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2 (a) Arctic tundra (Ny-A ˚ lesund), (b) lichen-tundra, (c) moss-tundra, (d) moss tundra is being invaded by macrofungi and angiosperm, (e) lichen and moss communities near glacier showing the invasion of a flowering plant, (f) flowering plant community with a few mosses
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Elastic parameters such as Young’s modulus and Poisson’s ratio are significant to demarcate the damage zone around circular opening of tunnels. In the present study, a three dimensional finite difference numerical code, FLAC3D has been employed to study the effect of elastic parameters (E and v) on the radial displacement along the longitudinal dir...
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Citations
... Currently, hard coal deposits in Poland are already being mined at a depth of 1290 m. Difficult geological and mining conditions as well as the great stresses in the rock mass result in significant deformations of the rocks that surround the workings [3] and also lead to the occurrence of tremors and rock bursts [4][5][6][7][8]. Yielding steel arch support has been utilised in the face of hard coal extraction under difficult conditions for many years both in Poland and globally [9][10][11][12][13][14][15][16][17][18][19][20][21]. ...
Difficult geological and mining conditions as well as great stresses in the rock mass result in significant deformations of the rocks that surround the workings and also lead to the occurrence of tremors and rock bursts. Yielding steel arch support has been utilised in the face of hard coal extraction under difficult conditions for many years, both in Poland and abroad. A significant improvement in maintaining gallery working stability is achieved by increasing the yielding support load capacity and work through bolting; however, the use of rock bolts is often limited due to factors such as weak roof rock, significant rock mass fracturing, water accumulation, etc. This is why research and design efforts continue in order to increase yielding steel arch support resistance to both static and dynamic loads. Currently, the most commonly employed type of yielding steel arch support is a support system with frames constructed from overlapping steel arches coupled by shackles. The yield of the steel frame is accomplished by means of sliding joints constructed from sections of various profiles (e.g. V, TH or U-type), which slip after the friction force is exceeded; this force is primarily dependent on the type of shackles and the torque of the shackle screw nuts.
This article presents the static bench testing results of ŁP10/V36/4/A, ŁP10/V32/4/A and ŁP10/V29/4/A yielding steel arch support systems formed from S480W and S560W steel with increased mechanical properties. The tests were conducted using 2 and 3 shackles in the joint, which made it possible to compare the load capacities, work values and characteristics of various types of support. The following shackle screw torques were used for the tests:
• Md = 500 Nm – for shackles utilised in the support constructed from V32 and V36 sections.
• Md = 400 Nm – for shackles utilised in the support constructed from V29 sections.
The shackle screw torques used during the tests were greater compared to the currently utilised standard shackle screw torques within the range of Md = 350-450 Nm.
Dynamic testing of the sliding joints constructed from V32 section with 2 and 3 shackles was also performed. The SD32/36W shackles utilised during the tests were produced in the reinforced versions and manufactured using S480W steel.
Since comparative testing of a rock bolt-reinforced steel arch support system revealed that the bolts would undergo failure at the point of the support yield, a decision was made to investigate the character of the dynamics of this phenomenon. Consequently, this article also presents unique measurement results for top section acceleration values registered in the joints during the conduction of support tests at full scale.
Filming the yield in the joint using high-speed video and thermal cameras made it possible to register the dynamic characteristics of the joint heating process at the arch contact point as well as the mechanical sparks that accompanied it. Considering that these phenomena have thus far been poorly understood, recognising their significance is of great importance from the perspective of occupational safety under the conditions of an explosive atmosphere, especially in the light of the requirements of the new standard EN ISO 80079-36:2016, harmonised with the ATEX directive.
... Tunnel excavation inevitably leads to the change of the initial stress of surrounding rock (Verma and Singh 2013). Stress releasing contributes to the development of rock fractures and the groundwater conserved in the rock along with sediment will flow into the tunnel, which causes water or mud inrush. ...
Water or mud inrush can not only hamper the normal construction of tunnel, but also cause severe casualties and property losses. Through the cause analysis and statistical theory, a total of 9 predictors based on 3 factors, the engineering geology, hydrogeology and construction, were put forward to control the happening of water or mud inrush. Based on the classification principles of forewarning, 3 alert levels, red, orange and yellow, were established. Using the AHP–TOPSIS evaluation theory, the risk prediction model of water or mud inrush was built based on the classification of disaster forewarning. The model was used in the diversion project of Fujian Long Jin–xi and achieved good effects.
An oversized pit-in-pit (PIP) excavation, which comprised an octagonal pit outside and two cross-shaped pits inside, was excavated in soil-rock mixed strata, Shenzhen, China. There were two shield tunnels connected to the north and south of the PIP excavation after the main structures completed. Extensive instruments were adopted throughout the construction process to guarantee the safety of the project. Based on the massive field data, the performance of the ground settlement, retaining structures and adjacent building deflection were investigated. Field data indicate that the influence zone of ground settlement in depth was above the stiff clay layer. The maximum lateral displacement (δhm) of the retaining structures occurred at 0.4 He (He is the excavation depth), and δhm decreased when the excavation depth was over 0.5 He. The maximum ground settlement δvm occurred at 0.2 He which gradually decreased with d (d is the distance from the monitoring point to the excavation edge). This large discrepancy of the ground settlement induced 3.13‰ tilting of the adjacent buildings. The ground settlement influence zone was 1.7 He away from the pit edge (d ≤ 1.7 He). A half-3D numerical model was established to investigate the influence of different excavation sequences. The results show that the maximum principal stress (σm) of the cover plate increased to peak value due to the excavation of subsoil, which indicated that the sidewall construction and subsoil excavation should be carried out simultaneously to reduce the stress concentration of the cover plate. TD excavation can effectively minimize the ground and building settlement, while the excavation may induce uneven displacement of the interior supporting columns. Push in failure of the sidewalls may occur during the construction which was the combined result of unloading and increase in the excavation depth.
