Experimental assessment of long-term durability of some weak rocks

Slake durability tests, point load strength tests and X-ray diffraction analyses were carried out on thirteen rock types in an attempt to correlate the durability of the rocks with their strengths and mineral compositions. A concept is proposed to describe the rock degradation characteristics from the results of slake durability test cycles. A new classification system is introduced for rock durability, which allows the prediction of the strength of a rock when it has been affected by the weathering process. The aim of the study was to predict the influence of the weathering process (simulated by wetting and drying and heating and cooling) on the durability and strength of the volcanic, metamorphic and sedimentary rocks outcropping in eastern Thailand. Field studies were carried out in an attempt to relate the heat absorption of the rocks in situ to that measured on the laboratory specimens.     

Correlation between slake durability and rock properties for some carbonate rocks

The paper reports a study to assess the relationship between slake durability indices and uniaxial compressive strength, Schmidt hardness, P-wave velocity, modulus of elasticity, effective porosity, water absorption and dry and saturated unit weight for seven types of carbonate rocks obtained from south west Turkey. It was found that the dry unit weight, saturated unit weight and Schmidt hardness gave the best relationship with first cycle slake durability (r = 0.99) while uniaxial compressive strength has a strong relationship with fourth cycle slake durability (r = 0.94). The results showed little difference in the correlation coefficients obtained after the fourth cycle. It is concluded that, for the rocks studied, the first and fourth cycles provide sufficiently good data on the durability for preliminary engineering/design works and that the second to fourth cycle results could be estimated using the first cycle slake durability index (r = 0.99–0.97).     

Weathering and its relation to geomechanical properties of Cavusbasi granitic rocks in northwestern Turkey

The effect of mainly mechanical weathering on the granodiorites, granites and quartz diorites of the Cavusbasi area of northwest Turkey are described, the samples having been taken from cores and field exposures. The primary characteristics of these rocks are affected by the weathering process which results in a significant constraint on their use in engineering works. The tests undertaken on samples in the various weathering grades included point load and uniaxial compressive strength, slake durability, porosity, loss on ignition, dry and saturated unit weight and water absorption. A tentative correlation between these properties is presented. Electronic Publication     

Fractal parameter approach on weathering grade determination of Çeşme (Izmir, Turkey) tuffs

Tuffs, classified as weak rock to hard soil with respect to their strength, slake on exposure, hence engineering problems occur as they weather and loosen. Weathering grades were determined in the field and in the laboratory using petrographic, chemical, physico-mechanical, P-wave velocity, and slake durability measures. Strong correlations were found between chemical weathering index, average porosity and fractal parameters based on the slake durability test results. The shapes of the tuff particles before and after the slaking test were investigated using the fractal dimension method to explain numerically the variations of the surface characteristics of the test samples due to weathering. Two fractal parameters are proposed for the second and fifth cycles of the slake durability test. The study has shown that for assessing the weathering state of tuffs, the fractal dimension approach could be a more effective tool than other methods of weathering grade determination.     

Experimental relation between shear strength under low pressure and S-wave velocity of rock subjected to mechanical weathering

The reduction in the shear strength of rock exposed on slope surfaces due to mechanical weathering is a ubiquitous phenomenon in regions where extreme environmental conditions prevail, i.e., repeated changes in temperature and moisture. In dealing with the slope instability problems in such regions, the long-term effects of weathering on the strength, deformation and durability characteristics of exposed rock are envisaged in this study. Therefore, in addition to conducting multiple-cycle standard slake durability tests on rock samples taken from the lithologies of Pakistan and Japan, and on artificial soft rock, the decrease in strength and stiffness is also studied by reproducing mechanical weathering in the laboratory. The reproduced laboratory weathering (RLW) is conducted with a new device that enables vacuumed saturation, freezing, thawing, drying and cooling under a maintained level of confining pressure. The decrease in strength, stiffness and durability is elucidated from the test results, which indicate that rock having a very low level of reference strain (shear strength/modulus at small strain) is resistant to RLW and slaking. Intact rock exhibits very low reference strain and this reference strain increases with an increase in the degree of weathering, which is the case of weathered rock. The decrease in the strength of rock is an important property for judging the safety of rock slopes undergoing weathering. Thus, the relation between the strength and the S-wave velocity of rock undergoing weathering is established. The authors recommend the use of this relation for a quick assessment of the strength of rock by briefly measuring the S-wave velocity of the weathered surface layer. The relationship will assist practitioners in quickly screening potentially unstable slopes.     

