What is a Shored MSE hybrid wall?

A Shored MSE hybrid wall, abbreviated SMSE, is a composite retaining structure combining a soil-nailed (or anchored) cut-face shoring system with a conventional MSE wall built in front of the shoring. The MSE wall provides the visible architectural facing and short-length reinforcement into the fill; the shoring provides the stability of the deep cut behind. The two systems work as a composite, sharing load through their interface zone.

When is SMSE preferred over standard MSE?

SMSE is preferred when the design requires an MSE-faced wall but the standard MSE reinforcement length (0.7 H minimum) cannot be achieved. This occurs on tight-cut sites where competent rock or stiff in-situ ground sits close behind the planned wall face, on sites with right-of-way constraints preventing full reinforcement reach, and on tall walls where the standard reinforcement length would be uneconomic. Anchored MSE (AnchorSOL) is an alternative that achieves shorter effective length without the shoring system.

What standards govern SMSE design?

The primary reference is FHWA NHI-09-087 (2009), Shored Mechanically Stabilized Earth Walls: Design Manual. Supporting references include FHWA NHI-10-024 for the MSE component, FHWA NHI-14-007 for the soil-nail component, and BS 8006-1:2010 for general reinforced soil principles. Project-specific design typically requires checks against all four standards plus a global stability analysis that includes both shoring and MSE elements.

Wall-type deep dive

Shored MSE hybrid wall (SMSE): when standard MSE cannot reach.

The standard MSE wall design requires reinforcement length of at least 0.7 times wall height. When that reach is not available, for instance on a cut into competent rock or stiff in-situ ground close behind the wall face, the reinforcement crosses no resistant zone and friction-based MSE design fails. The Shored MSE hybrid wall (SMSE) solves this by combining a soil-nailed or anchored shoring system in the cut face with a conventional MSE wall on the new fill in front. FHWA published the SMSE design methodology in NHI-09-087 (2009). This guide walks through when SMSE is the right answer, how it is designed, and how it compares to the anchored-MSE alternative.

By Dr. Ir. Lai Yip Poon, Founder & Chief Designer Â· AnchorSOLÂ® Wall Sdn. Bhd. Â· ~9 min read

The geometry problem SMSE solves

Standard MSE wall design requires the reinforcement to extend back through the active wedge of retained soil and into the resistant zone where pullout resistance can develop. For a vertical wall in granular fill at phi 35 degrees, the active wedge inclines at 45 + phi/2 = 62.5 degrees from horizontal, and the reinforcement length must be at least 0.7 H to provide adequate embedment beyond the wedge.

On many hillside and urban sites, this 0.7 H reach is not available. Examples:

Cut into competent rock or stiff in-situ ground sits 2 to 4 metres behind the planned wall face, less than 0.7 H for a 6+ metre wall
Right-of-way constraint prevents excavation and reinforcement placement behind the wall
Adjacent existing structure blocks the reinforcement reach
Buried utilities in the reinforcement zone preventing full installation

Two solutions exist: SMSE (the hybrid system) and anchored MSE (which substitutes a discrete deadman block for distributed friction). The decision between them is project-specific.

SMSE system components

Shoring component (the back system)

The shoring is built first, cutting back into the competent ground:

Soil nail wall (most common): grouted steel bars at 1 to 2 m spacing through the cut face, with shotcrete or sprayed concrete temporary facing. Provides stability of the cut during MSE construction in front.
Soldier pile and lagging: steel H-piles driven or bored at 2 to 3 m spacing with timber or precast lagging. Used for taller cuts or where soil-nail capacity is insufficient.
Tied-back diaphragm wall: reinforced concrete diaphragm wall with permanent tie-back anchors. Used for very tall walls or marine cuts.

MSE component (the front system)

Once the shoring is complete and the cut is stable, the MSE wall is built in front:

Precast concrete facing panels at the design front-of-wall position
Short-length reinforcement strips or grids extending from the facing to the shoring face
Engineered granular backfill placed between facing and shoring, compacted in lifts
Drainage layer between the MSE backfill and the shoring face

Composite zone interaction

The MSE reinforcement does not extend into the shoring zone. The composite is held together by friction at the soil-shoring interface and by the geometric constraint of the shoring face. Design analysis treats the entire system as a composite, with global stability checks accounting for shoring capacity, MSE internal stability, and the interaction at the interface.

SMSE design methodology (FHWA NHI-09-087)

The design sequence:

Define geometry: wall height H, planned front-of-wall position, depth from front face to shoring face (L_MSE), shoring system type
Design the shoring as an independent retaining structure: soil-nail, soldier pile, or diaphragm wall design per the respective FHWA manuals
Design the MSE component with reinforcement length equal to L_MSE, using the FHWA NHI-10-024 procedure but with shortened reinforcement
Check external stability of the composite: sliding along the foundation, overturning, bearing, global slope stability across the entire system
Check the interface between MSE backfill and shoring face: friction adequate to prevent local sliding, no concentrated load transfer that would crack the shoring face
Check tensile load on MSE reinforcement: with shortened length, the embedment beyond the active wedge is reduced. Tensile loads in the MSE reinforcement increase compared to standard MSE because more load is shed to the shoring
Drainage design considering both MSE backfill and shoring face

SMSE versus anchored MSE: the comparison

Both systems solve the same geometry problem (cannot extend reinforcement to standard length). The choice between them comes down to:

Factor	SMSE (hybrid)	Anchored MSE (AnchorSOL)
Construction sequence	Shoring first, then MSE in front (two phases)	Single MSE construction with deadman blocks
Programme	Longer (sequential phases)	Shorter (parallel)
Cost	Higher (two systems, two contractors often)	Lower (single system, single contractor)
Design code path	FHWA NHI-09-087 + NHI-14-007 + NHI-10-024	BS 8006 + AnchorSOL technical specification
Where it wins	Very tall walls (above 15 m), variable ground, where shoring is independently needed	Medium-tall walls, typical Malaysian hillside, cut-and-fill platforms
Architectural finish	MSE facing only (clean architectural)	MSE facing

For typical Malaysian hillside platforms in the 5 to 20 metre wall height range, anchored MSE is usually the more efficient answer. SMSE becomes competitive on very tall walls (above 20 m), on sites with existing shoring requirements, or on projects where the FHWA design path is mandated by the funding source.

SMSE in Malaysian practice

SMSE walls are less common than standard MSE or anchored MSE on Malaysian projects, but they appear in selected contexts:

ADB-financed infrastructure where FHWA standards are specified and the project geometry triggers SMSE design
Tall urban walls where right-of-way constraints prevent standard reinforcement reach and the project budget supports the composite system cost
Mining and quarry haul roads where significant excavation already exists and the shoring is independently needed for the cut stability

For most other contexts, anchored MSE provides the same engineering benefit at lower cost and shorter programme. AnchorSOL has delivered numerous projects on geometry that would have required SMSE under the friction-based approach.