Table of Contents
1 Introduction
As we look to explore and develop more of the world, the sites we would like to build on are becoming increasingly complex. From highways through steep, mountainous terrain to houses on the top of sheer cliffs to mines surrounded by water, it is clear that site access is growing more difficult with each of these complex projects.
Fortunately, the technology used to access these sites is also advancing. There are many reasons why equipment may need to be brought to a difficult access site; however, this article will focus on access for drilling equipment for geotechnical investigation, environmental investigation or exploration. The following sections will describe the two main categories of difficult access – restricted and limited access – along with site-specific challenges that may arise and how these challenges are addressed using existing drilling technology.
2 Restricted Access
Restricted access refers to sites with access challenges that limit the ability of a drill rig to get to the site. Some examples of this type of access challenge include steep slopes and dense forests, drilling over water or soft, saturated soils and remote access. This section of the article will describe a few of these examples and the challenges they bring, along with a few ways advances in drilling technology have helped overcome them.
2.1 Steep Slopes
Steep slopes are one of the most common and most difficult forms of restricted access for drilling companies to deal with. These slopes can be highly vegetated, unstable, and have no existing platform to accommodate a drill and the equipment needed to run it. Further, steep slopes often do not have any access roads, meaning that alternative means of transporting the equipment must be used if it is not deemed feasible or cost-effective to construct an access road.
If a slope has minimal vegetation, is not too steep and is not too far from an access road, it may be possible to grade a path to the desired drilling location and use a tracked rig to access and drill the hole. The process for completing this would normally involve contracting tree fallers (if there are trees in the path of the proposed road) followed by an excavator to create a path accessible for a tracked rig. A road-accessible track drill hole is likely the easiest and most cost-effective method to use when conditions allow for it. However, there are many cases where this is not feasible.
Suppose an access road cannot be built due to the steepness of the slope or the location’s proximity to a major road (needed for unloading the equipment from a flatbed truck). In that case, there are a variety of additional challenges introduced. Slopes may be too steep to accommodate a road without performing a significant (and expensive) soil cut. Trees may be too dense or large to remove cost-effectively. There may be a sensitive ecosystem in the path of the only possible road access point. It may be necessary to use either a helicopter or a large crane to move the equipment to the desired drilling location in these situations. Fortunately, many drilling rigs are versatile enough to be transported by crane or helicopter by breaking them apart into smaller components, along with the supporting equipment. These components can be arranged in different configurations depending on the dimensions of the working platform (pad), the direction of the hole (if it is a directionally drilled hole), and the size and number of pieces of equipment.
As described above, a drilling pad must be constructed before the equipment can be brought to the drilling location. Several different considerations would affect how the pad is built; however, in many cases, it is a task that must be performed manually, usually by the drillers. This can be a huge task that takes several hours or even days to complete, depending on the existing condition of the slope (material, steepness, etc.). For slopes with a high density of trees, tree fallers often need to be contracted to safely clear a large enough area of trees and ensure no hazardous trees (also known as danger trees). While removing trees requires significant effort, these trees (once they have been felled) can assist in creating the working platforms by providing structural support to a soil slope that may otherwise be difficult to stabilize.
Safety is another key factor to consider when creating a drilling program on steep slopes. Advances in the technology of tracked equipment allow many drill rigs to be operated using a remote control. This feature allows the operator to traverse access roads across steep slopes without fear of going along for the ride if the slope were to fail and cause the rig to tumble down the slope. Potentially injured workers could also be transported along the access road to be taken to a hospital. However, if the area is significantly vegetated and there is no access road due to the steep slope, how would an injured worker be evacuated?
It is possible that an injured worker’s life could depend on the emergency response plan. It is extremely important to ensure that a good emergency response plan is put in place and understood by the site supervisors and all workers at the site. In many projects where access is not particularly challenging, the emergency response plan can be as simple as understanding where the nearest emergency vehicle meeting point is relative to the work area. Putting together the emergency response plan must consider whether it is feasible to extract an injured worker to the emergency meeting point. In some cases, particularly when working on steep slopes, it may even be necessary to construct a helicopter landing pad if there is no other suitable way to extract a worker.
While steep slopes do create significant challenges, these can be overcome using drilling best practices and the best and most appropriate equipment available for the job.
2.2 Drilling Over Water
Many scenarios may require a drilling program to be completed over water. Bridges over rivers, dams and other infrastructure projects are just a few examples of this. The most common method to use when drilling over water is a barge-mounted rig. Usually, this consists of a tracked rig placed on a barge that can be anchored in place using long posts (sometimes referred to as spuds) driven into the ground. Alternatively, a series of anchors attached to the cable can stabilize the rig while drilling. This is particularly important when the barge is located in a body of water with a strong current, such as a river. Other drill rig applications can be considered for over-water work, including amphibious rigs (discussed in detail in the following section). Still, barges remain to be the most commonly used for their versatility and cost-effectiveness.
