What Does Control Parameter Mean?
Control parameters are factors that affect the selection of trenchless pipe installation methods. Trenchless construction techniques adopted for a particular project are determined based on many parameters including the latest geotechnical investigative reports, and existing records. This helps design the most suitable route with minimum cost and time overruns.
Trenchless construction projects such as horizontal directional drilling (HDD), horizontal auger boring (HAB) or microtunneling are carefully designed around specific parameters. These parameters include soil condition, presence of rock, variation in soil strata, and presence of existing utility structures, passing through the planned path.
Trenchlesspedia Explains Control Parameter
Control parameters become the controlling factor in the design of a route and selection of a method that is least obstructive and most economical. These parameters are determined based on an extensive geotechnical investigation that helps contractors to decide the most suitable method, rig, cutter head, or drill bit that will be required to carry out the project successfully. Some crucial control parameters include:
Every project has a unique site and soil conditions with regards to surface and subsurface conditions. The surface investigation is necessary to obtain information about the area, elevation, existing structures, borehole locations, and environmentally sensitive areas such as wetlands.
The subsurface investigation is carried out to gain information about the type of soil, depth of bedrock, water table, etc. Test pits, boreholes, ground-penetrating radar (GPR), etc. are used to obtain the same and it also includes data from previous site investigations and existing records.
Depth of Installation
Soil conditions largely dictate the depth of installation. For HDD projects, the maximum depth of excavation is recommended to be limited to 160 feet due to tracking system limitations and the absence of entry and exit shafts.
The risk involved in a project increases with an increase in the length of the installation. More driving force is needed due to the length of installation and complex soil conditions. The maximum driving force will depend on the capacity of the equipment, but the minimum drive length has to be economically justified because of the high costs of mobilizing and demobilizing equipment.
Pipe Diameter and Pipe Material
Pipe diameter is also an important parameter that controls the selection of a trenchless project. For example, HDD and HAB have a recommended diameter of 12 to 48 inches, while other methods such as pipe jacking, and microtunneling can be used to install larger diameter pipes.
The pipe material also is a necessary factor as pipes made of high-density polyethylene (HDPE), polyvinyl chloride (PVC) and vitrified clay pipe (VCP) cannot be used for methods like HAB, pipe jacking, and pipe ramming.
Type of Pipeline
HDD is limited to pressure pipe applications whereas microtunneling is limited to gravity applications. HAB and pipe jacking can be used for both pressure and gravity applications.
Launch and Retrieval Shafts
Entry and exit shafts are needed for all trenchless methods except HDD. The dimensions of these shafts will depend on factors such as equipment size, drive length, pipe length and diameter, thrust system, and spoil removal system.