Unconsolidated Layer Research Articles

Dating drainage reversal using mineral provenance along the Yangsan Fault, South Korea.

Tectonics is broadly accepted as one of the main factors controlling long-term landscape evolution. The impact of tectonics on short timescales is most often observed through earthquake rupturings that produce localized, metric-scale deformations. Although these deformations significantly affect the landscape, it remains challenging to precisely correlate major landscape changes with these localized earthquake deformations. Therefore, linking instantaneous deformation to long-term morphological changes often involves a thought experiment with potentially limited temporal resolution. At a paleoseismological site along the slow-moving strike-slip Yangsan Fault in South Korea, we employed optically stimulated luminescence (OSL) dating and detrital zircon analysis on all exposed unconsolidated layers in trench walls. The results reveal a significant provenance shift in the sediments accumulating in the trench, indicating a major reorganization of the drainage network. Based on our OSL and detrital zircon data, we estimate that this change occurred around 70ka. We propose that this drastic drainage reorganization was caused by a combination of very slow, yet continuous, earthquake activity and a temporary reduction in river erosion during the onset of the cold, dry spell characteristic of the MIS4 stage across the Korean Peninsula.

Imaging the Sedimentary and Crustal Structure of the Luoyang Basin, Central China, Using a Dense Nodal Seismic Array

Abstract The Luoyang basin lies in the southern margin of the North China block, separating the trans-North China orogen to the north and the Qinling-Dabie orogen to the south. Determining how the basin formed is important for understanding the history of the North China block and its evolution during the Mesozoic and Cenozoic times. Based on the teleseismic data recorded by a dense nodal seismic array, we used the receiver function method to image the sedimentary and crustal structures in the Luoyang basin. Common conversion point stacking images show that the Moho is at a depth of ∼35 km on the south and west sides and slightly uplifted to ∼30 km below the northeastern basin. Two sets of P-to-S conversions are imaged in the shallow crust, separating the near-surface sediments into consolidated, semiconsolidated, and unconsolidated layers. The top of the consolidated sedimentary layer is close to the surface at the southern basin and present at a depth of ∼2 km beneath the central basin, then deepens to a depth of ∼3 km below the northern basin. The discontinuous interface in the sediments indicates that the sedimentary layer was truncated by some blind north-dipping normal faults. The northeastward thinning crust, thickening sedimentary layers, and dipping normal faults together indicate that the Luoyang basin evolved in association with the deep crustal extension response to the lithospheric thinning of the North China block. By superimposing the deep crustal extension, we propose that the present-day landform of the Luoyang basin was also shaped by fluvial erosion at the surface, which was accompanied by the expansion of Yihe and Luohe riverbeds during the Quaternary.

Subsurface Characterization Using Downhole Refraction Survey: A Case Study of the Niger Delta

This study addresses the critical role of downhole refraction as a method for assessing subsurface characteristics, particularly in areas facing challenges such as ground roll issues and weak reflection signals during seismic data acquisition. Focused on the Agudama, Kenfa, and Yenegwe settlements in the Niger Delta region, where frequent engineering structure collapses occur, the research aims to understand the depth and velocity of unconsolidated zones through downhole refraction. The study emphasizes the limitations of relying solely on uphole refraction and highlights the necessity of downhole methods for accurate velocity determination. The research employs various techniques, including borehole drilling, velocity measurements, and seismic pulse generation. The study's primary objectives include investigating the causes of engineering structure failures, proposing geophysical solutions, and contributing valuable insights into the geological context of the Niger Delta region. The fieldwork involved a comprehensive approach, combining reconnaissance surveys, downhole refraction studies, and the use of specialized equipment such as a Geometrics Stratavisor NZXP seismograph and explosives for seismic sources. The results of the downhole refraction survey reveal a double-layer velocity model in the research areas, indicating variations in weathered or unconsolidated layer thickness and velocities. The study establishes a relationship between elevation, weathered layer thickness, and velocities in both weathered and consolidated layers, offering valuable information for engineering considerations. The research concludes that the downhole refraction method is crucial for evaluating weathered strata properties and provides cost-effective subsurface information. The study recommends drilling below the weathered zone for seismic energy source placement, excavation depths for stable structures, and future investigations focusing on closely spaced data points and additional soil properties. These recommendations aim to enhance the safety and durability of structures in the study area, contributing to the understanding and mitigation of engineering structure failures in the Niger Delta region.

