Relative contribution of various climatic processes in disintegration of clay-bearing rocks

The climatic processes of heating and cooling, wetting and drying, and freezing and thawing affect the disintegration characteristics of clay-bearing rocks (shales, claystones, mudstones, and siltstones) to varying degrees. Although heating and cooling, wetting and drying, and freezing and thawing are known to be the main processes responsible for physical disintegration of rocks under natural conditions, most of the previous investigators have used methods based only on water content variations (e.g., jar slake, slake index, and slake durability index tests) to assess the disintegration of clay-bearing rocks. Such assessments may not be adequate to explain the field behaviour of clay-bearing rocks subjected to a full range of climatic processes. In order to evaluate the combined effects as well as relative contributions of various climatic processes on the disintegration behaviour, samples of selected clay-bearing rocks, consisting of 5–6 particles, each weighing 85–150 g, were subjected to multiple cycles of heating and cooling, wetting and drying, and freezing and thawing. These treatments resulted in fragmentation of samples with fragments ranging from 50 to 2 mm and finer in dimensions. A new approach, referred to as the disintegration ratio, and defined as the area under the grain size distribution curve of the disintegrated material to the total area encompassing all grain size distribution curves of the samples, was used to account for fragmentation into varying sizes. Statistical analyses were performed to investigate the relationship between fragmentation, mineralogical composition, and physical properties.     

Durability Characterization of Marls from the Region of Dalmatia,Croatia

Durability is one of the most important engineering properties of weak and clay-bearing rocks. Weathering can induce a rapid change in rock material from initial properties to soil-like properties. The sensitivity of a rock type against weatherability is usually described by a durability parameter, such as the slake durability index. However, marl resistance is not detected satisfactorily by the durability indices by using slake durability test as suggested by ISRM for two wetting–drying cycles. The results of this study are obtained from samples of compact or laminated eocene marls from region of Dalmatia, Croatia. The samples were subjected to 4 cycles of slake durability, point load tests, determination of dry density, determination of carbonate content and absorption of water. The scatter of data suggests that strength probably has no influence on the durability of marls. On the other hand a separate group of marl samples have a second-cycle slake durability index higher than approximately 85%, and the durability of these samples is classified as “medium-high” to “high”, although the visual inspection of samples after testing, suggests that they should have “medium” to “low” durability classification. According to obtained results these samples of marl fulfil the criterions for the durability classification: a carbonate content lower than approximately 65%, a dry density lower than 2.4 Mg/m³, and values of water absorption higher than 5%.     

Slake durability study of shaly rock and its predictions

More than 35% of the earths crust is comprised of clay-bearing rocks, characterized by a wide variation in engineering properties and their resistance to short term weathering by wetting and drying phenomenon. The resistance to short-term weathering can be determined by slake durability index test. There are various methods to determine the slake durability indices of weak rock. The effect of acidity of water (slaking fluid) on slake durability index of shale in the laboratory is investigated. These methods are cumbersome and time consuming but they can provide valuable information on lithology, durability and weather ability of rock. Fuzzy set theory, Fuzzy logic and Artificial Neural Networks (ANN) techniques seem very well suited for typical complex geotechnical problems. In conjunction with statistics and conventional mathematical methods, a hybrid method can be developed that may prove a step forward in modeling geotechnical problems. During this investigation a model was developed and compared with two other models i.e., Neuro-fuzzy systems (combination of fuzzy and artificial neural network systems) and artificial neural network system, for the prediction of slake durability index of shaly rock to evaluate the performance of its prediction capability.     

