Application Research On Cross Prefabricated Foundation Pit Supporting Structure

Currently, the foundation pit engineering is facing a lot of problems, just like difficult construction, slow construction, the long construction period, high cost. This paper put forward the landslide engineering anchor lattice structure-square lattice, people come up with a new type foundation pit supporting form that is the cruciform and fabricated foundation pit supporting structure which has the advantages of convenient construction, high speed of construction, short construction period, low cost, recoverability and reusability. Because of the lattice unit stiffness is much larger than the soil stiffness, proposes the calculation model of lattice unit-the cantilever beam method, Compared with Winkler elastic foundation beam method trial found that the calculated results agree completely, so as to determine the applicable to the lattice unit and internal force calculation method of the simple and feasible, the cantilever beam method.According to project engineering geological conditions, using the method of cantilever beam with cross-shaped prefabricated foundation pit supporting structure design, determine the lattice unit test section design the anchoring force of 600kN, Anchor cable length of 25.0 m, anchorage length of 20.0 m, free segment length of 5.0 m. Through the field test, we know:1. Basal soil reaction force increases with the increase of anchor cable stress, in the largest near the anchor basement earth pressure, in the rib beam at both ends of the smallest, the difference increases with the increase of anchor cable stress.So, the approximate think basal soil counterforce evenly distributed.2. In the 600kN anchor cable under the action of stress, on surface of steel, the surface of steel plate and pipe internal force change trend of the rib beam is the same as the coupling beam, rib beam maximum stress is greater than the maximum stress coupling beam, the both are less than the tensile or compressive strength of Q235 steel design value. Rib beam and the beam on the surface of steel plate, the surface of steel plate and the square tube in near the anchor cable stress is the largest, in the rib beam and the beam stress on both ends of the smallest. In the near the anchor cable, on the surface of steel plate under the stress value of surface plate stress value of 1.6 times; in addition to other location near the anchor cable, on the surface of steel plate stress value is small, less than 10 MPa.3. From earth excavation to lattice unit installation is complete, test section in the top horizontal displacement and vertical displacement of the slope, slope after deep horizontal displacement is less than the alarm value of soil (plus or minus 50 mm), meet the specification requirements.Tests showed that:in the cross sectional foundation pit supporting, supporting structure from excavation to the lattice unit installation is complete the whole process, Foundation pit stability meet the requirements, the deformation is less than the alarm value, supporting structure strength meet the requirements, meet the specification requirements, cross prefabricated foundation pit supporting structure used in the foundation pit supporting project is safe and feasible.Finally, by comparing the analysis of the lattice unit internal force calculation value and experimental value, it is concluded that:1. Lattice unit rib beam and the beam under the surface of the steel plate, square tube, the section stress value is reasonable, the error is less than 5%, the lattice unit can be thought of rib beam and the beam tube, the surface of steel cantilever beam method is used to calculate the lattice unit internal force is in line with the actual situation;2. Lattice unit rib beam and the beam on the surface of steel plate in the anchor role stress value is far greater than other position, and also much larger than the calculated value, and in other position, the stress value is far less than the calculated value is less than 10 MPa;Therefore, optimize the lattice unit design:remove the lattice unit rib beam and the beam on the surface of steel plate; Will be 219 mm in diameter, the thickness of 10 mm round steel pipe anchor hole, optimized for 102 mm in diameter, the thickness of 10 mm round steel pipe cable hole; 200×100×10 square tube backbone optimization for 200×100×6 square tube backbone. And according to the experience of the project of nanning ever proposed A, B, C three types of lattice unit.