泥石流拦砂坝坝前沉积与坝基扬压力实验研究

摘要

Sediment deposition and pore water dissipation are two processes in which excess pore water pressure evolves into effective stress during debris flow deposition. Pore water dissipation directly affects the magnitude and variation of dam foundation uplift pressure,thus compromising the stability of check dams. In this study,a special experimental apparatus was designed to simulate debris flow deposition and dam foundation seepage. In order to investigate the sediment sorting characteristics and its influence on uplift pressure,six groups of laboratory model experiments were conducted. During each test,pore water pressure at the depositional bottom of debris flow and uplift pressure at check dam foundation were collected using six water pressure sensors. Slurry deposition rates of debris flows with different densities were measured by video recorders. The results indicated that sediment sorting and pore water dissipation properties were interrelated with the uplift pressures in the debris flow deposition process. Particle sorting occurred when dilute debris flows started to deposit,where the upper slurry deposition rates was found to be negatively correlated with debris flow density. Experimental results indicated that the pore water pressure at the depositional bottom attenuated logarithmically with an attenuation coefficient that correlated linearly with the upper slurry deposition rate. Meanwhile, the dam foundation uplift pressure attenuated logarithmically and showed a linear variation with the pore water pressure at the depositional bottom. By this study a comprehensive understanding about uplift pressure generating mechanisms in check dam foundations was obtained,with particular focus on the debris flow deposition and pore water dissipation processes. New perspective has been gained in determining uplift pressures in check dam designs,thus providing better technical support and reference for debris flow disaster prevention and mitigation.%泥石流在坝前堆积固结的过程发生泥石流浆体中固体颗粒沉降和孔隙水压力消散,它直接影响了坝基扬压力大小和变化,对坝体稳定性造成影响.本文通过自制实验模型装置模拟不同密度泥石流作用在坝前的沉积渗透过程,观测不同密度泥石流坝前沉积特征和浆体细颗粒沉降速率,并通过水压传感器测得坝前沉积底部孔隙水压力和坝基扬压力随沉积时间的变化过程,最后结合不同密度泥石流沉积特征分析了泥石流沉积过程对扬压力衰减过程的影响.研究结果表明:稀性泥石流沉积过程中具有明显的颗粒分选性,且浆体细颗粒沉降速率与泥石流密度表现出线性负相关性;泥石流沉积底部孔隙水压力随沉积时间呈指数衰减趋势,拟合指数函数系数与上部浆体细颗粒沉降速率满足线性正相关性;沉积过程中坝基扬压力与坝前沉积底部孔隙水压力具有相同的对数衰减趋势,两者呈线性正相关性.本研究着眼于拦砂坝扬压力产生机制,研究了泥石流坝前颗粒沉积和水力扩散过程对坝基扬压力变化过程的影响,为拦砂坝扬压力计算提供了新的视角,具有一定的工程和理论意义.