Theoretical And Experimental Researches Of Design And Calculation For Anti-slide Pile With Prestressed Cable

Anti-slide pile especially anti-slide pile with prestressed cable is an effective supporting structure for treating large landslides. The anti-slide pile with prestressed cable is used as a new anti-slide supporting structure, its design calculation theory has lagged far behind its engineering application. So it will take important theoretical and practical significance to strengthen theoretical and experimental study for reinforcement mechanism and design calculation supporting structure consist of anchors and piles. Therefor, by integrating Education Ministry Doctoral Fund (20050532021), Communication Ministry Western Project (200631880237) and Hunan Construction S&T Project(2006012), the anchor, common anti-slide pile and anti-slide pile with prestressed cable are systematically studied through laboratory model test and theoretical analysis in the paper, the main researches and results are as follows:(1) The condition that soil surrouding anchorage body will partly enter into plastic state when it is subjected to comparatively large drawing force, the soil shear stress and strain relationship is simulated by trilinear model, load transfer mechanism and bearing characteristic of anchorage body based on shear displacement method are studied, corresponding elastic and plastic limit loads calculation formulae are derived, shear stress and axial calculation formulae of anchorage body are obtained. The derived formula is applied to mechanical analysis of tension type and pressure type anchor respectively, some beneficial conclusions that can provide reference for engineering design are drawn.(2) Considering the condition that the most dangerous slip surface of slope is possible to change after setting anti-slide piles, the slope minimum stability safety factor is used as objective function, based on adaptive genetic algorithm(AGA), global optimization search method to arbitrary slip surface of slope retained by anti-slide pile is presented, and calculation program is programmed. The obtained slip surface and stability safety factor calculated by presented method are comparatively close to existing results, which shows the presented method is feasible. Furthmore, the calculation results for the common slope and slope reinforced by anti-slide pile show the most dangerous slip surface of slope will change due to the setup of anti-slide pile. (3) Semi-analytical and semi-numerical weighted residual method is imported, widely adaptive B spline function is acted as trial function, a new method to calculate internal force of anti-slide pile is put forward, the weighted residual solution for calculating internal force and displacement of anti-slide pile is obtained, calculation program is programmed. The presented method can calculate whole pile internal force unifiedly, and it overcomes the defect that existing method should separat the pile into thrust segment and anchorage segment and then calculat respectively, the foundation coefficient can be expressed as double parameter method. The presented method is applied to verification examples and calculation examples, the results show the effect of weighted residual solution in double parameter foundation are well. Simultaneously, for the case that the most dangerous slip surface of slope will change after setting anti-slide pile, according to the different slip surface of slope searched before and after setting anti-slide pile, the pile internal force is calculated, the two results are of great difference, so it is unreasonable for anti-slide pile if the change of the slip surface of slope is not considered.(4) The anchoring cable design tensile force and prestressing calculation methods of anti-slide pile with prestressed cable are summed and improved, the weighted residual method is introduced to calculate anti-slide pile with prestressed cable, direct to three different cases of anchoring cable acted on pile, displacement coordination between pile and anchoring cable is considered, the new method of internal force and displacement calculation based on weighted residual method is put forward. The calculation process of anti-slide pile with prestressed cable is discussed in detail, and program the calculation procedure. Example analysis shows the calculation results are consistent well with existing results, the presented method is feasible. According to further calculation, the more the anchoring tensile force , the less the shearing force of the pile, the more the maximum of negative bending moment, the less the maximum of positive bending moment. When the method that the maximum of negative bending moment and maximum of positive bending moment are about equal(the fifth method) is used to design, the obtained bending moment is most favorable for reinforcemet, but its construction difficulty is possible to increase, to specific example, it should compare all kinds of factors and use suitable design method.(5) Laboratory model tests on ordinary anti-slide pile and anti-slide piles with prestressed cable are self designed and accomplished. a series of testing data is obtained, The distributing rules of anti-slide pile landslide thrust, soil resistance in front of pile and internal force of pile in soil slope are studied, the weighted residual method is used to calculate anti-slide pile and anti-slide pile with prestressed cable in model test, the calculation values are fit close with testing measured values, which provide further reliability for the presented method to calculate the anti-slide pile and anti-slide pile with prestressed cable on the basis of weighted residual method.(6) A new method is put forward for calculating rational anchorage depth and pile spacing of anti-slide pile and anti-slide pile with prestressed cable by introducing unified strength theory to analyze soil stress state surrounding pile. The intermediate principle stress influences on calculation results is analyzed, the less the parameter b reacted intermediate principle stress influence, the higher the safety margin, the unified strength theory is just Mohr-Coulomb strength theory when b is equal to 0. anti-slide pile with prestressed cable has less anchorage depth and bigger pile spacing compared with common anti-slide pile because of the anchoring cable imposing.