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1.
The behaviour of an instrumented unstable slope in a profile of weathered overconsolidated clay has been analysed. Available field investigation data and laboratory tests were integrated in a coupled hydromechanical model of the slope. Particular attention was given to the unsaturated soil conditions above the water table and to the influence of the rainfall record. Recorded pore-water pressures helped to identify the hydrogeological conditions of the slope. The coupled model was used to compute slope deformations and the variation of safety with time. Actual rainfall records were also integrated into the analysis. Comparison of measurements and calculations illustrate the nature of the slope instability and the complex relationships between mechanical and hydraulic factors. Electronic Publication  相似文献   

2.
The Kualiangzi landslide was triggered by heavy rainfalls in the “red beds” area of Sichuan Basin in southwestern China. Differing from other bedrock landslides, the movement of the Kualiangzi landslide was controlled by the subvertical cracks and a subhorizontal bedding plane (dip angle < 10°). The ingress of rainwater in the cracks formed a unique groundwater environment in the slope. Field measurement for rainfall, groundwater movement, and slope displacement has been made for the Kualiangzi landslide since 2013. The field monitoring system consists of two rainfall gauges, seven piezometers, five water-level gauges, and two GPS data loggers. The equipments are embedded near a longitudinal section of the landslide, where severe deformation has been observed in the past 3 years. The groundwater responses to four heavy rainfall events were analyzed between June 16 and July 24 in 2013 coincided with the flood season in Sichuan. Results showed that both of the water level and the pore-water pressure increased after each rainfall event with delay in the response time with respect to the precipitation. The maximum time lag reached 35 h occurred in a heavy rainfall event with cumulative precipitation of 127 mm; such lag effect was significantly weakened in the subsequent heavy rainfall events. In each presented rainfall event, longer infiltration period in the bedrock in the upper slope increased the response time of groundwater, compared to that of in the gravels in the lower slope. A translational landslide conceptual model was built for the Kualiangzi landslide, and the time lag was attributed to the gradual formation of the uplift pressure on the slip surface and the softening of soils at the slip surface. Another important observation is the effect on the slope movement which was caused by the water level (H w) in the transverse tension trough developed at the rear edge of the landslide. Significant negative correlation was found for H w and the slope stability factor (F s), in particular for the last two heavy rainfall events, of which the drastic increase of water level caused significant deterioration in the slope stability. The rapid drop (Δ?=?22.5 kPa) of pore-water pressure in the deep bedrock within 1 h and the large increase (Δ?=?87.3 mm) of surficial displacement were both monitored in the same period. In the end, a four-level early warning system is established through utilizing H w and the displacement rate D r as the warning indicators. When the large deformation occurred in flood season, the habitants at the leading edge of the landslide can be evacuated in time.  相似文献   

3.
An early warning system can be an effective measure to reduce the damage caused by landslides by facilitating the timely evacuation of residents from a landslide-prone area. Early detection of landslide triggering across a broad range of natural terrain types can be accomplished by monitoring rainfall and the physical property changes of soils in real time or near-real time. This study involved the installation of a real-time monitoring system to observe physical property changes in soils in a valley during rainfall events. This monitoring included the measurement of volumetric water content, which was compared with the results of laboratory flume tests to identify landslide indicators in the soils. The response of volumetric water content to rainfall events is more immediate than that of pore-water pressure, and volumetric water content retains its maximum value for some time before slope failure. Therefore, an alternative method for landslide monitoring can be based on the observation of volumetric water content and its changes over time at shallow soil depths. Although no landslide occurred, the field monitoring results showed a directly proportional relationship between the effective cumulative rainfall and the gradient of volumetric water content per unit time (t/t max). This preliminary study thus related slope failure to the volumetric water content gradient as a function of rainfall. Laboratory results showed that a high amount of rainfall and a high gradient of volumetric water content could induce slope failure. Based on these results, it is possible to suggest a threshold value of the volumetric water content gradient demarcating the conditions for slope stability and slope failure. This threshold can thus serve as the basis of an early warning system for landslides considering both rainfall and soil properties.  相似文献   

