In order to improve the reinforcement effect of microbially induced calcium carbonate precipitation (MICP) technology on sand, the test of MICP-treated sand reinforced by pozzolan was designed and carried out considering the porous structure and activity characteristics of pozzolan. The enhancement effect and enhancement mechanism of pozzolan on the MICP-treated sand were systematically analyzed by integrating macroscopic physical and mechanical tests and microscopic tests. The results showed that: 1) Pozzolan could significantly improve the bacteria fixation rate and cementation material production in the process of sand microbial reinforcement, and the optimal amount of pozzolan content was around 10%, which increased the bacteria fixation rate by 118.28% and the cementation substance production by 29.55% compared with the conventional MICP. 2) The addition of pozzolan greatly improved the compressive strength and resistance to deformation of bio-cemented soil. Under different confining pressures, the compressive strength of the bio-cemented sand increased by 52.26%−62.96%, and the strain at failure increased by 100.00%−112.58%. 3) After the addition of pozzolan, the pore size and void ratio of the bio-cemented sand were decreased obviously, and the overall compactness and impermeability performance were further improved, with the void ratio decreased from 20.12% to 14.17% and the permeability coefficient reduced by an order of magnitude. 4) The enhancement mechanism of pozzolan on MICP-treated sand mainly included three aspects: for one thing, the pozzolan played a good filling effect between the sand particles, which significantly reduced the large pores between the particles and increased the compactness of the sample; for another, the good adsorption of pozzolan effectively increased the content of bacteria in the sample, which increased the production of calcium carbonate and enhanced the uniformity of distribution; on the third hand, the active substances in pozzolan participate in the reaction to generate gelling substances and calcium carbonate crystals to form a composite gel, which could further enhanced the cementation properties and compactness of the bio-cemented sand.
为研究露天煤矿顺倾软岩复合边坡失稳机理,采用3Dmine-Rhino-FLAC3D耦合建模,分析了同时受到采场开挖卸载与排土场堆叠加载双重效应的顺倾软岩复合边坡的稳定性.研究结果表明:顺倾软岩复合边坡随采场开挖和排土场堆叠滑坡类型由推动式转为牵引式,滑坡模式由以第三系黏土层为底界面逐渐过渡到以弱层为底界面的切层-顺层滑动;顺倾软岩复合边坡稳定性系数与采场开挖和排土场堆叠近似呈负相关的线性关系.研究结论可为类似边坡的工程设计、治理及滑坡预测预报提供技术参考.
为探究加速疲劳试验方法在评价沥青砂浆疲劳性能方面的适用性与可行性,对水性环氧乳化沥青砂浆(AC5-WEREA)、改性沥青砂浆(AC5-SBS)和基质沥青砂浆(AC5-70#)在弯拉受力模式下分别进行频率扫描试验、动态力学分析切片试验、线性振幅扫描试验和四点弯曲疲劳试验,并对试验结果进行对比分析.试验结果表明:动态力学分析切片试验、线性振幅扫描试验和四点弯曲疲劳试验确定得到的沥青砂浆疲劳寿命结果变化趋势一致,进一步得到加速疲劳试验方法在评价沥青砂浆疲劳性能方面不仅具有可行性和适用性,而且动态力学分析切片试验所需试件尺寸较小,能有效降低试验结果的变异性.
针对瓦斯突出等级评判方法预测准确度低的问题,提出一种基于拉普拉斯特征映射算法(LE)和改进的乌鸦搜索算法(ICSA)优化核极限学习机(KELM)的瓦斯突出预测模型.利用LE算法对瓦斯突出数据进行非线性降维,消除变量间的相互重叠;引入Tent扰动序列、自适应步长和自适应感知概率改进传统的乌鸦搜索算法(CSA),有效避免算法陷入局部最优,提高算法的收敛性能;采用ICSA算法对KELM的相关参数进行寻优,建立基于LE和ICSA-KELM的瓦斯突出等级评判模型.经过对比试验表明,该模型能够有效提高预测准确率.
为研究土岩二元地层区域下深基坑复合型支护结构的支护效果以及最优桩间距问题,以大连地铁5号线虎滩公园站深基坑工程为研究对象,通过Midas GTS软件建立该基坑的数值模型,对比复合型支护结构与"混凝土排桩+内支撑"支护结构下结构内力与变形和基坑周边深层土位移,讨论复合型支护结构在不同桩间距下支护桩的变形及受力.研究结果表明:复合型支护结构能有效减小灌注桩的水平位移与弯矩;基坑竖向位移随开挖深度的增加而增加,复合型支护结构下基坑竖向位移更为连贯且位移较小;随着桩间距的增大,灌注桩和钢管桩的水平位移并不以固定的比例增大,在桩间距为2.6m时,灌注桩和钢管桩桩身水平位移相对变化量较小、弯矩最小.
