What Does Spoil Mean?
Spoil or muck in the context of trenchless construction is the slurry of soil and broken rock fragments or drill cuttings produced as a result of the drilling process. Trenchless construction utilizes heavy machinery like rigs for Horizontal Directional Drilling (HDD), tunnel boring machines (TBM) for microtunneling, and augers for Horizontal Auger Boring (HAB). These methods excavate under the earth’s surface and the excavated material has to be brought back up to the surface. This excavated material is in the form of a slurry and is removed using a spoil removal system.
Trenchlesspedia Explains Spoil
Trenchless construction methods produce spoil or muck, that needs to be disposed of properly. If the muck is known to contain harmful constituents, care has to be taken to ensure that the spoil is disposed of away from inhabited areas and environmentally sensitive locations. Trenchless methods usually employ the use of bentonite slurry to stabilize the soil while lubricating the cutting tools and preventing spoil from sticking to the casing. The spoil generated from the construction process is passed out from the back as the machine advances. Once the spoil is out appropriate methods have to be employed for proper disposal.
Spoil Removal in Various Trenchless Techniques
HDD - Water jets are used to eliminate spoils from the borehole.
Horizontal auger boring (HAB) - the spoil is brought back to the drive shaft with the help of helically wound augers that rotate in a steel casing.
Pipe jacking - The spoil is removed physically by personnel inside the pipe who perform excavation either manually or by mechanical means.
Microtunneling - This method uses a slurry removal system. The pipe is installed simultaneously as the spoil is excavated.
When the spoil is removed from the borehole, it is necessary to remove the solids present in the slurry. The first step of the solids control system is to remove as many of the large cuttings as possible without impacting the commercial drilling fluid solids. This can only be done if the solids control equipment is properly designed and installed, and sized to process 100 to 125 percent of the mud circulation rate.
Before the final disposal of the used drilling fluid, the waste mud has to be relieved of its toxicity and reduced in volume. The options for treatment and disposal depend on the characteristics of the waste and the regulatory requirements. Some of the ways to treat and dispose of drilling waste are onsite burial, land farming, incineration, thermal desorption, deep-well injection, and vermiculture.