Slake durability and mineralogical properties of some pyroclastic and sedimentary rocks

Slake durability of rocks is an important property of rock-mass and rock-materials in geotechnical practice. The slake durability of rocks is closely related to their mineralogical composition. In this paper, mineralogical examinations and slake durability tests for argillaceous clastic rocks, especially pyroclastic rocks, sandstones and mudstones of Neogene Tertiary age from Japan, were performed in order to assess the slake durability and rock alteration process of these rocks as well as to understand the relationship between mineralogy and durability.The mineral composition and textural features of the rocks were studied by means of optical microscopy (OM), X-ray diffractometry (XRD), electron microprobe analysis (EPMA), and scanning electron microscopy (SEM). In addition, the slake durability test was carried out by using the standard testing method of ISRM [Int. J. Rock Mech. Min. Sci. 16 (1979) 148] in distilled water and in the aqueous solutions with dissolved electrolytes of NaCl and CaCl₂.The pyroclastic rocks and tuffaceous sandstone, rich in di-octahedral and tri-octahedral Fe smectite, respectively, show distinctively different slaking behaviors. The pyroclastic rocks show relatively high slaking (Id₂=55.5% and Id₁₀=10.5%) than the tuffaceous sandstone (Id₂=94.1% and Id₁₀=87.8%, refer to text for Id₂ and Id₁₀). This difference in the slake durability observed in these rocks is due to the microscopic occurrences of smectite present in the interspaces between the particles (pyroclastic rocks) and zeolite cementing the interspaces (tuffaceous sandstone) as alteration minerals. In addition, the durability results of tuffaceous sandstone show that the slake durability decreases as the degree of weathering increases (weathered material Id₂=88.7% and Id₁₀=65.3%). Furthermore, two mudstones of Miocene and Pliocene ages, having different clay mineral compositions (smectite vs. illite+chlorite), show the lowest and the highest slake durability among the tested clastic rocks. Hard mudstone shows the highest (Id₂=98.1% and Id₁₀=95.5%) while the soft mudstone shows the lowest (Id₂=33.9% and Id₆=0.4%.) slake durability. Thus, the slake durability of pyroclastic and sedimentary rocks is greatly affected by their mineral composition and texture, and is closely related to their alteration history. Slake durability is also affected by the kind of dissolved electrolyte and its concentration in the aqueous solution, providing some useful information for geotechnical practice.     

Artificial neural networks and nonlinear regression techniques to assess the influence of slake durability cycles on the prediction of uniaxial compressive strength and modulus of elasticity for carbonate rocks

Understanding rock material characterizations and solving relevant problems are quite difficult tasks because of their complex behavior, which sometimes cannot be identified without intelligent, numerical, and analytical approaches. Because of that, some prediction techniques, like artificial neural networks (ANN) and nonlinear regression techniques, can be utilized to solve those problems. The purpose of this study is to examine the effects of the cycling integer of slake durability index test on intact rock behavior and estimate some rock properties, such as uniaxial compressive strength (UCS) and modulus of elasticity (E) from known rock index parameters using ANN and various regression techniques. Further, new performance index (PI) and degree of consistency (Cd) are introduced to examine the accuracy of generated models. For these purposes, intact rock dataset is established by performing rock tests including uniaxial compressive strength, modulus of elasticity, Schmidt hammer, effective porosity, dry unit weight, p‐wave velocity, and slake durability index tests on selected carbonate rocks. Afterward, the models are developed using ANN and nonlinear regression techniques. The concluding remark given is that four‐cycle slake durability index (I_d4) provides more accurate results to evaluate material characterization of carbonate rocks, and it is one of the reliable input variables to estimate UCS and E of carbonate rocks; introduced performance indices, both PI and Cd, may be accepted as good indicators to assess the accuracy of the complex models, and further, the ANN models have more prediction capability than the regression techniques to estimate relevant rock properties. Copyright © 2011 John Wiley & Sons, Ltd.     

