Point Load Strength Test Research Articles

Reliability assessment of carbon fiber mortar: Combined pulse velocity, point load, and compressive strength tests

Cement mortar is used as an adhesive and plaster for brick walls, drainage channels or irrigation with river stones or mountain stones, and in the manufacturing of short revetments. The performance of cement mortar requires continuous improvement by construction materials researchers, scientists, and building contractors. Recently, carbon fiber sheet has gained popularity for use in retrofitting and improvement to the performance of building elements. This study aims to recycle small sheets of unused carbon fiber by cutting them into short carbon fiber (SCF) with a uniform length of 12 mm, which is used as an internal reinforcement in the cement mortar. All plain and fibrous mortar were prepared with a 50 mm cube mold. In addition, tests were conducted to provide reliable data regarding the application of recycled carbon fiber sheets as discrete fiber reinforcement in the improvement of cement mortar; these include ultrasonic pulse velocity (UPV), compressive strength, and point load strength index (PLSI) (known for performance rock testing in geotechnical and geological environments) tests. The test results for UPV, PLSI, and compressive strength showed that the addition of carbon fiber improves the performance of the mortar when compared to plain mortar. Furthermore, two simplified relationships are made: the first correlation was for PLSI with compressive strength, and the second correlation was for UPV with compressive strength. Finally, these correlations were compared with those of experimental tests obtained from published literature, thus demonstrating the correctness of the PLSI, compressive strength, and UPV values obtained in this study.

Study on the mechanical properties of anisotropic red sandstone under point load strength test and uniaxial compression strength

The red sandstone of Xiaopu 3# branch Cave in the Yuxi section of the Central Yunnan Water Diversion Project was taken as the research object. The uniaxial compression strength and point load strength test are conducted from the perspectives of vertical and parallel stratifications, respectively, and then the anisotropy of red sandstone was analyzed in detail. The data obtained from the field and laboratory test was analyzed, and the conversion relationship between point load strength index and uniaxial compression strength is a power function under both parallel stratification and vertical stratification. The study results showed that: The mechanical properties of red sandstone have obvious anisotropy. The difference in its mechanical properties is particularly evident in UCS and point load tests and Is(50) and UCS under vertical stratification are significantly greater than Is(50) under parallel stratification. The point load strength correction index m of red sandstone is m = 0.4096 under parallel stratification, and m = 0.4408 under vertical stratification.

Determining Dry and Saturated Strength of Rocks by Using the Schmidt Hammer

The main purpose of this research is to determine the dry and saturated strength of different sedimentary rocks including travertine, conglomerate, sandstone and limestone by using the Schmidt hammer test. To determine the strength of the studied rocks, comprehensive geotechnical tests including Brazilian tensile strength (BTS), block punch strength (BPS), point load strength (PLS) and uniaxial compressive strength (UCS) were performed in dry and saturated conditions on prepared standard specimens. Results show under BTS, BPS, PLS and UCS tests, the strength of the studied rocks after saturating is averagely reduced by 24.95, 31.80, 34.36 and 18.97%, respectively. Therefore, under saturated conditions, the strength of the studied samples reduced 27.52% averagely. The correlation between Schmidt rebound hardness and geotechnical properties in dry and saturated conditions was performed by simple regression analysis and experimental equations were obtained with a correlation coefficient from 0.65 to 0.93. For evaluating the performance of predictive models, some statistical parameters including RMSE, VAF, MAPE and PI were calculated and the 45° line and 95% confidence limit curves were also extracted for evaluating the validity of the concluded empirical equations. The results of this research demonstrate that the Schmidt hammer test is a reliable method for estimating the strength of rocks in dry and saturated conditions.

