAn elective module on geosynthetics was designed and made available to Civil Engineering students (within a 5 years’ integrated masters). This paper describes the problem-based learning (PBL) model implemented. Two different types of problems were used: summative, marked for assessment purposes; and formative, in-class problems used to drive the learning on topics not directly covered on the summative problems, thus creating PBL environments for all the course. A questionnaire was used to assess the impact on the students of the PBL model implemented. The students’ perceptions of the model are summarised. The advantages and disadvantages of implementing a PBL model, from the teachers’ perspective, are described and some suggestions for teachers willing to use PBL models are included, to contribute to successful experiences for both students and teachers. Although using PBL will increase the workload of the teacher, if successfully implemented, the students’ enthusiasm is quite rewarding. For a successful PBL course close to graduation, previous experiences of PBL or other inductive teaching models are ideal, for both students and teachers. One of the key messages to teachers is to start small and develop the PBL model gradually, making sure that students appreciate the teachers’ effort and understand how the students will benefit from those models, both short- and long-term
Evaluation of the quality of teaching and learning for 1st year engineering programmes – an initial contribution: the case of the University of Aveiro, Portugal
No full textA system for evaluating the quality of teaching and learning implemented at the University of Aveiro, Portugal, is briefly described. Data for five modules on the 1st year engineering programmes was collected (using questionnaires and reports filled in by students and teachers) and analysed using quantitative and qualitative approaches. The “strengths” and “weaknesses” emerging from the data were discussed. Both teachers and students showed a reflective attitude by focusing on their different roles in the teaching and learning processes. Students identified two main sets of strengths, related to material resources associated with the modules and the type of assessment, but also related to their attitudes (interest and motivation). The assessment methods, in particular the number of assessment elements, were identified as strengths by both groups (students and teachers). Teachers also identified the alignment of the modules as a strength. The weaknesses identified by students were related to their attitudes (attendance and punctuality, and the reduced number of times they contacted the teachers outside the timetabled slots) and to the teachers (their lack of/or limited support, feedback and availability). Students answering questions on the teachers’ competencies perceived those as strengths, including their pedagogical competencies. Such competencies may not have been put into practice adequately, as students did not feel supported properly by teachers in the learning process. Teachers identified the use of teacher-centred strategies and passive and deductive teaching approaches as weaknesses. However, the data analysed did not show any evidence of shifting the teaching and learning approach from teacher-centred to student-centred. The authors believe that there are several possible reasons that shape the resistance to more active learning approaches to learning and teaching: teachers are often overwhelmed by the workload associated with implementing student-centred strategies and active and inductive teaching approaches; what is verbalised and what is implemented by teachers often differs. This may indicate a “single-loop learning” approach, focused on the quality of teaching, without linking it to that of learning. Additionally, career progression often ignores completely the performance of academics as teachers, focusing on research performance. To improve the quality of teaching and learning, and academic success of students, while reducing dropout rates for 1st year engineering students, additional strategies are needed. Those include adopting student-centred teaching and learning approaches. Thus, higher education teachers should be supported and given adequate pedagogical training and resources. Simultaneously, teachers implementing such approaches to teaching and learning need to be encouraged and rewarded by their institutions
Influence of mechanical damage induced in laboratory on the soil-geosynthetic interaction in inclined-plane shear
No full textThis paper contributes to better understanding how mechanical damage associated with installation affects soil-geosynthetic interaction, particularly for inclined plane shear movement. The mechanical damage was induced in laboratory, adapting a standardised procedure to allow for large samples. Six geosynthetics were studied: two geotextiles, one geocomposite and three geogrids. The soil-geosynthetic interface was characterised using inclined plane shear tests. The laboratory mechanical damage affected the soil-geosynthetic interface strength and the sliding mechanisms observed. The results showed that the mechanical damage caused an increase in the skin friction available, due to the damage mechanisms observed. The structure of the geosynthetic affected the inclined plane shear response after mechanical damage. The