The effect of pH and salty solutions on durability of sandstones of the Aghajari Formation in Khouzestan province,southwest of Iran

Slake durability of rocks is a vital engineering geological property of rock materials that has an important role in the promotion of slope stability, evaluation of rock materials, as well as the estimation of stone degradability. This parameter is related to such factors as mineralogy, physical characteristics of rocks, and the environmental conditions. A major part of south and southwestern Iran embraces the Aghajari Formation whose sandstones are used to form the foundations for some structures in Khouzestan province where they are being extensively used as aggregate(s). In this paper, tests of mineralogical examinations, physical properties, and slake durability of sandstones from Ahwaz and Haftkel anticlines were administered in order to assess the durability and degradability of these rocks. The rock durability of each type was evaluated to be up to 15 cycles in acidic and alkaline watery environments and salt aqueous solutions. The results showed that durability of sandstones under study is related to their petrographical and physical characteristics. The durability index of the sandstone samples was decreased by pH reduction and by increasing the concentration of aqueous solutions. The durability index of Ahwaz samples, too, was decreased in basic solutions while this index increased for Haftkel sandstones with the increase in the pH of solutions. Also, the obtained results illustrated that durability index decreased with the increase in the number of cycles. Based on the results, all sandstones show that the durability in sodium sulfate solution is much lower than that for the sodium chloride. Moreover, the slake durability index of the sandstones is decreased with an increase in the concentration of aqueous solutions. As a final statement, the Ahwaz sandstones show lower resistance to weathering processes than Haftkel sandstones; therefore, the use of rocks as building stones is not recommended here.     

Investigation of the effect of aggregate shape and surface roughness on the slake durability index using the fractal dimension approach

Argillaceous rocks cover about one thirds of the earth's surface. The major engineering problems encountered with weak- to medium-strength argillaceous rocks could be slaking, erosion, slope stability, settlement, and reduction in strength. One of the key properties for classifying and determining the behavior of such rocks is the slake durability. The concept of slake durability index (SDI) has been the subject of numerous researches in which a number of factors affecting the numerical value of SDI were investigated. In this regard, this paper approaches the matter by evaluating the effects of overall shape and surface roughness of the testing material on the outcome of slake durability indices.

For the purpose, different types of rocks (marl, clayey limestone, tuff, sandstone, weathered granite) were broken into chunks and were intentionally shaped as angular, subangular, and rounded and tested for slake durability. Before testing the aggregate pieces of each rock type, their surface roughness was determined by using the fractal dimension. Despite the variation of final values of SDI test results (values of I_d), the rounded aggregate groups plot relatively in a narrow range, but a greater scatter was obtained for the angular and subangular aggregate groups. The best results can be obtained when using the well rounded samples having the lowest fractal values. An attempt was made to analytically link the surface roughness with the I_d parameter and an empirical relationship was proposed. A chart for various fractal values of surface roughness to use as a guide for slake durability tests is also proposed. The method proposed herein becomes efficient when well rounded aggregates are not available. In such condition, the approximate fractal value for the surface roughness profile of the testing aggregates could be obtained from the proposed chart and be plugged into the empirical relation to obtain the corrected I_d value. The results presented herein represent the particular rock types used in this study and care should be taken when applying these methods to different type of rocks.     

Estimation of Durability Aspects of Al Masjid Al-Haram Marble,Makkah City,Saudi Arabia

The durability is a measure of the rock’s ability to resist degradation during its working life. Rock durability is greatly related to the mineralogical composition of rocks, rock texture (crystal interlocking, crystal shape and size), and the nature of fluids that are in contact with rock. Marbles have been among the most important building materials since ancient times. The main aim of this study is to evaluate the durability of Al Masjid Al-Haram marble and Ordinary white marble “Carrara” (M₁ and M₂) and develop some correlations among the physical and mechanical properties such as P-wave velocity, slake durability index, dry uniaxial compressive strength (UCS_Dry), abrasion resistance, point load index, impact strength index, Brazilian tensile strength, and Shore hardness. After testing and the evaluation of the test results, strong statistical correlations were found between P-wave velocity and other rock properties. Statistical correlations between the UCS_Dry other tests were also carried out. The coefficients of regressions (R²) range from 0.6177 to 0.997. The study shows that the UCS_Dry values of M1 and M2 have positive relationship with P wave velocities. Concluding remark is that the rocks tested in the study have good durability characteristics and can be reliably used for construction projects. On the other hand, the derived empirical equations can be used for the estimation purposes for similar rock types.     