Correction of Point Load Strength on Irregular Carbonaceous Slate in the Luang Prabang Suture Zone and the Prediction of Uniaxial Compressive Strength

Uniaxial compressive strength (UCS) testing requires high-quality core samples, which is a difficult task for weak, highly fractured, thinly bedded, foliated, and weathered rocks. In addition, it is time-consuming and expensive. Because of the good relationship between rock point load strength (PLS) and UCS, the PLS could be used to estimate rock UCS quickly. The lump structure and layer structure of carbonaceous slate are revealed in the tunnels of the China–Laos Railway in the Laos Luang Prabang Suture Zone as one of the important factors leading to tunnel squeezing deformation and support structures. To reveal the relationship between the PLS and UCS of carbonaceous slate in the Luang Prabang Suture Zone, PLS tests and UCS tests of lump-structure carbonaceous slate (lamina plane inconspicuous) and layer-structure carbonaceous slate (lamina plane conspicuous) were performed. Results show that the Is(50) of lump-structure carbonaceous slate ranged from 0.06 MPa to 0.30 Mpa, the Is(50) of layer-structure carbonaceous slates which were loaded perpendicular to the lamina plane ranged from 0.64 MPa to 1.25 MPa, the Is(50) of layer-structure carbonaceous slates which were loaded parallel to the lamina plane ranged from 0.49 MPa to 0.71 MPa, and the correction power index m ranged from 0.42 to 0.51 with an average value of 0.47. Four correlation expressions of carbonaceous slate relationships between PLS and UCS were fitted by zero-intercept linear expression, nonzero intercept linear expression, power expression, and logarithmic expression, and the calculation results were compared with results calculated by the International Society of Rock Mechanics (ISRM) correlation equation. It is concluded that the correlation equation between UCS and PLS recommended by ISRM specifications easily causes soft rock strength overestimation, which affects the correct evaluation of the surrounding rock property and the structural design safety of tunnels and underground projects. The zero-intercept linear equation UCS = 18.45Is(50) has better goodness of fit and higher accuracy in predicting the UCS of the carbonaceous slate in the Luang Prabang Suture Zone.

Research on the Conversion Relationship between Dynamic Point Load Strength and Dynamic Compressive Strength Based on Energy System

Point load test is a simple and fast method to obtain the compressive strength of rock. According to the maximum load at failure and the distance between two cone ends, the compressive strength of specimens can be calculated by the empirical formula. Because the test process does not need to process the sample into laboratory size type, so it is widely used. At the same time, with the rapid development of rock dynamics, the dynamic strength index of rock becomes more and more important under dynamic load. But dynamic point load is seldom mentioned by scholars. In order to explore the correlation between dynamic point load test and dynamic compressive strength, a large number of dynamic point load and uniaxial dynamic compressive strength tests were carried out using a split Hopkinson pressure bar for granite. Based on the energy theory, the crushing energy consumption during dynamic point load and uniaxial dynamic compressive strength tests were statistically analyzed, and the transformational relation between uniaxial dynamic compressive strength and crushing energy consumption during the dynamic point load test was determined. At the same time, the influence of the cone angle on crushing energy consumption during the dynamic point load test was investigated by changing the conical angle. The results show that with the increase in conical angle, the energy consumption of rock crushing decreases gradually during the dynamic point load test. And the decreasing trend tends to be gentle. The conclusion can provide a reference for obtaining the numerical value of the dynamic compressive strength of the rock in the future.

Method of equivalent core diameter of actual fracture section for the determination of point load strength index of rocks

Point load strength test is one of the indirect methods to estimate the uniaxial compressive strength of rocks. Due to its ease of sample preparation, low cost, and simple testing, it has been widely used in rock engineering in the world. The common calculation method of point load strength index is the method of equivalent core diameter of minimum cross-section, followed by the method of actual fracture section and loading distance method. However, because there are different factors being considered in different methods, the point load strength indexes obtained from different formulas varies greatly, which will result in large errors when estimating the compressive strength of rocks. In this study, a large number of point load strength tests and uniaxial compression tests were carried out using four kinds of rock samples. Then, a series of statistical analyses were conducted based on the test data. The results indicated that the distance between two loading points and the width of actual fracture section played an important and non-negligible role for failure of rock specimens, but the effect of width of minimum cross-section of specimens could be ignored. Consequently, by combing the advantages of two traditional methods, a modified calculation method of PLSI was proposed. Finally, uniaxial compressive strength of four kinds of rocks estimated by different methods was compared. The results showed that the modified method had the least estimation error.