Measurements of the frequency dependence of geo-alpha in clayey silt at low frequencies

Transmission loss (TL) measurements in the Santa Barbara Channel, together with co-located chirp measurements, show that geo-alpha (dB/l) in clayey silt increases approximately linearly with frequency (f) at f < 3 kHz. TL was measured between a fixed source and fixed vertical array at 3.7 km at 0.3 < f < 5 kHz. Geo-alpha was inverted from the TL data at 0.3, 1.1 and 1.9 kHz. Inversion calculations at 1.1 and 1.9 kHz considered both geo-alpha and bio-alpha due to layer of anchovies at 12 m. Inversion calculations at 0.3 kHz considered only the effect of geo-alpha; the effect bio-alpha on TL was small. Geo-alpha was also inferred from chirp sonar measurements at 3.2 and 6.2 kHz at the ends and middle of the TL track. Chirp sonar showed that the bottom consisted of a layer of unconsolidated sediments overlying a layer of sand. Co-located cores revealed that the unconsolidated layer consisted of clayey silt. Bio-alpha data were compared to Biot and VGS theories and the theory of attenuation in suspended sediments (Pierce et al., 2017). The measured frequency dependence is consistent with Pierce et al.’s theory. This research was supported by The Office of Naval Research Ocean Acoustics Program.

An apex predator engineers wetland food-web heterogeneity through nutrient enrichment and habitat modification.

The potential for animals to modify spatial patterns of nutrient limitation for autotrophs and habitat availability for other members of their communities is increasingly recognized. However, net trophic effects of consumers acting as ecosystem engineers remain poorly known. The American Alligator Alligator mississippiensis is an abundant predator capable of dramatic modifications of physical habitat through the creation and maintenance of pond-like basins, but its role in influencing community structure and nutrient dynamics is less appreciated. We investigated if alligators engineer differences in nutrient availability and changes to community structure by their creation of 'alligator ponds' compared to the surrounding phosphorus (P)-limited oligotrophic marsh. We used a halo sampling design of three distinct habitats extending outward from 10 active alligator ponds across a hydrological gradient in the Everglades, USA. We performed nutrient analysis on basal food-web resources and quantitative community analyses, and stoichiometric analyses on plants and animals. Our findings demonstrate that alligators act as ecosystem engineers and enhance food-web heterogeneity by increasing nutrient availability, manipulating physical structure and altering algal, plant and animal communities. Flocculent detritus, an unconsolidated layer of particulate organic matter and soil, showed strong patterns of P enrichment in ponds. Higher P availability in alligator ponds also resulted in bottom-up trophic transfer of nutrients as evidenced by higher growth rates (lower N:P) for plants and aquatic consumers. Edge habitats surrounding alligator ponds contained the most diverse communities of invertebrates and plants, but low total abundance of fishes, likely driven by high densities of emergent macrophytes. Pond communities exhibited higher abundance of fish compared to edge habitat and were dominated by compositions of small invertebrates that track high nutrient availability in the water column. Marshes contained high numbers of animals that are closely tied to periphyton mats, which were absent from other habitats. Alligator-engineered habitats are ecologically important by providing nutrient-enriched 'hotspots' in an oligotrophic system, habitat heterogeneity to marshes, and refuges for other fauna during seasonal disturbances. This work adds to growing evidence that efforts to model community dynamics should routinely consider animal-mediated bottom-up processes like ecosystem engineering.

Load bearing capacity of arch structure in unconsolidated layers

Coal mining inevitably results in the movement of overlying strata, with the upward formation of the strata leading to surface subsidence, causing irreversible impact on the buildings, land, and ecological environment. The movement and deformation of the strata are controlled by the bearing structure in the overlying strata, whose failure results in the deformation and breakage of the overlying strata simultaneously. While studies have been conducted on the arch structure in unconsolidated layers (ASUL), its bearing performance has not been addressed. Therefore, this study develops a bearing mechanics model based on the morphological characteristics of the ASUL. The analytical expressions of the axial force, bending moment, and shear force of the cross-sectional area were determined using theoretical derivations. The model analysed the internal forces and showed the influence laws of the overlying load, horizontal pressure coefficient, and rise-to-span ratio of the ASUL. The failure criterion of the bearing was also further determined. The results indicated that with overlying and horizontal loads, the axial force and bending moment are symmetrically distributed, whereas the shear force is asymmetrically distributed. In addition, the axial force gradually increases from the dome to the base of the ASUL. Compared to the axial force and bending moment, the shear force has a lower impact on the stability of the ASUL. Most of the axial force and overlying load is received through the axial compression of the cross-section to maintain stability and play a bearing role on the overlying unconsolidated layers. As the overlying load, horizontal pressure coefficient, and rise-to-span ratio increase, the axial force, bending moment, and shearing force also increase gradually. This effect is more apparent at the dome, spandrel, and base of the ASUL. The stability of the dome and spandrel is key to the overall structural stability. Therefore, the failure criterion for the ASUL was determined based on the compression failure at the dome and spandrel. During the mining process of the working face, the ASUL served as load-bearing control for the overlying unconsolidated layers. Further, increasing width of the working face damages and shifts the base of the ASUL, resulting in compression failure at the dome and spandrel, further inducing dome lift and causing overall failure of the ASUL. Considering the aforementioned factors, a control method that reinforces the surface subsidence of the ASUL by 'one-time, upward, staged, and multiple-ground-drilling' compaction grouting has been proposed. During the mining process of the working face, the arch bead-like structure, combined with the ASUL, serves as the load-bearing control on the overlying strata and ground surface, reducing ASUL deformation in the unconsolidated layers, overlying strata, and ground surface. This process enables the controlling of ground subsidence of coal mining in thick unconsolidated layers.

