Sinkhole Remediation

Our work entails the monitoring of the remediation and reporting on the field work.  The two basic types of remediation include compaction grouting and underpinning.

GROUTING 

Compaction grouting is the process of placing grout (lean cement) into a drilled hole to a specified depth.  This borehole may be angled or vertical.  In our reports, a site plan is provided which details the locations of the grout or injection points.  These are laid out on an 8-foot spacing.  The points are generally laid out as vertical and angled.  The report also states an approximate depth of drilling for the injection points.  The foundation repair contractor is not to drill below the maximum depth recommended without our approval.

After mobilizing to the site, the contractor lays out the points and sets up the drilling rig.  The points are drilled to the anticipated depth.  Concrete trucks deliver the grout and it is pumped into the boreholes.  The grout specified has a maximum slump of 4 inches measured at the truck.  The grout is then placed by pumping into the boreholes.  Our personnel, for each five-foot increment, record the amount of grout placed in each borehole.  A record of the total amount of grout used in each borehole is made.  There is a limiting factor of no more than 10 cubic yards may be placed in any one five-foot interval.  Upon completion of the grouting operation, the contractor cleans up the site and leaves.  Our report then details the grouting operation, quantities used and depths drilled.  A registered professional engineer completes the report and signs and seals it.

UNDERPINNING

Underpinning of the structure comprises a similar setup in the field.  The site plan indicates the locations of the underpins, usually located on a six foot spacing.  The report also states an approximate depth of drilling for the underpins.  The foundation repair contractor is not to drill below the maximum depth recommended without our approval.  The underpins are placed by inserting the point into the soil and “pushing” it through.  The interlocking steel underpin is hydraulically advanced by use of a cylinder drive assembly.  The drive utilizes hydraulic pressure and the building structure as a counterweight for seating the underpin.  Each underpin is individually driven with the depth and pressure recorded for each depth interval.  At each location, the underpin is advanced until a maximum hydraulic pressure of 5000 psi is achieved or the structure begins to lift.

After each individual underpin has been successfully load tested to establish a minimum load bearing capacity, a lift of the structure is achieved. The underpins and jacking assemblies are tightened against the existing foundation and secured into place.  Then, by controlling the pressure to individual pins, the entire wall is lifted simultaneously to as close to its original elevation as the structure will allow. 

Each underpin is used to raise the house approximately 1/2 inch, as needed to level and/or close cracks. After verifying all elevations during and after the lifting process with a survey instrument, and completing any adjustments, the underpin and bracket assemblies are bolted together, the hydraulic lift unit removed, and the entire work area is then backfilled and the site cleaned up.

CHEMICAL GROUTING

Another facet of compaction grouting is chemical grouting.  This is what is used when there is light loads, such as pool decks and porches.  The chemical grouting is set up similar to compaction grouting.  The point layout is indicated within the subsidence investigation report.  The contractor lays out the points, as indicated, and proceeds to set the casing.  In most cases, the depth of the point is generally approximately 10 feet below ground.  This is the material which is not normally grouted during the compaction grouting operations.

The ½ inch diameter steel pins are used and are hydraulically driven into the soils to the specified depth.  The material is generally mixed on site and then pumped at a low pressure into the steel pins.  The quantity of material used at each location is then recorded by Madrid personnel.  A report is issued which details the procedure of the operation and quantities used at each point