强渗流地层中大直径旋挖钻孔桩施工技术

强渗流地层中大直径旋挖钻孔桩施工技术得到广泛应用,该技术优势显著,可推动钻孔施工的有序进行,保障孔壁的稳定性,解决工程施工中的诸多问题。经长期实践发现,该技术施工效率高、安全性强,可达到较为理想的质量控制效果,因此是一种值得广泛应用的施工方法。

倾斜煤层采空区瓦斯运移规律实验研究

运用自制的倾斜煤层采空区瓦斯流场实验平台进行相似模拟实验,研究倾斜煤层采空区瓦斯流场有、无挡风帘情况下的3区划分,确定强渗流区、渗流区、非渗流区的具体范围,进一步比较分析,确定上、下两巷采空区自然发火的具体范围。

通风对采空区瓦斯流场分布影响的实验

通过理论分析、实验室相似模拟及数值分析相结合的方法,运用自制的采空区流场分布试验台,以烟气做为示踪气体,对采空区流场分布规律进行实验研究。研究得出:采空区流场分布呈梯度分布,将其划分为3区,强渗流区的边界线呈抛物线形状;通风主要对强渗流区产生影响,且该区的瓦斯浓度低于可爆范围;随着工作面长度的增加,通风对回风巷附近采空区瓦斯的影响逐渐降低,因此容易形成瓦斯积聚;随着采空区孔隙率的降低,流场的运动速率降低。该研究结果对进一步研究预防采空区瓦斯爆炸提供了参考。

海域人工岛超深地连墙施工技术研究

结合港珠澳大桥岛隧工程,对在海水连通条件下,以高水头、强渗流、超厚人工填砂层为显著特点的人工岛上施工超深地连墙的一系列关键技术进行比选研究,为以后超厚人工填砂层和高水头情况下施工地连墙提供一些可借鉴的经验。

Stability analysis of shallow tunnels subjected to seepage with strength reduction theory

Based on strength reduction theory,the stability numbers of shallow tunnels were investigated within the framework of upper and lower bound theorems of limit analysis. Stability solutions taking into account of water seepage were presented and compared with those without considering seepage. The comparisons indicate that the maximum difference does not exceed 3.7%,which proves the present method credible. The results show that stability numbers of shallow tunnels considering seepage are much less than those without considering seepage,and that the difference of stability numbers between considering seepage and without considering seepage increase with increasing the depth ratio. The stability numbers decrease with increasing permeability coefficient and groundwater depth. Seepage has significant effects on the stability numbers of shallow tunnels.

Active earth pressure for subgrade retaining walls in cohesive backfills with tensile strength cut-off subjected to seepage effects

The commonly used Mohr-Coulomb(M-C) failure condition has a limitation that it overestimates the tensile strength of cohesive soils. To overcome this limitation, the tensile strength cut-off was applied where the predicted tensile strength is reduced or eliminated. This work then presented a kinematical approach to evaluate the active earth pressure on subgrade retaining walls in cohesive backfills with saturated seepage effects. An effective rotational failure mechanism was constructed assuming an associative flow rule. The impact of seepage forces, whose distribution is described by a closed-form solution, was incorporated into the analysis. The thrust of active earth pressure was derived from the energy conservation equation, and an optimization program was then coded to obtain the most critical solution. Several sets of charts were produced to perform a parameter analysis. The results show that taking soil cohesion into account has a distinct beneficial influence on the stability of retaining walls, while seepage forces have an adverse effect. The active earth pressure increases when tensile strength cut-off is considered, and this increment is more noticeable under larger cohesion.

Simulation of hydraulic fracture utilizing numerical manifold method

A 2nd order numerical manifold method(NMM) based method is developed to simulate the hydraulic fractures propagating process in rock or concrete. The proposed method uses a weak coupling technique to analyze the fluid phase and solid phase. To study the seepage behavior of the fluid phase, all the fractures in solid are identified by a block cutting algorithm and form a flow network. Then the hydraulic heads at crack ends are solved. To study the deformation and destruction of solid phase, the 2-order NMM and sub-region boundary element method are combined to solve the stress-strain field. Crack growth is controlled by the well-accepted criterion, including the tension criterion or Mohr-Coulomb criterion for the initialization of cracks and the maximum circumferential stress theory for crack propagation. Once the crack growth occurs, the seepage and deformation analysis will be resolved in the next simulation step. Such weak coupling analysis will continue until the structure becomes stable or is destructed. Five examples are used to verify the new method. The results demonstrate that the method can solve the SIFs at crack tip and fluid flow in crack network precisely, and the method is effective in simulating the hydraulic facture problem. Besides, the NMM shows great convenience and is of high accuracy in simulating the crack growth problem.

Percolation transport and magnetic transitions in a phase-separated manganite La_(0.55)Ca_(0.45)MnO_3

The structural, electronic and magnetic properties of La0.55Ca0.45MnO3 were measured. A rapid change of lattice parameters appeared around 190 K associated with the az2 orbital ordering and charge ordering （CO） states that were reflected by both magnetization and resistivity. Great difference of magnetizations between the field-cooling （FC） and zero-field-cooling （ZFC） modes below the charge ordering temperature Too in high magnetic field （H〉4 T） was clearly seen. A field of 5 T （threshold field） is sufficient to completely destroy the antiferromagnetic （AFM） CO state for FC mode in magnetization while it is not the case for ZFC mode. A much larger field （larger than 10 T from ZFC resistivity data） is needed to destroy the CO state for ZFC mode. This could be explained by the coexistence and transformation of two phases reported by Huang et al. For ZFC mode, with increasing H, Tco gradually moves to low temperature regime and the relationship between the critical field Hc （0） to destroy CO state and Tco conforms to a power law Hc = Hc（0）（1 - T/Tco（0））^γ, where Hc （0） is the critical field to destroy the CO state at 0 K, and Too （0） is the CO temperature in zero field.