Analysis of Overburden Deformation and Migration under Huge Thick Unconsolidated Layers Based on Multiple Approaches

Underground mining safety risk increases with the more complicated geological conditions in deep strata, so coal mines turn to the upper limit mining of shallow coal seams under the Cenozoic strata. Nevertheless, coal mines in the Northern China coalfield are mainly covered by thicker loose sandy layers with more abundant water. The analysis of overburdened strata deformation properties is essential for safe, efficient, and environmentally friendly production. This paper discusses the deformation and migration of overburdened strata through mechanical analysis, numerical and physical similar simulations, and in situ field measurement. A thorough understanding of overburdened strata deformation induced by mining has been obtained, and the results are as follows: The immediate roof first collapses to form the caved zone accompanied by the first weighting, and the fractured zone and bending deformation zone begin to develop in sequence; the separation layer is observed during the period of fracture development. However, the occurrence of the bending deformation subsidence results in the closure of the separation space; the ratio of fractured and mining height is quantified to 14.4:1.0 by the comparative analysis. The results may serve as technical evidence to support the mining safety of the study area and other coal mines with similar geological conditions.

Research Findings on the Application of the Arch Structure Model in Coal Mining, a Review

Studying the movement law and failure mechanism of overburden is important to underground safety production, aquifer protection, surface subsidence and ecological protection. A commonly used model, the arch structure model, for studying overburden movement is systematically reviewed in this paper. First, the arch structure in the mining field is divided into an unconsolidated layer arch, beam arch (hinged arch), and overburden arch according to arching medium. On this basis, the research progress and existing problems of these three arch structure models are discussed according to the research means, including theoretical modeling, numerical simulation, similar simulation, and field measurements. The application of the arch structure model focuses on the prediction and prevention of mining pressure and surface subsidence, and there are relatively few means to actively regulate overburden arch. Thus, three control methods of the arch structure in underground coal mining are proposed: the preset arch structure method before coal mining, process control arch methods during coal mining, and end reinforcement control arch methods after coal mining. Finally, the main research focus on the arch structure model in the future is discussed.

Green coal mining and water clean utilization under Neogene aquifer in Zhaojiazhai coalmine of central China

Coal plays an important role in the high-quality development of national economy and society, and overburden movement caused by coal mining has also caused groundwater loss and eco-environment damage. Under the national strategic goal of emission peak and carbon neutral, green mining and low-carbon clean production have become the mainstream production mode of coal enterprises. In this study, the overlying unconsolidated layer is divided into four aquifer groups in Zhaojiazhai coalmine of central China based on its characteristics and water yield coefficient of pumping experiment. According to the coal seam thickness, the damage range of the aquifer under the mining influence and the maximum hydrostatic reserves are accurately determined, and a combined up-down well drainage technology is proposed, which solves the water hazard threat of the safe mining under Neogene aquifer. Considering that the loss of groundwater resources will aggravate the surface subsidence , the distribution characteristics and formation mechanism of surface cracks under fully mechanized top coal caving mining are analyzed, the angular parameters of surface dynamic movement and deformation are obtained, the damage degree of mining subsidence area is divided into regions, and land reclamation measures are implemented. Combined with the clean production concept of waste heat utilization , and based on the life cycle theory, the life cycle cost model of mine heat supply mode is established. It is analyzed that the waste heat utilization of mine water and air compressor is the best way of heat supply in Zhaojiazhai coalmine, and has been successfully applied. The engineering application shows that the dewatering and drainage not only liberates the coal resource under water of 5.99 Mt, but also provides rich waste heat of mine water for coalmine clean production. The waste heat utilization saves 7000 tons of standard coal for the mine every year, which has the characteristics of low operation cost, high efficiency, energy conservation and green environmental protection. Meanwhile, using the surface movement parameter to guide the land reclamation in the subsidence area not only improves the land productivity, but also effectively improves the eco-environment of the mining area, speeds up the construction process of green mines, and provides a reference for the green mining and low-carbon production of coal enterprises. • The drainage technology is proposed to convert Neogene water into clean energy. • The waste heat utilization of coalmine is compared, analyzed and determined. • A new mode of green mine construction is proposed and implemented. • The findings are considered instrumental for green mine and low-carbon development.

