Assessment of the Efficiency of the Grout Curtain and Control of the Seepage at Nosice Dam Using Numerical Modeling

Integrated certainty and uncertainty evaluation approach for seepage control effectiveness of a gravity dam

Seepage control is a prerequisite for hydrocarbon storage in unlined rock caverns (URCs) where the seepage of stored products to the surrounding host rock and groundwater can cause serious environmental and financial problems. Practically seepage control is performed by permeability and hydrodynamic control methods. This paper employs numerical modelling and genetic programming (GP) for the purpose of seepage prediction and control method determination for the crude oil storage URCs based on the effective parameters including hydrogeologic characteristic of the rock and physicochemical properties of the hydrocarbons. Several levels for each parameter were considered and all the possible scenarios were modelled numerically for the two-phase mixture model formulation. The corresponding seepage values were evaluated to be used as genetic programming data base to generate representative equations for the hydrocarbon seepage value. The coefficients of determination (R2) and relative percent errors of the proposed equations show their ability in the seepage prediction and permeability or hydrodynamic control method determination and design. The results can be used for crude oil storage URCs worldwide.

Modeling dam deformation in the early stage of internal seepage erosion – Application to the Teton Dam, Idaho, before the 1976 incident

Grout curtains have been widely used in the United States in order to mitigate or control seepage under and around a civil works structures throughout the 20th Century. Using a variety of methods, the purpose of a grout curtain is to provide a reduction in the seepage across the installation. Reduction in seepage can be particularly important in karst geology where the presence of solution widened openings in the rock that occur along bedding, joints and other features in the rock can sometimes be quite large. These features may be partially or completely infilled with clay and other materials. Grouting operations may not fully remove infilled materials and can leave weak points in the curtain that are exploited by the groundwater flow over time. Even with a well-developed ground investigation, it is impossible to completely define all the water pathways in the karst rock. Fortunately, modern computer codes supply a means to model the effectiveness of a grout curtain and to explore the consequences of a breach of that curtain in the subsurface. For this study, a lock excavation problem was set up in RS2 using the geological context from a lock excavation project that reflects the karst issues that have been encountered in multiple lock and dam projects in Tennessee and Kentucky. Two known potential breach points were established, and the effects were modeled. The results led to insights into the size of features that could cause constructability issues. In addition, the results are used to target specific zone of interest with an instrumentation and monitoring program.

The Pidekso Dam is one of the major dams in the Central Java, situated in Wonogiri Indonesia. The stability analysis of the dam is required due to this dam is planned for national water and food security program covering the irrigation area of $$15 \times 10^6 \,{\text{m}}^2$$ , increasing the planting intensity from $$20 \times 10^6\,{\text{m}}^2$$ to $$36 \times 10^6 \,{\text{m}}^2$$ and as a source of water around 300 L/s for Wonogiri, Sukoharjo, Solo and their surroundings. The control is needed for the safety of the dam from seepage and piping. Excessive seepage can cause piping and lead to dam failure. Seepage control is carried out by 3 alternatives, extended curtain grouting, cut off wall and upstream blanket respectively. Each alternative is divided into 4 models: (1) original length (L), (2) 2/3L, (3) 1/3L and (4) 2/3L with doubles in the upstream and downstream of the dam. The result indicates that, the installation curtain grouting with model 1 is the most effective alternative to reduce seepage up to 67.82% of dams.

The Huilong pumped-storage power station is located in the Henan Province of China, in which there is an underground power plant with an installed capacity of 120 MW, an upper reservoir with a volume of 1.01 × 106 m3 and an upper dam of 54 m height. The upper reservoir near the local watershed is a small catchment basin with little runoff. The rock masses in the site of the upper reservoir are granite with many faults and numerous fractures, and are strongly weathered near the earth’s surface, which leads to obvious permeability of the rock masses in the directions of depth and level. Due to the heterogeneity as well as anisotropy of permeability of the rock masses, especially the strong permeability of the faults within, the leakage of the reservoir becomes very complex and is a problem concerned with engineering construction. If no impervious system exists, the largest volumetric rate of reservoir leakage is up to 17 × 103 m3/day, but the allowable leakage is only 2.0 × 103 m3/day. So an impervious system should be taken to control the reservoir leakage. Some treatments, e.g., concrete coverage on the bedrock of the reservoir, curtain grouting around the reservoir, grouting along faults within the reservoir, and shotcrete coverage on the bedrock of the reservoir, are considered in the design. If concrete coverage is laid only on the faults and both of their sides to prevent water seepage from flowing directly, the water in reservoir can still flow in the faults indirectly, through the weathering zones of rocks. Although the curtain grouting around the reservoir is a barrier to seepage flow, the leakage can also occur in deep rocks. Finding a more effective and economical seepage control measure system is critical to the reservoir design, and is thus a main goal of this paper. we used numerical simulation with a 3D flow model of a dual fracture system to analyze the patterns of 3D seepage flow in the rock masses according to the geological conditions in the reservoir area. For this purpose, the seepage field and seepage pattern are discussed in detail by comparing the leakage quantities of the four seepage control schemes. The scheme that combines concrete coverage on faults and shotcrete coverage on bedrock is optimal, and is suggested in the Huilong Power Station engineering design .