4.
降雨入渗下强风化软岩高填方路堤边坡稳定性研究   总被引：12，自引：1，他引：11  
降雨入渗是影响边坡稳定性、导致边坡失稳的最主要和最普遍的环境因素。强风化软岩用于高填方路堤填土边坡时,填土的压实度直接影响路堤土的渗透性和强度。利用饱和与非饱和渗流有限元模拟降雨入渗时高填方路堤的暂态渗流场,将计算得到的暂态孔隙水压力分布用于边坡的极限平衡分析,并考虑基质吸力对非饱和土抗剪强度的影响。探讨降雨强度、持时和压实度对边坡稳定性的影响。研究表明,强风化软岩用于高填方路堤压实度不能低于90 %;当暴雨强度为200 mm/d时,边坡就会失稳。其成果将为高填方路堤边坡防护设计提供科学依据。  相似文献   

5.
Peng  Qinge  Liu  Xingnian  Huang  Er  Yang  Kejun 《Natural Hazards》2019,98(2):751-763

Due to the steep slope of mountainous watersheds and large changes in vegetation coverage degree, flood response processes after rainstorms are complicated. The flow concentration time of the slope is a key parameter for the simulation of flood processes. The most widely used flow concentration time formula currently in the distributed hydrological model is T?=?L0.6n0.6i?0.4S?0.3, which is derived from the kinematic wave theory (Melesse and Graham in J Am Water Resour As 40(4):863–879, 2004; Lee in Hydrol Sci 53(2):323–337, 2008). The flow confluence time T is characterized by the constant exponent of the slope length L, roughness n, effective rainfall intensity i and slope S, and the influence of vegetation on the flow concentration time is implied by the roughness. In this study, a series of heavy rainfall slope surface confluence tests under different slopes and vegetation coverage were carried out, a vegetation coverage factor, C, which was introduced, a statistical analysis method was used, and the vegetation coverage index was fitted. The results showed that the types of vegetation have a certain influence on the flow concentration time of slope, and the flow confluence time under turf vegetation was larger than the flow confluence time under shrubs vegetation; especially in the slope of the larger slope, the relative impact is more significant; at the same time, the influence of vegetation coverage on the flow concentration time of slope was more significant; no matter the condition of turf or shrub, the slope confluence time increased obviously with the increase in vegetation coverage. The index of vegetation coverage factor C varied with the slope and rain intensity. In general, the index of vegetation coverage factor C increased with the decrease in slope and decreased with the increase in rain intensity. In regard to the turf vegetation coverage index, when the slope is 45° and 30°, the decreasing trend of the vegetation coverage index a0 is obvious with increasing rainfall intensity. When the slope is 15°, the vegetation coverage index a0 also decreases with increasing rainfall intensity. When the slope is 5°, the vegetation coverage index a0 basically has no change. In regard to the shrubs vegetation coverage index, when the slope is 45° and 30°, the decreasing trend of the vegetation coverage index a0 is obvious with increasing rainfall intensity. When the slope is 15°, the vegetation coverage index a0 also decreases with increasing rainfall intensity. When the slope is 5°, the vegetation coverage index a0 basically has no change.

  相似文献   

6.
The on-site observations, monitoring data, and results of back analyses of failures showed that large-scale failures occurred along both the interconnected sliding surfaces, consisting of (a) discontinuities in the dacites and the contact zone and (b) the circular surfaces through the weathered soil-like dacites at the Cakmakkaya and Damar open pit mines. Surface water infiltration through the weathered soil-like material after a short duration of rainfall contributed to the circular-shaped failures. After a heavy rainy period, an increase in the groundwater table above the contact zone played a major role in the initiation of bi-planar wedge failures. In addition, the stability of the slopes is likely to have been controlled by the orientation of this zone. The results of back analyses indicated that the shear strengths of the soil-like materials in the weathered dacites and the contact zone had reduced to their residual values at the time of initial sliding. The flattening of the slope angles with an effective surface drainage and long-term monitoring of the groundwater level is proposed as the most suitable remedial measure.  相似文献   

