Grout Curtain Research Articles

On the use of pore pressure measurements in safety reassessments of concrete dams founded on rock

In probabilistic stability analyses of concrete dams founded on rock, the uplift pressure is often a parameter of major importance. In previous literature, it has been suggested that assessing uplift with pore pressure measurements, instead of using empirical assumptions, could improve the calculated dam safety. This paper presents a coherent methodology to investigate whether incorporating pore pressure measurements has any impact on the calculated dam safety, based on Bayesian linear regression of pore pressure data in combination with series-system and the first-order reliability method. The study concludes that the probability of sliding failure is closely related to the probability of an extreme increase in uplift. Hence, measured uplift should only be incorporated while this probability remains sufficiently small, which requires proper programs both for uplift monitoring and for maintenance of drains and grout curtains.

Optimum depth of grout curtain around pumped storage power cavern based on geological conditions

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.

Geotechnical characteristics of Bakhtiary dam site, SW Iran: the highest double-curvature dam in the world

The Bakhtiary Hydropower Project with a 325 m high dam will be constructed on Bakhtiary River, in southwest Iran. The main dam has been designed as a double-curvature concrete structure which will be the highest one of its type in the world. Geologically, the dam site is located on siliceous limestone of the Sarvak Formation in the northwestern part of the folded Zagros. A large number of complicated geological structures in the study area, such as folding and duplex structure, faults, chevron folds, kink band zones as well as joint and fracture systems, raised concerns regarding the acceptability of the site for such a monumental dam. To create a comprehensive geotechnical model of the dam site and appurtenant structures, very extensive surface and subsurface investigations were carried out, including core drilling, water pressure testing, driving exploratory galleries for engineering geological mapping, a rock mass discontinuity survey and in situ rock mechanical tests. This research applies the results of the engineering geological and geotechnical investigations to define the geomechanical model of the dam site enabling options to be considered to achieve a safe dam design. The investigations show the rock mass of the dam site area is intersected by four main discontinuities namely, the bedding plane(s) of the rock mass and three major joint sets. Water pressure tests provide data about the permeability of the rock mass which is significantly dependant on the joint properties and the geological structures. These parameters, set the criteria for the design of the grout curtain at the dam foundation. The rock mass classification of the dam site was determined mainly based on the gallery survey and core logging using the rock mass rating, geological strength index (GSI) and Q system. Six classes of rock mass qualities were distinguished which show a fair to good rock mass at the dam foundation. From the plate load test results, a site-specific correlation was developed for estimating the modulus of deformation of the rock masses using GSI value. The estimated engineering geological and geotechnical parameters at the dam site are generally favorable and suitable for the safe design of the Bakhtiary arch dam with a height of 325 m.

Study on Parameters of Grouting Reinforced Circle for Water-Rich and Soft Fault Fracture Zone in Tunnel

Water-rich and soft fault fracture zone is the geologic disaster source of water and mud outbursts in tunnel while the curtain grouting is an effective management method. To determine appropriate parameters of the grouting reinforced circle, depending on fluid-solid coupling theory and numerical simulation of the seepage fieldstress field, the influence of parameters to the water inflow and stability is analyzed while grouting effect was evaluated from the two aspects of reinforcement and water plugging. The conclusion show: the permeabilitystrength and thickness of the grouting reinforced circle are important factors of water inflow and surrounding stability while the choice of the thickness is inflected by the permeability and strength, when which reached a certain value the minimum thickness of the grouting reinforced circle is gotten.

Seepage Analysis of Plane Finite Element on Clay Core Dam of Laojunshan

Through calculation of the seepage finite element, the result shows that the anti-seepage effect of clay core and grouting curtain is obvious. The phreatic line of dam conforms to the general law, and seepage stability of the dam meets the requirements. The sensitivity analysis of the different curtain depth indicate that there is a inflexion on the relation curve of seepage discharge and curtain depth, and to deepen continually the curtain have less effect on the dam seepage discharge when the curtain more than 50m.

Geological challenges in constructing the proposed Geba dam site, northern Ethiopia

It is proposed to construct a dam across the Geba River, Ethiopia. The paper reports the engineering geological investigations undertaken, including mapping, discontinuity surveys, core drilling, water absorption testing and sampling for laboratory tests. The complexity of the site, with limestones and interbedded limestone-shale horizons, is indicated by the variability of the RQD and Lugeon values. Of the 63 tests undertaken, some two-thirds had Lugeon values implying grouting was necessary. Following removal and replacement of the alluvial deposits in the central area, a grout curtain including two to three rows of grouting holes was recommended to a depth of 100 m for the left abutment, 35 m for the central foundation and 60 m for the right abutment.

