Experimental Study And Engineering Application Of Split Grouting In Loess Foundation

In the Western Loess region,the loess foundation is vulnerable to external factors,resulting in different degrees of damage to buildings and facilities.In view of such disasters,grouting technology,as one of the key technologies in various kinds of foundation treatment and soil reinforcement,is widely used in soil reinforcement.Its mechanism is the compaction of slurry on Soil and the formation of complex staggered "net" slurry vein structure,which acts on Soil by skeleton effect,improves the integrity and bearing capacity of soil,and realizes the key point of soil splitting.How to deal with the reinforcement of loess foundation quickly and the problem of slurry diffusion and effect prediction in grouting process has become a more concerned problem in engineering grouting.Based on this,a series of laboratory and field tests have been carried out in loess foundation to determine the control parameters of splitting grouting by analyzing the grouting pressure,grouting volume,time history change and diffusion performance during grouting.The effectiveness of splitting grouting in strengthening loess foundation is verified by means of load test,analysis of soil properties before and after reinforcement and observation of foundation settlement after reinforcement of existing buildings.The main contents of this paper are as follows:(1)The water cement ratio of grout is one of the key factors to realize splitting grouting.By analyzing the changing law of the properties of grout such as specific gravity,2H precipitation rate,stone rate,shear strength,compressive strength and viscosity of grout under different water cement ratio,it is found that when the water cement ratio of grout is between 0.6 and 1.2,the property of grout is stable and suitable for Loess grouting,which can be used for grouting model test and field test.The comparison design of grouting test provides a basis.(2)Using self-designed grouting model device,laboratory tests under various grouting conditions were carried out.Through monitoring and recording pressure changes,grouting pulse diffusion distribution,soil performance indexes before and after grouting,the conditions for realizing splitting grouting in loess foundation and reasonable evaluation of grouting effect were analyzed from multiple angles.The results show that the smaller the water cement ratio is,the larger the splitting grouting pressure is,and the smaller the diffusion distance is.When the pressure is not high,the compaction effect of grouting is dominant.When the pressure exceeds0.4 MPa,the splitting effect occurs,and the splitting effect is better when the water cement ratio is 1.0.The results can provide reference for the research of splitting grouting theory and later field grouting test.(3)On the basis of indoor model test,in order to achieve the effect of directional splitting,a "bottom-up" stratified splitting grouting experiment was designed to divide the vertical area of grouting holes.By analyzing the variation of grouting pressure and grouting volume with grouting time,combined with the distribution of grouting pulse and soil performance test after site excavation,grouting control parameters can be obtained in practical reinforcement engineering application.The results show that:(1)Compared with the traditional grouting method,layered grouting can form a "tree root" grouting vein in a vertical area of grouting holes.While achieving the splitting effect,directional splitting can be carried out on different soil layers to achieve the effect of layering and treatment.(2)The maximum diffusion distance of the grouting pulse after grouting is more than500 mm.Therefore,in the actual loess foundation grouting reinforcement project,the design of grouting hole spacing should be 0.8 m~1.0 M.Aiming at the problems of improper sealing of grouting holes and lack of specific split grouting device,a split grouting device and a split grouting device suitable for loess zones are proposed.(4)Based on the conclusions of grouting model test and field grouting test,the engineering application of grouting reinforcement under two different working conditions is designed and carried out.The results show that the splitting grouting method can effectively improve the bearing capacity of foundation,and the settlement of foundation can be effectively restrained after 30 days of grouting.