7.
The mineralogy and geochemistry of the massive pyrite-pyrrhotite mineralization, which contains minor magnetite, sphalerite and galena, the weathered profile and surface gossan at Mugga Mugga in Western Australia have been examined. Reactions between amphibolite wall rocks and acid waters from the oxidation of the iron sulfides have resulted in distinct mineralogical zonation of the weathered profile which is further modified near the surface by lateritization. At the base of the weathered zone an opaline chert (Opal-CT) has been precipitated from fluctuations of the water table. A gossanous zone from 25.14–68.80 m with boxworks after massive pyrite is modified by abundant kaolinite, dickite and an alunite-type mineral derived from amphibolite wall rocks, while above 25.14 m both plinthite and mottled clay zones of a laterite profile are evident. Some characteristics of a mature gossan profile – sulfate-phosphate-arsenate near the base, a carbonate zone higher in the profile, and an oxide zone near the surface – overprint the gross zonation.At the interface between sulfide and weathered rock Mg, Ca, K, S, Zn, Cd, Hg, Ba are depleted, As, Sb, Mo, Cr and V contents increase and in the weathered zone, SiO2, TiO2, P2O5, SO3, Pb, Zn, Hg, Sb, Co, Ni, W, Ba, Sr and Zr decrease up the profile whilst Al2O3, Fe2O3, CO2, Cu and As increase. Of the elements associated with the massive pyrite (Pb, Zn, Cu, Ag, As, Cd, Hg, Sb, Co, Ni) anomalous concentrations of Pb, Cu, Ag, As and Sb occur in the surface gossan despite the possibility of complete leaching by highly acidic solutions. These anomalies are similar to those found in gossans over pyrite mineralization elsewhere in the Yilgarn Block.  相似文献   

8.
王继成  俞建霖  龚晓南  马世国 《岩土力学》2014,35(11):3157-3162
对于大面积浅层风化土边坡,当下部含有浅水位或不透水基岩层时大降雨将导致下部气体被封闭。随着湿润峰的下移,气压不断增大。封闭气压力不仅降低了雨水在边坡土体的入渗率,而且对边坡的稳定有显著影响。通过分析封闭气压力的形成和相关理论,提出取 大小的气压力头来研究边坡的稳定性（Hc为一水头值,与土体孔隙尺寸分布有关; hd为土体进气值水头）。结合非饱和土的Mohr-Coulomb破坏准则和极限平衡法,将封闭气压力引入到边坡的稳定分析中,建立了考虑气压力影响下的稳定分析模型。与传统的不考虑气压力的稳定分析方法作对比,提出了气压力影响率概念。研究表明,封闭气压力显著降低了边坡的安全系数,传统的无限边坡稳定计算方法偏于危险。研究结果对无限边坡的强降雨安全预报具有较好的指导作用。  相似文献   

9.
 Several cases of instability of cut slopes along major highways in Jordan were reviewed in this study, in some detail. Emphasis was placed on the Amman-Irbid highway, but some cases along the Na'ur-Dead Sea highway were also reviewed, with the aim of establishing a wider database of case-studies and examining all possible mechanisms and factors influencing stability. The study showed that major cut slope failures were caused by the presence of weak cohesive layers (mainly clayey marl) interbedded within mostly stronger formations, in addition to the steep cutting angles and unfavorable dip of strata combined with relatively high piezometric surface brought about by poor surface and subsurface drainage. No remedies were implemented to stabilize major cut slope failures (at km 39+200, 44+300, and 56+400) along the Irbid-Jerash-Amman highway. The three major cut slope failures require extensive remedial work and probably advanced geotechnology, which is expected to be expensive. To investigate the influence of various parameters on slope stability, several analyses were performed in addition to back analyses to determine shear strength parameters; parametric sensitivity studies were also performed on some cases. Data was obtained from previous investigations by local and international firms and were screened and modified where needed before being used in stability analyses. Considerable difference between back analysis and test result values for shear strength parameters were observed in many cases. Failure surfaces and mechanisms were accurately depicted in most cases, allowing back analyses to be performed with considerable confidence. The effective residual shear strength parameters for clayey marl needed for stability analysis were found to be: c r ′=5–18 kPa, and φ r ′=13°–18°. The relation between total annual rainfall and occurrence of landslides was investigated; it was shown that all landslides occurred in years of very high rainfall, with values always exceeding 400 mm. The probability of exceeding the average total annual rainfall was found to be approximately 0.42 for the three gauging stations considered. Received: 28 October 1996 · Accepted: 23 September 1997  相似文献   