The tunnel passing through the loess stratum with high moisture content can easily lead to the seepage and mud burst accident and the instability and collapse of the tunnel face. Under the condition of high groundwater level, the seepage situation is more complicated, it is difficult to control the groundwater seepage, and the excavation progress is very slow. In order to solve the various disasters when the tunnel passes through the water-rich loess stratum, taking a water-rich loess tunnel in Gansu Province as an example, the method of comprehensive prevention and control of seepage and mud inrushing disaster by basement grouting and curtain grouting was introduced. Firstly, the basic situation of the Yulinzi tunnel is introduced, including site conditions, seepage collapse accident, and its cause analysis. On this basis, the design and construction methods of basement grouting and curtain grouting are introduced, and the effect of grouting reinforcement is evaluated in detail through on-site monitoring. The results show that the basement grouting and curtain grouting can effectively control the deformation of surrounding rock and the surface settlement, the decrease of the deformation of surrounding rock can reach 36%-71%, and the decrease of the surface settlement can reach 55%. After grouting, the deformation of the surface and surrounding rock can be controlled within the allowable value in the code. Grouting plus solid can effectively block the seepage of groundwater and prevent the surface cracks, water gushing, mud gushing, collapse, and other disasters in the process of tunnel excavation. It can be seen that the basement grouting combined with curtain grouting technology has a good reinforcement effect, which has significant engineering value for quickly and efficiently passing through high moisture content loess strata.

Many field observations have led to speculation on the role of piping in embankment failures, landslides, and gully erosion. However, there has not been a consensus on the subsurface flow and erosion processes involved and inconsistent use of terms have exasperated the problem. One such piping process that has experienced a lot of field observations but very limited mechanistic experimental work involves flow through a discrete macropore or soil pipe. Questions exist as to the conditions under which preferential flow through soil pipes: result in internal erosion, stabilize hillslopes by acting as drains, result in hillslope instability by causing pressure buildups, result in ephemeral gully formation or reformation of filled-in gullies. The objective of this paper was to review discrepancies in terminology to better explain the piping processes and highlight the experimental work done to date on the specific processes of soil pipeflow and internal erosion. The studies reviewed include those that examined the process of slope stability as affected by the clogging of soil pipes, the process of gullies reforming due to mass failures caused by flow into discontinuous soil pipes, and the process of gully initiation by tunnel collapse due to pipes enlarging by internal erosion. In some of these studies the soil pipes were simulated with perforated tubes placed in the soil, while in other studies the soil pipes were formed out of the soil itself. Analytical solutions of the excess shear stress equation have been applied to experimental data of internal erosion of soil pipes in order to calculate critical shear stress and erodibility properties of soils. Numerical models have been applied to describe flow through soil pipes but incorporation of internal erosion into such models has proven complicated due to enlargement of the pipe with time as well as temporary clogging of soil pipes. These studies and modeling approaches will be described and a discussion will ensue that considers the gaps in our understanding of pipe flow and internal erosion processes and our ability to model these processes.

In 1996, a grout curtain was constructed in the Zhangmatun Iron Mine near Jinan City, China, which is subject to large groundwater inflows, to decrease the water volume rushing into the mine workings. However, water inflow has recently been increasing in the southwestern area through a seepage channel, which has resulted from the failure of the grout curtain. To understand how the seepage channel formed, the microseismic (MS) activities located in this area were studied and a numerical model was supplementarily used to analyze the damage zone. It is found that the seepage channel formation process is significantly affected by the distance between mining activities and the grout curtain. Mining activities periodically approached and retreated from the southwest grout curtain, causing periodically active and inactive microseismicity, and eventually the grout curtain failure. The damage zone in the grout curtain obtained from the numerical analysis coincides with the seepage channel, especially in the area where the distance between the grout curtain and excavation is less than 35 m. Therefore, the combination of MS monitoring and numerical analysis of damage zones can provide us with an overall understanding of the formation process and causes of the seepage channel.

In this research, numerical modelling has been conducted to expand on existing research on cut-off walls mainly done by, [2] and [8]. This study is aimed at examining a unique geometric alignment that accommodates ‘branches’ on either side of a vertical 12-metre-deep cut-off wall and investigates the subsequent effect on seepage (discharge) and uplift force within the foundation of the dam. From the study conducted it had been observed that seepage was reduced with the inclusion of these branches whilst the cut-off wall was located at the centre base of a concrete dam. Subsequent testing of altering the branches’ angle presented a further reduction in seepage through the soil strata, with the optimum angle being around the range of 60–70 degrees. Further experimentation had shown that altering the position at two other distinct locations (dam’s heel and toe) has had a significant reduction in seepage with the heel being the most effective at reducing it. Uplift pressure has been evaluated to show that the best position for minimal uplift force is at the heel of the dam.