Comparison of three artificial neural network approaches for estimating of slake durability index

Slake durability index (I _d2) is an important engineering parameter to assess the resistance of clay-bearing and weak rocks to erosion and degradation. Standard test sample preparation for slake durability test is difficult for some rock types and the test is time-consuming. The paper reports an attempt to define I _d2 using other parameters that are simpler to obtain. In this study, three different artificial neural network approaches, namely feed-forward back propagation (FFBP), radial basis function based neural network (RBNN), and generalized regression neural networks (GRNN) were used for estimating I _d2. The determination coefficient (R ²), root mean square error and mean absolute relative error statistics were used as evaluation criteria of the FFBP, RBNN, and GRNN models. The experimental results were compared with these models. The comparison results indicate that the GRNN models are superior to the FFBP and RBNN models in modeling of the slake durability index (I _d2).     

Slaking durability and its effect on the doline formation in the gypsum

Texture and grain size is of great importance in understanding the mechanical properties of rocks. The aim of this study was to investigate textural and slaking durability characteristics, and correlate them with the gypsum types where the dolines occurred, with particular reference to the texture and crystal size. The investigation comprised two stages: field work and laboratory testing. Initially, rock samples were obtained from various representative karstified and non-karstified locations. Thereafter, mineralogical, physical and slaking durability characteristics of the gypsum samples were determined by means of laboratory testing. After the field and laboratory works, the geological, mineralogical and slaking durability characteristics of the study area gypsum were reviewed and discussed from the point of view of doline formation. Results showed that fine grain sized alabastrine gypsum tends to be karstified and leads to doline formation. This is closely related to the crystal size, texture and attributable to the slaking durability of the gypsum. Consequently, the results demonstrate that the texture, especially crystal size, and effective porosity are important parameters controlling the slake durability of the gypsum and doline formation.     

The effect of pH of water and mineralogical properties on the slake durability (degradability) of different rocks from the Lesser Himalaya, India

Slake durability is an important geotechnical parameter and is a measure of degradability of rocks due to the process of mechanical and chemical breakdown. It is closely related to the mineralogical composition and the texture of the rocks. In this paper, mineralogical examination along with slake durability tests under variable pH conditions, both in acidic and alkaline environments, on the limestone, shale and siltsone were evaluated to understand the relationship between mineralogy and the degradability of rocks. The study revealed that rocks rich in calcium carbonate and or magnesium carbonate are adversely affected in the acidic environment, whereas, the rocks rich in quartz, feldspar and muscovite are independent of the pH of the slaking fluid, which in turn, is more influenced by the texture of the constituent minerals. It has also been observed that fine grained rocks are more susceptible to degrade in comparison to the coarse grained rocks.     

Role of smectite-rich shales in frequent foundation failures in southeast Nigeria

