Groundwater Slope Research Articles

Influence Mechanism of Water Level Variation on Deformation of Steep and Toppling Bedding Rock Slope

The construction of major hydropower projects globally is challenged by slope deformation in reservoir areas. The deformation and failure mechanisms of large rock slopes are complex and poorly understood, making prevention and management extremely challenging. In order to explore the influence mechanism of the water level variation on the deformation of steep toppling bedding rock slopes, this paper takes the right bank slope near the dam area of the Longtou Hydropower Station as an example, and field investigations, deformation monitoring, physical simulation tests and numerical analyses are carried out. It is found that the slope deformation response is obvious under the influence of the reservoir water level variation, which is mainly reflected in the change in the slope groundwater level, rock mechanical parameters and seepage field in the slope body. The toe of the slope produces plastic deformation and maximum displacement. With the increase in the reservoir water level, the plastic zone expands and the displacement increases, which leads to the intensification of the slope deformation. This paper puts forward that the deformation and failure modes of the steep and toppling bedding rock slope caused by water level variation are due to shear dislocation, bending deformation and toppling fracture. This study reveals the influence mechanism of the water level variation on the deformation of steep and toppling bedding rock slopes, which can provide theoretical support for the construction of major hydropower projects.

Intelligent Control of Groundwater in Slopes with Deep Reinforcement Learning.

The occurrence of landslides has been increasing in recent years due to intense and prolonged rainfall events. Lowering the groundwater in natural and man-made slopes can help to mitigate the hazards. Subsurface drainage systems equipped with pumps have traditionally been regarded as a temporary remedy for lowering the groundwater in geosystems, whereas long-term usage of pumping-based techniques is uncommon due to the associated high operational costs in labor and energy. This study investigates the intelligent control of groundwater in slopes enabled by deep reinforcement learning (DRL), a subfield of machine learning for automated decision-making. The purpose is to develop an autonomous geosystem that can minimize the operating cost and enhance the system's safety without introducing human errors and interventions. To prove the concept, a seepage analysis model was implemented using a partial differential equation solver, FEniCS, to simulate the geosystem (i.e., a slope equipped with a pump and subjected to rainfall events). A Deep Q-Network (i.e., a DRL learning agent) was trained to learn the optimal control policy for regulating the pump's flow rate. The objective is to enable intermittent control of the pump's flow rate (i.e., 0%, 25%, 50%, 75%, and 100% of the pumping capacity) to keep the groundwater close to the target level during rainfall events and consequently help to prevent slope failure. A comparison of the results with traditional proportional-integral-derivative-controlled and uncontrolled water tables showed that the geosystem integrated with DRL can dynamically adapt its response to diverse weather events by adjusting the pump's flow rate and improve the adopted control policy by gaining more experience over time. In addition, it was observed that the DRL control helped to mitigate slope failure during rainfall events.

Groundwater Vulnerability towards Pollution in Area Around the Piyungan Landfill, Bantul Regency, D. I. Yogyakarta

The Piyungan landfill is located in Bantul Regency, Daerah Istimewa Yogyakarta, still uses an open dumping system. The open dumping system produced more quantity of leachate from other systems. Leachate spreads to the ground and seeps into the ground to the groundwater surface. These conditions have an impact on the environment. This study aims to assess the groundwater vulnerability to leachate contamination in the area around the Piyungan landfill. The research method used is survey and mapping, and data analysis is carried out using the Le Grand method. Geographic Information System (GIS) is also used to visualize data into maps. The Le Grand method considers as many as 5 physical environmental parameters, including the groundwater depth, absorption above ground, aquifer permeability, groundwater slope, and horizontal distance of wells with pollutant sources. Next, scoring is carried out for each of these parameters, and then a groundwater vulnerability map is made using the overlay method. The results of the study were three classes of the potential vulnerability of groundwater pollutions. That were large pollution potential (may or may be polluted), medium pollution potential (maybe polluted but slightly), and small pollution potential (very difficult to pollute).

Assessment of Hydraulic Parameters and Protection Zones of Catchment Aquifers for Water Supply Network in Ndé Division, West-Cameroon (Central Africa)

Ndé Division in West-Cameroon is facing with water supply although many attempts of restoring existing SCANWATER facilities by Bangangté Municipality. In order to address the issue, we assess the exploitable pumping flow rate of catchment aquifers and its hydraulic properties by using Jacob and Theis method, and define protection zones with Hoffman and Lillich method. It emerges that the hydraulic conductivity of aquifer is in the order of 10-4 m/sec, transmissivity varies from 10-4 to 10-6 m2/sec. Aquifer pumping flow rate (Q) varies between 1.5 and 10.5 m3/h. In volcanic rocks, aquifer is more productive (4.5 ≤ Q ≤ 10.5 m3/h). Transfer time of pollutants to aquifer varies from 3 to 56 days depending on rock-types and groundwater slope (0.03 - 0.13 m/m). Furthermore, 113,624 m and 1123 m are radius to be implemented for a better protection of groundwater against any form of pollutant.

