| The effective stabilization and scientific evaluation of reservoir landslides is of great significance to ensure the safe operation of reservoirs and the safety of people's lives and property in reservoir areas.Stabilizing piles are widely used for preventing the landslides within reservoirs.The evolution trend of deformation and stability of the reservoir landslide-stabilizing piles system are directly related to the success of landslides stabilization and safety operation of dams.Therefore,it is of great theoretical significance and application value to conduct the studies concerning the evolutionary process and stability of reservoir landslide-stabilizing piles systems.Landslides have the process of formation,development,acceleration and failure.Installation of stabilizing piles heavily affects the evolution process of landslides,and the reservoir landslide-stabilizing piles system show unique evolutionary characteristics under reservoir operation or rainfall.However,the studies on the evolution mechanism and stability of reservoir landslides-stabilizing piles system have not been conducted in depth,which cannot meet the requirement for the prevention and control of reservoir landslide-stabilizing piles system.It is urgent to further study the evolutionary process and multi-field evolutionary characteristic of reservoir landslide-stabilizing piles system based on the study of reservoir landslides.Then,revealing the evolutionary mode and studying the stability evaluation and identification of reservoir landslide-stabilizing piles system,which can provide support for the guarantee of long-term safety and stability.In this dissertation,the Majiagou landslide in the Three Gorges Reservoir area was chosen as the reference,and the physical model test was the main study method.The research focused on the evolutionary characteristics and failure modes of reservoir landslides as well as the evolutionary process,characteristics and modes of reservoir landslide-stabilizing piles system.A stability identification method of landslide-stabilizing piles system based on the multi-fields information of soil-piles system was proposed and applied to an engineering case.Main conclusions of this dissertation were summarized as following:(1)The simplification analysis of reservoir water level and loading design of model tests was conducted based on the reservoir water level and rainfall within the Three Gorges Reservoir area.The simplification analysis simplified the actual water level fluctuation as the water level change in the test frame.The loading applied on the rear part of the landslide model was used for simplifying the increasing of the residual thrust load caused by rainfall and deterioration of soil and rock material.Considering the two most unfavorable impacts of softening effect and dynamic pore water pressure caused by the water infiltration and water level fluctuations,test methods related to these two effects were redesigned.The methods correspond to the water level and loading design under the conditions of static water level and water level fluctuations,which can provide the foundation for future model test study.(2)The development of similar material for reservoir landslides was conducted,and the multi-fields information monitoring platform for reservoir landslide-stabilizing piles system in the physical model test was established.The composition and proportion of the optimal scheme of similar material was determined as standard sand(62.5%),sliding mass soil(28.5%),bentonite(1%)and water(8%)based on the direct shear test and fuzzy comprehensive evaluation method.The validity of the similar material was verified using the physical modelling and the theoretical analysis.The self-reaction apparatus of model test for reservoir landslide-stabilizing piles system was developed.The apparatus can accurately control the water level fluctuation and realize different pile spacing arrangements from 2.5 to 6 times pile width.Based on the self-reaction apparatus,the multi-field monitoring system and platform were established.The platform can realize the monitoring of seepage,stress,displacement temperature and strain field during the evolution process of reservoir landslide-stabilizing piles system.(3)The evolutionary characteristics and stability variation of landslides under statistic water level were analyzed using physical model test and numerical simulation methods.Results indicated that the increasing period of the pore water pressure inside the landslide is the critical period of landslide deformation.The deformation during this period is large,and the deformation near the reservoir area is obvious.The evolutionary process of the landslide was divided into four stages,namely initial,uniform,accelerated and failure deformation stage based on the displacement characteristic.The soil pressure,surface temperature and macro deformation showed unique evolutionary characteristic and associated each other.The landslide showed a higher stability under a higher water level rising rate or lower permeability during water level rising period,and the landslide stability continuously declined as water infiltrated during the water level maintaining period.If the effect from buttressing effect exceeded the effect from matrix suction dissipation,then the landslide stability increases,and vice versa.(4)The deformation characteristic and failure mode of a landslide with and without a reservoir were studied and the characteristic of landslide deformation under cyclic water level fluctuation was explored based on the physical model test.The model without a reservoir experienced multiple slip surfaces that extended from the base of the model to the surface and only partial landslide failed ultimately.In contrast,the model with a reservoir failed by sliding along a basal sliding zone.The first water level rising is most negative to the landslide among the five cycles.An increase of the water level drawdown rate is much more unfavorable to the landslide than an increase of the water level rising rate.The landslide was found to have an adaptive ability to resist subsequent water level fluctuations after undergoing large deformation during a water level fluctuation.The landslide deformation and observations in the field were found to support the test results well.(5)The deformation characteristics and failure modes of a landslide with and without piles under static water condition were studied.The deformation of the landslide with piles in the region behind piles is significantly reduced during water level rising stage,and the limit load and time to failure of the landslide during the loading stage are significantly increased.The landslide model without piles slips and failed along the contact between the landslide mass and the bedrock.In contrast,multiple surfaces extended from the interior of soil upheaval area behind piles to the surface and prompted the soil to slide over and downslope between piles in the model with piles,which causes the failure of soil-piles system.