Research On Freeze-thaw Mechanical Behavior Of Rock Mass And Collapse Formation Mechanism Along The Highway Located In Alpine And Strong Earthquake Regions

Through further investigation, I collected the geological diseases andenvironmental geological formations of537Km slope along the tianshan road locatedin alpine and strong earthquake regions; then I made detailed analysis and evaluationto86typical slope collapses disasters along highway by “general survey”、keyresearch and some kinds of means. At the same time, we introduced andindependently research equipment and test plan, obtaining the feature evolutionassociation laws of rock mass’ macro and micro level under the freezing-thawing andlarge temperature coupling circulation. Thus, I exploratorily defined the coefficient offreezing-thawing and large temperature coupling circulation in alpine region, andquantitatively defined the related coefficient and rock value range of different kinds ofrock mass; Based on it, I selected some typical collapse disasters as the prototype,systematically analyzed the disaster mechanism, instability failure modes anddynamic evolution development law of slope collapses along Tianshan highway frommultiple perspectives and dynamic-static joint numerical simulation technology underfreezing-thawing and large temperature coupling circulation. And also, I put forwardkey prevention technology countermeasures and prevention technologies of collapsein alpine and strong earthquake regions, which was verified by engineering example.The main results of this thesis are as follows：(1) The research finds out the distribution and development law of the geologicaldisaster along tianshan highway which is located in continental glacial alpine regionwith strong earthquake environment. Overall, geological disasters in north section ofthe tianshan highway are more serious. There are two possible factors contributed tothis phenomenon. Firstly, the north section of the tianshan highway primary buildingsequence stratigraphic confronted strong disintegration damaged by late activestructural destruction, while the southern highway belongs to mesozoic-cenozoicstrata continental building, the construction activity effect is relatively weak.Moreover，the length of north section located in strong cold aspic weatheringsections(above2800m) is obviously longer than south section.(2) There are four key factors to trigger geological disasters along tianshan highway：①the frequent seismic effect induced the slope rock mass sheardisplacement or tensile displacement, leading to stress release, fracture surface’sfrequent development， lower density and permeability enhancement. It is theprecondition of strong chilling weathering erosion in cold frozen mountain areas.②the biggest temperature difference is almost80℃within one year in this area, and thedifference of the day and night can reach40-50℃. Especially under the expansion andcontraction stress caused by cycle big difference of（-30℃～+50℃）, not only the bigtemperature difference inside and outside of the rocks but also the different coefficientof thermal expansion in different mineral of internal rocks will lead to furtherdisintegration, cracking, which were the material foundation of water infiltrationerosion and splitting force of strong ice water.Geological disaster activities were controlled by seasonal changes obviously.Summer(May-Sep) is not only the rush hour of water supplies but also the rush hourof geologic hazard. In addition, the increasing of human activities destructed theoriginal slope balance, which make related engineering geological diseases willbecome more and more serious.(3) Collapse is the most common and serious engineering geological disasters inalpine and strong earthquake regions. There are86collapses developed along tianshanhighway，including59small，28medium-sized and2large collapses. Collapsesmainly developed in slope above70°，and the slope height is between11m~30m.Sedimentary sections collapses happened in37places, extrusive rocks are distributedin16places, intrusive rocks are distributed in10places, and metamorphic rockcollapse in23places. Joint fissures development, adverse structure surfacecombination and steep terrain are the foundation of collapses. Earthquake,freeze-thaw-the large temperature difference coupling (freeze-thaw split, frozen largetemperature difference of stress produced by contraction), melting ice snow water,heavy rain and slope excavation are the inducing factors; Among them, the dynamicaleffect of internal damage caused by earthquake and the Frost weathering effect causedby the coupled of freeze-thaw-the large temperature difference influence the collapsemost. All of them construct the unique characteristic of collapse developmentevolution in strong earthquake and alpine geological environment.(4) In accordance with the mechanical system of the rock mass deformation,collapse can be classified to four types：compression cracking，sliding and fracturing，bending-fracturing-toppling and bending-bursting. According to collapse forms, itcan be divided into sliding, dumping and falling. The total volume of typical collapseis nearly3million cubic meters. Sliding type, falling type, dumping type occupied46%,30%and24%respectively. From stable degree analysis, stable, basic stable andunstable respectively to3%,30%,67%. We also found that sliding type collapse is themost common type and the number of falling and dumping type collapses is close to each other.