Abstract:

Expansive behavior of swelling rocks results in swelling pressure acting on foundations. Consequently, upward movement, differential heave on foundations, and foundation failures may be observed due to this phenomenon. The upward movement of swelling claystone layers increase when these layers are exposed to moisture content increase. There are limited studies on evaluating the effects of expansive rock layers such as claystone on the behavior of pier group foundations. In this investigation, the behavior of a group pier system is studied based on the swelling pressure of expansive claystone layers through a series of computational three-dimensional numerical analyses. Numerical results indicate that with increase of center-to-center spacing of the group pier, upward movement will increase. Also, with increase of superstructure pressure, the upward movement decreases. For a 100 percent increase of superstructure pressure, the upward movement is reduced by approximately 77, 72 and 66 percent for ratio of center-to-center spacing to pier diameter of 2.3, 3, and 3.6, respectively.

Introduction

Foundations constructed on weathered rocks especially claystone are subjected to heave and upward movement due to cyclic drying and wetting of expansive layers. Upward movement of foundations cause considerable damages on superstructures. Understanding of swelling behavior of rocks with high percent of clayey material such as claystone or shale is important to identify potential swelling of the ground. Investigation of the response of foundations and superstructure due to ground swelling is also crucial to determine any possible damages or deficiencies.

Different investigators have studied the swelling behavior of expansive rocks with clayey materials. Picornell and Lytton, 1984, and Huang et al., 1986 evaluated swelling responses of cemented claystone and shale, respectively. Mudrock swelling modes have been considered by Sarman et al., 1994. Moreover, the effects of cycling of wetting and drying in weathered mudrock was evaluated by Doostmohammadi et al., 2009. However, there are limited studies for evaluating the heave response of structures and foundations in swelling rocks. In a study conducted by El-Garhy et al., 2000, the soil-structure interaction of a raft foundation with an expansive medium is studied. Nowamooz et al., 2008, investigated on the behavior of shallow footing embedded on clayey ground using numerical and experimental tools. In the case of deep foundations, a 3D elasto-plastic numerical model is developed by Lee, 2012, to study the response of a group pile constructed in weathered rock and adjacent to a tunneling excavation. Several investigations have been conducted by Osouli et al., 2014a, Marino and Osouli, 2012, Zamiran et al., 2015, Zamiran and Osouli, 2015, and Osouli et al. 2014b to evaluate claystone strength reduction due to moisture content increase and its effect on heave and instability of coal pillar foundations.

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