| There are many problematic landslides and prominent prevention problem of landslide disaster in Three Gorges Reservoir. The geological condition of Three Gorges Reservoir is very complicated. Considering of the political significance, strong economical effect, tremendous social benefits of the Three Gorges Project, the distribution, causes, deformation mechanism, evolution and other difficult issues of these landslides need to be studied in the future. So it is a pressing issue to scientific and effectively prevent and mitigate the landslides hazards in the normal operation of the Three Gorges Project.Three Gorges Reservoir has many typical bank landslides, and the Huangtupo landslide, the largest, most complex landslide in the this area, is a dangerous mass on which the district of Badong has been inadvertently situated. However, different departments, different units, experts and engineering and technical personnel had many differences in famous Huangtupo, such as slope’s scope of the loess, boundary conditions, formation, long-term stability, etc. Given this, In 2009, based on the Huangtupo landslide as the main body, China university of geosciences (wuhan) began to built the Badong Large-scale Integrated Field Testing Ground (BIFTG) which is a integration platform for landslide disaster teaching, scientific research and production, the BIFTG’s excavation of tunnel group was the fully revealed to the Riverside Slump I#,, since the exploration study on Huangtupo landslide which provided favorable conditions to directly and deeply research the Huangtupo landslide.In this thesis, the Huangtupo landslide’s Controversial Issues had been researched. Based on the extensive collection of regional geological data, the deformation monitoring data and the groundwater monitoring data and depended on the (BIFTG), the methods of Field investigation, laboratory test, theoretical study and numerical simulation had been used in researching the many-times genesis mechanism and evolution laws of Huangtupo landslide. And there are the results as follows:(1) The research of Huangtupo landslide’s geological structural features.Through the detailed ground investigation, the analysis of early stage drilling data, the judgement of Monitoring data, the test tunnel method and the discriminant criterion of landslide, the plane range of the Riverside Slump I#, Riverside Slump II#, Substation Landslide and Garden Spot Landslide of Huangtopu slope landslide system had been determined accurately. And Huangtupo landslide’s weak interlaye and slip zone’s distribution had been identified which turned out that the Riverside Slump I#’s weak intercalation was the most development. Besides, based on the excavation of test revealed tunnel, the typical weak interlayers and the shear rupture zone s were found for 12, and there had found main slip zone in mian cave, branch tunnel BR-3 and branch tunnel BR-5 as well as shearing action discriminant mark in many places. This illustrates Riverside Slump I# had experienced many times change which was decided by badong group lithology characteristics of hard and soft. Through analysing the main cave, branch tunnel BR-3 and branch runnel BR-5’s slide zone and space morphology of rock, we can find the slide zone of main cave had the same occurrence with the branch tunnel BR-5. because it was better to stretch On the rock and the two exposing points had a same occurrence, the main cave and branch tunnel BR-5’s exposing was speculated belong to a slide zone. However, the slide zone which was exposed by the branch tunnel BR-3 had a farther distance and different occurrence with the others. Through analyzing their spatial relationship, the slide zone which was exposed by the branch tunnel BR-3 is not belong to the slide zone exposed by main cave and branch tunnel BR-5. that is to say, Riverside Slump I# consisted of two independent landslides which overturned the previous knowledge. Based on the statistical analysis of the measured data and the discussion of landslide fractures’s development rules, we can find the fractures’s development rules of the Riverside Slump I# had some relationship with background deformation characteristic of the tracks. Overall, the fractures’s development rules in slide bed was the most close to the background value. Even though the slide zone and slide body inherited parts of deformation characteristics of zone background, it generated a lot of new deformation which added to the trace of background deformation and led to distribution of optimal fractures’order and percent and formed the new deformation that contained the landslide’s characteristics. Base on this analysis, a contrast method about landslide’s deformation trace and zone background deformation trace was built.