The Study On Soil Nailing Based On Soil Arching Action

At present, soil nailing practice is on serious situation that theory lag behind the practice. The design Methods are restricted by difficulty to choose the correct soil parameters' mode lack of achieving a correct understanding about soil nailing mechanism and the experience. The study on the correct soil nailing mechanism, failure mode and soil pressure theory becomes the difficult problems which must be urgently solved. Because of lacking adequate understanding of soil nailing mechanism, a vast amount of tests data cannot be reasonably utilized and refined. This thesis has made a systematic study on these problems through theory analyses and example analyses.So far, the soil nailing mechanism is based on the mechanisms of anchoring bolting and reinforcement. It suggests that the reinforcement of soil nailing enhances the soils, strength and self-stability. But the test data suggest that the placement of soil nailing decreases the vertical stress of soil. So the soil's self-stability and bearing capability are increased, yet the soil strength is not be enhanced. In view of this phenomenon this thesis suggests that the placement of soil nailing forms the soil arching in the soil-nailed wall. This function can be described by Tezaghi's stress-transfer theory. It is the stress transfer that decreases the vertical stress of soil and increases the soil's self-stability and its bearing capability.Based on soil arching theory, the traditional external stability analysis is revised, The study on the maximum horizontal space of soil nailing and the maximum self-standing height are also carried out. The calculation methods and formulas are proved to be practical and reasonable through examples analyses.The accuracy degree of the study on the soil pressure and the soil nailing design are determined by the failure mode. The traditional failure mode doesn't considering the soil nailing's action on the failure plane. When the failure plane is defined, this thesis puts forward the "stress-deflection mechanism" and the "suppositional passive state mechanism" when there exists a rigid layer in the excavation's sides.The twomechanisms are used to modify the logarithmic-spiral slide curve. The example analyses show that the accuracy of this thesis's modified logarithmic-spiral mode is greatly enhanced. So there is no need to try to define the curve by a large amount of calculation, The mechanism of the "tension-crack-slide" is also suggested. The two-line failure plane is very simple, practical and accurate, so it can be directly used to soil nailing design and the study on soil pressure.The calculation formulas for soil pressure are suggested based on the two-line failure plane and those mechanisms suggested by this thesis. The example analyses show that the calculation results are identical to the test results in the aspects of quantity and distribution.Integrated with the calculation methods of soil pressure, the mechanism of soil pressure of fale is studied systematically and detailedly based on the mode of axial stress distribution of wholly grouted anchor. The calculation methods and distribution modes of the partial soil pressure of face, the soil pressure of face and the maximum tension stress are put forward.The theoretical analyses and the example analyses show that the suggested distribution modes of axial force and soil pressure mechanism of face are very reasonable. So the difficult problem of adopted standard of soil pressure of face is solved by the results of this thesis, and the quantitative standard can be used to the face design. The maximum tension force of soil nailing also can be directly used to determine the length of soil nailing.The study on soil nailing mechanism is the basis of design and study on the soil nailing. The active-restricting mechanism is put forward based on the soil arching mechanism. Comparing to the traditional active-restricting mechanism based on the reinforcement mechanism. The mechanism put forward by this thesis is more reasonable. It conforms to the tests datums and esta...