湖水位壅高条件下堰塞体土料变形特性DEM-PFV耦合模拟研究

我国西南地区多为高山峡谷地貌，易发生滑坡堵江事件，形成堰塞湖。堰塞湖水位壅高过程中，堰塞体为常剪应力路径，即剪应力保持不变，孔隙水压力不断增大。但已有的研究主要集中于固结排水剪和固结不排水剪，与堰塞湖水位壅高过程中的实际应力路径有别，因此开展常剪应力路径下堰塞体材料的变形特性研究，是深入分析湖水位壅高过程中堰塞体动态响应的有效途径。鉴于此，本文以2018年10月11日白格堰塞湖为例，以堰塞体的实际高度、漫顶前的最高堰塞湖水位及湖水位壅高过程中的实际应力路径为基础，基于细观尺度的离散元（DEM）—孔隙有限体积法（PFV）流固耦合方法，从敏感性分析的角度出发，开展了不同围压、不同初始应力条件下堰塞体土料的常剪应力剪数值模拟试验，并从材料的应力应变关系（宏观）及内部接触力（微观）的分布规律等角度出发，揭示了湖水位壅高过程中堰塞体不同位置的变形响应及其微观力学机理。研究表明，湖水位壅高条件下堰塞体土料变形特性受到土料位置、强度和湖水位壅高程度的联合影响。处于堰塞体不同位置的土料，围压与初始应力比条件不同，并且在堰塞体漫顶之前所遭遇的最大孔隙水压力也不同，从而导致在堰塞湖水位壅高过程中，不同位置的堰塞体土料呈现出不同的变形特性，一般呈现由里及外变形逐渐增大的规律。在相同围压条件下，靠近堰塞体上游外缘的土料，初始应力比相对较高，且遭遇的最大孔隙水压力也相对较高，从而在堰塞湖水位壅高过程中其应力路径会穿越失稳线，导致颗粒之间的接触力减弱，从而产生较大的变形，且大变形区的厚度与范围受到初始应力比及最高湖水位的限制。堰塞体内部初始应力比相对外缘较少，在湖水位壅高过程中应力状态穿过失稳线的可能性降低，从而变形也相对较小。

Application of DEM-PFV to Modeling Deformation Characteristics of Landslide Dam Materials During Rising of Water Level

Most of the landforms in southwest China are high mountains and valleys, which are prone to be dammed by the landslides and form dammed lakes. During the rising of water level, the encountered stress path is constant shear stress, namely the shear stresses was constant, but the pore water pressures increased gradually. Currently, most of the conducted tests of landslide dam were focused on the consolidated drained or undrained tests, it is different from the actual stress path in the process of rising of water level. Therefore, the study on deformation characteristics of the landslide dam under the constant shear stress path is an effective way to deeply analyze the dynamic deformation of the landslide dam during the rising of water level. Hence, taken the Baige dammed lake on October 11, 2018, as an example, considered the height of landslide dam, the highest water level before overtopping, and the actual stress path during rising of water level, parametric studies were carried out based on the micro-scale DEM-PFV coupled simulation to investigate the deformation characteristics of landslide dam materials under different confining pressure, different initial stress ratio, and constant shear stress path. The deformation characteristics of landslide dam during the rising of water level and corresponding micromechanics were revealed according to the macro stress-strain relationship and distribution of contact forces between particles. It suggests that the deformation characteristics of landslide dam materials during the rising of water level is highly dependent on the combined roles of location, strength, and extent of water level. At different locations, the confining pressure and stress ratio is different, and the max pore water pressure is different too. This induced different deformation characteristics during the rising of water level, and usually the deformation increased from the core of the landslide dam to the surface at upstream. At the same confining pressure, the materials closed to the side of landslide dam, the initial stress ratio is high, and the encountered pore water pressure is high, so it will be more easily deformed, and the extent of large deformation is restricted by the initial stress ratio and the final water level, this could be attributed to the weakening of contact forces between particles. At the internal part of landslide dam, the initial stress ratio is lower than the external part, hence the probability of passing the instability line is lower, and the deformation of the internal part is smaller.