Development of Site-Scale Conceptual Model Using Integrated Borehole Methods: Systematic Approach for Hydraulic and Geometric Evaluation

Understanding the physical flow mechanisms in aquifer systems is essential in effectively protecting groundwater resources and preserving subsurface environments from a wide range of contaminants. A conceptual model is a simplified representation of a groundwater system and gaining knowledge about the geological features and parameters controlling the flow and transport processes is a crucial first step towards properly constructing a site-scale conceptual model. In this study, we present a multi-step workflow that involves integrated borehole techniques to gain information concerning groundwater flow. Measurements from core-scale to field-scale enable us to better build a subsurface geological structure divided into the unconsolidated layer and the fractured bedrock. In addition, neutron logging and mercury injection capillary pressure techniques allow for the development of vertical porosity distribution in the alluvial layer. For fracture characterization, the fracture geometry is delineated using a series of borehole imaging techniques and single-hole tests to differentiate the individual permeable fractures from other hydraulically inactive fractures. Combining the hydraulic and geometric evaluations, the presence of large-scale connective fracture networks is identified. Our high-resolution three-dimensional (3D) site-scale conceptual model is expected to contribute to improving the reliability and availability of numerical groundwater models.

COMPARATIVE ANALYSIS OF PHYSICAL AND CHEMICAL PARAMETER OF SOIL IN NON IRRIGATED AND IRRIGATED (WELL OR CANAL) FIELD AREAS AROUND BIKANER CITY RAJASTHAN

The most vital and essential common asset is soil. The production of the sustenance to meet the requirements of people and animals is basically reliant upon agriculture which is dependent on soil. The word soil originated from Latin word Solum which means Flour. The soil is a dynamic natural body composed of minerals and organic material as well as living forms in which plant grow. Soil is the unconsolidated outer layer of Earths crust. Soils consist of four major components: mineral materials, organic matter, water, and air. The physical properties of a soil are important to determine the manner in which it can be used either for agricultural and non-agricultural purposes R. S. Meena and A. K. Mathur,2017 Properties viz. infiltration rate, water- holding capacity, permeability, aeration, plasticity and nutrient-supplying ability, are influenced by the size, proportion, arrangement and mineral composition of the soil particles.

Investigation of coordinated development of coal mining and pipeline protection under boundary effect of thick unconsolidated layer

Investigation of coordinated development of coal mining and pipeline protection under boundary effect of thick unconsolidated layer

Application of machine learning to quantification of mineral composition on gas hydrate-bearing sediments, Ulleung Basin, Korea

Mineral quantification is essential to evaluate gas hydrate (GH) resources because the mineral composition is closely related to the origin of sediment, the reservoir properties, and even the existence of GH. However, it is difficult to analyze the mineral compositions of GH-rich unconsolidated layers because of complex compositional combinations. Thus far, mineral composition has relied on experts’ analysis. In this study, a machine learning model was developed that can efficiently probe the mineral composition from the X-ray diffraction (XRD) patterns of GH sediments in the Ulleung Basin, Korea, which has a complex composition including 12 minerals. It is the first time that machine learning algorithms have been applied to complex natural GH sediment with 12 minerals, including amorphous materials. To build a reliable data-driven analysis model, after data acquisition and preprocessing were conducted, various machine learning algorithms were employed, including convolutional neural network (CNN), recurrent neural network (RNN), multi-layer perceptron (MLP), and random forest (RF). For data acquisition, 488 sediment samples were analyzed by XRD experiment, and the intensity profiles were manually analyzed by an expert to obtain their mineral compositions. In particular, the intensity profile according to the XRD angle of incidence serves as the input data, and the corresponding 12 mineral composition provides label data for supervised learning. The RF approach yields the best prediction result with an average mean absolute error (MAE) of 2.56%, and the other algorithms also exhibits reasonable performance with average MAEs of less than 3%. If XRD is newly performed for GH sediment, the intensity profile can be automatically analyzed by the trained machine learning model in seconds. This approach will enable experts to analyze mineral compositions efficiently and reliably. • Mineral composition was evaluated by machine learning (ML) from XRD profiles. • Gas hydrate (GH) sediment in Ulleung Basin, Korea comprises the twelve minerals. • The 488 data pairs (XRD profile, composition) were preprocessed by domain knowledge. • GH sediment including amorphous material was analyzed by ML for the first time. • The random forest approach performed better than deep learning algorithms.