Data Mining Techniques for the Prediction of Bohme Surface Abrasion Rates from Rock Properties

Abstract Abrasion refers to the wearing down of rock surfaces due to abrasive grains. Abrasion resistance refers to the ability of rocks to withstand wear. Abrasion resistance is used to determine the resistance of building materials produced for flooring, cladding, and pavements and to demonstrate suitability for higher movement areas. While it is, therefore, very necessary to determine the abrasion rate of building materials prior to construction, it is, however, highly demanding and time consuming to determine abrasion rates. Thus, the aim of this study is to use some rock properties to determine abrasion rates. The study samples, consisting of 32 different types of rocks (sedimentary, metamorphic, and igneous) collected from different regions in Turkey, were subjected to some physical and mechanical tests, namely the following: unit volume weight (UVW), apparent porosity (AP), modulus of elasticity (E), uniaxial compressive strength (UCS), tensile strength (TS), Shore hardness (SH), and point load strength (PL) and Bohme abrasion tests. To ascertain the abrasion rate from some physical and mechanical properties of rocks, the results of these tests were analyzed using data mining (DM) techniques. The results showed that there are high correlation coefficients between abrasion rate and the aforementioned rock properties with the support vector machines (SVM) and random forests (RF) models obtained as R = 0.882 and 0.881, respectively. This work has shown that the rock Bohme abrasion rate can be predicted from some of its physical and mechanical properties with significant level of confidence.

BÜYÜK ÖLÇEKLİ KÖMÜR ARININDA GERÇEKLEŞTİRİLEN SCHMİDT SERTLİK İNDEKSİ VE NOKTA YÜKLEME DAYANIMI DENEY SONUÇLARININ DEĞERLENDİRİLMESİ

Kömür ve kömür damarı içerisinde konumlanan ara kesmelerin (t=0,5m) yerinde malzeme özelliklerinin belirlenmesine yönelik bu çalışma, TKİ-GLİ-Ömerler yeraltı maden ocağında gerçekleştirilmiştir. Kömür arın yüksekliği 3,5 m ve uzunluğu ise 110 m olan A1 hazırlık panosunda, yaklaşık 385 m2’ lik yüzey alanı üzerinde her biri yaklaşık 15 m2 olan 4 deney alanı belirlenmiştir. Bu deney bölgeleri arının iki kenar uç tarafında ve arın ortasında konumlanmıştır. Deney bölgeleri kendi içlerinde toplam 238 birim hücreye bölünmüştür. Birim hücrelerin orta noktasında en az üç kez tekrarlanmak kaydı ile Schmidt sertlik belirleme deneyleri yapılmıştır. Nokta yükleme dayanımı indeks deneyi için A1 panosunun kömür arını yaklaşık 5’ er metre aralıklar ile toplam 21 birim bölgeye ayrılmıştır. Her birim bölge ise kendi içerisinde beş alt birim hücreye bölünerek her bir alt birim hücreden alınan düzensiz örnekler ile toplam 563 adet nokta yükleme dayanımı belirleme deneyleri yapılmıştır. Sonuç olarak yapılması pratik olan Schmidt sertlik ölçümleri ile nokta yükleme dayanım deney sonuçları arasındaki mekanik ilişkiler ve bu deney sonuçlarına dayalı kazı kolaylığına ait bir sınıflama bu çalışmada önerilmiştir.

Estimation of uniaxial compressive strength of pyroclastic rocks (Cappadocia, Turkey) by gene expression programming

Compressive strength of rocks is an important factor in structural design in rock engineering. Compressive strength can be determined in the laboratory by means of the uniaxial compressive strength (UCS) test, or it can be estimated indirectly by simple experiments such as point load strength (PLT) test and Schmidt hammer rebound test. Although the UCS test method is time-consuming and expensive, it is simple when compared to other methods. Therefore, many studies have been performed to estimate UCS values of rocks. Studies indicated that correlation coefficient of rock groups is low unless they are classified as metamorphic, sedimentary, or volcanic. Pyroclastic rocks are widely used as construction materials because of the fact that they crop out over extensive areas in the world. To estimate the UCS values of pyroclastic rocks in Central and Western Anatolia region, Turkey, multiple linear regression (MLR) analysis and gene expression programming (GEP) were employed and during the analysis, and PLT, ρd, ρs, and n were used as the independent variables. Based on the analysis results, it was detected that the GEP methods gave better results than MLR method. Additionally, the correlation coefficient (R2) values of training and sets of validation of the GEP-I model are 0.8859 and 0.9325, respectively, and this model, thereby, is detected the best of generation individuals for prediction of the UCS.

