Research On Instability Mechanism And Controlling Techniques For Cutting High Slope In Disintegration Rock Mass

At present, the stability of cutting high slope in disintegration rock mass has become a very attentional problem in engineering field. The problem especially stands out in geology condition complicated mountain district. Research achievements about this problem now are mainly the stability analysis and reinforced protective measure during design and construction, but for post-construction particularly post-construction slide instability of complicated mountain district cutting slope, the research works are less, the corresponding achievements are also less and the technical reserve is not enough. Therefore, with the western traffic scientific and technical project— 《Research on Mechanism and Control Technique of Landslide in Qianlong Section along Sichuan-Tibet Road》 , depending on Sichuan-Tibet highway engineering , this thesis develops research on the instability mechanism and controlling techniques for cutting high slope in disintegration rock mass. The research achievements are both directly applied to the disease prevention and cure engineering of Sichuan-Tibet Highway cutting slope, and have very important significance for design and construction of future similar engineering.Making an extensive investigation about the cutting high slope diseases in disintegration rock mass, The disease models are classified according to engineering geological features, and the regularity of occurrence and development of each kind slope disease is found. According to the investigation results ,the special attention is paid to the landslides of Qianlong Section, and the instability mechanism of typical landslides is studied,via making use of multidisciplinary theories — geology, geotechnical mechanics, etc. Meanwhile, on the basis of utilizing geological mechanic model test and numerical calculation analysis method to test and verify instability mechanism, the effective preventive and treatment measures are put forward. The main results gained can be summarized as follows:1. The disease types of the cutting high slopes and conversion of mutual relations are summarized.In these slope diseases, the larger damages are landslide, slump and collapse. The feature and mutual difference between these diseases are analyzed. The probabilityand condition of crumble, slump and collapse convert landslide are pointed out. There are many factors to influence disintegration rock high slope stability, in which the controllability of slope body structure to slope disease, water action and engineering factors have important influence on slope stability.2. The instability mechanism of the cutting high slope, the causes and developmental course are put forward.Taking Sichuan-Tibet Highway Qianlong section 1* slide for typical example, the reasons of the generation of 1* slide are mainly the outside influence factors such as slope body high and cliffy (the natural slope is greater than 40 degree), rock mass disintegration, intensity low, deformation large, add to rainwater infiltration and downcutting of Longdan brook, etc., which finally lead to slope instability. The instability mechanism can be summarized as follows: downcutting of Longdan brook—^leading to mountain body slump—?the sliding zone of old landslide developed in the slump zone—>the trend of slide generates after old sliding zone through—>old landslide trends to stable after sliding—?old landslide locally revivifies in the influence of rainstorm and mud-rock flow—?1* slide generates. The disease cause result from disintegration rock mass slope is slump earlier than slide. Slide is converted by the slump. Slide body attaches itself to slump body and sliding zone attaches itself to slump zone. It's developmental course as figure 3-3. 1* slide has gone through creeping deformation—^accelerator sliding—?intermittence motion—^compaction consolidation etc. several developmental course.3. The large-scale geological mechanic model test is done, with multilayer sliding zone in the slope body and the feature of rainfall infiltration to change the mechanics parameters.Taking 1* slide for an example, the large-scale geological mechanic model test is done for testing and verifying the instability mechanism of the cutting high slope. It can simulate the situation that mechanics parameters are changed by multilayer sliding zone and rainfall infiltration. The results of tests indicated that the deformation zone of slide body concentrate on trailing edge viz. range from the rock of nearby highway above to shallow sliding zone under the action of natural power. The power of slope body deformation is mainly the gravity extrusion action of rock mass and the sliding action of shallow sliding zone. The slump extrusion of overlying rock massplays main role in the whole course.The retaining structure effectively restrains the fractional action resulting from the sliding deformation of middle-level and deep-level sliding zone to shallow rock mass. The influence of the slump extrusion action of pile back rock mass on the deformation of pile front rock mass is greatly weakened. The horizontal displacement, vertical displacement, sliding deformation of the sliding zone of slope body is more reduced by a wide margin than natural state.Comparing the results of numerical analysis to experimental, it is revealed that the deformation regularity of slope body, the main deformation region, the loading of retaining structure and the retaining consolidation effect are fundamentally uniform.4. Some improving opinions about the design method of elastic foundation beam of the prestressed anchor wire framework beam are put forward. The distribution of node load is suggested to allocate by crisscross beams rigidity. The use method of design parameters and foundation anti-force coefficient are given. Using anti-slide pile in the engineering of disintegration rock mass high slope, when the rock and soil mass of anchoring segment has larger rigidity, it is suggested to consider the pile as elastic one. The calculation method is adopted according to the lateral constraint elastic foundation beam. When the rigidity of rock and soil mass of anchoring segment is much smaller than pile, it is suggested to consider the pile as rigid one. The calculation method is adopted according to rigid pile. By comparing design calculation of engineering example to test result of site, these design methods are proved to be reasonable.5. The semi-slope pile with longer length and long anchor wire is still rare at home and abroad. Its design calculation theory and other correlative problems are all studied further. Some problems about the design of semi-slope pile, namely, the difference between semi-slope pile and toe pile, the set-up of semi-slope pile place and the handling method of pile front anti-force are discussed in this thesis. The calculation formula of pile place considering the stability of pile front rock and soil mass and the several principles of ascertaining pile front anti-force are put forward.6. The method that the design calculation of pre-stress anchor wire pile should consider its construction procedure and the actual load condition of pile is put forward. Meanwhile, this calculation should proceed by phase. It is suggested that the sectionfrom finishing anti-pile construction to stretching anchor to the design value is calculated according to elastic foundation beam model. After finishing anchor to stretch and slide thrust increasingly act on anti-pile, the calculation of the pile segment above sliding surface is adopted by static force structure of top-pile elastic restraint, not by elastic foundation beam model, and the calculation of the pile segment below sliding surface still by elastic foundation beam. At this condition, the slide thrust acting on the pile should be modified considering two section conditions. The calculation results are nearly uniform with the test results.7. Some control conditions are provided to calculate rational spacing between adjacent piles. These conditions are the static equilibrium equation between slope thrust on the soil arch and resistance on its two end sections near the two piles, intensity principle of the point at internal edge of medial cross-section of the soil arch and the intensity condition of two end sections of the arch. The rational calculation formula of spacing between adjacent piles is got. According to the formula, it is quantitatively shown that the spacing is increasing with the increase of cohesion or internal friction angle of soil behind piles and decreasing with the increase of slope thrust behind piles while other effective factors are not varying. The calculation procedure of spacing between adjacent piles is illustrated by a practical project and the result is rational.8. The eight influence factors of anchor prestressing force loss are got. Some remedial measures on these factors are raised. The quantity of anchor prestressing force loss caused by every factor is given. And a simple practical calculation method used to calculate prestressing force loss of anchor system is also given.