Research On The Influence Of Reservoir Water Level Fluctuation On The Stability Of The Underlying Ice Rock Pile Slope

With the development of national economy and the further promotion of infrastructure,the talus slope will be more and more in building railway,highway,water conservancy facilities in the mountains.This paper is based on the example of the Da Qian Shi Ling Talus slope in Tian Huan Railway Project.The law about the reservoir water level fluctuation of the talus slope with ice at the bottom of it is studied by theoretical derivation formula,simulation test on site and PFC2D numerical simulation.The conclusions were drawn:(1)Based on the traditional residual thrust method and the parabola failure criterion of frozen earth,the paper improves and deduces the computational formula of stability coefficient of substratum ice layer region and then applies the formula in engineering case calculation followed by analyzing.Analysis result shows that as reservoir water level increases,ice layer in talus below the reservoir water level melts and the stability(coefficient)of talus slop decreases gradually.As reservoir water level decreases,groundwater level in talus falls and the stability(coefficient)of talus slop increases to some extents,yet it is still lower than the initial coefficient when the talus slope has not retained water.(2)By virtue of the physical simulation experiment of talus slope containing substratum ice layer,the author simulates impact of reservoir water fluctuation on the talus slope under the condition when the slope is not reinforced and when the slope is reinforced by friction pile respectively.Results are as follows.1)Under the condition that the slope is not reinforced:From the perspective of macroscopical deformation,when reservoir water level increases,the talus slope suffers many landslides from the front to the end,focusing on landslides deformation and fracture.When the reservoir water level falls,the existed landslide area does not expand obviously and sees rolling stones the most,which shows that the stress state of talus slope during the stage shall be adjusted further.From the perspective of subsidence monitoring result,when reservoir water level increases,the subsidence in the front edge of talus slope is the largest,followed by that in middle part and that in the back.Thereinto,the increase in subsidence in the front edge and middle part is consistent with the increase in reservoir water level,yet,the increase in subsidence in the the back lags behind the increase in reservoir water level.As reservoir water level falls gradually,the slope is under creeping state impacted by gravity action and subsidence in different monitoring points all increases gradually.From the perspective of stress change,when reservoir water level increases,stress in the front slope body changes obviously and that in the back slope body changes slightly.2)Under the condition that the slope is reinforced by friction pile:As for the deformation amount,the settlement deformation of talus slope can be seen when reservoir water level is increasing and water remains at the highest level.The deformation amount is less than that of talus slope without being reinforced.That means that friction pile is very effective to deal with talus slope.As for the deformation range,deformation is concentrated in the part in front of the friction pile.Therefore,it is suggested to take control measures in parts in front of the friction piles,so as to reduce the impact of reservoir water fluctuation on the front edge of talus slope with substratum ice layer.(3)Particle follow code modeling was respectively applied on the numerical simulation calculations to test the reservoir water fluctuation influence on underlying ice talus slope under the two conditions of non-reinforcement and anti-slide pile reinforcement.The conclusions were drawn:The maximum value of the internal displacement variation of the slope is slope front displacement greater than middle slope displacement greater than trailing edge displacement,slope surface displacement greater than slope internal displacement.Through the simulation results under the two conditions of un-reinforcement and anti-slide pile reinforcement,there both generated a large fissure in the talus slope.So it can be speculated that the transfixion crack may be the possible sliding surface position of talus slope.The talus slope internal X direction stress mostly appeared as tensile stress,and the Y direction stress was compressive stress.When the reservoir water level is shallow,the slope stability is good,the cracks are relatively less,and the internal stress variation is small.While in the process of rising to the relatively high water level,the displacement of the slope changes greatly,resulting in a large number of cracks and a large variation of internal stress.In the process of reservoir water level decline,the displacement also changes,but the proportion of the change to the total displacement variation is smaller.Compared to the corresponding part of the un-reinforcement slope,the displacement of the reinforcement rock heap slope above the anti-slide pile is smaller.When not reinforced,there is transfixion crack emerging in the middle part and the trailing edge of the slope.And the crack runs through to the bedrock.Although there is also crack generating on the slope surface with anti slide pile reinforcement,the crack doesn't pass through.