To explore the feasibility of cemented paste backfill with phosphogypsum (PG), bleeding water and rheological tests (slump and on-site pipeline loop tests) were performed with PG backfill slurry (PGBS). In the bleeding water test, the PGBS concentration with minimal bleeding water was measured between 60.87 and 67.61&#x0025;; in the rheological slump test, values of 61 to 68&#x0025; were determined for the on-site pipeline loop test. The rheological pipeline loop test demonstrated that the resistance coefficient is lowest when the concentration is no higher than 65&#x0025;. Through industrial experiments, PG slurry with a concentration of 64&#x0025;&#x2013;65&#x0025; backfill was successfully applied to the goaf. The experimental results demonstrate that PGBS with characteristics of &#x201C;less bleeding water&#x201D; and &#x201C;improved pumpability&#x201D; is obtained when its concentration is between 61 and 65&#x0025;. Paste-like PG slurry was proven to be optimal for cemented PG backfilling technology.

Zhiwei Cao

Bing Liu

Xibing Li

Diyuan Li

Longjun Dong

Experimental Study on Backfilling Mine Goafs with Chemical Waste Phosphogypsum

Fractured rocks are a type of complex media that widely exist in various projects including energy, hydraulic, and underground space engineering, whose permeability properties are a hotspot in current rock mechanics domain. Aiming at investigating the seepage characteristics of the fracture surfaces in different rock strata, uniaxial compressive test and permeability test were performed on single-fracture homogenous and heterogeneous rocks. Specifically, rock&#x2019;s physical and mechanical parameters were measured in uniaxial tests while the initial width of the single fracture was determined through CT scanning. In combination with test results and the calculation model of the displacement of single-fracture heterogeneous rock under triaxial stress condition, the calculation formula of the permeability coefficient of single-fracture heterogeneous rock was derived. Results show that hydraulic pressure in the fracture can affect the permeability coefficient of the fractured rock. Hydraulic fracturing effect occurred with the increase of hydraulic pressure in the fracture, which then generates slight normal deformations of the rock masses on both two sides of the fracture surface, decreases the contact area in the fracture, and leads to the increases of both fracture width and permeability coefficient. For single-fracture rock, the lithological properties of the rock masses on both two sides of the fracture surface impose significant effects on the permeability coefficient. Under same hydraulic pressure and confining pressure, the permeability coefficient of single-fracture coarse sandstone is greatest, followed by that of single-fracture heterogeneous rock, and finally by single-fracture fine sandstone. Theoretical calculation results agree well with the test results, suggesting that the derived theoretical formula can adequately describe the variation tendencies of permeability coefficient with confining pressure and hydraulic pressure in the fracture.

XianZhou Lyu

Zenghui Zhao

Xiaojie Wang

Weiming Wang

Study on the Permeability of Weakly Cemented Sandstones

Rainfall-triggered landslides are one of the most deadly natural hazards in many regions. Seismic recordings have been used to examine source mechanisms and to develop monitoring systems of landslides. We present a semiautomatic algorithm for detecting and locating landslide events using both broadband and short-period recordings and have successfully applied our system to landslides in Taiwan. Compared to local earthquake recordings, the recordings of landslides usually show longer durations and lack distinctive <i>P</i> and <i>S</i> wave arrivals; therefore, the back projection method is adopted for the landslide detection and location. To identify the potential landslide events, the seismic recordings are band-passed from 1 to 3&#x2009;Hz and the spectrum pattern in the time-frequency domain is used to distinguish landslides from other types of seismic sources based upon carefully selected empirical criteria. Satellite images before and after the detected and located landslide events are used for final confirmation. Our landslide detection and spatial-temporal location system could potentially benefit the establishment of rainfall-triggered landslide forecast models and provide more reliable constraints for physics-based landslide modeling. The accumulating seismic recordings of landslide events could be used as a training dataset for machine learning techniques, which will allow us to fully automate our system in the near future.

En-Jui Lee

Wu-Yu Liao

Guan-Wei Lin

Po Chen

Dawei Mu

Ching-Weei Lin

Towards Automated Real-Time Detection and Location of Large-Scale Landslides through Seismic Waveform Back Projection