Engineering geological behaviour of recent conglomerate deposits in dam foundation. The case of Agiokampos dam in Thessaly, Cen- tral Greece.

A typical example of dam foundation on Neogenic conglomerate deposits is presented in this paper. The case of Agiokampos dam in east Thessaly in central Greece. The level of natural compactness and the nature of the cementing material are crucial elements for the strength, the bearing capacity and the permeability of these formations. These conglomerates of medium consistency, do not allow relying on traditional sampling and tests in the boreholes. Lugeon tests are meaningless and falling head tests are recommended. Back analysis on slopes is certainly a useful tool for approaching the strength parameters of the global rock mass. Thus it is understood that the engineering geological assessment before any testing and analysis is of prime importance.Due to the fine nature of the cement, permeability is generally low and no leakages are expected. However, an impermeable grout curtain must be created due to some higher values. Conglomerates are not easily groutable and a combination of a diaphragm wall is suggested. Finally, a carpet grouting is designed since the surficial zone is susceptible to internal erosion.

The possible negative consequences of underground dam and reservoir construction and operation in coastal karst areas: an example of the hydro-electric power plant (HEPP) Ombla near Dubrovnik (Croatia)

Abstract. The Ombla Spring represents a typical abundant coastal karst spring located in the vicinity of the town of Dubrovnik (Croatia). Its outlet is at an altitude of 2.5 m above sea level (m a.s.l.) and the water from it immediately flows into the Adriatic Sea. The minimum and maximum measured discharges are 3.96 m3 s−1 and 117 m3 s−1, respectively. The Trebišnjica River traverses through its catchment. The mean annual discharge, after the canalization of over 60 km of its watercourse with spray concrete (in the time span 1981–2011), is 24.05 m3 s−1. Before massive civil engineering work which took place during 1968–1980, the mean annual discharge was 28.35 m3 s−1. There is a project for construction of the hydro-electric power plant (HEPP) Ombla, which will exclusively use groundwater from the Ombla Spring karst aquifer. The underground dam will be constructed about 200 m behind the existing karst spring outflow in the karst massif, by injecting a grout curtain. The top of the grout curtain is planned to be at an altitude of 130 m a.s.l. This karst system is complex, sensitive, vulnerable and ecologically extremely valuable. The grout curtain, as well as the HEPP Ombla development, could lead to extremely dangerous technical and environmental consequences. In this paper some probable, negative consequences of the HEPP Ombla construction and development are explained. The HEPP Ombla could result in many large and hard-to-predict negative consequences which are specific for this particular HEPP, for example (1) severe spring discharge change; (2) unpredictable regional groundwater redistribution; (3) threatening of endemic fauna; (4) induced seismicity; (5) induced sinkholes; (6) occurrence of landslides; (7) conflict regarding internationally shared karst aquifers; (8) intensification of karst flash floods; (9) sea water intrusion in coastal karst aquifer; etc.

The Influence of Engineering Factors to Groundwater Recovery in Mountain Tunnel

Groundwater flow into mountain tunnel can lead to drawdown and groundwater loss in tunnel construction and operation stages under drainage and limited drainage principle conditions. The author defines groundwater recovery degree of drawdown and volume change, and simulate drawdown and groundwater recovery process adopting nonhomogeneous and anisotropic equivalent tunnel flow model, and study influencing effect of various factors to groundwater recovery by numerical method. The results show that the essential condition of groundwater recovery in tunnel is that groundwater recharge is greater than groundwater inflow volume, which can be controlled by efficient waterproof and drainage measures. The efficient measures include curtain grouting, radial grouting and high impermeability performance of shotcrete.

New passages in old dams

A number of new passages have been excavated in existing dams. These penetrations are to improve access, provide new outlets or access for grout curtains, and upgrade dams and outlets to meet modern standards. Potential damage to adjacent grout curtains, waterproofing details or appurtenant facilities from excessive vibration is a major concern. This paper reviews available excavation techniques and considers issues to be addressed for each. Vibration thresholds are also reviewed. Case histories for Klingenberg dam, Spelga dam, San Vicente dam and Warmwithens dam are used to illustrate the discussion of the different techniques.

