High Overburden Pressure Research Articles

Fractal study on the nonlinear seepage mechanism during low-permeability coal water injection

In the initial stage of coal seam water injection, due to the high density and low permeability of coal bodies, an obvious startup pressure gradient is observed in relation to water seepage; this phenomenon leads to low-velocity nonlinear seepage. In this paper, we study the nonlinear seepage law and the main influencing parameters of the water injection process. First, based on the startup pressure gradient, the nonlinear seepage equation, and the fractal theory, we formulated a nonlinear seepage model of coal seam water injection that considered the fractal characteristics of a complex coal structure. Subsequently, we carried out coal seam water injection and gas radial seepage experiments under a high overburden pressure, obtaining the startup pressure gradient according to the seepage characteristics and the changes of dynamic parameters. Then, the dynamic parameters of water injection, the structural parameters of the coal samples, the physical parameters, and the fractal dimension were substituted into the theoretical model to obtain the theoretically calculated value. Finally, through comparative analysis of theoretical and experimental startup pressure gradient calculation results, it is found that with the increase in the overburden pressure, the permeability of coal and the connectivity effect are reduced, while the fracture tortuosity and the startup pressure gradient increase. Moreover, coal seam permeability does not seem to be the single decisive factor for the nonlinear startup pressure gradient.

A numerical approach for simulation of stress-controlled cyclic shear loading in a soil column considering partial drainage

A numerical approach for simulation of stress-controlled cyclic shear loading in a soil column considering partial drainage

Stress effects on thermal conductivity of soils and heat transfer efficiency of energy piles in the saturated and unsaturated soils

Stress effects on thermal conductivity of soils and heat transfer efficiency of energy piles in the saturated and unsaturated soils

Pullout testing and Particle Image Velocimetry (PIV) analysis of geogrid reinforcement embedded in granular drainage layers

Pullout testing and Particle Image Velocimetry (PIV) analysis of geogrid reinforcement embedded in granular drainage layers

Empirical correlations for prediction of tunnel deformation in squeezing ground condition

Empirical correlations for prediction of tunnel deformation in squeezing ground condition

Prospects for application of mining systems with caving in stoping blocks with manmade bottoms at deep levels in Donskoe Chromite Mine

The main and constitutive criteria in selecting methods and engineering plans for ore mining are the geological conditions of ore bodies and enclosing rocks, their structure, strength, deformability and stability. After these criteria are scrutinized, the geotechnical behavior of rock mass during mining is assessed, the parameters of engineering procedures with the assumed mining system are determined, as well as the issues of mining safety, reliability and efficiency are addressed. In this respect, it is required to reveal the nature of possible implications, reveal geotechnical patterns in the course of mining, select processes flow charts and their designs to avoid accidents and to ensure sound subsoil use. Thus, justification of engineering solutions for deep-level chromite-bearing ore mining in difficult geological conditions by Donskoe GOK is a relevant scientific problem. Stoping operations form underground enclosed areas which need to be dealt with at the preserved efficiency of the mining technology and economy. In this regard, the most promising geotechnology involves creation of artificial bottoms at the intersections of drift pillars in the zone of ore drawing and haulage. These manmade floors should be capable to sustain extremely high overburden pressure. From the accomplished calculations of strength of a vertical and square reinforced concrete column–support 7–9 m high, its factor of safety is assumed as 1.51. By the estimates, the proposed technology of stoping in extraction blocks with manmade bottoms can save up 1,347,2 million Kazakhstani tenge per block.The study was supported by the Ministry of Education and Science of Kazakhstan, Grant No. AR05131352. The authors appreciate participation of PhD A. T. Abakanov, Researcher at the Integrated Subsoil Management Laboratory of the Kunaev Institute of Mining, and Doctoral Student B. K. Bektrur from the Satbayev University in this study.

Applicability of manmade bottoms in extraction panels toward sustainable stoping with caving at deep levels in mines

The authors discuss applicability of manmade bottoms (MB) in extraction panels, with fast reinforced-concrete support platform at the ore drawing and haulage level in stoping with caving. The structural components of the proposed-design MB capable to stand high overburden pressure in mining of thick ore bodies using the systems of stoping with caving in the conditions of unstable ore and enclosing rocks, including deep-level mining.

