Study On The Mechanism Of Pre-stress Anti-slide Pile With Numerical Simulation

Anti-slide pile with pre-stressed anchor cables is a new pattern of compound stress structure which uses anti-slide pile and anchor cables to resist the pushing force of landslide. It can change the passive anti-slide structure of the general anti-slide pile to active anti-slide structure, improve the illegitimate stress states of the cantilevered anti-slide, which has widely used in the project of landslide control. However, the study on mechanism of anti-slide pile with pre-stressed anchor cables is still in the stage of exploration, for the complexity of the interaction between pile-anchor system and landslide body, both the design theory and standard are still not perfect. The selection of anchor cable and anti-slide pile is only some of experience value in the practice of engineering design,and the anchor pile and anti-slide pile are considered as the independence supporting structure in the previous research,some simple combined calculations are adopted in the design,but the influence of the pile-anchor system to the structure internal force distribution has not been considered.The reasonable design should be comprehensively considered the load distribution between prestressed anchor cable and anti-slide pile,the effect of different stiffness and strength to the whole structure bearing capacity. And the combined action of anchor cable and anti-slide pile should be considered,to make them achieve the limit state simultaneously.Firstly, a synthesize analysis is carried out on the research situation of the anti-slide piles with pre-stressed anchor cables, combined with its mechanical feature and application scope. It is pointed out the main problems in current project designing. Secondly, the research results of the interaction among piles,anchor cables and landslide have been summarized,and gave a deep research and discussion aimed at the existing main problems:coordinated deformation and stress between piles and cables, in mechanical calculated model of anti-slide pile with pre-stressed anchor cables, achieved a new mechanical model for anti-sliding pile with prestressed anchor cable which is more anastomotic to the realistic structures.Thirdly, a new method to calculate internal force on the anchor anti-slide piles is put forward, which considering the internal force and deformation of re-stressed anchor. Finally, taken the instance of the design of prestressed anchor cable slide resistant pile for the harnessing of Baiyangou landslide in Badong county, the Three Gorges reservoir, established the finite element model in the ANSYS, and the mechanism and effect of anchored anti-slide pile with different combination of anchoring force and anchoring angle is simulated by numerical simulation method, so that the optimum combination of anchoring force and angle can be got. On the premise of ensuring engineering safety, the anchoring cable and anti-slide pile can be achieved the reasonable forced state, the result will be provided valuable reference to design and construction.The mainly results are as follows:1. Pile-anchor's coordinate deformation conditions were studied and three of that conditions proposed in some literatures were analyzed, and some problems existed in which were pointed out. Based on the interaction analysis theory between piles and anchors.An improved pile-anchor's coordinate deformation condition was put forward, taken the pile-anchor's practical working status into accout: the pile body's deformation occurred already in the phase of pre-stress applied,and the pile-anchor's coordinate deformation equation was established.The improved pile-anchor's coordinate deformation equation can obtain the satisfying cable stress value, which is proper and safe, and accord to pile-anchor's practical stress status.2. In the phase of cables'pre-stress applied, it must be given a extrusion action on the soil behind pile through the pile, and change the distribution rule of the soil stress on the pile. By the analysis of the influence of pre-reinforce effect to mechanical calculated model of anti-slide pile with pre-stressed anchor cables, and on the basis of physical content of landslide thrust, realized that the pre-reinforce effect induced by the pre-stress should be considered in the design of anti-slide pile with pre-stressed anchor cables, can not be reduced or deducted simply. It should be deducted in the total stress graph, after calculating the stress collection degree around the piles by the suitable distribution functions. So as to make the mechanical models are more accordance with the practical stress situation.3. Chosing a suitable mechanical calculation model can play an important role in the design of anti-slide pile with prestressed cable. Selected the mechanical model which considering force coordination between pile and anchor, anti-slide pile and anchor cables can resist the pushing force of landslide.The anchor cables can not only exert antislide force, but also apply tension to the anti-slide pile and restrict the deformation of pile. So as to ensure structure play its total effects and reduce project cost.4.The system of rock and soil around piles and anchor cable is considered as a whole system,it considered as an statically indeterminate structure.The piles can simplified as elastic foundation beam which is subject to the restriction of transverse deformation.According to the principle of displacement deformation coordination,the anchor cable tension and the internal force of piles can be determined by the foundation co-efficients method.5. Basis for the optimized analysis of numerical simulation on the engineering example, some conclusions can be obtained in the article.The suitable pile's cross-section and the number of anchor cable rows should be chosen according to the landslide thrust in the design of anti-slide pile with prestressed cable. If selected the landslide piles with large cross-section for the sake of safety, it can only make the displacement of anti-slide pile decrease slightly.And if set excessive number of anchor cable rows or applied excessive anchoring force, it will make the anti-sliding piles bear huge passive soil pressure, cause the anti-slide pile to be at the stress unreasonable status even in the critical condition.6. The working condition of the anchor anti-slide piles can be simulated by the large general structure analysis software ANSYS,and the optimum design of the related parameters can be carried on conveniently.It is a feasible approach to design the pre-stessed anchor cable anti-slide pile fast and accurately,for the related standard is also imperfect as present.7. Taken the Baiyangou landslide as example,and carried on the optimization design using general-purpose finite element program ANSYS to verify and analysis the improved mechanical model. In order to show the advantages of the impoved model, the other calculating models are employed in this engineering example, and the results show that the improved model reduced the design value of pile and cable's bearing capacity greatly, because of considering the pile-anchor's coordinate stress condition, thus deduced the cost effectively and advanced the design level.8. In the design of anti-slide pile with prestressed cable, enlarged the cross section of anti-sliding pile or increased the numbers of anchor cable row and the pre-stressed value can reduce the displacement of piles effectively. However, compared to two methods, adopted the bigger section anti-slide pile can achieve a better effect. The pre-stressed value in each row may be different when established the multi-row pre-stressed anchor cable. It suggested that the upper row of pre-stressed value is smaller than the lower row slightly. So that the stress of each row's anchor cable under active status stress is equivalent approximately. This conclusion is very important especially regarding rigid pile.