The relationship between physical and chemical weathering indices of granites around Seoul,Korea

In order to assess the relationship between chemical weathering indices and physical properties of granite, physical and chemical analyses were performed on both natural and artificially weathered granite samples from the Seoul area, where the pH of the rainfall occasionally drops to below 5. The results suggest that slake durability, uniaxial compressive strength, Ruxton ratio, Parker index, modified weathering potential index, chemical alteration index and loss on ignition effectively revealed changes of the degree of chemical weathering. However, the study showed no such good correlation between chemical and physical properties except dry density against loss on ignition and modified weathering potential index against uniaxial compressive strength. It is recommended that both physical and chemical indices should be used for the classification of weathering grade for the granites in the Seoul area.

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A proposed weathering classification for basalts and their engineering properties (Turkey)

Most of the volcanic rocks widespread in Turkey are basalt. The effect of weathering processes on the physical and mechanical properties of this type of rock is important. To assess these properties and relations to each other, a study was undertaken in the Niksar region. A detailed investigation was carried out on basalts in the road cuttings of the Niksar ring road and Ünye-Akku?-Niksar highway alignments. A new classification system for basaltic rocks which are substantially influenced by weathering is proposed. The basic engineering properties of the basalt representing each weathering grade were determined. The properties tested are dry density, porosity, coefficient of permeability, uniaxial compressive strength, tensile strength and Young’s modulus. Interrelationships were determined for all test results. It is concluded that there is a substantial degradation in the engineering properties of the rock beyond a specific degree of weathering.     

A correlation between P-wave velocity,impact strength index,slake durability index and uniaxial compressive strength

Impact strength index, slake durability index and uniaxial compressive strength (UCS) are important properties of a rock mass which are used widely in geological and geotechnical engineering. In this study, the mechanical properties of one igneous, three sedimentary and three metamorphic rock types were determined in the laboratory and correlated with P-wave velocity. Empirical equations have been developed to predict the impact strength index, slake durability index and UCS from P-wave velocity, which may avoid the necessity for time-consuming and tedious laboratory testing. To check the sensitivity of the empirical relations, a t test was performed which confirmed the validity of the proposed correlations.      

Predicting the unconfined compressive strength of the Breathitt shale using slake durability, Shore hardness and rock structural properties

Compressive strength is the most widely used design parameter in the construction industry and in rock engineering. For example, Bieniawski [Bieniawski, Z. T., Estimating the strength of rock materials, Is. J. S. Afr. Inst. Min. Metall., 1974, 74, 312–320.] reported that mining engineers request the uniaxial compressive strength (UCS) more often than any other rock property. However, standards set for specimen preparation are very demanding. Therefore it is quite difficult and sometimes impossible to fulfill these requirements using weak rocks and especially shales. This paper evaluates the use of the slake durability and Shore hardness tests to estimate UCS, based on laboratory correlations performed for this study and others and based on analysis of structural and physical material properties affecting both strength and durability.     

Estimation of strength and deformation properties of Quaternary caliche deposits

The aim of this study was to develop and evaluate statistical models for predicting the uniaxial compressive strength (UCS) and average Young’s modulus (E _av) for caliches, using some index and physical properties. The caliche samples, from Adana, southern Turkey, were of low strength and difficult to sample. X-ray diffraction and microscopy were undertaken and the following physical parameters established: unit weight, apparent porosity, Schmidt rebound number, Shore hardness, P-wave velocity, slake durability, point load, uniaxial compressive strength and average Young’s modulus. Simple and linear regression variable selection analyses were performed. The best relationships were obtained for UCS with P-wave velocity and unit weight and for average Young’s modulus with P-wave velocity, porosity and slake durability. Empirical equations are proposed, although it is emphasised that these may only be applicable for caliche of a similar geological character.      

