Schmidt Hammer Hardness Research Articles

The relationship between mechanical properties and mineralogical composition of some sedimentary rocks

The physical and mechanical properties of rock material are remarkably associated with the comprising mineralogical composition and textural characteristics. Therefore, a meticulous understanding of the role of mineralogical composition in the engineering behaviour of sedimentary rocks is essential. For this purpose, both the matrix and aggregates of rocks must be thoroughly analysed to obtain comprehensive insight into this aspect. The main objective of this study is to investigate the extent of the complexity of the relationship between mineralogical and mechanical properties of some sedimentary rocks. Several sedimentary rock samples from different regions of Iran were analysed in this study. The same samples were then tested to determine uniaxial compressive strength, tensile strength, Schmidt hammer hardness and the Cerchar abrasivity index. The relationship between these properties and the mineralogical composition is described by linear and multivariate regression analyses. The research unequivocally establishes a significant correlation between specific mechanical parameters and mineralogical composition. Moreover, the findings highlight the relative importance of each parameter, with some being more crucial than others.

Estimation of uniaxial compressive and indirect tensile strengths of intact rock from Schmidt hammer rebound number

Abstract A number of destructive and non-destructive tests were conducted on rock samples collected from various zones in northern Iraq. So far, for Iraqi rocks, few studies have correlated Schmidt hammer rebound (R) with both unconfined compressive strength (UCS) and Brazilian tensile strength (BTS). In this study, the objective is to develop a relationship between the rebound number of Schmidt hammer surface hardness (rebound number) and both the BTS and the unconfined compressive strength (UCS) of different types of northern Iraqi rocks. The required relationship should be based on measured values of the UCS, BT, and Schmidt hammer hardness. To determine the relationship between R and both the UCS and BTS, 120 intact rock samples were prepared and tested using a uniaxial compressive test machine, a Brazilian test apparatus, and an L-type Schmidt hammer test (BTS). Three different types of rock samples (sandstone, claystone, and limestone) were collected from several locations in northern Iraq (Domeez, Baadra, and Zawita). For the three types of rocks, a new linear correlation with a high value of the regression coefficient R 2 is presented, linking the UCS and BTS separately versus R. For the three types of rocks studied, the correlation between UCS and R is better than the correlation between Brazilian tensile strength (BTS) and R.

Investigation of Some Property Changes of Light-Colored Turkish Natural Stones after High-Temperature Treatments

Natural stones are a widely used construction material for both structural and decorative purposes. It is a material used for many floors and cladding due to its special beauty and quite aesthetic appearance. However, natural stones are exposed to different temperatures due to natural, urban or industrial activities and they lose their physico-mechanical properties. It is known that high temperatures and fire cause degradation of construction and building stones. There are many studies investigating the effect of high temperatures on physical and mechanical properties of natural stones, while there are very limited studies on color and gloss. In this study, the changing physical and mechanical properties, color and gloss of different light-colored polished natural stones exposed to room temperature up to 1000 °C in the oven were investigated. For this purpose, natural stones were gradually exposed to 200, 400, 600, 800 and 1000 °C, starting from room temperature. After exposure to different temperatures, water absorption, porosity, Schmidt hammer hardness, point load strength, color and gloss were measured and compared to reference samples (at room temperature). However, all samples were decayed at 1000 °C, changes at this temperature value could not be determined. The results obtained at other temperature values were evaluated separately for each parameter. While the change in physico-mechanical properties of all samples up to 400 °C was limited, a dramatic change was observed with increasing temperature. In all samples, point load strength losses were observed due to an increase in porosity and water absorption. In addition, all samples darkened at 400 °C, while the whiteness value (L*) of samples increased at 800 °C. Gloss values gradually decreased due to the increase in temperature.

