Study On Engineering Properties Of Polyurethane Grouting Materials And Strengthening Properties Of Fine Sand

In the construction process of underground engineering,such as subway tunnel and mine tunnel,weak strata with poor engineering properties and different types often appear.Once not properly handled,construction quality will be affected,and even the safety of original buildings will be threatened.Therefore,in the actual construction process,grouting reinforcement technology and relevant supporting facilities are often used to ensure the safety of construction and subsequent tunnel project operation.Polyurethane grouting materials with isocyanate,polyol pre polymers as the main agent of the preparation of polymerization reaction,and through the grout foundation structure,combined with soil,minerals and other particles generated a certain cohesive force,flexibility,strength,and insoluble in water body of consolidation grout material,is widely used in underground engineering of waterproof plugging,foundation reinforcement,etc.In this paper,the engineering characteristics of polyurethane grouting material are taken as the starting point,and it is applied to the reinforcement of sand and soil samples.The strengthening performance of polyurethane grouting material to weak sandlayer is studied in detail,so as to provide design parameters for its practical application in the construction of underground engineering.The main research ideas and conclusions of this paper are as follows:(1)High performance environment-friendly polyurethane grouting material was prepared by prepolymer method.A series of environmental friendly polyurethane grouting materials with different properties were synthesized by using diphenylmethane diisocyanate(MDI)and high-hydrophilic polyether polyols as main agents with a certain dose of auxiliary agents.By changing the dosage of diluent,catalyst,retarder and other auxiliaries,the influence of them on pulp properties was analyzed.The appropriate diluent dosage and the catalyst and retarder with better effect can be obtained through the test.(2)Through the laboratory grouting reinforcement test,the strengthening degree of polyurethane on sand samples and the influence of acetone as diluent on the strength of solid sand body were studied.At the same time,the sand solid body was placed in acidic,alkaline and neutral solutions to explore the change trend of compressive strength of the sand solid body in water environment with different pH.It is found that the strength of the solid sand body in different water environments decreases to different degrees,but the overall strength is not completely lost.(3)In practical projects,it is often necessary to combine different site conditions to prepare corresponding modified mixed polyurethane grout.In thispaper,two inorganic materials,calcium carbonate powder and fly ash,were used to explore the modification effect of them on polyurethane pulp material,and the strength change trend of corresponding solid sand bodies after hydrolysis.It is found that these two inorganic materials have different modification effects on polyurethane pulp,so their application sites are not the same.(4)An important reason why polyurethane pulp is difficult to be widely used in practical engineering lies in its high price,which is more than ten times of the engineering cost of cement slurry.In view of this shortcoming,polyurethane cement composite grouting material is prepared by means of blending,aiming to overcome the shortcomings of polyurethane with high cost and complicated construction technology,and to overcome the shortcomings of cement as grouting material in permeability and construction operation.However,it is found that although cement slurry can increase the strength of solid sand body of polyurethane slurry,the injectability of mixed slurry is also limited.