Determining of Sand behavior through model tests of Strip Footing with Micropile Skirts

Recently, the modification of bearing capacity and the reduction in settlement of existing foundations and buildings has become one of the important topics in the field of geotechnical engineering. Also, the foundation of the buildings on the problematic and flowing sand bed, especially in the coastal strips is inevitable. In general, when faced with problematic soils such as loose soils with low load-bearing capacity, high settlement, liquefaction, disturbed soils, etc., there are two ways for geotechnical engineers, one of which is to use bearing elements in the soil and the other is to improve and modify the physical-mechanical properties of the soil mass. In addition to acting as a bearing and settlement-resistant element, the micro pile also improves the bearing strength of the surrounding soil due to the injection of cement slurry. In many projects, micro piles are used as structural elements. In fact, micro piles are small replacement piles (usually less than 300 mm in diameter) that are often accompanied by steel reinforcement and cement grout injection. Micro piles can be designed and used at any angle and for different purposes, including bearing axial and lateral loads, replacing conventional piles, or as part of a soil-pile system, depending on the purpose of the design. In this study, by physical modeling, the effect of using micro piles on the edge the foundation on sand bed was investigated. For this purpose, the effect of the boundary conditions of the chamber was first investigated. The parameters included the width of the foundation (B), the distance of the foundation from the end surface of the tank (Z), the distance of the foundation from the right/left wall of the chamber (X, X'), unreinforced bearing capacity (Q0) and unreinforced sand settlement (S0). Also, the investigation of the effect of the distance of the foundation from the lower surface of the steel chamber to the width of the foundation (B) showed that when the distance of the foundation from the lower surface of the chamber was less than twice the width of the foundation, the lower boundary affected the results of physical modeling. The evaluation of the lateral boundaries given the distance of the foundation from the chamber wall (X) to the width of the foundation showed that for X/B≥5, the lateral boundary had no effect on the results. Influences of various micropile skirt configurations were investigated, including micropile length (L) and spacing between two consecutive micropiles (S) on bearing capacity-settlement. The micropile skirts improved the bearing capacity of shallow foundations, depending on the L/B ratio and spacing between micropiles depending on the S/D ratio. Analysis of the results indicated that improved bearing capacity upon increasing the length of micropile skirt and reducing the spacing between two consecutive micropiles. Comparison of the pressure-settlement curves showed that in constant micropile lengths, the optimum Bearing Capacity Ratio (BCR) was in S/D=2. Further, the skirt piles reduced the settlement of strip footing. The Micropile Skirted Strip Footing (MSSF) led to increased failure surface and, depending on the pile length and spacing micropiles, it changed the failure pattern of the soil.