Study On The Engineering Characteristics Of Expansive Rock Mass And Pile-Soil Interation

As the domestic high-speed rail is moving forward to the mountains,there are sometimes special engineering geology problems..The Jianshanying super large bridge in Guiyang to Guangzhou the high speed railway as an example,anomalous uplift of piers seriously limits the railway speed.In order to minimize the upper structure settlement,the basis of the structure adopts the form of pile foundation.Due to the complexity of bedrock and soil mass,pile group foundation still produces different degree of uplift,which seriously affects the safe operation of high-speed railway.Therefore,it is of great theoretical value and practical significance to study the engineering geological characteristics and pile-soil interaction of the control site of Jianshanying bridge.Based on the comprehensive analysis of the survey data and the research status of abnormal pile foundation lifting at home and abroad,through the self-developed high-pressure deformation test equipment,this paper adopts the research methods of laboratory test,field monitoring,pile-soile simulation test,theoretical research and numerical analysis,and has obtained the following main research conclusions:1.On the worksite have dilatability of undisturbed rock mass deformation test under the condition of high load,high water pressure.Interior of undisturbed expansive rock mass and dilatability of disturbed soil compaction test showed that Wujiaping formation has strong water absorption expansion feature,and is also possible to raise the superstructure by 38 mm.2.The regression equation of expansion force and expansion strain of rock mass was established through the indoor expansion and contraction test of compacted expansion rock in Jianshanying area of Guiyang to Guangzhou high-speed railway,which provided a basis for practical foundation uplift calculation theory.3.Considering the influence of foundation uplift during the load transfer process of pile foundation in expansive rock and soil mass foundation,the analytical solution of the lifting amount of single pile is established.Based on the comprehensive analysis of the influence of each parameter on the result,the simplified calculation formula of pile foundation lifting amount is put forward.The reliability of the simplified calculation formula is proved by comparing with the existing data and the results of simulation test.4.The regression equations of strength parameters(cohesion,internal friction Angle,elastic modulus)with water content change are proposed by means of indoor strength attenuation test,which provides a theoretical basis for the secondary development of the modified expansion constitutive model applied to the expansive rock in the study area.By comparing with the experimental results,it is proved that it has better reliability and engineering practicability.Through the numerical analysis of single pile-expansive soil,the results are obtained which are similar to those obtained in the analytical solution of single pile.It is found that increasing the pile diameter is not as effective as increasing the pile length.5.The modified expansion constitutive model proposed in this paper is used to calculate the no.16 pier of Jianshanying bridge.The stress characteristics of pile group composite foundation during the uplift process in the expansive rock mass are obtained,which explains why the reinforced pile foundation does not restrain the uplift effect.6.The comparative calculation results of friction pile foundation and pile foundation of high bearing cap show that the pile foundation of high bearing cap can effectively alleviate the uplift of foundation.Numerical analysis of belled pileshows that belled pile foundation through the thickness of expansion layer can effectively alleviate pile foundation uplift.