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This paper presents numerical results from a two-dimensional discrete element method (DEM) simulation study on the influence of lateral boundary condition on shaft resistance of a pile driven into a crushable sand. The study was conducted by comparing simulation results from the pile penetration test and the interface shear test employing parallel-bonded agglomerates for modeling of the particle breakage. The interface shear test was performed under three different types of normal boundary conditions; namely, constant normal load (CNL), constant normal stiffness (CNS), and constant volume (CV) boundary conditions. For the pile penetration test, a series of sampling windows were identified on the initial ground configuration to monitor the stress-strain, volume change, and particle breakage behavior of particle groups located within the sampling windows. A detailed investigation was then undertaken by comparing the behavior of particle groups with that from the interface shear test to find out which type of normal boundary condition best describes the lateral boundary condition in the pile penetration test. It has been found that the behavior of a particle group reaches the peak state below the pile tip and the critical state after it reaches the pile shaft. The influence of normal boundary condition on the stress ratio at the critical state is not obvious. The conventional interface shear test (i.e., CNL) can provide valuable information on the determination of skin friction along the pile shaft. [ABSTRACT FROM AUTHOR]

Drilled shaft foundations supporting mast arm assemblies are subjected to significant torsion and lateral load during severe wind loading (e.g., hurricane). Past centrifuge studies in granular soils suggest that the design of such foundations should be performed for a coupled load case, since the lateral resistance is considerably reduced by the concurrent application of torsion. However, current design practice still considers lateral load and torsion independently due to the lack of field verification of centrifuge results. This paper reports on a full-scale test program to investigate the coupled load behavior of drilled shafts. A novel load test setup (with a heavy-duty mast arm assembly) and instrumentation were used for the combined torsion and lateral loading (e.g., wind loading). The study revealed a significant reduction in lateral resistance due to the influence of torque as observed from previous centrifuge studies. Torsional resistance was reduced (approximately 20%) by the impact of lateral load when compared with the anticipated torsional resistance based on unit skin friction values, derived from the axial load test results (i.e., no influence of lateral load). A comparison of measured torsional resistance during the combined loading with the predicted values using different approaches was also made. O'Neill and Hassan's beta ( β) method (sand) and alpha method (clay) are found to predict the torsional resistance reasonably well (±10%), while all other methods based on the standard penetration test and cone penetration test considered in the study overpredicted or underpredicted the resistance. [ABSTRACT FROM AUTHOR]

A simple analytical approach for nonlinear analysis of the load-displacement response of a single pile is presented. Two models are adopted in the proposed approach. One model uses a softening nonlinear relationship to simulate the degradation behavior between the unit skin friction and the pile-soil relative displacement developed in the pile-soil interface, and the other model adopts a bilinear load-displacement relationship to capture the pile-end response. Based on the two proposed models, a highly effective computer program has been developed for nonlinear analysis of the load-settlement behavior of a single pile. Comparisons are made between the present method, other analytical methods, and a well-documented field experimental pile loading case. The results of the comparisons indicate that the proposed method is generally in good agreement with field-observed behavior and the calculated results derived from other approaches. A parametric study is conducted to assess the influence of the parameters related to the proposed model on the load-displacement response of a single pile. [ABSTRACT FROM AUTHOR]

In the last few decades there has been a rapid increase in the number of piled foundations where the piles have been employed as settlement reducers; in some recent projects, the piles have been separated from the raft by a granular layer, which creates a more uniform pressure distribution on the raft bottom and reduces constraint reactions in the soil, foundation, and superstructure. A series of centrifuge model tests has been performed to investigate the load transfer mechanisms between a square rigid raft and a group of instrumented piles jacked in dry dense sand, in direct contact with the raft or separated from the raft by an interposed granular layer. The test results have shown that contact piles act as settlement reducers by diffusing the load applied to their heads to greater and deeper volumes of soil. The insertion of a deformable layer between a raft and pile heads does not ensure displacement compatibility, and the pressure diffused by the granular fill acts partly on the pile heads and partly produces shallow soil settlements, which mobilize negative skin friction on the upper part of the pile shaft. Noncontact piles act mainly as soil reinforcement. [ABSTRACT FROM AUTHOR]

This paper investigates the failure of three gravity walls due to the 1999 Chi-Chi earthquake. Characteristics of the damaged walls were carefully recorded and backfill materials behind the damaged walls were collected and tested in the laboratory. Both the simplified analysis based on the Mononobe–Okabe method and the simplified dynamic analysis based on the Richards–Elms method were adopted. For the first case, the sliding of concrete wall blocks along the construction joint was observed. It was found that, during the earthquake, the frictional resistance at the untreated construction joint was not sufficient to resist the dynamic lateral thrust. For the second case, the retaining wall settled significantly and tilted about its toe. Seismic analysis of the wall indicated that, under the same horizontal acceleration, the factor of safety against bearing capacity failure was lower than that against overturning and sliding. A stability check against bearing capacity failure for the retaining wall should never be neglected. For the third case, the retaining wall built on top of the Che-Lung-Pu fault was severely damaged by the fault rupture. During the earthquake, the vertical displacement of the hanging wall uplifted the backfill, causing the wall to overturn. Horizontal displacement of the hanging wall caused the wall to slide and the soil in front of the toe to heave. [ABSTRACT FROM AUTHOR]

The article discusses the mechanics of the Casagrande liquid limit percussion test to measure soil strength. Topics include the measurement of undrained strength of soil using the fall cone liquid limit, the shear strength of fine-grained soils based on viscous shear resistance and frictional shear resistance, and the difference in soil properties measured by the two methods.

The article discusses the mechanics of the Casagrande liquid limit percussion test to measure soil strength. Topics include the measurement of undrained strength of soil using the fall cone liquid limit, the shear strength of fine-grained soils based on viscous shear resistance and frictional shear resistance, and the difference in soil properties measured by the two methods.