Column-forming Mechanisms Of Jet Grouting In Water-rich Sands And Its Engineering Application

Jet grouting is a common mean for soil treating and is used widely in the realm of engineering for its stabilization and water-sealing effect.However,at present,the design of construction parameters mainly depends on the experience rather than theory.The process of jet grouting is concealed and the quality of the column cannot be observed during construction,so unreasonable construction parameters may lead to unsatisfactory engineering results.Especially for the water-sealing project,unreasonable construction parameters will cause the discontinuity of the cut-off wall,and then weaken the watersealing effect.In view of the existing problems of the jet grouting technology,such as unclear column forming mechanism,difficulty to predict the column diameter and the lack of theoretical basis for the design of construction parameters,the following work has been done in the column diameter prediction,mechanical property of the soilcrete,and the effect of defects in jet-grouted cut-offs.The research work and the main conclusions are as follows:(1)SPH and ALE methods were used to respectively analyze the interaction between the jet and the soil in unsubmerged and submerged conditions,and the erosion laws of jet and the deformation behavior of soil were obtained;(2)Based on turbulent jet theory,the calculation formula of the jet impact force was obtained.Combined with the estimation of the soil resistance,a theoretical model for estimating the column diameter was obtained.The model for diameter prediction was then verified by numerical simulation results and several engineering cases;(3)The influence factors of the column strength and permeability coefficient were analyzed.The relationship between the cement content and the strength besides permeability coefficient of a column were discussed.The core samples from different radial parts of columns were tested by XRD and TG-DSC.The distribution law of cement content in radial direction of a column was obtained,then the theoretical distributions of strength and permeability coefficient in radial direction were obtained.The influence of the radial non-uniformity of a column on engineering was evaluated;(4)The probability distributions of the factors causing geometric defects in the jetgrouted cut-off walls were analyzed.Simulation models of the jet-grouted cut-off wall considering geometric defects were established.A simplified theoretical seepage model with a cut-off wall was deduced.The simulation model was related to the simplified theoretical model according to the equal seepage flow,and a theoretical model of a jetgrouted cut-off wall considering defects was obtained.The theoretical model was validated by numerical simulation and field observation;(5)A similar model experiment was carried out by a customized system.The diameter prediction model and the distributions of the strength and the permeability coefficient on the radial direction were further validated;(6)The construction parameters of jet grouting in Shifuying station of Beijing Subway Line 3 were designed by using the theoretical models proposed in this paper.The test results of the water seepage observation,coring and the pore water pressure monitoring show that the water-sealing effect of the jet-grouted cut-off wall is remarkable and the jet grouting technology is suitable for non-dewatering construction of an undermined subway station.The research results of this paper play a positive role in the design of jet grouting construction parameters and the popularization of the non-dewatering construction.Meanwhile,the numerical simulation methods and the model test equipment of jet grouting adopted in this paper can provide references for other similar researches.