Study On The Application Of WPC Helical Soil Nail In Foundation Pit Slope Reinforcement Project

Soil nailing supporting technology is applied widely in foundation pit support engineering, when the reinforcing steel bar is used as main material of soil nailing; its advantage of high strength is not fully played. When the foundation pit which used as temporary works reach the end of their useful lives, a great deal of steel materials are buried permanently under the ground every year. It causes much waste of steel materials and has negative effects on the underground which may be utilized in the future. Wood-plastic composite (WPC) is a new material with high efficiency, environmental protection and economy; it will replace steel as the main material of helical soil nail and be widely used in practical engineering.A calculation formula is derived to study the uplift capacity of helical soil nail, and field experiment for uplift capacity are held both on helical soil nail and commonly used soil nail on the same conditions. The experiment results show that the uplift capacity of both helical soil nail and commonly used soil nail affects respectively by diameter of soil nail, length of soil nail in the strata and soil property. The experiment and calculation results are compared and analyzed at last. The fields experiments are done to study the forces on WPC helical soil nail drilling into the soil strata. Then a calculation formula of the drilling torque is derived according to the experimental phenomenon. At last, the experimental and analytical results show that the drilling process of helical soil nail are affected by many factors, such as effective length of soil nail in the strata, width of screw thread, diameter of soil nail, pitch of screw thread, soil property and the pattern of screw thread. The main work and results are as follows:(1)The uplift capacity of helical soil nail meets the requirement of engineering and helical soil nails have strong complementarities with commonly used soil nails when are used for project. Wood-plastic composite is a new material with high efficiency, environmental protection and economy; it will replace steel as the main material of helical soil nail and be widely used in practical engineering.(2) Under the same conditions:the shorter the effective length of soil nail in the strata and the smaller the width of screw thread, the lower the needed torque. The smaller the rod body diameter and the bigger the screw thread diameter, the lower the needed torque. The minimum torque occurs when pitch of screw thread is slightly larger than the diameter of screw thread. The drilling torque of helical soil nail with trapezoidal screw thread is smaller than that with rectangle screw thread.(3) It is difficult for WPC helical soil nail to drill in hard soil so that it is suitable for soft soil.(4) According to the conclusions of the preceding analysis, WPC helical soil nail with optimal pattern can be divided into four sections from head to tail by function, they are the drilling bit section, the main anti-tensile section, the main anti-torsion section and the nut section.