Chemical corrosion plays a significant role in affecting the properties of rock materials. To understand the effects of chemical corrosion on the pore structure and mechanical properties of sandstones, porosity, <svg xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg" style="vertical-align:-3.18148pt" id="M1" height="12.1436pt" version="1.1" viewBox="-0.0498162 -8.96212 12.249 12.1436" width="12.249pt"><g transform="matrix(.013,0,0,-0.013,0,0)"><path id="g113-85" d="M620 675H597C578 656 570 650 541 650H144C112 650 104 653 94 675H72C59 618 42 552 23 493L53 491C71 534 88 564 105 585C124 608 144 615 238 615H290L197 121C182 40 174 34 88 28L82 0H361L367 28C275 34 266 38 281 121L374 615H441C522 615 543 608 553 583C562 560 566 531 565 493L597 494C603 551 612 629 620 675Z"/></g><g transform="matrix(.0091,0,0,-0.0091,7.176,3.132)"><path id="g50-51" d="M414 144C384 79 371 75 317 75H135L276 221C367 316 408 376 408 465C408 570 327 635 237 635C179 635 131 609 100 575L42 494L67 471C94 510 138 565 205 565C277 565 321 517 321 435C321 348 258 270 195 195C146 137 88 81 33 26V0H411C423 44 433 88 446 135L414 144Z"/></g></svg> spectrum distribution, and NMR images of sandstone specimens were measured after every 10 days of immersion in chemical solutions using the nuclear magnetic resonance (NMR) technique. Static uniaxial compressive tests and dynamic compressive tests were conducted using a conventional servo-controlled testing machine and a split Hopkinson pressure bar (SHPB) system for specimens treated with chemical corrosion. The test results showed that after being treated with chemical corrosion, the porosity of a specimen increased, the <svg xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg" style="vertical-align:-3.18148pt" id="M2" height="12.1436pt" version="1.1" viewBox="-0.0498162 -8.96212 12.249 12.1436" width="12.249pt"><g transform="matrix(.013,0,0,-0.013,0,0)"><use xlink:href="#g113-85"/></g><g transform="matrix(.0091,0,0,-0.0091,7.176,3.132)"><use xlink:href="#g50-51"/></g></svg> spectrum distribution would successively shift towards the right, and the distribution of pores tended to become more irregular. Additionally, all of the compressive strength and elastic modulus of sandstone treated with chemical corrosion under static and dynamic loads decreased, and the peak strain increased. The effect order of a chemical solution on the pore structure and mechanical properties of sandstone was H<sub>2</sub>SO<sub>4</sub>&gt;NaOH&gt;distilled water, which would be related to the different mechanisms of a water-rock reaction. According to the experimental results, the correlations between the mechanical properties and porosity were established. The results can serve as a reference for research in related fields.

Yun Lin

Keping Zhou

Rugao Gao

Jielin Li

Jian Zhang

Influence of Chemical Corrosion on Pore Structure and Mechanical Properties of Sandstone

Terrestrial water storage (TWS) is a key element in the global and continental water cycle. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) has provided a highly valuable dataset, which allows the study of TWS over larger river basins worldwide. However, the lifetime of GRACE is too short to demonstrate long-term variability in TWS. In the Beishan area of northwestern China, which is selected as the most prospective site for high-level radioactive waste (HLRW) disposal, the assessment of long-term TWS changes is crucial to understand disposal safety. Monthly and annual TWS changes during the past 35 years are reconstructed using GRACE data, other remote sensing products, and the water balance method. Hydrological flux outputs from multisource remote sensing products are analyzed and compared to select appropriate data sources. The results show that a decreasing trend is found for GRACE-filtered and Center for Space Research (CSR) mascon solutions from 2003 to 2015, with slopes of &#x2212;2.30&#x2009;&#x00B1;&#x2009;0.52 and &#x2212;1.52&#x2009;&#x00B1;&#x2009;0.24&#x2009;mm/year, respectively. TWS variations independently computed from the water balance method also show a similar decreasing trend with the GRACE observations, with a slope of &#x2212;0.94&#x2009;mm/year over the same period. Overall, the TWS anomalies in the Beishan area change seasonally within 10&#x2009;mm and have been decreasing since 1980, keeping a desirable dry condition as a HLRW disposal site.

Wenjie Yin

Litang Hu

Shin-Chan Han

Menglin Zhang

Yanguo Teng

Reconstructing Terrestrial Water Storage Variations from 1980 to 2015 in the Beishan Area of China

This paper proposes a new roadheader-assisted coal cutter (RACC) based on the tensile failure mechanism of coal. An innovative mining method, called the cutting inside and spalling outside mining (CISOM) method, is developed based on this new RACC. The mechanical model is established, and the working mechanism of the new CISOM method is illustrated using a column model and a beam model. The mechanical models reveal that the tensile stress causes greater deflection than compressive stress. The deflection and mining width demonstrates a quadratic relationship. To understand the stratum behaviors and improve mining efficiency, the stability of a working face owned by Jincheng Coal Mining Group in Shanxi is analyzed using UDEC numerical simulation. Numerical results indicate that the optimal values of the parameter are 0.8&#x2009;m width for the inside cutting and 0.4&#x2009;m width for the outside spalling at #1305 working face. The newly developed RACC was successfully applied at #1305 working face. The field results showed that the recovery rate of CISOM method is over 90&#x0025;; i.e., it is improved by 20&#x0025; in comparison with the traditional method.

