Study On The Effect Of Pile Foundation Voids In Karst Areas On The Consolidation Creep Characteristics Of Surrounding Building Foundations

Karst is a very common geological condition in China.At present,when holes are formed in the construction of pile foundations in karst areas,when they are not poured in time,they can have an impact on the foundations of the surrounding buildings.This paper takes the hollow holes generated by construction in Xingye County as the research object,firstly,through a series of basic tests on the overlying soil in the karst area to derive the relevant calculation parameters;secondly,for different long semi-axial cavities,the impact of a single hole on the surrounding environment is derived by using finite element software analysis;again,the settlement law of the group of holes on the foundation of the surrounding pre-built buildings is derived by superposition method and compared with the actual field measurements;finally,through the Finally,the influence of different creep parameters on the foundation deformation of existing buildings is investigated through a single-parameter lateral comparison of different creep parameters.The main research results are as follows:(1)Through creep tests on the overlying soil,it is found that: at each level of compression,its strain shows a similar pattern of change,and its ε～ t curve is a decaying creep line.During the process of loading,there is distortion or deformation of varying lengths and degrees,which slows down over time and recovers rapidly,while the rate of deformation stabilises after 100 min.Under low stress conditions,in the range of P≤200 k Pa,the strain variation under each load level is not significantly different,and there is no obvious jump;when the load reaches 200 k Pa,the strain difference between each load level remains basically constant.The red clay consolidation settlement curve is divided into primary and secondary consolidation stages,and the pore ratio e of the overlying soil and the logarithm of time lgt are roughly inverse "S" shaped curves,and are in accordance with the consolidation settlement deformation formula.(2)Based on the traditional Drucker-Prager(D-P)model,an extended D-P consolidation creep model for the overburden in karst areas was obtained.The parameters m,n and A in the creep model can be derived by fitting the one-dimensional consolidation creep test data,and the model can be used to analyse the creep settlement pattern of the overburden in karst areas.(3)Meanwhile,combined with the field test data of a building in Xingye County,the extended Drucker-Prager damage criterion in abaqus,the time-hardened flow criterion and the non-associated flow law are used to establish an axisymmetric model for cavities with different long semi-axes,and the results show that:(1)The hollow holes generated by the pile foundation hole construction will cause the formation of a critical surface on one side of the geotechnical body,and the stress of the soil body near the borehole wall is reduced.And the cavity is completely filled with the same boundary conditions and loading,and its stress change is independent of the long semi-axis of the hole diameter.(2)The loss of support of the wall of the hollow pile borehole will produce an internal shrinkage effect and cause soil deformation.The strength of the sub-clay layer is lower compared to the red clay layer,which leads to the largest displacement near the borehole wall in the absence of restraint on the side of the borehole wall.As one moves away from the centre of the borehole,the vertical displacement begins to decrease and uneven settlement of the ground surface occurs.(4)By selecting different creep parameters for analysis,it was found that: m values were taken in the range of-1 to 0,and the parameter m values were positively correlated with the settlement as a whole,with the larger the m value,the greater the degree of settlement;there was a significant positive association between n and the settlement,with the difference in settlement increasing with the increase in the parameter n.When the value of n is greater than 0.85,the difference in settlement is obvious,especially for creep settlement causing a great impact.The value of the parameter A is positively correlated with the settlement as a whole;as the value of A is of a small order of magnitude,it has a small effect on the final settlement.