The success of trenchless projects depends on the provision and assimilation of several critical inputs during the planning and execution phases. Such inputs, if provided in sufficient extent at an opportune time, will lead to a successful trenchless project, else it will be a failure of varying extent depending upon inadequacies, writes Prof (Dr) Niranjan Swarup.

Subsurface space offers immense opportunities for housing public or private utilities like pipes, appurtanances, and related structures. Installing one set of utilities does not preclude installation of subsequent utilities at a different level above or below the previous one and for an observer stationed on ground surface, the space to develop more utilities is ever available, only the specific location gets consumed by one utility construction operation. More utility networks could be planned with additional structures at alternate depths, levels, or alignments. Though on plan view all of which would appear existing at the same location, these can be planned and developed with a clear possibility of more future developments. Any failed or malfunctioned trenchless project, however, will have the propensity to fritter away a substantial part of such opportunities forever, as it would create an ill/non-performing structure and at the same time consume the specific right-of-way. In cases of aggravated malfunction, the damage could spill-over to more subsurface spaces leading to the hazard of a larger space loss. To prevent such situations, it is necessary to apply adequate counter-measures, or inputs, capable of proper risk mitigation. Prior to discussing the specific inputs, let us take a look at the hazard control mechanisms for trenchless projects.

Hazard control for trenchless projects

Trenchless projects are planned to be executed as a remote controlled operations set. Such consideration, in turn, exposes the works and ultimate structures to hazards of damage due to many causes ranging from inefficiencies of the executing agencies, incompatible technology, improper layout, inadequate traffic management plans, erroneous execution methodologies, bad workmanship, or material/equipment malfunction or failure. Each of these hazards could be controlled by applying appropriate countermeasure. Controlling these hazards is an essential component of any trenchless construction project and therefore, the importance of the matter.

Controlling any hazard is a matter of planning, and then executing the plan by applying the identified counter-measures to the fullest possible extent. Let us discuss the method to identify counter-measures.

Management strategies in controlling hazards The philosophy behind identifying and evaluating the counter-measures for such hazard control is a stepwise process, employing different technical or managerial strategies, conducted on a hierarchal manner. The core of the process is ten logically distinct technical strategies for control for each expected deficiency, as discussed hereafter.

• Principle 1: Prevent the creation of the hazard.
• Principle 2: Reduce the amount of the hazard.
• Principle 3: Prevent the exposure of the hazard.
• Principle 4: Modify the rate of release of the hazard from its source.
• Principle 5: Separate the hazard from that which is to be protected in time and space
• Principle 6: Separate the hazard from that which is to be protected by a physical barrier.
• Principle 7: Modify relevant basic qualities of the hazard.
• Principle 8: Make what is to be protected more resistant to damage from the hazard
• Principle 9: Begin to counter damage done by the hazard.
• Principle 10: Stabilise, repair, and rehabilitate the object of damage.

These principles are the generic process steps to be followed in sequence till the specific issue is addressed. The aim would be to address the issue in as less steps as possible. The next step would only be applicable if the concluded step is unable to mitigate the hazard.

Take for example, if one is evaluating site safety obvious measure here would be to eliminate all hazardous substances and equipment from the battery limits altogether (Principle 1). Where this is not possible or practical, or where the hazards are more specific, reduction in the amount of hazard should be considered (Principle 2). This step must be complimented with the arrangements of preventing the exposure of hazardous situation (Principle 3). Subsequent principles have to be applied in sequence till the hazard is mitigated. These strategies help to identify and prioritise technology based safety counter-measures for trenchless projects. It is expected that the proper application of these can help the identification and assessment of risks, and provide a structured way to develop controls.

Application of hazard controls

Trenchless projects depend on several critical inputs that can make or mar any trenchless project. Common examples of such inputs include trenchless equipment, skills of operating manpower, consumables, installed materials, and other related issues like working space availability, or urban settings, or other constraints/impediments. It is important to address issue related requirements for a successful project. Failure to address the related issues would lead to a failed project and a damaged surrounding zone. Before discussing those let us discuss the basic attributes of trenchless projects.

Trenchless attributes

Prior to discussing the critical inputs, we need to discuss the trenchless attributes that will define the critical input for projects. These attributes are as follows:

Specialised nature: Trenchless techniques are state-of-the-art systems. Each project needs to be conceived, planned, structured, designed, executed, and concluded in its entirety; incomplete or inadequate construction works will lead to unsafe or unsound structure.

Technique selection: Improper or inadequate technology selection may lead to failures. Primary objective of these techniques is to develop maintain or manage subsurface networks and there are several competing techniques that appear to be suitable for a project but the best suited technique needs to be selected. For an example, if a pipeline required critical grade and alignment and if the technique selected cannot offer it within the required limits, the pipeline produced will fail operationally.

