Impact moling, also known as earth piercing or trenchless moling, is a widely adopted trenchless technology used for installing small-diameter pipes, ducts, and cables without the need for extensive excavation.
The moling method offers several benefits that revolutionise industries and construction practices. It significantly reduces surface disruption and minimises the need for disruptive excavation, therefore speeding up project timelines and reducing costs. This efficiency makes it particularly valuable in urban or protected environments where minimising disruption to traffic and existing wildlife or infrastructure is crucial.
Impact moling also ensures minimal environmental impact, making it a preferred choice for modern construction projects aiming to achieve both operational efficiency and environmental sustainability. In this guide, we will discuss moling technology, what challenges may arise during the process, and how these challenges can be minimised and overcome.
The moling method involves the percussive action of a pneumatic piercing tool to compact and displace soil, creating a bore path rather than removing soil outright.
Moling provides numerous benefits, however, there are a few challenges that could arise during the process that need to be addressed and mitigated before work can be successfully carried out.
Impact moling is sensitive to ground conditions. Moling equipment is extremely effective in ground conditions that are relatively loose, stable, and free from significant obstacles that could deflect or obstruct the mole’s progress underground.
Ideal conditions include soils that are not densely packed or composed of non-compactible materials like dense dry clays, compacted sand, and gravel as these materials can significantly hinder penetration rates and cause deviations from the planned path. These difficult ground conditions can lead to surface upheaval or force an early termination of boring attempts to avoid further complications.
An experienced and knowledgeable moling contractor can navigate these challenges effectively. Their expertise allows them to anticipate how different ground conditions might affect the moling process.
Path control in impact moling poses challenges, especially in varied ground conditions and when encountering hard materials like rocks. These conditions can cause the mole to deviate from its intended path, which can complicate the installation process. Achieving a precise path is essential, demanding meticulous planning and occasionally several attempts to get the alignment just right.
By assessing the soil type, identifying potential obstacles, and strategising the borehole route accordingly, skilled moling contractors are adept at adjusting the moling technique on-site, adapting to unforeseen challenges as they arise.
Ensuring precise depth control and alignment of the bore path can be challenging, especially in varying ground conditions. Maintaining the intended bore axis and depth throughout the project requires skilled operators and sometimes additional surveying equipment.
Experienced contractors play a pivotal role in overcoming these limitations. They assess site conditions thoroughly before starting, allowing them to devise strategies to mitigate challenges. This may involve adapting installation methods, selecting appropriate mole heads, or considering alternative techniques when necessary.
Despite some constraints, skilled contractors can optimise moles to perform effectively in various conditions. Their expertise ensures that impact moling projects proceed smoothly and accurately, even in less favourable terrains or when encountering obstacles underground.
As discussed previously, before the operator begins directing the mole along the bore path several preparatory steps are typically undertaken. These include a site risk assessment, ground condition assessment, locations for optimal entry and exit pits for the mole, health and safety considerations, equipment assessment and ensuring compliance with local regulations.
Then, two pits are excavated at the required entry and exit points to accommodate the insertion of the mole and associated equipment. Typically the distance between the pit will not exceed 12 meters.
The operator, looking along the line of vision, is responsible for directing the mole. They must ensure that the mole stays within the desired working depth and follows the intended bore axis. The operator ensures the mole stays within the desired working depth and follows the intended bore axis.
Depth control is crucial as it determines the tunnel’s location and impacts factors such as installation ease and suitability for its purpose. The bore path, or planned tunnel route, must be followed as accurately as possible by the operator guiding the mole.
Small diameter moles are typically placed at the bottom of the pit and aimed towards the receiving pit. Once aligned, the tool should be cautiously driven into the ground with reduced power until it reaches one-third of its depth. At this point, launching should pause to verify and, if needed, adjust the alignment. Throughout the process of burying the mole entirely underground, it may require multiple checks and corrections to ensure the correct line and grade are maintained.
Impact moling equipment includes pneumatic piercing tools designed to deliver powerful percussive blows for displacing soil to lay pipes. These tools are usually compact and lightweight, making them easy to handle and manoeuvre during projects. Advanced mole equipment may feature replaceable heads to accommodate different soil conditions, making them versatile for many applications.
