Prediction of Uniaxial Compression Strength of Limestone Based on the Point Load Strength and SVM Model

Uniaxial compression strength (UCS) is a fundamental parameter to carry out geotechnical engineering design and construction. It is simple and efficient to predict UCS using point load strength (PLS) at engineering sites. However, the high dispersion of rock strength limits the accuracy of traditional fitting prediction methods. In order to improve the UCS prediction accuracy, 30 sets of regular cylindrical specimen tests between PLS and UCS are conducted on limestone mines. The correlation relationship between PLS and UCS is found by using four basic fitting functions. Then, a prediction model is established by using SVM algorithm. Multiple training test data are used to achieve high-precision prediction of UCS and the results show it is less different from the actual values. Especially, the R2 coefficient reached 0.98. The SVM model prediction performance is significantly better than the traditional fitting function. The constructed SVM model in this study can accurately predict the UCS using the PLS obtained in the field, which has a great significance to the rock stability judgment in the actual construction environment.

Experimental Study on Mudstone’s Strength Characteristics in Deep-Buried Coal-Measure Formation: A Case Study of Permian Longtan Formation

To investigate the strength characteristics of mudstone in deep-buried coal-measure formation, four types of experiments have been conducted: (i) the X-ray diffraction (XRD) test; (ii) the scanning electron microscope (SEM) scanning test; (iii) the point load strength index test; and (iv) the uniaxial compressive strength test. It was concluded that the mudstone of the deep-buried coal measures in the Longtan Formation is dominated by chlorite, quartz, and albite using the XRD test, of which chlorite is primary, accounting for 74.3%. It was found that the three minerals in the mudstone are unevenly distributed using the SEM scanning test, albite is irregularly distributed in chlorite, and quartz is present in the albite and chlorite. Sixty-five specimens were tested for the point load strength index. After processing the data using the method suggested by the International Society for Rock Mechanics and Rock Engineering(ISRM), it was found that the maximum value of Is(50) was 6.10 MPa, the minimum is 0.14 MPa, and 53% of the specimens’ Is(50) values are below 2.0 MPa. The RMT-150C rock mechanics testing machine was used to conduct uniaxial compression tests on six specimens. The maximum uniaxial compressive strength (UCS) value is 59.26 MPa, the minimum value is 31.77 MPa, and the average is 45.64 MPa. Linear fitting and logarithmic fitting are carried out for the correlation between UCS and Is(50). The goodness of fit R2 of the linear fitting is 0.863, and that of the logarithmic fitting is 0.919, indicating a strong correlation between them. When it is challenging to make standard specimens, Is (50) can be used to estimate UCS.

Strength Weakening Effect of High Prestatically Loaded Marble Subjected to Low-Frequency Dynamic Disturbance under Point Load

The deep high prestatically loaded rock is often subjected to low-frequency dynamic disturbance and exhibits unusual strength characteristics, and thus, it is important to investigate the strength characteristics under the coupling effect of prestatic load and low-frequency dynamic disturbance loading conditions. In this study, a series of point load tests were conducted on the high prestatically loaded marble subjected to low-frequency disturbance by the MTS system, focusing on exploring the role of prestatic load level and low-frequency disturbance frequency in the process of rock strength change. Based on the average static failure load (Fmax) of samples under the static point loading, the high prestatic load levels (Fp) were selected as 70%, 80%, and 90% of Fmax, the corresponding low-frequency dynamic disturbance was loaded by sinusoidal waves with amplitudes of 60%, 40%, and 20% of Fmax, and the low-frequency dynamic disturbance frequencies (f) are 1, 2, 5, and 10 Hz. The change curve of the point load strength with the prestatic load level or the disturbance frequency was analyzed, which indicates that the point load strength under the coupled high prestatic load and low-frequency dynamic disturbance load was significantly lower than that under the pure static loading, presenting a significant point load strength weakening effect. Only when Fp or f reaches a certain level, the point load strength decreases significantly as f or Fp increases. Moreover, the point load strength weakening rate was proposed to characterize the degree of strength weakening. The comprehensive analysis demonstrates that Fp has a greater effect on the point load strength weakening effect than f, which is mainly reflected in the point load strength weakening level dominated by the Fp, and the weakening degree is affected by f.

