Foundation grouting or curtain grouting is often used in the construction of dam. It is carried out at the centre core of crest below the foundation level of crest at the initial stage before the formation of the foundation of dam. The main reason to carry out fissure grouting is to strengthen fissured rock or to reduce the permeability of fissured rock or to grout between rock and concrete lining where no large void exists.

 

Foundation grouting in carried out in stages using thin grout mix. The base of crest is drilled with multiple numbers of holes setting out in series of rows. Depending on the actual depth of fissures rock, each drilled hole will be grouted to specific pressure (usually to withstand the top water level of dam). Upon completion of drilling to a specified depth, packer will be attached to the end of the grout supply pipe before grouting. Once the grout is set i.e. after 24 hours the grouted holes will be bored through and continued with the second stage of grouting. The next stage shall then be grouted at the required pressure allowing the packer to remain in place until there is no back pressure. Upon completion, the grout supply pipe and packer will be withdrawn and drilling for the next stage will follow. The process of drilling, sealing off the previous grouted hole with packer followed by grouting will continue until the specified grout hole meets the closure test.

 

The second type of grouting that is known as contact grouting is carried out after the foundation grouting. The main purpose of Contact grouting is carried out is to seal the contact between the core of embankment and the foundation. One of the important procedures that shall be considered before carrying out any contact grouting is to ensure the thickness of centre core fill is attained a minimum depth before any grouting.

 

Contact grouting is carried out through 80 mm diameter sleeve-grouted PVC pipes installed through the clay core fill terminating about 300 mm above the core/foundation contact surface. Each drilled hole of diameter 76mm shall be extended to about 1000 mm below the core/foundation contact after the installation of the PVC pipe, and grout shall be injected through a packer set inside the bottom of the PVC pipe.