Investigation of Dynamic Mechanical Properties of Coal after Freeze-Thaw Cyclic Conditions

Due to the extensive excavation of the mine pit, a special frozen rock slope is formed, which transforms the permafrost (coal rock) of certain thickness in the frozen state to the melting state. To evaluate the dynamic mechanical properties and deformation characteristics of coal under cyclic freeze-thaw conditions, freeze-thaw experiments with different cycle times were conducted. And the mechanical properties of coal under quasistatic and dynamic conditions were investigated by using GCTS multifunctional rock mechanic experimental apparatus and SHPB dynamic loading apparatus, respectively. The results show that with the increase of freeze-thawing times, mass of both water-saturated and dried coal samples gradually decreased, the postpeak becomes gentler, and the specimens show ductile damage characteristics. The damage of the coal samples changed more after 30 freeze-thaw cycles, when deterioration of the coal samples was highest. The elastic modulus of the coal sample after freeze-thawing decreases continuously with the increase of the number of freeze-thaw cycles, and its trend decreases approximately linearly. Dynamic compressive strength of the coal samples decreases after freeze-thaw cycles, and this trend is consistent with the quasistatic loading conditions.

Mineralogical, Geochemical, and Rock Mechanic Characteristics of Zeolite-Bearing Rocks of the Hatrurim Basin, Israel

The Hatrurim Basin, Israel, is located on the western border of the Dead Sea Transform. This is one of the localities of a unique pyrometamorphic complex whose genesis remains problematic. This paper deals with zeolite-bearing rock that is known in the Hatrurim Basin only. The strata subjected to zeolitization is called the “olive unit” and consists of anorthite–pyroxene (diopside–esseneite) hornfels. Zeolitization occurred in an alkaline environment provided by the interaction of meteoric water with Portland-cement-like rocks of the Hatrurim Complex. The resulting zeolite-bearing rocks contain 20–30% zeolitic material. The main zeolitic minerals are calcic: thomsonite-Ca ± Sr, phillipsite-Ca, gismondine-Ca, and clinoptilolite-Ca. The remainder is calcite, diopsidic pyroxene, garnets (either Ti-andradite and/or hydrogrossular), and less frequently, fluorapatite, opal, and others. Their major mineralogical and chemical compositions resemble carbonated zeolite-blended Portland mortar. Rocks show different values of porosity. Their mechanical characteristics are much better for samples with porosity values below 24%. The related parameters are like those of blended concretes. The minimal age of zeolitization is 5 Ka. The natural zeolite-bearing rocks are resistant to weathering in the Levant desert climate.

Numerical Simulation and Experimental Studies of Karst Caves Collapse Mechanism in Fractured-Vuggy Reservoirs

Karst cave collapse usually occurs during the process of drilling and reservoir development. Karst cave collapse increases drilling risk and seriously affects oil production. In order to reveal the collapse mechanism of karst caves in fractured-vuggy reservoirs in Tahe oil field, rock mechanic experiments and numerical simulation studies were conducted. In rock mechanic experiments, three types of rock mechanics tests (uniaxial compression, triaxial compression, and Brazilian splitting) were carried out to obtain the basic rock mechanics parameters. In numerical simulation studies, the collapse conditions of a single karst cave and a cave system were studied. Numerical simulation results indicate that for a single karst cave, the size and geometrical features of karst caves are the main factors influencing collapse condition. For a cave system, a combination pattern and distance between caves are two main factors affecting collapse condition. In order to facilitate the application of these research results, the authors present formulas for calculating the critical conditions of karst cave collapse by means of multivariate linear regression method. The calculation formulas and prediction chart were verified as consistent with actual field results. The research results in this paper have great theoretical and practical value for revealing the mechanism of karst cave collapse in fractured-vuggy carbonate reservoirs.

PERANCANGAN ALAT UJI BEBAN TITIK MENGGUNAKAN PRESSURE GAUGE SERTA MENENTUKAN KORELASINYA TERHADAP UJI KUAT TEKAN UNIAKSIAL PADA BATULANAU

Dengan semakin majunya bukaan tambang dengan massa batuan yang berbeda-beda, diperlukan pengambilan keputusan yang secara cepat dalam penanganannya, sehingga diperlukan bukaan tersebut akan di berikan support atau tidak diberikan support selama aktifitas penambangan terus berlanjut sesuai kegunaannya. Untuk mensupport kebutuhan tersebut dengan cepat, maka dapat dilakukan dengan uji indeks. Yakni dengan uji beban titik, dimana Indeks franklin (Is) dapat mempresentasikan besarnya nilai kuat tekan dari sampel batuan yang diambil. Selain itu, uji beban titik merupakan metode alternatif yang digunakan untuk mengukur nilai kuat tekan menggantikan metode kuat tekan uniaksial terkait biaya dan waktu yang lebih efisien.Dari penelitian ini akan dihasilkan alat uji beban titik yang dirancang menurut International Society for Rock Mechanic (ISRM) vol.22-2 (1985), serta IS 8764 (1998) yang kemudian akan dilakukan pengujian sampel untuk mengetahui kehandalan alat yang dibuat dengan mengkorelasikan hasil dari uji beban titik dan uji kuat tekan uniaksial dengan batulanau sebagai sampel.Dari hasil pengolahan data didapatkan nilai uji kuat tekan uniaksial dari 10 kali percobaan yang dilakukan pada batulanau yaitu berkisar 3,18 – 7,32 Mpa dan uji beban titik berkisar 0,3702 – 1,0387 Mpa dengan jumlah pengujian sampel total uji yaitu 20 kali percobaan, sehingga didapatkan nilai koefesien korelasi R2 = 0,938 dan didapatkan persamaan korelasi antara uji kuat tekan dan uji beban titik yaitu, sc = 4,6308(Is50) + 2,2965. Kata-kata kunci: Uji Beban Titik, Kuat Tekan Uniaksial, Batulanau