Water-induced variations in mechanical properties of clay-bearing rocks

This study presents the results obtained from laboratory tests carried out on different types of clay-bearing rock collected from various parts of Turkey, to quantify the effects of water content on mechanical properties of the rocks, and to develop a method for estimating the rock strength and deformability at any water content based on physical properties. For this purpose, in addition to physical properties of the rock types collected, needle penetration resistance, uniaxial compressive strength, tensile strength and modulus of elasticity were determined on a number of specimens with different water contents. The results suggest that with increasing the water content the reductions in the uniaxial compressive strength, modulus of elasticity and tensile strength are up to 90%, 93% and 90%, respectively, from oven-dried to saturated conditions. Based on a series of empirical models developed and the comparisons between the experimentally determined mechanical properties and those predicted from the models, it is concluded that the suggested models seem to be very practical tools to estimate the mechanical properties of the clay-bearing rocks at any water content using the coefficients related to some physical properties of the rock material such as dry unit weight, water absorption by weight and porosity. In addition, needle penetration test is particularly suitable for such rocks to indirectly estimate their uniaxial compressive strength.     

Estimation of strength parameters of rock using artificial neural networks

The accurate determination of geomechanical properties such as uniaxial compressive strength and shear strength requires considerable time in collecting appropriate samples, their preparation and laboratory testing. To minimize the time and cost, a number of empirical relations have been reported which are widely used for the estimation of complex rock properties from more easily acquired data. This paper reports the use of an artificial neural network to predict the deformation properties of Coal Measure rocks using dynamic wave velocity, point load index, slake durability index and density. The results confirm the applicability of this method.     

The effect of the pH of the testing liquid on the slake durability of gypsum

It is known that foundation problems are caused by the dissolution of gypsum due to both chemical and mechanical processes. In order to investigate the combined effect of physico-chemical agents on the erodability of gypsum, a series of slake durability tests were carried out on eight different types of gypsum using testing solutions with different pH values. XRD, chemical and petrographical analyses, and basic strength tests such as unconfined compression, Brazilian tensile, and point load were performed on the eight rock types. The slake durability results ranged from medium to very high under the different pH conditions but it was concluded that the slake durability of gypsum is independent of the pH of the testing solution. Mineralogical composition and fabric are considered to have a greater influence on the slake durability of gypsum.     

Physical and mechanical characterization of phyllites and metagreywackes in central Portugal

This work defines the physical and mechanical characteristics of phyllites and metagreywackes belonging to a schist–greywacke complex in central Portugal. The index properties, point load strength, uniaxial compressive strength, slake durability and Schmidt rebound hardness were determined. In general, the metagreywackes gave a higher strength than phyllites with the same weathering degree. Possible correlations and estimation models were established and compared with the equations obtained by different researchers.     

Evaluation of simple methods for assessing the uniaxial compressive strength of rock

Published data on 48 different rocks are used to evaluate the correlations between the uniaxial compressive strength (UCS) values and the corresponding results of point load, Schmidt hammer, sound velocity and impact strength tests. The variability of test results for each test and each rock type was evaluated by calculating the coefficient of variation. Using the method of least squares regression, the UCS values were correlated with the other test values. Also, the test methods were evaluated by plotting the estimated values of compressive strength vs. the measured values of compressive strength for each test. The results indicate that the least variability is shown in the impact strength test. So, among the test methods included in this study, the impact strength test is the most reproducible test; but the variability of test results for the other test methods is within acceptable limits for most engineering purposes. Strong linear relations between the point load strength index values and the UCS values were found for the coal measure rocks and the other rocks included in this study. The Schmidt hammer and the sound velocity tests exhibit significant non-linear correlations with the compressive strength of rock. In the sound velocity test, the data points are scattered at higher strength values. There is no clear relation between the impact strength values and the compressive strength values for the coal measure rocks. A weak non-linear correlation was found between the impact strength values and the compressive strength values for the other rocks. All test methods evaluated in this study, except the impact strength, provide reliable estimate of the compressive strength of rock. However, the prediction equations derived by different researchers are dependent on rock types and test conditions, as they are in this study.     