(5) Using freezing-thawing and a large temperature difference coupling cycle tosimulate different frost weathering cycle life in alpine mountain areas(15years,30years, and50years), the author got the decay law of physical and mechanicalproperties changed with strong frost weathering of hard rock, medium-hard rock andsoft rock in alpine mountain areas by experimental study. Thus, we could define thefreezing-thawing and large temperature difference coupling coefficient parameters inalpine mountain areas which successfully qualified the freezing-thawing and largetemperature difference coupling coefficient of various representative rocks under frostweathering cycle in50years. This provided qualified basic parameters for latesubsequent collapse mechanism of rock slope and dynamic evolution law.(6) Combined with strong frost weathering conditions in alpine mountain areas,the author carried out the micro-scanning experiment SEM of rocks and achievedquantization law equation of micro cracks-macroscopic physical and mechanicalcharacteristics under the action of frost weathering of granite which typicallyrepresented the hardest rocks and sandstone which typically represented themedium-hard rocks in alpine mountain areas: that is, the equation between granite,sandstone micro-cracks evolution and macroscopic uniaxial compressive strengthattenuation trend, the equation of granite, sandstone micro-cracks evolution andmacro-porosity increasing trend, and the equation of granite, sandstone micro-cracksevolution and macro water absorption increasing trend. These qualification laws laidthe technical foundation for future in-depth study of rock fracture mechanics in suchareas.(7) Considering the five typical predisposing factors “cold, shock, high, steep,cut” under strong earthquake environment and three typical highway slopes collapsesof sliding tilting and falling types in alpine mountain areas, combined with fieldinvestigation and laboratory test results and four kinds of stress mechanism, failuremechanism, mechanical calculation model of rock deformation includingunloading-crack, slipping-crack, bending-cracking-dumping and bending-collapse, theauthor introduced the idea of freezing-thawing and large temperature differencecoupling coefficient and applied the discontinuous deformation analysis techniques(DDA) to rock stability and dynamic evolution law of related rock collapse, whichwas closely related to typical strong earthquakes and frost weathering under conditionof freezing-thawing and large temperature difference coupling. Associated with finiteelement numerical analysis of deep-seated law correlation between slope stress andstrain and destabilization of collapsed rocks at the starting point of the disaster, theauthor built a set of theoretical analysis of the technical system of highway rock slopecollapse hazard in alpine mountain areas under strong earthquakes and obtained thecollapse hazard mechanism and dynamic evolution of highway rock slope. On thisbasis, the author selected the typical slipping type of rock collapse as the specific research example, and made in-depth corresponding stability calculation analysis ofdangerous rock slope and key prevention techniques focusing on weight,freezing-thaw and seismic conditions under unfavorable factors like freezing-thawingand large temperature difference coupling effect and strong earthquakes in alpinemountain areas. After it, the author applied the associated analysis by means ofnumerical simulation analysis.The main innovative points of this thesis specific are as follows：(1)Through the experiment study on the mechanical properties of hardest rock,hard rock and soft rock which situated in alpine region in different natural freeze-thawcycle times, we not only got decay laws related to the physical-mechanical propertiesunder the coupling action of different cycles (on behalf of the alpine region for15years,30years,50years of natural cold aspic weathering), but also establishedrelevant linear and nonlinear physical mechanics equation. On the base of these work,the author preliminarily defined the coupling coefficient of freeze-thaw and the largetemperature difference，distinguishing correlation coefficient and value range ofdifferent kinds of rocks. All of these provided a quantitative parameters basis for lateresearch of rock slope collapse forming mechanism and dynamic evolution law.(2)This paper focused on relationship between the cycle times of freeze thawing-large temperature difference and the rock microcosmic structure change, analyzedin-depth variation characteristics of corresponding macro physical and mechanicalindexes, and also constructed typical macro-microscopic characteristics constitutiveequation.(3) Combining with field investigation, indoor and outdoor tests, the authorapplied Discontinuous Deformation Analysis technology (DDA) to analyze the slopestability and collapse evolutionary rules considering the earthquake and couplingcoefficient of freeze-thaw and the large temperature difference. At the same time, thefinite element technique was employed to analyze the relation between collapse andthe stress and strain of slope. This thesis sets up a theoretical analysis system which issuitable for the slope collapses occurred in strong earthquake environment of alpineregions, thus obtaining the slope collapses forming mechanism and dynamic evolutionin alpine regions.(4) The paper developed key prevention technology for rocky slope collapsehazard along the highway located in strong earthquake and alpine regions, andconstructed a set of comprehensive prevention theory system with three approaches:theory calculation, experience formula evaluation and numerical simulation stressanalysis evaluation. This theory system has been verified in specific cases of hazardprevention.