Renovations, repairs, or redecoration of existing buildings often involves drilling holes in floors, walls, or ceilings.  These coreholes may be small and shallow (e.g. for hanger bolts) or large and through-going (e.g. for plumbing, electrical, signal, or HVAC lines).  Whether to preserve safety, structural integrity, or simply drilling ease, it is desirable and sometimes essential to position holes to avoid reinforcing bars (rebar), electrical, fire alarm, or signal cables, and especially post-tensioning (PT) cables.

Enviroscan has provided clearance for literally thousands of coreholes using state-of-the-art magnetic, electromagnetic (EM), sonic/acoustic, subsurface interface radar (SIR) and live line detector techniques to detect and mark electric conduits, rebar, PT, fire alarm wires, and other obstructions in the vicinity of proposed drilling or coreholes. The use of multiple techniques at every location ensures detection of both metallic and nonmetallic targets. Note that SIR is the same technology as ground penetrating radar or (GPR), but it is applied to walls, floors and structures rather than the ground.

At each corehole, rebar, PT, conduits, and other obstructions are marked on the slab using color-coded paint, chalk, grease pencil, or tape.  The clearance zone diameter surrounding each borehole or excavation location can be specified by the client to allow for adjustment of the hole location based on drill rig or machinery access or other concerns.  Usually, field markings are all that is required. However, Enviroscan is also capable of providing highly accurate surveying of markings.  The survey data is used to make overlays for computer aided design and drafting (CAD) systems.

Advanced SIR techniques now allow 3-D imaging of the interiors of walls or floor to provide footprints, depths, and dimensions of obstructions.  As described in the table below, the SIR method (particularly in combination with EM) is greatly preferred over X-ray techniques since the SIR signal is harmless and does not require an exclusion zone or special permitting.  In addition, the SIR images provide depth information not typically available from X-ray images, and do not require access to both sides of the wall or floor to be scanned, and provide immediate results onsite. Click here to view an example 3-D SIR image.

Comparison of 3-D SIR and EM with Radiography (X-ray) X-ray SIR EM Required Access BOTH SIDES ONE SIDE ONLY ONE SIDE ONLY Radiation Hazard HIGH NONE NONE Permits or Licenses REQUIRED NEGLIGIBLE NONE Setup Time LONG SHORT NONE Data Collection SLOW MODERATE RAPID Data Storage FILM DIGITAL FIELD MARKINGS Immediate Results NONE COMPLETE COMPLETE X-Y Target Location HIGHLY ACCURATE HIGHLY ACCURATE HIGHLY ACCURATE Z Target Location NONE HIGHLY ACCURATE NONE Target Discrimination NO NO SOMETIMES Live Line Detection NO NO YES 100% Guaranteed NO NO NO

Other applications of the 3-D SIR technique include detection and imaging of voids in or behind concrete and masonry structures (e.g. ungrouted cells in cinder blocks or bridged voids in poured concrete), concealed bugging devices, hidden evidence (e.g. weapons, bodies, etc. in or under concrete or soil), and suspected unexploded ordnance (UXO).