| Slope engineering problems play an important role in roadway construction, which, if not correctly dealt, would result in the increase of construction time and expense, and affect on the safety during construction. Two deficiencies existing in the current study on slope engineering are: (1) there is lack of recognition of the occurrence geological environment of slope, (2) researches on the failure modes of various types of slope haven't go far enough. Supported by the research project of Jilin communications department—'Research on failure type and prevention-control method of highway slope in southeastern mountain area of Jilin province', this paper conducts in-depth study on the geological environment of Jilin province and analyzes the failure mechanism and analysis method of stability of various types of slope.Generally, the terrain of Jilin province is high in southeastern and low in northwestern, with the new Cathaysian System and Cathaysian System Formation which control the landform features, among which Changbai Mountain area in the southeastern mainly, controlled by northeast-southwest mountains, presents apparent basin-mountain landform with basin and mountain alternating distribution. Middle and low mountains are dominant in the southeastern, with wide distribution of volcanoes, karst and platform, there are lots of hills in the western, with extensive river valleys and plain, the overall terrain of Song-Liao plain is high in eastern and low in west, with relatively rugged platform in eastern and extensive alluvial plain and large-area dune.Stratigraphic regionalization is based on strata age, lithologic features, sedimentary thickness and contact relationship, so that the strata of Jilin province could divide into four subareas which are Liaodong, Jilin-Yanbian, Song-Liao plain and Xing'an. Thereinto, Liaodong subarea includes Hunjiang district, Jilin-Yanbian subarea includes Jilin district and Yanbian district, Song-Liao plain subarea includes Nong'an district and Changling district, Xing'an subarea includes Baicheng district. Liaodong subarea belongs to north China stratigraphic region and the other three subareas belong to Tianshan-Xing'an stratigraphic region. Magmatic rock is widely distributed in Jilin province, much more in the eastern, with the formation of a complex rock type made by plutonic intrusive rocks, hypabyssal intrusive rocks and extrusive rock. Acid rock is the most widely distributed, such as granite, and there are some distributions of basic rock and ultrabasic rock. Jilin province divides into two primary geotectonic structures of China-Korea metaplatform in the southern and Tianshan-Xing'an geosynclinal fold area, which are subdivided into three subareas, five secondary partitions and twelve third-level tectonic elements, according to different geological structure characteristics and development history.Based on the analysis of geological environment of southeastern mountain area in Jilin province, the failure mechanism and stability calculation are carried out for four types of slopes, low dip angle consequent rock slope, namely low dip angle consequent rock slope, anti dip layered rock slope, block-fracture slope and fragmental structural collapse.For low dip angle consequent rock slope, some studies have been done as followings:(1) Both internal and external causes affecting the stability of consequent slope are discussed, while internal causes include the geometrical characteristic of slope, formation lithology, strata inclination, and geological structure. The influence of structure plane on the slope stability is emphatically analyzed, which is classified into layered and non-layered structure planes, including different genetic and classification of layered structure planes, the thickness of filling materials, the filling factor, roughness and cementation degree. For external causes, earthquake, excavation unloading, groundwater have been discussed, among which groundwater has adverse effect on the slope stability with kinds of actions, such as erosion, dissolution, softening, physicochemical and mechanical effect, meanwhile, groundwater hydraulics model for slope has been built. At last, analyses inter restricted and connected relationship of various causes affecting the stability of consequent slope and obtain some useful conclusions.(2)Study the typical geological condition of slope, and then analysis the failure mechanism of low dip angle consequent slope, the failure modes of which can be divided into four stages, namely unloading rebound stage, pressure-induced tension crack extending stage, fracture plane cutting through stage and sliding-pressure-induced tension crack stage. Generally, the failure mechanism of this type of slope can be summarized that sliding plane creeping results in the strength of rock mass reduced and the joints, micro fissures increased and the permeating path of rain enlarged, and then the deformation of slope increases because of the decreased strength of structure plane and reduced friction. Therefore, for the formation of sliding plane of low dip angle consequent rock slope, weak structure plane is the internal cause while the precipitate water is the external cause.(3)Using the methods of SARMA and JANBU, calculate the stability coefficient of typical slope under the conditions of drainage ratio being 0, 20%, 50%, 80% and 100%, obtain the stability coefficient of linear-circular potential sliding plane, and analysis the location of the potential sliding plane. Then make the conclusion that the stability coefficient decreases first and then increases as the distance between the trailing edge of structure plane and the toe of slope.(4)Considering the importance of precipitate water to the stability of slope, build a two-level fuzzy comprehensive assessment model of the influence of precipitate water on the stability of slope under the condition of different weight. Adopt different forms to determine the membership degree for the influencing factors of both discrete and continuous types. Do the fuzzy evaluation after correcting the weight of various factors under pre and post precipitate water, and determine the stable state of slope according to maximum membership degree law. By the comparison of the traditional limit equilibrium method and fuzzy comprehensive assessment method, the results are in agreement.Based on the investigation of the engineering geological condition, analyze the failure process of anti dip layered rock slope, which is made of three stages, namely plate girder bending, tension crack surface extending and moving, and overall breaking. As to study the failure mechanism of slope, generalize the blocks of anti dip slope into cantilever beams under dead weight moment and force, study the failure mode by the bending-tension