Probabilistic prediction of intact rock strength using point load tests using a Bayesian formulation

ABSTRACT This paper develops probabilistic predictive models for the unconfined compressive strength of intact rock based on the point load strength tests. A database of point load strength and unconfined compressive strength measurements for sedimentary, igneous and metamorphic rocks is first developed. The measurements are corrected to their standard equivalent values, namely unconfined compressive strength and point load strength for specimens with 50 mm diameter. A Bayesian framework is used to assess different candidate model forms and to estimate the corresponding model parameters. This Bayesian approach uses the prior information for the values of the unconfined compressive strength and point load strength measurements to develop an unbiased method for prediction of unconfined compressive strength based on point load strength tests. The Bayesian estimation of the model parameters accounts for the relevant sources of uncertainty including aleatory and epistemic uncertainties and for possible measurement errors in the point load strength test data. Probabilistic models are developed for sedimentary, igneous and metamorphic rocks. It is found that (i) a model of form provides the best fit to the laboratory data, and (ii) accounting for measurement errors and separating the database into subgroups based on different rock types decrease the model uncertainty.

Theoretical and Experimental Validation of Point Load Strength Test for Irregular Lumps

AbstractThe possibility of testing irregular lumps under the point load strength test (PLST) was investigated theoretically and experimentally. In particular, a new analytical solution for stress d...

PREDICTION OF UNCONFINED COMPRESSIVE STRENGTH OF ROCKS BY POINT LOAD STRENGTH INDEX

The point load testing is widely used to determine rock strength indeces in geotechnicalpractices as a result to simplicity. The present study presents correlation equations betweenthe unconfined compressive strength (qu) and point load strength index Is(50) adopted fordifferent types of rocks. In order to estimate a new correlation between the unconfinedcompressive strength and point load strength test, more than 166 tests were performed. Thetests were conducted on four rock types including Sandstone, Siltstone, Limestone and Basalt.The soil samples were collected from different sites along the new administrative capital ofegypt. The study shows a reliable correlation between the unconfined compressive strengthestimated from the two test approaches.

Factor influencing point load tests on concrete

The main purpose of this paper is to predict the in situ compressive strength of concrete by means of point load strength test as a partially destructive test method. This test method is examined by extracting core specimen from concrete blocks and applying two point loads to the lateral surface of the core specimen. The failure in the core specimen occurred in the direction of applying load where most normal stresses are tensile, while some compressive stresses are generated in the contact surface of load cell with the core specimen. In this study, point load index (PLI) in which a force is divided by the square of the distance between the platen points and cube compressive strength was determined under wet and dry curing conditions at the ages of 7, 14, 28 and 42 days. The effects of various parameters such as core diameter and length to diameter (L/D) ratio were considered experimentally and numerically by means of finite element method using ABAQUS software. A three-dimensional finite element model was constructed to study the stress magnitude and stress distribution at the failure surface. The results showed that the PLI in wet curing conditions were about 12% higher than those in dry curing conditions. In addition, The PLI increased particularly steep when the L/D ratio is less than 1, while then becomes less steep when the L/D ratio is between 1 and 1.8. Meanwhile, it seems that there is no significant difference among PLI values for the ratios of L/D more than 1.8.