Characterization of rock material by point load strength index test and direct cut

The objective of this work is to establish a relationship between the cutting time in rocks, determining a speed and the point load strength index test, Is (50), to characterize the rock in terms of resistance and avoid sending samples to laboratories. As a first stage, on andesite samples, 5 x 5 x 10 cm test tubes were made. After the elaboration they were subjected to cutting, using an electric floor cutter and the time was evaluated. This cut was made in a transversal way and two parts were obtained, one of them with dimensions 5 x 5 x 5 cm, approximately. In a third stage, the point load strength test was carried out in a press built for this purpose. Finally, the cutting speeds were correlated with the point load test values and only when rock samples do not pigeonhole on the proposed relationship, send them to the laboratory. Keywords: Mining fortification, uniaxial compressive strength, rock cutting, point load strength test index. References [1]P. Feijoo, R. Aucay, D. Ordoñez, "Aplicación del esclerómetro para la determinación de resistencia a compresión de rocas", presentado en el IV Congreso Internacional de Minería y Metalúrgia (MINEMETAL), Varadero, Cuba, 2018. [2]P. Feijoo y M. Román, «Correlación entre la Deformación y la Resistencia a la Compresión de rocas», uct, vol. 23, n.º 91, p. 6, may. 2019. [3]P. Feijoo, A. Bravo, N. Escandón, "Aplicación “UDAFORMIN” para la determinación del tipo de fortificación minera", presentado en el XII Congreso Iberoamericano de Computación para el Desarrollo (COMPDES), San Salvador, El Salvador, 2019. [4]P. Feijoo y C. Iñiguez, «Corte en las Rocas y su Relación con la Resistencia a Comprensión Simple», RISTI, n.º E 30, p. 59-67, jun. 2020. [5]P. Feijoo y J. Padrón, «La Resistividad de Rocas y su Relación con la Resistencia a Comprensión Simple en Mina», UCT, vol. 24, n.º 99, pp. 61-67, abr. 2020. [6]M. González. El terreno. Ediciones UPC. Barcelona. España, 2001. [7]E. Besoain. Mineralogía de Suelos. Turrialba: Instituto Interamericano de Ciencias Agrícolas de la OEA, 1970. [8]P. Feijoo, A. Flores, B. Feijoo, "The Concept of the Granulometric Area and Its Relation with the Resistance to the Simple Compression of Rocks", presentado en la 7th International Engineering, Sciences and Technology Conference (IESTEC), Panamá, Panamá, 2019, pp. 52-56, doi: 10.1109/IESTEC46403.2019.00018. [9]F. Blyth. Geología para Ingenieros. Cecsa. México D. F. México, 2003. [10] E. Tarbuck & F. Lutgens. Ciencias de la Tierra: Una introducción a la Geología Física. Pearson. Madrid. España, 2005. [11]L. Suarez del Rio, A. Rodríguez, L. Calleja, V. Ruiz de Argandoña, «El corte de rocas ornamentales con discos diamantados: influencia de los factores propios del sistema de corte», CSIC, vol. 48, n.º 250, pp. 53-59, abr-mayjun 1998. [12]Universidad Politécnica de Madrid. Explotaciones de Roca Ornamental. Diseño de explotaciones y selección de maquinaria y equipos. UPM. Madrid. España, 2007. [13]Catalog, Covington, (2019). LAPIDARY & GLASS MACHINERY, USA. Retrieved from https://covington-engineering.com/content/pdf/Covington-Catalog.pdf. [14]D. Burbano, T. García, «Estimación empírica de la resistencia a compresión simple a partir del ensayo de carga puntual en rocas anisótropas (esquistos y pizarras)», FIGEMPA, vol.1, n.º 2, pp. 13-16, dic. 2016. [15]P. Ramírez, L. de la Cuadra, R. Lain, E. Grigalbo. Mecánica de rocas aplicada a la minería metálica subterránea. Instituto Geológico Minero. Madrid. España, 1984. [16]P. Cordero, "Manual de prácticas de laboratorio de Mecánica de Rocas (Parte I)" tesis, Universidad Nacional Autónoma de México, México D.F., México, 2019. [17]L. González de Vallejo, M. Ferrer. Manual de campo para la descripción y caracterización de macizos rocosos en afloramientos. Instituto Geológico y Minero de España. Madrid. España, 2007. [18]P. Pohjanpera, T. Wanne, E., Johansson. Point Load Test Results From Olkiluoto Area Borehole Cores. Posiva. Finlandia, 2005. [19]P. Ramírez, L. Alejano. Mecánica de rocas: fundamentos e ingeniería de taludes. Universidad Politécnica de Madrid. Madrid. España, 2004. [20]M. Navarrete, W. Martínez, E. Alonso, C. Lara, A. Bedolla, H. Chávez, D. Delgado, J. Arteaga. «Caracterización de propiedades físico-mecánicas de rocas ígneas utilizadas en obras de infraestructura», ALCONPANT, vol. 3, n.º 2, pp. 133-143, ago. 2013. [21]P. Feijoo, "Manual de mecánica de rocas y estabilidad de túneles y taludes" tesis, Universidad del Azuay, Cuenca, Ecuador, 1997.

