The Theoretical Analysis And Experimental Study Of Fracturing Grouting Of Collapsible Loess

The technique of grouting is widely used in many geotechnical engineering applications,such as foundation pit support,slope support,ground improvement,pile foundations,foundation underpinning,and structural reinforcement.Though in-depth research has been conducted into this technique,there is very little technical or theoretical research on grouting in collapsible loess-covered areas.Given the special structural characteristics of loess,there must be special requirements on the application of grouting in loess-covered areas.This study focused on the application of hydrofracture grouting in reinforcement works in a region covered with collapsible loess,and involved a combination of laboratory experiment,theoretical analysis,numerical modeling and field trial of a new grouting technique.It systematically investigated the grout properties and influencing factors,the corrosion resistance of the hardended grout and the mechanism responsible,failure characteristics of loess,factors affecting fracture growth induced by hydrofracture grouting,and variations in loess mass' s stress field,flow field,and displacement field during hydrofracture grouting.The main content of the study is outlined below:(1)Experimental study and microscopic analysis of basic grout peroperties.Pure cement grout and cement-based grout were tested for their basic peroperties under the influence of different factors and the consolidated grouts' corrosion resistance was analyzed.The test results show that different factors had different effects of grout properties and the durability of the consolidated grouts was most susceptible to these factors.Based on the results and the characteristics of collapsible loess-covered areas,optimal mixing ratios were recommended for different conditions,in order to provide guidance on how to select proper grouts for hydrofracture grouting in these areas.(2)Failure characteristics of collapsible loess.The failure characteristics of loess were studied through triaxial shear test on intact and disturbend loess samples,uniaxial tensile test on intact and fractured loess samples,and loess collapsibility test.A hydrofracturing experiment was designed to observe the loess' s fracture toughness in different conditions.An analysis of the experimental results suggests that the structural strength of the loess was correlated with the loess' s water content,dry density,void ratio,matric suction,and internal fracture planes.The loess' s failure during hydrofracturing was not only caused by fracture,but was also affected by loess parameters.(3)Application of cavity expansion theory based on D-P revised criterion in splitting grouting of loessFor the study of soil fracturing grouting pressure in collapsible loess area,based on t the D-P revised criteria of cylindrical cavity expansion theory,considering the drainage condition,undrained conditions and hydraulic crack conditions,such as loess fracturing grouting pressure analysis model is established and derived fracturing grouting slurry bubble around the elastic zone and the plastic zone of stress field and displacement field of the theory of soil solutions,and the radius of plastic zone and the splitting grouting pressure is derived,the analytical solution of the final with engineering examples.Results show that based on the D-P revised criteria expansion theory model of radial stress and tangential stress decrease with the increase of ru/rp a non-linear relationship;Three kinds of soil conditions as the material parameters(c,?,E,?),vertical and horizontal slurry to split the increase trend of fracturing pressure is nonlinear when soil.(4)Factors affecting grout pressure during hydrofracture grouting and fracture modes.A crack growth equation for predicting fracture growth during hydrofracture grouting was created using relevant theories of fracture mechanics.Finite element modeling was performed to analyze the fracture modes under pressure and the factors influencing it.It was found that though the fracture planes in the loess mass affected fracture propagation,large fracture planes can cause excessively high grout pressure and thereby prevent significant changes in the direction of fracture growth during grouting.(5)Variations in loess mass' s stress field,flow field,and displacement field during hydrofracture grouting.A non-linear cohesive finite element model was constructed based on theories of rheology,fracture mechanics,and rock and soil mechanics.The cohesive element method was employed to investigate variations in stress,flow,and displacement fields during hydrofracture grouting in loess mass in two conditions: a single fracture and a group of parallel fractures.Later,the relationship of grout pressure to grouting duration and grout diffusion radius was determined using a grout diffusion model with a constant grout flow.(6)A new technique of hydrofracture grouting in collapsible loess and its field trial.According to the theories of fracture mechanics and the law of conservation of energy the basis,we assumed that the fracture growth is a self-similar process.An analysis shows that the energy release rates for mode I and mode II fracture growth were directly proportional to fracture toughness.Base on this finding,a device that enables reverse pressurization and directional output was developed.After being installed at the bottom of a grouting pipe,it can work in cooperation with the stop plug on the pipe top to transfer pressure towards fracture openings and thus reduce energy loess.This can help achieve precise pressure control and promote application of hydrofracture grouting in collapsible loess-covered regions.