Effects of Ground Water on Blasting Operations

Ideally, every blaster would prefer that all boreholes be dry. However, this is seldom the case. Water in a borehole creates problems in that it limits the explosive products that can be used. Explosive products that float or are not water resistant will interfere with blasting operations where water can be expected in the blasting boreholes. Where the blaster uses low water resistance explosives, the boreholes must be dewatered before loading and protected from water reentry. Even small amounts of water can degrade most ANFO products. The blastholes may be loaded with water resistant ANFO or can be redesigned and loaded with pumped bulk emulsion. Water resistant cartridged explosives could also be used but will increase costs.

Where excavations are deep or underground, entire dewatering systems may need to be set up and protected during blasting operations. The need for site dewatering should be addressed during the site characterization and should be included in the plans and specifications. As of 2015, the most common way of dealing with dewatering at a site is to require a contractor to assess the dewatering necessary and propose a plan to USACE personnel in the form of a submittal. This method has certainly been used with great success on many projects. However, the need for dewatering and the extent of the dewatering expected should also be quantified to the extent possible during the design process and the information gathered communicated to the contractor. Inclusion of measurement and payment and separate contract line item numbers (CLINs) for dewatering should be very carefully formulated as they have resulted in excessive and unnecessary costs on some projects.

Pre-blast well surveys are often needed where wells are used for water supply near a blasting site. These are usually conducted by the contractor before blasting, but well surveys completed before construction can give the geologist or engineer a good idea of the surrounding groundwater conditions. Where artesian conditions are expected, this information should be communicated to the contractor in the plans and specifications.