Numerical simulation of coupled liquid water, stress and heat for frozen soil in the thawing process

PurposeThe purpose of this paper is to perform the thermo-hydro-mechanical (THM) numerical analysis in order to study the thawing process for frozen soil and to predict the thawing settlement.Design/methodology/approachA new one-dimensional multi-field physical coupled model was proposed here to describe the thawing process of saturated frozen soil, whereby the void ratio varied linearly with effective stress (Eq. 10) and hydraulic conductivity (Eq. 27b). The thawing process was simulated with different initial and boundary conditions in an open system with temperature variations. The mechanical behavior and water migration of the representative cases were also investigated.FindingsThe comparisons of representative cases with experimental data demonstrated that the model predicts thawing settlement well. It was found that the larger temperature gradient, higher overburden pressure and higher water content could lead to larger thawing settlement. The temperature was observed that to distribute height linearly in both frozen zone and unfrozen zone of the sample. Water migration forced to a decrease in the water content of the unfrozen zone and an increase in water content at the thawing front.Research limitations/implicationsIn this study, only the one-directional thawing processes along the frozen soil samples were investigated numerically and compared with test results, which can be extended to two-dimensional analysis of thawing process in frozen soil.Originality/valueThis study helps to understand the thawing process of frozen soil by coupled thermo-hydro-mechanical numerical simulation.

Ca2+ Ions Decrease Adhesion between Two (104) Calcite Surfaces as Probed by Atomic Force Microscopy

Solution composition-sensitive disjoining pressure acting between the mineral surfaces in fluid-filled granular rocks and materials controls their cohesion, facilitates the transport of dissolved species, and may sustain volume-expanding reactions leading to fracturing or pore sealing. Although calcite is one of the most abundant minerals in the Earth’s crust, there is still no complete understanding of how the most common inorganic ions affect the disjoining pressure (and thus the attractive or repulsive forces) operating between calcite surfaces. In this atomic force microscopy study, we measured adhesion acting between two cleaved (104) calcite surfaces in solutions containing low and high concentrations of Ca2+ ions. We detected only low adhesion between calcite surfaces, which was weakly modulated by the varying Ca2+ concentration. Our results show that the more hydrated calcium ions decrease the adhesion between calcite surfaces with respect to monovalent Na+ at a given ionic strength, and thus Ca2+ can sustain relatively thick water films between contacting calcite grains even at high overburden pressures. These findings suggest a possible loss of cohesion and continued progress of reaction-induced fracturing for weakly charged minerals in the presence of strongly hydrated ionic species.

Effect of Field Drainage on Seismic Pore Pressure Buildup and Kσ under High Overburden Pressure

AbstractThis paper studies the effect of a high effective overburden pressure [σv0′= ∼600 kPa (6 atm)] under two drainage conditions on the field liquefaction behavior of saturated Ottawa sand. A s...

Shale Gas Reservoir Evaluation by Geophysical Measurements: A Case Study of the Upper Ordovician–Lower Silurian in the Fenggang Block, Northern Guizhou Province

AbstractWith the aid of geophysical measurements, including seventeen two‐dimensional (2D) seismic lines and the well logging curves of well FGY1, the structure and reservoir characteristics of the Upper Ordovician–Lower Silurian strata in the Fenggang block, northern Guizhou Province, were analyzed thoroughly to identify desert areas and favorable intervals. The results show that Longmaxi‐Wufeng is the most prospect‐rich formation, consisting of a thick succession of overmature black shale, this formation remaining partially in the Suiyang, Fenggang and Jianchaxi synclines. The Longmaxi‐Wufeng shale, especially the lower member, was deposited in a reducing low‐energy environment with relatively high U content and a low Th/U value. In this shale, the organic matter type (sapropelic and humic‐sapropelic), total organic carbon (TOC) content, gas content, gas adsorption capacity, vitrinite reflectance and brittle mineral content are profitable for shale gas preservation and development. The fractures of this shale were closed because of its high overburden pressure. The gas adsorption capacity of this shale increases with increasing TOC content and Ro. In the Longmaxi‐Wufeng Formation at well FGY1, the most favorable intervals are in the depth ranges of 2312.4–2325.1 m and 2325.8–2331.1 m.

