Overbreak and underbreak in underground openings Part 2: causes and implications

Summary The newly developed light sectioning method has been used to investigate some of the causes and costs of overbreak and underbreak. Investigations at the Aquamilpa Hydroelectric Project in Mexico have shown decreased overbreak and increased underbreak as a result of increased rock quality and decreased explosive energy. A new measure of explosive energy, the perimeter powder factor (PPF), has been defined and shown to be useful in the context of tunnel-wall rock damage. Tentative results indicate that explosive energy (PPF) may be a more important factor in producing underbreak, whereas rock quality may be a greater factor in producing overbreak. A site-specific equation is given for predicting overbreak or underbreak as a function of rock quality and explosive energy, with an evaluation of the cost of underbreak and overbreak.     

利用CAD次开发程序计算超欠挖的研究

应用CAD平台进行二次开发,研究了超欠挖的计算方法,发现利用CAD平台计算超欠挖可实现计算过程自动化、可视化,并介绍了其工作原理、软件组成部分。结果表明,CAD二次开发程序能很好地计算隧道超欠挖。     

高精度扫描仪在地铁隧道施工中的应用

以北京地铁7号线为例,介绍了在复杂地质环境中,运用三维激光扫描技术对隧道开挖的现状进行测量,确定隧道的超欠挖情况,并监控隧道施工的风险,以防发生隧道塌方事故等的一种新方法,可广泛用于地铁及其他行业的隧道断面测量等相关施工工程中。     

光面爆破在邛崃宝珠山电站引水隧洞工程中的应用体会

介绍在邛崃宝珠山电站隧洞掘进中，采用光面爆破的一些技术措施和组织保证措施，以及所取得的经济效益。     

Overbreak and underbreak in underground openings Part 1: measurement using the light sectioning method and digital image processing

Summary Quick, simple, reliable, and inexpensive measurements of overbreak and underbreak are needed for proper evaluation of tunnelling by the drill and blast method. Problems causing rock damage can be identified and remedied while the work is still in progress. The measurements are also useful in identifying causes of overbreak and overbreak, and in helping to settle contractual disputes relating to payment for replacement concrete and secondary blasting of tights (zones of underbreak). A newly developed method to measure underbreak and overbreak is presented here. The light sectioning method (LSM) uses a radial sheet of light to define the tunnel profile. An image of the final tunnel profile is acquired and digitized, using digital image analysis. This profile is superimposed over the design profile, and from this zones of overbreak and underbreak are identified, quantified, and presented graphically.