Investigations of Support Failure and Combined Support for Soft and Fractured Coal-Rock Tunnel in Tectonic Belt

The structural integrity of coal and rock tunnel affected by structural belts is generally poor, and the fracture development leads to the failure of support. Therefore, in this study, the tunnel deformation characteristics and deformation control technology were conducted using a combination of field investigation, laboratory experiment, theoretical analysis, field test, and other methods based on the Mukong coal mine. First, field investigations show that the main structural support failure often starts from some key parts associated with weak strengths, and the deformation is basically unevenly distributed. For this, the structural plane of tunnel rock mass was investigated and the internal structural deformation of the surrounding rocks was also monitored through the peepholes. In addition, point-load strength test was also conducted. Field observations and testing results show that rock fissures in the tunnel are well developed and a large loose circle will be formed after excavation. According to Barton Classification Q value and rock mass rating value, the mining tunnel stability falls into the category of Class V, i.e., the surrounding rock is poor or extremely poor. Finally, the support principles concerning surrounding rock stability control technology were proposed. The core idea is using support reinforcement repeatedly for several times until both internal and external load-bearing capacities of the surrounding rock are met. For the support reinforcement, a test with combined support scheme was conducted, including short bolts, long anchor cables, and U-steel brackets. Monitoring results of site application show that the proposed scheme contributes to the long-term stability of tunnel surrounding rock.

Strength Estimation by the Point Load Test of the Sewage Sludge Solid Refuse Fuel

Recently, interest has increased about sewage sludge solid refuse fuel. So, Studies have conducted on sewage sludge, the production method of solid fuel and the characteristics as fuel. However, studies on the mechanical properties of sewage sludge solid fuel have not been conducted. In this study, the point load strength of sewage sludge sloid fuel was measured by the point load strength test of rock and the uniaxial compressive strength was derived based on this. We propose the mechanical strength of sewage sludge solid fuel through the result of this study. As a result, the size corrected point load strength (Is(50)) of sewage sludge solide fuel was max. 3.74 MPa and min. 0.04 MPa. And, the uniaxial compressive strength of sewage sludge solid fuel estimated by the point load strength was max. 89.78 MPa, min. 1.08 MPa and the average was 24.86 MPa. The result of study should be observed all data and should be use according to the application. because the range and distribution of the point load strength and the uniaxial compressive strength of the sewage sludge solid fuel are wide. Key words: Sewage Sludge Solid Refuse Fuel, The Point Load Strength, Uniaxial Compressive Strength

A case study on the application of destructive and non-destructive methods for evaluating jet-grouting column integrity for bridge-pier scour protection (Cuneo, NW Italy)

A case study on the use of direct and indirect investigations for the effectiveness evaluation of jet-grouting interventions for bridge scour protection is presented. The major concern of this scour countermeasure is that a reliable verification and imaging of the exact dimensions and shape of the grouted elements and their related strength and integrity are difficult to obtain. An integrated cost-effective and slightly invasive approach, by means of indirect surveys, is proposed in this work to limit re-drilling and core sampling of jet columns. Tests are performed on a bridge located in the Province of Cuneo (NW Italy). On site, active fluvial activity was scouring four of the 19 bridge piers and jet-grouting interventions were designed to prevent bridge collapse. A dual approach was consequently applied to evaluate the goodness of jet-grouting treatments: results of direct tests (visual and mechanical characterization of core drillings, with Point Load and Uniaxial Compressive Strength tests) have been compared to indirect investigations (seismic down-hole tests and 2-D cross-hole tomography, laboratory Ultrasonic Pulse Velocity measurements). All the techniques showed potentiality in identifying variations of the jet-grouting properties within the columns. Generally, worsening in jet-grouting properties was coherently identified by a decrease in the seismic velocities and in the mechanical parameters and confirmed by visual inspection of core drillings. Local anomalies and discrepancies between the adopted method were however highlighted and critically discussed as a function of the limitations, disturbances and investigated volumes of each method.