Influence of physical and geometrical properties of granite and limestone aggregates on the durability of a C20/25 strength class concrete

This paper presents an experimental study to evaluate the influence of physical and geometrical properties of granite and limestone aggregates on the durability of a C20/25 strength class concrete. Different granite and limestone aggregates were collected from seven quarries. Physical, geometrical and mechanical properties of aggregates as well as the rock weathering state were quantify by several tests such as, abrasion, surface hardness, uniaxial compressive strength, ultrasonic pulse velocity, water absorption by capillarity, vacuum water absorption and oxygen permeability.

Using aggregates from each quarry, several C20/25 strength class concrete mixes have been produced, with the same workability and volume proportions. Concrete specimens have been cured under water for 90 days; after that time concrete durability parameters were obtained through tests such as, vacuum water absorption, capillarity water absorption, water permeability and oxygen permeability.

Relevant statistical correlations have been obtained between absorption and permeability test of rock material and rock deterioration state (weathering). Valid statistic correlation was also obtained between durability parameters as well as among aggregates geometrical properties and concrete durability parameters.     

Investigating effects of water salinity on geotechnical properties of fine-grained soil and quartz in a sandstone case study: Ajichay project in northwest Iran

The effect of water salinity on the geotechnical properties of a CL soil and mechanical properties of a quartz sandstone has been studied using samples from the Ajichay project, located in the northwest of Iran. The purpose of this investigation is to investigate the feasibility of using saline water in processing the clay core of earthen dams in this area. One-dimensional consolidation, swelling, and uniaxial compressive strength tests were performed on the soil with distilled, half-saline, and saline water. To evaluate the effect of water salinity on the sandstones placed in the abutments of the dams, the slake durability index and uniaxial compressive strength were investigated. Results indicated that the compressibility index decreased, hydraulic conductivity decreased, and uniaxial compressive strength of the soil increased with increasing water salinity. The soil swelling percent with all three waters was less than 1 % after 24 h. However, swelling percent increased by 23 % with saline water and decreased by 32 % with half-saline water. Some damage in the rock texture such as disaggregation, weathering, and corrosion of the feldspars along with the dissolution of carbonate cement was observed in thin sections after 6 months of immersion in saline water. The strength of the sandstones exposed to saline water for 5 months decreased by between 5 and 13 %.

     

Investigation of the effects of wetting–drying and freezing–thawing cycles on some physical and mechanical properties of selected ignimbrites

This study was performed to investigate the changes in the physical and mechanical parameters of ignimbrites of different colors (black, red, yellow, gray) from Central Anatolia under the influence of wetting–drying and freezing–thawing cycles. For this purpose, 96 NX-size core samples were prepared. The unit weight, specific gravity, apparent porosity, water absorption by weight, slake durability index, uniaxial compressive strength, and P-wave velocity of each ignimbrite sample before conversion were determined. All of these parameters were then redetermined every 10 cycles (for a total of 50 cycles) for each sample. The changes in the values of the parameters after these set numbers of cycles were evaluated statistically. The petrographic and chemical compositions of the volcanic rocks influence their physical and mechanical properties, so some changes were also observed in the ignimbrite samples after these physical processes. Freezing and thawing cycles were observed to have an obvious impact on the physical and mechanical properties of the samples. The greatest changes were observed in black ignimbrite (with ferromagnesian minerals).     

Essais d’altération chimique accélérée au laboratoire par le double extracteur Soxhlet. Application à des roches granitiques de Corée du Sud

A double Soxhlet extractor was used in the laboratory to perform accelerated chemical weathering tests in order to simulate the leaching of granitic rocks under tropical climate. Several types of granitic rocks corresponding to various initial weathering grades were sampled on two test sites in South Korea. They were subjected to leaching with hot and pure water in the double soxhlet extractor in order to measure the evolution of some of their physical and mechanical properties. Tests showed a decrease of the physical characteristics, more particularly the P-wave velocity and quick water absorption ratio. This decrease mainly occurred during the first leaching cycles. Uniaxial compressive strength also decreased during the leaching test, and the fresher the granitic rock, the most important the UCS decrease. This kind of test allows the evaluation of the chemical weathering effects and also the estimation of the long-term mechanical properties of the rock.