Crusher run as MSE wall backfill: spec, performance, and why it works.

The core question

Every MSE wall specification asks the same question of the backfill: is the soil-reinforcement interaction reliable enough to design against?

The interaction is governed by two soil properties:

1. Internal friction angle (φ). The bigger the angle, the more shear resistance the soil mobilises against the wall's lateral pressure, and the more friction (or passive resistance, in anchored systems) the reinforcement develops.
2. Compactibility. The fill must reach a high relative density under realistic site equipment to deliver the design friction angle in service.

Premium granular fill (typical specs require ≥36° friction angle, narrow gradation envelope, low fines content) is the conservative answer. But for anchored MSE walls where the pullout resistance lives in a discrete deadman block rather than along the full reinforcement length, the friction-angle requirement relaxes to ≥34°, which crusher run meets routinely.

What is crusher run, exactly?

Crusher run is unwashed quarry product: granite, limestone, or igneous rock that has been mechanically crushed and screened to a maximum particle size (typically 19 mm, 20 mm, 25 mm, or 40 mm depending on the supplier). It contains a continuous gradation from the maximum particle size down to dust-sized fines.

In Malaysian quarries, the typical "crusher run" specification you'll receive on a delivery docket is one of:

• Type A (or "20 mm crusher run"): well-graded, max particle 20 mm, fines content typically 8 to 12%
• Type B (or "40 mm crusher run"): well-graded, max particle 40 mm, fines content typically 5 to 10%
• Aggregate base course (ABC): a tighter-graded crusher run sometimes specified for road sub-base, with stricter gradation envelope

For anchored MSE backfill, Type A or Type B both work. The choice depends on lift thickness and compaction equipment available on site.

The friction angle question

Quarry-fresh crusher run from Malaysian granite quarries typically delivers a friction angle of 36° to 42° in standard direct-shear or triaxial tests on well-compacted samples. This comfortably exceeds the 34° requirement for anchored MSE backfill, with margin.

The takeaway: crusher run delivers premium-fill friction angle at 30 to 50% of the cost. On a typical 10 m × 200 m wall with ~14,000 m³ of reinforced fill, that is a ~RM 700,000 to RM 1 million saving in backfill alone.

Gradation: what to specify

The specification you put in the tender document for an anchored MSE wall backfill should look like this:

The 75 µm fines limit is the most important QC check. Fines above 15% start to introduce clay-like behaviour, which reduces friction angle and pullout resistance.

Compaction: hand or mini-compactor only

One of the practical advantages of anchored MSE walls with crusher run is that you do not need a heavy roller inside the reinforced zone. The wall's structural performance depends on the deadman block, not on friction along the full bar length, so adequate compaction (95% MDD) of the immediately-surrounding fill is sufficient.

Typical compaction equipment for crusher run lifts behind the facing panels:

• Hand-operated plate compactor for the first 1 m behind the facing (avoids overstressing the panels and tendon connections)
• Walk-behind vibratory roller (1 to 2 tonne) for the bulk of the reinforced zone
• Mini-compactor or rammer in tight corners and around the deadman anchor blocks

The absence of heavy rollers is what makes anchored MSE walls suitable for sites adjacent to schools, hospitals, residential areas, or sensitive structures. See Capabilities →

Standards that recognise crusher run

For specifiers writing a tender, the references that authorise crusher run as MSE backfill are:

• BS 8006-1:2010, Annex A: Specifies acceptable fill characteristics for reinforced soil structures. Crusher run with the gradation above meets the "selected fill" definition.
• JKR Standard Specification for Roadworks (Section 2): Specifies crusher run for road sub-base. The same material is acceptable as MSE backfill when the friction angle is verified.
• FHWA NHI-10-024, Chapter 3: US Federal Highway Administration MSE design manual. Section 3.6 (Reinforced Backfill Specification) accepts well-graded granular fill with φ ≥34°.
• Eurocode 7 (BS EN 1997-1): Geotechnical design, general rules. Provides the analytical framework for friction-angle verification.

If your tender currently specifies "premium granular fill imported per Reinforced Earth specification", you can substitute crusher run by referencing BS 8006-1 Annex A and including the verification QC clauses above. AnchorSOL® can help draft the substitution language for tender submissions.

QC checks to require in the tender

To make crusher run substitution defensible to the supervising engineer, your tender should specify these checks at the rates indicated:

These checks are standard practice on Malaysian infrastructure projects and any reasonable supervising engineer will accept them as adequate QC.

When NOT to use crusher run

Crusher run is the right backfill for the vast majority of anchored MSE walls, but there are cases where premium granular is justified:

• Bridge abutments with strict deformation tolerance. Where wall deformation during bridge construction must be tightly controlled (less than 25 mm at the bearing seat, for example), premium graded fill with tighter compaction gives more predictable performance.
• Highly variable quarry supply. If the only available local quarry has inconsistent gradation between batches, the QC overhead may exceed the cost saving.
• Coastal sites with saline groundwater. Salt-laden water can accelerate corrosion of the reinforcement. Specifying lower-fines fill plus a more conservative sacrificial-thickness allowance is appropriate.
• Walls above 25 m. Some very tall MSE walls justify premium fill for the lower courses where lateral pressure is highest. Crusher run remains adequate for upper courses.

Bottom line

For 90% of anchored MSE walls in Malaysia, crusher run is the correct backfill choice. It meets the friction angle requirement, it is locally available, it is roughly half the cost of premium imported fill, and it is recognised in the relevant standards (BS 8006, JKR, FHWA). The cost saving on a typical infrastructure-scale wall runs into hundreds of thousands of ringgit.

Tell us your project details and we will scope the backfill spec with you: Send brief on WhatsApp →