Sub-soil Exploration/Investigation in Foundation Engineering

I. Introduction

Sub-soil exploration/investigation plays a crucial role in foundation engineering. It involves the study and analysis of the soil and rock layers beneath the ground surface to determine their properties and suitability for supporting structures. By conducting sub-soil exploration/investigation, engineers can gather essential information about the subsurface conditions, which helps in designing safe and cost-effective foundations.

II. Objectives and Planning of Exploration Program

Setting clear objectives for the exploration program is essential to ensure that the investigation is focused and comprehensive. The objectives may include determining the soil type, identifying potential geotechnical hazards, assessing the bearing capacity of the soil, and evaluating the groundwater conditions. Based on the project requirements, the exploration program is planned, which includes selecting appropriate exploration methods and determining the locations and depths of the borings.

III. Methods of Exploration

There are various methods of sub-soil exploration, including wash boring and rotary drilling.

A. Wash Boring

Wash boring is a commonly used method for sub-soil exploration. It involves the use of a wash boring rig, which consists of a drill bit attached to a drill rod. The drill bit is rotated and simultaneously water is injected through the drill rod to wash away the soil cuttings. The depth of boring in wash boring method can vary depending on the project requirements and the soil conditions.

B. Rotary Drilling

Rotary drilling is another widely used method for sub-soil exploration. It involves the use of a rotary drilling rig, which consists of a drill bit attached to a drill string. The drill bit is rotated, and downward pressure is applied to penetrate the soil. The soil cuttings are brought to the surface using drilling fluid. The depth of boring in rotary drilling method can be much greater compared to wash boring.

IV. Soil Samples and Soil Samplers

Obtaining representative and undisturbed soil samples is crucial for accurate geotechnical analysis. Representative sampling involves collecting soil samples that are representative of the soil conditions at a particular depth. This is typically done using a split spoon sampler or a thin-walled sampler. Undisturbed sampling, on the other hand, involves collecting soil samples without disturbing the natural state of the soil. This is achieved using specialized samplers such as Shelby tubes or piston samplers.

V. Field Penetration Tests

Field penetration tests are conducted to assess the engineering properties of the soil. Some commonly used field penetration tests include the Standard Penetration Test (SPT), Cone Penetration Test (CPT), and Dynamic Cone Penetration Test (DCPT).

A. Standard Penetration Test (SPT)

The SPT is a widely used field penetration test. It involves driving a split spoon sampler into the ground using a standard hammer and counting the number of blows required to penetrate the soil a certain distance. The SPT results provide information about the soil's resistance to penetration and can be used to estimate the soil's strength and stiffness.

B. Cone Penetration Test (CPT)

The CPT is another commonly used field penetration test. It involves pushing a cone-shaped penetrometer into the ground at a constant rate and measuring the resistance encountered. The CPT provides continuous data on the soil's resistance, which can be used to determine the soil's strength, stiffness, and other geotechnical properties.

C. Dynamic Cone Penetration Test (DCPT)

The DCPT is a simplified version of the SPT. It involves driving a cone-shaped penetrometer into the ground using a dynamic hammer and measuring the penetration resistance. The DCPT is often used in areas where the SPT cannot be performed, such as on rocky terrain or in areas with limited access.

VI. Introduction to Geophysical Methods

Geophysical methods are non-intrusive techniques used to investigate the subsurface conditions. These methods involve measuring and interpreting the physical properties of the soil and rock layers. Some commonly used geophysical methods in sub-soil exploration include seismic refraction, electrical resistivity, and ground-penetrating radar.

VII. Bore Log

A bore log is a detailed record of the subsurface conditions encountered during the exploration program. It includes information such as the depth of the borings, soil and rock types, groundwater levels, and any geotechnical hazards encountered. Maintaining a comprehensive and accurate bore log is essential for future reference and for designing suitable foundations.

VIII. Report Writing

Writing a detailed and accurate sub-soil exploration report is crucial for effective communication of the findings and recommendations. The report should include a summary of the project objectives, a description of the exploration methods used, a presentation of the data collected, an analysis of the soil properties, and recommendations for foundation design. The report should be organized, well-structured, and easy to understand.

IX. Real-world Applications and Examples

Sub-soil exploration/investigation is carried out in various construction projects to ensure the safety and stability of structures. Some examples of real-world applications include the construction of high-rise buildings, bridges, dams, and tunnels. Case studies highlighting the importance of thorough sub-soil investigation can provide valuable insights into the challenges faced and the solutions implemented.

X. Advantages and Disadvantages of Sub-soil Exploration/Investigation

There are several advantages of conducting sub-soil exploration/investigation, including:

• Accurate assessment of soil properties
• Identification of potential geotechnical hazards
• Optimization of foundation design
• Cost-effective construction

However, there are also some disadvantages and limitations, such as:

• High cost and time-consuming
• Limited access in certain areas
• Uncertainty in interpreting the results

XI. Conclusion

In conclusion, sub-soil exploration/investigation is a critical aspect of foundation engineering. It involves setting clear objectives, planning the exploration program, selecting appropriate methods, obtaining representative and undisturbed soil samples, conducting field penetration tests, and analyzing the data. Geophysical methods and maintaining a detailed bore log are also important components of the exploration process. Accurate reporting and real-world applications further emphasize the significance of sub-soil exploration/investigation in ensuring safe and reliable foundations.

Summary

Sub-soil exploration/investigation is a crucial aspect of foundation engineering. It involves setting clear objectives, planning the exploration program, selecting appropriate methods, obtaining representative and undisturbed soil samples, conducting field penetration tests, and analyzing the data. Geophysical methods and maintaining a detailed bore log are also important components of the exploration process. Accurate reporting and real-world applications further emphasize the significance of sub-soil exploration/investigation in ensuring safe and reliable foundations.

Analogy

Sub-soil exploration/investigation is like conducting a thorough investigation before building a house. Just like you would assess the land, soil conditions, and potential hazards before constructing a house, sub-soil exploration/investigation involves studying and analyzing the soil and rock layers beneath the ground surface to determine their properties and suitability for supporting structures.