Application of the Controlled Source Radiomagnetotellurics (CSRMT) in the Study of Rocks Overlying Kimberlite Pipes in Yakutia/Siberia

Тhe task of searching for kimberlite pipes in covered areas of the Yakutia kimberlite province is very difficult due to the significant heterogeneity of the rocks overlying kimberlite pipes. The overlying strata of terrigenous sediments contain rocks of the trap complex (dolerite sills, tuff bodies). We consider the results of the controlled source radiomagnetotelluric (CSRMT) soundings in Yakutia/Siberia. Due to the great thickness of the overlying rocks (near 100 m) and the relatively small horizontal sizes of kimberlite pipes (80–200 m), they cannot confidently be detected directly. An additional difficulty in identifying pipe anomalies is the presence of a layer of conductive carbonaceous siltstones in the overlying strata. Therefore, the main aim of the CSRMT surveys was the study of overlying rocks and the search for indirect indications of the presence of pipes. Possibilities to study the structure of dolerite sills located within overlying sediments and to map the top edge of hosting carbonate rocks are demonstrated using the CSRMT data. The pinching out of dolerite sills above pipes («windows in traps») and the lowering of the top edge of hosting rocks at pipes can be considered as indirect indications of the presence of pipes.

Performance Research of Materials and Engineering Application of Overburden Strata Separation-Zone Grouting Technology

To solve the ground subsidence problem associated with thick coal seam mining under the railway in the Tangshan Mine, the technology of overburden strata separation-zone grouting (OSSG) was proposed. Based on the analysis of the full height overlying strata structure in the range of the six working face areas of the second mining district, the spatial distribution characteristics of the separation zone within the overlying strata are obtained after fully mining the six working faces. Then, emphasis was placed on the selection ratio of grouting materials and the hydrodynamic properties of different grout types, and grouting grout with a high concentration, slow precipitation rate, and good stability was obtained by taking fly ash and local clay as aggregates. The designed grout concentration was approximately 40%; the bulk density was approximately 1.20; and the clay content in the aggregates was approximately 40–50%. The separation-zone grouting plan was designed for the six working faces, and continuous grouting technology with the characteristics of multiple separation zones within the full-height section with a large flow and a high concentration was proposed to form a complete grouting system and reasonable grouting process. After engineering verification, the technology has an ash injection ratio of 24.2%, a grouting ratio of 100.3%, and a reduction in the ground subsidence ratio of 51.5%, effectively reducing mining damage to the ground surface and ensuring the safe operation of ground surface railways. Simultaneously, this advancement improves the resource recovery rate of coal mines and provides greater benefits for mining enterprises.

Study on Overlying Strata Movement and Surface Subsidence of Coal Workfaces with Karst Aquifer Water

The overlying strata layers of coal workfaces with karst aquifer water normally causes serious safety problems due to the precipitation, drainage and water inrush, such as a wide range and long term of surface subsidence. In this study, by taking 10,301 working faces of the Daojiao coal mine in Guizhou Province as the engineering background, the numerical model of water-bearing strata with fluid-solid coupling was established by using UDEC to illustrate the laws of overlying strata movement and surface subsidence. A theory model was proposed to calculate the surface settlement caused by the drainage of aquifer based on the principle of effective stress modified by the Biot coefficient αb. The results showed that the corresponding maximum value (0.72 m) and the range of the surface subsidence with the occurrence of karst aquifer water were larger than that of the overlying strata without karst aquifer water (e.g., the maximum value of surface subsidence with 0.1 m). Moreover, the surface subsidence caused by the drainage of aquifer accounted for 17.8% of the total surface subsidence caused by coal mining. According to the field monitoring of surface subsidence in 10,301 working faces, the maximum value was 0.74 m, which was highly consistent with the results of numerical simulation and theoretical analysis. It verified the accuracy and reliability of the numerical model and the theory model in this study.

Characterization by Cone Penetration Tests of the decalcified Zandvliet Sand (Lillo Formation, North Belgium)

The sandy Zandvliet Member represents a particular, decalcified facies in the top of the Pliocene Lillo Formation in northern Belgium. Based on the correlation with nearby boreholes at the type locality of the Zandvliet Member, we were able to characterize this unit on Cone Penetration Tests. Compared to the underlying Merksem Member, the Zandvliet Member generally shows markedly lower cone resistance values. Since besides the decalcification, the Zandvliet Member is lithologically nearly identical to the underlying Merksem Member, the lower cone resistance values in the Zandvliet Member compared to the Merksem Member can only be the result of the decalcification of the Zandvliet Member. Indeed, the partly decalcified top of the Merksem Member also gives similar cone resistance values as the Zandvliet Member. Decalcification of the Eocene Brussel Sand in central Belgium is also known to have resulted in lower cone resistance values. Our Cone Penetration Test interpretations show that the thickness of the Zandvliet Member strongly varies across short distances (>10 m across 1 km). As the Zandvliet Member thickens, the underlying Merksem Member thins and vice versa. This trend is not in line with that of the under- and overlying strata, i.e. intraformational, nor with the depositional environment of these units. The thickness changes of the Zandvliet Member therefore purely reflect changes in depth of the post-depositional decalcification into the original shell-bearing sand (i.e. original Merksem Member). This confirms the existing hypothesis that the Zandvliet Member actually represents the decalcified part of the Merksem Member. The anomalous heavy mineralogy of the Zandvliet Member compared to the other members of the Lillo Formation cannot be readily explained by the acid chemical weathering which caused the decalcification. This may rather be related to a change in the primary heavy mineral signal of the upper part of the Merksem Member and equivalent Zandvliet Member compared to the underlying sequences of the Lillo Formation. The reason for the post-depositional decalcification could be similar to the Pleistocene changes in soil acidity invoked for decalcification of time-equivalent Red Crag sand in England.

