Definition - What does Spoil mean?
Spoil or muck in context of trenchless construction can be defined as waste material like earth and rock that is excavated during the tunneling process. Trenchless construction utilizes machinery like Horizontal Directional Drilling (HDD), Micro-tunnel Boring machine (MTBM), Horizontal Auger Boring (HAB), Moling, etc. All of these methods involve drilling horizontally under the earth's surface while replacing the borehole with the required pipe.
Trenchlesspedia explains Spoil
Trenchless Methods of laying pipelines has helped prevent problems associated with open excavation methods. However; both methods produce spoil or muck, which needs to be disposed of properly. If the spoil is known to contain harmful constituents, care has to be taken to ensure disposal is done away from areas inhabited by humans or wildlife. 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 is passed out from the back as the machine advances. For example, in HDD, water jets are used to eliminate spoil from the borehole, and in HAB, augers rotate and remove the spoil from the casing. Once the spoil is out appropriate methods have to employed for proper disposal.