Lugeon Test Research Articles

Evaluation of watertightness and slope stability analysis of Upper Guder dam, West Showa, Central Ethiopia

Ethiopia is currently emphasizing the construction of micro dams to enhance agricultural productivity and assure food security. The Upper Guder Dam, situated in the West Shoa Zone, Central Ethiopia, is one such project. However, the dam faces challenges due to complex geological and structural conditions, including leakage and slope instability. Hence, this study focuses on addressing the abutment slope stability and watertightness condition of this dam. Accordingly, the study employed discontinuity surveying, Seismic Refraction Tomography (SRT), Rock Quality Designation (RQD), and Lugeon testing to assess the water tightness. Additionally, kinematic analysis and the Limit Equilibrium Method (LEM) were used to evaluate abutment slope stability. Results from surface geological mapping and core drilling showed that the dam site is constituted by quaternary soil, tuff, and basalt. The Lugeon test results indicate that the left abutment of the dam is susceptible to leakage down to a depth of 40 m, which suggests that the permeable zone extends deeper than the results revealed by the SRT. Furthermore, this test demonstrated that the dam's right and central foundations are susceptible to leakage to the drilled depths. The SRT revealed that the central foundation, right, and left abutments of the dam are susceptible to leakage to the depth of 35 m, 30 m, and 34 m, respectively. Moreover, the kinematic analysis revealed that a section of the left abutment of the dam is susceptible to wedge mode of failure due to the intersection of JS1 and JS2. The LEM modeling of the right abutment of the dam also depicted that this section of the dam is unstable under saturated conditions which illustrates the importance of precipitation as the major slope destabilizing factor in the study area. Based on the study findings, this study recommended the use of curtain grouting to address the water tightness issue and slope angle reduction to mitigate the slope instability problem.

A Comparison of Statistical Validity of In-Situ Hydraulic Conductivity Prediction Models of Rock Mass Inferred from Borehole Logs and Lugeon Test Data

In-situ hydraulic conductivity is a vital property in rock engineering for jointed rock mass. Understanding its correlation with rock mass parameters is crucial for water circulation. Therefore, a study was carried out to develop statistically significant empirical relationships between hydraulic conductivity and various rock mass parameters to estimate in-situ hydraulic conductivity from Lugeon test and various rock mass parameters obtained from borehole logs.The study initially aimed to establish a correlation between hydraulic conductivity and Rock Quality Designation (RQD). However, the outcomes were unsatisfactory, prompting further research. Later, two more robust models were developed, namely the HC-model and modified HC-model. The HC-model incorporated four rock mass parameters, including Rock Quality Designation Index, Depth Index, Gouge Content Designation Index, and Lithology Permeability Index, achieving a maximum coefficient of determination (R2) of 0.46. The modified HC-model included six parameters, encompassing fracture frequency and theoretical aperture, resulting in an improved R2 of 0.69. Both models significantly outperformed RQD-alone predictions (R2 < 0.10), highlighting the need for incorporating multiple rock mass parameters in predicting hydraulic conductivity due to a complex interplay of various factors. However, the effects of joint persistence and roughness are limiting in the present analysis.

Integrated Underground Analyses as a Key for Seasonal Heat Storage and Smart Urban Areas

The design and performance of a shallow geothermal system is influenced by the geological and hydrogeological context, environmental conditions and thermal demand loads. In order to preserve the natural thermal resource, it is crucial to have a balance between the supply and the demand for the renewable energy. In this context, this article presents a case study where an innovative system is created for the storage of seasonal solar thermal energy underground, exploiting geotechnical micropiles technology. The new geoprobes system (energy micropile; EmP) consists of the installation of coaxial geothermal probes within existing micropiles realized for the seismic requalification of buildings. The underground geothermal system has been realized, starting from the basement of an existing holiday home Condominium, and was installed in dry subsoil, 20 m-deep below the parking floor. The building consists of 140 apartments, with a total area of 5553 m2, and is located at an altitude of about 1490 m above sea level. Within the framework of a circular economy, energy saving and the use of renewable sources, the design of the geothermal system was based on geological, hydrogeological and thermophysical analytical studies, in situ measurements (e.g., Lefranc and Lugeon test during drilling; Rock Quality Designation index; thermal response tests; acquisition of temperature data along the borehole), numerical modelling and long-term simulations. Due to the strong energy imbalance of the demand from the building (heating only), and in order to optimize the underground annual balance, both solar thermal storage and geothermal heat extraction/injection to/from a field of 380 EmPs, with a relative distance varying from 1 to 2 m, were adopted. The integrated solution, resulting from this investigation, allowed us to overcome the standard barriers of similar geological settings, such as the lack of groundwater for shallow geothermal energy exploitation, the lack of space for borehole heat exchanger drilling, the waste of solar heat during the warm season, etc., and it can pave the way for similar renewable and low carbon emission hybrid applications as well as contribute to the creation of smart buildings/urban areas.