Stress Distribution and Failure Characteristics of Stope Overburden of an Inclined Coal Seam

The stress distribution, failure depth, and shape and range of overlying strata of the stope are important bases for the prevention of roof water hazards and determination of reasonable locations of roof roadways. Based on the hydrogeological data of the E9103 workface, FLAC numerical simulation software was used to establish a numerical calculation model of the overlying strata of the E9103 inclined coal seam, and the stress distribution and failure characteristics of the overlying strata were analyzed. The development height of the caving and water-flowing fractured zones in the overlying strata of the workface was determined. Results showed that the stress reduction area appeared above the goaf in the form of an “arched” distribution, and tensile stress occurred in the local area of the overburden. The overburden relief arch of the workface was symmetrically distributed along the advanced direction and asymmetrically distributed along the inclined direction, with the arch crown deflecting above the workface. The horizontal and vertical displacements of the overlying strata of the stope increased with the advancing distance of the workface. The horizontal displacement in the x -direction presented two obvious regions, and the critical points of the two regions moved forward with the advancement of the workface and showed a certain degree of symmetry. The horizontal displacement in the y -direction presented an “inverted bowl” distribution and increased with the advancement of the workface. The main failure forms of the overlying strata of the workface were a tensile and shear failure, and shear failure was dominant in the upper direction. The height of the overburden caving zone in the workface had little relationship with the advancing distance of the workface and increased slowly as the advancing distance of the workface increased. The development height of the caving zone is 7.2–18.13 m. The development height of the water conduction fissure zone increased rapidly with the increase in the advancing distance of the workface. When the advancing distance was equal to the length of the workface, the development height of the water conduction fissure zone was flat and basically maintained at a stable value. The development height of the water conduction fissure zone is 30.8–62.2 m. These research findings have important engineering importance for ensuring safe and efficient mining of E9103 workface.

Physical Modeling of the Controlled Water-Flowing Fracture Development during Short-Wall Block Backfill Mining

Short-wall block backfill mining (SBBM) technology is an effective method to solve the environmental problems in the mining process. Based on the technical characteristics of SBBM technology and the physical similarity criterion, the physical similarity models for comparing the control effects of water-flowing fracture (WFF) development using short-wall block cave mining (SBCM) and SBBM were established, and the deformation and the WFF development of overlying strata above gob were monitored. The test results determined that the composite materials of 5 mm thick pearl sponge+5 mm thick sponge+10 mm thick paper+6 mm thick board were adopted as the similar backfill materials by comparing the stress-strain curves between the similar backfill materials and the original gangue sample. When the backfilling body was filled into the gob, it would be the permanent bearing body, which bore the load of the overlying strata accompanied with the protective coal pillar. At the same time, the backfilling body also filled the collapse space of overlying strata, which was equivalent to reduce the mining height, and effectively reduced the subsidence and failure height of the overlying strata. Compared with SBCM, the test results showed that the maximum vertical deformation, the height of water-flowing fractured zone, and activity range of overlying strata using SBBM were reduced by 91.4%, 82.5%, and 64.9%, respectively. SBBM had a significant control effect on strata damage and WFF development, which could realize the purpose of water resource protection in coal mines.

Groundwater Vulnerability to Pollution in Kediri City, East Java Province, Indonesia

Groundwater is a water resource that is still a mainstay for humans. The need for groundwater increases with the growth of population and the development of the industrial and agricultural sectors. The residents of Kediri City still use wells from shallow aquifers to fulfill their water needs. Shallow aquifers are prone to pollution due to the influence of shallow groundwater depths and human activities. The purpose of this study is to determine the vulnerability of groundwater pollution in Kediri City. Groundwater vulnerability was conducted by the GOD method (Groundwater Occurrence, Overlaying Lithology, and Depth of Groundwater) that consists of 3 parameters, namely the groundwater confinement, the type of overlying strata, and the depth of the groundwater level. The analysis results show that the level of groundwater vulnerability according to the GOD method in Kediri City consists of moderate and high classes. The western and the eastern part of Kediri City is classified as a high level of vulnerability. In contrast, in the middle of Kediri City, it tends to experience a moderate level of vulnerability.

Overlying Strata Movement and Abutment Pressure Evolution Process of Fully Mechanized Top Coal Caving Mining in Extra Thick Coal Seam

Taken overlying strata of fully mechanized top coal caving mining (FMTCCM) in 15 m extra thick coal seam as the research object, the comprehensive research methods such as field investigation, theoretical calculation, and numerical analysis are used to systematically analyze. During the mining of extra thick coal seam, the overlying strata form the structure of lower cantilever beam and upper hinged rock beam. The downward transmission caused by the interaction of this combined structure is the fundamental reason for the strong periodic ground pressure behavior of working face and roadway blow. The movement process of overlying strata movement is divided into four stages, and dynamic distribution characteristics of lateral abutment pressure in different stages are obtained. It is considered that the gob side roadway can be in a relatively stable overburden structure and stress environment during the stable stage of abutment pressure. The distribution range of the internal and external stress fields is determined, which provides a theoretical basis for the reasonable roadway layout. At last, the fracture position and abutment pressure evolution process of overlying strata along the goaf side of the extra thick coal seam are further verified by drilling stress measurement.