Study On Pre-Stressed Multi-Anchor-Wire Anti-slide Pile In Large-scale Thick Landslide

Landslide, as a main kind of geological hazards, often stops traffic, blocks rivers and destroys factories, mines, villages and farmland. It causes great loss to the human life and property. Owing to the varied, changeable and complicated developing conditions, acting factors, and movement mechanism, it is very difficult to forecast the occurrence of landslide and the cost for prevention and control is more and more expensive. So, the study and control of landslide have become one of the important geological engineering problems concerned by the scholars in China and abroad.As the main engineering measure for controlling landslide, the anti-slide retaining structure has been widely used since 1950's. It includes normal retaining wall, anti-slide pile with rectangle and circular cross sections, anchor rod, anchor wire, anchor wire frame and anchor wire anti-slide pile as well as bent pile, h-like pile wall, mini-pile cluster, small steel pile and pile with anchor wire, etc.The anti-slide piles have been used widely with the advantages of small excavation face, powerful anti-slide capacity, less cubic meter of excavation stone and flexible location since it was used for controlling Shabei landslide in 1967. Because the structure is a large cantilever force-subjected one, the internal force is large in the pile shaft and the depth of embedment beneath the sliding plane reaches l/2to 2/5 of the whole shaft, so that great deal of steel and cement are used and the cost is expansive. In order to improve the state of unreasonable force subjected by cantilever of the normal anti-slide piles, Northwest Research Institute of CREC successfully developed pre-stressed anchor-wire anti-slide pile in 1989 through the studies for more than three years. The anchor wire is added near the top of pile and pre-stress is exerted. It seems to set up a twist fulcrum, the state of force-subjected is similar to that of the beam with simply supported ends and the cost of engineering is reduced by 50%-25%. So the new structure is spread quickly and used widely.This paper, on the bases of the stability judgment and thrust calculation of landslides, optimizes the design of pre-stressed anchor-wire anti-slide pile with single anchor point and puts forward the new structure of pre-stressed anchor-wire anti-slide pile with multi-anchor points. It analyses, by using FEM, the distribution of internal force of normal anti-slide pile, anti-slide pile with single-anchor point and with multi-anchor points at the conditions of varied force-subjected (small, middle and large thrust of landslide), compares the mechanics, considers comprehensively the factors of technique, technology, distribution of internal force and cost, and carries out the comparison of the above mentioned three structures. It summarizes the methods of optimized design and construction technology of anchor-wire anti-slide pile with multi-anchor points used at Jietaisi landslide, analyses, compares and verifies the test data, and demonstrates controlling effect and characteristics of anti-slide structures subjected to force on the bases of the monitoring of displacement and deformation carried out at the ground surface and deep hole location of the landslide and tests on the tensile stress of anchor wire and the stain of pile.It is economical and rational to adopt the pre-stressed anti-slide pile with multi-anchor points at the condition of large thrust (more than 3300kN/m), and the cost of pile with multi-anchor points is reduced separately by 34.9 % and 11.9% as compared with that of the normal pile and pile with single anchor point. It is obvious that the pile with multi-anchor points is a new economical structure with great future.New ideas of the paper:1. It puts forward the landslide conditions of pre-stressed anchor-wire anti-slide pile with multi-anchor points through the calculation of internal force in pile using FEM.2. It puts forward the optimum method for the best place of anchor wire of pre-stressed anchor-wire anti-slide pile with multi-anchor points.3. It puts forward the best design method to determine tensile range of anchor wire of pre-stressed anchor-wire anti-slide pile with multi-anchor points.4. It puts forward the method to optimize structure design of pre-stressed anchor-wire anti-slide pile with multi-anchor points.