Physico-mechanical properties of the sandstones and effect of salt crystallization on them: A comparative study between stable and unstable slopes (a case study of the Khorramabad-Zal highway in Iran)

The Khorramabad-Zal highway is a road constructed in Lorestan province (southwest of Iran). With a length of 104 km, it connects Khorramabad and Andimeshk cities. Performing many excavations in sandstone outcrops along this highway has created stable and unstable slopes. The release of Na+ and SO42- ions due to weathering and dissolution of the marl and gypsum rocks has formed Na2SO4 salt in this area. Permeating this salt into the sandstones has led to the salt crystallization process in them. The present study investigates sandstones’ physico-mechanical properties in the stable and unstable slopes before and after salt crystallization test up to 15 cycles. To this end, 14 sandstone samples belonging to stable and unstable slopes were collected. Next, their physico-mechanical properties are characterized by determining their porosity (n), point load index (PLI), Schmidt hammer hardness (SHH), and slake durability index (SDI) before and after salt crystallization test in Na2SO4 solution (i.e., untreated and treated samples, respectively). The results indicate that samples of unstable slopes in untreated conditions generally have a higher n, and lower PLI, SHH, and SDI than those from the stable slopes. With increasing the salt crystallization test cycles, the samples’ n increased, while their PLI, SHH, and SDI decreased with different levels depending on the slope types. Overall, the deterioration effects of salt crystallization were more significant on the samples’ physico-mechanical properties belonging to unstable slopes, especially those subjected to salt crystallization under field conditions. This result was confirmed by the rate of loss (RL) of the samples’ physico-mechanical properties, and microscopic and macroscopic observations after the salt crystallization test. The deterioration in the physico-mechanical properties of sandstone samples caused by salt crystallization in field conditions increased slope instability near marl and gypsum rock outcrops. Finally, regression analyses showed that the SDI has good correlations with n, PLI, and SHH with determination coefficients (R2) of 0.919, 0.882, and 0.837, respectively. These correlations are accurate enough for use in the preliminary assessment of samples SDI from their n, PLI, and SHH. Finally, these correlations obviate the need to perform SDI as a laborious and time-consuming test.

Correlation between Schmidt Hammer Hardness, Strength Properties and Mineral Compositions of Sulfate Rocks

Correlation between Schmidt Hammer Hardness, Strength Properties and Mineral Compositions of Sulfate Rocks

Statistical models for estimating the uniaxial compressive strength and elastic modulus of rocks from different hardness test methods

In engineering projects (dams, tunnels, slope stability) the strength characteristics of the rocks affect the construction operations. It is sometimes difficult, time-consuming, and expensive to evaluate the engineering properties of solid rocks by performing direct tests. For this reason, various laboratory studies have been carried out by many researchers to predict important engineering properties such as uniaxial compressive strength (UCS) and elastic modulus (E) of rocks in a practical way. One of the engineering properties used to estimate UCS-E practically is the hardness of rocks. Hardness tests are easy to apply and non-destructive, and in many of these tests very small specimens are needed. The main objective of this study is to analyze the relations between the UCS-E of the rocks and the various hardness methods (Schmidt hammer hardness, SHH; Shore Scleroscope hardness, SSH; Vickers hardness, HV; Brinell hardness, HB; and Indentation hardness index, IHI). For this purpose, the most appropriate and meaningful relations between hardness tests and UCS-E were determined by simple regression (SR) techniques. Relationships between main engineering properties (UCS, E) and physicomechanical properties were analyzed by multiple regression (MR) techniques using SPSS software. The statistical analyses made revealed the existence of strong correlations between UCS-E and hardness properties of rocks.

Profiles of Near‐Surface Rock Mass Strength Across Gradients in Burial, Erosion, and Time

AbstractRock mass strength is recognized as an important control on landscape morphology and evolution. However, the controls on rock strength in mountainous topography remain poorly characterized, in part because strength remains challenging to quantify at spatial scales relevant to geomorphology. Here we quantify the mechanical properties of rock masses using subsurface S‐wave velocities, Schmidt hammer hardness values, and Geological Strength Index (GSI) observations. We produce shallow depth profiles of rock mass shear strength using intact rock hardness as measured from a Schmidt hammer, and assessment of the structure and surface conditions of fractures using GSI. We apply these techniques to the Western Transverse Ranges, southern California, USA, where gradients in stratigraphic age and erosion rate allow us to evaluate our methodology. We resolve strength differences of 200 kPa to ∼5 MPa that appear to be related to diagenetic changes associated with the maximum burial depth of young clastic sedimentary rocks. For rocks of the same lithologic type, stratigraphic age, and inferred burial histories, we resolve smaller differences in strength (300 kPa–1.5 MPa) that appear to be positively correlated with mean erosion rates. We suggest that the increase in strength with increasing erosion rate reflects decreased residence time in the weathering zone for ranges experiencing faster fault slip rates. These findings demonstrate up to an order of magnitude variability in strength with respect to burial, erosion, and time for lithologically similar rocks. As such, lithology alone is unlikely to adequately capture the role of rock strength in landscape evolution.