(6)The evolutionary process analysis and stages identification of the landslide-stabilizing piles system under static and cyclic water level were conducted using physical model test.The results show that the evolution mode of the system under the condition of static water level can be summarized as the erosion and collapse of the landslide toe,the cracking appearing in the rear edge,the anti-slide pile inclining forward,upheaval behind the piles,penetration of sliding surfaces behind the piles,soil extruding between the piles,the soil sliding over the pile top.The evolution mode of the system under the condition of cyclic water level can be summarized as pile-soil slow deformation,erosion of landslide toe,uplifts behind piles,formation of sliding surfaces behind piles,collapses in the front toe and pile-soil system failure.Considering the deformation characteristics,the anti-sliding performance of piles,the soil movement tendency between piles,the upheaval deformation behind piles and other macro-deformation characteristics,the stability of the system during the reservoir impoundment and deformation and initial stage was determined as stable,moderate stable,less stable and unstable in different stages or periods.A method for identifying stability of reservoir landslide-piles system based on multi-field information of soil-pile and decision tree C5.0 algorithm was proposed.In this method,the pile top displacement rate,slop surface displacement rate,variation rate of pile strain and variation rate of soil pressure behind piles were set as input terms,and the stability of the reservoir landslide-piles system(stable,moderate stable,less stable,and unstable)were set as output items to generate threshold criteria of stability identification.The results showed that the current stability of the Majiagou landslide-piles system is less stable.The Majiagou landslide-piles system is currently in the early period of the accelerated stage.Although the deformation of the system is not serious,stabilizing measures are required to avoid further deformation or even failure.The current stability of the Majiagou landslide-piles system obtained from the field monitoring agreed well with the results from the threshold criterion.The main innovations of the dissertation are summarized as follows:(1)Deformation characteristics and failure modes of reservoir landslides were revealedThe multi-field evolutionary characteristics of the landslide was revealed under static water level conditions using the physical model test.The evolutionary process of the landslide was divided into four stages,namely initial,uniform,accelerated and failure deformation stage based on the displacement characteristic.The correlation between landslide displacement field and seepage field during water storage was established,and the increasing period of the pore water pressure inside the landslide is the critical period of landslide deformation.The evolution law and underlying mechanism for the landslide stability variation during reservoir filling were revealed.If the effect from buttressing effect exceeded the effect from matrix suction dissipation,then the landslide stability increases,and vice versa.The model without a reservoir experienced multiple slip surfaces that extended from the base of the model to the surface and only partial landslide failed ultimately.In contrast,the model with a reservoir failed by sliding along a basal sliding zone.The first water level rising is most negative to the landslide among the five cycles.An increase of the water level drawdown rate is much more unfavorable to the landslide than an increase of the water level rising rate.The landslide was found to have an adaptive ability to resist subsequent water level fluctuations after undergoing large deformation during a water level fluctuation.The landslide deformation and observations in the field were found to support the test results well.(2)Evolution modes of reservoir landslide-stabilizing pile system were revealedThe landslide model without piles slips and failed along the contact between the landslide mass and the bedrock.In contrast,multiple surfaces extended from the interior of soil upheaval area behind piles to the surface and prompted the soil to slide over and downslope between piles in the model with piles,which causes the failure of soil-piles system.The deformation of pile-soil system and the development of sliding surfaces are very similar under the conditions of static and cyclic water level,but only partial erosion occurs at the landslide toe under the static water level,while large soil collapses occur under the condition of cyclic water level fluctuations.The evolutionary process analysis and stage identification of the landslide-stabilizing piles system under static and cyclic water level were conducted using physical model tests.Considering the deformation characteristics,the anti-sliding performance of piles,the soil movement tendency between piles,the upheaval deformation behind piles and other macro-deformation characteristics,the stability of the system during the reservoir impoundment and deformation and initial stage was determined as stable,moderate stable,less stable and unstable in different stages or periods.(3)A method for identifying stability of reservoir landslide-piles system was proposed based on multi-field information of soil-pile systemA method for identifying stability of reservoir landslide-piles system was proposed based on multi-field information of soil-pile,the qualitative stability evaluation of the system and decision tree C5.0 algorithm.In this method,the pile top displacement rate,slop surface displacement rate,variation rate of pile strain and variation rate of soil pressure behind piles were set as input terms,and the stability of the reservoir landslide-piles system(stable,moderate stable,less stable,and unstable)were set as output items to generate threshold criteria of stability identification.The relationship between the pile-soil multi-field information and stability state of the system was established,and the threshold criteria of stability identification for the system was obtained.Current stability state of the Majiagou landslide-piles system was identified using the pile-soil multi-field information from field monitoring and the threshold criterion,and then related stabilizing suggestions were proposed. |
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