Hydrogeological characterization of low permeability medium for conceptualization of a mine site in Eastern Turkey

The mining site in Eastern Anatolia of Turkey were encounter a significant risk of slope instability within the operational area. One of the processes that govern slope stability is the pore water pressure distribution. The conceptualization and characterization of porous media serve as fundamental prerequisites for the implementation of numerical methods aimed at predicting pore water distribution. This study aims to characterize the hydrogeological properties of water bearing rocks in the active mining site in Eastern Anatolia of Turkey. A total of 21 wells and drill holes were drilled in the study area to conduct in-situ tests, monitoring, and sampling. The large diameter wells drilled in surrounding the carbonate rocks were to determine the groundwater flow and boundary conditions and also wells tapped metasediments and diorite unit for hydraulic testing. The lugeon tests and installation of vibrating wire piezometers were carried out at small diameter drill holes to obtain localized hydraulic conductivity of metasediments and diorite at different depths and monitoring pore water pressure distribution along some critical cross-sections. The results obtained from these tests are used for developing hydrogeological conceptual model for groundwater flow. The results of in-situ tests show that the metasediment and diorite units act as a single hydrostratigraphic unit. The metasediments and diorite have high total porosity and low specific yield indicating that the pore water is retained by electrostatic forces in the medium and it resists flow due to low hydraulic conductivity. The vertical variation in hydraulic conductivity values indicates that the medium is highly heterogeneous.

Evaluating rock mass groutability at shallow depths: a novel approach based on geo-structural surveys and permeability tests

The study describes the geological and geo-structural setting of an unstable sea arch in a very attractive landscape of Southern Italy. It evaluates the applicability of some reinforcement work designs consisting of rock mass grouting at shallow depths along the arch vault and abutments. To this aim, the hydraulic conductivity of the rock mass and its groutability were evaluated in detail, integrating field geo-mechanical surveys, boreholes, Lugeon tests, and grouting tests with different grout compositions. Results from site tests were compared with grout take values calculated by applying classical empirical approaches available in the literature, based on rock mass permeability, or by using a novel deterministic approach based on geo-mechanical field surveys. Considering the shallow depths of the tests, the results suggest that the former gave high values, inconsistent with grout tests. On the contrary, the novel deterministic approach provided grout take values consistent with the results of grouting tests, resulting in the most reliable approach for the arch’s thin, shallow, and highly fractured structure.The use of different grout compositions in the site tests proved that extensive use of highly dense and viscous slurries is required (bentonite-cement grout) due to the high-grade weathering and karstification of joint surfaces, which deeply increases their hydraulic conductivity. However, the rock mass grouting must be considered complementary to other reinforcement measures such as bolting, especially along the arch vault.

Assessment of engineering geology and grouting applications in Yalnızardıç Dam Site (Antalya, Türkiye)

The Yalnızardıç roller compacted concrete (RCC) dam, constructed in 2015, is located in the Mediterranean region of Turkey, intended for electric power production. It is approximately 303 m long and 92 m in height. In this paper, it is aimed to determine the performance of the grouting method, conducted to control the water seepage and improve the foundation of the Yalnızardıç dam. The engineering properties of the site were introduced by geological mapping, drilling, and laboratory tests. The seepage of the foundation was determined by the in-situ Lugeon test method, also referred to as a water pressure test, which is estimate the mean hydraulic conductivity of rock mass. As a result of the tests, high-permeable and permeable zones were determined in the dam axis area. To make a barrier layer for these permeable zones, grout curtains were built in the left abutment, thalweg and right abutment with two lines of grouting holes which is proposed according to the Lugeon test and rock quality designation (RQD) results. Consolidation grouts were built to increase the density of the soil which makes the strength of the dam's foundation. After the groutings, check boreholes were drilled and water pressure tests were performed to control the seepage along the foundation and dam site. The results indicated that average Lugeon (LU) values reduced, and the values were within the recommended limit. The process shows considerable accuracy in evaluating grouting efficiency.

