Research Of The Bearing Mechanism And Ultimate Bearing Capacity Of Rock-socketed Pile In Karst Region

Karst landform is widely distributed in China,the bearing mechanism and ultimate bearing capacity of rock socketed pile in karst area have always been the hot and difficult points in the research of pile foundation in karst area.In current regulation,the design of rock socketed pile in karst area usually directly determines the safe thickness of the top plate of the karst cave based on experience,and conducts stability calculations and bearing capacity reviews,ignoring many complex factors in engineering practice.In some cases,the foundation pile designed according to this method still cannot meet the bearing capacity requirements.At this time,these foundation piles need to pass through the karst cave and be embedded in the bottom plate of the karst cave to a certain depth.The bearing mechanism of this type of rock socketed pile that passes through the karst cave is still unclear.In response to the above issues,this thesis conducted in-depth research on the bearing mechanism and ultimate bearing capacity of rock socketed pile in karst area,revealed the bearing mechanism of rock socketed pile in karst area,clarified the impact mechanism of the ultimate bearing capacity of foundation pile,summarized the failure mode of the "foundation pile-formation-karst cave" system,and proposed a calculation method for the safe critical thickness to diameter ratio of underlying karst cave type rock socketed pile.The main research content is as follows:(1)A physical test plan for the ultimate bearing capacity of rock socketed pile in karst area was designed based on the separation and similarity design method.A physical test system was independently processed and built,achieving synchronous collection of stress and settlement data during the progressive failure process of the "pile-foundation-karst cave" system.(2)Conducted physical experiments,numerical simulations,and theoretical analysis research have been conducted on the underlying karst cave embedded pile.In physical experiments,the top plate of the karst cave underwent punching failure,resulting in punching failure bodie.Multiple numerical models were established using numerical simulation software to analyze the progressive failure process and ultimate stress state of the "pile-formation-karst cave" system.The results of physical experiments and numerical simulations indicated that the ultimate bearing capacity and failure mode of the underlying karst cave embedded pile are jointly affected by the radius of the karst cave,position deviation,and roof thickness.The failure mode of rock socketed pile can be summarized as shear failure,punching failure,eccentric compression failure,and plastic zone failure.Analyzing the load settlement curve,pile end bearing characteristics and pile body stress law,the bearing mechanism of rock socketed pile was revealed,and the reliability of the work was verified.Based on the above results,the generalized Hoek-Brown criterion was introduced into the limit analysis method for the punching failure mode of rock socketed pile,a calculation method for the safe critical thickness to diameter ratio of karst cave roof that meets the stability requirement was proposed.(3)Physical experiments and numerical simulation studies have been conducted on rock socketed piles crossing a single karst cave.In the physical experiment,a symmetrical tensile failure body was formed at the top plate of the karst cave,and the foundation pile subsequently underwent axial compression failure.Multiple numerical models were established to analyze the progressive failure process of rock socketed piles,and the influence mechanism of ultimate stress distribution characteristics was discussed.By comparing and analyzing the results of physical experiments and numerical simulations,it can be found that the ultimate bearing capacity of rock socketed pile crossing a single karst cave is mainly affected by the radius and position deviation of the karst cave.Its failure mode are mainly divided into axial failure of the foundation pile and tensile failure of the karst cave roof,which are greatly affected by the radius of the karst cave.The load-settlement curve,pile end bearing characteristics,and pile body stress law were analyzed to reveal the bearing mechanism of a single karst cave embedded pile.(4)Physical experiments and numerical simulations have been conducted on rock socketed pile that pass through bead shaped karst cave.In physical experiments,the upper layer of the karst cave roof formed a symmetrical tensile failure body,followed by compressive buckling failure of the foundation pile,and no damage occurred to the lower layer of the karst cave roof.The numerical simulation adopted the same scheme as crossing a single karst cave type rock socketed pile.By comparing and analyzing the results of physical experiments and numerical simulations,it can be found that the results of physical experiments and numerical simulations are in good agreement.The failure mode of rock-socketed pile are mainly divided into axial failure of foundation pile,tension failure of partial cave roof and full-penetration failure.The bearing mechanism of the rock socketed pile crossing a bead shaped karst cave is generally similar to that of a single karst cave,but there are also differences at some levels.