model, build mechanical model of plate girder for anti dip layered rock slope, calculate the resultant moment on each plate girder, and then gain the tension stress on the side of the plate girder. Based on the maximum tension stress theory, give the instability criterion of block toppling to judge the stability of slope. Quantitative analysis of each influencing factor has been done to obtain the relationship of toppling failure of anti dip slope and the shape of each plate girder, including the height, width, inclination of the bottom surface and rock weight, and the conclusions are: there exist inverse proportions between the stability coefficient of slope and rock weight, 2-th power relationship between the stability coefficient of slope and the height of plate girder, proportional relation between the stability coefficient of slope and the width of plate girder, the toppling failure would happen when the inclination of bottom surface is in a certain range relevant to the height and width of the block. Supported by the typical toppling slope of Jilin belt highway, calculate the stability of each block and result in agreement with actual situation.Taking Ji'an-Gumaling cutting slope for example, study the stability of block-fracture slope. The slope in research area is located at Hunjiang district of Liaodong subarea and belongs to China-Korea metaplatform and Tianshan-Xing'an geosynclinal fold area. There are outcrop of granite in early stage of Yanshan and violet red siltitestone with gultenite inclusion in Heiwaizi group of cretaceous period. Controlled by Ji'an-Songjiang fault, the magmatite in research area is granitoid inrusion. For the block-fracture slope, there exists apparent potential sliding plane underlying, weathered and crushed block overlying, and more joints and fractures. Adopt limit equilibrium method to calculate the stability of two typical slope under different drainage ratio, and draw the two conclusions: (1) the stability coefficient of slope during K6+646 segment is 1.03 under the condition of no water, (2) the slope during K7+606 segment is stable whether there is underground water or not. Based above works, adopt gray relational analysis method, select the two calculated slopes as mother sequence and 8 slopes to be studied as subsequence to carry out gray relational analysis. The results show that No. 16 and No. 18 slopes, similar as No. 4 and No.8, are stable, while other six slopes are unstable, which are well agreed with the situation on site.As for the study of fragmental structural collapse, make induction and summarization of the characteristics of various structures in the rock slope, including primary structure plane and secondary structure plane, classify the collapse into toppling collapse, sliding collapse, bulging collapse, pulling collapse and faulted collapse, and give each type a stability calculating formula for unstable rock. Combined with slope engineering of Ji'an-Gumaling highway, make the statistic of the situation of fractures and physico-mechanics parameters of rock, and then analysis the mechanism of collapse, with the calculation of stability. The conclusion shows that the dangerous rock is unstable under the action of underground water or earthquake. On the other hand, build rapid evaluation index system for dangerous rock stability and obtain the value of each parameter to evaluate the stability of unstable rock. The results are consistent with those calculated by theory formula.In conclusion, this paper conducts in-depth study on the geological environment of Jilin province and analyzes of the failure mechanism and analysis method of stability of various types of slope, which is of great significance to the similar project construction in Jilin province.The main innovative points of paper:1,This paper is strating with the geological environment of Jilin Province in southeastern mountain. The stratum structure of Jilin Province ,tectonic divisions, the distribution and scale of the important folds and fractures, the formation age and intrusive condition of rocks like magmatic rock, the types and distribution of the underground water have been deeply understanded. Form over various points to research the geological environment of every typical slope, it is seldom on the domestic slope engineering research to combine geology with the slope failure mechanism and stability analysis .2,In the study of the sustained angle maleic layer rock slope, it is systemic induced and summarized the factors which affect the stability of slope. It uses the method of secondary fuzzy comprehensive evaluation and the traditional limit equilibrium method to calculate the stability of bedding rock slope. Considering the signify effect of the soft maleic layer rock, the secondary fuzzy comprehensive evaluation is modified. Undering different weight conditions, the judging system of slope stability which is affected by rainfall is put forward. The slope stability grade is calculated by changing the weight conditions of different factors which are before and after rainfall. The calculations are agree well with the limit equilibrium method and actual situations.3,Each bands of the anti-dip layered of rock slope is simplified as cantilever beam which suffers the dead weight moment and exogenous process. Then researching the failure mechanism of anti-dip slope by establishing bent-fracture model. Mechanical model of each plate girders is built by using structural mechanics method. The stability of each plate girders is judged by using maximum normal stress theory. On this basis, the quantitative relationship between the stability of plate girder and the factors such as the height, width, dip angle and bulk density are analysed.4,For the split-block structure of rock slope, the current study is still based mainly on the limit equilibrium method. It calculates two typical slope stability by using this method. Then calculated the other slopes which have the similar geological conditions by using the gray relational analysis method. Selected two calclated slope and other similar slopes as the parent sequence and the other eight slopes as the subsequence carry out gray relational analysis. The calculated results coincide well with the actual situations.5,Combined with the collapse example of Jian-gumaling highway slope and on the basis of counting the main factors which are influence the stability of the dangerous rock body, the rapid-evaluation index system and the quantitative taken values of evaluation index are established by using interaction relation matrix method .Then establishing the calculation method of dangerous rock unstable index and stable degree grade of the dangerous rock to judge the stability of the collapse dangerous rock.
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