Lugeon test: new insights into calculated hydraulic conductivity

While the Lugeon test was initially designed to aid in determining the grouting needs of dam foundations in fractured rock, its outcomes have been utilized by geotechnical engineers and hydrogeologists to estimate the hydraulic conductivity. Most of the practitioners use the long-established relation of 1 Lu ≈ 1 × 10 −7 m s −1 to calculate the hydraulic conductivity based on the determined Lugeon value. However, this relationship does not cover all the potential boundary conditions encountered in field conditions where the Lugeon test is applied, and the consequences on the estimated hydraulic conductivity are poorly understood. This paper aims to address this issue by revisiting existing mathematical formulations to calculate the hydraulic conductivity from the Lugeon test under the various boundary conditions. The paper also examines how the flow conditions and length of test intervals impact the recorded Lu and hydraulic conductivity values. It was found that the long-stablished relationship of 1 Lu ≈ 1 × 10 −7 m s −1 and the equation presented in the commonly used reference of the Code of Practice for Site Investigation (BS 5930:1999 + A2:2010) only present one of the potential boundary conditions for the Lugeon test.

Enhanced estimate of fracture network dimensions by injection of non-Newtonian fluids

Lugeon tests, also known as water pressure tests, are widely used to estimate the transmissivity of rock-fracture networks and are considered standard testing for grouting of dam foundations. The Lugeon test consists of injecting water into an isolated borehole section intersecting several fractures and monitoring water pressure and flow rate over time to estimate the rock fractures’ transmissivity. An average fracture aperture for the whole section is then estimated from the transmissivity value, which is used for selecting the appropriate grout mix. However, the current procedure does not provide any information on the variability in aperture sizes within the investigated rock interval. This paper presents a new approach for performing Lugeon testing that allows for providing a probabilistic distribution of fracture apertures by injecting bio-degradable non-Newtonian fluids at different pressures/flow rates. The theoretical framework demonstrating the ability to estimate the dimensions of multiple fractures, in parallel and in series, from non-Newtonian fluid injection tests is presented. Then, experimental results on different combinations of simple fractures, made of parallel plates, are used to validate the derived model and evaluate its performance.

Comparison of time-dependent viscosity slurry and cement-clay slurry for anti-seepage grouting on faults

The complex rock mass structure in fault fracture zone weakens the permeability of strata. This has led to curtain grouting being used to improve the anti-seepage properties of fault zones. This study evaluates the groutability and impermeability of a time-dependent viscosity slurry and a cement-clay slurry in a shattered fault zone. Rheology, setting time, mechanism, and permeability were tested to evaluate the groutability, and Lugeon and grouting field tests were carried out to evaluate the anti-seepage grouting characteristics of a fault zone. The results show that the time-dependent viscosity slurry had higher initial fluidity, a shorter and more controllable setting time, and higher strength than cement-clay slurry, better ensuring the slurry diffusion radius, pores filling rate, and bearing capacity and durability of the consolidated body. The permeability coefficient of the two grouts was less than 1×10−7 cm/s, and the blocking rate of heavy metal ions was more than 98%, sufficient to effectively control the leakage of sewage. The P∼Q curve of the Lugeon test showed that the original strata were of the washout type (>200 Lu), and the rock mass quality grade was the D grade (Poor). Under the same grouting depth, the amount of time-dependent viscosity slurry required was 72.6% of that of cement-clay slurry, and the permeability decreased to 10 Lu, far lower than the 50 Lu of the cement-clay slurry. The time-dependent viscosity slurry improved the quality of the rock mass from D to B-C grade, while the cement-clay slurry test area is remained C-D grade. In general, the time-dependent viscosity slurry performed better than cement-clay slurry in the water-bearing fault zone.

