Study On Anchoring Mechanism Of Inflatable And Expansive Controlled Bolt In Cohesive Soil

As a new structural bolt,inflatable expansion control bolt is made after an improvement and processing of the inflatable bolt.Its basic principle is: according to the characteristic that soft soil can deform largely under the external force,great frictional resistance is produced by the contact of the extruded bolt steel sheet of the gas expansion device in the inner bolt and soil so as to provide anchoring force and achieve anchoring effect.Compared with traditional grouting anchor,the new structural bolt is characterized by a greater applicability,a better economical efficiency,a greater applicability in technical demands of foundation pit support engineering and a more broad application prospect.In the actual construction of geotechnical engineering,the limitations of traditional bolt are gradually exposed due to complex supporting environment and space caused by different geological conditions.For example,anchoring force is not easy to control and relatively small.The traditional bolt,which has a higher cost,can not be recycled,encroach on underground space in the surrounding and are not applicable to the foundation pit supporting of soft soil.Considering the above limitations,various new structural bolts have been created in recent years followed by changing technologies and increasing varieties of bolts,including screw anchor,umbrella-shaped self-expanding bolt,concrete bolt,pressure-dispersive bolt and inflatable bolt.Inflatable expansion control bolt mentioned in this paper belongs to expansion frictional bolt,whose structure is mainly composed of five parts: soil-squeezing device(four steel sheets),expansion device(a gasbag),force transmission device(four pull rods),inflatable device(an air compressor)and control device(a barometer).Inflatable expansion control bolt has the basic function of general frictional bolt and can be recycled with the advantages of controllable anchoring force,low cost,convenient usage and simple structure,and can bear large surrounding rock deformation and remain inflatable in soft soil.Inflatable expansion control bolt have become popular once it was created due to its numerous advantages.Vice professor Yang Xuexiang in our university and his team have been authorized by the patent,took it into the actual engineering practice and made phrased achievements,which has laid a foundation for the actual application of inflatable expansion control bolt in the foundation pit support engineering.However,it is beyond controversy that the theoretical study of bolt support in engineering application falls behind the engineering practice.And this paper mainly did the following studies: test program was improved and new test tools and devices were introduced;after field test and theoretical analysis,the formation mechanism of anchoring force of inflatable expansion control bolt in clay was studied,and its working principles and unique structural characteristics were introduced;comprehensive evaluation which was made according to the field statistics provided a reference for its practice and theoretical study;after the field test,the relations among ultimate drawing force of inflatable expansion control bolt and bolt displacement,gasbag pressure and earth pressure on the surface of bolt steel sheet were analyzed;the calculation methods of anchoring force of inflatable expansion control bolt were deduced and the factors causing the anchoring force of inflatable expansion control bolt were analyzed combined with test data;the calculation value of bolt anchoring force and its test value were compared and analyzed to prove the correctness of the deduction formula of bolt anchoring force,which provided a reference and theoretical support for the promotion and application of inflatable expansion control bolt.