Research On Application Of Composite Soil Nailing Wall Supporting Structures In Deep Excavation Engineering

The composite soil nailing wall support with simple construction, low cost, effective support and other significant advantages is widely used in deep excavation engineering. Now, the research about the mechanism of supporting form is less, the corresponding theory is not perfect and the design is too conservative, which caused great waste of resources. In order to make the composite soil-nailing wall supporting technology is applied to the engineering practice better, making deep research on it become very important.In this paper, a deep foundation pit engineering of Xi’an was taken as the research background. Comparing and analyzing the common deep foundation pit support scheme, the composite supporting structure of micro pile plus with nailing was proposed to choose. Based on ABAQUS finite element software, the three-dimensional model was established and then the whole process of excavation was simulated, in which the bond-slip effects of soil nailing, micro pile and soil and the method of node displacement of the coupling between components was adopted. Compared with the actual measured data, the rationality of using ABAQUS to analyze the change of supporting structure and the deformation of foundation pit was verified. Through the analysis of the model, the influence regularity of unearthed nail, miniature pile and the parameters of surface layer on the deformation of foundation pit was concluded. Finally, finding out the optimal design optimizing and the original plan, which provide a reference for the design and construction of similar engineering. The main research results of this paper are as follows:(1) Micro-pile and composite supporting structure of soil nailing in the control of the displacement of slop have achieved significant results. The horizontal displacement of the top of the slope showed a small, large central “bulge” distribution and lower convergence trends. The maximum ground surface settlement was in leave face a certain location, and tends to be stable; heave value from excavation face is far more, and finally tends to be stable.(2) The first two rows of axial force of soil nails appear at both ends is small, central larger “dates” type distribution, from the third row of nail, the maximum axial force gradually to the pit wall and the distance between the surface layer to move a certain distance,the maximum axial force of soil nail in third rows. The fourth and fifth rows of axial force of soil nails in the maximum value appeared near the excavation surface, explained here slope that the pit wall shear stress concentration, prone to accidents.(3) After each step excavation support of foundation pit, the micro-piles of maximum shear are negative shear, the direction toward the outside of the foundation pit. As the excavation step, corresponding to the maximum shear force is also increasing, the excavation of the bottom position, the absolute value of shear, the largest in the micro pile embedded in certain depth below bottom, shear value and becomes zero.(4) composite supporting structure arrangement, diameter of middle earth nail, horizontal spacing, dip angle and miniature pile spacing and the thickness of the layer are the main factors influencing foundation pit deformation; Micro-pile diameter and soil depth to control the deformation of the effect is not obvious.