Experimental Research On Bearing Characteristics Of The Cantilever Anti-slide Pile Exposed To Sulfate Environment

With the advancement of major national strategic decisions such as the"Western Development","One Belt,One Road",and"Transportation Power",large-scale transportation infrastructure projects have been constructed on a large scale in the Three Gorges Reservoir area with complex geological conditions and frequent geological disasters.The stability problems of rock-soil slopes are increasing day by day.The cantilever anti-slide pile has the advantages of strong anti-sliding ability,flexible and simple structure,and has become the most widely used slope prevention technology in the field of geotechnical disaster prevention and mitigation and protection engineering.However,as a large number of anti-slide pile treatment projects have gradually entered the middle aging stage of the service period,especially in the harsh sulfate erosion environment in the west,the anti-slide piles will inevitably produce damage accumulation and performance degradation during the service period.There is even a potential safety hazard of premature failure of the structure.Ensuring that the anti-slide pile structure can effectively achieve the intended function within the design service life and the 50-year long-term safety of the prevention and control project itself has become an urgent problem in the field of landslide prevention and control engineering.Therefore,studying the evolution of the bearing characteristics of the cantilever anti-slide piles exposed to sulfate environment has important scientific guiding significance and important engineering practical value in order to ensure the long-term service performance of anti-slide piles.This article relies on the key project of Chongqing Natural Science Foundation“Research on the long-term performance of the anti-slide pile under the coupling effect of concrete degradation and thrust”（cstc2020jcyj-zdxm X0012）and Chongqing Jiaotong University Graduate Education Innovation Fund project“Research on the long-term performance of the anti-slide pile based on concrete degradation”（2019S0147）,uses indoor accelerated tests combined with sulfate erosion damage mechanism,studies the evolution law of the concrete physical and mechanical properties and the evolution law of bearing characteristics of the cantilever anti-slide pile under sulfate attack.In the paper,the influence of sulfate erosion on the evolution of the bearing characteristics of the anti-slide piles is discussed.The main research work and conclusions are as follows:（1）The sulfate-thrust coupling erosion test device of the cantilever anti-slide piles is designed.The coupling method of mass fraction 5%,10%sodium sulfate solution and0.5 times load stress ratio are used to erode the cantilever anti-slide piles.The evolution laws of bearing characteristics such as residual bearing capacity,lateral displacement,crack distribution and failure characteristics,and bending moment of the cantilever anti-slide piles are studied.（2）The residual bearing capacity of the cantilever anti-slide piles presents a trend of increasing first and then decreasing under sulfate attack.After 30 days of erosion,the residual bearing capacity of the cantilever anti-slide piles increases slightly,and the maximum reduction rate is-3.3%compared with the P₀ pile.The residual bearing capacity of the cantilever anti-slide piles has been reduced during the 60 d and 90 d erosion,and the maximum reduction rate is 4.0%compared to the P₀ pile.（3）The bending moment of the cantilever anti-slide piles is non-linear in the pile length direction.The bending moment is concentrated in the range from 30 cm above the sliding surface to 20 cm below the sliding surface.There is a peak bending moment,which is located near the sliding surface.The bending moment gradually attenuates from the peak point to the two ends,and the farther away,the faster the attenuation.The bending moments of the P_S5 pile group and the P_S10 pile group at 15 cm,30 cm,45 cm and 60 cm measuring points are basically greater than the bending moments of the corresponding measuring points of the P₀ pile.The average growth rate of the bending moment of the P_S10 pile group at 15 cm,30 cm,45 cm and 60 cm is greater than that of the P_S5 pile group,but the average growth rate of the P_S5-90 pile bending moment is the largest,the maximum is 30.6%.（4）The lateral displacement curves of P₀ pile,P_S5 pile group and P_S10 pile group show a“triangular”distribution as a whole.But subdivided from the relative magnitude of each level of displacement value,P₀ pile,P_S5 pile group and P_S10 pile group show different lateral displacement evolution laws.The top displacement of the cantilever anti-slide piles shows a downward trend.The lateral displacement of the cantilever anti-slide piles top of the P_S10 pile group drops the fastest.When the P_S10-90 pile fails,the maximum reduction rate of the pile top lateral displacement is 32.1%compared to the P₀ pile.The lateral displacement mode of the loaded section of the P₀ pile shows a rigid rotation around the sliding surface,which is linear.However,the displacement mode of the loaded section of the P_S5 pile group and the P_S10 pile group has different evolution processes at different stages.Under sulfate attack,the crack distribution range of the cantilever anti-slide piles becomes larger,the crack number is smaller,the crack spacing is increased,but the crack width is smaller.the cantilever anti-slide pile has the characteristic of"damage lighter"under sulfate attack.