For insights into rainfall infiltration on soil slopes and coupled transmission mechanisms, two-phase flow and finite element analysis were employed to examine water and air movement during the Shuping landslide. The results indicated a division of the landslide surface into two zones: an upper inflow area and a lower overflow area, driven by contrasting inflow and outflow directions. The total water and air flux remained stable, minimally affected by external factors such as rainfall attributes, surface runoff, and air temperature variations. In the inflow area of the slope surface, when rainfall intensity was greater than the total rate of the infiltration of water and air, the magnitude of infiltration equalled to the total rate infiltration of water and air, and runoff generation occurred in this area. Conversely, when infiltration matched rainfall intensity, runoff was absent in this area. In addition, water pressure in the saturated area of the slope surface can be transferred to the groundwater of the slope by pore air pressure, which could also increase the pressure head of the groundwater, and this was also detrimental to slope stability. Regarding uniform rainfall, it significantly reduces the safety factor, potentially making it the most hazardous pattern for slope failure.

寒冷地区的混凝土面板堆石坝在经历长期冻融作用后,其面板渗透性逐渐增大,从而影响大坝安全稳定.为此,通过解决冻融作用下混凝土表面不平整等问题,利用Autoclam渗透性测试仪测试了不同水胶比、掺粉煤灰以及引气剂下混凝土渗透性随冻融次数的变化规律.结果 表明,不同水胶比混凝土的渗透系数随冻融次数的增加均呈指数增长趋势,水胶比较小的混凝土其渗透系数增长的最缓慢;高冻融循环次数后,同时掺粉煤灰和引气剂对增强混凝土的抗渗性效果最明显.此外,还探究了冻融条件下混凝土渗透性与其抗压强度之间的相关性.

Abstract: Rainfall is the most important factor to induce landslide, of which rainfall pattern is the main influence parameter. Generally, during the analysis of slope stability under different rainfall patterns, the influence of pore water pressure in saturated zone is mostly considered, while the influence of pore air pressure in unsaturated zone is seldom analyzed from the angle of water-air coupling. Based on the theory of water-air two-phase flow, this paper calculated and simulated the variation of pore air pressure changing with the rainfall time under three typical rainfall patterns (weakened, concentrated and enhanced), and combined the slope stability analysis model of considering pore air pressure to study the influence of pore air pressure on slope stability. The results show that the influence of pore air pressure on slope stability is detrimental under the three rainfall patterns. And the response duration of the pore air pressure is the longest under the weakened rainfall pattern, the concentrated pattern is the second, and the enhanced pattern is the shortest. The influence of pore air pressure on the safety factor of slope stability is the greatest under the weakened rainfall pattern, which can easily lead to the instability of the slope. Thus, we shall take the necessary engineering measures in advance in the event of such rainfall pattern prediction.

On the basis of the theory of two-phase ( water and air) flow, the law of water-air movement caused by rainfall infiltration in slope was revealed by means of finite element method. Daping landslide in Three Gorges Res-ervoir was taken as a case study. The simulation results show that the slope surface can be divided into the inflow area and the outflow area according to the inflow and outflow of water and air. Usually the upper part of slope is in-flow area, and the lower part is outflow area. The total infiltration rate of water and air in slope is relatively stable, slightly affected by rainfall characteristics, slope surface runoff and temperature changes. In the inflow area, when rainfall intensity is greater than infiltration rate, water in slope will run off, otherwise water or air will completely infiltrate. The saturation pressure of slope surface could transmit to groundwater surface through pore air, which in-creases the groundwater pressure head, unfavorable for slope stability.

As the change of the pore air pressure during rainfall infiltration is an important factor to affect slope stability， a method for analyzing slope stability under the consideration of the effect from the pore air pressure is proposed herein for analyzing the effect concerned. In this method， the distributions of the pore water pressure and the pore air pressure as well as the saturation-degree of slope are calculated at first based the relevant theory and method of water-air two phase flow， and then the load variation caused by pore air pressure during the rainfall infiltration is obtained. Moreover， combined with the theory of unsaturated soil shear strength and the residual thrust method， pore air pressure is introduced into the slope stability analysis. Thereafter， a simulative analysis on the slope stability is made under the consideration of the effect from the pore air pressure by taking Tanjiahe Landslide as the study case. The result shows that the surface layer of the slope tends to be saturated by rainfall and the change of the pore air pressure between the slope surface and the sliding zone is more sensitive， while the pore air pressure attenuates during its transmission along the sliding bed to the deep direction and the pore water pressure in the slope saturated zone is transmitted to the slope toe through the pore air， which forms a gradient of the pore air pressure along the direction of the slope toe and increases the downwards thrust of the sliding body. Under the same seepage condition， the consideration that the effect of the pore air pressure makes the safety coefficient on the same sliding plane decrease unfavorable for the analysis made on the slope stability. The effect of this method is significant for considering the pore air pressure effect when slope is critically instable and it is more practical for reflecting the landslide phenomena of some specific projects as well.