10.
The section of about 12 km of National highway 222 passing through the Malshej Ghat experience frequent slope failure due to complex geological condition, heavy rainfall and slope geometry. The area is part of Western Ghat Deccan trap and slope masses are made of basalt and its weathered crust (debris/soil). The soil slope failure problem mainly occur in rainy seasons due to induced pore water pressure and reduced strength of the slope mass. The present study has been carried out to investigate the slope forming material and assess the stability of soil slopes by numerical approach. For the identification of the vulnerable zones, field study has been carried out and five vulnerable soil slopes identified namely MGS1, MGS2, MGS3, MGS4 and MGS5 on the basis of degree of weathering and slope geometry. The laboratory experiments were carried out to determine the strength properties of the geomaterials. All the input variables acquired from the field and laboratory experiments have been used for numerical simulation, which was performed with the help of limit equilibrium method (LEM) and finite element method (FEM). Numerical analysis provides understanding of the slope behaviour and illustrates that MGS1 and MGS3 are stable slopes, MGS2 and MGS4 are critically stable, whereas, slope MGS5 is unstable. This study recommend the protection of soil slopes and suggest that more detailed investigation is required for long term remedial measures to prevent risk of damage in Malshej Ghat.  相似文献   

11.
The Qianjiangping landslide is a large planar rock slide which occurred in July 14, 2003 shortly after the water level reached 135 m in the Three Gorges Reservoir, China. The landslide destroyed 4 factories and 129 houses, took 24 lives, and made 1,200 people homeless. Field investigation shows that the contributing factors for the landslide are the geological structure of the slope, the previous surface of rupture, the water level rise, and continuous rainfall. In order to reveal the mechanism and failure process of the landslide, numerical simulation was conducted on Qianjiangping slope before sliding. Based on the characteristics and the engineering conditions of the landslide, the topography and the geological profiles of Qianjiangping slope before sliding is reconstructed. The seepage field of Qianjiangping slope before sliding was simulated with the Geostudio software. The results show that ground water table rises and bends to the slope during the rise of water level, and the slope surface becomes partially saturated within the period of continuous rainfall. Using the ground water table obtained above, the failure process of Qianjiangping slope is simulated with the Flac3D software. The results demonstrate that the shear strain increment, displacement, and shear failure area of the slope increased greatly after the water level rose and continuous rained, and the landslide was triggered by the combined effect both of water level rise and continuous rainfall. The development of shear strain increment, displacement, and shear failure area of the slope shows that the landslide was retrogressive in the lower part of the slope and progressive in the upper part of the slope.  相似文献   

12.
《Geodinamica Acta》2013,26(1-3):49-64
The astronomical and geodetic observatory OCA, located on the karst plateau of Calern (Caussols, France), has been monitoring earth deformation for several years. Two medium baseline tiltmeters have been installed in a shaft in 2007, along with classical hydrogeological monitoring tools in order to investigate the relationship between current karst deformation and hydrology. Dye tests have shown that the plateau is drained towards the East, to the spring of Bramafam, except for its Western third. Karst tilting, as recorded by the tiltmeters, is linked to rainfall events. These instruments bring additional information to characterize different reservoirs: the deep karst aquifer of Bramafan with high amplitude oscillations of its water table, up to 100 m, the perched aquifer of Moustiques shaft whose response is attenuated, and several slope aquifers with reduced oscillations (Fontaniers, Castel Bon Pré).

