Journal of Geotechnical and Geoenvironmental Engineering

This paper presents a laboratory investigation of the influence of simulated tube-sampling disturbance on lightly overconsolidated intermediate soils by varying their plasticity and degree of sampling disturbance. Samples consisting of varying proportions of kaolin and silica silt that produce five plasticity indexes of 0%, 4%, 9%, 16%, and 32%, are mixed as slurry and then consolidated to an overconsolidation ratio of 1.8. All specimens are tested in a stress-path triaxial cell using the ideal sampling approach (ISA), which involves applying undrained shearing with axial strain cycles of $\pm 0.5\%$, $\pm 1.0\%$, and $\pm 3.0\%$, corresponding to three different degrees of tube-sampling disturbance. The results show systematic trends in the soil response with decreasing plasticity to the induced ISA disturbance. At the same degree of ISA disturbance, the subsequently measured undrained shear strength for the low-plasticity soils increases compared with the reference undisturbed specimen and the percent change increases with decreasing plasticity. This is significantly different from the reported findings from ISA testing of clays, indicating that intermediate soils and clays can have contrastingly different responses to sample disturbance.

Comparative field tests were carried out on two straight-sided piers and two belled piers under combined uplift and lateral loads on arid loess sloping ground with an inclination angle of 20°. The pier-head uplift and lateral displacements, ground surface deformation, and soil pressures on the pier and bell were obtained. For both straight-sided and belled piers on sloping ground under combined uplift and lateral loads, the curves of the applied loads versus pier-head uplift displacement and pier-head lateral deflection exhibited an initial linear segment, a curvilinear transition, and a final linear region, and their capacities should be interpreted from the load test results. The pier-head uplift displacement and pier-head lateral deflection increased nearly at the same displacement increment, and the limit state of a pier on a slope under a combined uplift-lateral load may be primarily governed by the pier-head lateral deflection due to lateral soil failure. Belling may cause greater load-transfer depths and can effectively mobilize more soil to resist the combined uplift and lateral loads, and additional pier embedment in a slope can increase the uplift and lateral resistance to match the level-ground capacity for both straight-sided and belled piers.

A general approach for calibration of resistance factors for load and resistance factor design (LRFD) of pullout and tensile failure internal limit states of soil nail walls is presented. The calibration of resistance factor values includes the influence of nominal load and nominal resistance model type and accuracy (method bias), bias dependencies, uncertainty in nominal load and resistance values, and possible cross-correlation (dependency) between nominal load and resistance terms. The current default Federal Highway Administration simplified method and an improved version are used to compute maximum nail loads under operational (in-service) conditions. Nail pullout capacity is calculated using the effective stress method adopted in Hong Kong and a more accurate modified version. Resistance factors are calibrated for a range of load factors and target reliability indexes. Example design outcomes for internal limit states of a soil nail wall using different load and resistance model combinations are presented. The benefit of using the more accurate improved load and resistance models for soil nail wall pullout design is demonstrated by a reduction in total length of soil nails.

Moreover, a two-dimensional finite-element model has been developed by incorporating unloading-reloading responses into the monotonic load-transfer curves to define the soil–energy pile interaction during heat exchange operations. In this paper, the development of the finite-element model and information on the full-scale field test are presented along with the validation of the model with the observational data for the application of pure temperature cycles. This study reveals that the proposed model yields satisfactory results in terms of cyclic thermal behavior of energy piles, where the development of appropriate load-transfer curves representing the soil–pile interaction is of paramount importance.

The paper explores the application of conventional (DMT) and seismic (SDMT) dilatometer tests to an important case of deep excavation design. The work presents finite-element analyses simulating a deep excavation close to Barcelona (Spain). A thick layer of soft interbedded sandy and silty soils made characterization based on laboratory testing very difficult. SDMT offered an alternative for estimating the soil stiffness and its stress-strain dependency. Numerical results and high-quality monitoring data show quite close agreement for most phases of the construction process, supporting the use of seismic dilatometer tests in numerical analyses of deep excavations. The paper also indicates the importance of incorporating stiffness data at low strains. FE analyses involved some uncertainties derived from the presence of jet-grouting soil treatments. On this point, a parametric study illustrates the effects of different modeling approaches.

Soil arching is one of the most important mechanisms in piled embankments. To investigate the development of soil arching in piled embankments, 14 unreinforced and 8 geosynthetic-reinforced model tests were carried out using a two-dimensional (2D) multitrapdoor test setup with analogical soil. This study revealed that basal geosynthetic reinforcement changed the three deformation patterns into two development patterns with concentric elliptical arches under the same conditions. The stress reduction ratios (defined as the ratio of the average pressure on the trapdoor at a certain settlement to the initial pressure on the trapdoor at zero settlement) corresponding to the three deformation patterns in the unreinforced tests were distinctively different. The change of the stress reduction ratio during the settlement of the subsoil also showed how basal reinforcement affected soil arching in piled embankments. The geosynthetic with lower tensile stiffness resulted in more soil arching than that with higher tensile stiffness.