Study On Piles-soil Interaction Mechanism Of Double-row Drilling Anti-slide Piles And Its Scope Of Application

Double-row anti-sliding piles have been used in the landslide, but its pile-soil interaction mechanism, the calculation methods and range of application is not ripe.It still needs to further study. This paper relies on Bureau of Land Resources and Housing Managemeaant of Chongqing Municipality Scientific and Technological projects(ID:CQGT2012018). The author applies numerical simulation and model test to investigate the main influence factors and the mechanism of the interaction between piles and soil, and puts forward its simplified calculation method, and discusses its application scope. The main research results are as follows:(1) Based on the numerical simulation method,and the displacement of piles’ top, the internal force of pile, landslide thrust on the front and back row piles of allocation proportion as the indexes,the main influence factors are analyzed by univariate analysis. We suggest arranging Cushion cap double-row drilling anti-slide piles in landslide which is thinner and sliding surface angle is smaller. For landslide deformation control strictly, it is recommended that the pile diameter should not be less than 1 m.In the construction condition is feasible, we appropriately use drilling anti-sliding piles of larger diameter. When pile spacing from 3d to 6d, both front and back row piles of soil arching effect more obvious, and make front and back row piles bear landslide thrust proportion gap is smaller. So we suggest using the optimal pile spacing from 3d to 6d in the design of double-row drilling anti-slide piles. Within a reasonable range of row spacing increases row spacing, the overall moment of inertia and the overall stiffness increases, and the structure of anti-sliding ability was improved. So we suggest using the optimal pile row spacing from 3d to 6d.(2) According to the results of model test: Cushion cap double-row drilling anti-slide piles’ pile top load-displacement is a concave curve, indicating that played a better deformation coordination function, its whole structure showed obvious integral space performance. Reached the limits of the carrying capacity of the structure in the process, the structure can be transformed by the force system load, it failure process is complex and has a safety reserve. Pile row spacing on the structure effect is obvious. Within a reasonable range of row spacing increases row spacing, the overall moment of inertia and the overall stiffness increases, the structure of anti-sliding ability was improved.(3) Through model test: back and front row piles of the pile body bending moment distribution was "S" curve. Absolute maximum moment near the sliding surface, there is inflection point above the sliding surface. Back row piles inflection point above the sliding surface is about 0.27 h height,and front row piles inflection point above the sliding surface is about 0.45 h height, and the back row piles inflection point is lower than the front row piles. Inflection point of Cushion cap is present,but inflection point near the front row pile. With the increase of the length of Cushion caps, the inflection point close to the midpoint.(4) According to the results of model test: when the landslide body is sand, the landslide thrust of back row piles can be approximated by the triangular distribution consideration,and the landslide thrust of the front row piles can be approximated by the rectangular distribution consideration. For landslide is loose media(such as sand), within the appropriate pile row spacing, we suggest that the back and front row piles bear the landslide thrust allocation proportion can take 0.7: 0.3 as a reference value in the design. The action of resistance in front of the pile is not considered in the landslide body,as the safety reserve.(5) Through model test: the transfer of the landslide thrust through the soil between front and back row piles is less, but mainly through the soil arch(horizontal soil arch) which is formed between pile and soil and even the beam between the front and back row pile interaction,which work together throughout the anti-slide structure. Between the front row anti-slide pile and landslide body around showing obvious "arch" crack, it proved the existence of soil arch.(6) Based on the numerical simulation method, indoor model test and bridge construction theory of the pile foundation, and through the theoretical derivation and reference for engineering examples, the author puts forward the design calculation method of Cushion cap double-row drilling anti-slide piles.(7) Conduct comparative study of cantilever double-row piles and cushion cap double-row piles, through numerical simulation analysis and monitoring engineering case,at last Cushion cap double-row drilling anti-slide piles is considered to be a better anti-slide Structure type.(8) Based on the chongqing region landslide engineering example, conduct a comprehensive between cantilever anti-slide piles,anchor anti-slide piles and cushion cap double-row drilling anti-slide piles,and with cost calculation results,advantages and disadvantages.The author conclude cantilever anti-slide piles scope of application: the slide body thickness is less than 7m, and the landslide thrust is less than 1400 KN/m; the slide body thickness is between 7m and 16 m, and the landslide thrust is less than 900KN/m; the sliding body thickness is more than 16 m, and the landslide thrust is less than 500KN/m. The author conclude anchor anti-slide piles scope of application: the slide body thickness is less than 7m, and the landslide thrust is between 1400KN/m and 2000KN/m; the slide body thickness is between 7m and 13 m, and the landslide thrust is between 900KN/m and 2000KN/m; the sliding body thickness is more than 13 m, and the landslide thrust is more than 500KN/m. The author conclude cushion cap double-row drilling anti-slide piles scope of application: the sliding body thickness is less than 13 m, and the landslide thrust is more than 2000KN/m.