Experimental Research on the Effect of Bedding Angle on the Static and Dynamic Behaviors of Burst-Prone Sandstone

AbstractIn order to understand the mechanism of some unconventional failures such as rockburst caused by deep rock excavation, the failure characteristics of burst-prone sandstone specimens under static and dynamic loads were studied by using the MTS816 rock mechanics testing system and the split Hopkinson pressure bar (SHPB) experimental system, as well as the effects of bedding angle and impact pressure on rock mechanical properties and failure patterns. The uniaxial compression test used a cylindrical specimen with a height of 50 mm and a diameter of 100 mm, and cylindrical specimens with height and diameter of 50 mm were adopted in the SHPB tests. The bedding angles in the tests are 0°, 45°, and 90°. In the dynamic impact test, three different impact pressures were applied to observe the magnitude of impact load on the mechanical behaviors of the burst-prone sandstone specimens. The results show that with the increase in the bedding angle, the uniaxial compressive strength firstly decreases and then increases. When the bedding angle is 45°, the uniaxial compressive strength is the lowest. The uniaxial compressive strength is highest when the bedding angle is 0°. The burst-prone sandstone specimens with different bedding angles had three different failure pattern types. Under the dynamic loading, the stress-strain curves show springback phenomenon; with the increase in impact pressure, the dynamic strength of the burst-prone sandstone specimens with each bedding angle increases; the fracture degree of the bedding sandstone specimens gradually increases. The dynamic strength of the 45° burst-prone sandstone specimen is the lowest, and it has the highest fracture degree

Paste Backfill Corrosion Mechanisms in Chloride and Sulfate Environments

To study paste backfill corrosion mechanisms in chloride and sulfate environments, we studied the effect of chloride and sulfate on the strength of paste backfill after 7, 14, 28, and 40 days. The chloride solutions and sulfate solutions in concentrations are 0 g/L, 0.5 g/L, 1.5 g/L, 4.5 g/L, or 15 g/L. The obtained specimens were analyzed by performing uniaxial compressive strength tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results show that chloride and sulfate significantly increased the uniaxial compressive strength of the specimen at a very fast speed in the early stage of the test, and the original structure of the specimen was destroyed and its uniaxial compressive strength decreased with the gradual corrosion. The reason for this characteristic is because the chloride reacts with the paste backfill to form calcium chloroamine hydrate (Ca4Al2O6Cl2·10H2O), and the sulfate reacts with the paste backfill to form dihydrate gypsum (CaSO4·2H2O), mirabilite, and ettringite. In the early stage, these substances can fill the pores to improve the compressive strength, and then expand to damage the structure of the backfill and reduce its compressive strength. In addition, sulfate can enhance the decomposition of C-S-H, which results in a faster destruction of specimens than in chloride environments

Investigation of the Effectiveness of a New Backfilling Method: “Multi-Arch Pier-Column”

Owing to the shortcomings of blindness and inaccuracy when backfilling in goafs and based on the key stratum theory, we propose the “multi-arch pier-column” backfilling method. This method involves drilling holes at specific locations on the surface to inject filling and slurry materials into the goaf and separation area under the key stratum. This allows the broken gangue to be cemented to form a stone body, to improve its overall strength. This process, along with filling in the separation area under the key stratum, ensures that the key stratum does not break, forming a joint medium of “separation area filling body + backfilled pier-columns + key stratum + coal column”, which prevents new subsidence on the surface layer. Using the Gaojialiang coal mine as an example, the effects of the proposed method on controlling surface subsidence were determined using a numerical simulation based on FLAC3D simulation software. The results indicate that this method can effectively control the key stratum and ensure that the surface subsidence is within a safe range. The multi-arch pier-column backfilling method utilises the self-bearing capacity of the overburden structure and greatly reduces the backfilling workload and the cost of backfilling for controlling surface subsidence. At present, the multi-arch pier-column system of the new backfill method is an unexplored and new area of research

Molecular cloning, expression, purification and crystallographic analysis of PRRSV 3CL protease

Recombinant PRRSV 3CL protease was crystallized and the crystals diffracted to 2.1 Å resolution

Structural Diversity, Magnetic Properties, and Luminescent Sensing of the Flexible Tripodal Ligand of 1,3,5-Tris(4-carbonylphenyloxy)benzene Based Mn(II)/Cd(II) Coordination Polymers

Four three-dimensional (3D) Cd­(II)/Mn­(II) coordination polymers, namely, {[Mn_1.5(TCPB)­(H₂O)­(μ₂-OH₂)]­·H₂O}_<i>n</i> (<b>1</b>), {[Cd_3.5(TCPB)₂­(H₂O)₃­(μ₂-OH₂)­(μ₃-OH)]­·H₂O}_<i>n</i> (<b>2</b>), [Mn_1.5(TCPB)­(bib)_0.5­(DMF)]_<i>n</i> (<b>3</b>), and {[Cd₂(TCPB)­(HCOO)­(bib)­(H₂O)]­·0.5dioxane}_<i>n</i> (<b>4</b>), have been constructed from the flexible tripodal ligand of 1,3,5-tris­(4-carbonylphenyloxy)­benzene (H₃TCPB) with or without the help of bib auxiliary linker (bib = 1,4-bis­(imidazol-1-yl)­benzene). On the basis of the one-dimensional (1D) rod-like {Mn₃(COO)₈­(μ₂-H₂O)₂}_<i>n</i> secondary building units (SBUs), complex <b>1</b> displays a 3D (4,8)-connected <b>flu</b> net with the point symbol of {4¹².6¹².8⁴}­{4⁶}₂. Complex <b>2</b> shows a novel 3D 12-connected {3¹².4⁴⁰.5¹².6²} net based on the 1D {Cd₆(COO)₁₂­(μ₃-OH)₂­(μ₂-OH₂)₂}_<i>n</i> SBUs. When the bib bridging ancillary linker was introduced, a trinuclear {Mn₃(COO)₆} SBU based 2-fold interpenetrated 3D (3,8)-connected {4³}₂{4⁶.6¹⁸.8⁴}-<b>tfz-d</b> net for <b>3</b>, and a binuclear {Cd₂(COO)₃} SBU based 3D (3,7)-connected {4.6²}­{4⁷.6¹⁴} net with interesting self-penetrating features for <b>4</b> were obtained. Variable-temperature magnetic susceptibilities of <b>1</b> and <b>3</b> have been investigated. The results display the antiferromagnetic exchange interactions between the adjacent Mn^II ions of the SBUs in <b>1</b> and <b>3</b>. Fluorescence measurements show <b>2</b> and <b>4</b> have highly selective and sensitive detection for Cr³⁺ cations in aqueous solution and nitrobenzene derivatives in DMF