friction mobilised in solid area of the geogrids increased after mechanical damage, which depended on the geogrid and on the consequences of mechanical damage. The reduction factors for mechanical damage associated to installation showed that the interface strength did not change significantly. The reduction factor obtained from tensile tests was, in most cases, conservative to represent the changes observed on the soil-geosynthetic interface strength. The structure of the geosynthetics had a higher impact on their tensile response after mechanical damage than on the soil-geosynthetic interface in inclined plane shear. For the interface strength in inclined shear plane movement, the mechanical damage induced in laboratory of the woven geotextile was conservative compared to field installation damage, while for the woven geogrid the mechanical damage induced in laboratory was within the range of damage induced in the field. Despite some heterogeneity of responses, the standardised laboratory tests to induce mechanical damage in laboratory seem to be able to represent the effect of the mechanical damage associated with installation on the inclined plane shear response of soil-geosynthetic interfaces
Simple constitutive models to study the influence of installation damage on the load-strain response of two geogrids
No full textA key factor affecting the tensile response of geosynthetics is installation damage, represented by a reduction factor capturing changes in tensile strength. Although often geosynthetics are represented in numerical models by simple linear-elastic constitutive models and a stiffness, the response of geosynthetics to loading can be represented more realistically by non-linear constitutive models. Herein, simple constitutive models were used to represent the short-term tensile response of two geogrids (woven geogrid and uniaxial extruded geogrid). The tensile response of samples exhumed after field installation under real conditions was compared to that of the corresponding undamaged samples (as-received). The changes in response, particularly the change in tensile strength and stiffness, were presented and discussed. The polynomial models (order 6) approximated the experimental data better than the hyperbolic models. Contrary to what has been reported in the literature, for the materials and test conditions presented herein and for the hyperbolic models, the parameter b cannot be estimated as the inverse of the materials tensile strength and the parameter α is not a material constant. Both polynomial and hyperbolic models approximated well the tangent stiffness for 2% strain obtained experimentally. The model parameters were normalised to the reduction factor for installation damage; for the hyperbolic models, the parameter b was practically unchanged after exhumation of the samples, while parameters a and α showed no clear trend; the values of the stiffness normalised to the reduction factor for installation damage were not constant
Using different and complementary teaching tools in project-based learning: application to civil engineering - courses on Soil Mechanics
No full textThis paper describes the use of different and complementary teaching tools on two consecutive courses on Soil Mechanics (on an integrated master in Civil Engineering). In these courses, project-based learning with collaborative or cooperative teamwork was implemented. The teaching tools adopted and described herein include text processors, spreadsheets and presentations, as well as specialized geotechnical software. The students' perceptions were collected using a questionnaire and the impact of those different tools on the students' perceptions are analysed. Some considerations for future implementations of similar approaches are put forward. The students' perceptions collected allowed concluding that using different and complementary teaching tools in project-based learning can be effective in promoting students' learning. The use of such tools may contribute to the development of both technical knowledge of students and of soft skills. For this case study, the results show that the students considered the computer tools useful in promoting and facilitating the construction of knowledge and in developing several competencies, i.e., in developing their learning processes. Nevertheless, a positive attitude and commitment by both the students and the instructors are essential to successful teaching and learning processes. Getting students on board, by discussing the aims of using specific strategies, is key to promote academic success. Therefore, students must be the centre of all the teaching and learning processes.</p
On surfaces of general type with q=5
Get PDFWe prove that a complex surface S with irregularity q(S)=5 that has no irrational pencil of genus >1 has geometric genus p_g(S)>7. As a consequence, one is able to classify minimal surfaces S of general type with q(S)=5 and p_g(S)3 that have no irrational pencil of genus >1 and with the lowest possible geometric genus p_g=2q-3. This gives some evidence for the conjecture that the only irregular surface with no irrational pencil of genus >1 and p_g=2q-3 is the symmetric product of a genus three curve. The research that lead to the present paper was partially supported by a grant of the group GNSAGA of INdA
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