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.      

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.      

Experimental study of polyurethane foam reinforced soil used as a rock-like material

In this study, polyurethane foam type thermoset polymerizing, due to chemical reaction between its liquid ingredients, was tested as binder after solidifying and then a rock-like material mixing with a sandy silt type soil was prepared. The uniaxial compressive strengths(UCSs) of polyurethane foam reinforced soil specimens were determined for different polyurethane ratios in the mixture. Additionally,a series of tests on slake durability, impact value, freezingethawing resistance, and abrasion resistance of polyurethane reinforced soil(PRS) mixture was conducted. The UCS values over 3 MPa were measured from the PRS specimens. The testing results showed that treated soil can economically become a desirable rock-like material in terms of slake durability and resistances against freezingethawing, impact effect and abrasion. As another characteristic of the rock-like material made with polyurethane foam,unit volume weight was found to be quite lower than those of natural rock materials.     

Water-induced softening behavior of clay-rich sandstone in Lanzhou Water Supply Project,China

The strength of clay-rich sandstone decreases significantly when in contact with water due to softening effects.This scenario can pose a severe threat to the stability of water diversion tunnels during construction and operation periods.To address the issues related to water-induced softening in clay-rich sandstone zones in a water diversion tunnel of Lanzhou Water Supply Project,the microscopic and micromechanical variations of rocks due to increasing water content in two different zones i.e.zones A and B,were determined by various testing methods,such as X-ray diffraction(XRD),scanning electron microscopy(SEM),thin section microscopy,micro-indentation test,sonic velocity test,and slake durability test.The microscopic analysis confirms the presence of montmorillonite mineral which is the dominant problematic geomaterial in engineering application.The integrity and durability of clay-rich sandstone were determined with sonic velocity and slake durability tests to calibrate the results obtained by the micro-indentation test.It shows that the elastic modulus and hardness of clay-rich sandstone decrease with the increase of saturation time,up to 144 h,which is more significant and rapid during early stage of saturation.After 144 h of saturation,the elastic modulus decreases by 89% and97%,and the hardness decreases by 89% and 99% for zones A and B sandstones,respectively.The results of slake durability and sonic velocity indicate that zone A sandsto ne remains 56.19% durability after 144 h of saturation,while zone B sandstone loses its durability merely after 72 h of saturation.The clay-rich sandstone starts to dissolve in water when the saturation time exceeds 144 h.The significant decreases in strength and durability of clay-rich sandstone due to water-induced softening are serious threats to tunnel stability.The improvements in the strength of surrounding rock mass by grouting and permeability by installation of drainage galleries can reduce the damage caused by water-induced softening.     

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.     

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).     

Estimating the uniaxial compressive strength of pyroclastic rocks from the slake durability index

Because the preparation of standard samples may not always be possible for weak or soft rocks, the prediction of uniaxial compressive strength (UCS) from indirect methods is widely used for preliminary investigations. In this study, the possibility of predicting UCS from the slake durability index (SDI) was investigated for pyroclastic rocks. For this purpose, pyroclastic rocks were collected from 31 different locations in the Cappadocian Volcanic Province of Turkey. The UCS and SDI tests were carried out on the samples in the laboratory. The UCS values were correlated with the SDI values and a very strong exponential relation was found between the two parameters. Since some data were scattered over the UCS values of 20 MPa, the correlation plot was redrawn for above and below the UCS values of 20 MPa, respectively. Very strong linear correlations were developed for two cases. Our concluding remark is that the UCS of pyroclastic rocks can be estimated from the SDI.

     

Effects of water intrusion on thermal conductivity and durability of carbonaceous rocks

This study aimed to investigate the role of water intrusion on thermal conduction and durability of three types of carbonaceous rock with different mineralogical components. The soaking method was selected to simulate water intrusion, and the respective evolutions of thermal conductivity k and slake durability index I_d2 during soaking period were assessed. Scanning electron microscopy was conducted to explore the mechanism controlling these revolutions. The results revealed that the magnitude of moisture content and density of carbonaceous rocks at their natural state was clearly correlated to the content of illite mineral. Water intrusion was beneficial to the thermal conduction of carbonaceous rocks, where thermal conductivity increased with an increase in soaking time and exhibited a moderate increment after 8 days of soaking. Slake durability index I_d2 was sharply decreased as soaking progressed and reached a low level after soaking. This deterioration in durability was mainly attributed to the absorption of free water, which in turn yields the anisotropic expansion of specific minerals. An unstable structure with more pores and new morphology minerals were identified in carbonaceous rocks at the completion of soaking procedure. An empirical relationship was developed successfully for predicting slake durability index using thermal conductivity.     

