泥石流孕育-启动过程中的细粒运移堵塞效应

In recent years, because of frequent occurrences of extreme weather climatic events,the number of geological disasters such as debris flows showcontinuously increasing trend every year under intensive rainfall, which pose a immense threat to the safety of life and property in the affected area. The mechanism of rainfall-induced debris flow has always been the key issues and difficult problems in the study field of slope disaster. Based on particles transport in soil pores and its clogging effect on permeability decrease, the mechanism of the debris flow preparation and initiation will be analysed by means of microscopy, XRD analysis ,permeability tests in soils column and rainfall simulation tests in slope model and so on. The microscopic structure, mineral composition, physical chemistry and water physical, mechanical properties of the slope soil will be studied ,and will reveal the premise of particles transport. In other words,the relationship between the soil internal characteristic and the reasons for soil particles transport will be found. On the Basis of permeability tests in soils column, rainfall simulation tests in slope model and the corresponding theoretical analysis, the formation conditions, mechanical reasons and influence factors of soil particles transport during the process of rainfall infiltration will be identified, and the evaluation methods for the effect of pores clogging due to soil particles transport will be established, and pores clogging effects by soil particles transport on the mechanism of debris flow preparation and initiation under intensive rainfall will be explored.Then, infiltration model and slope stability analysis method for debris flow will be established based on pores clogging effect by particles transport.This project will provide new ideas for the mechanism of rainfall-induced debris flow, and a theoretical basis for disaster prevention and mitigation.

近年来，受强降雨事件增多的影响，泥石流发生的频率正不断增大，对其影响区域内人们的生命和财产安全造成了巨大的威胁。泥石流的启动机理一直是斜坡灾害研究领域的核心问题与难点问题。本项目针对在降雨入渗过程中泥石流土体细粒会发生运移,堵塞土体孔隙而导致土体渗透性能降低的特点，研究细粒迁移堵塞效应对泥石流孕育-启动过程的影响机理。借助各类观察、测试手段，采用自制土柱渗透堵塞试验与斜坡模型试验，以及相应的理论分析来达到研究目的。首先通过分析泥石流土体的微观结构、矿物组成、理化-水理-力学特征，揭示土体细颗粒发生运移机理；然后根据土体渗透系数随渗流时间的变化规律定量化评价细粒运移堵塞效应，并建立考虑土体特性的细粒随机运移堵塞模型；在此基础上，建立适合泥石流斜坡的降雨入渗模型与稳定分析方法，最终提出细粒运移堵塞效应对泥石流孕育-启动过程的影响机理。

云南蒋家沟是世界著名的由降雨导致泥石流、浅层滑坡频发的沟谷之一。通过分析蒋家沟泥石流源区土体的微观结构、矿物组成、理化-水理特征揭示土体细颗粒发生运移机理；蒋家沟泥石流土体土体具有孔隙度高、级配宽、不均匀系数远大于20，级配曲线为上凹型，具有中-高分散性，为内在不稳定性土；原状土普遍存在一种特殊的“桥式”胶结结构，且胶结物联结强度较弱，在遇水条件下发生断裂，不仅降低了微弱粘聚力，而且土颗粒容易分离成粒径为数十微米的散微粒；粒径小于1 mm 的细粒部分主要由绿泥石和伊利石等粘土矿物及次生石英组成，次生粘土矿物的形成与蒋家沟所处的环境密切相关，即炼铜产物二氧化硫进入地下水形成硫酸，加速矿物风化进程，在地下水成分中能得到反映。在室内土柱自滤试验中，采用了两种分散性不同的土（强分散性和非分散性土）来研究在常水头渗流过程中，细颗粒运移与堵塞效应对土柱不同部位渗透性的影响不同，土体的分散性在颗粒运移过程逐渐占主导地位，即强分散性土自身颗粒的运移明显，能抵消一部分外来颗粒的积聚、堵塞作用；从试验结束后土柱的外观图像观察也发现，入渗的悬浮颗粒在土柱的各个位置都有分布，但主要沉积在入口处，这与土柱各层渗透性的变化相吻合；此外，两种土流失的颗粒都只是集中于渗流的开始阶段，流失颗粒粒径范围集中在数微米至数十微米之间。利用自制的泥石流模型槽研究泥石流土体的细粒组分（d≤0.075mm）在降雨入渗和渗流过程对泥石流孕育与启动机理的影响，设计了三种细粒含量的土体制作室内斜坡模型，进行了人工降雨诱发斜坡泥石流试验，研究了泥石流土体斜坡在降雨入渗过程中坡面产流的形成特点、水土流失特征以及斜坡失稳模式；斜坡土体细粒含量对斜坡破坏模式和坡面产流的形成有重要作用，且考虑由细粒堵塞效应导致坡面产流的斜坡稳定性分析模型得到的安全系数更能接近实际情况。