Effects of air-injection pressure on airflow pattern of air sparging

Air sparging is a remediation technology for treating soil/groundwater contaminated with volatile organic compounds (VOCs). VOC removal during air sparging is rendered less effective because of the random formation of air channels, creating preferential paths for airflow, thus limiting remediation to these channels, referred to as a zone of influence (ZOI). Pulsation is a popular method used to improve the effectiveness of air sparging through cyclic operation, with the hope that air channels would form elsewhere. Pulsation makes air sparging more time-consuming. This paper studies the effects of one cycle of pulsation and air pressure on the airflow pattern and presents a laboratory study that investigated the effects of initial and further increases in the injected air’s pressure on the airflow pattern within a glass-bead medium used as a medium analogous to the soil. Digital images of airflow patterns were collected; these images show a larger radius of influence (ROI) and ZOI due to the initial air-pressure increase, particularly when a higher overburden pressure (i.e. the stress due to the partially saturated layer on top of the saturated soil-simulant layer) exists above the water-saturated zone. Further air-pressure increases seem to have no measurable effect on the ROI and the shape of the ZOI.

Numerical Simulation of the Effect of High Confining Pressure on Drainage Behavior of Liquefiable Clean Sand

This article presents numerical simulations investigating pore pressure buildup of a sand layer with a free drainage boundary at the top under both low and high overburden pressures and subjected to earthquake base excitation. The numerical runs simulate two centrifuge experiments previously conducted and reported. In these tests, a 5-m layer of clean Ottawa sand with relative density Dr=45% was tested under overburden pressures of ∼100 and ∼600 kPa (1 and 6 atm). The simulations were performed using Dmod2000, a nonlinear effective stress numerical one-dimensional (1D) site response analysis code. The tests revealed that the response was partially drained rather than undrained, with much more partial drainage at ∼600 kPa (6 atm) compared to ∼100 kPa (1 atm). The simulations correctly modeled this behavior, with very good agreement between simulated and measured centrifuge excess pore pressures. A key aspect of this good accord in the simulations was the correct selection in the simulations of the 1D drained volumetric stiffness of the sand, M′=1/mv, because the coefficient of consolidation, cv, is proportional to M′. Both cv and M′ were 2.5–3 times greater at ∼600 kPa (6 atm) than at ∼100 kPa (1 atm) in both centrifuge tests and simulations. Any future simulation of pore pressure response of sand under field drainage conditions needs to consider this large increase in volumetric stiffness at high overburden pressure. Good agreement was found between values of M′ back-calculated from the centrifuge tests and from a consolidometer test on a different sand reported in the literature. The value of M′ seems to increase approximately with the root square of the overburden pressure, and future simulations for high overburden and realistic field drainage conditions should account for this increase. The proper high-pressure correction factor, Kσ, to be used in conjunction with liquefaction charts may be higher than 1 for some realistic field drainage conditions due to this substantial decrease of sand compressibility under high overburden pressure.

Pore Pressure and Kσ Evaluation at High Overburden Pressure under Field Drainage Conditions. II: Additional Interpretation

AbstractThis article is the second of two companion papers studying the effect of a high overburden pressure on the liquefaction behavior of saturated Ottawa sand. A series of four centrifuge exper...

Pore Pressure and Kσ Evaluation at High Overburden Pressure under Field Drainage Conditions. I: Centrifuge Experiments

AbstractThis article is the first of two companion papers studying the effect of overburden pressure on the liquefaction behavior of saturated Ottawa sand. A series of four centrifuge tests were co...

