Study On Lifting Mechanism And Influence Factors Of Capsuled Grouting

The construction of underground engineering will affect the adjacent environment,resulting in settlement or inclination of adjacent buildings and structures,which will reduce the service performance of structures.As an active displacement control technology of underground engineering,capsuled grouting can effectively reduce the impact of underground construction on structures.The lifting mechanism of capsuled grouting in clay and sand has been studied by numerical simulation and experiment.However,the existing research still has insufficient consideration on the dilatancy characteristic of sand,the structure of natural undisturbed clay and the creep characteristic of soft clay,which will lead to the inaccuracy of the existing theoretical research in predicting the engineering performance of capsuled grouting lifting to a certain extent.Based on numerical simulation,this paper studies the effects of sand dilatancy,natural undisturbed clay structure and soft clay creep on the engineering performance of capsuled grouting lifting.Considering the critical void ratio and initial state parameter of sand,the influence of sand dilatancy characteristic on the engineering performance of capsuled grouting lifting is studied.Firstly,the rationality of the numerical model is verified by experiments,and then the effects of initial state parameter of sand and overlying load on grouting efficiency and grouting pressure are analyzed.The results show that the efficiency of capsuled grouting in sand increases as a quadratic function with the decrease of initial state parameter of sand,while the overlying load has little effect on the grouting efficiency.When the initial state parameter of sand is not less than zero,the Capsuled grouting pressure increases with the increase of grouting volume,and finally tends to be stable.When the initial state parameter of sand is less than zero,the capsuled grouting pressure increases linearly with the increase of grouting volume firstly and then decreases.The peak pressure of capsuled grouting increases linearly with the increase of overlying load and the decrease of initial state parameter.Considering the different mechanical states of structured clay,the influence of natural undisturbed clay structure on the engineering performance of capsuled grouting lifting is studied.Firstly,combined with the previous research experience,the state parameter of structured clay S_nat and relative state parameter of structured clay S_nat,r are proposed to measure the mechanical state of structured clay,and the calculation formula and upper and lower limits of the parameter are given.Secondly,the hypoplastic constitutive model of structured clay is numerically realized through the user-defined model platform.Finally,the influence of structure on grouting efficiency and grouting pressure under different mechanical states is analyzed.The results show that the engineering performance of the capsuled grouting lifting in structured clay changes with S_nat,r.When S_nat,r takes the minimum value,the grouting efficiency and peak grouting pressure increase with the increase of structure,and the grouting pressure first increases and then decreases during grouting.The engineering performance at this time is similar to that of the capsuled grouting in over consolidated clay.When S_nat,r takes the maximum value,the grouting efficiency decreases with the increase of structure,and the grouting pressure is basically the same as that of the capsuled grouting in reconsolidated clay.When S_nat,r is between the maximum value and the minimum value,the grout efficiency and grout pressure decrease with the increase of S_nat,r.There exists a certain value of S_nat,r which makes the grout efficiency and grout pressure of the structured clay equals to that of the reconsolidated clay.Considering the different consolidation ratio of clay,the influence of creep characteristic of soft clay on the engineering performance of capsuled grouting lifting is studied.Firstly,the accurate numerical simulation of the whole process of grouting consolidation creep is realized by the cooperation of SS model and SSC model,and it is revealed that the negative grouting efficiency in engineering practice and laboratory experiment is caused by creep.Then the creep settlement of clay in capsuled grouting under different consolidation ratio and grouting volume is analyzed.The results show that the creep of soft clay is affected by the consolidation ratio and stress,and grouting can change the consolidation ratio and stress level to a certain extent.The creep in underconsolidated clay and normally consolidated clay decreases with the increase of grouting volume,while the creep in overconsolidated clay increases with the increase of grouting volume.