Study On Calculation Method Of Composite Structure Of Stable Pile-Vaulted Board-retaining Wall In Landslide Control

A new type of complex support structure(named stable pile-vaulted board-retaining wall)which is applied to the treatment of small and middle-scale landslides located in V-shaped valleys was proposed based on the Majiapo landslides in this paper.As its name indicates,this complex support structure consists of stable piles and a retaining wall which are linked by a vaulted board.The characteristic and mechanism of mechanics as well as the calculation method for the internal force of the complex support structure was studied by theoretical and numerical methods.(1)According to the improved correlation theories of arches,stable piles,gravity retaining walls and structural mechanics,as well as the characteristics of landslide in the V-shaped valleys,catenary,gravity retaining wall and common square pile were chosen to make up the complex support structure.Fixed hinges were used to link the three parts in this complex support structure which is placed along the leading edge of landslides.(2)The complex support structure is a statically indeterminate structure after simplified into two-dimensional(2D)model.Transmitting coefficient method was used to calculate the landslide thrust.In this 2D model,the catenary double hinged arch model as well as cantilever method and "m" method were used to calculate the internal force of vaulted board and stable piles,respectively.Besides,the displacement of gravity retaining wall was assumed to be 0 due to its own characteristics.The calculation formulae of the internal forces for the three sub-structures were derived based on the static equilibrium method of structural mechanics,and the displacement at the pile top and the arch foot was revised by using iteration method.This paper summarized a series of formulae available for the calculation of the internal forces of the complex support structure.(3)The terrain landform and geological engineering conditions of Majiapo landslide are analyzed based on the field investigation data.Engineering geological analogy method and laboratory tests were conducted to obtain the physical and mechanical parameters of the rock and soil,which were used to calculate the stability coefficient and residual sliding force of different shear outlets of three section planes based on the transfer coefficient method.And the results show that the ?-? section plane was the main section,which was susceptive to shear out at the foot of the landslide under the rainstorm conditions,with the stability coefficient of 0.979.The unstable state throws great threats to more than 740 people's lives and highway traffic facilities at downstream,which is in urgent need of treatment.(4)The sectional dimension of the complex support structure system is determined by engineering geological conditions and terrain landform.And the thickness,span and vector height of the vaulted board is 0.8m,3.0m and 0.5m,respectively;the section size of stable pile is 3.5m×3.0m,and the length is 7m,with 3m above the sliding surface and 4m under the sliding surface;the retaining wall is 4.5m high,and the width of the top and the bottom is 1.5m and 3.0m,respectively.The derived theoretical formula was used to calculate the structural system,and the displacement at the top of stable pile was 0.026m.The stability of the complex support structure was checked and the results were in accordance with the relevant provisions.(5)Three dimensional(3D)numerical models of ?-? section plane and entire slope were set up by FLAC3D and GID to study the stability of Majiapo landslide under rainstorm and natural operation conditions.The results show that the safety factor of ?-? section plane under rainstorm and natural operation conditions were 1.06 and 0.95,respectively,and the safety factor of the entire slope under rainstorm and natural operation conditions were 1.08 and 0.98,respectively,which indicated that the landslide was unstable under rainstorm conditions.(6)FLAC3D was used to analyze the stability of ?-? section plane of the landslide after been treated with the complex support structure,as well as the internal forces of the structural system.After the treatment,the slope was stable,and the distribution of internal force of the structural system was consistent with the theoretical calculation,which proved that the derived formula is scientific and reasonable.