Jet Grouting

The most versatile of all ground improvement methods, grouting has long played a significant remedial role in ground improvement. Over the years, the introduction of new grouting technologies, refinement of established techniques, and the development of more sophisticated equipment have expanded that role to include site improvement for new construction. Moretrench’s expertise includes permeation, compaction, fracture and compensation, rock curtain, jet, and structural seepage grouting.  This wide range of techniques allows the company to offer the optimum solution for the problem at hand.

Compensation Grouting

Permeation Grouting

Permeation grouting is typically defined as the flow of a low-viscosity grout (sodium silicate, microfine cement, acrylate or polyurethane) into the pores of the soil without displacing or changing the soil structure. The characteristics of the ground are modified with the hardening or gelling of the grout. Depending on the requirements of the project, grout materials can be temporary or permanent.

Permeation grouting may serve two purposes: to increase the strength and cohesion of granular soils, or to decrease the permeability of the soil and provide “watertightening.” Primary applications include:

  • Soil stabilization for excavation support
  • Utility and footing support
  • Increasing stand-up time to facilitate soft ground tunneling
  • Water cut-off
  • Exclusion or in situ containment of contamination on environmental projects
  • Closure of windows or gaps in "bathtub" excavations
  • Sealing off of high permeability backfill
PCS Phosphates, White Springs, FL:  Low mobility grouting to seal the throat of a phosphogypsum stack sinkhole measuring approximately 300 feet in surface diameter.

Compaction Grouting

Compaction or low mobility grouting involves injecting the in situ soil with a relatively stiff, low slump grout under pressure. The grout does not permeate the soil matrix but rather forms a bulbous cement mass. Strategically placed grout bulb “columns” within the target soil zone displace and densify the surrounding soil. Compaction grouting is commonly used for:

  • Increasing bearing capacity
  • Arresting or reducing foundation settlements
  • Mitigation of liquefaction potential
  • Sinkhole pretreatment or remediation or stabilization of karstic formations
North Shore Connector, Pittsburgh, PA: Installation of grout pipes for compensation grouting between a building footprint and underlying soft ground tunneling.

Fracture and Compensation GroutIng

Fracture (or claquage) grouting is the intentional fracturing of the ground by high-pressure injection of cement-based grout through sleeve port pipes to form intertwined lenses or veins of grout in order to provide reinforcement and even some consolidation of the soil.  Grouting is typically performed in several phases, with repeat injections at each port to ensure the formation of multiple fractures through the soil.

When performed concurrently with underground construction such as soft ground tunneling, fracture grouting of the soils between the tunnel and overlying structures has the specific design intent of providing a controlled ground heave to compensate for potential structural settlement. Such an application of fracture grouting is referred to as compensation grouting.

Watres Dam, Spring Brook, PA: Injection of a balanced stable cement-based grout through a single line of grout holes to reduce the permeability of the weathered rock upstream of the dam spillway and eliminate leakage potential prior to spillway expansion.

Rock Curtain Grouting

Rock curtain grouting is the filling of fractures and fissures in rock to reduce permeability, strengthen or stabilize the rock, or both. The grout curtain is constructed by the drilling and grouting of closely-spaced drill holes oriented to optimize the intersection of rock joints.

The most common application is to reduce water seepage and pressure beneath a dam or other structure. Other applications include:

  • Control of seepage beneath a cut-off wall for "bathtub" excavations
  • Pretreatment of permeable rock masses
  • Control of seepage under a frozen cut-off wall
  • Grouting of a water bearing zone to minimize the quantity of water to be handled within a shaft excavation
Consolidated Edison-Harlem River Tunnel, New York, NY: Jet grouting techniques to displace infill material in defective secant piles and weathered rock features to prevent further ground inflow into a shaft excavation.

Jet Grouting

Jet Grouting uses high-pressure, high-velocity jets to hydraulically erode, mix and partially replace the in situ soil or weak rock with cementitious grout slurry to create an engineered soil-cement product of high strength and low permeability. Jet grouting can be performed above or below the water table and in most subsurface stratigraphies from cohesionless soils to highly plastic clays.

The three basic systems in general use are single-fluid, double-fluid and triple-fluid jet grouting. Selection of the most appropriate system is dependent on the in situ soil characteristics and the application.

Jet grouting has a number of construction-related applications, including:

  • Structural underpinning
  • Groundwater control or cut-off
  • Utility support
  • Excavation support
  • Temporary or permanent soft soil stabilization
  • Slope stabilization
  • Hazardous waste containment
World Trade Center, Manhattan, NY: Urethane grouting to seal groundwater flow paths through the damaged “bathtub” foundation.

Structural Seepage Grouting

Structural seepage grouting is the sealing off of flowpaths by grouting directly into defects (cracks, joints or open separation) in the floors, walls or roof of a structure. Since the work is typically accomplished under flowing water conditions, quick-acting water-reactive polyurethane grouts are commonly used. Cement-based materials and epoxies can be utilized in less difficult situations. Candidates for permanent structural seepage grouting include basements and underground chambers. Temporary earth support candidates may include slurry walls, steel sheeting, or mud slabs.

Fracture Grouting

Hot Bitumen Grouting

Hot bitumen grouting is the injection of a very fluid bitumen grout to plug high-volume water flow paths through rock formations. As the bitumen comes into contact with water it loses heat, rapidly becoming extremely viscous and resistant to washout. Injections are repeated until full closure of the flow path is achieved.  Candidates for hot bitumen grouting are quarries and dams.