| Nearly 30 years of engineering practice shows that dip slope and nearly vertical layered slopes often occur in dump deformation instability mode, and then evolved into deep landslide.Large and giant landslide often became the key problem in hydropower project construction and geological disaster prevention.For this kind of deformation instability mode is still lack of system,the condition of the dump slope deformation and instability is not very clear, and the dumping of instability criterion has not yet been established.Theory research base is located in Lixian,the northwest of Sichuan, which is of mountain valley area.On both sides ofriver lies amount of dumping and dumping body, which provide good conditions for carrying out theoretical research.Through the existing geological data collected in the study area and site engineering geological investigation, to find out slope shape characteristics of the slopebefore the slope deformation and instability, slope body structure characteristics, rock mass structure characteristics and dumping of deformation and failure characteristics, and preliminary slope geological prototype in the study area is established.Through the analysis of deformation and failure phenomena, the "conceptual model" of the dump slope instability can be established in the study area.On the basis of indoor rock physical and mechanical test results, combined with the feature of rock mass structure, rock mass quality evaluation in research area was finished.On this basis, to, in order to deepen the understanding of dump slope deformation instability mechanism, the bottom friction test and discrete element simulation methods respectively were chosen to verify the "conceptual model" of the deformation of slope instability analysis. The main understanding and the results were as follows:Xishan Village slope was aconvex slope, which has a steep slope toe, lower steep in the middle and upper slope, and had a flat. Above the altitude of 1800 m was the gentle slope, which average slope angle was 28-32 °. The steep section could be classified as extremely steep slope and gentle slope. Field survey and exploration shows that the height of steep slope section of the slope was between 330-360 m, which average slope angle was greater than 40 °. The steepest section was 70-80 °, elevation of 100-120 m.Xi Shan Village slope was a soft rock slope of layered structure. Phyllite, carbonaceous phyllite and a small amount of quartz and limestone constituted the body of the slope. Rock occurrence is N80-90 ° E/SE ?80-86 °. Rivers moves towards nearly east-west, in the left bank of which, concave bank side located the slope. There are four groups of structural joints. Schistosity plane in phyllite is developed, which layer thickness is for 3-5 cm, with thin layer of rock mass structure.Though field measurement and statistical analysis ofoccurrence of rock mass in different altitude,there is a significant difference in dumpingdirection and dumping degree in different areas of the landslide. The Fouth partition is divided from bottom to top. A zone is located in the position of slope toe, dumped outside the slope, with the dumping direction of S10-20°W. Trailing edge of B area is bounded by around 2300-2350 m above sea level, dumping to S50-60°W direction. C and D area are all dumping to N60°W direction similarly. Drilling data revealed that thedepth of the bottom of the landslide slip surface presents the regularity of "deep shallow- deep change." The right boundary in this part ofthe landslide is shear extrusion fracture zone, which shows that the landslide displacement at the direction and the right side of the border was to a larger angle intersection.According to the different characteristics in each partition of deformation and damage, combined with the engineering geological environment conditions of the geological prototype, the "conceptual model" of the slope deformation and instability is established.Xi Shan Village dump slope deformation and instability is the result of long-term evolution with special slope body structure characteristics. With rapid incised valley, stress concentration degree in slope foot position increases, and the maximum shear stress is formed within the slope belt. Controlled by the long-term strength of phyllite, rock mass around the maximum shear stress in slope foot came to the state of yielding first. Controlled by the slope shape, slope body structure and rock mass structure characteristics, a steep slope at the bottom bend first. With the increase of bending degree in rock mass of foot, rock mass weathering and unloading degree deepens, thus further weaken rock mass physical and mechanical properties, which had an effect on increasing deformation instability, eventually a crack in the root of bending strata occurred and strata was broken ultimately. With the increasing of the broken rock, fractured surface gradually become weak internal control surface in slope foot, slope deformation pattern has changed to slipping-cracking, which result from bending-cracking with development for a potential slip surface.Slope toe instability had an effect on the upper slopes with airport and unloading effect at the same time, accelerating deformation and instability of the upper slope.Through indoor conventional rock physical mechanics test, to observe deformation and damage properties of phyllite in load condition vertical and parallel schistosity plane. Experimental results showed that along the shear plane vertical the schistosity, rocks was made into powder; while parallel schistosity plane, failure surface is relatively smooth, the difference of deformation and strength properties of phyllite revealed the mechanical properties of phyllite are closely associated with schistosity plane orientation. Uniaxial test results showed that the destruction of phyllite mainly is suppressing-cracking mode, and the saturated uniaxial compressive strength is 54 Mpa, belonging to a more hard rock.Combined with the feature of rock mass structure in the study area, the number of joint volume for the JV is estimated for 30 to 44 / m3, which is of the broken rock mass. Rock mass integrity coefficient for Kvtakes 0.216. On the basis of “the engineering rock mass classification standard”,and “the specification for water resources and hydropower engineering geological investigation”, rock mass basic quality index BQ = 279, total score of surrounding rock T '= 41.64, determining rock mass in the study area is for ?, and strong weathered rock mass with ? level of rock mass, providing the basis for the parameter selection of rock mechanics.In order to further verify the analysis of deformation and instability mechanism, bottom friction test and discrete element calculation model is established based on the "conceptual model". Test shows that under the condition of the slope and slope structure, slope foot first bend, whose rear boundary for the first time was at an altitude of 1850-1900 m, and the depth of dumping developed 150-180 m.Slope deformation and instability in the steep slope had an effect of unloading and international airport, and was multi-level characteristics of slope deformation and instability.Quick incise of valleyleadto field stress distribution. The differentiation in slope toe was more obvious and forming a maximum shear stress area. Maximum principal stress level is 20 to 30 MPa, the minimum principal stress value is 0 to 5MPa in slope toe. The slope rock mass unloading rebound at the same time, and the springback of uneven caused shear dislocation along the steep rock slice plane and existing structure surface modification. From the point of view of the rock mass stress and strain in the slope rock mass mechanics environment conditions significantly worse, before and after the incised valley, becoming easy to deformation instabilityof the whole slope.With the increase of iterative computation times, the steep section bent first, and bending the dumping of instability scope is focused inthis section. With setting linemonitoringthe horizontal and vertical displacement, we can preliminarily determine the scope of the bending deformation of slope instability. Dump body developed depth levels between 120-180 m, line 4 in less developed depth, for 60-120 m. Dump body vertical depth development between 120-180 m, at line 5 and 6 to 60-120 m. Trailing edge is at an altitude of 1900 m or so.Through rock mass excavation simulation of the slope toe dump part instability, the airport and unloading effect placed by instability of the steep section on the upper slope deformation was verified.its scope of slope deformation is roughly below elevation 2150-2250 m, which shows that the slope deformation and instability mechanism in the study area was the steep section bent first, pulling the upper slope bend and come to instabilitystep by step. |
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