What are the best practices for drilling boreholes during a geological site investigation?

1 Choose the right drilling method

There are different types of drilling methods that can be used for borehole drilling, such as rotary, percussion, auger, sonic, and jetting. Each method has its own advantages and disadvantages, depending on the site conditions, the depth and diameter of the boreholes, the type and quantity of samples required, and the budget and time constraints. Therefore, you should select the most suitable drilling method for your GSI based on a careful evaluation of these factors. For example, rotary drilling is effective for hard and consolidated formations, but it can be expensive and time-consuming. Percussion drilling is fast and cheap, but it can cause disturbance and contamination of the samples. Auger drilling is simple and clean, but it can only reach shallow depths and soft soils. Sonic drilling is versatile and efficient, but it can generate noise and vibration. Jetting drilling is useful for underwater or loose soils, but it can wash away the fines and alter the natural moisture content.

2 Follow the drilling standards and guidelines

Drilling boreholes is not a random or arbitrary activity. It requires adherence to certain standards and guidelines that specify the procedures, equipment, quality control, and documentation of the drilling process. These standards and guidelines are established by various organizations, such as the American Society for Testing and Materials (ASTM), the International Society for Rock Mechanics (ISRM), the International Association of Engineering Geology and the Environment (IAEG), and the National Ground Water Association (NGWA). You should familiarize yourself with the relevant standards and guidelines for your GSI and follow them strictly to ensure the accuracy and consistency of the borehole drilling. For example, you should follow the ASTM standards for borehole spacing, diameter, depth, inclination, casing, grouting, and sealing. You should also follow the ISRM guidelines for borehole logging, sampling, testing, and reporting.

3 Use the appropriate drilling equipment and personnel

The quality and efficiency of borehole drilling depend largely on the equipment and personnel involved in the operation. You should use the appropriate drilling equipment and personnel for your GSI based on the drilling method, the site conditions, the project objectives, and the safety requirements. You should choose the drilling equipment that can handle the expected geology, depth, diameter, and inclination of the boreholes, as well as the sampling and testing devices that can collect and analyze the required data. You should also hire qualified and experienced drilling personnel who can operate the equipment safely and correctly, follow the drilling standards and guidelines, and troubleshoot any problems that may arise during the drilling. You should check the credentials, references, and reputation of the drilling equipment and personnel before hiring them, and monitor their performance and progress throughout the drilling.

4 Minimize the environmental and social impacts of drilling

Drilling boreholes can have some environmental and social impacts that should be minimized as much as possible. These impacts can include noise, dust, vibration, water consumption, waste generation, land disturbance, vegetation damage, wildlife disturbance, traffic disruption, and community annoyance. You should assess the potential environmental and social impacts of your borehole drilling program and implement measures to reduce them to acceptable levels. For example, you should use low-noise and low-emission drilling equipment, install noise barriers and dust suppression systems, limit the drilling hours and frequency, recycle and dispose of the drilling fluids and cuttings properly, restore the land and vegetation after drilling, and communicate with the stakeholders and the public about the purpose and benefits of the drilling.

5 Review and interpret the drilling data carefully

The final and most important step of borehole drilling is to review and interpret the data obtained from the drilling process. The drilling data can include the borehole logs, the soil and rock samples, the in-situ tests, and the laboratory tests. These data can provide information about the stratigraphy, lithology, geotechnical properties, groundwater conditions, and geohazards of the subsurface. You should review and interpret the drilling data carefully and critically, using appropriate methods and tools, such as geostatistics, geospatial analysis, and geotechnical software. You should also cross-check and validate the drilling data with other sources of information, such as geophysical surveys, geological maps, and historical records. You should use the drilling data to develop a conceptual model of the subsurface conditions and to design and optimize your construction project accordingly.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?