药芯焊丝填充稳定性影响因素分析

以JL-YJQ5011药芯焊丝为例,对药芯焊丝填充稳定性影响因素进行分析。结果表明,药粉中金红石60目通过率100%,200目通过率≤15%,锰硅合金60目通过率100%,200目通过率≤40%,还原钛铁60目通过率100%,200目通过率≤20%,锆英砂80目通过率100%时,药粉的填充稳定性最好;金红石烘干到900℃左右,还原钛铁烘干到300℃左右,锰硅合金烘干到400℃左右,锆英砂烘干到800℃左右时,药粉的流动性最好;采用4连辊模拉拔,成90°交叉布置,4道次药粉受力方向成90°,双向变形,可以改善药粉流动性,解决药粉填充稳定性问题。

Stability analyses of vertically exposed cemented backfill:A revisit to Mitchell's physical model tests

Mitchell's solution is commonly used to determine the required strength of vertically exposed cemented backfill in mines. Developed for drained backfill, Mitchell model assumed a zero friction angle for the backfill. Physical model tests were performed. Good agreements were obtained between the required strengths predicted by the analytical solution and experimental results. However, it is well-known that zero friction angle can only be possible in terms of total stresses when geomaterials are submitted to unconsolidated and undrained conditions. A revisit to Mitchell's physical model tests reveals that both the laboratory tests performed for obtaining the shear strength parameters of the cemented backfill and the box stability tests were conducted under a condition close to undrained condition. This explains well the good agreement between Mitchell's solution and experimental results. Good agreements are equally obtained between Mitchell's experimental results and FLAC3 D numerical modeling of shortterm stability analyses of exposed cemented backfill.

Stability study on naturally filling body in gob-side entry retaining

In the construction of the filling gob-side entry retaining in a lane, we utilize the self-slide natural phenomenon of a falling gangue in an inclined coal seam goaf. First, we put the falling gangue of goal above the laneway and made it the main filling material by adopting the measurement of flexible supporting system combined with those of rigid supporting system. Then we made the filling material gunited and solidified to maintain the filling goal of the gob-side entry retaining beside the lane. Considering the law of energy conservation and law of pressure distribution for retaining the active and Static soil of the wall, we analyzed the reliability of a gangue blocking facilities and the stability of the filling mate- rial in the lane. We analyze the figures to see the stability. The result shows that the gangue block sup- porting system is reliable, and has been successfully practically applied.

Mechanics criterion and factors affecting overburden stability in solid dense filling mining

The effect of controlling strata movement in solid filling mining depends on the filling rate of the goal. However, the mechanical property of the overburden in the backfill stope and the designed size of the backfill mining workface should also be considered. In this study, we established a main roof strata model with loads in accordance with the theory of key strata to investigate the stability of the overburden in solid dense filling mining. We analyzed the stress distribution law of the main roof strata based on elastic thin plate theory. The results show that the position of the long side midpoint of the main roof strata failed more easily because of tensile yield, indicating that this position is the area where failure is likely to occur more easily. We also deduced the stability mechanics criterion of the main roof strata based on tensile yield criterion. The factors affecting the stability of the overburden in solid dense filling mining were also analyzed, including the thickness and elasticity modulus of the main roof strata, overlying strata loads, advanced distance and length of workface, and elastic foundation coefficient of backfill body. The research achievements can provide an important theoretical basis for determining the designed size of the solid dense filling mining workface.

Position-optimization on retained entry and backfilling wall in gob-side entry retaining techniques

This study investigates the stability problem of gob-side entry retaining （GER） and backfilling wall which located under the key block B. Based on the combined research of elastic-plastic mechanics, structure mechanics and modern theory of mining-induced pressure, the caving characteristic and roof structure over the GER were analyzed, and the vertical force and the torque on retained entry roof were also derived as the position for the retained entry varies. On the basis of the specific geology in Huainan mining area, the results indicate that a relatively more stable position for retained entry neighbors the hinge point of block A and B, and it also located at a scope ranging from this point to the one-third length of block B in horizontal direction. As to appropriate position for backfilling wall, this study recommends partial- road-in backfilling method for GER. Field trial conducted at panel face 12418 of Xieqiao Mine demonstrates that the recommended width for original entry is 3.6 m and the preferred width proportion between original retained entry and original entry is 75 % or so whereas the avoidable one is 88 % or so. These findings provide qualitative references to the mines which share similar geology as what Huainan mining area characterized.

Extraction of locked-up coal by strengthening of rib pillars with FRP--A comparative study through numerical modelling

In some of the coalfields in India, coal seams are only developed but no extraction of pillars is possible due to the presence of surface or sub-surface structures and also non-availability of stowing materials which leads to huge amounts of coal being locked-up underground. Spontaneous heating and fire, accumulation of poisonous gases, severe stability issues leading to unsafe workings and environmental hazards are the major problems associated with the developed coal pillars. So, there is a pressing need for a technology for the mining industry to extract the huge amount of coal locked-up under different constraints. In this study, the locked-up coal is proposed to be extracted by artificially strengthening the rib pillars. The detailed comparative study is carried out to know the increase of extraction percentage of locked-up coal by strengthening the rib pillars with FRP. Extraction methodology is designed and studied through numerical modelling for its stability analysis to evaluate its suitability of application in underground.

Influence of filling velocity on stability of subgrade with marine soft soil

Filling velocity and thickness of soft layer are major factors affecting subgrade stability according to an example study by means of finite element stress method(FESM). A case is studied and shows that the subgrade was slided because of excessive filling velocity. To determine a reasonable filling velocity is a key problem to a subgrade with marine soft soil.