Research On Influence Of Foundation Pit Dewatering On Settlement Of Composite Foundation Of High Speed Railway

The construction of high-speed railways has promoted the flow and reorganization of urban economic elements along the line,especially the economic effects generated by high-speed railway stations will become a new growth pole for the regional economic development,as well as important hubs for cities.However,due to the lagging construction of comprehensive transportation hub,the other structural groups of transportation hub have to be constructed at the same time during the construction period of the high-speed railway stations,especially the urban rail transit projects connected with the hub.Because of the complexity of the composite foundation of high-speed railways,there are many parameters affecting the calculation of composite foundation settlement,the settlement calculation theory is not that mature,particularly the calculation of the composite foundation settlement caused by the dewatering of the nearby deep and large foundation pit in the large high-speed railway construction yard,which often falls behind the requirement of the engineering practice.Therefore the settlement problem of the adjacent composite foundation should be solved when planning the dewatering scheme for the deep and large foundation pit.Based on the investigation and analysis of the related domestic and foreign research data on the settlement of the foundation and buildings caused by the dewatering of the nearby foundation pit,this paper have adopted theoretical analysis,on-site test monitoring and numerical simulation method and systematically studied and discussed the settlement influences of the composite foundation caused by the dewatering of the nearby foundation pit in the large high-speed railway construction yard,the main work and achievements are as follows:(1)Settlement mechanism of composite foundation inside precipitation funnel caused by foundation pit dewatering is revealed.Water lowering increases the self-weight stress acting on soil between piles.As a result,soil is compressed and decreased.The differential settlement between pile and soil increase and the pile toe penetration increases for pile negative friction,resulting in settlement of composite foundation.(2)Pile tip penetration method is put forward to calculate the settlement of composite foundation inside precipitation funnel caused by foundation pit dewatering.The settlement caused by the increase of the self-weight stress acting on soil between piles is calculated through layer-wise summation method.Considering pile-soil interaction,composite foundation additional settlement caused by foundation pit dewatering is calculated through pile tip penetration.(3)The additional physical load,caused by dewatering within the scope of precipitation funnel adjacent to composite foundation,was simplified to be the rectangular linear distributed load that is imposed on the surface of composite foundation based on the principle of equivalence.The M-B union solution law was used to compute the additional stress.Settlement increment of reinforced area and substratum is calculated by layer-wise summation method.The improved M-B union solution law was proposed,which is used to compute the additional settlement of composite foundation,through adjusting settlement formulae of composite foundation.(4)In combination with the project example of the west railway station in Jinan,the 3D composite foundation model with pile raft and pile-net are respectively established in thick soft clay and soft soil region.In the model the stage filling subgrade and disposable precipitation is considered.The effect of parameters of pile raft and pile-net on the settlement of composite foundation caused by foundation pit dewatering is investigated.