(2) The research of Huangtupo landslides multi period origin mechanism. In consideration of the special factors such as the complexity of the geological structure and Particularity location of huangtupo landslides, Therefore, first research the region (Yangtze River Three Gorges area), then Section (Badong section),and finally focused monomer (loess Iandslide).First research the Huangtupo landslide multi period sliding geological background, discovered that in Quaternary period Three Gorges area was dominated by tectonic uplift with short-term stability, different river has slightly different incision rate.After the operation of The Yangtze River, The strong effect of hydrodynamic made Three Gorges of the Yangtze River cross slope memrged a series of changes in physical and chemistry, Its evolution process can be summarized as follows: slope strong unloading-looseing-Cracking-rotating-mudding-collapsing-landslide-Terrace overlap-forming a compound accumulation body;The Three Gorges of the Yangtze River in Badong section of the reservoir bank slope system was formed in the background of the Yangtze River operation and rapid cutting, analysis from the aspect of material composition, these landslides were developed in the Middle Three Triassic Badong formation second, three lithology; Analysis from the aspect of material structure, The landslide material structure was Layered vertically and plane zoning. The slip surface generally generated in the contact of weak zone and rock soil surface. Carried out the chronology research of Huangtupo landslide multi period sliding, besed on U series dating method, analysis the age of Huangtupo landslide Slip zone at different positions. The results showed that:Riverside Slump I# exposed in the main hole and No.5 branch tunnel and Riverside Slump II# belt exposed in the TP4 adit was closed in The formation time of calcite veins.Ten Million years ago, confirmed that the slide belt in the main hole and No.3 branch tunnel was the same, and had the coordination deformation rules; the formation time of calcite veins in Riverside Slump I# and BR-3 branch tunnel slide belt was new, closed to two Million years, present the characteristics of different periods, evidenced the speculation that Riverside Slump II# was composed of 2 independent sub landslide.Combining the Huangtupo landslide dating data, reverted the historical fact of Huangtupo riverside slumping mass multi period sliding, The riverside slumping mass was experienced 5 times the mass of the slide,were formed(40-38)×104 as (31-30)×104 a, (22-18)×104 a、10×104a、5×104a ago; Substation landslide occurred later than riverside slumping mass, was formed (19-13)×104 a in late Middle Pleistocene. Horticultural field landslide occurred after the substation landslide, was formed in (13-11)×104 a. After compared the formation time with the Yangtze River Three Gorges region other ancient landslide, found that the Huangtupo landslide’s sliding cycle was coincided with temporal regularity of ancient landslide in Three Gorges Area, this illustrates the Huangtupo landslide formation reason was not only influenced by its own characteristics,but also controlled by regional geological environmental factors as other ancient landslide.These ancient landslide appeared into batches concurrency rules because of these factors control. The influence factors of Huangtupo landslide multi period sliding can be divided into two categories, the first one was the internal factors, including the lithology, joint fissure (structural plane and slope structure); The second one was the external factor, including the crustal uplift/Yangtze river incision, fracture tectonic (earthquake) and ancient climate, Research showed that there is good correlation between Huangtupo landslide multi period sliding and external factors. On this basis, the formation mechanism of Huangtupo landslide multi period sliding can be summarized as fllow:Slope development stage, unloading creep stage, landslide, landslide stage overlap stage, gravity loading creep phase and the transformation stage.(3) Experimental study on mesoscopic characteristics and physical mechanical properties of rock and soil of Huangtupo Landslide. As rock and soil of Huangtupo landslide for the study, carried out petrographic analysis, water chemistry analysis, X-ray diffraction analysis and geotechnical parametric analysis, etc., revealing mesoscopic characteristics and physical mechanical properties of Huangtupo Landslide’s rock and soil. Lithology analysis showed that the lithology of BR-3 adit and BR-5 adit inside the Riverside Slumping I# is mainly to Micrite, microcrystalline, rose quartz and fine-grained limestone,marl,It can be inferred that Badong carbonate are deposited in shallow marine carbonate platform type under arid climatic conditions in tidal flat-lagoon or sea phase transition phase. Nearing the slip zone, shear fault zone (weak interlayer), calcite veins the number of Calcite veins in sheet rock increased significantly, it is indicated that in the breeding process of landslide, it would produce a series of macro, micro outlook fissures near the sliding zone, shear fault zone,under the action of Groundwater seepage, some macro, micro cracks is filling with calcite veins, forming a current form, so we can consider this law as a auxiliary identification method of slide zone and shear zone. Water chemical analysis showed that the surface water, groundwater, rainwater has different ion composition and relative content are different, for groundwater, the intensity of reaction is different between different ions and water-rock interactions of landslide of rock and soil; Also found there is significant hydraulic