Study Of Mechanical Model Of Reinforced Soils By Pre- Grouting And Its Application In Tunnelling Practices

In present, the parameter design of fracture grouting is still in a semi-theoretical and semi-empirical method which has not combine organically with grouting purpose or grouting quality. Moreover, the existing detection method of grouting quality is cursory and far from enough economical & reasonable. All of these are probably cause material waste and hide some engineering dangers. The reasonable parameter design method and the economic quality detection method of fracture grouting are studied by using laboratory tests, theoretical analysis and numerical simulation. The specific contents and the main results of this paper are as follows:(1) The phosphoric acid-water glass and cement-water glass were selected and their relationships between setting time and material ratio, mechanical properties and permeability, as well as variation of microstructure with time were studied. Results showed that:①Setting time of phosphoric acid-water glass grout first increased and then decreased with increasing volume ratios of water/phosphoric acid, while it has a complex variation with Baume of water glass.②Setting time of cement-water glass grout first decreased and then increased with increasing water-cement ratio, while it increased with increasing Baume of water glass.③Both of the two grout can meet the requirement of impervious layer.④ Phosphate-water glass grout is suitable for emergency water seal grouting. ⑤Cement-water glass grout is suitable for the layer both needing of water seal and strengthening in the same time.(2)A simplified 2D model for equivalent unit cell was developed for composite soils with fracturing grouting, and the analytical solutions of the equivalent elastic parameters of this model were derived based on deformation compatibility principle and homogenization theory. Then, finite element method (FEM) was employed to calculate and analyze the equivalent elastic parameters of the simplified model and existing model, respectively; meanwhile, the comparisons were made between the FEM and analytical results of the simplified model. Finally, the influence of grouting volume ratio, soil elastic parameters, and grouting concretion elastic parameters on equivalent elastic parameters were analyzed by means of the analytical solution. Results showed that:①the method of equivalent grouting area is feasible, and the simplified model can be applied to theoretical analysis in the elastic deformation stage.②the analytical results are in good agreement with the finite element results.③the equivalent elastic modulus and equivalent Poisson’s ratio of composite soils are mainly influenced by the grout volume ratio and modulus of grouting concretion body.(3)A three-dimensional model was proposed for composite soils with fracturing grouting, and a volume and stress distribution diagram of grout-soil was developed following principle of equivalent grouting volume. Then the analytical solutions of the equivalent elastic modulus and equivalent Poisson’s of the model were derived based on transversely i so tropic constitutive equations. The same elastic parameters of the model for specific conditions were calculated by (FEM), and results were compared with analytical solutions. Finally, the Flac3D was employed to calculate the settlements of a thermal tunnel using the proposed model and its analytical solutions. The calculated results were compared with the observed ones. Results showed that:①the analytical solutions of proposed model highly agree with FEM results.②the engineering case indicates that the proposed model and its analytical solutions are reliable and valid for engineering practice.(4)Based on the elastic model of the fracture grouting composite soil, the vertical displacement of soil and the stress of lining were analyzed by numerical analysis method. Results showed that:① Results of the two models have little difference, and the plane model are relatively conservative.②Grouting can significantly control soil deformation induced by tunnel excavation and reduce lining stress. The control effect increased with increasing grouting circle thickness. However, the increase rate is reduced. Composite soil elastic modulus has the same regularity. ③In this paper, the economical and reasonable grouting circle thickness could be 2.5m, composite soil elastic modulus could be 30MPa-35MPa and grout injection rate could be 0.132-0.164.(5)Two acquisition methods of grout injection rate are proposed and a quantity detection method of fracture grouting is obtained based on analysis of grout injection rate. Acquisition methods include theoretical calculation method (TCM) and digital image processing method (DIPM). The grout injection rate could be calculated by TCM only using the physical parameters of soils before and after grouting. While a digital image of soil is need formed after grouting of DIPM. Reliability of the two methods was verified by field test. Results showed that:①the actual grouting amount is about 1.2 times of the calculated one of TCM.②the grout injection rate judged by the DIPM has little variability and good repeatability. Comparing with the true quantity of grout injection recorded in project site, and the grouting volume calculated based on the DIPM is about 0.8～0.9 times of the actual one. The grout injection rate judged by the DIPM shows a little variability and good repeatability as well as sound agreement with project data.③ There was an apparent linear correlation between the results obtained by 2 methods, and the TCM values are smaller.(6)A method-system of grouting parameters was discussed combined with thermal tunnel practices. Practical results have proved the reliability of this system. The mechanical model is also reasonable and valuable to practices.