Study Of Model Test On The Influence Of Construction With Water On The Anti-pulling Force Of Soil Nailing

With the development of the city,the underground space is currently exploited vigorously to face the limited space on the ground.In the process of underground space development,it will involve the support of foundation pit.Soil nailing technology has become one of the important methods for supporting the foundation pit because of its following advantages such as rapid construction,simplicity and convenience.During the construction of soil nailing,dry drilling and drilling with water are two kinds of pore-forming modes of soil nailing.The construction of soil nailing in Hefei area(expansive soil)is usually made by method of dry drilling.But in the practice construction process,drilling hole with water is adopted in construction of soil nailing in order to prevent the wall of hole from collapsing.However,expansive soil has the characteristics of swelling by absorbing water and shrinking by losing water.Therefore,using the method of drilling with water will cause the expansive soil to be soaked by water,which leads to the reduced intensity index.It will have a great influence on the anti-pulling force of soil nailing.At present,in Hefei area,the influence of anti-pulling force on soil nail which was constructed with water has been seldom carried out.Therefore,this paper tries to explore the influence of construction with water on the anti-pulling force of soil nailing by the method of model test,so as to provide reference for construction with water on soil nailing structure.(1)In order to study the attenuation of the bond strength of the contact interface after soaking in water,the soil samples in the ring cutter were removed in half.And then the direct shear specimens of contact interface were made by grouting,which the contact interface is not soaked in water and soaked in water by 1h,2h,4h,6h,12 h,24h.Through the shear test,it draws a conclusion that the shear strength of the interface between the anchor body of soil nailing and expansive soil is attenuated by water soaking and the attenuation rate is decreased with the prolongation of the soaking time.(2)In order to test the ultimate anti-pulling force of soil nailing,two kinds of pore-forming modes of soil nailing,dry drilling hole and drilling hole with water,are simulated in the laboratory.By using the method of drilling with water,soil nailing hole was soaked in water by 1h,2h,4h,6h,12 h,24h.Then,the model of soil nailing was made by inserting nail into the hole.After 3 days of conservation,the pullout test was carried out in the laboratory.The test result shows that,with prolonged water soaking time,the ultimate anti-pulling force of the soil nailing is decreased,while its attenuation rate is fast before 6h,and the attenuation rate are slow down during 6h to 24 h.(3)Based on the pull-out test data of the soil nailing models,the cohesion of the contact interface between the anchor body of soil nailing and the expansive soil is estimated according to the formula of anti-pulling force of soil nailing.Then a comparative analysis will be made between the above the cohesion value and the cohesion value from direct shear test.According to the analysis results,there is little difference between the calculated values of cohesion and experimental values.It is proposed to test the attenuation intensity of the contact surface between the mortar and the expansive soil by the direct shear test.the purpose is to provide the data basis for the calculation of anti-pulling force of soil nailing construction in Hefei area,and to provide parameters for the calculation of the anti-pulling force for the construction of soil nailing in similar areas.