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.

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.

Correlation relationships between mechanical parameters of Bulgarian crushed-rock aggregates utilized in railway construction

Crushed-rock aggregates from 11 railway ballast-producing quarries in Bulgaria have been investigated. The test materials consist of igneous and sedimentary rocks of different ages: basaltic andesite, trachyte, diabase, andesitic tuff, quartz-cemented sandstone, dolomite and five varieties of limestone. The standard laboratory tests (Los Angeles, micro-Deval and point load) and in-situ test (Schmidt hammer) were carried out for determination of the following mechanical properties of aggregates: resistance to fragmentation; wear resistance; strength; and rock hardness. Results show that Los Angeles coefficient (LA) values range from 11.9% to 28.4%. The micro-Deval coefficient (MDE) varies between 3.7% and 22.4%. The point load strength index (IS(50)) is between 4.0 MPa and 8.8 MPa. The Schmidt hammer rebound value (SHV) ranges from 34.4 to 60.2. The possibility of predicting the Los Angeles and micro-Deval coefficients from the Schmidt hammer rebound value and the point load strength index was studied. Regression analysis shows a strong correlation between Los Angeles coefficient and point load strength index (coefficient of determination R2=0.93), a good correlation between the Los Angeles coefficient and the Schmidt hammer rebound value (R2=0.62) and moderate correlation between the micro-Deval coefficient and the Schmidt hammer rebound value (R2=0.51).

CORRELATIONS BETWEEN PHYSICAL PROPERTIES AND POINT LOAD STRENGTH INDEX OF PRASINITES: A CASE STUDY FROM EAST ATTICA PREFECTURE

The aim of this study is to investigate the statistical correlations between the point load strength index and certain physical properties, e.g. the dry density and the dry longitudinal ultrasonic wave velocity of prasinites (metabasites). Statistically significant correlations established between the physical properties as well as between each physical quantity and the point load strength index. According to bibliography, this is one of the first efforts to develop relations between physical and mechanical properties for this particular petrological type, and therefore the derived equations can be a useful tool to the investigation of these petrological types, either in the study area or in other sites, where prasinites of similar structural characteristics, are examined for the foundation of various constructions.