Operator skills: Operator skills for trenchless applications are quite important. Untrained or undertrained operators may produce unsafe or failed structures. This is one of the most critical, but often ignored, aspect of any trenchless project. The most common mistake any project executioner does is to assume that the deployed equipment will produce a structure irrespective of operator skills. The fact is that undertrained and uncertified operator may operate the equipment in a completely incorrect way leading to a damaged structure. Suitable equipment: Equipment capacity and quality needs to meet the project requirements. Use of under-capacity or poor quality equipment may lead to damaged structure or failed projects, or inherently weak structures.

Installed materials: Installed materials and consumables proposed to be used in project must meet the project and site requirements as without this important compliance one can never have a structure as expected and designed.

Technique related limitations: Each technique has its own requirements like equipment sizes and weights, operational prerequisites or site conditioning requirements and likewise. In case such conditions are not met the results will be catastrophic and may lead to project failures even. One also has to understand the importance of inspections and supervision during the construction activities as its failure may lead to unsound or unsafe works defeating the complete purpose of the developmental activity.

Proper subsurface data requirements: Subsurface constructions are fraught with the risks that are unknown as most of the proposed system is to be developed underground and there very little amount of project information generally available. Most of the survey reports are only for a finite set of locations and for all other places it is an interpolation from such reports. This leads to a possibility of unforeseen construction works and may lead to time and cost overruns if the extent of interpolation is too high. At the same time if the survey is too elaborate, the related costs are too high making the project unwieldy. A proper balance, therefore, between the less and too much survey is very important.

Impact of surrounding structures: Developing networks amidst several operational and abandoned utility networks existing in the subsurface space make the works challenging. Further, above surface structures make the activities more challenging. Solutions to these issues lies in a better subsurface and surface surveys and a proper technique selection based on the survey reports.

Critical inputs

As mentioned in earlier sections, trenchless projects are prone to several hazards and proper planning is quite important for the risk mitigation. Such expected hazards could be controlled if appropriate planning is done in the initial phases of project conception and planning. Some of the most critical inputs necessary for trenchless projects should include the following:

a) Required attributes of executing agency;
b) Technology selection;
c) Proposed utility route plan;
d) Traffic management plan;
e) Method statement;
f) Third party inspection.

Required attributes of executing agency

Based on the points discussed in Section 5, it is imperative that the executing agency must have the following attributes:

• Knowledge and experience to execute such projects;
• Appropriate equipment capable to execute such projects;
• Adequately trained and certified operators;
• Adequate capabilities for subsurface investigations.

Technology selection

As discussed in the previous section, trenchless technology selection is an iterative process and before one specific technology is adopted for any project the complete iterative process must be completed. This being a technology driven exercise must be done by the executing agency/trenchless consultant and the most appropriate technology suiting the project requirements must be selected in accordance the stipulated guidelines.

Proposed utility route plan

Having selected the technology the next step would be to identify the proposed utility route plan. This route plan must not foul with the existing utilities. To achieve this, the Utility Owner must compare the plans with the layouts of existing utilities falling within the expected construction influence zone. It is natural that the final utility alignment may have to be altered during execution stage to meet unforeseen situations while project execution. It would therefore be imperative that the utility owner must prepare and record the final subsurface map detailing the new utility as well as the existing utilities. This mapping should be a three dimensional mapping of the stretch of work executed covering the entire construction influence zone with external coordinates clearly identified. This map would then be retained as the current map to be used in future works in the same patch.

Traffic management plan

Utility owner must prepare a traffic management plan on the basis of the technique selected and the above surface permanent or temporary works. The plan needs to be developed in line with the basic hazard mitigation process as identified earlier. A copy of this plan must be used for project execution.

Method statement

A method statement describing the proposed project execution and supervision methodology, material and worker management plan, and disposal of excavation, and construction wastes must be developed prior to embarking upon physical project execution activities. It helps in assessing the requirements of traffic diversion, deployment of supervision personnel and therefore its importance.

Third-party inspection

Trenchless being a state-of-the-art construction method, adopts several generic techniques in a single project. There are possibilities that certain trenchless projects may be using a combination of trenchless techniques. In such projects, the project execution and supervision methodology, material and worker management plan, or disposal of excavation, and construction wastes would become complex and might change with different projects. The owner department, or the right-of-way owners of such projects, may or may not be in a position to inspect all the works and the QA/QC of the project might become suspect. Third-party inspection is the most important tool to overcome this impediment in the way of project execution.

The way ahead

The Success of any trenchless project depends upon proper project planning, execution and conclusion activities. These critical inputs must be appropriately documented and recorded so that the responsibilities can be fixed and onus of damage, if any, can be properly placed. For the user organisation, the question would be: where does it start? The answer would be to access the technical information of trenchless technology. Indian Society for Trenchless Technology (IndSTT) has published several books and manuals for the use of industry stakeholders. In addition, it also conducts various training programmes ranging from very short term to research programs leading to doctoral degrees. Interested readers may consider contacting IndSTT for further details.

The author is Executive Director, Indian Society for Trenchless Technology. Email: indstt@indstt.com