Sensitivity Analysis and Numerical Simulation Study on Main Controlling Factors of Surface Movement and Deformation in Strip Filling Mining under Thick Unconsolidated Layers

In many mining areas, there is a lot of pressed coal under buildings, railways, and water bodies, and there are geological conditions of thick unconsolidated layers, so the surface subsidence has certain particularity. The key to solve the problem of pressed coal is the control technology of surface subsidence. The development of strip filling technology provides a kind of economical and effective surface subsidence control technology. With the passage of time, the natural weathering, flow, and fracture of some coal pillars may lead to the instability and failure of some coal pillars. Therefore, the selection of filling parameters plays an important role in the stability of coal pillars. In order to study the influence factors of surface movement and deformation, considering the influence factors of filling rate, key layer thickness, filling body strength, and unconsolidated layer thickness, FLAC 3D was used to simulate the surface movement deformation, and the orthogonal test method was used to analyze the simulation results, and the sensitivity of the main control factors affecting the surface deformation affected by strip filling mining was studied. The results show that the order of importance of the four factors on the four surface movement and deformation parameters is filling rate > key layer thickness > filling body strength > unconsolidated layer thickness. The influence of these four factors on the surface movement and deformation parameters is gradually decreasing, but the influence degree of different factors has drawn a certain gradient.

Review: Hydrogeology of weathered crystalline/hard-rock aquifers\u2014guidelines for the operational survey and management of their groundwater resources

Hard rocks or crystalline rocks (i.e., plutonic and metamorphic rocks) constitute the basement of all continents, and are particularly exposed at the surface in the large shields of Africa, India, North and South America, Australia and Europe. They were, and are still in some cases, exposed to deep weathering processes. The storativity and hydraulic conductivity of hard rocks, and thus their groundwater resources, are controlled by these weathering processes, which created weathering profiles. Hard-rock aquifers then develop mainly within the first 100 m below ground surface, within these weathering profiles. Where partially or noneroded, these weathering profiles comprise: (1) a capacitive but generally low-permeability unconsolidated layer (the saprolite), located immediately above (2) the permeable stratiform fractured layer (SFL). The development of the SFL’s fracture network is the consequence of the stress induced by the swelling of some minerals, notably biotite. To a much lesser extent, further weathering, and thus hydraulic conductivity, also develops deeper below the SFL, at the periphery of or within preexisting geological discontinuities (joints, dykes, veins, lithological contacts, etc.). The demonstration and recognition of this conceptual model have enabled understanding of the functioning of such aquifers. Moreover, this conceptual model has facilitated a comprehensive corpus of applied methodologies in hydrogeology and geology, which are described in this review paper such as water-well siting, mapping hydrogeological potentialities from local to country scale, quantitative management, hydrodynamical modeling, protection of hard-rock groundwater resources (even in thermal and mineral aquifers), computing the drainage discharge of tunnels, quarrying, etc.

The Prediction Model of Super Large Subsidence in High Water Table Coal Mining Areas Covered with Thick Unconsolidated Layer

In mining engineering, after the extraction of underground resources, the maximum surface subsidence is usually less than the mining thickness of coal seam. However, under the condition of thick loose layer, some special phenomena appear in surface subsidence, for example, the maximum surface subsidence value is greater than the mining thickness of coal seam. This special phenomenon cannot be predicted by traditional subsidence prediction methods. To solve this problem, by using the numerical simulation software Fast Lagrangian analysis of continua (Flac), we study the changing rules of subsidence with different strata lithology and unconsolidated layer thickness and reveal the formation mechanism of this law. The results show that the effect of the thick unconsolidated layer on the hard rock is greater than that of the soft rock. When the rock is soft, the unconsolidated layer moves as a whole following the bedrock during the whole mining process. The surface subsidence decreases approximately linearly with the thickness ratio increase of the unconsolidated layer to bedrock. However, when the rock is hard or medium hard, there are supporting structures formed inside the rock stratum, which has supporting effect on the overlying strata. The surface subsidence undergoes three proportional sections, first increases, then decreases, and finally increases with the thickness ratio increase of the unconsolidated layer to bedrock. Combined with these laws, based on the theory that the rock strata space can be completely compressed gradually, we derive the calculation method of surface subsidence under the condition of thick unconsolidated layer and apply it to practice. The results show that the prediction results are consistent with the actual situation and meet the engineering requirements. The research results can provide a reference for the subsidence prediction of similar conditions.