2.3 Soft Saturated Soils or Mine Tailings
Tailings storage facilities or tailings ponds are large structures that contain the waste product produced from mining operations. These tailings ponds can be filled with various materials ranging from solid to fluid (depending on the pond’s age and the type of material being deposited) or a mixture of both. Often, drilling companies are sent into and on the banks of these tailings ponds to perform various types of drilling and sampling to facilitate the design of the structure or for environmental reporting purposes. The main challenge for tailings ponds that do not have a water cap is that traditional overwater drilling methods like using a barge (described above) will not work since the material has too high of a solids content, causing a boat propellor to get stuck immediately. This access challenge exists not only in tailings ponds but could exist in any scenario where the ground is highly saturated and too soft to support the weight of a track or truck-mounted rig. Some other examples of soft soils include peat bogs, swamps containing organic material or fine saturated sand.
An option for accessing sites containing the material described above is an amphibious tracked rig. This usually consists of a barge attached to two large pontoons that double as tracks. The benefit of using these rigs is that it allows for access to sites that otherwise would prove to be extremely challenging. The amphibious rigs usually combine with an amphibious excavator that uses its bucket to pull the drill rig to each drilling location. This is not always necessary if the ground is sufficiently solid but necessary when the ground becomes too soft to provide enough traction for the tracks to propel the rig forward.
2.4 Extreme Weather
Whether the drilling scope is for geotechnical, environmental or exploration purposes, it is not uncommon to need to access a site in an extremely remote location. These sites are often also prone to extreme weather, whether extreme cold in the arctic regions or extreme heat in regions close to the equator. Several challenges and risks are introduced by these conditions that must be mitigated before beginning a drilling program in such a location.
In some situations, a drill rig that is fully enclosed could be used in extreme weather to keep workers safe by maintaining a safe working temperature. These rigs can be heated or cooled as needed and are very versatile, usually running on tracks or tires. This may not always be feasible if the site is too remote; in these situations, other methods, including proper personal protective equipment and regular breaks, must be used to keep the equipment operating and the workers at a safe temperature.
3 Limited Access
Limited access drilling refers to locations that can be accessed by a drill but have limited space to manoeuvre or are otherwise limited in what operations they can perform due to external factors. While the challenges introduced by restricted access in the previous sections are often overcome using a team effort of correct planning and combining different equipment like helicopters and excavators, limited access is different. Limited access drilling challenges are primarily solved directly using innovative drilling technology since it is often done in a location that cannot be disturbed for various reasons. This section will go through some examples of limited access challenges and how drilling technology can help solve them.
3.1 Space Restrictions
Whether the site is located in a parking lot, an alley or any other tight urban setting, space restrictions can be detrimental to a drilling program. Of course, if there is insufficient space for the drill rig to reach the location (restricted access), an alternative must be considered. However, even if a rig can reach the location, there still must be sufficient space to perform the drilling (limited access). Recently, drill rig setups have become more compact and versatile, allowing access to tighter spaces using smaller, often remote-controlled rigs.
3.2 Traffic
In urban settings, it is often necessary to drill on roads near traffic. This challenge brings a significant level of risk when considering the obligation to protect the public. Different traffic considerations must be made depending on the speed, width, and number of lanes on the road. This could include different traffic management strategies, such as using single lane alternating traffic (SLAT) or closing lanes on a highway to create space to work on the shoulder. It is necessary to slow down the vehicles in most scenarios to create a safe environment for the drillers. In many cases, it may be advantageous to use a smaller drill rig with rubber tires to ensure the setup time is fast and traffic is impacted for as short of a time as possible. This decision would be made by the engineer supporting the drilling and would depend on the scope of the drilling work and the level of impact of traffic that is allowed.
3.3 Noise Restrictions
When drilling in many urban or suburban settings, it is necessary to maintain a certain noise level not to disturb residents or people working in the area. While this can sometimes be achieved by drilling during specific hours (when residents are away from home), disturbing residents is often unavoidable when using a noisy drill rig. Advancements in electric drill rigs have progressed significantly in recent years and battery technology, allowing for much quieter drilling in urban settings. For longer drilling programs where it is not feasible to use battery power, it may be possible to hook up an electric drill rig directly to the power grid. As battery technology continues to progress, this will be even more feasible and make drilling in urban or suburban settings significantly quieter and less intrusive to nearby residents.
3.4 Environmentally or Culturally Sensitive
Drilling sites are often located near environmentally sensitive ecosystems or are culturally sensitive. A common environmentally sensitive site would be any flowing body of water, particularly if it is fish-bearing. If any drilling fluid is used on a site close to a flowing body of water, contaminants can flow into the water and adversely affect the ecosystem. It is important to capture and remove any drilling fluid used or to use a rig that does not produce any drilling fluid.
It is also important to consider culturally sensitive sites when drilling, specifically burial sites or sites containing artefacts or middens. Middens contain various items associated with past human occupation, including shells, bones, fragments of pottery, and other domestic waste. If these conditions can exist at the site, cultural monitors are often required to ensure proper measures are taken to avoid drilling through these sites.
These considerations are becoming increasingly important as drilling companies strive to become more environmentally and socially responsible in a time where this is often a significant focus.
4 Conclusion
The need for drilling on restricted access sites is becoming increasingly common. While some solutions are currently available in the market, for each challenge introduced by a difficult access site, an opportunity arises to develop more innovative technological approaches to solving these problems. As sites continue to become more difficult to access, the drilling technology used to provide the important subsurface data that many engineers rely on must continue to evolve to meet the challenges.