Estimating the dynamics of the groundwater in vegetated slopes based on the monitoring of streams

Rainfall is commonly considered to be responsible for landslides, but strictly, it is the groundwater recharged by rainfall that triggers slope failures. The dynamics of the groundwater in slopes is meaningful for assessing landslide hazard. Groundwater monitoring methods through boreholes or wells are effective but invasive, slow and expensive. In addition, these approaches are unsuitable for vast alpine environment prone to frequent landslides. To find an easy and inexpensive approach of estimating the dynamics of the groundwater in vegetated slopes, the response behavior of the stream flow to rainfall in the Touzhai valley (Southwestern China) is investigated based on in-situ monitoring. Combined with Complete Water Quality Analysis (CWQA) and a range of experiments (leaching test, in-situ infiltration and dye tracer infiltration), the source of the stream and its response mechanism to rainfall are determined. Some results are obtained: (1) the monitored stream flow fluctuates sensitively with the variation of rainfall without obvious hysteresis whether it is in the high- or low-water period; (2) the CWQA suggests that the stream water is derived from the slope groundwater rather than the direct rainfall or overland flow; (3) what leads to the stream flow rapid response is the macropore system (comprising of root–soil interstices, rotten root channels, inter-aggregate pores, worm pores and earth–gravel interstices) developed in the unsaturated zone of the slopes, which offers preferential conduits for rainfall infiltration. Therefore, monitoring streamflow rates can be an inexpensive and practical method to estimate the dynamics of groundwater in vegetated slopes, which, ulteriorly, provides the basis for diagnosing the stability of remote headwater slopes subject to failures. More than that, the alternative monitoring sites could be placed in inhabited valley bottoms or alluvial fans to avoid the absence of electric power and communication in uninhabited headwater catchments.

An improved siphon drainage method for slope stabilization

The siphon drainage is an effective measure for the slope groundwater control. However, for the traditional siphon drainage, limitations such as siphon lift restriction and poor reliability in longterm service prevent it from being widely used. In this study, an improved siphon drainage method with inclined borehole penetrating the deep part of the slope is proposed to overcome the limitations suffered by the traditional method. Through experimental research, theoretical analysis and engineering practice, the reliability and capability of the proposed method are investigated. The results demonstrate that with the inclined pipe the height difference between the control point of the groundwater level and the orifice can be controlled to be less than the height of the water column corresponding to the local atmospheric pressure. As a result, deep drainage can be achieved. In addition, by controlling the diameter of siphon drainage pipe not larger than 4 mm, a plug flow can be formed in the siphon pipe, which can prevent air accumulation in the siphon process and a continuous and effective siphon drainage is achieved. Through a practical project running smoothly since September 2013, it is found that the proposed method can effectively drain the groundwater deep in the slope and the maximum drawdown of groundwater level in boreholes can reach 8.5 m with an average drainage flow of 5.5 m3/d. The practical results also illustrate that 4 mm siphon pipe can be used to realize deep slope drainage and restart siphon automatically.

Anti-Sliding Stability Analysis of Saturated Rock Slope

Based on the assumption of the improved groundwater pressure distribution, the calculation expression of anti-sliding stability factor for typical water-saturated rock slope is deduced through limit equilibrium method. Considering the combined effect of slope overload, seismic load, anchoring effect, ice frost, slip surface drag force and slope groundwater pressure, the comparative analysis of typical rock slope sliding stability under waterless and saturated conditions shows that, the outflow joint blocking and the groundwater levels rising have obvious adverse effects on the anti-sliding stability of rock slope. Figures about the relationship of stability factors and geometric factors were drawn and the anti-sliding stability factor can be directly obtained from these figures. All would be the references for the similar engineering projects.