Evaluation of empirical approaches in estimating mean particle size after blasting by using nondestructive methods

It is well-known that rocks have heterogeneous properties, and these properties played a curial role in blasting operations to obtain fragmented rocks with different particle size distributions. Therefore, the estimation of the particle size distribution of the rock is one of the most important parameters in terms of the economic operation of open-pit mines as it is directly related to mining operations such as loading, transporting, crushing, and grinding. Many parameters divided into controllable and noncontrollable affect the efficiency of blasting operations. This study aimed to suggest new empirical models based on nondestructive test methods including P wave velocity and Schmidt hardness to predict the mean particle size of the rock after blasting. WipFrag software was used to evaluate the pictures taken after blasting and to determine the average particle size distribution of the rock mass. Experimental results obtained from simple and multiple regression models show that there is a good agreement observed between the mean particle size of rock mass and its Schmidt hammer hardness and P wave velocity properties.

Evaluating the Effects of Mineral Grain Size and Mineralogical Composition on the Correlated Equations Between Strength and Schmidt Hardness of Granitic Rocks

Uniaxial compressive and Brazilian tensile strengths (UCS and BTS) of rocks are considered important properties in the design of most the geotechnical projects that interact with rock such as slope stability and underground excavation. Indirect tests such as Schmidt hammer hardness (SH) can be used for prediction of UCS and BTS of rocks. The aim of this study is to correlate the UCS and BTS of granitic rocks with SH with an emphasis on influence of petrographic characteristics. For this purpose, 10 different granitic rocks were selected from Iran’s quarries and their UCS, BTS, SH and petrographic characteristics including mean mineral grain size (MGS) and mineralogical composition (Quartz/Feldspar ratio) (Qz/Fl) were determined. Using data analysis, correlation between UCS and BTS with SH, MGS and Qz/Fl statistically were investigated using multiple regression analyses. In these analyses, the UCS and BTS were considered to be the dependent variable, which are dependent on the independent variables of the SH, MGS and Qz/Fl. It was found out that there are moderate correlations (R2 = 0.523 to 0.759) between UCS and BTS with SH, whereas there are strong correlations (R2 = 0.868 to 0.955) between UCS and BTS with SH when MGS and Qz/Fl are considered. Finally, it was concluded that the regression equations proposed in this study are in good accuracy for prediction of UCS and BTS, and thus making a rapid assessment from UCS and BTS of granitic rocks.

Multivariate probability distribution for some intact rock properties

A multivariate probability distribution model for nine parameters of intact rocks, including unit weight (γ), porosity (n), L-type Schmidt hammer hardness (RL), Shore scleroscope hardness (Sh), Brazilian tensile strength (σbt), point load strength index (Is50), uniaxial compressive strength (σc), Young’s modulus (E), and P-wave velocity (Vp), is constructed based on the ROCK/9/4069 database that was compiled by the authors. It is shown that the multivariate probability distribution captures the correlation behaviors in the database among the nine parameters. This multivariate distribution model serves as a prior distribution model in the Bayesian analysis and can be updated into the posterior distribution of the design intact rock parameter when multivariate site-specific information is available. In this paper, the parameters for the posterior distribution of the design intact rock parameter are summarized into user-friendly tables so that engineers do not need to conduct the actual Bayesian analysis. Caution should be taken in extrapolating the results of this paper to cases that are not covered by ROCK/9/4069, because the resulting posterior distribution can be misleading.

