Yanlin Zhao

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.

Antiflotation design for water tank using pressure relief technique

ABSTRACT A pressure relief technique has been proposed to reduce hydrostatic pressures by opening drainage holes around a water tank. This solution is evaluated by laboratory experiments and numerical parametric investigation. After seepage flow is allowed, the hydraulic head acting on the water tank is reduced due to seepage losses. The drainage holes should be opened on the base slab near the sidewalls, and at a certain height on the sidewalls. Given a fixed total opening area, the number of drainage holes with smaller diameter should be allowed near the edge of the water tank to increase the efficacy of the approach. The properties of the surrounding soil influence the results significantly, where a cushion layer with a higher hydraulic conductivity and a greater thickness is beneficial to the stability of the water tank, and a backfill layer with adequate thickness and hydraulic conductivity should be selected. An illustrative example is given in the end to demonstrate the advantage of the proposed antiflotation design strategy compared to the conventional enhanced self-weight method, and more economic design using less reinforcement and concrete can be achieved.

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.

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...