Research on dynamic prediction model of surface subsidence in mining areas with thick unconsolidated layers

In order to improve the accuracy of the surface dynamic prediction model in mining areas with thick unconsolidated layers and improve Knothe time function, the influence coefficient was firstly changed into the coefficient in exponential form, and the influence coefficient of unconsolidated layer was added. Then, a subsidence basin prediction model for mining under thick unconsolidated layers was established. Next, the model was combined with the improved Knothe function, thus constructing a new mining subsidence prediction model. The new subsidence prediction model was applied in 1414 (1) working face in Huainan mining area. The results showed that the integrated model could better reflect the subsidence process, and the prediction values and the measured values agreed well.

Research on Prediction Model of Mining Subsidence in Thick Unconsolidated Layer Mining Area

Accurately forecasting the scope of coal mining subsidence area is of great significance to the protection of surface structures. Due to the peculiarities of the unconsolidated layers rock formation, the surface movement of the thick unconsolidated layers mining area converges slowly at the boundary of the basin, and the boundary of the subsidence basin is larger than under conventional conditions. It is found that the existing models have a poor prediction effect at the boundary, and the predicted subsidence basin range is smaller than the actual basin range. To solve this problem, a new surface deformation prediction model based on Boltzmann function (IB) is proposed in this paper. Aiming at the problem that the model function is highly nonlinear and difficult to obtain parameters, the multi-population genetic algorithm (MPGA) is introduced into the parameter solution of the prediction model, and the parameter calculation model based on multi-population genetic algorithm (MPGAIB) is constructed. The simulation experiment and engineering example analysis show that both the overall fitting effect and the fitting effect at the boundary of IB model are closer to the actual situation, The MPGAIB model has good ability to anti-random error and gross error, and the result is stable.

Study on the clay weakening characteristics in deep unconsolidated layer using the multi-point monitoring system of FBG sensor arrays

A large area of thick unconsolidated stratum layer overlying the coal seam of eastern China, which brought the regional disaster prevention issue under the circumstance of unconsolidated layer settlement triggered by mining activities. In this paper, the multi-point monitoring system based on fiber Bragg grating (FBG) sensors array was implemented into the deep unconsolidated layer to realize a long-term ground monitoring, which investigated the compression process of ground rock layers at different burial depths and revealed the mechanical weakening characteristics of clay. The deformation characteristics of the aquifers were analyzed, including a sand layer, gravel layer, and clay water barrier, as well as the weakening characteristics of the clay layer aquifer. The monitoring results of the FBG sensing system show that unconsolidated layer settlement usually occurs in thick and stable aquifers and adjacent clay layers, and the peripheral part of the deep clay layer in contact with the aquifer will become a weakened zone. The clay layer at such locations should also be a key monitoring layer with increasing depth. The survival rate of FBG sensors were discussed to propose the suggestions of system installation. These findings could provide important guidance for predicting the unconsolidated layer settlement process and for the timely implementation of governance measures.

Research on Arch Model and Numerical Simulation of Critical Water and Sand Inrush in Coal Mine near Unconsolidated Layers

With the continuous increase of the upper limit of coal mining, in mining areas near unconsolidated layers, water and sand inrush disasters occur from time to time, seriously threatening the safety of mine production. In this paper, the process of water and sand inrush accidents induced by mining near unconsolidated layers is analyzed using mechanical analysis and numerical simulation methods, based on the principle of silo unloading and arching and combined with actual water and sand inrush characteristics; the critical water and sand inrush arching mechanism is explained. The paper also proposed and established three critical arching mechanics models (interlocking arch, bonded arch, and transition arch), deduced the mathematical expression of interlocking arch and transition arch, and obtained the critical instability conditions of the arch and its influencing factors. The research results have guiding significance for the occurrence of water and sand inrush disasters and the judgment of the degree of damage in mining near unconsolidated layers.