Examine the Correlation between Physico-Mechanical properties of Selected Granite rocks in Ondo State, Nigeria

This research examines the correlation between physico-mechanical properties of some selected granite rocks in Ondo State, Nigeria. Samples were collected at Zibo FM Quarry, Aaye and Samchase Quarry, Itaogbolu and tested in the laboratory for the determination of rock density, hardness, and strength. An average density of between 2.57g/cm3 and 2.67g/cm3 was recorded. Schmidt hammer and Rockwell hardness machine wereused for the determination of rock samples hardness. An average uniaxial compressive strength of rock sample was estimated from the values obtained from Schmidt hammer rebound value. The Hardness test varies from 115.90MPa to 185.00MPa (classified to have high strength) while the average Rockwell hardness varied from 45.1HRA - 57.32HRA. The average point load index ranges from 7.402MPa - 7.505MPa classified to have very high strength. Multiple regression analysis using computer-aided solution (Statistical Package for Social Sciences - SPSS) was used to analyze data obtained from the laboratory and field tests. Five parameters were input into the multiple regression analysis to generate the models. Two parameters which are Schmidt hammer rebound value and Rockwell hardness value out of five parameters are dependent variables, while point load index, uniaxial compressive strength, and density are independent variables. The result of the models developed shows positive correlations – an indication that the hardness of rock gives a significant contribution in drilling bit selection. Keywords : Rock density, Schmidt hardness, Rockwell hardness, uniaxial compressive strength, point load strength, and SPSS

A correlative study on textural properties and crushability of rocks

Rock texture is a term representing the mineral grains, grain sizes, and matrices of rocks. Crushability properties of rocks are very important parameters on an industrial scale and they can be determined by different methods. This study investigated the effects of textural properties of rocks on their crushability. For this purpose, some physical and mechanical tests were carried out on 12 different rock samples, which were divided into igneous, metamorphic, and sedimentary rock groups. All rock samples were crushed by using jaw and roll crushers, and crushability indices (CI) and particle sizes (d50, d80) were determined for all rock samples. The textural properties of rocks were defined by using the texture coefficient (TC) approach on thin section images. The test results were statistically analyzed, and firstly the physical and mechanical properties were correlated with CI and TC, respectively. Positive linear correlations were found between TC and uniaxial compressive strength (UCS), Brazilian tensile strength (BTS), and Schmidt hammer hardness (SHH). When the rock samples were grouped based on their geological origins, there were strong or good linear relationships between CI and UCS and BTS for both the jaw and roll crushers. Then, TC was correlated with CI, d50, and d80. It was found that TC was influential on CI especially for the roll crusher. However, when the rocks were separated as igneous, metamorphic and sedimentary, strong linear relationships were found for both crushers. The same was observed for the relationship between TC and both d50 and d80; the correlation coefficients were higher and more reliable for the roll crusher than the jaw crusher. The results of this study showed that the textural properties of rocks are more influential on the results obtained in a roll crusher than a jaw crusher. However, more rock samples are required to verify the results of this study.

PERFORMANCE PREDICTION OF CHAIN SAW MACHINES USING SCHMIDT HAMMER HARDNESS

Schmidt hammer hardness (RL) provides a quick and inexpensive measure of surface hardness
 that is widely used for estimating the mechanical properties of rock material such as strength,
 sawability, cuttability and drillability. In this study, RL
 as predictors, which is thought to be a
 useful, simple and inexpensive test particularly for performance prediction of chain saw machine
 (CSM), is suggested. This study aims to estimate CSM performance from RL
 values of rocks.
 For this purpose, rock cutting and rock mechanics tests were performed on twenty four different
 natural stone samples having different strength values. In this study, Chain Saw Penetration
 Index (CSPI) has been predicted based on RL
 which is one of the two models previously used for
 performance prediction of CSMs. The RL
 values were correlated with UCS, CSPI and SE using
 simple regression analysis with SPSS 15.0. As a result of this evaluation, RL
 has a strong relation
 with UCS and SE. It is statistically proved that the model based on RL
 for predicting CSPI is valid
 and reliable for performance prediction of CSM. Results of this study indicated that the CSPI of
 CSMs could be reliably predicted by empirical model using RL
 . 