Lugeon Test and Grouting Application Research Based on RQD of Grouting Sections

Rock quality designation (RQD) and permeability coefficient are important reference indexes for grouting application. Based on the readily available RQD, RQD is found to have no relationship with the depth of rock stratum, and a method for calculating the mean RQD (RQDm) of long stratum is proposed, which is applied to the calculation of RQD of grouting sections. Through Lugeon and grouting tests on the grouting sections, RQDm of the grouting sections is found to be directly related to the average permeability coefficient, permeability, and units of grouting per amount of rock mass. It is found that RQDm has a symmetrical relationship with permeability and grouting volume as well as a negative exponential correlation with unit grouting volume and average permeability coefficient. According to the curve of RQD varying with depth, the grouting amount at different depths can be obtained by using the fitting formula of unit grouting amount and RQDm.

Using multivariate adaptive regression splines to develop relationship between rock quality designation and permeability

The assessment of in situ permeability of rock mass is challenging for large-scale projects such as reservoirs created by dams, where water tightness issues are of prime importance. The in situ permeability is strongly related to the frequency and distribution of discontinuities in the rock mass and quantified by rock quality designation (RQD). This paper analyzes the data of hydraulic conductivity and discontinuities sampled at different depths during the borehole investigations in the limestone and sandstone formations for the construction of hydraulic structures in Oman. Cores recovered from boreholes provide RQD data, and in situ Lugeon tests elucidate the permeability. A modern technique of multivariate adaptive regression splines (MARS) assisted in correlating permeability and RQD along with the depth. In situ permeability shows a declining trend with increasing RQD, and the depth of investigation is within 50 m. This type of relationship can be developed based on detailed initial investigations at the site where the hydraulic conductivity of discontinuous rocks is required to be delineated. The relationship can approximate the permeability by only measuring the RQD in later investigations on the same site, thus saving the time and cost of the site investigations. The applicability of the relationship developed in this study to another location requires a lithological similarity of the rock mass that can be verified through preliminary investigation at the site.

SIMULATION OF ROCK CRACK AND PERMEABILITY IN DAM FOUNDATION DURING HYDRAULIC FRACTURING

Hydraulic fracturing is one type of thedam internal erosion leading to concentrated leaks and dam failure. During reservoir impounding,cracks in rock or soil can be initiated and expanded by water pressure. The crack expansionincreasesthe permeability of the soil or rock foundations.A numerical model of crack deformationwas established based on the finite elements methodto study crack characteristics due to hydraulic fracturing pressure.The crack of 1 mm wide and 600 mm long is modeled on 1x1 m of rock mass with the overburden pressure and pore pressure in the crack. The permeability of crack rock with orientations was examined using the equivalent permeability based on crack width due to hydraulic fracturing.The results revealed that crack closure variedwith the elastic modulus of the fillerand the orientation along the crack surface. During reservoir impounding, the crack openingswere related to hydraulic pressure and crack orientation. The model of crack opening indicated that the vertical crack orientation was likely to widen more than the horizontal crack orientation,with crack openings in the range0.003-0.37 mm. The range inrock crack permeability with such crack openings was 5x10-6-1.65 m/s thatagreedwell with the range of field permeability based on the Lugeon test of 1.27x10-4 to 4.96x10-3 m/s. Crack openings due to hydraulic fracturing can be used to predict the rock crack permeability within the hydraulic fracturing area in the dam or its foundation.

Determining the appropriate sealing conditions through a permeability and groutability evaluation: a case study of the Sivaki Dam, Iran

The Sivaki Dam is an earth dam that is located near Yasuj city, 5.3 km NW of Sepidar village. During excavations at the dam construction site, the high potential of water seepage from the foundation and its abutments has been proven. Some cavities and dissolution have been observed on both sides of the dam, suggesting the possibility of karstification at greater depths. Most of the rocks cropping out in the study area comprise Asmari Limestone. These rock masses, despite their medium–high strength, have provided unfavourable conditions in terms of permeability and weathering. In this study, the foundation and both abutments of the dam were evaluated and analysed to determine the permeability and groutability characteristics. To achieve this goal, the engineering characteristics of the rock mass of the construction site were examined by performing rock mass rating (RMR) and geological strength index (GSI) classifications. The Lugeon test, secondary permeability index (SPI), rock quality designation (RQD) and monitoring hydraulic flows were used for this purpose. According to the results of this study, for abutments of the dam and in the case of alluvial substrates, a grout curtain and cutoff wall, respectively, are the best and most compatible methods available.

