Study On The Integration Theory Of Subsurface Structure At The Periphery Of Soil-rockbimodal Strata

Rock mass has structure,and good quality rock mass has considerable bearing capacity and stability,so "scientific utilization of rock mass structure" is the direction of high quality development of foundation pit engineering.At present,engineers and technicians lack understanding and attention to the structure of rock mass.In the design of excavation support and basement exterior wall structure of earth-rock dual stratum,rock is often regarded as soil and calculated and analyzed according to earth pressure and circular failure mode,which leads to a large amount of waste of building materials and high carbon emission,which does not meet the requirements of new development concept and high-quality development.Aiming at the characteristics of soil-rock dual stratum,this paper systematically studies the integration theory of underground structure of soil-rock dual stratum by using finite element theory and method based on practical engineering,and makes the following progress:(1)Define the three stages of underground structure design and development,and determine the content of underground structure outside the soil rock stratumThis paper summarizes the development of underground structure design concept into three stages:"complete separation","passive integration" and "active integration",and summarizes the existing problems in underground structure design.By analyzing the engineering system of underground structure,it is determined that the foundation pit support and basement exterior wall are the main contents of the general peripheral underground structure.At the same time,considering the structure of rock mass,it is determined that the peripheral underground structure of soil and rock dual stratum includes rock mass structure,supporting structure and main structure.(2)Define the constitutive relation and parameter selection method for numerical analysis of the peripheral underground structureIt is suggested that the HSS model should be selected when the excavation depth of soil-rock dual stratum exceeds 17m,otherwise the MC model can be selected.MC or Hoek-Brown model can be used in rock deformation analysis,and Hoek-Brown model is recommended for stability analysis.Based on the concept of depth effect of foundation pit,this paper analyzes the depth effect of three different support types:stilt pile+rock shotcrete,rock-socketed supporting pile,stilt pile+micro pile.It is found that the support type has little influence on the depth effect.In the numerical simulation of soil and rock two-element stratum,the proper constitutive model should be selected based on the depth effect concept according to the excavation depth and analysis content of soil.(3)The measured deformation law of typical support type of soil-rock dual stratum is obtainedThe monitoring data of typical cases are analyzed,and the results show that the maximum deformation of soil-rock dual stratum foundation pit is mainly surface settlement,which decreases significantly compared with the final surface settlement of soil foundation pit.The surface settlement and lateral wall deformation of three different typical supporting foundation pits are compared and analyzed.It is found that the slope excavation is the best to control the surface settlement,and the horizontal displacement of rock-socketed supporting piles is the largest.Comprehensive consideration of stilt pile has higher safety,economy and cost performance.(4)Put forward the peripheral underground structure system and its design method of integrated soil-rock dual strataBased on typical cases,the lateral pressure and deformation characteristics of the basement exterior wall are obtained for the permanent use of foundation pit support.The integrated design of the outer underground structure of the soil and rock dual stratum selects the permanent supporting structure of hanging pile+micro pile.The integrated peripheral underground structure system is put forward,the integrated design and analysis method is suggested,and the structural characteristics and key points of the underground peripheral structure are clarified.