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Existing projects indicate that a large number of pile boreholes formed via cement fly ash gravel (CFG) pile construction in soft soil could produce a borehole group effect in the absence of timely backfilling. The borehole group effect could cause ground settlement and threaten the safety of adjacent buildings, tunnels, and pipelines. However, the mechanism of the borehole group effect, causing serious deformation in surrounding soil, has seldom been studied, and there exists no simple simulation method to predict the borehole group effect. In this study, a case involving CFG pile boreholes in a soft soil area causing a significant settlement of surrounding buildings was introduced. Based on this case, a centrifuge test was designed to simulate the influence of a single borehole and multiple boreholes on the surrounding soft soil. The mechanism of the borehole group effect was investigated via centrifuge tests and the finite-element method. In the case of a single borehole, a horizontal circumferential stress arch and vertical stress transfer arch were formed in the soil, which effectively limited the shrinking deformation of the borehole wall. In the case of a large number of boreholes with a small spacing, the horizontal and vertical stress arches around the boreholes affected and weakened each other. As a result, the shrinking deformation of the borehole group was greater than that of the single borehole. In other words, the borehole group effect was found to cause serious deformation in the surrounding soil. To overcome the difficulty in the simulation of a large number of pile boreholes in engineering, the borehole-type conversion and multihole merging method was proposed. The simulation results indicated that the simplified method was reasonable. [ABSTRACT FROM AUTHOR]

A hand-calculation method for estimation of nonlinear load–settlement response of piled raft foundations (PRFs) embedded in sandy soils is developed using three-dimensional finite-element (FE) analysis in which the elastoplastic constitutive behavior of the soil is modeled using the unified Clay And Sand Model (CASM). Three types of PRFs with rectangular, strip, and circular rafts and with a variety of pile dimensions and arrangements are considered in the study. The PRFs are assumed to be embedded in five different sands (Ottawa sand, Erksak sand, Sacramento sand, Portaway sand, and Decomposed Granite sand) with different elastic properties, critical state parameters, and relative densities. Systematic parametric studies are performed to develop equations for the estimation of the average nonlinear settlement of PRFs. The maximum and differential settlements are also estimated from the average settlement. The proposed equations require the relative density, elastic constants, and critical state friction angle of sand, and the piled raft geometry and properties as inputs. The settlement equations are applicable to PRFs of sizes similar to those considered in the study and can be used by practitioners for quick, initial estimation of PRF settlement as part of design calculations. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to establish a complete analytical solution concerning the linear pressure distribution under rigid rectangular spread footings. An eccentricity diagram is developed to map the unique footing deformations and compression zones in each one of five distinct regions. For each region, the linear soil pressure, neutral axis position, and pressure values at the four corners are expressed in closed forms. The accuracy and consistency of the explicit expressions are verified by presenting several special boundary cases, whereas the physical interpretation is brought out by analyzing the eccentricity diagram. A generic nomogram providing the maximum soil pressure is also formed to promote efficient structural footing design. The developed analytical formulas for responses and resultants enable algorithmic implications without iterations and offer high computational efficiency. Proper examples, generated via developed computer software, exhibit how the theoretical content of this article is applied in practice. The software enables three-dimensional (3D) viewing of the deformed and undeformed physical and mathematical model of the structure, allowing detailed visual inspection of the results. [ABSTRACT FROM AUTHOR]

In the present paper, the response of cylindrical storage tank foundation resting on stone column-reinforced ground has been studied considering the separation between the bottomraft and ground under liftoff condition. The bottomraft of the tank is idealized by a circular plate. The stone column-reinforced ground ismodeled as a tensionless foundation. Soft foundation soil and granular fill are idealized as a spring-dashpot element and Pasternak shear layer, respectively. Stone columns are modeled as stiff nonlinear springs. The stone columns are converted into equivalent concentric rings with one stone column at the center to simulate the axisymmetric condition for the analysis. The governing differential equations are derived fromthe classical theory of thin plate and solved using the finite-difference technique. A parametric study is performed to investigate the differences between the response of tensionless and conventional elastic foundation systems. It is observed that tensionless foundation idealization is essential to analyze the liftoff and avoid erroneous design of the raft for the cylindrical storage tank. Recommendations are also suggested to avoid possible liftoff. [ABSTRACT FROM AUTHOR]

