How to Install Grouted Mattress: Contractor Guide

Grouted mattress installation follows five steps: prepare the subgrade to the specified profile, place and secure fabric panels (top-down on slopes), mix grout to the project specification, inject from the lowest point upward until each panel is full, and cure the filled panels as the specification requires. Tolerances, mix, rates and curing periods come from the project specification and the method statement, not from a general guide.

Grouted mattress is not a complex system, but installation quality determines performance. Common field problems trace to three mistakes: grout that is too wet and loses strength, injection from the wrong point so air is trapped, and inadequate curing so the surface dries before the grout has gained strength. This guide covers the steps and flags the common errors at each stage.

This guide is for contractors installing grouted mattress on canal lining, slope protection, river bank and coastal revetment projects. For the hydraulic design basis, see Articulated Concrete Mattress: Technical Guide. For specific application guidance, see Canal Lining or Slope Protection.

Equipment Required

Step 1: Subgrade Preparation

This is the most important step, because inadequate preparation is a frequent cause of poor installation quality. Requirements come from the project specification, and generally cover the following.

• Profile tolerance: trim the slope or canal invert to the design profile within the tolerance in the specification. Humps can make the mattress bridge across, leaving an unsupported void that may crack under load.
• Remove all vegetation: grass, roots and organic matter decompose under the mattress and create voids.
• Compact: to the degree of compaction the geotechnical specification sets. Loose fill consolidates after grouting and lets the mattress sag into voids.
• Moisture condition: the subgrade should be moist but not saturated or muddy. A saturated subgrade creates water channels that can dilute the grout at the interface. A very dry subgrade draws water from fresh grout, so it is usually dampened beforehand.
• Geotextile separator (where required): on soft or gap-graded soils susceptible to piping, the geotechnical engineer may specify a separator under the mattress. The filter design decides this.

Step 2: Panel Placement

Panel placement sequence for slopes, working from the crest downward:

1. Position the roll at the top of the slope. The injection nozzles should be at the downslope end of the panel.
2. Unroll the panel down the slope. Do not drag it, because dragging damages the fabric.
3. Secure the top of the panel with anchors at the spacing and depth the design gives.
4. Position the adjacent panel with the overlap or joint the specification gives. The upslope panel goes on top (shingle lap), so that water passes over the joint, not under it.
5. Where longitudinal panel joints are needed, follow the same rule with the upflow panel on top.
6. At the bottom of the slope, terminate the mattress in a prepared toe trench or onto the flat invert, as designed.

Common mistake: rolling the panel with the injection nozzles at the upslope end. Grout then has to travel uphill from the nozzle, fills unevenly, and air is trapped at the upslope end. Inject from the bottom of each panel upward.

Step 3: Grout

The grout is a fine-aggregate cement grout. Its mix proportions, water-cement ratio, workability test and required strength belong to the project specification and the supplier's instructions. GRI GT16 is a manufacturing quality control specification for the geotextile fabric and does not set the grout mix or grout strength.

• Mix as specified. Use a mixer that gives full shear for fine grout, and follow the mixing time the specification gives.
• Control the water. Extra water raises flow but lowers strength. Solve workability problems with an admixture approved in the specification, not with more water.
• Cement type. Marine or sulfate exposure may need a different cement. The engineer sets this.
• Test. Grout strength is checked on cylinders to the project's test standard (for example ASTM C39) at the frequency the specification sets.

Most common mistake: adding water on site to improve flow. It reduces strength, and the loss may not show until cylinder results come back.

Step 4: Grout Injection

1. Connect the pump hose to the injection nozzle at the base (downslope end) of the first panel.
2. Start pumping at a controlled rate set by the method statement, and watch the panel inflate.
3. Watch for even inflation across the panel width. If one side inflates faster, reposition the nozzle toward the slow side.
4. Move the nozzle upward along the panel as the bottom cells fill.
5. The panel is full when grout reaches the top edge, as the manufacturer's instructions describe. Stop pumping, because overfilling increases the risk of seam damage.
6. Connect to the next panel and repeat. Work across the slope in rows, completing each row before starting the next.