Curtain grouting experiment in a dam foundation: case study with the main focus on the Lugeon and grout take tests

The Baihetan super-high arch dam is constructed under complicated geological conditions, including large-scale columnar jointed basalt (CJB) with closely spaced joints and multiple interlayer and intralayer shear belts at the lower part of dam base, which may increase a risk of seepage in adjacent dam foundations. Therefore, curtain grouting is used to reduce the permeability of dam foundations. Lugeon and grouting field tests and geological exploration were carried out to investigate curtain grouting characteristics of the dam foundation. The findings were as follows: (1) the permeability coefficient of the first type of CJB and breccia lava without unloading is 2 × 10−5 ~ 5 × 10−5 cm/s; that of the second type of CJB without unloading is 2.5 × 10−5 ~ 5 × 10−5 cm/s; and that of the unloaded third type of massive basalt is 1 × 10−5 ~ 3 × 10−5 cm/s. (2) The rock core shows that the slurry caused repeated splitting of the rock mass and widened the cracks of the rock mass, which resulted in plastic deformation of the rock mass. The P ~ Q curve of the five-point Lugeon test shows that the curve shape is turbulent and that the maximum Lugeon value appears at the highest pressure. (3) The phenomenon of low-permeability conditions with a large grout take can be frequently observed. The proportion of the hole stages with a water permeability less than 1 LU and grout take greater than 50 kg/m ranges from 12.5 to 37.5%. The proportion of holes with permeability greater than 10 Lu and grout take greater than 50 kg/m is 0 to 12.5%. The findings from this case study can provide a reference for engineering construction.

Case Study: In Situ Experimental Investigation on Overburden Consolidation Grouting for Columnar Jointed Basalt Dam Foundation

The dam foundation rock mass, at the Baihetan hydropower station on the Jinsha River, is mainly columnar jointed basalt, with faults and fissures developed. Considering adverse factors such as the unloading relaxation or the opening of the fissures due to excavation blasting, consolidation grouting is needed to improve the integrity of the dam foundation rock mass. According to the physical and mechanical properties of columnar jointed basalt and the continuity of construction, the effectiveness of overburden consolidation grouting is experimentally studied. The results show that this grouting technology can obviously improve the integrity and uniformity of a dam foundation rock mass and reduce the permeability of the rock mass. After grouting, the average increase in the wave velocity of the rock mass is 7.3%. The average improvement in the deformation modulus after grouting is 13.5%. After grouting, the permeability of 99% of the inspection holes in the Lugeon test section had Lugeon values of no more than 3 LU. This improvement is considerable and provides a case to engineering application.

ISRM Suggested Method for the Lugeon Test

ISRM Suggested Method for the Lugeon Test

Electrical resistivity imaging and engineering geological investigation of Gereb Segen dam, northern Ethiopia

The paper presents results of electrical resistivity imaging and engineering geological investigations conducted at the Gereb Segen dam site and reservoir to evaluate water tightness and stability. A programme of 2D resistivity imaging, discontinuity surveying, core drilling and Lugeon testing was conducted to assess the engineering geological performance of the dam and reservoir area. The geology of the dam site comprises alluvial deposits, dolerite, micritic limestone and marl-limestone-shale intercalation units. The investigations revealed dissolution cavities up to meters in size showing a preferred alignment along the valley; the separate lines of investigation correlated well to provide confidence in the findings. A karstified zone was identified at the base of the marly limestone unit at the dam site. A layer of gypsum found at shallow depth (9.5 m) along the dam axis may pose a dissolution hazard to water tightness and ground quality. Lugeon test results define very-low- to low-permeability units (shale with gypsum lenses and shale-mudstone) and high-permeability units (marly limestone and dolerite) and very-high-permeability zones associated with the karstic features. The presence of discontinuities and/or weak zones at the abutments and cavities at the dam foundation will affect the stability of the dam and facilitate leakage. Multiple line grout curtains for the karst zones and grouting for the jointed limestone at the dam axis and both abutments are recommended to reduce the possible leakage that will occur at the dam.