Use of stable water isotopes to assess sources and influences of slope groundwater on slope failure

This study employs stable oxygen and hydrogen isotopes as natural tracers to assess the headwater of a landslide next to a drainage divide and the importance of the slope's headwater in the study area. The study is undertaken near Wu-She Township in the mountains of central Taiwan. Because a reservoir is located on the other side of the divide, this study evaluates the relationship between the reservoir water and headwater of the landslide as well. Over a 1-year period, water samples from September 2008 to September 2009, including local precipitation (LP), Wu-She Reservoir's water (WSRW), slope groundwater (SGW), upper-reach stream water (USTW), and down-reach stream water (DSTW), were analysed for deuterium (δD) and oxygen (δ18O) stable isotopes. Results indicate that WSRW is the predominant component in SGW: approximately 70% of SGW originates from WSRW and 30% from LP based on a two end-member mass-balance mixing model for δ18O. The similar two end-member mixing model is also employed to assess the contributions of USTW and SGW to DSTW. Model results indicate that SGW is the major source of DSTW with a contribution of about 67%. Accordingly, about 47% of DSTW sources from the WSRW. In short, owing to reservoir leakage, WSRW contributes the greater part of both SGW and DSTW. Plentiful WSRW in SGW threatens the stability of the slope in the divide area. To avoid subsequent continuous slope failure, necessary mitigation steps are required. Copyright © 2011 John Wiley & Sons, Ltd.

Application of Geographic Information System (GIS)in Mapping Groundwater Quality in Uyo, Nigeria

In recent years there has been serious concern on the deteriorating groundwater quality due to the activities of man. Geographic Information System (GIS), a high performance computer based tool is playing a critical role in water resource management and pollution study. In this work, the GIS software was used to analyze the effects of various data layers (topographic slope, groundwater table variation, soil porosity and land use activities) on the distribution of groundwater pollution in the Nigerian city of Uyo. Spatial variability map of different groundwater quality parameters were generated using interpolation operation in the software. A good correlation exists between some of the pollution indicators (total dissolved solids, TDS and conductiveity, CN, 0.8; chloride and TDS, 0.17 as well as TDS and sulphate, 0.23). The results of spatial variability maps of different groundwater quality parameters indicate an increase in the percentages of pollution levels during the last five years. Cross operation was also used to explain the effects of various data layers viz. topographic slope, groundwater slope, depth to groundwater layer and land use activities on the distribution of groundwater pollution.

Identification of groundwater sources of a local-scale creep slope: Using environmental stable isotopes as tracers

Summary Water plays an important role for slope stability and typically consists of local precipitation (LP) and original slope groundwater (OSGW); high amount of the OSGW leads the slope groundwater (SGW) easily to exceed the critical level that causes slope failure in a heavy raining event. This study was to verify the source and significance of the OSGW for a creep slope adjoining a hydropower plant, northern Taiwan by an environmental stable isotope approach. Isotope results indicate that the source of the OSGW derived from leaking of the water-transporting system of the power plant; the leaking fraction in the SGW is as high as 70–80%. High leaking component in the SGW indicates that the leaking water rather than local precipitation is the crucial factor for the mass movement of the creep slope. Since the mass movement poses a potential threat to the hydropower plant safety, the most important measure for the remedial project is to perform a comprehensive check and repair the leak of the water-transporting system.

Numerical models for 2D free boundary analysis of groundwater in slopes stabilized by drain trenches

A numerical model for 2D free boundary analysis of groundwater in slopes stabilized by drain trenches has been developed. It consists of a front-tracking method (based on an original way of adapting the space derivatives), very effective in saving calculation time respect to classical fix-grid methods. The method analyses the trenches effect inside slopes in which the soils above the water table are partially saturated, for which a boundary can be recognized between the saturated domain (water table) and the unsaturated one (above the water table). In this case pore pressure lowering, due to trenches, can be analyzed considering the progressively reduction of the saturated domain. This approach efficiently solves the problem of fixing hydraulic boundary conditions on the sides of the trenches. Results have been compared with those obtained by a fix-grid method, observing difference less than 0.14%. Applying the method, the capability of drain trenches to control the effect of heavy rainfalls has been investigated, calculating (during the transient process of water table lowering) limit values of water recharge for which water table keeps on constant.

Using hydrogen, oxygen, and tritium isotopes to identify the hydrological factors contributing to landslides in a mountainous area, central Taiwan

Over a 1-year period, 343 samples, including precipitation, creek, pond, and groundwater, were collected from June 2003 to May 2004. Analyses were performed for stable oxygen and hydrogen isotope compositions. Selected samples were also analyzed for tritium. The goal was to identify possible hydrologic factors contributing to a severe landslide in the Li-Shan area, central Taiwan. The isotope characteristics indicate that groundwater from Fu-Shou-Shan farm located up-slope from the landslide area is a major source for slope groundwater, in addition to precipitation. The groundwater is mainly recharged by pond water at Fu-Shou-Shan farm. According to the calculation of a two-end member equation with δ18O, the contribution of farm groundwater to slope groundwater is significantly higher than that of precipitation, up to a factor of five. The estimated drainage efficiency of the existing system is only 23%. Draining off the slope groundwater in the up-slope region to decrease farm groundwater flow into the slope area is a feasible strategy to effectively reduce the risk of landslide.