The present research intends to study the effects of the seismic soil-pile-structure interaction (SSPSI) on the dynamic response of buildings with various heights by conducting a series of shaking table tests on 5-, 10-story, and 15-story model structures. Two types of foundations for each case are investigated, including (1) a fixed-base structure, representing the situation excluding the soil-structure interaction; and (2) a structure supported by an end-bearing pile foundation in soft soil. An advanced laminar soil container has been designed that uses three-dimensional numerical modeling to minimize the boundary effects and to simulate free-field motion during the shaking table tests. Four real earthquake events, including Kobe 1995, Northridge 1994, El Centro 1940, and Hachinohe 1968, are imposed to each model. According to the experimental measurements, it is observed that the SSPSI amplifies the maximum lateral deflections and in turn interstory drifts of the structures supported by end-bearing pile foundations in comparison with the fixed-base structures. The rocking component plays an important role in increasing the lateral deflection of the superstructures, which can shift the performance level of the structures to near collapse or even collapse levels and as a result should be assessed precisely in the seismic design of buildings resting on soft soils. [ABSTRACT FROM AUTHOR]

Meshfree method is one of the numerical methods that typically use higher-order approximate functions and a weighted-residual approach to formulate the shape functions that are independent of the grids. In this paper, a series of computational modeling were conducted using the meshfree local Petrov-Galerkin (MLPG) method to evaluate the bearing capacity and response behavior of extended-length piles. The computational program codes and boundary conditions were generated based on the elastic-plastic behavior of the surrounding soil, reinforcements, and the noncontinuous interfaces between the piles and the soil. Compared to the traditional finite-element method (FEM), the MLPG exhibited higher accuracy in the results and indicated that the optimal length of the pile is directly related to the stiffness of the soil, i.e., the stiffer the soil, the longer the allowable pile length. Overall, the MLPG meshfree method was found to be a reliable and potentially promising numerical method for studying the bearing behavior of pile foundations. [ABSTRACT FROM AUTHOR]

Pile-soil interaction in an expansive soil foundation has been primarily analyzed by an analytical solution in our previous study. As a complementary work, this paper briefly reviews the derivation process in more detail and extends the capability of the solution in dealing with the pile-soil interaction issue under various conditions. The results show that (1) increasing pile length is able to effectively decrease the upward pile movements, but meanwhile, the tensile stresses along the pile shaft increase as well; (2) a critical pile diameter exists (d≈0.04L); (3) when the diameter is less than this value, the upward pile movements can be reasonably reduced, but for the pile with a larger diameter, it has little effect on reducing the upward pile movements, and as irrigation proceeds, both the displacements and tensile stresses increase and both tend to be much less sensitive to the water's incoming over time; and (4) a critical applied pressure for preventing the upward pile movements that is induced by soil's swelling pressure is found to be 2.5 times of the maximum tensile stress of the free pile only under swelling pressure in expansive soil foundation. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study on the thermal conductivity of a soft saturated clay (Bangkok clay) carried out in relation to an investigation into thermal ground improvement using prefabricated vertical drains. The thermal conductivity of clay specimens was measured, at different porosities and temperature levels, using a simple nondestructive steady-state test method. In addition, a theoretical mixture model to simulate the evolution of thermal conductivity of saturated fine-grained soils has been introduced. It is formulated in terms of thermal conductivity and volume fraction of each soil phase (solid and water), and a morphological parameter controlled by the soil fabric condition. The proposed model has been validated against thermal conductivity results reported in the literature and results obtained from the present investigation. Reasonable agreement has been obtained between the predicted and measured thermal conductivity values. [ABSTRACT FROM AUTHOR]