connection between groundwater and surface water, when the top of the landslide rained, it will occur phenomenon of flow rate increasing at the seepage points of the test tunnel, but there is a significant lag effect, indicating that between the rainfall and the underground water inside landslide exists supply relationship, but rainwater happened chemical action with rock and soil after it infiltration into the landslide, resulting in changes in water quality, also a larger change of ion concentrations. X-ray diffraction analysis showed that the mineral of slip zone soil of Huangtupo landslide is mainly to Clay minerals, content of about 40%, which in turn made the clay mineral montmorillonite, illite and chlorite minerals such as hydrophilic, reflect the slippery slope soil of Huangtupo landslides have hydrophilic properties and water swelling softening properties. It were carried out Rock mechanics tests with the soil and rock mixed with soil slip compaction test, compression test, triaxial shear test, triaxial rheological test, and has been related to the physical and mechanical parameters.(4) The research is about seepage field of Huangtupo slope under the impact of reservoir level fluctuation and rainfall. The analytical model of bank slope seepage line was derived and established based on partial linearization simplified method of water level fluctuation and rainfall, further to propose the correction model considering slope gradient. It was the seepage field analysis of the Huangtupo slope under the reservoir level fluctuation and rainfall by the means of module SEEP/W in Geo-Studio.According to the four conditions about initial steady state, rainfall, reservoir level fluctuation and the joint action of the two, it seted and analysised eight working conditions.The results showed:under the condition of rapidly rising water, landslide front about within 300 m of the saturation line change is bigger, frontal saturation line inside the outgoing slope for bending, the more powerful and the higher the water line of the bend, forming high backwater, it showed that with the rise of water level, water recharged to the landslide, the slide body seepage line rised obvious hysteresis, so the connection of water and landslide was not so closely. Under the condition of water levels fall, the change of frontal saturation line was large and trailing saturation line was small, frontal saturation line with water falls and convex to the water, the drop of underground water level process existed hysteresis, then produced the head, thus forming a slope to the slope in vitro penetration in the body. Under the condition of rainfall, the regularity of landslide surface in different rainfall types was different, when the type for a few days small rain,flooding effect was on the landslide surface, the matrix suction was reduced, the early rain damping matrix suction was larger, with the end of the rainfall process, the matrix suction was stable gradually, by the contrast of pore water pressure distribution at the back and front of landslide, it could be seen at the back of the landslide the matrix suction was bigger, during the rainfall, the matrix suction at the back of the landslide was extremely significant, close to saturation, due to the easily affected by reservoir water,the matrix suction of landslide leading edge was small, the rain was also easier via the boundaries of the reservoir water overflow when it was raining, therefore dissipated quickly, and pore water pressure curve showed local bending or sharp corners, its reason related to the thickness of the landslide and slope shape; When the rain type for short-time rainstorm, landslide trailing edge formed the transient saturated zone, with the end of the rainfall process, saturated zone began to decrease, the matrix suction of landslide front and centra droped obviously, already becoming saturated, it showed the effects of short-term rainstorm of landslide surface was greater than the light rain days, after rainfall and the pore water pressure of the landslide surface responsed immediately by monitoring, and with the increase of depth, monitoring of pore water pressure changed with the delay of startup time, this reflected the rainfall lagging phenomenon, the reason was that it taked time to rainfall infiltration, the landslide rock mass permeability materials was not ideal,the lag phenomenon also existed in the body, when the rainfall had effected after a period of time, the landslide body of saturation line began to rise, this was the actual situation. Under the joint action of drop of water and rainfall, with declining water level, and the change of landslide frontal saturation line was bigger, trailing saturation line range was small, frontal saturation line with water failed with convex to the water, the drop of underground water level existed hysteresis, produced the head, thus forming a slope to the slope in vitro penetration inside body, because of rainfall recharged, seepage line speed slowed down; When long rain had effected, saturation line found some uplift, the landslide surface matrix suction has generally been declining, after the long time rain, landslide pore water pressure began to dissipate, but the