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Geomechanics and Engineering
  Volume 12, Number 2, February 2017 , pages 295-312

Soil and ribbed concrete slab interface modeling using large shear box and 3D FEM
Jian-Gu Qian, Qian Gao, Jian-feng Xue, Hong-Wei Chen and Mao-Song Huang

    Cast in situ and grouted concrete helical piles with 150-200 mm diameter half cylindrical ribs have become an economical and effective choice in Shanghai, China for uplift piles in deep soft soils. Though this type of pile has been successful used in practice, the reinforcing mechanism and the contribution of the ribs to the total resistance is not clear, and there is no clear guideline for the design of such piles. To study the inclusion of ribs to the contribution of shear resistance, the shear behaviour between silty sand and concrete slabs with parallel ribs at different spacing and angles were tested in a large direct shear box (600 mm × 400 mm × 200 mm). The front panels of the shear box are detachable to observe the soil deformation after the test. The tests were modelled with threedimensional finite element method in ABAQUS. It was found that, passive zones can be developed ahead of the ribs to form undulated failure surfaces. The shear resistance and failure mode are affected by the ratio of rib spacing to rib diameter. Based on the shape and continuity of the failure zones at the interface, the failure modes at the interface can be classified as "punching", "local" or "general" shear failure respectively. With the inclusion of the ribs, the pull out resistance can increase up to 17%. The optimum rib spacing to rib diameter ratio was found to be around 7 based on the observed experimental results and the numerical modelling.
Key Words
    soil and ribbed concrete interface resistance; cast in-situ concrete helical piles; optimum rib spacing; undulated shear failure surface
(1) Jian-Gu Qian, Qian Gao, Mao-Song Huang:
Department of Geotechnical Engineering, Tongji University, Shanghai, 200092, China;
(2) Jian-feng Xue:
School of Engineering and IT, Federation University, Churchill, 3842, VIC, Australia;
(3) Hong-Wei Chen:
Department of Underground Structure & Geotechnical Engineering, East China Architecture Design & Research Institute Co., Ltd., Shanghai 200002, China.

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