Calculation method of first collapse span with superhigh water material backfill mining
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Lateral earth pressure
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Snow drifts are frequently observed at roof steps, that is, at the common wall between two nominally flat roof surfaces at different elevations. When wind blows from the lower roof towards the upper roof, some of the snow on the lower roof is transported towards and settles at the roof step, resulting in a windward roof step drift on the lower-level roof. When wind blows from the upper roof towards the lower roof, some of the snow on the upper roof settles on the lower roof adjacent to the roof step, resulting in a leeward roof step drift on the lower roof. Current building code provisions relate the size of these drifts to the size of the snow source area (i.e., upper-roof length for leeward drifts). In the 1998 version of the ASCE 7 Load Standard, provisions for windward roof step drifts were changed. These changes result in somewhat higher loadings compared to previous versions of the ASCE 7 Standard. Herein, we attempt to justify these new provisions for windward drifts by reviewing the research upon which the previous provisions were based and by analyzing a group of new windward roof step case histories.
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The mechanical model of the basic roof fracture structure is established on the basis of key block theory to study the roof breaking mechanism of gob‐side entry retaining under roof cutting and pressure relief, and the analytical formula of roof support resistance is derived when the key block of the basic roof is stable. The influence of roof cutting angle and cutting height on roof support resistance is also analyzed. Determining the cutting seam parameters of the retained roadway roof is necessary to identify the support resistance of the roadway roof due to the correlation between the roof cutting parameters and the support resistance. Taking the II 632 haulage drift of the Hengyuan coal mine as the engineering background, FLAC3D numerical simulation is used in this paper to analyze the influence of different roof cutting angles and cutting heights on the surrounding rock structure evolution of retained roadways. Results show that the roof cutting angle and cutting height respond to the support resistance of the retained roadway roof, and the support resistance required by the roof increases with the roof cutting angle and cutting height. This condition ensures that the side roof of the gob can be cut off smoothly, and the support resistance required by the roof of retained roadways is within a reasonable range. Through theoretical and numerical simulation analysis, the reasonable roof cutting height of II 632 haulage drift is 8 m and the roof cutting angle is 15°. The theoretical analysis and numerical simulation results reveal that the required support resistance to maintain the stability of the roadway roof is 0.38 MPa. The supporting scheme of the roof of the II 632 haulage drift in the Hengyuan coal mine is then designed. Finally, the field industrial test is used for verification. The borehole imaging results show that the overall line of the retained roadway roof is small based on the description of field monitoring results. The deformation of the surrounding rock surface of the retained roadway is less than 100 mm, and the roadway is 40 m from the lagging working face. The deformation rate of surrounding rock decreases with the increase in distance from the working face. The integrity of the retained roadway roof is good, and the deformation of the surrounding rock is effectively controlled.
Haulage
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This paper draws on borehole core data,offers estimates of sandstones occurring within 30 m from roof in the Luling coal mine No.10 seams and immediate roof thickness,and analyzes coal roof lithology and structural types according to hard rock percentage and immediate roof thickness / shear height ratio(Km).The result shows that the coal roof lithology of No.10 can be divided into three kinds of hard,medium and soft rock masses,accounting for about 50%,35%,15% of the mining area respectively;the coal roof structural types are divided into four kinds,such as the main roof cover type,the false roof and main roof,the immediate roof and main roof type and the false roof and immediate roofs;the engineering geological type of the roof are divided into three kinds: no periodic weighting roof,periodic weighting roof and strong periodic weighting roof,accounting for about 49%,50%,and 1% of the mining area respectively.The coal mine is blessed with a better geological condition and the study serves as a basis for developing layout methods and selecting roof supporting patterns for working faces.
Lithology
Coal measures
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Lateral earth pressure
Moment distribution method
Shear force
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Lateral soil movements due to deep excavation works for substructure construction may induce excessive bending and lateral deflection on existing pile foundations in the vicinity. As field data on such cases are almost impossible to collect, a series of centrifuge model tests has been performed to investigate the pile responses due to excavation-induced soil movements on piles in sand with various relative densities. The test results are presented in terms of bending moment and pile deflection profiles. Comparison of maximum bending moment and pile head deflection for different tests are reported. The practical implications of the findings are also discussed in this paper.
Centrifuge
Substructure
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In the present study, a new method for designing the cantilever sheet pile wall having a strip load present on the backfill is proposed in cohesionless soil. The method uses the limit-equilibrium approach by establishing the partial mobilized earth pressure diagram in static and seismic conditions. The partial mobilization of earth pressure has been taken as a function of amount and type of wall movement and associated mobilized soil–wall friction angles. Analytical expressions are derived for the cantilever sheet pile wall to determine the earth pressure, shear force, and bending moment. It is observed that the earth pressure diagram of cantilever sheet pile walls varies with the displacement at the dredge level. Furthermore, the shifting of strip load of magnitude 20 kPa away from the cantilever sheet pile walls reduces the maximum bending moment by 10% when the width of the strip load is 1.6 m. A parametric study is carried out and presented in the nondimensionalized form of bending moment, penetration depth, and location of the pivot point. The results of the present study are compared with the existing conventional solutions available in the literature.
Lateral earth pressure
Shear force
Structural load
Seismic loading
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The 277W Building high bay roof area was load tested according to the approved load-test procedure, WHC-SD-GN-TP-30015, Revision 1. The 277W Building is located in the 200 West Area of the Hanford Site and has the following characteristics: roof deck -- wood decking supported by 4 x 14 timber purlins; roof membrane -- tar and gravel; roof slope -- flat (<10 deg); and roof elevation -- maximum height of about 63 ft. The 227W Building was visited in March 1994 for a visual inspection. During this inspection, cracked areas were visible in the decking, but it was not possible to determine whether these cracks extended completely through the decking, which is 2-in. thick. The building was revisited in March 1994 for the purpose of writing this test report. Because the roof requires personnel access, a test was determined to be the best way to qualify the roof. The conclusions are that the roof has been qualified for 500-lb total roof load and that the ``No Roof Access`` signs can be changed to ``Roof Access Restricted`` signs.
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Domed roof is the composite structure that consists of roof plates that are made from thin steel plate and roof frames that are made from shaped steel. There is possibility that external pressure is loaded to domed roof under construction and at the abnormal operation. Therefore roof shall be designed to have enough strength for external load. This paper shows establishment of analysis method for domed roofbuckling and application of this analysis method to the actual tank.
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The 3701U Building roof area was load tested according to the approved load-test procedure. The 3701U Building is located in the 300 Area of the Hanford Site and has the following characteristics: Roof deck--metal decking supported by steel purlins; Roof membrane--tar and gravel; Roof slope--flat (<10 deg); and Roof elevation--height of about 12.5 ft. The 3701U Building was visited in August 1992 for a visual inspection, but because of insulation an inspection could not be performed. The building was revisited in March 1994 for the purpose of writing this test report. Because the roof could not be inspected, a test was determined to be the best way to qualify the roof for personnel access. The test procedure called for the use of a remotely-controlled robot. The conclusions are that the roof has been qualified for 500-lb total roof load and that the ``No Roof Access`` signs can be changed to ``Roof Access Restricted`` signs.
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