Study Of The Stability And Anti Seepage Reinforcement Of Abandoned Mine Landfill Slopes

With the increasing of the waste production,the number of landfills increases year by year, and the area that can be used for the construction of landfill sites are decreasing, The sites of landfill become more and more difficult to find. And this has become an important restriction factor of sustainable development of landfill. The use of abandoned mines for solid waste landfill treatment, can be a comprehensive solution of the security problems both the difficulty of finding the large area of landfill sites, and also the ecological and secure disposal of abandoned mine. So it's an effective way of locating the solid waste sanitary landfill site. One of the key scientific issues of abandoned mine landfill is the stability and anti seepage of the high and steep slope. Landfill stability and anti seepage interacts to each other, slope failure is the damage of impervious system, and the leak point of anti seepage layer also affected the stability of the slope, the slope reinforcement and seepage control study should be as a whole. In this paper, based on the systematic analysis of abandoned mine slope stability factors, by the combination means of the indoor experiment, theoretical analysis and numerical simulation investigation, and intensively studied the stability and control technology of abandoned mines. The major achievement of this paper are as following:(1) Features and influence factors of the abandoned mine type landfill slope stability and anit seepage reinforcement are analysed in depth. By the systematic investigation of the landfill slope stability, The formulas of the multi-layer liner system slope stability calculation and shotcrete reinforced rock slope stability analysis applied the limit equilibrium theory are proposed.(2) Using the HDPE geomembrane of Landfill liner impervious system as a study object , through the monitoring data of a series of outdoor and indoor laboratory test, carried out the tests of the slope covered with a single and double layers liner under pressure load , studied the mechanical properties of the slope impervious liner system under varous conditions, the results show that:While stretching of the membrane, the early changes in the elastic stage, and late into the plastic phase. Bye the parallel tension, the membrane grows into a lesser extent intensity of the plastic stage; By the increasing of the load, the slope toe is the place where prone stress concentration, and where the geomembrane is not safe, and it is also found that the stress of the top of the hill is higher than the middle.(3) Through the study of composite cement impervious material, the relationship between the strength and impermeability of the cement under different conditions. The results show that:①the permeability coefficient of clay-cement grout, is closely related to the proportion of concrete and clay, the clay does more seepage resistance than the concrete, the firming agent can only enhance it's early strength, with the increaseing dose of firming agent its permeability coefficient decreases;②The effects of leachate seepage resistance depends on the time of infiltration lasted. With the extending of infiltration duration time, permeability coefficient of grout decreases to a particular value and became stable seepage;③The impermeability is also affected by the characteristic of leachate. The impermeability effects of the clay-cement grout vary with the different leachate reconstituent,according to the experiment : heavy metals> organic> distilled water;④Migration velocity of the leachate pollutants is constrained and limited by their own concentration. Above all, the higher concentration, the more apparent permeability coefficient decreased;⑤The effect of seepage resistance of Clay solidified grout affects by the value of the pH, heavy metal ions under acidic conditions, is prone of migration, alkaline environment is in favor of block pollutants migration.(4) Based on the Mohr-Coulomb strength failure criteria and limit equilibrium method the slope stability mathematical model of abandoned mine type landfill cement composite is established, and optimization Mathematical models of the inverse problem establishment of the seepage in the saturated-unsaturated soil of the abandoned mine type landfill site, and using gradient regularization method, the related parameters are inverse calculated, under different conditions (composite liner system, anchoring and grouting anchor overlay level) abandoned mines Landfill Site Slope stability is studied . Research results show that:①Using the gradient regularization method to inverse calculate the water migration parameter of unsaturated soil, obtained optimal values of the model parameters, and the inversion results have good agreement with the experimental results, indicating the feasibility of this method;②The maximum shear stress of the landfill heap distribute in the bottom layer (in contact with the geomembrane). Maximum shear strain in the slope near the surface of the geomembrane, but because of the presence of weak interlayer, it causes the stress of the heap transmisses in the out-ward direction. With the increasing altitude of landfill heap the stability is getting worse.③Through the calculation of mining type landfill slope stability under the conditions of bare, grouting, anchoring etc., proposed the feasibility of clay solidified grouting paving stage technology. provided technical support to the design and construction of mining type slope stability reinforement project.(5) Based on the experimental study and numerical calculation analysis, considering engineering geological conditions of the rock and soil of the mining slope, comprehensive analysis of bolt-grouting reinforcement technology, composite liner reinforcement and controllable clay grouting reinforcement and seepage resistance technology, abandoned mine type cement composite landfill slope stability and seepage control technology program is proposed.The results above can provide important decision support on design, construction and running of assessment and analysis of mining type landfill sites, and be important to theoretical and engineering applications.