Estimating the sawability of large diameter circular saws based on classification of natural stone types according to the geological origin

Different physico-mechanical parameters (density, uniaxial compressive strength, Brazilian tensile strength, Cerchar abrasivity index, Schmidt hammer hardness, Shore scleroscope hardness, and mean grain size) were used to find out the sawability of large diameter circular saws in the metamorphic and sedimentary natural stones. The simple, multiple linear and non-linear regression models were developed for estimation of the areal slab production rate of the large diameter circular saws. First, simple regression analyses were performed to find out the best relationships between the dependent variable (areal slab production rate) and each independent variable (physico-mechanical properties) in three different groups of natural stones as metamorphic, sedimentary, and metamorphic/sedimentary (combined). Second, multiple linear and non-linear regression analyses were carried out using selected independent variables. Then, the significances of these models were statistically validated. The models developed in this study could be used by planners and natural stone producing companies for cost prognosis and sawing operation schedule in the metamorphic and sedimentary stones.

Estimation of uniaxial compressive strength of North Algeria sedimentary rocks using density, porosity, and Schmidt hardness

This study aims to establish new correlations to assess uniaxial compressive strength (UCS) of northern Algeria sedimentary rocks. This estimation is based on the measurements of density, porosity, and Schmidt hammer hardness. To achieve this goal, a geological and geotechnical characterization campaign was conducted on 19 types of sandstone and carbonate rocks which have been collected from different geological areas of the Maghrebides chain. Petrographic analyses were conducted to identify the geological characteristics of each kind of rock. Subsequently, physico-mechanical tests (i.e., density, porosity, hardness, and uniaxial compressive strength) were carried out for all the sampled rocks. The results were then used to develop correlations between UCS values and the other parameter values determined. Finally, the UCS predictive equations which have the best predictive powers (coefficient of determination R 2 of 0.75 to 0.94) were discussed taking into account the geological specificities of the rocks, and then compared to similar studies developed by other authors in different areas of the world.

Study of correlation between specific energy of cutting and physical properties of rock and prediction of excavation rate for lignite mines in Çayırhan area, Turkey

Laboratory specific energy (SE) is a reliable indicator to evaluate the rock cuttability and efficiency for mechanical excavation in mining and tunneling applications. In this study, various geological units encountered in lignite mines were studied through laboratory tests and measurement of specific energies in nine different rock types and two different lignite samples from Cayirhan area, Ankara, Turkey. The correlation between the physical and mechanical properties of various rock including uniaxial compressive strength, tensile strength, cone indenter hardness, shore hardness, Schmidt hammer hardness, and density with measured SE of cutting were also investigated. A prediction model for SE based on statistical analyses using regression technique of laboratory test results are also introduced. The model can be used for estimating the SE from the rock physical and mechanical properties, and in turn offer an estimate of machine performance for pertinent mechanical excavators such as roadheaders, continuous miners, and drum shearers.

Characterization of building stones from the ancient Tyana aqueducts, Central Anatolia, Turkey: implications on the factors of deterioration processes

Many archaeological and historical monuments constructed by different civilizations over the last 5500 years can be observed in the Nigde region located in central Anatolia. The Tyana aqueduct as a continuation of the Roman Pool is one such important historical monument. The aqueducts that carried the water of the Roman Pool to the ancient city of Tyana were constructed during the time of the Roman emperors Trajan, Hadrian and Marcus Aurelius Antoninus. Half of the total length of the aqueducts (3 km) is on the surface and the rest is buried. The engineering properties of the rocks used in such archaeological and historical buildings are very important in terms of conserving these structures for future generations. In this study, the geomechanical and geotechnical features of the Tyana aqueducts were investigated to understand the rock types, deterioration in the stones over time and problems originating from these features. Also, for restoration purposes, the ancient stone quarry areas for the aqueducts were identified, and the chemical, petrographical and geomechanical properties of fresh travertine blocks from these quarries were determined. The main rock type used as building stones in the aqueducts is Mio-Pliocene travertine. Laboratory studies were performed to determine the mineralogical, petrographic and petrophysical properties of the building stone samples. Fresh and used travertine samples were composed exclusively of calcite crystal. The results of chemical analyses were similar for fresh and used travertine samples. To determine the geomechanical properties of the travertines, dry unit weight, water absorption, effective porosity, P-wave velocity, Bohme abrasion test, capillary water absorption and uniaxial compressive strength experiments were conducted. In addition, Schmidt hammer hardness measurements were performed on site for the different levels and different textural characteristics of the belts on the travertines. According to the experimental data obtained, higher strength was displayed by samples with fine grains, massive texture and low porosity. The deterioration effects in most of the travertines used in the original structure are very low. In addition to human effects, the use of small stone dimensions (especially the stones used in belts as keystones) and the use of stone from the same quarry but with features that differ or are inferior are thought to be factors in the destruction of the Tyana aqueducts.

