High Overburden Research Articles

Utilisation of waste rock backfill materials in deep gobs for mitigating mining-induced water inrush risks: compression deformation and seepage characteristics

ABSTRACT In deep backfilling coal mines, granular waste rocks face complex stress and water environments after being backfilled in the goaf. To characterize the compression deformation and seepage of granular waste rock backfill materials in the deep goaf, a fluid-structure interaction (FSI) test system for granular waste rocks was developed. Influences of overburden stress on deformation and seepage characteristics of granular waste rocks were investigated. The research shows that the high overburden stress in deep underground coal mines can continuously change the structure of granular waste rocks. In the process of increasing overburden stress from 15 to 22.5 MPa, the porosity of granular waste rocks decreases rapidly and the permeability reduces fast accordingly. After the axial pressure exceeds 22.5 MPa, the porosity and permeability of granular waste rocks both tend to be stable. In the seepage process of confined groundwater under single overburden stress, the increase in water pressure can improve the porosity and permeability of granular waste rocks. Small waste rocks in samples play the leading role, they can achieve a waterproof state under relatively low overburden stress. The backfilling method that combines large and small particles can be considered, which can achieve rapid water proofing at a low cost.

Stability Challenges and Remedial Practices in Himalayan Hydro-power Tunnels – A Review

The instability in tunnels is mainly affected by geological anomalies, rock mass quality, complex geological structures, active tectonics, and stress anisotropy. This review article presents challenges associated with stability and applied remedial measures prevailing in hydropower tunnels in the Himalayas. The review covers nine hydropower tunnels located in different parts of the Himalayas. The review found that rock bursting/spalling frequently occurs when the tunnel passes through a high overburden with good rock mass quality. On the other hand, plastic deformation (squeezing) occurs when a tunnel passes through the weak and schistose rock mass. It has been found through the review that the tunnel crew was able to successfully solve instability challenges. Effective planning, design, and selection of appropriate construction techniques help to complete tunneling projects in the Himalayas.

Study on significance of pillar dimensions on stability of caverns in rocks with high overburden

Study on significance of pillar dimensions on stability of caverns in rocks with high overburden

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.

Rock engineering evaluation of existing and planned Salang Tunnels with high overburden through Hindukush Mountains, Afghanistan

The Kabul – Mazar Highway connects Kabul, the capital of Afghanistan, to northern provinces of the country, and further extends into Central Asian countries through the Hindukush mountains. The Salang Tunnel, which is 2600 m long, was designed by Soviet engineers in 1958 and constructed using conventional techniques in 1964. During its construction, the tunnel ranked the distinction of being the highest-altitude tunnel at 3400 m. The socioeconomic importance of the tunnel is exceptionally high, as the Hindukush Mountain range to the east and south of the country is crossed by it. Since 1964, there has been a significant increase in traffic volume. Due to the narrowness of the existing tunnel, the Ministry of Public Works (MOPW) of Afghanistan has planned the construction of new twin-tube tunnels. Although there have been rehabilitation and enlargement efforts for the existing tunnel, none of these renovation works have been proven effective, and challenges persist. In 2008, the MOPW initiated a pre-feasibility study for new tunnels, which was finalized in 2012, presenting various options. Subsequently, in early 2018, the MOPW commenced feasibility and detailed studies, leading to the proposal of new twin-tube tunnels, which are designated as the planned tunnels in this paper. In this study, the available geotechnical and environmental data are used to evaluate the rock engineering aspects of the tunnels, including an assessment of the in-situ stress state. A particular emphasis is placed on the reassessment and design of the support system for both the existing and planned tunnels according to RMQR and another system, respectively. The evaluation of the response and stability of the tunnels is concluded, and the implications are subsequently discussed.

Enhancing the performance of open geothermal tunnelwater systems by heat absorbers

Enhancing the performance of open geothermal tunnelwater systems by heat absorbers

Evaluation of Consolidation Degree from CPTu using Rahardjo (2016) Method – Case Study of Consolidating Soil in East Kalimantan

