Mechanism Of Grouting Reinforcement Of Water-rich Fault Fractured Zone And Its Application In Tunnel Engineering

The dimension, quantity and difficulty of tunnel and underground engineering construction in our country have become the largest around the world. With the focus of transportation infrastructure construction shifting to the mid-west mountainous area and karst area, tunnel and underground engineering construction is confronted with the problem of "complex geological structure, changeable geological environment and frequent disaster." According to statistics, nearly80%of the significant safety accidents in transportation, hydropower and other underground construction have been caused by inrush of water (mud) disaster or its improper disposal, leading to a large number of casualties, economic loss and construction delay, and even suspension or design alteration of the tunnel construction. Additionally, inrush of water (mud) can easily induce geological disaster like water resources depletion and surface subsidence, which severely threaten social stability and economic development. Thus, inrush of water (mud) encountered in underground construction is a world class engineering problem.Inrush of water and mud in fault fractured zone is a common geological disaster during tunnel construction, while grouting is an effective method of treatment. However, due to the complexion of the interaction relationship of geological environment, different types of grout and the inner structure of injected media, the grouting treatment theory is far behind engineering practice, causing a urgent demand for investigation. This paper investigated grouting consolidation mechanism, characteristic of consolidation body excavation and the law of gradual instability under high water pressure, and compound controlling grouting method in aquiferous fault fracture zone, using a combination of theoretical analysis, laboratory test, simulation test and field test. Then a series of research results were made.(1) Geological factors and engineering factors leading to inrush of water and mud were deeply analyzed, through a large amount of data on inrush of water and mud. With the background of high angle fault zone of soft rock-hard rock interaction strata region development and the model of grouting consolidation engineering practice of aquiferous fault fracture zone during tunnel excavation, three engineering geological model types of advancing grouting consolidation, disaster emergency grouting consolidation and post-disaster rescue grouting were established.(2) The strength and ductility of homogeneous fault rock grouting consolidation body obtained a relatively high growth; the failure of fault mud consolidation body presented a noticeable structure effect, and the stress-strain curve presented a multi-crest value characteristic; the failure of fault breccia consolidation body was similar to that of rock mass. Grouting pressure is the main factor on the strength of consolidation body, while the dry density is a miner factor, which increases the grouting compression effect as it reduces. Grouting materials distributed in the fault breccia as an cement material, whose influence is larger than the initial dry density. The single liquid slurry increases both the c and φ value on grout-rock interface, while C-S double liquid slurry only increases the c value; compared with the original fault slurry, the c value of the compressing consolidation fault slurry increased which the φ value decreased, which is why the grout-rock interface is the most stable, and the compressing consolidation soil is the most likely to break. Fault gouge transformed from loose flocculent structure into an integral structure; grout-rock interface is a three dimensional structure composed of cement surface, permeability transition zone and micro fracturing transition zone, which combining closely internally.(3) The consolidation mechanism of homogeneous fault zone was revealed. Fault gouge mainly follows the fracturing-compressing grouting consolidation model, while fault breccia mainly follows penetration grouting consolidation model. Grouting consolidation was divided into two parts of direct consolidation and indirect consolidation. The former increased the strength on grout-rock interface, changed the failure pattern of the rock mass and prolonged the failure occurrence; indirect consolidation changed the inner stress field and its propagation path, and improved its mechanical properties.(4) The advantageous structural surface system of the fault fracture zone was deeply analyzed. The advantageous fracturing grouting concept was proposed. The fault fracture zone grouting diffusing model containing advantageous path was established. The advantageous fracturing grouting diffusing controlling equation considering the time-varying viscosity of the general Bingham slurry was constructed. The consolidation scope is synthetically determined by grouting pressure po, grouting velocity q, grouting viscosity pi and occurrence of the advantageous structural surface (α、b)and other factors, the first three of which are main factors. The heterogeneous fault rock grouting consolidation mechanism involves four aspects of weak band fracturing (penetrating or filling), homogeneous rock compressing, grout-rock coordination and coupling and compound grouting.(5) A three dimensional simulation experiment system on adverse geological body grouting consolidation under complicated geological conditions was established, and then consolidation simulation test on post-disaster rescuing grouting consolidation and advancing grouting consolidation in aquiferous fault fracture zone was conducted. During grouting, the reacting space-time characteristics of the model rock physical field was controlled by a combination of the relative position of the monitoring point-grouting point and grouting advantageous diffusing path. Comparing with normal surrounding rock, the stability of the grouting consolidation rock is relatively lower, and the border area of the surrounding rock-disturbing loose fracture consolidation zone generated a grouting weak band with advantageous penetrating path. On condition of h<3ho, inner damage of the grouting consolidation body gradually accumulated, causing a generally stability of the consolidation body; after h>3h0, the quality of the surrounding degrades strikingly, thus forming pipe inrush path, leading to an integral instability.(6) Theory of compound controlling grouting consolidation and its design method was put forward. Research findings were testified by field test in grouting integrated treatment engineering for water and mud inrush disasters in F2fault fractured zone in Yonglian tunnel, Jilian express way, Jiangxi province, which has generated crucial technical system of composite-control grouting treatment for water and mud inrush disaster in aquiferous fault fractured zone, with a broad prospect of engineering application.