This paper investigated the geotechnical properties of smectite-rich shale, and its implications as foundation material. Ten expansive shale samples were collected from foundation materials at Akpugo in Nkanu West L.G.A. of Enugu State, southeast Nigeria. Samples were subjected to grading, Atterberg limits-cum-compaction tests, slake durability, specific gravity, permeability, undrained triaxial tests and x-ray diffraction scan. Fines and sand contents of the soil samples range from 51–97% and 3–49% respectively. Liquid limit, plastic limit and plasticity index have average values of 60.7, 19.1 and 43.3% respectively. Linear shrinkage and free swell showed average of 16.3% and 76%. These results are indicative of predominant clay soil with high plasticity, compressibility and water holding capacity. XRD scan established presence of smectite and illite clay minerals, confirming soil high plasticity, capable of causing instability in foundation soil. The shale achieved maximum dry density range between 1.79 and 1.94 kg/m³ at optimum moisture content range of 6.9–12.8%, indicating poor to fair foundation materials. The shale cohesion ranges from 15 to 30 kPa while the angle of friction ranges between 10° and 18°, signifying an average strength soil material. Samples slake durability index and specific gravity fall within 24–55% and 2.50–2.58 respectively, suggesting non-durable and weak soil. Permeability of the samples ranges between 7.36 ×10^?6 and 4.77 ×10^?8 cm/s which suggested low drainage capable of causing water-log at sites. Therefore, the shale could be generally classified as poor to fair foundation material, which on moisture influx experience reduction in strength due to deterioration of its constituent minerals, especially clay and cement materials during the lifespan of engineering structures. Authors therefore recommend modification of foundation soil, appropriate foundation design and good drainage control as ways of improving stability of engineering structures underlain by expansive shale.     

Interaction study of clay-bearing amphibolite–crude oil–saline water: Molecular level implications for enhanced oil recovery during low saline water flooding

Low saline water flooding (LSWF) had proved to be an efficient method for enhanced oil recovery in clay-bearing hydrocarbon reservoirs, but the interaction mechanisms among in-situ rocks – fluids and injection fluids within the reservoir – are not yet known properly. Understanding the molecular level interaction among these components is critical for designing and field scale implementation of LSWF in clay-bearing crystalline reservoir rocks, which is very limited in the existing literature. A weathered amphibolite rock and one dead crude oil from the Bakrol field (Cambay basin, India) have been used in this study. The presence of clay minerals in the weathered amphibolite rock was observed using a polarising microscope and characterised by the X-ray diffraction (XRD) and Fourier transform infrared (FTIR) techniques. The crude oil and its fractionated SARA components have been extensively studied by spectroscopic techniques for their characterisation. The interaction study among the rock powder, hydrocarbon crude oil and saline water has been performed in the present work for gaining better insight for designing the injection fluid for LSWF. The weathered amphibolite rock powder was mixed with the dead crude oil and kept for 30 days in room temperature (T) and pressure (P) for proper interaction. The XRD, FTIR and cation exchange capacity results clearly demonstrated the incorporation of crude oil components in the interlayer surfaces of clay minerals. The oil removal efficiency, from the oil-treated rock powder of three saline water samples having NaCl concentration of 3000, 5000 and 8000 ppm, was investigated using the UV–Vis and fluorescence spectroscopies. The low saline NaCl water is capable of removing the maximum amount of polar components from the oil-treated rock powder. These molecular level insights are valuable for designing effective injection fluid for enhancing the oil recovery from the clay-rich crystalline reservoir rock.     

泥质膨胀岩崩解物粒径分布与膨胀性关系试验研究

崩解性是膨胀岩最基本的特性之一,但在膨胀岩膨胀性的快速判别指标中少见关于崩解性及崩解物的定量指标。因此,有必要开展膨胀岩崩解物粒径分布特征和崩解性与膨胀性之间关系的研究,以对膨胀岩的快速判别进行补充。以浙江台州黑洞、蛇蟠岛和新疆大阪隧洞泥质岩样品为例,进行了干燥饱和吸水率和干燥饱和崩解试验,并分析了干燥崩解物粒径分布特征、耐崩解性指数及其与基于干燥饱和吸水率的膨胀性判别结果之间的关系。结果表明,膨胀岩膨胀性的强弱与其崩解物的最大含量粒组颗粒粒径、有效粒径和耐崩解性指数呈反相关关系。膨胀岩崩解物粒径分布的差异性对其膨胀性具有一定的指示意义。     

