Guoxiong Mei

Displacement-Dependent Earth Pressures on Rigid Retaining Walls with Compressible Geofoam Inclusions: Physical Modeling and Analytical Solutions

AbstractA rigid nonyielding retaining structure needs to be dimensioned to have adequate stiffness, such that it can resist mobilized lateral earth pressures. This corresponds to the at-rest condition, as there are, in general, negligible lateral deformations in the backfill. Measures that can mobilize higher soil shear strength and reduce lateral thrust are therefore sought to provide a more efficient design. The present study investigates the possibility of inserting compressible geofoam panels against rigid walls using physical model testing. Controlled yielding is allowed in the backfill with the occurrence of deformations in the geofoam. The mobilized earth pressures vary from the maximum at rest, to the intermediate, and finally to the minimum full active state depending on the magnitude of displacement. The effects of geofoam thickness and stiffness on lateral earth pressure reduction are explored. The measured pressure and displacement distributions form a comprehensive reference for use in calibr...

Model Tests of Buoyant Force on Underground Structures

Conventionally, buoyant foundations are designed based on Archimedes’ principle, by which the buoyant force is computed by simply measuring the weight of groundwater that is displaced. However, soil at shallow depths is generally unsaturated and should be considered as a multiphase porous medium with heterogeneous properties. The efficacy of the Archimedes’ calculation of buoyant force is questionable because recent field evidence indicates that the measured buoyant force is actually much smaller, and the foundation design is always conservative. This article presents a series of model tests on shallow foundations embedded in different surrounding types of materials, such as pure water, clay, and sand to clay-sand composites. Both the transient and sustained hydrostatic uplift forces were measured. It has been demonstrated that the measured buoyant force increased with time and was always less than the theoretical value. A reduction coefficient was consequently suggested to scale down the Archimedes’ buoyant force for use in design. For shallow foundations in clay, a value of 0.3–0.4 should be used to evaluate the transient uplift force, and a higher value of 0.7–0.8 is recommended for the estimation of the steady-state buoyant force. For sand, the reduction coefficient varies between 0.85 and 0.95 for transient and sustained uplift conditions, respectively.

Use of Drainage Holes on Reinforced Concrete Pipe Piles to Accelerate Soil Consolidation

This paper investigates the application of permeable piles (reinforced concrete pipe piles with drainage holes) to accelerate soil consolidation during pile driving. To achieve that, finite element models are generated in ABAQUS with infinite element boundary condition. The results of numerical analyses show that the performance of permeable piles can be improved by drilling drainage holes. However, the influence of these openings on the structural performance of permeable piles has not been evaluated before. The structural behavior of permeable piles is investigated in this study using uniaxial compression tests and four point flexure tests. Although drainage holes could reduce the ultimate compressive strength of pile specimens, the measured values were much larger than design specifications. For bending tests, cracks with smaller width were initiated and propagated over an increasingly wider area in permeable piles, and an improved flexural capacity was obtained. These results of the current study show that permeable pile is an attractive alternative to accelerate soil consolidation.

Analytical solution for one-dimensional consolidation of double-layered soil with exponentially time-growing drainage boundary

In this article, the exponentially time-growing drainage boundary is introduced to study the one-dimensional consolidation problem of double-layered soil. First, the one-dimensional consolidation equations of soil underlying a time-dependent loading are established. Then, the analytical solution of excess pore water pressure and average consolidation degree is obtained by utilizing the method of separation of variables when the soil layer is separately undergone instantaneous load and single-stage load. The validity of the present solution is proven by the comparison with other existing analytical solution. Finally, the influence of soil properties and loading scheme on the consolidation behavior of soil is investigated in detail. The results indicate that, the present solution can be degraded to Xie’s solution utilizing Terzaghi’s drainage boundary by adjusting the interface parameter, that is to say, Xie’s solution can be regarded as a special case of the present solution. The interface parameter has a significant influence on the excess pore water pressure of soil, and the larger interface parameter means the better drainage capacity of the soil layer.

Time Effects on Settlement of Rigid Pile Composite Foundation: Simplified Models

The behavior of pile composite foundation is studied using the flexibility method. During the analysis, determination of the flexibility matrix (settlement) is critical. However, conventional methods of Winkler and elastic half-space foundation models are incapable of considering the time effects of soil consolidation and creep. The foundation model of Zaretsky and Tsytovich [1965] can be used to evaluate settlement for unsaturated soils, but the complexity of numerical integration over an arbitrary loading area hinders its application. In this paper, a novel scheme is proposed for numerical integration by rotating the loading surface using the equiareal transformation technique. Therefore, a simplified closed-form solution is developed to calculate time dependent settlement for foundation soils. The efficacy of the proposed technique is demonstrated using illustrative examples of an elastic half-space, a rigid raft foundation without piles, and rigid pile composite foundations with multiple piles under s...

Consolidation Theory for a Stone Column Composite Foundation under Multistage Loading

The consolidation theories considering instant load cannot fully reveal the consolidation mechanism of a stone column composite foundation used in the expressway embankments due to the time effect of loading; that is, the expressway embankments are often constructed in several stages for a long time. Meanwhile, owing to the special property that the pile-soil stress ratio is larger than 1, the consolidation theory for sand drain well foundation cannot be used directly in the consolidation analysis of stone column composite foundation. Based on the principle that the vertical load applied on the composite foundation is shared by the stone column and the surrounding soil, the governing solutions for the stone column composite foundation under a multistage load are established. By virtue of the separation of variables, the corresponding solutions of degree of consolidation for loading stage and maintaining load stage are derived separately. According to the Carrillo theorem, the solution for the average total degree of consolidation of entire composite foundation is also obtained. Finally, the reasonableness of the present solution has been verified by comparing the consolidation curve calculated by the present solution with that measured by site test.