Three-dimensional Numerical Simulation Of The Soil Nailing Retaining Structure

The soil nail support is a new retaining technique that is incorporated into soil excavation and slope stability. Because of its economy, reliability and quick, simple construction, this technique has been widely used and rapidly developed in our country. In addition, following the pile, the wall, the pile-strut bracing and the anchor supporting structure, it now has become a relatively mature support technology.Combined with engineering example for soil-nail retaining structure, By used ABAQUS finite element software, establish finite element model of soil-nail retaining structure system, based on this to stimulate staged construction of soil-nail retaining, then compare and analysis of simulating results with measured data of horizontal displacement of slope and vertical settlement; to analysis the tension stress of soil-nail.1.In the process of excavation, horizontal displacement of tunnel face increases gradually. When excavation begins, the lateral restraint of the slope is gradually lifted, and hence the lateral displacement emerges. each excavation depth is1.5m, so the curve shapes with the change of excavation steps are also very similar. As the continually displacement of the support, the displacement of the support structure of each homogeneous soil is in a linear change along the height and the maximal displacement occurs in the top of the foundation pit. However, as the excavation proceeds, the position of the maximum horizontal displacement moves a short distance within the soil, corresponding the cracks of the surface.2.Excavation leads to the break of the original stress equilibrium state, the stress distribution in the soil and the formation of the secondary stress field. Soil on excavation face trends to move down and have a extrusion effect on the operation excavation soil with less pressure. Therefore, the soil of working surface has a trend of upward movement and uplift is forming.3.The ground surface settlement is curve distribution with the distance from the excavation, and each excavation distribution curve of the ground surface settlement is very similar. The maximum settlement occurs on the excavation face, and the settlement gradually decreases as the distance from excavation face is farther; In all four steps of the excavation process, when the distance from soil slope to excavation is H-the excavation depth of foundation pit., the ground surface settlement will reduce to zero. On the top of the foundation pit slopes have certain settlement increment every excavation step, and the settlement distribution curve shape are similar.4.The tension of the same row of soil nails has a similar curve distribution while extending along the soil nails. There will be certain tension incremental with the tension of the soil nails. and each increment is roughly the same, hence the final distribution curve shape is very similar. When the excavation is in the process, the tension of the soil nails will increase with the increasing of the depth. This is because that the horizontal load soil caused by the soil unloading increases gradually with the excavation, so the soil nails will work more and share in most of the horizontal load.5.For every soil nail, the maximum tension is usually in the middle of the length of the nail and is close to the end that the soil nail and the concrete surface layer link together, and the maximum tension declines gradually along the both ends of the soil nails. In addition, after every excavation, the tension of every row of soil nail is almost close to certain value near the soil nails of excavation foundation pit; but the tension of every row of soil nail is almost close to zero far from the soil nails of excavation foundation pit in the same circumstances. In conclusion, the worst part of soil deformation is generally of the biggest tension, and the biggest tensional parts of each row of soil nails are relatively dangerous.6.The length of soil nail should be increased properly to control the deformation of foundation pit. However, if the soil nail is too long, the effect of deformation controlling will be unconspicuous and the tensile force will also increase slowly. Thus, the strength is used in a too small range to be wasteful. When soil nail is arranged closely, all of the numerous soil nails are responsible for excavation loads. The group role can restrain the soil deformation effectively. After the excavation of foundation pit, the lateral of the slope is mainly under the action of excavation load. In consideration of controlling the horizontal deformation of foundation pit, soil nail is appropriately horizontal or close to horizontal setting. The arrangement of the length of soil nailing has great influence on the deformation of foundation pit. Therefore, the design schemes of setting long soil nailing in the central of foundation pit and in the upper of foundation pit are preferably better.