| GRF(Geo-Reforcing type Foundation)foundation is a new type of special pile, firstly used in Japan and given patent. This type of pile has some advantages, including simpler construction technology, higher bearing capacity, less settlement, saving cost, obvious economic benefits and social benefits, which is especially suitable for the large foundation composed of one pile and one pillar. This pile is a developing direction of large diameter pile and has wide application prospect. Although this new technology has remarkable results in the practical project, it is still at the stage of development and application, and is lack of systematic research in theory. In order to clarify the GRF foundation's bearing mechanism and anchor's action mechanism under vertical load, the study adopts model test and FLAC3D numerical simulation to analyse its load transfer law and deformation and failure mode systematicly, and it also investigates the GRF foundation bearing capacity with different anchor spaces, anchor lengths, anchor numbers and anchor row numbers. The main achievements are shown as follow:1)The results of model test and numerical calculate show that GRF foundation has the characteristics of bigger bearing capacity, less settlement and so on. The side resistance and end resistance of GRF foundation are bigger than that of strainght pile with equal diameter. Under vertical load, the side resistance and end resistance of GRF foundation bear the top load togethor and the side resistance (including anchor function) plays main role. GRF foundation is a new type of foundation fixing anchor to normal strainght pile, and the anchor makes the characteristics of GRF foundation different from that of normal strainght. According to the results of model test and numerical calculate, the anchor improves the GRF foundation's bearing capacity by three aspect: a) arousing more soil beside pile to provide side resistance; b) anchor inserting the soil, moving downstairs together with pile under vertical load, and supporting by the soil, which is called"Stent"function; c) anchor makes the end resistance of GRF foundation bigger than that of normal strainght pile.2) Under the same top load, the axial force of GRF foundation gradually decreases along the pile, which is influenced by anchor and shows"step"mutation at the anchor position; the axial force at the same position of GRF foundation gradually increases with the increase of top load. GRF foundation performance its advantages at the aspects of bearing only on the condition that the load is bigger and the pile's displancement reaches a certain value. Under vertical load, the anchor of GRF foundation moving downstairs together with the pile, the interaction between anchor and soil can influence the stress distribution of the GRF foundation near the anchor. Numerical calculate results show that the pile near anchor can generate tensile stress, and when the tensile stress exceeds the tensile strength of pile material, it will generate tension crack at the pile surface, which is proved by the model test.3) When the top load is small, the displacement of GRF foundation is also small and anchor does not function or functions little, so, the influence that anchor acting on the bearing characteristics of GRF foundation is little; when the top load is bigger, the anchor movesdownstairs with the pile and interacts with soil, which will effect the bearing characteristics of GRF foundation. According to the result of indoor model test, increasing the anchor space and adding anchor number can improve the bearing capacity of GRF foundation. The model test shows that anchor has a critical length. When the anchor length is less than the critical length, the bearing capacity of GRF foundation will increase with the increase of anchor length; when the anchor length is more than the critical length, the bearing capacity of GRF foundation will change little. But the numerical calculate result shows that the bearing capacity will increase with the increase of anchor length, which does not show the critical anchor length. Changing anchor row number on the premise of certain anchor total number, the bearing capacity of GRF foundation will improve to some extent with the increase of anchor row number. |
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