The main objective of this work was to study the design rationale for the optimum grout curtain around the power cavern of the Rudbar Lorestan pumped storage power plant. This grout curtain will prevent water inflow into the power cavern after Rudbar Dam is impounded. This study was based on a combination of geotechnical investigations, geological investigations, and numerical modeling. The power cavern is located in the Dalan Formation, which consists of limestones and dolomite limestones. Geological features such as faults and major joints in limestones as well as the close proximity of the power cavern to the downstream reservoir increase the hazard associated with water inflow from the reservoir into the power cavern. Because of this close proximity, accurately estimating the water inflow into the cavern is an essential task. Three exploratory boreholes were drilled near the power cavern, and permeability tests (Lugeon tests) were conducted in all boreholes. Records at the boreholes were employed as the main source of data for seepage calculations, and it was determined that the permeability of the limestones is approximately 1.25 × 10−3 m/s. This study used a finite element model to estimate groundwater inflow into the power cavern after the downstream reservoir is impounded. Results show that without a grout curtain, water would seep into the cavern at a rate of about 0.8–1 m3/s, which would make it difficult to operate the power plant. Accounting for geological conditions such as the Rudbar Fault and fractured limestones, as well as the limitations on construction, a grout curtain was designed. The design calls for a curtain that is about 50 m from the power cavern and extends from 1,735 m.a.s.l. to 10 m below the cavern. Modeling the effect of the grout curtain around the cavern with the finite element method showed that the seepage would decrease to a low rate of 0.1 m3/s with the installation of the curtain.

Internal erosion is susceptible to occur in conditions where there are cracks or pre-formed cavities at the interface between the dam foundation and embankment. The initiation of internal erosion is related to the critical gradient (Ic ) and hydraulic gradient (Ixy ) at a certain position. The addition of repair materials in foundation improvement will change the total head, especially on the dam foundation, so the value of the hydraulic gradient will also change simultaneously from upstream to downstream. This study examines the value of the hydraulic gradient (Ixy ) at certain points on the dam foundation under the condition of foundation with and without improvement. Several scenarios were simulated using Geostudio Seep/W software to get an estimated value of the hydraulic gradient. The upstream blanket foundation improvement method increases the hydraulic gradient in the upstream zone when compared to the curtain grouting method, thereby increasing the potential for internal erosion in a related area. Increasing the depth of curtain grouting from 25 m to 35 m does not significantly reduce the value of the hydraulic gradient in the dam foundation. Research results can be used for analysis to improve design and construction, and as a reference for similar dams.

Evaluation of groundwater flow through a high rockfill dam foundation in karst area in response to reservoir impoundment

Haig Mill Dam was constructed in 1993 and 1994 for water supply in the Dalton area of northwest Georgia. The 17m (55 ft.) high embankment created a ½ million m2 (110 acre) reservoir. Foundations underlying the central portion of the reservoir site consist of upper Ordovician highly karstic limestones of the Valley and Ridge fold and thrust belt. The initial design of the foundation treatment for the embankment was to include construction of a 23m (75 ft.) deep triple line grout curtain within the karstic limestones. During construction of the grout curtain it was found that the grout holes collapsed through the karst voids when they were drilled with a high powered percussion rig. This made it impossible to insert packers and to use conventional upstage grouting techniques. This paper describes the nature of the karstic rock encountered, the difficulties encountered and techniques used during the grouting program, the results obtained from before and after packer tests in two test grout sections and the amendments that were made to the design of the dam during construction to accommodate the karst conditions. Grouting of the karstic limestones was found to be highly variable and consistent closure of the curtain through tertiary and quaternary grout holes was difficult to achieve. During construction, additional parametric seepage analyses were completed based on the encountered site conditions. As a result of these analyses, modifications were made in the overall seepage control system design of the dam. The final configuration of the embankment consists of an upstream clay blanket, a 6.7m (22 ft.) deep grout curtain beneath a core trench keyed into rock, and a downstream blanket drain and pressure relief trench system. The seepage control system has been designed to reduce reservoir water losses, minimize seepage gradients through the karstic foundations, relieve potential pressures within the downstream portions of the embankment, and control piping of fines through the embankment and underlying rock.

Considering the material non-uniformity and time-varying mechanics performance in seepage development of soil levee, the particle flow code (PFC) method and the fast Lagrangian analysis of continua (FLAC) approach are combined to implement the numerical analysis and evaluation for seepage behavior and its control effect in soil levee engineering. Based on the coupling characteristics of particle and water in soil levee, a PFC-based numerical simulation method of seepage development is introduced. To improve the accuracy and efficiency of above method, the soil particle generation technology according to soil grading curve is presented. An approach, which refers to geotechnical centrifuge test and similarity principle, is developed to build the scale model of prototype levee. The calculation restriction of PFC method, which is integrated into FLAC tool, is broken. Lastly, the numerical simulation for seepage behavior of one actual levee engineering with seepage control measures is implemented by the proposed method. The seepage control mechanisms of selected measures are analyzed. The macroscopic and mesoscopic effects of selected measures on different levee foundations are evaluated. It is indicated that the seepage control effect can be described more finely with the average coordination number and the vertical effective stress which are obtained by the proposed numerical method.