PHYSICAL PARAMETERS, TENSILE AND COMPRESSIVE STRENGTH OF DOLOMITE ROCK SAMPLES: INFLUENCE OF GRAIN SIZE

The purpose of this paper is to investigate the strength, physical and engineering index parameters of selected dolomitic rocks with emphasis on grain size. For this purpose, three groups of dolomite from north western Iran, with the same mineral composition but different grain size, were selected; fine grain, medium grain and coarse grain. Three sets of laboratory experiments are performed on 32 samples: first; petrography tests for determining mineral composition and their percentage, and microstructure of rock containing grain size and grain size distribution, second; experiments to determine the physical properties of the rocks included density, compressional and shear wave velocity, and the third category of experiments included uniaxial compressive strength test, Brazilian tensile strength and point load strength. According to the results; there are significant positive correlation between grain size and uniaxial compressive strength (r = 0.89), point load strength (r = 0.58), Brazilian strength (r = 0.69), and average Young’s modulus (r = 0.64). Also, with increasing grain size, density decreases (r = –0.77). There is strong correlation between compressional wave velocity and shear velocity (r = 0.88). There are also a strong correlation among the uniaxial compressive strength, Brazilian tensile strength and point load strength.

Classification of Engineering Properties of Tropical Boulder in Completely Weathered Granite in Johor, Malaysia

Engineering properties of tropical weathered granite mass have been widely investigated and classified for engineering purposes. However, the engineering properties of tropical boulder in weathered granite profile is poorly understood and not well classified. This study aims to examine and classify the physico-mechanical properties of granite boulder in completely weathered zone. A total of 34 in-situ boulders were examined from two granite quarries located in Southern Johor, Malaysia. Microstructure-mineralogical alterations were analyzed based on petrographic analysis and scanning electron microscopy (SEM). The mechanical properties were including dry density, porosity, point load strength, uniaxial compressive strength and permeability. Three properties were identified as significant indicators to differentiate between tropical boulder and completely weathered granite when it is evaluated from the soil investigation drilling work namely; texture characteristics, discolourations and degree of weathering. Analysis revealed that the alteration of microstructures and minerals such as feldspar, biotite, and plagioclase from corestone (Grade I/II) to saprolite (Grade IV/V) zone were significantly reduced the dry density, point load strength, uniaxial compressive strength and permeability with 32%, 99.5%, 98.6% and 84.8%, respectively. It has also significantly increased the porosity up to 11.6 times or 1065% from corestone to saprolite. The significant different of physico-mechanical properties of material surrounding boulder due to weathering can be classified and useful in evaluation of geotechnical design and geological engineering applications.