Rock strength assessment based on regression tree technique

Uniaxial compressive strength (UCS) is one of the most important parameters for investigation of rock behaviour in civil and mining engineering applications. The direct method to determine UCS is time consuming and expensive in the laboratory. Therefore, indirect estimation of UCS values using other rock index tests is of interest. In this study, extensive laboratory tests including density test, Schmidt hammer test, point load strength test and UCS test were conducted on 106 samples of sandstone which were taken from three sites in Malaysia. Based on the laboratory results, some new equations with acceptable reliability were developed to predict UCS using simple regression analysis. Additionally, results of simple regression analysis show that there is a need to propose UCS predictive models by multiple inputs. Therefore, considering the same laboratory results, multiple regression (MR) and regression tree (RT) models were also performed. To evaluate performance prediction of the developed models, several performance indices, i.e. coefficient of determination (R2), variance account for and root mean squared error were examined. The results indicated that the RT model can predict UCS with higher performance capacity compared to MR technique. R2 values of 0.857 and 0.801 for training and testing datasets, respectively, suggests the superiority of the RT model in predicting UCS, while these values are obtained as 0.754 and 0.770 for MR model, respectively.

열적외선영상을 이용한 동결된 암석의 파괴특성 연구

Mechanical energy is accumulated in the object when stress is exerted on rock specimens, and the failure is occurred when the stress is larger than critical stress. The accumulated energy is emitted as various forms including physical deformation, light, heat and sound. Uniaxial compression strength test and point load strength test were carried out in low temperature environment, and thermal variation of rock specimens were observed and analyzed quantitatively using thermal infrared camera images. Temperature of failure plane was increased just before the failure because of concentration of stress, and was rapidly increased at the moment of the failure because of the emission of thermal energy. The variations of temperature were larger in diorite and basalt specimens which were strong and fresh than in tuff specimens which were weak and weathered. This study can be applied to prevent disasters in rock slope, tunnel and mine in cold regions and to analyze satellite image for predicting earthquake in cold regions.

The analytical solutions for the stress distributions within elastic hollow spheres under the diametrical point loads

This paper presents an exact analytical solution for the stress distributions within an elastic hollow sphere subjected to diametrical point loads. The solution is suitable for both thin and thick hollow spheres. New variables are introduced in order to uncouple the system of governing equations so that explicit differential equations are obtained for displacement components and stress components. Moreover, Fourier–Legendre expansion technique is employed in order to determine the unknown coefficients in the analytical solutions for hollow spheres. The present solution can be considered as an extension of the classical solution by Hiramatsu and Oka (Int J Rock Mech Min Sci 3:89–99, 1966) for solid spheres under the point loads, which provided the theoretical basis for the point load strength test. Unlike in solid spheres, the stress concentrations within the hollow spheres under the point loads are usually developed at the joint point of the inner surface and the loading axis, and the thinner the hollow sphere, the larger the tensile stress concentrations developed at the inner surface. This numerical result indicates that the failure of the hollow spheres usually starts at the inner surface, and the normalized tensile stress at the inner surface increases with the increase in Poisson’s ratio and internal pressure, but decreases with the increase in the size of the loading area. Moreover, significant shear stress zone is usually developed in the areas immediately inside the outer surface, and the maximum shear stress is often developed at the point immediately inside the outer surface jointing the edge of the loading area and the center of the hollow sphere. The present solution can be used to analyze the failure mechanism of bulk foams made up of hollow spheres in engineering.

Estimation of the compressive strength of concrete under point load and its approach to strength criterions

The point load strength (Is(50)) is an alternative mechanical parameter to predict the compressive strength of concrete. The scope of this investigation is to develop an empirical equation relating the point load strength and compressive strength of concrete. In this context, crushed limestone aggregates at two different strength levels were used in concrete mixture. Point load strength and compressive strength tests on concrete specimens which had 6 different compressive strengths were performed for each limestone aggregate. A series of regression analyses was applied using any general statistical package to evaluate the ratio of point load strength test to cube compressive strength of concrete, (Is(50)/fcu). The accuracy and reliability of the equation in this investigation was assessed by means of the Mean Absolute Percent Error (MAPE). The relative error can be considered reasonably well for the empirical relationship. The ratio of Is(50)/fcu was also verified by a large database collected from previous studies. The proposed equation is quite compatible with the database. Furthermore, the ratio of Is(50)/fcu indicates significant material property of concrete and defines the material constant in strength criterions. It can be used to estimate the axial compressive strength of concrete under confining stress without performing triaxial tests, considered Hoek-Brown and Johnson empirical failure criterions.