Research purposes: With the settlement control criterion increasing of high speed railway, the depth of bridge pile increases，which may lead to change the hydrodynamic conditions, and induce the karst collapse. It is important that how to evaluate the influence of karst collapse about the pile foundation construction. In this paper, beyond induce the karst collapse. It is important that how to evaluate the influence of karst collapse about the pile foundation construction. In this paper, by analyzing the influence factors of karst the human element to hydrodynamic condition variation has been researched，particularly the pile foundation construction aggravates karst collapse risk，which must be paid more attention in survey and design.
Research conclusions ;(1)The degree of karst development and the overlying soil properties are the inner factors of karst collapse，generally do not change with the environment，while the hydrodynamic condition is external factor, often affected by human factors. ( 2)Pile foundation construction has obvious effect to pore water and karst water connectivity under the natural condition，the human factor should be considered for analyzing and evaluating the risk of karst collapse.(3)Pile foundation construction will increase the risk of ground deformation or karst collapse, the change of hydrodynamic condition depends on the degree of karst development and the pressure between karst water and pore water, the more the karst develops，the greater the pressure is，the more serious the pile foundation construction effect to hydrodynamic condition is，the more easily ground collapse appears.(4)In the paper the effect of pile foundation construction which could increase the risk of karst ground collapse is proposed，and it will provide significance for similar geological survey in karst region.
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