Research On Excavation Deformation Of Limited Rock-soil Foundation Pit In Strata With Soil And Rock

The stability of deep foundation pit excavation in urban subway open excavation station is an important aspect of the research of construction and environmental safety.Qingdao Metro Blue Silicon Valley Line Miao Ling Road Station,which is excavated under "upper-soft lower-hard" special geology and formation conditions,is a transfer station.The excavation and support engineering of foundation pit is complex and needs many construction steps,coupled with this area close to many existing buildings,the requirements of strata deformation is extremely high during the construction period.How to analyze deformation of the reasonable supporting system and structural force of limited rock-soil foundation pit in strata with soil and rock and how to analyze the impact of the surrounding and existing building foundation form and construction of building foundation pit on the excavation is the key and difficulty to ensure the safety of construction and the environment.In this paper,the problem of limited rock-soil supporting and deformation in Miao Ling Road Station foundation pit is systematically studied through the theoretical research,field test and numerical simulation methods.The main contents are as follows:(1)The finite element model of retaining structure-rock and soil-adjacent building is constructed.The limited rock-soil deformation and lateral displacement of retaining pile is analyzed.Comparing with the measured data,it verifies the rationality of the numerical model.(2)The numerical model of rock and soil-retaining structure interaction is established and their interactions are analyzed.It gets the following characteristics and laws.The maximum value of ground settlement and the influence range of ground settlement increase with the thickness of overburden in strata with soil and rock.The maximum value of surface settlement and the maximum lateral displacement of pile is quadratic parabola relationship with the thickness of overburden.The maximum value of ground settlement and the maximum lateral displacement of the pile increase with the thickness of strong weathered rock.The surface settlement curve is "groove-shaped".The abrupt displacement of the retaining pile occurred at the boundary of the soil and rock strata.The maximum value of surface settlement and the maximum lateral displacement of pile is a linear relationship with the thickness of strong weathered rock.The width of the reserved rock shoulder can be optimized from 0.8 to 1.5 m.Increasing the depth of embedded lock foot and stiffness of the pile to control the deformation of the foundation pit is limited,1～2m lock foot rock-socketed depth is more appropriate.It can be appropriate to reduce the pile stiffness.(3)The numerical model of retaining structure-rock and soil-adjacent building with raft foundation and pile-raft is established separately.The result shows that the existing building affect the stress and displacement distribution of foundation pit.The distribution curve of the limited rock-soil between retaining structure and the building foundation is“s-shaped".The thickness of the overburden layer significantly affects surrounding ground settlement of the foundation pit.The displacement of the pile top is the largest,followed by the lateral displacement of the upper part of the pile,the lateral displacement of the lower part of the pile is the smallest,and the deformation of the pile at the location of the soil and rock is large.The curve of earth pressure of pile side was"triangle shape".The foundation of adjacent building has a different effect on the ground settlement,the lateral displacement of the pile and the earth pressure of the pile side in the limited rock-soil area of foundation pit,near the construction side of the ground settlement,the lateral placement of pile and pile side of the earth pressure are greater than away from the building side,the double-decked basement raft is larger than that of double-decked basement raft third floor.(4)The model of adjacent foundation pit excavation is established and the interaction analysis is carried out.When the pit spacing is less than 10m,overall lateral displacement of the foundation pit retaining structure excavated previously occurred to the direction of the foundation pit excavated afterwards.As the spacing increases,the interaction between adjacent excavations decreases gradually.The settlement pattern of the limited rock-soil between the foundation pit is generally shown as "groove-shaped"on both sides and convex "parabolic" in the middle part.The larger the thickness of the overburden layer,the greater as a whole lateral displacement of the foundation pit retaining structure excavated previously occurring to the direction of the foundation pit excavated afterwards is,the greater settlement of limited rock-soil ground is,the greater deformation of the two sides of the limited rock-soil is.The research results directly serve the Qingdao Metro Miao Ling Road Station project design and construction and provide a guiding role in ensuring the stability of the limited rock-soil between the foundation pit and the surrounding basement and proposing protective measures for adjacent buildings.The above research results also provide a theoretical basis for the subsequent design.It is of great significance to ensure the safety of the project,saving investment in engineering.