Geological assessment for tunnel excavation under river with shallow overburden using surface site investigation data and electrical resistivity tomography

Tunnelling is a challenging task as many geotechnical uncertainties involved during construction, especially under a river crossing with shallow overburden. This study focussed on geological assessment for the New Austrian Tunneling Method excavation that crosses under Kerau River with shallow overburden. 3D filtered tunnel models using Boolean filter for rock mass weathering grade, rock quality designation, and Lugeon value are developed. Results predict that 53.3% of the tunnel excavation under the Kerau River crossing are highly weathered rocks (Grades III and IV), and 64.51% are in the moderately to highly fractured zone (0%–75% RQD) along the roof of the tunnel granitic bedrock. The Lugeon value models show that 71.64% of the excavating rocks possess a Lugeon value of 5–50 (6–60 × 10−5 cm/s), which denotes considerably high permeability. 2D electrical resistivity tomography is used to verify the permeability results from the Lugeon test.

The effect of scale on the water leakage from the reservoir and abutment of Beheshtabad Dam

Dam construction on karstic carbonate formations usually involves leakage problems from their abutments and reservoirs. Constructing a dam in such formations can lead to reservoir leakage to downstream or adjacent basins. In karstic areas, hydraulic conductivity has a direct correlation with scale. In other words, hydraulic conductivity is far lower in sub-local scales (Slug test and Lugeon test) in comparison with local scales (pumping test) and large scales (dye tracing test and recession curve). The present study was conducted to investigate the scale effect on water leakage from the reservoir and abutment of Beheshtabad Dam. This dam is located approximately at the end of an anticline axis named Sangvil, which is mainly composed of dolomite-limestone with a thickness of about 700 m. The righthand side of the reservoir is in contact with this formation. Several methods have been used for the evaluation of hydraulic conductivity and for determining the reservoir leakage in the righthand side of the dam, including Lugeon tests, Uranine tracer, a gradient approach, and spring recession curves. Also, a pumping test was carried out by considering pumping well assumptions. The results showed a range of hydraulic conductivity values for the rock mass from 2.1×10−6 m/s at the sub-local scale (Slug test) to 1.7 × 10−4 m/s at the regional scale (dye tracing test). In such a context, reservoir leakage is calculated at approximately 0.1 l/s iayn the sub-local scale to 2.7 l/s at a regional scale. By considering that reservoir scale is correlated with regional scale, leakage in the righthand side of Beheshtabad dam is calculated according to a regional scale, and the leakage amount was predicted to be within the range of 5.4 to 7.8 m3/s.

Understanding the need for pre-injection from permeability measurements: What is the connection?

Pre-grouting ahead of tunnels has three main functions: to control water inflow into the tunnel, to limit groundwater drawdown above the tunnel, and to make tunnelling progress more predictable since rock mass quality is effectively improved. It helps to avoid settlement damage caused by consolidation of clay deposits beneath built-up areas, since towns tend to be built where terrain is more flat, due to the clay deposits. There are so many instances of settlement damage that the profession needs to take note of the need for high-pressure pre-grouting, to use micro-cements and micro-silica additives. The use of high-pressure injection may cause joint jacking, but this is local in extent when the rapid pressure decay away from an injection hole is understood. This effect is variable and depends on the geometrical parameters of the joints. This pressure-decay advantage must not be violated by maintaining high pressure when grout flow from the injection hole has ceased. The latter can cause damage to the grouting already achieved. Simplified methods of estimating mean hydraulic apertures (e) from Lugeon testing are described, and from more sophisticated three-dimensional (3D) permeability measurement. The estimation of the larger mean physical joint apertures (E) is based on the joint roughness coefficient (JRC). Comparison is then made with the empirical aperture-particle size criterion E > 4d95, where d95 represents almost the largest cement particle size. Depending on joint set orientations and on the available micro-cements, the decision must be made of which range of pre-injection pressure should be aimed for, using successive reductions of the water-cement ratio w/c. More simple estimation of permeability, also with depth dependence, can be made with the empirical link between a modified rock mass quality Q and permeability, which is termed QH2O. The value of this parameter can be based on core-logging or in-tunnel face logging. The 3D before-and-after-grouting permeability measurements have been used to justify the quantification of rock mass quality Q-parameter improvement, and the consequent increases in expected P-wave velocity and deformation modulus, for application in dam foundation treatment and its monitoring.