Application of statistical methods for predicting uniaxial compressive strength of limestone rocks using nondestructive tests

Uniaxial compressive strength (UCS) of an intact rock is an important geotechnical parameter for engineering applications. Using standard laboratory tests to determine UCS is a difficult, expensive and time-consuming task. The main purpose of this study is to develop a general model for predicting UCS of limestone samples and to investigate the relationships among UCS, Schmidt hammer rebound and P-wave velocity (V P). For this reason, some samples of limestone rocks were collected from the southwestern Iran. In order to evaluate a correlation, the measured and predicted values were examined utilizing simple and multivariate regression techniques. In order to check the performance of the proposed equation, coefficient of determination (R 2), root-mean-square error, mean absolute percentage error, variance accounts for (VAF %), Akaike Information Criterion and performance index were determined. The results showed that the proposed equation by multivariate regression could be applied effectively to predict UCS from its combinations, i.e., ultrasonic pulse velocity and Schmidt hammer hardness. The results also showed that considering high prediction performance of the models developed, they can be used to perform preliminary stages of rock engineering assessments. It was evident that such prediction studies not only provide some practical tools but also contribute to better understanding of the main controlling index parameters of UCS of rocks.

Predicting performance of impact hammers from rock quality designation and compressive strength properties in various rock masses

Predicting the performance of the impact hammers is one of the major subjects in determining the economics of the underground excavation projects in which they are utilized. Therefore, researchers have been attracted to developing performance prediction models for these machines. Physical and mechanical properties of rocks have been used to estimate the performance of impact hammers over the last few decades. In this study, the instantaneous breaking rate (IBR, m3/h) of an impact hammer used in construction of Levent-Hisarüstü metro tunnel (Istanbul) is recorded in detail. Sixty rock samples are obtained from tunnel route during the excavation of which the machine is employed. Physical and mechanical property tests are performed on the obtained samples. A data set including uniaxial compressive strength (UCS), rock quality designation index (RQD), Brazilian tensile strength (BTS), density (ρ), Schmidt hammer hardness (SHH), Shore scleroscope hardness (SSH), Cerchar abrasivity index (CAI), and IBR is formed. Regression analysis techniques are applied to the created data set in order to develop a performance prediction model. The investigation results in a model that can predict IBR based on UCS, RQD, and the output power of the impact hammer. The proposed model passes both F-test and t-test at 0.95 confidence level. The soundness of the model is successfully tested against two formerly developed models. Covering a wide range of application and requiring only two of the most common and versatile rock properties as input parameters are the other advantages of the suggested model.

An Experimental Study of Cutting Performances of Worn Picks

The best means to assess rock cuttability and efficiency of cutting process for using mechanical excavation is specific energy (SE), measured in full-scale rock cutting test. This is especially true for the application of roadheaders, often fitted with drag-type cutting tools. Radial picks or drag bits are changed during the operation as they reach a certain amount of wear and become blunt. In this study, full-scale cutting tests in different sedimentary rock types with bits having various degree of wear were used to evaluate the influence of bit wear on cutting forces and specific energy. The relationship between the amount of wear as represented by the size of the wear flats at the tip of the bit, and cutting forces as well as specific energy was examined. The influence of various rock properties such as mineral content, uniaxial compressive strength, tensile strength, indentation index, shore hardness, Schmidt hammer hardness, and density with required SE of cutting using different levels of tool wear was also studied. The preliminary analysis of the data shows that the mean cutting forces increase 2–3 times and SE by 4–5 times when cutting with 4 mm wear flat as compared to cutting with new or sharp wedge shape bits. The grain size distribution of the muck for cutting different rock types and different level of bit wear was analyzed and discussed. The best fit prediction models for SE based on statistical analysis of laboratory test results are introduced. The model can be used for estimating the performance of mechanical excavators using radial tools, especially roadheaders, continuous miners and longwall drum shearers.