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.     

The effect of weathering on durability and deformability properties of granitoid rocks

In this paper, the effects of weathering on durability and deformability properties for three different types of granitoid rocks were investigated. Five weathering grades ranging from fresh to completely weathered rocks were considered for each rock type. Deformability has been evaluated based on failure strain, tangent and secant modulus. For measuring these parameters, at least five uniaxial compressive strength tests with axial strain recorded were conducted on each weathering grade. To assess the weathering effect on the durability behavior of these rocks, a slake durability test was performed up to 40 cycles. The obtained results indicated that uniaxial compressive strength and elastic modulus dramatically decrease with increasing weathering grade. After moderately weathering grade, remarkable damage was observed in the structure and fabric of considered rocks. The results from slake durability tests showed that the slake durability index for each weathering grade has a certain changes trend which can be used in determination of the weathering grade and the long-term durability assessment. Moreover, the results showed that for evaluation of the long-term durability of the mentioned rock types, at least eight cycles should be considered, while two cycles were sufficient for estimation of weathering grade.     

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.     

Inconsistency of changes in uniaxial compressive strength and P-wave velocity of sandstone after temperature treatments

It is generally accepted that the uniaxial compressive strength(UCS)and P-wave velocity of rocks tend to decrease simultaneously with increasing temperature.However,based on a great number of statistical data and systematic analysis of the microstructure variation of rocks with temperature rising and corresponding propagation mechanism of elastic wave,the results show that(1)There are three different trends for the changes of UCS and P-wave velocity of sandstone when heated from room temperature(20
C or 25
C)to 800
C:(i)Both the UCS and P-wave velocity decrease simultaneously;(ii)The UCS increases initially and then decreases,while the P-wave velocity decreases continuously;and(iii)The UCS increases initially and then fluctuates,while the P-wave velocity continuously decreases.(2)The UCS changes at room temperaturee400
C,400
Ce600
C,and 600
Ce800
C are mainly attributed to the discrepancy of microstructure characteristics and quartz content,the transformation plasticity of clay minerals,and the balance between the thermal cementation and thermal damage,respectively.(3)The inconsistency in the trends of UCS and P-wave velocity changes is caused by the change of quartz content,phase transition of water and certain minerals.     

Determination of the thermal conductivity from physico-mechanical properties

Samples of limestone, dolomite, dolomitic limestone, marble, travertine, sandstone, siltstone, andesite, basalt and porous basalt from different parts of Turkey were tested to obtain their UCS, porosity, water absorption, density, P-wave velocity and thermal conductivity (TC). It was observed that while TC increased with density, P-wave velocity and UCS, it decreased with increasing porosity. Equations are presented to allow an assessment of TC from these physico-mechanical properties.      

颗粒级配对残积土MICP灌浆效果的影响评价

微生物诱导碳酸钙沉淀加固砂性土的试验研究较为丰富,但在固化崩解性软岩残积土的可行性及效果评价方面目前仍未涉及。考虑到崩解性软岩残积土与砂性土颗粒的诸多不同以及自身颗粒级配产生的差异,选用4种不同粒径范围的松散泥质软岩残积土颗粒进行微生物灌浆试验研究,并通过渗透性能、无侧限抗压强度(UCS)试验、碳酸钙生成量及孔隙率测试,分析颗粒级配对残积土MICP灌浆效果的影响;再借助于扫描电镜(SEM),观测全级配残积土颗粒表面的MICP反应效果。结果表明:不同粒径级配的崩解性软岩残积土在经过微生物灌浆处理后,其胶结效果差异明显。全级配崩解性软岩残积土灌浆过程中更易沉积具有胶结作用的碳酸钙晶体,其胶结试样力学性能较间断级配提升显著,且其孔隙率降幅和单位质量碳酸钙生成量也较大,胶结效果更佳。研究成果可为软岩弃渣填方路堤的微生物加固工程提供借鉴。     

Evaluating the influence of rate of undercutting on the stability of slopes

Cut slopes of alternating soft and hard layers along roads in Jordan are subject to differential weathering, erosion and human activities. This can result in undercutting, leading to rockfalls that endanger traffic. The factors affecting the rate of undercutting and the influence of this on the stability of ten selected road cuts along the Amman–Irbid highway in Jordan were determined. The depth of undercut was measured at selected points and the mean rate of undercutting found to vary from 10 to 73 mm/year. Grain density, bulk density, slake durability, Atterberg limits, porosity and grain size distribution were determined and correlated with the rate of undercut. A positive relationship was found between undercutting and the sand fraction and porosity values and a negative relationship with the slake durability index.      

