Experimental Study On The Collapse Treatment Method Of Lime-soil Compacted Pile Holes In The Binary Layer Of Loess On Silt Fine Sand

With the layout and implementation of China’s "five verticals and seven horizontals" highway planning network,the road transportation industry has developed rapidly.When using lime-soil compaction pile foundation treatment,the problem of hole collapse during pile formation is becoming more and more prominent.Due to the specialty and complexity of the loess binary stratum overlaid with silty sand on the project site,it not only treats the collapsed hole without disturbing the soil layer,but also ensures the requirements of the construction schedule.The grouting method has many advantages such as simple operation and short cycle.The collapse of pile holes in the treatment of road foundations at various levels has been more and more widely used.The strength of the stratum after grouting treatment is obviously improved,and the stability is enhanced,which can be used to effectively guide the construction in conjunction with the conclusion.This paper relies on the treatment of the pile hole collapse of the silty overlying loess in the JZ-8 section of the Jingzhong Expressway and according to the characteristics of the distribution of the engineering soil,the binary formation is grouted.The effects of grouting pressure and grouting volume on the diffusion state,law and strength of stone in the formation were studied.A series of laws and conclusions were obtained after a certain analysis and calculation.(1)Through the analysis of the causes of pile hole collapse,the engineering characteristics and injectability of binary formations,influencing factors and evaluation criteria,the selection of slurry materials,the selection of ultra-fine particles with smaller particle size and easier to be poured into the formation Cement slurry.(2)Develop a new type of test device that can realize the test simulation of binary and multiple soil layers and grouting process.The device can realize the grouting model test on the soil layers with different soils,different distributions,different densities and different grouting control conditions,and can obtain the changes of slurry parameters and slurry dispersion during the grouting process.Using pressure control method and flow control method to grouting binary formation,through comparative analysis,the permeability and reinforcement effect of ultra-fine cement is obviously better than that of ordinary cement slurry.Provide guidance for construction.(3)Revealed the infiltration and diffusion state and law of ultra-fine cement slurry in binary formation and the strength law of stone body.The amount of grouting,grouting pressure is positively correlated with the shape and reinforcement depth of the stone body;the same grouting pressure and grouting volume,the reinforcement strength of each position of the grouting stone body is basically uniform;the grouting pressure and the strength of the poured soil It was positively correlated and had no obvious effect on the grouting volume.(4)Use the finite element calculation software FLAC3 D to establish a binary stratum grouting reinforcement model,and perform numerical analysis of the binary stratum grouting reinforcement with different loess distribution thicknesses.The analysis shows that the silty sand has a poor hole-forming effect,and the stress concentration after hole-forming is the cause of pile hole collapse.The plastic zone is introduced to judge and identify the collapsed hole.With the increase of the soil layer parameters,the distribution of the plastic zone is significantly reduced.When the soil layer strength parameter is increased by 30%,there is basically no plastic zone distribution in the silty sand layer.Obviously resolved.When the strength parameter of the soil layer is increased by 50%,only the local plastic zone is distributed,and the subgrade structure is stable,which meets the normal traffic requirements.