Bo Liu

Zhiliu Wang

Wei Xu

Zhiwei Yu

Zhendong Yan

Biao Yao

A Roadheader-Assisted Coal Cutter Based on Tensile Failure Mechanism of Coal

In the literature, the mean penetration depth (MPD) calculated by “walk on spheres” or “walk on cubes” was used to quickly estimate the intrinsic permeability of digitized porous media. However, these two methods encounter difficulties such as irregular boundaries and the determination of arrivals at a boundary. In this study, an MPD method that is based on a more flexible “random walk on grid” (WOG) is explored. Moreover, the accurate MPDs for the pores of simple shapes are derived with Green’s functions to validate the WOG-based MPD. The results suggested that MPDs based on Green’s functions and WOG are consistent with each other; the factor <svg xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg" style="vertical-align:-0.2064009pt" id="M1" height="8.8423pt" version="1.1" viewBox="-0.0498162 -8.6359 8.8162 8.8423" width="8.8162pt"><g transform="matrix(.013,0,0,-0.013,0,0)"><path id="g113-68" d="M645 631C614 643 545 666 457 666C215 666 23 519 23 283C23 90 158 -16 337 -16C412 -16 489 2 522 10C543 39 590 127 606 167L580 181C519 89 459 18 348 18C201 18 122 136 122 287C122 464 244 632 435 632C544 632 602 595 608 472L639 475C643 526 645 581 645 631Z"/></g></svg> in the permeability expression is slightly dependent on roundness of the cross sections and is approximately 1.125 on average, according to analytical and numerical results. In a synthetic complex pore, the permeability estimated by WOG is comparable to, but greater than, the estimate based on the pore-scale dynamics simulation in COMSOL.

Tongchao Nan

Jichun Wu

Kaixuan Li

Jianguo Jiang

Permeability Estimation Based on the Geometry of Pore Space via Random Walk on Grids

In coal mines, underground reservoir systems can increase the availability of water and are an effective technical approach for the protection and utilization of water resources. The stability of coal pillar dams is the key factor in the safety and stability of these underground water storage systems. However, coal pillar dams must operate in complex environments that combine dynamic-static superimposed stress fields and water immersion; moreover, coal pillar dams subjected to both stress and seepage are more susceptible to damage and even collapse. In this study, a seepage-stress coupling model of a coal pillar dam was constructed using the Universal Distinct Element Code (UDEC) simulation software. This model provides a platform for analyzing the characteristics of fracture development in surrounding rock in active mines and the coupled development of crack fields and seepage fields in coal pillar dams. Methods were developed for (1) calculating the water content for the coal pillar dam numerical simulation model and (2) reducing water immersion weakening. The maximum seepage width of a coal pillar dam subjected to water immersion was obtained, and a damage and failure evolution mechanism for coal pillar dams experiencing flooding was developed. The results provide a scientific basis for enhancing the stability control of coal pillar dams and are of great significance for realizing water conservation in coal mines.

Fangtian Wang

Ningning Liang

Gang Li

Damage and Failure Evolution Mechanism for Coal Pillar Dams Affected by Water Immersion in Underground Reservoirs

An original 3D numerical approach for fluid flow in fractured porous media is proposed. The whole research domain is discretized by the Delaunay tetrahedron based on the concept of node saturation. Tetrahedral blocks are impermeable, and fluid only flows through the interconnected interfaces between blocks. Fractures and the porous matrix are replaced by the triangular interface network, which is the so-called equivalent matrix-fracture network (EMFN). In this way, the three-dimensional seepage problem becomes a two-dimensional problem. The finite element method is used to solve the steady-state flow problem. The big finding is that the ratio of the macroconductivity of the whole interface network to the local conductivity of an interface is linearly related to the cubic root of the number of nodes used for mesh generation. A formula is presented to describe this relationship. With this formula, we can make sure that the EMFN produces the same macroscopic hydraulic conductivity as the intact rock. The approach is applied in a series of numerical tests to demonstrate its efficiency. Effects of the hydraulic aperture of fracture and connectivity of the fracture network on the effective hydraulic conductivity of fractured rock masses are systematically investigated.

Chi Yao

Chen He

Jianhua Yang

Qinghui Jiang

Jinsong Huang

Chuangbing Zhou

A Novel Numerical Model for Fluid Flow in 3D Fractured Porous Media Based on an Equivalent Matrix-Fracture Network

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<p><em>Geofluids</em> publishes research relating to the role of fluids in mineralogical, chemical, and structural evolution of the Earth’s crust.</p>


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Geofluids publishes research relating to the role of fluids in mineralogical, chemical, and structural evolution of the Earth’s crust.

Geofluids