Tilt deformation reaches 8 μad with a definite orientation between N90°E and N100°E. The best correlation between hydrology and tilts is observed for the deep aquifers. If the first autumn rainfall is ineffective on tilt, it recharges the epikarst and refills the reserves. The winter rains cause the water to flush towards the eastern deep aquifer and provokes a quick tilting of the plateau. Finally, the long term variations in tilt and water table show a very good correlation.

The relationship between current hydrological deformations and tectonics is also analyzed; broken and shifted speleothems in the shafts indicate a general shift of the plateau towards the south.  相似文献   

13.
张晨阳  张明  张泰丽  孙强  杨龙 《岩土力学》2018,39(7):2617-2625
岩脉侵入是一种普遍的地质现象,侵入岩脉及其风化壳对斜坡的渗流场和稳定性具有重要影响,但目前国内外在该方面的研究鲜见报道。我国东南沿海约50×104 km2的白垩系火山岩地层中广泛分布侵入岩脉及其风化壳,改变了该地区残积土斜坡的失稳机制。以浙江省文成县中林滑坡为对象,研究花岗岩脉风化壳对其渗流场和稳定性的影响。中林滑坡主要由凝灰岩及其残积土组成,后部有侵入的花岗岩脉及其残积土,利用室内土柱试验获取降雨作用下两种残积土渗透性质的差异,利用不同含水率下的直剪试验获取非饱和抗剪强度参数;利用Geo-studio软件中的Seep/W模块反演土柱降雨试验,获取两种土体的非饱和渗透参数;接着将上述参数应用于中林滑坡的渗流场模拟,获取降雨入渗下坡体的渗流场;将渗流场耦合到坡体稳定性计算中,获取了坡体的稳定性变化曲线及最危险滑面。结果表明,降雨通过侵入岩脉风化壳快速入渗,并顺着基覆面向凝灰岩残积土区侧向渗流,导致侵入区与原始斜坡的交界处以及基覆面附近的地下水位快速升高,孔隙水压力迅速增大,斜坡在该位置最易变形破坏,且失稳深度远大于普通的浅层残积土斜坡,可达6～10 m。该研究成果可为东南沿海地区有岩脉侵入的残积土斜坡的稳定性评价与防治设计提供理论依据。  相似文献   

14.
蒋泽锋  朱大勇 《岩土力学》2016,37(Z2):25-34
降雨持时较长且雨强较大时,雨水的入渗不仅会增大孔隙水压力,且易使张裂缝充水形成静水压力,对边坡稳定不利。结合降雨条件下饱和-非饱和渗流分析,考虑降雨过程中的瞬态孔隙水压力场与瞬态强度场,并同时考虑张裂缝充水时的静水压力,对边坡临界滑动场法进行改进,提出降雨条件下具有张裂缝边坡临界滑动场数值模拟方法,且对其进行了验证。将该方法用于一个典型均质黏土边坡算例,结果表明,（1）文中方法可考虑张裂缝具体位置、深度及其充水状态下对边坡稳定性的影响,并能搜索出任意形状危险滑面,计算结果合理可靠;（2）降雨条件下张裂缝中静水压力对边坡稳定性及滑面形状有较大影响;（3）降雨条件下张裂缝位置对边坡稳定有较大影响,距坡肩越近,张裂缝对边坡稳定性影响越大;（4）张裂缝处在最不利位置且充水时存在一个最不利深度。  相似文献   

15.
辛鹏  吴树仁  石菊松  王涛  石玲 《地质论评》2015,61(3):485-493
降雨诱发的浅层黄土泥流规模小、流速快、冲击力强、发育范围广、难以防御、致灾频率高,近两年造成了大量人员伤亡,急需开展其形成机制与强度的研究。黄土物质组成与水敏性、坡体形态对降雨入渗—积水的响应、黄土斜坡对降水入渗的力学响应机制、富水黄土粘滞性流动特性是制约浅层黄土泥流形成的四种主要因素,分析这四种因素的对浅层黄土泥流形成的制约作用需解决斜坡降雨入渗的水文过程、非饱和土的力学效应及水土耦合的机制等前沿问题。本文对影响泥流形成的各因素研究的最新进展进行了综述,同时讨论了研究中的核心问题,并提出了相应的对策与方案,认为可从三方面开展研究:(1)定量描述泥流体积扩容特征,建立浅层黄土泥流启动与流动模式;(2)分析泥流与原状黄土物质成分、组成结构差异,开展黄土非饱和增湿力学变形试验,监测0°~60°单面坡与坡肩平缓斜坡的降雨入渗过程,研究坡体形态对雨水汇聚、入渗及基质吸力变化的控制特征,揭示泥流流体运动过程中水土响应机制;(3)对浅层黄土泥流物理力学模型进行解析,讨论泥流流动能量转化特征,建立降雨诱发泥流灾害的强度计算模型,为降雨泥流灾害危险性定量计算提供理论支撑。  相似文献   