A geotechnical investigation comprised 13 CPTu and 23 dissipation testing were performed on a site in East Kalimantan due to landslide triggered by 15 to 30m thick soft clay underlying 75m high overburden embankment. The investigation covers an area of about 250m x 275m wide on the area next to the toe of the embankment. From geological map, the site situated at borders of Balikpapan Formation (Tmbp) and Kampung Baru Formation (Tpkb) with Alluvium (Qa) formation from Heliosen period nearby. Measurement from penetration showed high pore-water pressure higher than the hydrostatic pressure. Result from dissipation testing showed that the soft clay is still consolidating with residual excess pore pressure (uf) still exist. Rahardjo (2016) Method was developed using CPTu data as its basis especially soft clay data to determine overconsolidation ratio (OCR). However, it can also be used to determine the degree of consolidation. The method uses Pore Pressure Ratio (Bq) value, excess pore pressure divided by net cone resistance – Bq = Δu/(qt – σv0), which was obtained when performing CPTu test. The formula proposed was 1/(1.2Bq+0.1). The method stated that the value of Bq=0.75 equals to OCR=1 which is showing a normally consolidated clay. Bq value higher than 0.75 will show a degree of consolidation of a consolidating soil and for Bq value lower than 0.75 will show an OCR value of overconsolidated soil. Applying Rahardjo (2016) Method to the dissipation data performed showed an agreement on soft clay where the soil is still consolidating. However, when applied to over consolidated soil near surface this method will show a greater OCR value.

Enhancing Chuo Shinkansen tunnelling with high overburden: addressing geological and groundwater conditions

Enhancing Chuo Shinkansen tunnelling with high overburden: addressing geological and groundwater conditions

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

Numerical Modeling of Tunnel Support System in Himalayan Rock Masses for Seismic Resilience

This study uses numerical modeling in combination with rock mass classification approaches to develop tunnel support systems that are safe from earthquakes, ultimately contributing to the seismic resilience of the important infrastructure. A case study of tunnel in Himalayan region of Nepal has been considered for seismic assessment of tunnel supports in different geological conditions. For better quality rock masses (GSI>30), strain-softening model was used, and for weaker rock masses (GSI<30), elastic-perfectly-plastic model was used. To ensure safety in the case of extremely poor rock mass, shotcrete thickness had to be increased by 100 mm over that recommended by empirical methods. In both models, shotcrete in the sections with high overburden showed a significant decrease in FOS. Even though this type of unusual finding has also been reported in the Melamchi water supply tunnel after 2015 Gorkha Earthquake, no further studies to investigate the influencing factors have been done. While this condition occurred in the model used in this study because of the application of higher in-situ stress for sections with a larger depth of overburden, the actual reason for the occurrence of this situation as a result of an earthquake remains unexplained. Future research should take into account the effects of discontinuities, epicentral distance, aftershocks, and the incorporation of actual stress measurements from the field for numerical modeling.

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

The Floor Heave Mechanism and Control Technology of Gob-Side Entry Retaining of Soft Rock Floor

Extensive soft-rock floor heave in gob-side entry retaining considerably restricts the efficient and sustainable production of the mine. The mechanical capacities of roadway roof and floor strata are discussed through laboratory tests by taking the N2301 fully caving surface auxiliary transport gate road of the Ancient City Coal Mine in the Lu’an Mining Area of Shanxi Province as an engineering background. The stress distribution law of gob-side entry in mining the working surface was explored based on numerical simulation. After that, the mechanical mechanism of floor heave was studied through theoretical analysis. High lead abutment pressure and horizontal stress were superimposed in front of the working surface to cause soft-rock floor heave. The bulk weight of the high overburden was unevenly transmitted to the two sides because of the roof cantilever structure of entry retaining in the rear of the working face. The roadway floor produced an asymmetric sliding force, which caused the occurrence of floor heave. The control technology of floor heave combining the pressure relief of floor blasting and roof cutting was proposed taking account of the mechanism of floor heave. Then, the stress environment of the surrounding rock was improved by the deep hole blasting of the floor. Gob-side roof cutting was used to reduce impact of the bulk weight of the overburden on the surrounding rock deformation of the roadway. A test was conducted after verifying the control effect of blasting pressure relief on roadway floor heave through a similar simulation. Field tests indicated that the maximum floor heave was 168 mm at 250 m in the rear of the working surface, and floor heave was controlled. This study offers a more scientifically sound theoretical reference for controlling floor heave in gob-side entry retaining, which can significantly advance the sustainable development of gob-side entry retaining technology in coal mining.

Forecasting and controlling two main failure mechanisms in the Middle East’s longest highway tunnel

Forecasting and controlling two main failure mechanisms in the Middle East’s longest highway tunnel

Assessment of state-of-practice use of field liquefaction charts at low and high overburden using centrifuge experiments

Assessment of state-of-practice use of field liquefaction charts at low and high overburden using centrifuge experiments

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.

Evaluation of field sand liquefaction including partial drainage under low and high overburden using a generalized bounding surface model

Evaluation of field sand liquefaction including partial drainage under low and high overburden using a generalized bounding surface model

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...