tailieunhanh - Systematic Drilling and Blasting for Surface Excavations Part 10

Tham khảo tài liệu 'systematic drilling and blasting for surface excavations part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | EM 1110-2-3800 1 Mar 72 Table 6-2. Clayey Fillings Occurring Along Rock Joints Mineral or Mineral Mixture Host Rock Remolded clay Same minerals as in host Kaolinite Shale Highly weathered rocks hydro-thermally altered rock Montmorillonite Chlorite Sericite Vermiculite Tuff shale Tuff andesite and chlorite schist Hydrothermally altered rocks Note Where one or more of the listed host rocks has in the geologically recent past overlain the rocks at the project site the clayey fillings may have been washed downward along fractures into the new host. an excavation slope should be a factor along with geological factors considered in designing or modifying a blasting technique. The change should of necessity be made at an early stage of construction. 1 Orientation in Various Geological Settings. a Idealized systems of fractures may sometimes be predicted for the more common geological settings expected on construction jobs. The simplest is an orthogonal system that can be expected in flat-lying sedimentary strata. This system consists of horizontal joints parallel to the bedding and one or two sets of vertical joints. b The free face may be carried parallel rather than perpendicular to major vertical joints. Not only are large fractures already developed in the major direction but it can also be expected to be a potentially weak direction in which additional blast fracturing will take place see e below . c Where this orientation is included in the design of the excavation as a final surface overbreakage often may be minimized and the slope should be more stable. Conceivably a through-going natural joint surface might be substituted for a presplit surface. d A favorably oriented system of prominent fractures that can be worked into construction design is not necessarily a panacea. It can be detrimental if not properly evaluated. For example excessive charges can lead to excessive gas migration along these fractures and 6-8 EM 1110-2-3800 1 Mar 72 movement of a long block of