GROUTING
Grouting is often attempted as a means of controlling seepage through soluble rocks. However,
this method frequently is not successful or is only temporarily successful because the solution
passages usually are partially filled with residual clay or other material that erodes when
subjected to changed seepage forces. If one passage is plugged with grout, the seepage often
finds another passage around the plug. Therefore, more aggressive methods may be required
to ensure permanent and reliable seepage control in soluble rock. These seepage control
methods require careful analysis on a case-by-case basis. In current practice, more use is
being made of positive remedies such as concrete cutoff walls at the dam centerline.
Pressure grouting using a mixture of cement and water or other materials is probably the most
frequently used method to remedy serious foundation or abutment seepage problems in rock.
However, it should not be used indiscriminately. Before any grouting effort, conduct an
investigation to determine the seepage conditions and locations. The investigation may include:
• Installing weirs or flumes to measure seepage quantity and monitor any particle movement.
• Drilling and sampling to determine rock type and joint and crack size and orientation.
• Conducting pump tests or pressure tests in drill holes to provide data on permeability, flow
quantities, and lateral extent.
• Installing and monitoring piezometers or observation wells to measure water levels and
pressures.
• Putting tracer dyes in the reservoir or drill holes to pinpoint locations of seepage.
• Using geophysical-type tests to determine material properties and flow patterns.
• Conducting a pilot grouting program to determine eventual grout quantities, mixes,
pressures, and set times.
If grouting is feasible, the investigation will help to determine the type of grout mix best suited
for the site. The type of grout may consist of solids suspended in water such as cement,
bentonite, or chemical grouts.
Because of limitations of cement grouts to penetrate small joints or cracks and mediumgrained
to fine-grained soils, micro-fine cement or chemical grouts may be considered, although
they are quite expensive. When using cement grout, the chemical composition of seepage
water and its effect on the type of cement used must be considered. For example, sulfateladen
water will attack ordinary cement and the grout curtain will deteriorate.
There are many different types of chemical grouts. Choose the type of grout based on
characteristics of the material being grouted, such as permeability, void size, continuity of voids,
and the overall effect on the environment.