Microtunneling & Pipe Jacking Good Practices Guidelines
Overview of Trenchless Technology for New Installations
In this section we shall be discussing Overview of Trenchless Technique for New Installations. Trenchless, as the name goes, is the method to construct an underground network without excavating continuous trenches. The networks can be of two types:
1. Allowing man entry &
2. Not allowing man entry.
Horizontal Directional Drilling falls under non man entry type i.e. where the excavation or drilling is conducted without sending a man underground. The technique is quite powerful and versatile for laying underground networks and crossing geological or man made barriers without disturbing the aboveground structures. This section deals with the introduction of various techniques generally employed to develop subsurface utilities. for more details
Techniques and theory of Microtunneling Operations
Introduction to Microtunneling and its role in underground construction
Creation of new as well as rehabilitation or removal of older subsurface networks entails removal of subsurface soil mass, present naturally or otherwise, from the network locations to permit placement of network components (generally pipe segments). Such spoil removals coupled with simultaneous component placements without excavating continuous trenches is the basis of pipe jacking technique. The technique works on the principle of soil excavation & spoil removals either of the following ways:
1. Mechanical excavations along with spoil removal by augur trains or;
2. Slurry assisted excavations and spoil transportations or;
3. Earth Pressure Balance excavations along with hydraulic mucking. for more details
Parameters affecting- work at a site
Summary of parameters affecting the microtunneling
There are various factors impacting subsurface drilling projects. Any professional prior to getting engaged in the activities of Microtunneling needs to be aware of such factors and their possible effects over the entire project.
One should also realize that a designer has to optimize the project with regards to the available time & funds and the checks therefore have to be prioritized so that no excesses occur either on the fronts of time or funds.
The primary aims of this chapter are to raise awareness of the many practical details which need to be given careful consideration if microtunneling is to be successfully carried out (See box).for more details
Guidelines for Geotechnical Investigations
A properly planned and well executed geotechnical investigation program prior to construction will provide a firm basis for design and the preparation of contract documents, and will also reduce the risk of encountering "differing site conditions." Subsurface conditions are extremely important in assessing the feasibility of microtunneling methods, comparing alternative pipeline alignments, and for determining appropriate microtunneling equipment and construction methods. The goal of the geotechnical investigation program is to develop an accurate understanding of the subsurface conditions and the physical properties of the materials that will be encountered during microtunneling and shaft construction. This information is critical for planning and constructing a successful and cost effective microtunneling project and for avoiding problems during construction.
Subsurface information is of utmost importance for contractors and engineers working on Horizontal Drilling projects so that future projects proceed as planned. The explorations prior to horizontal drilling projects are considered here in a broad sense: they include collection of geological, hydrogeological and geotechnical data, as well as hidden natural or artificial obstacles, which can interfere with the drill path.for more details
Guidelines for the choice of machines and attachments
Till now we have discussed the various methods to develop new subsurface networks, basics of Microtunneling, factors impacting Microtunneling Projects & Geotechnical investigations. In this chapter we shall be dealing with the guidelines on equipment selection.
In the course of operations the boring machines perform the following main functions:
Guidelines for project design, dimensions of pipes
and the pipe jacking system
Project design is the process to evaluate and workout the most optimum operational system including the sizing of various inputs so that a successful MT project is conducted.
The operation involves activities like project planning, casing / jacking pipe design, shaft designs, working stress analysis & selection, bore fluid design and other related activities. Through this chapter we are discussing all such issues.
Project design operations start with the basic or empirical project planning where the basic or key design criteria are identified. Key design criteria for a microtunneling project must include at least the following:
· Alignment Considerations;
· Cover Requirements;
· Design Grade;
· Produce Pipe Requirements;
· Casing Requirements;
· Line-and-Grade Tolerances;
· Environmental and Regulatory Considerations.for more details
Guidelines for the site supervision
Till now we have been discussing the issues related to planning, design, and equipment selection for MT projects. Now comes the issue of transferring the materials from the drawing boards to the real ground i.e. Project execution. We are dealing these issues in this chapter.
Construction Monitoring Approach
During construction, it is very important to monitor the progress of the work, and to document the subsurface conditions encountered. Construction monitoring requires careful attention and responsiveness by the field inspectors and the construction manager. Once the pipe or casing is pushed into the ground it is not possible to change its position even if the problem is the result of the contractor's installation procedures. Therefore, timely monitoring as construction proceeds is important so that, owner / construction manager and contractor both are aware of potential problems as they develop and, can make changes to correct the problems before it is too late. This section focuses on the important construction monitoring requirements relative to microtunneling including: job site safety, preconstruction surveys, pipe materials testing, microtunneling operations, and instrumentation provisions.for more details
Economics and Contractual Aspects of MT & PJ Projects
Application of Microtunneling techniques to jack pipelines helps avoiding open cuts for developing networks in difficult geographical settings like crossing water bodies, environmentally sensitive zones, coastal areas etc. Working costs naturally will have to cover expenses to overcome such difficulties apart from the direct costs. That is, it will have to cover the actual input costs and the costs to overcome these difficulties. When one is comparing the costs of a project done by open cut method to that of a trenchless method economics does play a vital role. An open cut process may be economical when evaluated on the basis of direct costs to the project but the same may not be the case when all the costs, i.e. direct and indirect costs, are accounted for. The process however is like comparing apples to grapes. But the project working, at times, justifies such comparisons. At times when a subsurface network has to pass a natural or manmade barrier, trenchless techniques do provide cost effective solutions in some cases. Another issue is the contractual aspects of MT and PJ projects. Such projects being of specific and tailor made nature require special attention on contractual matters. This chapter deals with such economics and contractual matters.for more details