Sequence Stratigraphic Framework of the Jurassic Samana Suk Carbonate Formation, North Pakistan: Implications for Reservoir Potential

The paper aims to establish a possible link between the sequence stratigraphy and reservoir potential of the Middle Jurassic carbonates of Samana Suk Formation, Kala Chitta Range, North Pakistan. The Samana Suk Formation is comprised of a monotonous sequence of thin- to thick-bedded bioturbated, cross-bedded, ripple marked, sandy, bioclastic carbonates with shale interbeds. The rock unit is the best analog of shallow to marginal marine carbonates due to its pronounced thickness, enhanced lithological variations, and diverse diagenetic features. To establish a possible link between the sequence stratigraphy and reservoir potential of the rock unit, the outcrop and petrographic features are used to record eight microfacies, deposited in a wide range of shallow to marginal marine environments including mudflats, lagoon, back shoals, and sand shoals. Based on the vertical stacking pattern of microfacies in a given time of deposition (170–160 Ma), one second-order local cycle (SLC-1), three regressive systems tracts (RSTs) and two transgressive systems tracts (TSTs) are delineated within the succession. The primary and secondary porosity of selected microfacies from each systems tracts are investigated using petrography, scanning electron microscopy, and energy-dispersive spectroscopy. The direct measurements of porosity and permeability of these microfacies types are carried out using high overburden pressure plug porosity and permeability analyses. Based on these investigations, higher reservoir potential is recorded for mudstones/wackestone microfacies of RST as compared to grainstone microfacies of TST. The higher porosity within RST and higher interconnectivity of available pores both in RST and in TST suggest that the Samana Suk Formation carries good reservoir potential.

Development of a new deformation-controlled rock bolt: Numerical modelling and laboratory verification

Development of a new deformation-controlled rock bolt: Numerical modelling and laboratory verification

Shaking Table Study on PET Strips-Sand Mixtures Using Laminar Box Modelling

Daily increase in plastic waste amounts is a serious environmental problem and it is among the major challenges worldwide. Reusing this waste material can be therefore an appropriate solution to overcome this problem. Besides, recycling plastic waste as reinforcing material has become a cheap and viable alternative for soil improvement schemes. In the current study, PET plastic waste strips (water bottles) were randomly mixed with sandy soil to improve the soil strength parameters. Due to the lack of comprehensive seismic studies on soils reinforced with PET strips, a series of 1-g shaking table tests was performed to evaluate the dynamic properties of the sand-PET mixtures with different PET contents (0%, 0.5%, 0.75% and 1% by the sand weight) and aspect ratios (1 and 5). Effect of various parameters, including excitation amplitude, PET strip content and PET strip aspect ratio on response of the mixtures were elaborated. It was found that addition of the PET strips to the sand, could reduce the soil brittleness under low overburden pressures. Therefore, at the inclusion ranges used in this study, increase of the PET strips content or aspect ratio, caused an increase in the damping ratio and decrease in the shear modulus values compared to the plain sand model. Opposite trends of PET strips inclusion contribution were reported under the influence of high overburden pressures through carrying out some cyclic large-scale direct shear tests.

Load reduction on high-filled cut-and-cover tunnel using discrete element method

Load reduction on high-filled cut-and-cover tunnel using discrete element method

Backfill mining alternatives and strategies for mitigating shallow coal mining hazards in the western mining area of China

This study addresses the major geo-environmental hazards caused by shallow coal mining in China's western eco-environment frangible area. These hazards are related to the high overburden pressure, surface subsidence, soil and water losses, and land desertification, with consequent vegetation and wildlife losses. To mitigate these hazards, three alternative backfill mining methods are proposed, for three typical shallow coal mining conditions, using aeolian sand-based backfilling materials, which are readily available in this area. The main influencing factor is the backfill material compaction ratio. Its effect on aquiclude deformation and water-conducting fracture evolution are assessed by numerical and physical simulation methods. The potential application of the proposed backfill coal mining alternatives is evaluated and discussed in detail. The results obtained are considered to be valuable for developing a strategy for the coordinated exploitation of coal resources and environmental protection in China's western frangible eco-environment area.