MSE walls with structures: bridge bearings, columns, concentrated loads.

The two abutment philosophies

Bridge abutments are the most common case of MSE walls supporting structures. Two distinct philosophies exist:

True MSE abutment

The bridge bearings sit directly on a reinforced concrete ground beam (sometimes called a bearing shelf or bearing pedestal) cast at the top of the MSE wall. The bridge dead load (typically 50 to 200 kN per metre of bridge width per bearing) and live load (typically 20 to 100 kN per metre) transfer through the bearings, into the ground beam, and into the reinforced soil mass below.

The reinforced soil mass behaves as a wide composite footing distributing the bridge load over the foundation. The bottom-of-MSE bearing pressure increases above the value computed for embankment retention alone, but the wider footprint of the reinforced block means the increase is often manageable on competent foundations.

False abutment

A separate conventional pile-supported abutment carries the bridge bearings and the bridge structural load. The MSE wall is built in front of the piled abutment, retaining only the approach embankment fill and providing the architectural facing. The bridge structural load path is completely separate from the MSE wall.

This arrangement is more common in Malaysian practice for two reasons: (1) it separates the engineering risks (MSE settlement does not affect bridge bearings), and (2) it simplifies the design code path (MSE designer is separate from bridge designer).

Designing a true MSE abutment

Step 1: Define the bridge loading

From the bridge designer:

• Dead load reaction per bearing per metre of bridge width
• Live load reaction (peak vehicular plus pedestrian)
• Horizontal forces (brake, traction, wind, seismic)
• Settlement and rotation tolerances for the bearings (typically 25 mm vertical, 10 mm horizontal, 0.005 rad rotation)
• Bearing dimensions and bearing-shelf detailing requirements

Step 2: Design the ground beam

A reinforced concrete beam cast at the top of the MSE wall, supporting the bridge bearings on top and connected to the wall facing panels on the front. Typical dimensions: 800 to 1,500 mm wide, 600 to 1,000 mm deep, full bridge width long. Reinforced to BS 8110 / Eurocode 2 to span between MSE reinforcement positions or to act as a wide rigid load-distribution element.

Step 3: Increase the MSE wall design for the new loading

The bridge bearing load applies as a concentrated vertical line load on the ground beam. This load:

• Adds to the bearing pressure under the reinforced block
• Increases the lateral active earth pressure on the wall
• Increases the tensile load on the top reinforcement layers
• May add horizontal load from bridge brake or traction

The MSE wall design redoes external stability (sliding, overturning, bearing, global) and internal stability (tensile capacity, pullout) including the new loading.

Step 4: Settlement analysis

Critical check. Predict the total settlement at the bearing position under combined embankment and bridge loading. If predicted settlement exceeds bearing tolerance (25 mm typical), implement mitigation:

• Ground improvement below the MSE wall to reduce settlement (PVDs, stone columns, jet grouting)
• Pre-consolidation: build the embankment first, wait for primary consolidation, then install bearings
• Settlement-compensating bearings: bearings that can be re-shimmed during their service life

Step 5: Construction sequence

1. Build the MSE wall to design height per standard sequence
2. Cast the ground beam on top of the wall with appropriate reinforcement and bearing-shelf detailing
3. Wait for sufficient consolidation (3 to 12 months depending on foundation soil)
4. Install bridge bearings on the ground beam
5. Construct the bridge superstructure
6. Place finish surfacing and movement joints

Designing a false abutment

Simpler in concept: the piled abutment is designed independently to bridge design code (BS 5400 / Eurocode 2), and the MSE wall is designed independently to BS 8006 with no abutment loading. The interface between them needs detailing:

• Approach slab: a reinforced concrete slab spanning from the piled abutment to a point well behind the MSE wall, riding across the differential settlement between abutment (no settlement) and MSE wall (some settlement)
• Joint: a movement joint between the bridge deck and the approach slab to accommodate cyclical bridge expansion
• Facing: the MSE wall facing forms the visible face of the abutment area; the architectural treatment must integrate with the bridge structural elements behind

Building columns on MSE wall platforms

Township and commercial development platforms often have buildings constructed on the retained backfill above MSE walls. Building columns produce concentrated loads on the platform behind the wall.

Column loads as surcharge

A column load Q kN at distance x behind the wall produces a lateral pressure distribution on the wall via Boussinesq elastic-half-space stress propagation. For typical building columns (500 to 2,000 kN service load) at 5 to 15 m behind the wall, the lateral pressure addition is small (10 to 30 kPa peak) but acts at the column depth, which may concentrate on specific reinforcement layers.

Design approach

• Identify column positions and loads from the architectural / structural designer
• Calculate the Boussinesq lateral pressure distribution on the wall
• Add to standard active earth pressure as additional surcharge term
• Check internal stability of affected reinforcement layers
• If column is very close to the wall (within 0.7 H), consider providing additional reinforcement at the column-elevation level

Settlement check

Building column loads produce settlement that combines with embankment settlement. Building tolerance for column settlement is typically 25 to 50 mm differential between adjacent columns. The MSE wall foundation design must account for this.

Concentrated loads from industrial equipment

Gantry cranes on the platform

Gantry rail loads (typically 200 to 800 kN per crane wheel) at the rail position behind the wall. Similar Boussinesq analysis. May require local reinforcement enhancement at the rail depth.

Storage tanks and silos

Distributed area loads (often 50 to 200 kPa for liquid or granular storage). Treat as surcharge. May require widening the reinforced block at the loading position.

Heavy plant operations on the platform

Compaction equipment, haul trucks, mobile cranes. Transient loads typically 30 to 100 kPa contact pressure. Standard MSE wall designs include some live-load surcharge (typically 12 to 30 kPa) that absorbs normal site traffic. Heavy plant operations may require project-specific load assessment.

The AnchorSOL track record on structures

AnchorSOL has delivered numerous projects where the MSE wall supports structures:

• NKVE Jalan Meru Link abutments: PLUS Expressways, MSE bridge approach walls
• EKVE bridge abutment ramps: LLM concession, MSE walls supporting interchange bridge bearings
• DUKE Phase 2 bridge approaches: Ekovest, false abutment arrangement
• SUKE CA1 abutments: Prolintas, MSE walls at flyover ramp positions
• KL-Putrajaya Highway Packages 3 and 4 abutments: LLM / Maju Holdings
• KTMB sub-track bridge approaches at Sungai Buaya: cyclic-load supporting structure

For project-specific structural-load assessment, contact our engineering team.