基于超声波测试的冻融循环作用下混凝土强度损伤演变研究

针对高寒地区混凝土抗冻耐久性问题,在混凝土中加入不同掺量的粉煤灰研究其抗冻性能,通过非金属声波检测仪进行冻融循环过程中混凝土强度无损测试,研究了冻融循环作用下混凝土强度损伤和动弹性力学参数的演化特征,分析了冻融循环过程中混凝土声波波速与力学性能变化规律。研究结果表明:掺入引气剂能够提高混凝土的抗冻性,相同引气剂掺量下,粉煤灰掺量为10%的混凝土抗冻性较好;冻融循环过程中,超声波纵波波速、横波波速与动弹性模量、动剪切模量均随着冻融循环次数的增加呈相似性衰减,且存在较高相关性。     

Dynamic fragmentation of microwave irradiated rock

The microwave-assisted rock fragmentation has been proven to be a promising approach in reducing cutting tools wear and improving efficiency in rock crushing and excavation.Thus,understanding the influence of damage induced by microwave irradiation on rock fragmentation is necessary.In this context,cylindrical Fangshan granite(FG)specimens were exposed to microwave irradiation at a power of 6 kW for different durations up to 4.5 min.The damages of the specimens induced by irradiation were quantified by using both X-ray micro-CT scanning and ultrasonic wave measurement.The CT value and Pwave velocity decreased with increase of irradiation duration.The irradiated specimens were then tested using a split Hopkinson pressure bar(SHPB)system to simulate rock fragmentation.A momentum-trap technique was utilized to ensure single-pulse loading on the specimen in SHPB tests,enabling valid fragment size distribution(FSD)analysis.The dependence of dynamic uniaxial compressive strength(UCS)on the irradiation duration and loading rate was revealed.The dynamic UCS increased with increase of loading rate while decreased with increase of irradiation duration.Using the sieve analysis,three fragmentation types were proposed based on FSD,which were dictated by both loading rate and irradiation duration.In addition,an average fragment size was proposed to quantify FSD.The results showed that the average fragment size decreased with increase of loading rate.A loading rate range was identified,where a dramatic reduction of the average fragment size occurred.The dependence of fragmentation on the irradiation duration and loading rate was also discussed.     

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).     

Effects of fibers on expansive shotcrete mixtures consisting of calcium sulfoaluminate cement,ordinary Portland cement,and calcium sulfate

The mining industry often uses shotcrete for ground stabilization. However, cracking within shotcrete is commonly observed, which delays production schedules and increases maintenance costs. A possible crack reduction method is using expansive shotcrete mixture consisting of calcium sulfoaluminate cement (CSA), ordinary Portland cement (OPC), and calcium sulfate (CS) to reduce shrinkage. Furthermore, fibers can be added to the mixture to restrain expansion and impede cracking. The objective of this paper is to study the effects of nylon fiber, glass fiber, and steel fiber on an expansive shotcrete mixture that can better resist cracking. In this study, parameters such as density, water absorption, volume of permeable voids, unconfined compressive strength (UCS), splitting tensile strength (STS), and volume change of fiber-added expansive mixtures were determined at different time periods (i.e. the strengths on the 28th day, and the volume changes on the 1st, 7th, 14th, 21st, and 28th days). The results show that addition of fibers can improve mixture durability, in the form of decreased water absorption and reduced permeable pore space content. Moreover, the expansion of the CSA-OPC-CS mixture was restrained up to 50% by glass fiber, up to 43% by nylon fiber, and up to 28% by steel fiber. The results show that the STS was improved by 57% with glass fiber addition, 43% with steel fiber addition, and 38% with nylon fiber addition. The UCS was also increased by 31% after steel fiber addition, 26% after nylon fiber addition, and 16% after glass fiber addition. These results suggest that fiber additions to the expansive shotcrete mixtures can improve durability and strengths while controlling expansion.