Geotechnical Engineering Assessment of the Nargesi Damsite, Southwest Iran

This paper describes the results of the engineering geological investigations and geotechnical studies performed in the Nargesi dam site. The dam foundation located on the sedimentary rocks of Neogen period. To conduct this study, the steps including field and laboratory investigations, surface discontinuity surveying, drilled borehole data, and permeability were performed on dam foundation. Besides, the evaluation of the dam foundation was carried out by water pressure tests, which indicate the necessity of creating a grout curtain below the dam foundation. The permeability and groutability characteristics of the Nargesi dam foundation are significantly affected by geology of the site. The rock mass properties of the test section obtained from secondary permeability index (SPI) completed with the degree of jointing of the drill core acts as a useful reference for ground treatment design. Here, the performed laboratory tests were as: determination of density, moisture percent, porosity percent, water absorption, uniaxial compressive strength, Point-load strength index (Is50), p-wave velocity (Cp), s-wave velocity (Cs), deformability, and triaxial tests. The rock mass properties and classifications of the damsite is assessed using rock mass rating, the rock quality (Q), and the geological strength index classification systems. The strength and modulus elasticity of rock masses were determined through the equations proposed by different researchers. According to the findings of this work, except for some cases, there is a reasonable correlation between SPI and rock quality designation values. Based on these results, grout type and composition was suggested for the design of grout curtain.

Mechanism Analysis of Water-Filling Based on Material Properties in Jinjie Mine, NW China

This paper taking Jinjie Mine in northwest China as an example, on the basis of the hydrogeological analysis of the mineral deposit, explores the structure and influence factors of mine water inflow. The result shows that Jinjie Mine coal mining has destroyed the water-resisting roof layer, and then conducted the water channels. As a result, the original mode of hydrological cycle is changed, resulting in pore water, fissure water and surface water flow into the goaf through the water channel, and this help the water inflow be quite large (even reach 5380 m3/h). In order to coal mine safety production and protection of the areas fragile water environment, the curtain grouting technique using fly ash cement materials mainly is taken for preventing water.

Engineering Practice of Water Control by Nearly Orebody Curtain Grouting in Laixin Iron Mine

The paper introduces the practical application of underground nearby orebody curtain grouting in Laixin iron mine. Based on the analysis of hydrogeology condition in the mine and the technical requirements of water control plans, the final water control plan introduced in the paper is chosen. Roadway horizontal drilling water-prospect grouting and transverse and slant drilling encrypting grouting are described, and quantities of the two projects are given. Finally, significant economic and environmental benefits caused by underground nearly orebody curtain grouting in Laixin iron mine are analyzed.

Long-Term Geological Challenges of Dam Construction in a Carbonate Terrane

Many carbonate foundations of dams are afflicted with zones of broken or fractured rock and karstification prior to construction. Rock fractures develop because of tectonic stresses but also because of the removal of overburden loads imposed upon the rock. This is the case with valley stress relief. As fractures control many of earth9s dynamic processes, including fluid transport in the crust, an understanding of valley stress relief is essential for an understanding of karstification. Because water impounded by a structure imposes an increased hydraulic gradient, and because this gradient facilitates the solubility of that carbonate foundation, fractures or bedding planes undergo accelerated transformation by the karstification process and enhance additional dynamics affecting the dissolution rate of carbonates. In a state of nature, karstification requires a time scale of 10,000 to more than 100,000 years. However, when subject to the imposed-increased hydraulic gradients associated with impoundment, the rate of karstification may accelerate a thousand-fold. Civil engineers and geologists have noted that grout curtains or concrete cut-off walls, structures typically used to deal with this problem, offer mixed success in terms of extending the design life of a water retention structure. Traditional repairs impose a new hydraulic gradient causing increased infiltration of the minute, non-groutable, clay-filled microfractures. Construction is an incremental process. The imposed hydraulic gradient increases incrementally as ungrouted microfractures become susceptible to karstification, accelerating development of new seepage channels. Eventually, seepage becomes intolerable as karstification renders the impoundment susceptible to another round of repairs. Four case histories illustrate these concepts.

Seepage Phenomenon for Wadi Megenin Dam

Most of the recorded dam failures in different parts of the world were related to seepage problems. Avoiding earth dam's failure due to seepage usually requires evaluating settlement, and piping, through field monitoring. The problem of dam seepage was experienced in The 38 m high rock fill Megenin dam is a at located at Souk AL khamis area 75 Km south of Tripoli. The dam was constructed in 1972, for two main purposes; to provide flood controls of the downstream areas, the cultivated fields and Tripoli city, and also provides water for irrigation purpose . The rock-fill dam was supported with an upstream reinforced concrete membrane on the upstreamface consisted of a number of concrete panels, linked together with central rubber water stops, and surface-sealed with a bituminous sealant. A concrete cut-off wall and grout curtain were constructed below the dam body to prevent reservoir seepage through the foundation. It was observed during the 3rd filling of the reservoir at the reservoir storage water level at +271.86 m on 15thMay 2003, seepage occurred at the wadi bed downstream of the main dam. The seepage occurred at a piezometric water level higher than the previously measurements during the period of 1973 to 1974. Seepage problem was also encountered in previous reservoir operation. To assess the seepage phenomena and it's impact on the dam safety, a study was carreied out through appliaction of t ground penetrating radar survey (GPR), piezometric analysis, and temperature field evaluation techniques as well as the construction of a flow net model for the dam. The results of the study showed that: the GPR profiles have delineated the critical zones in the dam body ,identify the water seepage paths from the reservoir to the down stream side of the dam, estimated the seepage rate through the dam foundation as 0.08 Ɩliter / ssecond and suggested measures to avoid problem that may occur in the future in Megenin dam due to seepage problems The study revealed the needs to design and implement effective monitoring program ,establish surface water gauging for any sudden increase in the seepage discharge in bed wadi at downstream , groundwater water levels fluctuation in the observation and seepage water beyond the dam. Maintain the upstream concrete facing joints and in case of alert condition occurred undertake additional raw of grouting curtain along the full length of the dam to protect dam foundation from flow.

