| Enshi Prefecture is located in the folded mountain area of southwestern Hubei Province,where karst landform is well developed,surface cutting is deep,and the mountain body is steep.Highways in Enshi Prefecture mostly adopt the form of half filling,Half Digging and deep cutting,thus forming a large number of high and steep rock slopes.Through collecting and analyzing a large number of domestic and foreign literature and engineering geological survey data in this area,it is found that most of them are for the study of hydropower engineering and mine slope,and the literature on the stability of high and steep rock slope of highway engineering is relatively few,and no relevant literature on the stability of high and steep rock slope of highway in the study area has been found.In the geological survey of slope stability research,more methods are still manual field investigation,but this method will be restricted by topography in the investigation of high and steep slope,and can not achieve a comprehensive understanding of the geological conditions in the study area.This paper takes the high and steep rock slope in section K2+050~450 of Honggao Line in Enshi City,Hubei Province as the research object.In this area,we innovatively use the method of combination of field investigation and UAV aerial photography modeling to survey and measure the slope in the study area.We also use the experience of predecessors to interpret the structural plane information,and thoroughly analyze the rock physical and mechanical properties,rock mass structural characteristics and rocks of the slope in the study area.Classification of mass and slope stability,and numerical analysis method is used to simulate slope excavation according to different slope ratios,analyze the characteristics of stress-strain field and predict the stability of slope after excavation,which provides design basis for the engineering projects relied on in this paper,and also fills in the blank of research on the stability of high and steep rock slope of highway in this area,and provides reference for related projects in the future.This paper mainly achieves the following research results:1.Geological survey and measurement of the slope in the study area are carried out by means of combination of manual field investigation and UAV aerial photography modeling.The study area belongs to the deep valley-cliff landform.There are no faults,folds and other structures in the area.The occurrence of the strata is nearly horizontal inclined.The lithology of the strata revealed is mainly the light-gray-white mediumthick layer to massive limestone of the Carboniferous Huanglong Formation and the thick-gray-black carbonaceous limestone of the Qixia Formation of the Lower Permian.2.According to the analysis of the results of field investigation and threedimensional model information interpretation of UAV,it can be seen that the slope in the study area does not develop grade I and II structural planes.There are a group of grade III structural planes: 315°?11°,and two groups of grade IV structural planes:(1)12°?85°?(2)160°?80°,and four groups of grade V structural planes:(1)35°?76°?(2)120°?74°?(3)215°?65°?(4)70°?79°?Through comparative analysis,it can be seen that the difference between the measured values of inclination and the interpretation results of UAV aerial photography is generally less than 5°,and only a few values are larger.It can be concluded that the interpretation results are basically consistent with the field measured values.3.The structure types of slope rock mass in the study area are monolithic block structure,block structure and layered reverse structure.In the slightly inclined slope of the slope rock layer,and the weak layer is not developed,the sliding deformation of the slope rock mass has no motive force and bending deformation has no space,so there is no sign of overall deformation and failure;the local steep dip structural plane produces bending-tension crack deformation,and the local mid-dip structural plane causes sliding deformation.The main failure types of slope rock mass are wedge failure and toppling failure caused by combination of local structural planes.The factors affecting slope stability mainly include rock type and weathering degree,rock mass structure characteristics,hydrogeological conditions and human engineering activities.4.The rock mass quality of the slope in the study area is classified by various methods of rock mass quality classification.Finally,considering the characteristics of rock mass structure and deformation and failure modes of the slope in the study area,the classification results are synthetically evaluated,and the results suitable for rock mass quality classification in the study area are obtained.According to the classification results,the rock mass quality grade of the slope in the study area is closely related to the slope height and the type of rock mass structure: the rock mass structure of the slope below 30 m is monolithic block structure,and the rock mass quality is type II;the rock mass structure of the slope between 30 m and 90 m is mainly layered reverse structure and block structure,and the rock mass quality is mainly type III and IV.5.According to the research results of Engineering zoning,the overall stability of the slope in the study area is qualitatively evaluated.It can be seen that the slope in areas I and IV is basically stable,and the rock mass structure of the slope is the main controlling factor;the slope in areas II and III is not stable,and the rock mass quality of the slope is the main controlling factor.6.Six semi-deterministic blocks were found in the study area,mainly concentrated in the middle and lower parts of K2+050~ 270 section,with fewer upper parts.The main failure modes are single-sided and double-sided sliding.According to the block theory analysis method,the stability of blocks is calculated.The results show that the stability coefficients of these blocks are mostly about 1.05,and the stability coefficients of individual blocks are around 1.15.This indicates that most blocks are basically stable to under-stable,and the stability of blocks is poor.7.Flac3D numerical analysis software is used to select typical sections to simulate excavation according to the slope ratio of 1:0.2 and 1:0.3 respectively.The results show that stress concentration occurs at the foot of slope and the inner side of the first and second excavation platforms at the lower part of slope after excavation,resulting in the maximum shear strain increment.Comparing the two schemes,it can be seen that the stress generated by excavation of slope under the 2 # scheme is lower than that under the 1 # scheme,but it decreases.The increment of displacement and shear strain is larger than that of scheme 1 #,and the range of maximum increment of shear strain is enlarged.According to the displacement curve of monitoring points,the displacement of rock mass in the middle of slope after excavation is the largest,and the displacement after excavation according to the 2 # scheme is obviously larger than that of the 1 # scheme.The comprehensive analysis shows that the displacement variation of the slope after excavation is small as a whole,and there is no possibility of overall instability.Only the foot of the slope and the first and second excavation platforms at the lower part of the slope may produce local deformation,and the stability of the slope after excavation according to the 1 # scheme is better than that of the 2 # scheme. |
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