How To Read Borehole Logs | What You Need to Know To Correctly Interpret Soil Data

Summary

This video explains how to read borehole logs, using an example to guide viewers through key sections such as drilling, sampling, and geological descriptions. It covers general information like client details and project location, and focuses on symbols, soil classifications, moisture levels, and density. The video also highlights the importance of ground water level readings and the significance of soil tests like Standard Penetration Test (SPT) and undisturbed sample collection. The presenter emphasizes the relevance of these logs in engineering and site investigations, encouraging viewers to explore other related topics.

Takeaways

• 📝 Borehole logs provide essential details about the site, including the client, project location, and drilling date.
• 🛠️ The type of drilling method used is indicated in the logs. For example, 'AD' refers to auger drilling and 'T' stands for a TC bit.
• 💧 Groundwater levels, if present, are recorded in the logs, and specific symbols represent water depth.
• 🌍 Depth information is given for each geological unit, starting from the surface, with soil classification symbols like 'M' for silt and 'C' for clay.
• 💦 The moisture content of the soil is identified, where 'M' stands for moist, 'D' for dry, and 'W' for wet.
• 🔍 Soil density is described using terms like 'firm', 'stiff', or 'very loose,' which can indicate the suitability for foundation purposes.
• 📊 Borehole logs also include data on where samples were collected and if the material is natural or fill.
• 🔨 The Standard Penetration Test (SPT) results are provided, showing the number of blows required to penetrate the soil, indicating its strength.
• 🧪 'U50' indicates that an undisturbed sample with a 50mm diameter was collected, which is crucial for accurate soil testing.
• 📏 Pocket penetrometer values are also recorded in the logs, offering additional insight into soil strength.

Q & A

What is the general information provided at the top of the borehole log?

The general information at the top of the borehole log includes details such as the name of the client, the project, the location, the drill rig position, the depth of the borehole, and the dates of drilling and checking.

What does ADT stand for in the context of drilling methods?

ADT stands for Auger Drilling with a TC (Tricone) bit. 'AD' refers to Auger Drilling, while 'T' refers to the TC bit used during the process.

How is ground water level recorded in borehole logs?

Ground water level is recorded in the borehole log with a specific symbol, showing at what depth groundwater was encountered. If no groundwater is found, it will be indicated as such in the log.

How are geological units or soil types represented in the borehole log?

Geological units or soil types are represented using Unified Soil Classification System symbols, such as 'M' for silt and 'C' for clay. These symbols are accompanied by descriptions of the material, like color, moisture content, and consistency.

What is the importance of the moisture column in borehole logs?

The moisture column indicates the moisture content of the soil, with symbols like 'M' for moist, 'D' for dry, and 'W' for wet. This helps assess the soil's suitability for construction and its current condition.

How is soil density indicated in the borehole log?

Soil density is described in terms such as 'firm', 'stiff', or 'very loose' based on field observations and standard tests. Loose or very loose soil might raise concerns for foundation stability.

What is indicated by the presence of 'fill material' in a borehole log?

The presence of 'fill material' in the borehole log, usually found at the upper levels, indicates that the soil has been artificially placed and may not be natural. Below the fill, natural materials like clay or sand may be encountered.

What is the significance of the Standard Penetration Test (SPT) in borehole logs?

The SPT provides a measure of soil strength. The number of blows required to penetrate 30 cm of soil is recorded, and low values (e.g., 2) indicate soft or weak soil, while higher values (e.g., 19) suggest denser and stronger soil.

What does 'U50' mean in the context of soil sampling?

U50 refers to an undisturbed sample collected with a diameter of 50 millimeters. This type of sample retains its natural structure and is ideal for testing soil properties in a controlled environment.

What does 'PP' indicate in the borehole log and why is it important?

'PP' stands for Pocket Penetrometer, a device used to measure the unconfined compressive strength of soil. A high value, like 140 kPa, indicates stronger soil, and this information helps engineers assess soil stability.