Geotechnical and mineralogical properties of weak rocks from Central Greece

Thirty bulk samples of hard soils-soft rocks such as marls, originating from Euboea Island and Peloponnesus area, were investigated to evaluate their geotechnical behavior. Specifically, by conducting a series of physical and geotechnical tests, such as liquid limit and plastic limit tests, along with the estimation of the grain size fraction, Slake Durability and Point Load Test. Certain parameters were determined and used for empirical correlations with their mineralogical characteristics. The mineralogical composition was determined by X-ray diffraction, thermo-gravimetric and thermal analysis, succeeded by textural analysis performed by Optical Microscope. With the help of the above mentioned tests, we interpreted the observed geotechnical behavior of the examined weak rocks by means of mineralogical composition and texture. Durability and the unconfined compressive strength was found to be influenced by high percentages in carbonate minerals. In addition, it was found that a decrease in clay content resulted in higher strength and durability values. The concluded empirical correlations verified the influence of these parameters and gave a general overview of the engineering behavior of the examined weak rocks.     

滇中红层软岩微观结构及水理特性试验研究

滇中红层软岩具有成岩作用差、易产生较大变形、遇水易软化、易崩解等特征,本文采用环境扫描电镜试验和水理特性试验,对红层软岩的微观结构特征,崩解、膨胀、软化等水理特性进行了研究。试验结果表明,红层软岩矿物粒间空隙大多被粘土矿物填充,粘土矿物以伊利石和蒙脱石为主,为混层结构,结晶程度相对较差,多数有蚀变的痕迹。具有微小裂隙的红层软岩在1~2次充分饱水烘干后,崩解性开始显现;随着干湿循环次数增加,岩样的质量变化呈减小趋势;干湿循环次数继续增加,崩解性指数趋于平缓。红层软岩由于风化作用影响程度和自然含水率的差异,岩体内部崩解张力具有明显不均匀性。经过自由浸水48h后,红层软岩的单轴抗压强度降低29.83%~58.47%,各地层软化系数在0.4~0.7之间,遇水后呈现显著软化效应。这些结果为红层软岩地区公路工程建设的工程地质研究提供了一定参考。     

Textural evidences for dissolution of silica-rich rocks of the Ypresian phosphatic series,Gafsa-Metlaoui basin,southwestern Tunisia: implication of biogenic silica supply on genesis of fibrous clays

The present work aimed to determine the mineralogical composition of Ypresian series and to clarify the influence of the dissolution of siliceous frustules on the genesis of fibrous clay minerals. The specimens sampled from CPG trench are mainly constituted of silica-rich rocks at Mides area located at the western part of Gafsa-Metlaoui basin. The samples were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM) in order to determine texture of constituents. The data obtained indicate that the bulk rock samples are mainly made up of opal CT and clay minerals. The latter consists of palygorskite-sepiolite minerals associated with smectite and few amount of illite. The trend of mineralogical composition indicates that fibrous clay minerals are more concentrated at the upper part. SEM observations indicated that palygorskite mineral appears as thread-like facies, which surround foliated texture of smectite in the lower part of the Mides section, although with the low Mg activity confirmed by the absence of dolomite. But, at the upper part of the Mides section, SEM observations revealed the occurrence of siliceous frustules, which have numerous dissolved areas and replacement of carbonate tests by silica. The dissolution saturated the depositional environment with silica which is required for the formation of palygorskite and sepiolite minerals, in addition to high Mg activity confirmed by the presence of dolomite in the bulk rock, which is required basically for the formation of sepiolite. Although the genesis mode of palygorskite and sepiolite is similar with very little difference, the genesis of sepiolite needs a high alkalinity than the formation of palygorskite.     

