Drilling Documentation

Drilling is vitally important to support almost all rock excavation projects and blasting operations. Subsurface characterization is very difficult without drilling unless there are already existing rock walls that can be mapped and conditions that can be projected back into the rock mass. Angled drilling may be more effective at locating potential problems in the rock mass.

It is important that all exploratory boreholes be accurately surveyed and completely backfilled, and that all lost tools be carefully documented. The presence and condition of exploratory boreholes will need to be accounted for in the design. Poorly backfilled or open holes can destroy a shot, leading to damages and claims.

While it is seldom possible to completely replace the information from drilling with geophysics, many geophysical tools can be used to extract the maximum amount of information from each borehole. Although it is an older method, gamma-gamma has been used successfully for many years to located shales and clay seams. Newer camera-based methods such as the Optical and Acoustical Televiewer can be of great benefit to the geologist who assesses the site because these methods reveal the true in-situ conditions of the rock. Additionally, these methods can be used to get orientations of structural features encountered in the borehole, replacing the far more cumbersome oriented core methods. Although these methods are likely impractical for use in boreholes intended as part of the blast design, thy can give invaluable site characterization data to the geologist during an exploratory program. Many other methods are available with extensive information available in published literature.

Drilling information will also be gathered during construction as the blasting program is executed. However, the boreholes drilled as the blasting proceeds should be reviewed not only by the blaster, but also by other qualified personnel such as the geologist or engineer assessing the site to determine that site conditions are as expected based on the exploration and the design. This can be particularly crucial in karst conditions where additional voids and cavities are frequently located during blasting even when the site characterization is excellent. The rock-quality designation (RQD) values, the percent recovery and the length of intact core pieces can give the blaster important information about the formation and how to load the blastholes. The blaster should review the core boxes pre-bid to be able to give a realistic blasting price.

Reports and Documents. All information gathered in the site exploration should be used to create a report that explains all of the pertinent data and conclusions based on that data. This data must be included in the Design Documentation Report (DDR) and should be incorporated to the extent possible into the plans and specifications or in attached data provided to the contractor. The particular vehicle used to convey this information to the contractor may vary based on the contracting method. However, as has been discussed in this section, it is vitally important that the blaster understand the geological conditions of the site. Site characterization information that is more interpretive may be more appropriate to include in the Engineering Considerations and Instructions to Field Personnel to provide the Quality Assurance (QA) staff the benefit of the design rationale.

Drilling Logs. The blaster is required to keep a drilling log to be able to identify unusual geologic features such a voids and soft seams in each blasthole. This is essential so that the blaster can properly load the holes. The blaster must be required to use the drilling log to prevent overloading weak areas ,which can result in blow outs, violence, flyrock, excessive air overpressure and overbreak in the final walls. The drilling log should be compared to the blasthole loading diagrams to be sure that the blaster is properly loading the blastholes.

Congratulations, you have completed the knowledge section of the course.

You may now complete the course by successfully passing the course quiz.