An Experimental Investigation On The Propagation Mechanism Of Grout Injected Into Transparent Fractured Medium

Groundwater inrush is mostly related to the faults and fractures of rock mass. Fractures with certain opening and ductility might be the advantage pathway of water inrush. With strong practicability and wide applicability, grouting has a broad development and has become one of the key technologies to control and prevent water inrush disaster. The experimental simulation method combined with theoretical analysis was applied in this paper. A geologic model of fractured rock mass with the risk of water inrush was established based on the research of field characteristics of the fracture according to grouting practice and pre-existing theoretical research. The transparent soil test method which can be used to realize real-time visualization and no-artificial interference was introduced to build two experimental models. One is the rough plate single-fracture model, the other is the model of network fractures generated in rock mass. The mechanism of Newton fluid grout and Bingham fluid grout grouting into fracture replica was researched. The grouting effect and its influence factors of grouting into plate fracture and network fracture in rock mass with flowing water were also investigated. The main conclusions were as follows.(1) An investigation of fracture characteristics in Wushan county was conducted, which was mainly for studying the development of fractures and the filling and roughness characteristics. A method of fractal dimension was applied to calculate the fracture roughness. The JRC values from six fracture images are between 6 ~ 23 according to the empirical formula of fractal dimension corresponding JRC, which have a good corresponding relationship with Barton standard curve.(2) An experimental investigation on Newtonian fluid seepage in rough plate single-fracture which filled with fused silica was conducted using transparent soil materials with flowing water condition. Results show that the flow propagation pattern of Newtonian fluid along the flow water direction can be roughly divided into three stages. In the initial stage, the fluid diffused approximate in an elliptic form and propagation edges are serrate along the angled rough fracture. In intermediate stage, the spread of the propagation front of the Newtonian fluid gradually transformed into irregular trapezoid. In the end, the shape of propagation front was nearly straight, showing a nearly arc propagation pattern. The propagation of Newtonian fluid against the flow direction is not obvious.(3) An experimental investigation on Newtonian fluid seepage in fracture net-work of rock mass which filled with fused silica was conducted using transparent soil materials with flowing water condition. Results show that the fitting formula about the fluid propagation radius and the propagation time has certain similarities with Maag’s spherical propagation formula. It indicates that the propagation characteristics of Newtonian fluid in the fracture network of rock mass shows similar characteristics of pore propagation in sandy soils, and the fillings in fracture influences the seepage characteristics significantly.(4) An orthogonal test on Bingham fluid grouting into rough plate single-fracture which filled with fused silica was conducted using transparent soil materials with flowing water condition. Results show that the three factors influence the experiment result on the primary and secondary order of grouting pressure > seep of water flow > gel time. Grouting pressure is the main influence factors of grout propagation effect through intuitive analysis and variance analysis, which the effects were significant when α value is 0.05 and 0.10. While the effects on the penetration length of the water flow speed and grout gel time under different levels are not very significant.(5) The grout propagation form according to its form changing law can be divided into two types, nearly round flow propagation and anterograde propagation. Nearly round propagation can be divided into serrated propagation and flatness propagation based on propagation boundary edges. Suborbicular zigzag dispersion type appeared mainly in low level grouting pressure and higher levels of grout gel time and with little correlation with flow water levels. Nearly round flat type propagation appeared mainly in condition of low water flow and low grout gelation time and with little correlation with grouting pressure levels. Anterograde propagation type appeared mainly in a higher level of grouting pressure and high dynamic water flow speed, and with little correlation with level of gel time.(6) Results also show that the grout propagation type can be divided into partition propagation and no-partition propagation. The grout propagation partition type can be further divided into two-subregion type, three-subregion type and two-subregion shear crack according to the solidification characteristics of grout. The curves of pore pressure can be roughly divided into three categories; "response to follow" pore pressure curve, "first getting down then up" pore pressure curve ", first getting up then down " pore pressure curve. The main cause is the characteristics of grouting pressure difference and different grout solidification area in the end.(7) Based on the derivation method of the “cubic law”, according to the stability of grouting pressure and grouting flow characteristics, mathematical models of grout propagation for Newtonian fluid in smooth flat single fracture, Newtonian fluid in flat single fracture containing coarse sand filled, Bingham fluid in smooth flat single fracture, Bingham fluid in flat single frature containing coarse sand filled were respectively deduced. The propagation mechanisms of the four kinds of experimental conditions are analyzed. An experimental investigation on Newtonian fluid seepage in fracture network of rock mass which filled with fused silica was conducted using transparent soil materials with flowing water condition. The grout propagation shape in the bottom is similar to isotropic circular at the most of the time, which has obvious difference of the fracture network without fillings. Thus, the sand fillings had a significant effect on the seepage flow characteristics of fracture. Result shows that the maximum propagation radius of the image in experiment is 4.087 cm, while the propagation radius is 4.586 cm according to the formula calculation using Su’s formula. As the result, the Su’s formula can be used as a quantitative research reference in propagation radius.