Underground water plays a vital role in construction projects. This includes water extraction for various purposes, underground contaminated water removal, and tunnel construction dewatering. It also includes remediation, groundwater sampling and monitoring, and analysis of earth properties.
Water can be extracted from beneath the ground level by digging a bore or well and pumping the water out. It is quite a simple task when required at a new construction site. But at times it becomes a complex matter, considering the future layout of the proposed civil works.
It is even more difficult when it comes to the already constructed projects. The task gets complicated and more technical on the sites where you have to preserve the existing structure or where digging of a well is prohibited. Horizontal Directional Drilling (HDD) is the answer to all these challenges.
Horizontal Directional Drilling Technique
HDD is an underground drilling technique, mostly used for laying gas or water pipelines, cables, and other utility services. It also establishes utility services while crossing waterways, roads, and railroads. Oil and gas extraction is one of the best utilizations of this technique.
HDD is a horizontal boring method that runs below ground level at a pre-determined path. It starts with digging a pilot hole up to a pre-defined depth. Then the drilling bit is guided for drilling below the surface on the predetermined route till it reaches the targeted point where it comes out of the ground.
A specialized drilling machine is used for this purpose. Once the horizontal bore is made, the pipeline, conduit, or cable is then pulled back through this horizontal bore. This technique is also used for water wells and environmental wells.
Water Wells and Environmental Wells
A well is an excavation and structure to reach the liquid resources under the ground. In many civil engineering projects, a well is mainly excavated to extract water for domestic or commercial use. This type of well is known as a water well.
The depth of water wells is variable depending on the underground water level. There are different water layers in the subsurface. The upper layers are not considered suitable for human consumption. The deeper layers of the water are appropriate for domestic use.
An environmental well is similar to a conventional water well but its utility and application differ. Environmental wells’ main purpose is not to extract water for human consumption. An Environmental Well is created for the following purposes.
- Groundwater sampling
- Underground water level monitoring
- Groundwater testing
- Groundwater measurement
- Analysis of Earth’s properties
- Extraction of contaminated water
Based on the purpose, the environmental wells are of different types which include:
- Remedial wells for remediating the contaminated underground water.
- Monitoring wells for getting water samples to avoid possible mix-ups of contaminated and potable water.
- Observation wells for keeping an eye on the groundwater level.
- Dewatering wells for tunnel construction.
- Piezometers for monitoring the pressure of water in a well.
- Slope stability and monitoring wells are used to monitor the stability of the slope so that it may not collapse due to internal or external pressure.
- Soil vapor wells are typically useful for the extraction of contaminated soil vapors.
- Vibrating wire piezometers to measure the water pressure in a well.
While a simple water well can be made by any professional contractor, environmental wells can only be constructed by a licensed or authorized contractor that is well-experienced in this field. The minimum depth of an environmental well is 15 feet whereas it might need to be extended even deeper per the project’s requirement.
HDD Methods for Creation of Water and Environmental Wells
Vertical water well is rarely seen in most civil engineering projects. This type of well is only feasible for small domestic water extraction purposes. For most construction projects, a well must be made under compelling circumstances, especially environmental wells. Here, the only solution is the Horizontal Directional Drilling technique.
Different HDD methods are used for various types of environmental wells. However, most HDD techniques use a basic engineering and drilling method. The concept is based on the oil and gas exploration and extraction projects that is, drilling the bore beneath the hurdles. The basic process of HDD is drilling a horizontal bore on a pre-determined route, which includes:
- Drilling with a rotary drilling machine
- Injection of drilling fluid, usually bentonite, facilitates the drilling and provides much-required stability to the bore.
- Drilling fluid is also important for cooling the drilling head and drilling bit.
- Removal and extraction of cuttings from the drilled bore.
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Difference Between Dewatering and Other Environmental Wells
In most HDD techniques for environmental wells bentonite is used as the drilling fluid. But the dewatering wells are different. Here bentonite is not suitable. Instead, they use biodegradable polymer material for this purpose. It is useful for the reduction of the porousness of the bore in case of dewatering wells.
