Experimental Study On The Effect Of Lower Karst Cave On The Stability Of Anti-slide Piles

With the increasing emphasis on geological disaster prevention and control in China,and the increasing number of foundation ditches in various types of engineering construction,the landslide(side slope)control project and foundation ditches engineering have emerged in large numbers,and anti-slide piles have been widely used as never before.At the same time,the stability research of anti-slide piles has become the focus of scholars'research.The stability of anti-slide piles in karst areas is particularly prominent.In view of the lack of research in this field at home and abroad,based on the similar model theory,this paper establishes two models with no karst caves and lower karst caves(long axis is horizontal).By means of indoor model test and numerical simulation,the influence of the lower karst cave on the stability of anti-slide piles was studied,and the following conclusions were obtained:1.The failure modes of the two models are all brittle fractures under tension and to make the piles unstable.There was no macroscopic crack on the surface of the models before the failure,but the cracking sound inside the model could be heard during the test,and the sound was intensified in the post-loading phase.2.The crack initiation positions of the two models are all on the active side of the pile bottom.When there is a lower cave,the crack propagation direction will deflect toward the cave and penetrate along the short axis of the cave,that is,the cave affects the crack initiation and expansion.3.The existence of the cave reduces the bearing capacity of the anti-slide pile,that is,the bearing capacity of anti-slide piles is significantly affected when the lower karst cave exists.The model test results show that the horizontal ultimate bearing capacity of the anti-slide pile with karst cave is about 0.58 times that of the non-dissolved cave model,and 0.8 times in the simulation calculation.Using the ideal elastoplastic model simulation calculation,it is found that the ultimate bearing capacity of the non-dissolved cave model is 1.09 times of the ultimate bearing capacity of the model test,and the lower karst model is 1.50 times.For this reason,the bearing capacity of the simulation calculation should be reduced when used in actual engineering.4.The model test found that the existence of karst cave will make the horizontal displacement of the pile and the displacement of the passive zone larger,resulting in a decrease in bearing capacity.Specifically,when the first-stage load is 6.4KN before the failure of the karst cave model,the ratio of horizontal displacement is 1.27 between the karst cave pile and the non-dissolved cave pile,and the ratio of the displacement of the passive zone is 41.82.But the displacement of the active zone is close,the ratio is 0.995.Both the model test and the simulation calculation show that when the load is large,the maximum principal strain under the pile is mostly tensile strain,and the local compressive strain is generated.When it comes to the karst cave model,the maximum principal strain is all tensile strain.The maximum and minimum principal strains of the active zone under two model piles are tensile strains,so both models eventually lead to tensile failure.Due to the existence of the cave,and the maximum principal strain value around the cave is larger than the non-dissolved cave model,the crack is deflected toward the active zone when there is a cave.6.The non-dissolved cave model and the karst cave model loading failure process can be divided into three stages:compaction,linear growth and accelerated growth.The linear increase and the accelerated increase curve of the karst cave model are steeper,and the displacement under the same load is larger.7.The conclusion of the three-stage analysis of the two models is:before the 1/4 times of the failure load,both the initial pores and the voids are closed,the acoustic emission phenomenon is less and the absolute energy value is lower;when the load is between 1/4 and 2/3 times the failure load,the crack inside the model is in a stable expansion stage,and the acoustic emission phenomenon is relatively stable and the energy value is relatively high;when the load is above 2/3 times the failure load,the small cracks inside the model formed large cracks and the new small cracks continue initiation,and the acoustic emission phenomenon is dense and the energy is high.