Numerical Modeling Analysis Of Tunneling-induced Effect On Nearby Existing Piled Foundation Based On Fluid-solid Coupling Effect

The rapid urbanization and an ever-increasing demand have necessitated the need for underground space development.In the urban environment,tunnel construction underneath or near existing structure(especially piled foundation)is an inevitable trend,and the induced effect can be damaging.By far,dewatering technique has been widely used in tunnelling construction,especially when a tunnel being constructed in a water-rich stratum in which water bursting and inrushing are prone to occur.However,the negative impact of dewatering construction on the surrounding environment is obviously considerable.Considering the above factors,the safety-oriented tunnelling construction method in water-rich stratum without dewatering will be the trend of future,but the knowledge gap still exists.In order to limit the damage of existing structure,it is necessary to increase the understanding of the stability of tunnel excavation and the tunnelling-induced effect on the nearby piled foundation with considering fluid-solid coupling effect.This increased understanding will enable the tunnelling-induced effect to be accurately predicted and allow for improvement of tunnel design and construction.Based on the progressively deepened research strategy,the numerical modelling based research was proposed to be divided into three parts:(i)Back analysis of centrifuge model test published by Loganathan et al.(2000)with using numerical modelling method;(ii)Investigate the pile group response with various volume scales of piled foundation,constrained with or without pile cap and different tunnel-pile relative positions;(iii)In order to compare the stability of surrounding rock and tunnelling-induced effect on piled foundation with or without considering fluid-solid coupling effect,a case study of Beijing subway was selected as background.The main contents are addressed as follows:(1)In order to verify the correctness and reliability of the numerical modelling analysis,research method of applying three-dimensional numerical modelling analysis was conducted to simulate centrifuge model test,which reproduced the main trends and key features of the centrifuge model test measurements.A reasonable estimation of soil-pile interface parameters were put forward in the process of research.Additionally,single pile progressive response during the tunnel advancement was investigated.(2)When the tunnel was constructed beneath or side-cross piled foundation,the pile group response changed significantly.In order to increase the understanding of pile response due to tunnelling,several scenarios have been involved,such as various volume scale of the piled foundation,the pile cap effect,and different tunnel-pile relative locations.Moreover,a case study of 2x2 pile group was designated to evaluate the shielding effect.(3)The concept of 'interior balance' and 'exterior balance' were introduced to interpret the different load transfer mechanics within single pile and pile group.The loading share patterns of each pile within large-scale pile group were significantly distinct.The load transfer mechanics of pile group subjected to vertical load has been analysed and summarized by varying the pile spacing and vertical load levels.(4)When considering the fluid-solid coupling effect,seepage field has a great effect on the stability of surrounding rock.The basic principle of effective stress was applied to analyze the fluid-solid coupling effect on the distribution of seepage field,displacement field,stress field and plastic zone.Under the circumstance of considering the fluid-solid coupling effect,the bearing capacity loss of piled foundation due to tunnelling has changed dramatically.By comparing the construction conditions with or without fluid-solid coupling effects,it is concluded that when considering the fluid-solid coupling effect,the tunnelling-induced pile settlement,lateral movement,bending moment and axial force has increased 66%,64%,56%,and 13.3%,respectively.The tunneling-induced pile side shear stress has decreased 15.7%.Consequently,in order to accurately predict the tunnelling-induced effect on surrounding environment when concerning tunnel design and construction in a water-rich stratum,the fluid-solid coupling effect as a vital aspect in which need to be paid great attention to detail.