Two Types of HDD Wells Installation
HDD water wells and Environmental wells are mainly differentiated into two types based on the method of installation/completion of wells.
Single Entry Well Completion
A single entry well is constructed when you can’t access the reception pit. In this situation, the entire well construction has to be done from one end, the pilot pit or pilot hole. Here, the drilling bit is withdrawn once the bore is made.
The rest of the process is completed by pushing the reamers into the bore while gradually increasing the diameter of the bore. This type of well is feasible for limited lengths. Hence, its utility is also limited compared to other types of HDD well completion.
Double Entry Well Completion
The bore consists of two openings in this installation type: the pilot and reception pit. The bore runs beneath the surface, parallel to the ground, from the pilot hole to the reception hole. Once the bore is completed, the drilling bit is removed and the reamer bit is attached to the machine.
The reamer bit is then pulled back, increasing the hole’s size to make it convenient for further utilization. This well-installation type is more popular than the single-entry type.
Installation of Well Screen
Well Screen is the most vital part of the water and environmental wells. It is a filter that keeps sand or other particles away from entering the well from the bore. Only the water is filtered-in, into the well, which can then be pumped out for different purposes.
A Well Screen or filter installation is very easy and simple in vertical water wells. However, it is quite a complex matter in the case of horizontal directional wells. Reason? The HDD wells are larger in length as compared to the vertical wells.
Moreover, the direction or path of the bore is not consistent; rather it deviates in direction depending on the route of the bore. Due to the extended length of the well screen, it is made up of stainless steel in the case of HDD wells.
Similarly, this type of well screen’s open area is less than the conventional vertical well. This is a crucial factor for the strength and reliability of the well screen in HDD wells.
Advantages of Horizontal Directional Drilling Technique
The Horizontal Directional Drilling (HDD) method has several advantages over conventional open-cut excavation techniques. Among the main advantages are:
- Reduced Surface Disruption : Horizontal Directional Drilling eliminates the need for open trenches, thereby minimizing surface disruption and reducing environmental impact. This is especially advantageous when traversing environmentally sensitive areas, such as wetlands, parks, or urban landscapes, as it preserves the aesthetic value of the surrounding area.
- Due to the fact that HDD only requires tiny entry and exit points for drilling, there is minimal damage to roads, landscaping, and existing infrastructure. This saves time and money by substantially reducing the restoration and rehabilitation efforts required after installation.
- Reduced Environmental Impact: Horizontal Directional Drilling (HDD) minimizes disturbance to ecosystems, water bodies, and protected areas. It reduces the likelihood of soil erosion, habitat devastation, and water contamination, thereby promoting environmental sustainability.
- HDD installation is typically quicker than conventional excavation techniques. Once the drilling rig has been installed, the installation process can proceed comparatively quickly, resulting in a reduction in project duration and a quicker conclusion.
- Greater Installation Flexibility HDD permits greater alignment and depth flexibility for the installed pipelines or conduits. It can accommodate curvilinear or non-linear paths, allowing for more routing options around obstacles or along preferred routes.
- Even though HDD can have higher initial costs due to specialized equipment and skilled labor, it frequently results in overall cost savings. The reduced surface disturbance, minimal restoration requirements, and shortened duration of the endeavor all contribute to cost effectiveness.
- HDD decreases the likelihood of accidents and injuries associated with exposed trenches. Workers are not exposed to open excavations, heavy machinery, or traffic hazards, thereby improving the overall safety of the job site.
- HDD installations are renowned for their durability and dependability. This method results in pipelines and conduits that are less susceptible to damage from external factors such as ground movement and corrosion, thereby ensuring long-term service reliability.
Well construction and installation is an essential part of every construction project. Different techniques are used to dig and install a well depending on the purpose and utility of the well.
Compared to the conventional vertical well, mainly used for getting water for domestic use, the HDD water and environmental wells are somewhat difficult to install. However, using the latest HDD techniques, the construction of wells has been made easy and convenient.
The HDD methods of well construction have solved many of the problems associated with boring in difficult areas, such as crossing rivers and roads and the areas where open trenches are not allowed or are not feasible.
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