红层软岩崩解性路用控制方法研究

采用灰色关联度分析法对红层软岩的矿物成分、化学成分、崩解试验等数据进行了分析。分析表明, 水理特性不稳定的粘土矿物始终是影响软岩崩解的主要因素之一, 而不同的化学成分对红层软岩崩解性的影响程度不同。通过以纯水、MgCl2, FeCl3, NaCl, CaCl2盐溶液作为红层软岩岩块浸泡液的崩解试验, 说明纯水浸泡下软岩的崩解性最强, 而所选3种盐溶液对所选红层软岩样品的崩解性均有抑制作用, 其中又以CaCl2抑制作用最强。在此基础上提出公路施工中填筑前以浇水作为加快红层软岩崩解, 填筑压实中以掺入石灰作为抑制软岩崩解路用控制方法。     

Influence of Hematite Coating on the Activation of the Swelling Potential of Smectite-Bearing Rocks

The fraction of swelling-type clay minerals (smectites) is a first measure to estimate the swelling potential of natural rocks. This swelling potential is only activated if water can be incorporated in the sheet silicates. The samples studied in this work are volcanic rocks from the Southern Andes. According to the petrographic and mineralogical studies, the rocks are characterized as vulcanite with high content of smectite. Undisturbed samples showed minor swelling behaviour in conventional swelling tests, although X-ray diffraction and differential thermal analysis revealed swelling clay contents of more than 70 % in some samples. Powder swelling tests were performed on ground and recompacted rock samples. The results of these tests show a better agreement with those expected according to the mineralogical composition of the samples. The reason for the non-activation of the swelling potential in undisturbed samples was suspected to be the influence of the iron-oxide/hydroxide content, which was on average around 11 %. Scanning electron microscope images showed that the edge terminations of the clay particles are coated with hematite. The hydrophobic properties of hematite impede the access of water between the interlayers of the clay minerals and, in addition, hematite cementation prevents the expansion. In a further series of swelling tests water was replaced by a reducing solution (0.1 molar hydroxylammonium chloride) which removes the Fe-oxide coating. It can be shown that thus the swelling potential of the clay minerals in such undisturbed rocks can be activated.     

Settlement and slaking problems in the world's fourth largest rock-fill dam, the Ataturk Dam in Turkey

The Ataturk Dam is the fourth largest clay cored rock-fill dam in the world. Located in southeastern Turkey, it is the centrepiece of a project called the Southeastern Anatolian Project (GAP). The construction of the dam was finished in the short time of 3 years and 8 months in August 1990. As the reservoir level started to rise, settlement problems started to occur along the crest reaching considerable levels by May 1992 and the weathered vesicular basalt used in the rock-fill section of the dam started to slake seriously. The elevation of the crest has fallen down to such an extent that now the upper part of the dam is being reconstructed to the original height of 549 m in order to maintain the 7 m freeboard and keep the dam operational. The settlement and slaking problems of the dam were investigated both in the field and the laboratory using soil and rock mechanical techniques. Standard proctor tests were run to determine the optimum moisture content at which the highest dry density (best compaction) is obtained during compaction of the impervious clay core. Consolidation tests were performed on undisturbed compacted clay core samples to determine if the field compaction of the clay core was done to the standards determined in the laboratory. Unconfined compression tests were run on the two different (sound aphanitic and weathered vesicular) basalts used in the rock-fill section of the dam to determine their unconfined compressive strengths. Slake durability tests were run on the same basalts to determine their durability under wetting and drying cycles. Petrographic and X-ray analysis were done so as to study the mineralogical contents of the two basalts and in turn, to determine the cause of rapid slaking of the vesicular textured weathered basalt. The consolidation test results show that, the field compaction of the impervious clay core of the dam was not done to the standards determined through the proctor tests in the laboratory. The unconfined compressive strength of the sound aphanitic basalt is more than ten times greater than the weathered vesicular basalt, and while the former has extremely high durability the latter only has medium durability. Because of nontronite (iron montmorillonite) and secondary calcite amygdules filling the vesicles, the weathered vesicular basalt used in the rock-fill section is slaking badly causing additional settlement and landslides both in the clay core which is already settling and the rock-fill section of the dam. With the continuing slaking, the present reconstruction of the crest up to the theoretically intended height of 549 m to maintain the 7 m freeboard and keep the dam operational seems only to be a temporary solution.