process was slow, and 180 days, dissipate continued,it showed long rain has long-term adverse effects on landslide; When it was short-term rainstorm, it would cause the transient saturated zone of landslide surface, although the rain lasted shorter, only for 3 days, then caused the landslide surface matrix suction dropped speedly, after the heavy rain, the transient saturated zone began to decrease, but has been to 122 days, the transient saturated zone to disappear entirely, it showed that short-time storm rainfall was larger, more than the infiltration capacity of landslide surface; Through the study of pore water pressure curve of the landslide on the same vertical direction at different depth of monitoring points under the joint action of water level and rainfall, it found that when water level and rainfall effected at the same time, pore water pressure of the landslide surface monitoring immediate responsed, and with the increase of depth, monitoring of pore water pressure changed the delay of the startup time, reflected certain hysteresis, it also existed in the body, as a result of rainfall, the landslide body of saturation line damped slowly, rainfall had slowed the trend of Saturation line downward due to the slope seepage of groundwater. By comparing the numerical simulation and the measured results of the seepage field, it found that the two results was basically identical,supported each other and revealed the seepage dynamic rule of Huangtopo slope under the joint action of the reservoir level fluctuation and rainfall comprehensively.(5) Research on deformation evolution law and stability of Huangtupo landslide. Deep analysis about deformation evolution law and stability state of Huangtupo landslide. Firstly on the basis of landslide’s deformation monitoring,the surface deformation law and deep deformation law of Huangtupo landslide were researched. Then based on numerical simulation method, Huangtupo landslide’s deformation law and stability characteristics under self-weight stress and under rainfall and reservoir water fluctuation were investigated. Deformation monitoring data showed that Riverside Slump Ⅰ#’s annual average rate of surface deformation had apparent zoning (i.e.,the front>the middle>the lateral edge>the posterior edge). There was deep displacement in this zone. Most amount of deformation were located around main slide belt. A small amount of sliding deformation were located around secondary slip belt too. The displacement rate around main slide belt was generally faster than the displacement rate around secondary slip belt. A small amount of sliding deformation were located around secondary slip belt too. The displacement rate around main slide belt was generally faster than the displacement rate around secondary slip belt. Both the surface and deep of Riverside Slump Ⅱ# had some deformation and these displacement rate were roughly equal. But totally, Riverside Slump Ⅱ#’s the accumulating displacement of the surface and deep were less than the Riverside Slump Ⅰ#.The accumulating displacement of Biandianzhan landslide was litte and it was basically stable.There was no obvious signs of acceleration displacement of Biandianzhan landslide recently. Yuanyichang landslide was basically stable for now and its accumulating displacement was not big. Under rainfall and reservoir water level fluctuation, the numerical simulation results show some characteristics as follows:the deformation of rock and soil of Huangtupo landslide has different intense degree in different parts and depth with reservoir water level fluctuation and displays apparent zoning in various location. Even if the same monitoring profiles with different depth position were different deformation and existence mutation slip, which reflects the influence of the weak inter layer sliding slip. For the rainfall condition, the change of stress field, displacement field caused by short term rainstorm is larger than by several days of light rain.When the rainfall is finished, the stress-field and displacement-field is still in the adjustment with hysteresis effect. In under the action of rainfall, sliding zone appeared the stress and displacement concentration phenomenon caused by deformation and displacement in the slide zone, which indicates the similar to formation mechanism of landslide induced rainfall. The superposition effect has reflected by the stress-field and displacement-field under rainfall and reservoir water level fluctuation, which was larger than only under conditions of reservoir water level fluctuation.Huangtupo landslide is basic stability-stable state, the stability coefficient of shallow surface located in the front of Riverside Slump Ⅰ# was high, that of deep sliding surface was slightly lower, the stability coefficient of some working conditions close to 1; Compared with Riverside Slump Ⅰ#, Yuanyichang landslide stability is higher, the stability control is basically not controlled by the reservoir water level fluctuation, but controlled by rainfall.In summary, Huangtupo landslide overall instability probability is recently low, but should pay attention to local instability phenomenon in the front edge position. |
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