Common mistake: starting injection at the top of a slope panel. Grout flows to the bottom under gravity, the bottom cells fill first, and a cold joint can form where the injection point later reaches material that has already started to set. Start at the bottom.

Step 5: Curing

Curing is the step most often cut short on site, and poor curing is a common reason for low strength results. General practice:

• Apply covers or curing compound immediately after each panel is filled, not at the end of the shift.
• Keep the surface moist for the curing period the specification gives.
• Hot or windy weather: increase misting and shade the work where possible.
• Cold weather: protect fresh grout from freezing, using measures the method statement sets.
• Test samples: cast and test grout samples as the project specification requires, and keep records with the panel locations.

Common Installation Mistakes and How to Avoid Them

Standards: GRI GT16 (Geosynthetic Research Institute) is the manufacturing quality control specification for the fabric. It does not cover installation or grout strength, which come from the project specification. ASTM C39 is the standard test method for compressive strength of cylindrical concrete specimens.

Before installation, see our grouted mattress specification guide and our ACM technical guide for product selection.

When This Installation Guide Does Not Apply

This guide describes a general sequence for placing and filling grouted mattress on prepared ground. It does not apply where a project specification or method statement sets a different sequence, and it is not a substitute for either. Work under water, wave-exposed faces, unstable slopes and sites with active seepage or artesian water need a method written for those conditions, usually with the designer and the geotechnical engineer involved. Other lining systems, such as geomembranes, turf reinforcement mats or cast-in-place concrete, follow different procedures.

This guide also cannot set grout strength, tolerances, anchor layout, overlaps, pump settings, weather limits or curing requirements. Those belong to the project designer, the specification and the supplier's instructions for the panels delivered. If the written method and this article disagree, follow the method and ask the designer to resolve the difference.

Before You Order Panels for Installation

Installation goes more smoothly when panels arrive sized to the work face. Stock sizes dispatch in 3 to 5 days, and custom-size panels take 5 to 7 working days to produce, so a site with irregular geometry should confirm panel sizes and nozzle positions early rather than at mobilization. Thickness runs from 75 to 200 mm and follows the design velocity: 2.5 m/s for 75 mm, 3.5 m/s for 100 mm, 4.5 m/s for 150 mm and 6.0 m/s for 200 mm. Panels are made at the factory in Inner Mongolia, China.

To get a quote and a sensible panel layout, send the design velocity, area, location and drawings through the contact page, and mention the slope length, the pump access and whether any work is under water. Pricing is by project. The engineering team replies within 48 hours.

Sources and Further Reading

Open each document to confirm its current edition and scope before you rely on it.

• GRI GT16: The manufacturing quality control specification for the geotextile fabric used in grout-filled mattress. Checked 2026-10-24 (link and title).
• Geosynthetic Institute specifications index: Index of GRI test and specification documents. Checked 2026-10-24 (link and title).
• ASTM geotechnical engineering standards: Catalogue page for ASTM geotechnical standards. Checked 2026-10-24 (link and title).
• CEN EN 13254, geotextiles for reservoirs and dams: European standard for geotextile characteristics in reservoirs and dams. Checked 2026-10-24 (link and title).

Frequently Asked Questions

What pump pressure is required for grouted mattress installation?

Pressure depends on mattress thickness, grout, and the length and height of the pump run, so no single figure applies. Stay within the pump and hose rating, and do not modify the injection arrangement supplied with the panels. If pressure rises beyond the equipment rating, stop and check for a blockage in the panel or injection line.

How much area can one crew install per day?

There is no fixed figure. Output depends on pump capacity, slope, access, the grout supply and crew organization, and it is normally lower on steep slopes than on flat surfaces. The contractor's method statement sets the planned rate for the site, and a trial section is a reliable way to confirm it before programming the full works.

Can installation continue in rain?

Rain can dilute grout at the panel face and make curing covers ineffective once saturated. The project specification or method statement should state the weather limits for placing. Panels placed in heavy rain should be inspected, and strength test results reviewed before the work is accepted.

Send your project conditions, area, location and drawings to our engineering team. They will reply within 48 hours. Contact the engineering team before mobilization, or view the specification sheet.