Impact moles can be equipped with replaceable heads tailored for various soil conditions. These heads include tapered heads for loose and wet soils, splined heads for dry and compact soils with obstacles, and stepped heads for soils containing rocks and other challenges. Proper selection of the tool head improves directional stability, ensuring efficient bore path creation without deviations.
Some moles (not widely used) offer optional tracking capabilities using a sonde (beacon or probe). This technology allows operators to monitor the mole’s depth and location using a walkover receiver. It facilitates real-time adjustments to the bore path, ensuring precise alignment and minimising the risk of path deviations.
Impact moles are available with both fixed and moving heads. Fixed head moles have fewer moving parts, simplifying maintenance and maintaining reliability during the project. Moving head moles, on the other hand, are designed to handle challenging soil conditions more effectively due to their ability to hammer during operation. They employ a two-stage action with a chisel tip for obstacle penetration and a stepped-cone body for soil displacement, providing high performance in varying and more difficult ground conditions.
Several processes can be implemented to effectively address challenges in impact moling:
Successful impact moling projects begin with thorough site assessments to evaluate ground conditions and identify potential obstacles such as utility lines, tree roots, or rocks. Strategic planning ensures that the chosen borehole route aligns with the capabilities of the chosen mole equipment, minimising the risk of deviation and maintaining operational efficiency.
Despite their few limitations, Impact moles can effectively displace minor obstacles and navigate through stable, unchanging soils. In scenarios where ground conditions are stable and no significant obstructions are expected, impact moles remain a cost-effective and reliable choice for trenchless installations.
Impact moling continues to be favoured for its cost-efficiency and minimal disruption compared to traditional excavation methods. On smaller projects, where the bore length and diameter requirements are within the capabilities of the mole equipment, it is possible to significantly reduce time during the project. This is due to the reduced need for extensive site preparation, the ability to complete installations with reduced workers during the process, and the need for large excavation equipment.
The penetration rate of impact moles varies depending on soil conditions, ranging from 1 to 5 feet per minute. Special attachments, such as steel sleeves or smooth coned heads, can enhance penetration rates in specific soil types. Continuous lubrication, controlled by an in-line lubricator, is essential for optimal tool performance. Using manufacturer-recommended oils prevents damage to the tool’s seals and ensures efficient boring operations.
Outside air temperature affects trenchless moling operations. In cold conditions, compressed air expansion within the mole can lead to tool cooling and ice formation, halting operations. Heating compressed air and using specialised lubrication oils mitigate these issues, ensuring uninterrupted performance even in challenging weather. Using lubrication and preheating compressed air before it enters the mole can help maintain optimal operating temperatures inside the tool, ensuring work can continue during less-than-ideal temperatures.
After completing the borehole, product pipes are typically pulled into place using attached air hoses or driven with pipe-driving heads. This method minimises disruption and streamlines installation processes, particularly for small-diameter pipelines and cables used in residential and urban settings.
By efficiently installing pipes through the borehole created by impact moling, this approach reduces the need for extensive excavation and associated disturbances to infrastructure and surrounding areas, ensuring smoother project execution and enhanced operational efficiency.
Using effective moling equipment that is responsibly selected to tackle specific ground conditions can ensure that projects proceed smoothly and efficiently. When choosing equipment, considerations such as soil type, project scale, and environmental factors play crucial roles in determining the success of impact moling operations.
Despite a few limitations and potential challenges, impact moling remains a robust and trusted trenchless technology for installing small-diameter pipelines and cables. By understanding and mitigating the challenges above through careful planning, enhanced ground condition assessment, and adherence to operational guidelines, impact moling can reliably meet the demands of utility installations while minimising costs and operational disruptions.
At EPS Trenchless Installations, we understand that each project we undertake has different needs, goals, and objectives. Our approach is to tailor solutions that address the specific requirements of your moling project.
At EPS Trenchless Installations, we specialise in providing expert underground moling services tailored to your project needs. Our team of professionals is equipped with the knowledge and tools necessary to navigate various ground conditions and overcome challenges associated with impact moling. We understand that each project is unique, which is why we offer personalised assessments and strategic planning to ensure optimal results.
Whether you are looking to install pipelines or cables in residential, urban, or commercial settings, our expertise in trenchless technology allows us to deliver efficient and effective solutions.
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EPS Trenchless Installations Ltd, Company number: 07739433, Registered office address: 55 Earl Street, Northampton, NN1 3AX Incorporated in England and Wales on 12 August 2011
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