Geotechnical Investigation – Horizontal Directional Drilling

A geotechnical investigation is vital to determining the subsurface conditions of various construction projects, including horizontal directional drilling (HDD). An HDD method avoids the need for open-cut excavations by installing underground pipelines, cables, and conduits.

Engineers must first assess the underground conditions before installing any pipes or cables. This inspection assesses whether the ground is suitable and stable enough to permit the drilling process to commence safely. Geotechnical investigations are conducted as part of the process.

The report analyzes the physical characteristics of soil earthworks and provides recommendations for repairing subsurface distress. Businesses can save thousands of dollars by utilizing the information gathered through this process.

Let’s discuss in detail what geotechnical investigation is all about, its advantages, and how it helps assess the area where horizontal directional drilling (HDD) will be carried out.

How Does a Geotechnical Site Investigation Work?

Geotechnical site investigations are critical to construction because they provide insight into the properties of the soil at a site. To understand the subsurface conditions of soil, this investigation ultimately aims to obtain data on the soil.
Measuring the soil’s thermal conductivity, hydrological conditions, engineering problems, and soil types is also possible. These conditions determine a number of factors, such as the project’s cost, the kind of foundation necessary, and the construction method. Before starting any HDD project, there will be a complete site geotechnical investigation.
A geotechnical investigation must be conducted in any construction project regardless of size or complexity.

What is Horizontal Directional Drilling?

There are three primary steps in horizontal directional drilling: pilot holes, drill pipe expansions, and drilling production pipe. As a first step, a horizontal directional drill bore a pilot hole. Small-diameter holes are drilled using drill bits and drill pipe assemblies.
The drilling fluid facilitates the cutting action of the drill bit on rock and soil. As a result, the drill bit is lubricated and cooled. Also, it is responsible for returning cuttings to the surface from the hole.

Advantages of HDD Drilling

Compared to other types of construction, horizontal directional drilling offers several advantages.
With underground utility installation, you can disrupt the surface as little as possible. This is an excellent choice for urban and residential areas. In addition, it could be a useful solution for a congested underground.
Compared to traditional trench installation methods, HDD requires less equipment, fewer individuals, and less fuel. It is more economically advantageous to use directional drilling because it requires less surface restoration and has a lower environmental impact after installation.
A horizontal drill is more efficient than one that drills down and across. After laying the pipe, there is no need to perform extensive surface restoration. A pipeline installation requires a deeper excavation than a trench installation. As a result, there is a reduced risk of causing damage to other underground utility systems.
Lastly, directional drilling permits are much simpler to obtain than traditional drilling. HDDs cause fewer disturbances, produce less waste, and occupy a smaller space. Permitting goes more smoothly this way.

Importance of Geotechnical Investigation in Horizontal Directional Drilling?

Before beginning the actual HDD process, a geotechnical investigation is conducted by drilling boreholes. This information helps identify potential challenges and plan the drilling route accordingly.
For this investigation, soil samples are taken, tested in the laboratory, and analyzed, and a foundation recommendation will be recommended based on the results. These tests help engineers understand the stability of the soil and its suitability for HDD.
In addition to recommending the type of foundation, the geotechnical engineer determines whether a deep or shallow foundation is needed. Pile foundations or strip footings can be used for the foundation.

An Overview of the Geotechnical Site Investigation Process

A geotechnical investigation is specific to the project and the land since the requirements and the land are different for every project. Even so, they must be carried out using the same essential steps. These are:

1. Site Knowledge

   Geotechnical engineering is conducted here to obtain a better understanding of the geology of the region. A geologic map, a photogrammetric map, or a geophysical map can accomplish this task. Essentially, the test aims to assess the soil’s physical condition. Identifying the limits of the soil and developing solutions to overcome any challenges is essential. HDD method can help assess site knowledge.

2. An Assessment of the Site’s Potential

   Following this, the engineers will discuss construction options with the client. The soil samples are usually extracted using borings or drillings. These samples may also be subjected to laboratory testing depending on the client’s requirements, as discussed above. Engineers will also inspect the soil visually for rocks and water.

3. Assessing Construction Feasibility

   According to the type of construction needed, a more detailed assessment may be necessary in some instances. A geophysical investigation and scientific study are usually called these types of investigations. These investigations are quite beneficial in identifying the existence of underground utilities and anomalies.

4. Providing Final Recommendations

   Engineers will then need to develop solutions based on the results of their investigation. They will then advise on how to proceed with the site’s construction. In the case of HDD, they will advise where to start drilling and how long to drill.
   Building structures safely and ensuring proper support requires a comprehensive understanding of the subsurface conditions before construction.

What is The Value of Geotechnical Investigation?

Geotechnical investigations are worth the investment. Without soil information, building any solid structure can feel like a gamble. As a contractor, you are responsible for answering specific questions.

• Does the site contain geological hazards, for example, expansive soils, inadequately compacted fill, debris beneath the surface, collapsible soil and rock, sinkholes, etc?
• Do excavations, crawl spaces, or basements have shallow groundwater that may seep in?
• How can you balance cut and fill by utilizing onsite soils?
• What is the proper method for compacting your fill?
• What is the most suitable and cost-effective foundation for your project?

You can best answer these questions by conducting a geotechnical investigation.

Is Geotechnical Investigation The Only Option To Assess Surface Conditions?

When considering alternative methods, you should always proceed with caution. Home builders sometimes use soil maps, the results of prior excavations, or surface soil samples instead of geotechnical investigations.

Some of these methods may be effective in small, undisturbed areas with a low risk of disturbance. These methods are unlikely to yield the desired results in the long run.

Short lateral distances between lots within a single subdivision can considerably affect the subsurface conditions. In geotechnical engineering, there is no rule of thumb regarding subsurface conditions. Only by drilling or digging can we discover what lies beneath the surface.

Conclusion
Geotechnical investigation is vital to the success and safety of horizontal directional drilling (HDD) projects. Engineers can make informed decisions regarding drilling techniques, equipment, and stabilization measures by thoroughly assessing subsurface conditions, including soil and rock properties.
Geotechnical analysis helps identify potential hazards, optimize drilling paths, and ensure the long-term stability of installed pipelines or conduits.

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