颗粒运移对蒋家沟土体渗透性影响的试验研究

对蒋家沟流域泥石流源区两种分散性不同的土(G1土具有强分散性,G2土无分散性)进行室内土柱自滤试验,研究了土柱在常水头(水头为5 cm)渗流过程中颗粒运移对土柱不同部位渗透性的影响。入渗液采用了煮沸过的清水与浓度为1 g/L的悬浮液(悬浮颗粒的粒径范围为1.6～104.74μm)。在清水渗流过程中,两种土样的入口处土层渗透性随着时间而增大,出口处土层的渗透性先增大后减少。在悬浮液渗流过程中,两种土的各土层的渗透性都有下降趋势,但在入口处土层最为显著,G1土样下降了一个数量级以上,G2下降了近两个数量级,且G2土所用时间较G1土短,即G2土的渗透性减少速率更加明显;两土柱中渗透流量都有显著减少。研究表明: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。

Effects of particle transport characteristics on permeability of soils from Jiangjiagou ravine

Permeability variations of two types of soils (G1 soil with high dispersibility, G2 without) from debris flow source area in Jiangjiagou ravine (Yunnan province) due to fine particles transport were evaluated under constant head condition (the constant pressure head is 5 cm) in soils column. Boiled tap water and suspension of 1 g/L particles (the size range: 1.6－104.74 μm) was successively used as inflow water for both soil column experiments. During the stage of boiled tap water seepage flow, permeability coefficient of both the soil layers near the inlet of the column decrease, while that of both the soil layers near the outlet of the column first increased, then decreased. During the stage of particles suspension seepage flow, permeability coefficient of both the soil layers along the column decreased; and the most severe decreases of permeability occurred near the inlet of the columns. The permeability coefficient of soil G1 reduced by more than one order of magnitude; the permeability coefficient of soil G2 reduced by about two orders of magnitude; and the amount of time spent reaching those values in soil G2 was less than in soil G1. That is the rate of the decrease of permeability coefficient in soil G2 was more than in soil G1. Flow rate for both soils significantly decreased in this stage. The results show that the dispersion played a leading role in the seepage process. In other words, the process of itself particles release and transport can affect the pore concentration and offset the clogging effect induced by the deposition of the foreign particles. After the experiments, the pore space of both the soil layers near the inlet of the columns were almost filled by the foreign particles, and the filling rate gradually decreased along the column by observed with the naked eye, which was in agreement with the results of the permeability coefficient decrease of the soils along the column. In addition, the mass loss of particles only occurred in the first several tens of minutes, and the sizes of the loss particles from the two soils fell within the same range of 1–100 μm