| Malan loess is a kind of soil which is widespread around the northwest area of China with the total area of 640000 km2. The physical and mechanical property of the provinces has caused water and soil loss, landslide and some other geological disasters which have different degrees of influence on human production and construction. It involves mine engineering, hydraulic and hydro-power engineering, road and bridge engineering, railway engineering and many other fields, with the implementation of the western development strategy, the project construction scale and difficulty of the northwest of China which are covered by loess are increasing year by year and the research for the physical and mechanical property of loess and the engineering geological condition of the northwestern loess plateau is also developing year by year. Hequ County is located at the east edge of the northwestern loess plateau which is bordered by the Yellow River in the west and Shanxi and Inner Mongolia are at its opposite across the River. It is the economic and cultural city which is located at the neighboring region of Shanxi, Shanxi and Inner Mongolia. And in recent years, the water power resources, mineral resources, power development and some other newly developed industry have been developed based on above factors. Through several decades’constant human engineering activities and the increasingly heavy water and soil loss of the loess plateau, the geological condition of the mineral engineering in Hequ is increasingly deteriorating. Under the rainfall, human activities and some other conditions, the frequency of landslide, collapse and some other geological disasters increase year by year. Because the main mining method of Hequ is the strip mining, many high loess slopes are formed in stope slopes of many mining areas. With the deepening of mining depth and the improvement of the mining technology, the slope mining design, stability checking calculation and the later regulation of the mines have become the problems that need to be solved. The engineering geological research of the mine loess high slopes in Hequ will effectively solve the stability problems of the stope slope in mining areas, guarantee the safe production of the mining in mining areas and effectively promote the address of the geological environmental treatment recovery in Hequ and areas which are similar with the northwest loess slope mines.Aiming at the unsaturated physical property of the soil of Malan loess slope and the corresponding high slope stability research, this paper takes the typical mining slope in Hequ, Shanxi as the research material. It researches the micro influence of the matric suction and the moisture content on loess particle through the laboratory test and the laboratory model test, obtains the fitting formula of the volumetric water content and the intensity index, makes some reliability analysis of the stability of the unsaturated Malan loess slope, discusses the failure probability of high slopes under different rainfall conditions and makes some comments on the safety and reliability of the engineering. It establishes the numerical simulation combining the laboratory model test and the FEFLOW finite element software, studies the saturation process, rainfall infiltration depth and the slope damage process of Malan loess slopes under the rainfall condition, develops numerical model appropriate for the real engineering conditions, puts forward the stability evaluation methods of unsaturated Malan loess slope based on the laboratory physical model test results, and then gives the stability status of slopes in different working conditions and the reasonable treatment suggestions. The main research contents and achievements of this thesis are as follows:1.Through the material collection and the field investigation, this paper illustrates the physiographic condition, formation lithology, landform, geological structure and some other regional engineering geologic features of Liang Jiaqi mines in Hequ County and the damage features of Malan loess high slopes. Malan loess fracture at the inner slope of the mines is more developed, most slopes in mining areas are high and steep due to long-term coal mining, and the hand excavation, rainfall and other external forces often lead to labile factors existing in slopes. According to the site investigation, the deformation and damage of the regional Malan loess high slopes are mainly reflected on partial collapses. The steep slope angle, developed joint fissure, rainfall erosion and excavation slope surface of Malan loess slope in mines have damaged the slope angle, which are the main internal factors for the partial damage of slopes. The mine excavation and rainfall in the mining areas are the leading induction factors for the partial collapse of slopes. Influenced by the excavation unloading and rainfall, the slope soil unloads along the loess joint fissure in the air direction and will be partially damaged at the root of the slope, so it is easy to cause landslide under the induction of the rainfall and earthquake.2.1n order to study the internal influencing factors of the stability of Malan loess high-slope, it will emphatically study from the macro-angle on the relationship of the slope stability and the moisture content and matrix suction. Based on the above research thinking, we have collected the sample of Malan loess and made 4 sets of remodeling samples according to the different dry densities of the soil sample. We stimulated the matrix suction data of samples under the dehumidification condition according to the V-G model, and then made the SWCC. It will also discuss the corresponding slope height suction variation curves of different dry densities, compute and stimulate the permeability coefficient of unsaturated Malan loess under the dehumidification condition according to the V-G model of the statistics.3.In order tocouple the previous testing results into the stability analysis better, we have analyzed the instability condition influenced by the rainfall, slope height and slope ratio of Malan loess high-slope, established slope models in different rainfall and slope conditions using test cell and rainfall equipment. Three levels of slopes for 45°,60° and 70° have been designed according to engineering experience and related references, the slope range is designed as 45cm,60cm and 70cm, and the landslide model has been built with 1:100 of model similarity proportion and 12% of the natural moisture content. According to the level of the heavy rain and intense rain, the rainfall intensity has been arranged as 60mm,90mm and 120mm. In order to directly reflect the influence of the rainfall on the internal pore water pressure and moisture ratio of slopes, we have collected the pore water pressure meter and moisture meter installed in the slope root, top, center and the internal slope which are piled by human, observed the pore water pressure and the slope moisture ratio variation in different working conditions by connecting data collection system. We also observe the slope deformation and damage status through the gridding of the experiment tank, HD camera, camera and other equipment. We analyze the factor variance by designing the slope damage condition of the orthogonal test on different working conditions and using software spss. The result has shown that the influence degrees of the three influence factors of the slope ratio, rainfall and slope height on the stability are in the following order:rainfall intensity> gradient>slope height. Therefore, in actual engineering, the larger rainfall intensity, higher slope height and steeper slope surface will greatly increase the landslide frequency of unsaturated Malan loess high-slope.4.1n order to show the interaction of all parameters and test the correctness of the model, we will introduce the model test results and laboratory physical test results into FEFLOW for simulation observation, build the seepage flow field model of slope in order to observe the variation of the pore water press and moisture ratio for the internal slope under the rainfall condition. It is calculated by one day’s time step and for the total of 5 days, and it is found that there is a transient saturation belt on the surface of the soil under the rainfall and it is more difficult for slope rainfall saturation line to further influence the overlying soil under the influence of the saturation belt. The saturation belt caused by the slope root will influence the overall stability.5.This paper summarized the research methods of the saturated and unsaturated soil slope stability in domestic and international, and makes stability checking and calculation design of unsaturated Malan loess high-slope in mining areas on rainfall condition, and puts forward related suggestions after testing the slope optimal plan. The slope geometry parameter design value for 1040m of the eastern sea level elevation should be:the unit slope height is 10m, the slope angle is 55° and the stair width adopts 6m and 10m interval arrangements according to related specifications which will achieve good stability effect. |