Numerical Simulation and Optimization of Hole Spacing for Cement Grouting in Rocks

The fine fissures of V-diabase were the main stratigraphic that affected the effectiveness of foundation grout curtain in Dagang Mountain Hydropower Station. Thus, specialized in situ grouting tests were conducted to determine reasonable hole spacing and other parameters. Considering time variation of the rheological parameters of grout, variation of grouting pressure gradient, and evolution law of the fracture opening, numerical simulations were performed on the diffusion process of cement grouting in the fissures of the rock mass. The distribution of permeability after grouting was obtained on the basis of analysis results, and the grouting hole spacing was discussed based on the reliability analysis. A probability of optimization along with a finer optimization precision as 0.1 m could be adopted when compared with the accuracy of 0.5 m that is commonly used. The results could provide a useful reference for choosing reasonable grouting hole spacing in similar projects.

Water supply spring zone Novljanska Žrnovnica (Croatia) – new quantities of drinking water in the conditions of salt water intrusion

This paper presents an approach for solving the problem of exploitation of freshwater in the coastal karst aquifer during summer dry periods in the conditions of potential salt water intrusion. The approach is presented on the example of spring zone Novljanska Žrnovnica, situated in the northern part of Croatian Adriatic coastal region. The spring zone is used for water supply (about 250 l/s) of an important tourist area of Crikvenica and Novi Vinodolski. After unsuccessful attempts of physical separation of freshwater system from the sea influence, by construction of grout curtain, hydrogeological studies have focused on the possibility of groundwater capturing in the hinterland of discharge zone, outside of the zone of periodical salinity. The final research results with the exploitation well in the spring hinterland can serve as a model for research and exploitation of drinking water in natural conditions of unstable freshwater-saltwater interface in similar natural conditions.

Design, construction and performance of seepage barriers for dams on carbonate foundations

The design, construction and performance of concrete cut-offs, and grout curtains, as dam seepage remediations in carbonate foundations are reviewed. Recent experiences when attempting to build concrete cut-offs through hard and highly permeable rock masses have led the author and associates to develop the concept of “composite cut-offs” for seepage control. A campaign of high-quality drilling, permeability testing and grouting is first conducted to pretreat the very permeable and/or clay-filled zones, to seal the clean fissures and to provide an extremely detailed geological basis upon which to design the location and extent of the subsequent concrete wall (if in fact needed). Bearing in mind that the average cost of a concrete wall is many times that of a grouted cut-off, and that there is currently a shortfall in industry capacity to construct the former, the concept of a “composite wall” is logical, timely and cost-effective. Following presentation of the basic concepts, the paper provides details of a recent case history in Alabama.

Research on the Optimization of Dam Foundation Seepage Control System

The starting time of Dragonite hydropower station in Dadu River Sichuan delayed, which led to the depth of the cofferdam cut-off wall reduced in actual construction. In order to adapt to this situation, it’s necessary to optimize the processing scheme of sand layer dam foundation which is put forward in the feasibility study stage. Combined with the characteristics of engineering, considering to reduce or cancel the curtain grouting in coarse grain granite foundation of riverbed on the right bank in the feasibility stage design, this paper is aimed to study on the optimization design of Dragonite hydropower station dam foundation. The paper has not only a great guiding significance in engineering construction process, but also gives references to the similar earth-rock dam project for treatment of sand layer dam foundation and the arrangement of dam foundation seepage control system.

Groundwater Inrush Channel Detection and Curtain Grouting of the Gaoyang Iron Ore Mine, China

The complex hydrogeological conditions of the Gaoyang Iron Mine area were responsible for two water inrush accidents that occurred during tunneling at the horizontal level of −245 m on August 17, 2000 and August 29, 2004. Borehole computerized tomography in the key areas of the mine and groundwater level monitoring data were used to identify the main underground hydraulic channel and its characteristics. A grout curtain, designed and emplaced based on the results of this study, was highly effective in reducing the groundwater levels in the mine area and amount of water pumped from the mine.