盾构掘进过程中孤石爆破预处理爆破块度效应及其影响机理研究

Spherical weathering body is one of normal bad geological phenomena in the developed granite area of southeast coastal areas of China. Serious problems of frequently-changing cutter and clipped cutter head will be occurred due to easily-damaged cutter head and cutter body, while shield tunnel pass through the stratum with spherical weathering body in urban subway construction. In order to solve the above problems and ensure the shield tunnel can successfully pass through the bad stratum, the method of blasting deep hole on ground surface is commonly adopted for pre-crushing the stratum, making the crushed rock fragmentation meet the requirement of minimum fragmentation size for outlet. At present, the index of blasting fragmentation for blasting deep hole with overlaid ground is mainly determined by empirical method at home and abroad, lacking the systematic and in-depth study. This project will be carried out by theoretical analysis, model tests and numerical simulation. The law of fractal feature of fragmentation influenced by overlaid ground with different characteristics will be analyzed, and internal essence of the effect of the overlaid ground on fragmentation will revealed. On this basis, crossing model tests will be carried out to study the effect of explosive consumption on fragmentation size and amplification effect of overlaid stratum on explosive consumption will be investigated. Then, the prediction model of fragmentation size and the quantitative evaluation index of amplification effect will be established. The calculation model of explosive charge will be built for satisfy special requirement of the blasting fragmentation, and the influence mechanism of blast fragmentation size on that will be revealed. Finally, the influence model of blasting fragmentation size under multiple factors will derived after theoretical and testing results will be summarized. For special case, filed tests will be conducted to verify the research results. Through this study, the theoretical basis for controlling blasting fragmentation size to pretreat boulders during shield tunneling can be provided.

球状风化是我国东南沿海花岗岩发育区常见的一种不良地质现象。当城市地铁盾构隧道穿越隐伏球状风化体地层时，面临刀盘、刀具磨损严重而频繁换刀及卡刀盘等难题，为此常采取地表钻孔爆破方法进行预破碎，使其块度满足出渣最小尺寸要求，以确保盾构顺利掘进。目前国内外对上覆岩土条件下钻孔预爆破的破碎块度指标主要依据经验法，尚缺乏系统深入的理论研究。本项目采用理论分析、室内模型试验和数值模拟方法，分析上覆不同介质特性对爆破块度分形特征的影响规律，构建孤石爆破破碎损伤模型，揭示不同特性介质影响爆破块度的内在本质；通过研究炸药单耗对岩石块度的控制作用以及上覆介质对炸药单耗的放大效应，建立爆破块度预测模型并提出放大效应的定量评价指标，构建满足特定块度指标的炸药单耗计算模型和方法，揭示盾构掘进中孤石爆破预处理爆破块度影响机理，并针对具体工程开展试验验证，为盾构掘进中孤石预处理爆破块度控制提供理论依据。

球状风化体是我国花岗岩发育区常见的一种不良地质现象，为降低其对盾构掘进的不利影响，常采用地表钻孔爆破的方法对其进行预处理，使其平均块度满足盾构机出渣系统的尺寸要求。但目前国内外球状风化体爆破预处理的参数凭借经验确定，缺乏相关机理研究。课题采用理论分析、模型试验和数值模拟分析方法，构建了80MPa和100MPa孤石在0~10.5m埋深时，炸药单耗和上覆层厚度与平均块度的影响关系，得出炸药单耗与平均块度呈反比关系而上覆层厚度与平均块度为正比关系。基于此，推导出满足特殊块度要求时的炸药单耗和上覆层厚度关系，修正了实体工程中的孤石爆破处理预设计，并通过钻孔取芯和盾构机掘进参数验证了修正设计的应用效果。与此同时，利用分形理论、基于块度筛分实验、引入分形维数对爆破后的块度分布进行了研究，得出上覆层厚度为定值时，炸药单耗和分维数基本呈线性递增关系，而炸药单耗为定值时，分形维数与上覆层厚度近似为线性递减关系，且在炸药单耗和上覆层厚度相同的条件下，低强度孤石爆破后的分形维数一般大于高强度孤石爆破后的分形维数。另外，当上覆层厚度超过孤石尺寸的6.7倍时，上覆层厚度对平均块度的影响超过炸药单耗对平均块度的影响，此时为降低爆破后的平均块度而仅仅增加炸药单耗是不科学和不经济的，因此课题从爆源角度进行了研究，开展了3种不同炸药材料与不同强度岩石的匹配性实验，基于爆破后的块度筛分实验并采用K50、K80和大块率为评价指标，分析了3种不同炸药材料与不同强度岩石爆破后的块度分布关系，得出了炸药与岩石波阻抗最佳匹配值范围为2.53~3.30。. 课题的研究成果为一定埋深下不同强度孤石爆破时的炸药单耗计算提供了科学依据，结束了依据经验确定炸药单耗的现状，揭示了孤石爆破的块度分布规律和影响机理，为交通运输、城市轨道和深埋矿山等领域的近似研究提供了重要的参考价值和良好的应用前景。