Study On Failure Mechanism Of Anti-slide Piles Of Pengjiacao Landslide In Three Gorges Reservoir Area

The Jurassic argillaceous siltstone layer is widely distributed in the Three Gorges reservoir area.There are a large number of landslides in this type of stratum.Examples of the failure of anti-slide piles in the landslide control project frequently occur in this type of stratum.Considering that the rock mass embedded in the anti-slide pile in this type of rock formation is degraded by the water-rock cycle and the failure of the anti-slide pile is less.In view of this,this paper takes Pengjiacao landslide as an example,through field investigation and theoretical calculation.The method of numerical analysis,etc.,studied the deterioration law of the rock mass embedded with the anti-slide pile with the water-rock dry-wet cycle,the relationship between the failure height of the anti-slide pile embedded section and the water-rock circulation,and revealed the anti-sliding.The failure mechanism of the pile is as follows: due to the influence of water-rock circulation,the physical and mechanical properties of the rock mass in the anti-slide pile are gradually degraded,the strength is gradually reduced,and the plasticity of the wedge body appears in the rock mass of the anti-slide pile.The area is gradually enlarged,resulting in an increase in the failure height of the embedded section,and the effective insertion length is continuously reduced,resulting in insufficient depth of the anti-slide pile.At the same time,for the landslide where the sliding bed is a Jurassic argillaceous silty sandstone stratum,the optimization suggestions for the anti-slide pile embedding depth of the treatment project are put forward,specifically: the anti-slide pile embedded section is increased by the length of the original embedded section at 30%,the long-term effectiveness of the anti-slide pile can be ensured.The specific research contents and achievements are as follows:1)The deterioration law of rock mass in the anti-slide pile is analyzed,and the deterioration law is obtained.The rock mass embedded in the anti-slide pile is degraded by the water-rock dry-wet cycle,and its mechanical properties are related to the water-rock dry-wet cycle.The number of actions increases and gradually decreases.In the early stage of the cycle,the rate of deterioration is relatively fast,and when the number of cycles increases gradually,the rate of deterioration becomes slower,and the deterioration of various mechanical parameters tends to be slower,and the tendency of internal friction of cohesive force is basically the same.However,the effect of rock mass cohesion on the dry-wet cycle is more significant than the internal friction angle,that is,the cohesion is more deteriorated than the inner friction angle under the same number of cycles.When the number of water-rock cycles is 15,the cohesion is degraded by 26% and the internal friction angle is degraded by 14%.Comparing with the indoor test rock mass parameter degradation curve,it is not difficult to find that the two trends are basically the same,but the curve is smoother,which means that when the number of cycles is the same,the rock mass is subjected to natural water-rock dry and wet cycle.The magnitude of the degradation at the time of action is smaller than that under the "saturation-air-drying" cycle of the laboratory test.2)The failure height of the rock mass in front of the landslide anti-slide pile is analyzed and the function of the failure height of the embedded section is compared with the number of water-rock cycles.The results show that the number of water-rock cycles The increase of the plastic zone near the wedge body appears in the rock mass before the anti-slide pile,and the plastic zone range increases with the increase of the number of water-rock cycles,and the failure height of the rock mass in the anti-slide pile is accompanied by water.-The number of dry and wet cycles increases,and the relationship between the two curves is logarithmic.The initial failure height increases rapidly,and then the failure height increases slowly.3)The reason for the failure of anti-slide piles is that with the increase of the number of water-rock cycles,the deterioration degree of rock mass is gradually deepened,the plastic zone of rock mass before the anti-slide pile is gradually increased,the failure height of the embedded section is increased,and the anti-slide pile is effective.The embedded length is reduced.When the number of water-rock cycles is 15,the failure height is 1.73 m,and the effective embedded length is 6.19 m.At this time,the embedded depth of the anti-slide pile is insufficient.Combined with the numerical analysis results,with the increase of the number of cycles of water-cycle,the plastic zone range,pile top displacement and pile side stress of the piles embedded in the anti-slide piles tend to increase gradually.When the number of water-rock cycles is 15,the plastic zone appears in a large area of the rock mass in the embedded section.The displacement of the pile top reaches 1.529 m,and the maximum stress on the pile side reaches 3872,which exceeds the allowable bearing capacity.Therefore,the anti-slide pile is lost.Steady destruction4)The variation law and trend of the displacement of the pile body with the number of water-rock cycles are studied.The results show that with the increase of the number of water-rock cycles,the displacement of the pile body tends to increase gradually.The displacement of the anti-slide pile body changes linearly,and there is no obvious bending deformation.This indicates that the anti-slide pile mainly has the rigid body rotation failure around the rock mass,indicating that the failure form of the anti-slide pile of the Pengjiacao landslide is the pile body being pushed.5)Keep the pile spacing constant,the section size of the pile is unchanged,increase the length of the anti-slide pile,and select the anti-slide pile to increase the length of the original embedded section by 10%,20%,30%,40%.The variation of the top displacement of the anti-slide piles under the initial conditions and the water-rock dry-wet cycle of 5 times,10 times,15 times,20 times and 25 times is calculated.The results show that: when the anti-slide pile embedded section increases the length of the original embedded section by 30%,it can ensure the stability of the anti-slide pile and save engineering materials.