Supporting active learning in an undergraduate geotechnical engineering course using group-based audience response systems quizzes

The use of audience response systems (ARSs) or ‘clickers’ in higher education has increased over the recent years, predominantly owing to their ability to actively engage students, for promoting individual and group learning, and for providing instantaneous feedback to students and teachers. This paper describes how group-basedARSquizzes have been integrated into an undergraduate civil engineering course on foundation design. Overall, theARSsummary quizzes were very well received by the students. Feedback obtained from the students indicates that the majority believed the group-based quizzes were useful activities, which helped to improve their understanding of course materials, encouraged self-assessment, and assisted preparation for their summative examination. Providing students with clickers does not, however, necessarily guarantee the class will be engaged with the activity. If an ARS activity is to be successful, careful planning and design must be carried out and modifications adopted where necessary, which should be informed by the literature and relevant student feedback.

Relationship between electrical resistivity and basic geotechnical parameters for marine clays

Recently, considerable efforts have been made in the attempt to map quick clay areas using electrical resistivity measurements. However there is a lack of understanding regarding which soil parameters control the measured resistivity values. To address this issue, inverted resistivity values from 15 marine clay sites in Norway have been compared with basic geotechnical index properties. It was found that the resistivity value is strongly controlled by the salt content of the pore fluid. Resistivity decreases rapidly with increasing salt content. There is also a relatively clear trend of decreasing resistivity with increasing clay content and plasticity index. Resistivity values become very low (˜5 O·m) for high clay content (>50%), medium- to high-plasticity (Ip ˜ 20%) materials with salt content values greater than about 8 g/L (or corresponding remoulded shear strength values greater than 4 kPa). For the range of values studied, there is poor correlation between resistivity and bulk density and between resistivity and water content. The data studied suggest that the range of resistivity values corresponding to quick clay is 10 to 100 O·m, which is consistent with other published limits. A comparison is made between two-dimensional electrical resistivity tomography (ERT) and resistivity cone penetration test (RCPTU) data for two of the sites and the two sets of data show similar trends and values irrespective of scale effect.

Reuse of construction waste: performance under repeated loading

The use of recycled aggregates has increased greatly over the last decade owing to enhanced environmental sensitivities. The level of performance required by such materials is dependent upon the applications for which they are used. Many recycled construction wastes have adequate shear strength in relation to various geotechnical applications. However, a possible drawback of these materials is the risk of crushing during repeated loading. The work reported in this paper examined two waste materials: crushed concrete and building debris, both regarded as construction wastes. Tests were also performed on traditionally used crushed rock, in this case basalt. The materials were subjected to repeated loading in a large direct shear apparatus. The amount of crushing was quantified by performing particle size analysis of the tested material. The results have shown that both recycled construction wastes were susceptible to particle crushing. The amount of crushing was influenced by both the vertical pressure and the number of loading cycles. This leads to a marked decrease in peak friction angle

The effect of anisotropic elasticity on the yielding characteristics of overconsolidated natural clay

Quantitative application of elastoplastic theory to the yielding behaviour of natural soils has always been uncertain. Part of the reason is that the theory was developed for reconstituted materials with isotropic structure, in contrast to natural soils that are usually anisotropic. The approach considered in this study assumes that pre-yielding behaviour is governed by the theory of linear anisotropic elasticity and that yield loci in the mean effective stress ( p') – deviator stress (q) plane are aligned approximately along the coefficient of earth pressure (K0) line. The assumption of a rotated yield locus associated with anisotropic elastic behaviour within the state boundary surface indicates that the elastic wall within the state boundary surface is inclined. The form of the state boundary surface has been determined mathematically in terms of anisotropic elastic and Cam-Clay soil parameters. Stress path tests were conducted on samples of Belfast Upper Boulder Clay removed from a depth of 28 m below ground surface. Good agreement was found between predicted and measured yield loci. The study also examined the influence of subsequent isotropic compression on the yielding characteristics of the natural clay. The indications are that the anisotropy developed during deposition disappears when the sample is loaded to a stress level at least twice the stress generated during the original deposition process. The methods developed in the paper have also been applied to test results reported previously on Winnipeg clay, and good agreement was obtained.

Delayed failure of a deep cutting in lodgement till

Recent research on the delayed failure of cuttings in clay clearly recognises and predicts progressive delayed failure of deep cuttings. This is due to a combination of strain-softening, weathering, dissipation of negative excess pore water pressure generated at the time of excavation, and frequent occurrence of prolonged periods of wet weather. There have been several slope failures of this kind in Northern Ireland. This paper discusses a case study based on a failure of a deep cutting, excavated at a slope of 1 in 2, on the A1 near Dromore (County Down) in Northern Ireland. The cutting was in lodgement till, a stiff, heavily overconsolidated clay. The failure occurred approximately 30 years after the cutting was excavated, following a prolonged period of heavy rainfall. An analysis of the failure, together with laboratory test data on soil samples taken from the site, confirmed that by using long-term soil strength parameters the factor of safety of this slope was unity. The conclusion of the analysis is that slopes excavated in this soil should be designed (and assessed) on long-term strength parameters.