16.
Rainfall has been considered the cause of the majority of slope failures and landslides that happened in regions experiencing high seasonal rainfalls. The mechanism of the failures was mainly due to the lost of matric suction of soils by rainwater. This paper presents the results of a laboratory model study on the effect of slope angle and surface cover on water infiltration into soil and soil matric suction. A field infiltration test is carried out for comparison. A parametric study is also done to examine the effect of permeability ratio, development of perched water table and rainfall intensity on the factor of safety against instability of a soil slope. Results of the model study show that different surface covers on slopes have an effect on the water infiltration. Generally the covered surface (grass or geosynthetic net) has a lower infiltration rate compared with the bare (no cover) surface. On the effect of slope angle, it was observed that water infiltration decrease with increase in the slope steepness. With regards to the movement of the wetting front, it appears that water infiltration is more at the toe compared with the top of the model slope. Based on the parametric study, it is found factor of safety of the slope against instability drops for slope with higher ratio of permeability for the permeable and impermeable stratum. As the perched water table is formed, the factor of safety decreased. The rainfall intensity also has a marked effect on the slope factor of safety. The higher the intensity of the rainfall, the higher is the infiltration rate into the soil, hence the lower is the factor of safety against slope instability.  相似文献   

17.
Soil hydraulic properties such as soil infiltration rate and hydraulic conductivity are closely linked to runoff generation and infiltration processes but little is known about them on karst hillslopes. The objectives of this paper were to investigate the change in soil stable infiltration rate (q s) and near-saturated hydraulic conductivity (K ns) in different slope positions and to understand their relationship with rock fragment content and soil texture within the topsoil in subtropical karst regions of southwest China. Tension infiltrometers (20 cm in diameter) were used to measure q s and K ns at pressure head of −20 mm on hillslopes 1 (a disintegrated landslide failure) and 2 (an avalanche slope). The change of q s and K ns was great and they mostly had a moderate variability with coefficient of variations (CV) between 0.1 and 1.0 in the different slope positions. On average, q s ranged from 0.43 to 4.25 mm/min and K ns varied from 0.75 to 11.00 mm/min. These rates exceed those of most natural rainfall events, confirming that overland flow is rare on karst hillslopes. From bottom to top, q s and K ns had a decrease–increase–decrease trend due to the presence of large rock outcrops (>2 m in height) on hillslope 1 but had an increasing trend on hillslope 2 with less complex landform. They tended to increase with increase in total rock fragment content (5–250 mm) within the topsoil as well as slope gradient on both hillslopes. Pearson correlation analysis suggested that higher coarse pebble (20–75 mm), cobble (75–250 mm), and sand (2–0.05 mm) contents as well as total rock fragment content could significantly facilitate water infiltration into soils, but higher clay (<0.002 mm) content could restrict water movement. This result indicated that rock fragment, sand, and clay contents may remarkably affect water flow in the topsoil layers, and should be considered in hydrological modeling on karst hillslopes in subtropical regions.  相似文献   

