| The three traditional support forms of frame beams,prestressed anchor and soil nails have been widely used in slope engineering because of their outstanding advantages,and these three forms of support have been combined to form a new type of support technology for frame prestressed anchor composite soil nails.At present,there is a lack of theoretical research on this kind of technology.This paper makes use of finite element simulation software and regular rock slope stability analysis software to study the composite support technology of frame prestressed anchor composite soil nail.The main contents of the research are:(1)In the soil slope,ABAQUS is used to conduct three-dimensional numerical simulation and comparative analysis of the step-by-step excavation process of unsupported,frame prestressed anchor composite soil nailing and frame beam composite soil nailing supporting slopes.At the same time,the stability analysis software of regular rock slope is compared and studied in three cases,and the variation of slope displacement and safety coefficient with excavation depth is analyzed.(2)When the cohesive force and internal friction angle change in the soil slope,the change of safety factor of the slope is discussed.The application of the frame prestressed anchor composite soil nail and frame beam composite soil nail support system to different internal friction angles and cohesive slope is obtained.(3)The effects of five design parameters,such as tilt angle,length,prestress value,tilt angle and length,on the support effect of the frame prestressed composite soil nail support system are discussed.The results of finite element simulation and regular rock soil analysis show that the displacement of slope increases and the safety coefficient decreases with the excavation of slope.The effects of three conditions on slope displacement constraints are: frame prestressed anchor bolt composite soil nailing support & GT;Block beam composite soil nailing support & GT;Not supported;Safety factor is: frame prestressed bolt composite soil nailing support & GT;Block beam composite soil nailing support & GT;Not supported;The law of soil nail axial force is as follows: soil nail axial force always presents two small,large law in the middle,soil nail axial force basically increases with the increase of excavation depth,the soil nail with the greatest force is located in the middle and lower parts of the slope,and the soil nail axial force is horizontally compared.The biggest force is near the slope boundary;When the cohesive force and internal friction angle of the slope are different,the applicable conditions for the support form are: When the cohesive force is greater than 20 k Pa,and the internal friction angle is greater than 20°,it is recommended to adopt the framework beam composite soil nail support form.When the cohesive force is less than 20 k Pa,and the internal friction angle is less than 20°,the support form of frame beam composite soil nailing can not guarantee the stability of the slope,and the support form of frame prestressed anchor composite soil nailing can guarantee the stability of the structure.By analyzing the effects of five design parameters on the safety factor,displacement and axial force of the frame prestressed bolt composite soil nailing support system,the optimal range of parameters is obtained.The results of the analysis are: The length of the bolt,the length of the soil nail,and the pre-stressed value have not contributed much to the displacement constraint and the increase of the safety factor after reaching a certain value.It should be controlled within a certain range.The soil nail inclination is recommended to take 10°~15°,Anchor inclination is recommended to take 5°~10°. |
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