18.
Groundwater mounds and hinge lines are important features related to the interaction of groundwater and lakes. In contrast to the transient formation of groundwater mounds, numerical simulations indicate that permanent groundwater mounds form between closely spaced lakes as the natural consequence of adding two net sinks to a groundwater flow system. The location of the groundwater mound and the position of the hinge lines between the two lakes are intimately related. As the position of the mound changes there is a corresponding shift in the position of the hinge line. This results in a change in the ratio of groundwater inflow to outflow (Qi/Qo) for the lake. The response of the lake is an increase or decrease in the lake level. Our simulations indicate that the movement of the hinge line in a natural system is a consequence of the dynamic interrelationships between recharge, the slope of the water table upgradient and downgradient of the lake, and the loss of water from the lake by evaporation. The extent of the seasonal movement of the hinge line will vary from one year to the next depending on local changes in the magnitude of the hydrologic variables. Electronic Publication  相似文献   

19.
Predictions of rainfall-induced fast-moving mass flow and/or debris flows require better knowledge of the mechanism controlling the debris discharge of slopes in debris source areas. A series of rainfall tests on 0.32 m-deep, 0.7 m-high, 1.35 m-wide sandy slopes resting on a bi-linear impermeable rigid base was performed. Soil moisture content and solid discharge measurements were performed to gain insights into the rainfall-induced retrogressive slope failure. The solid (or debris) discharge is a result of the wash-out of the fluidized slope toe by the interflow along the soil–bedrock interface. Characteristics of the failure process for the slopes are represented by mass wasting curves or ‘solid discharge (Qs) vs. time (t)’ curves which are functions of the rainfall intensity and/or the cumulative rainfall. The mass wasting curves have inflection points representing transitions from minor toe failures into remarkable retrogressive failures. The first inflection point of the soil moisture (ω) vs. t curve measured at the soil–bedrock interface signaling the arrival of the descending ‘wet front’, may serve as a precursor for predicting the onset of an abrupt solid discharge induced by shallow slope failures. The time of peak water content measured at the soil–bedrock interface may approximate the time of 5% total solid volume discharge. Up to the time of 5% of total slope volume discharge, a fully saturated state (Sr  100%) was never observed at the 0.2 m-below-surface zone; however, it was observed along the soil–bedrock interface at near-toe zone of the slope, regardless of the intensity of rainfall investigated. Retrogressive failures were essentially associated with nonuniformly distributed water content in the slope. For both the 0.2 m-below-surface zone and the soil–bedrock interface, a more uniform distribution of Sr along the full height of the slope was found for slopes subjected to high rainfall intensities of 47 and 65 mm/h than that for the slope subjected to a low rainfall intensity of 23 mm/h. At the inflection point of the Qs vs. t curve and 5% of total solid volume discharge, values of Sr at a certain distance from the toe for the soil–bedrock interface were higher than those measured at the same distance from the toe for the 0.2 m-below-surface zone, indicating the effect of infiltration-induced interflow along the soil–bedrock interface and its effects on the fluidization of the slope toe and the retrogressive failure of the slope.  相似文献   

20.
Well hydrographs from 275 piezometers between 1998 and 2001 in the southeastern parts of peninsular India were used in this study. The area has a monsoon-type climate. Hard rocks cover 85% of the area. The form (shape) of the hydrograph depends upon (1) climatic and hydrogeologic parameters and (2) the scale of the graph. Therefore, hydrographs are drawn to a defined and standardised scale, which allows comparison of hydrographs and helps in bringing out reasons for different forms of the hydrographs. Hydrographs can be divided into seasonal segments and the slope of each segment then used as the basic element of a classification scheme. Slopes are classed as flat (inclination <20°), obtuse (between 20 and 45°), acute (45 and 80°), right angled (80 and 90°) and homoclinal (segments of hydrographs are either rising or falling during one complete water year). Hydrographs are assigned names that are a combination of these classes and begin with the rising segment, such as acute-obtuse. Seventy-six percent of segments were homoclinal-falling in 1999, which had a poor monsoon. Flat segments constitute 27% of all segments in confined Mesozoic aquifer systems. Water table fluctuations suggest an approximate recharge of 120 to 180 mm per annum constituting 18% of the annual precipitation. Cumulative rainfall required to affect a rise in water table is between 45 to 200 mm and lag time varies from 30 minutes to 200 rainy days, which suggests that moisture in the vadose zone holds a part of the annual replenishment for these aquifers.  相似文献   

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