Earth Retention & Anchors Archives - Moretrench

Soil & Rock Anchors

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Soil and rock anchors are typically pre-stressed bar or multi-strand tendons that carry vertical and lateral earth pressures and uplift forces. Temporary tieback anchors are frequently installed with conventional excavation support systems. Permanent tiebacks are used extensively with marine bulkheads. Permanent tieback or vertical tiedown anchors are also used to increase dam stability to meet seismic codes. In aggressive soils, permanent rock and soil anchors may be double corrosion protected for long service life.

Soil Nailing

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Soil nailing is an economic, top-down earth retention method in residual or highly cohesive soils. Closely spaced reinforcing bars (nails) are installed in the face of the excavation. A structural concrete fascia bridges the nails and supports the soil/rock between nails. Soil nails are passive elements that become tensioned when the soil/rock deflects laterally as excavation depth increases.
Soil nail walls can be a temporary measure for support of excavation or structural underpinning, or they can function as permanent retaining walls or slope stabilization systems. This technique is most advantageous in difficult soil conditions such as cobbles, boulders or weathered rock, where space or headroom is limited, and a permanent wall is required.

Secant/Tangent Piles

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Secant Pile Walls:
Secant pile walls can be used for temporary rigid support of excavation or to form permanent earth retention systems. This technique is suited for dense, urban environments. Walls are constructed by the sequenced drilling and construction of overlapping, reinforced concrete piles. Although more costly than sheeted excavation support, this system offers greater alignment flexibility and increased wall stiffness and can be drilled through bouldery or cobbly soils.
Tangent Pile Walls
Tangent pile wall construction is similar to that used for secant pile walls except that the piles are designed to touch rather than overlap. Since tangent pile wall construction eliminates the need to drill through previously placed wall elements, construction is faster. This type of system is typically not used where a groundwater cut-off is required.

Beams and Lagging

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Beams and lagging is the most common method of temporary excavation support. Beams may be drilled in, driven, or in very difficult ground, installed as micropiles. The lagging is installed top-down as excavation proceeds. This is a free-draining system and dewatering must be provided when installation proceeds below the water table.

Overview

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Temporary earth retention for excavation support may be the first stage of construction. Traditional techniques such as steel sheet piling or tied back soldier beam and lagging walls can be a very economical. However, not all sites are amenable to the vibration of driving sheet piling, the interference of underground utilities or other structures. This is particularly true in urban environments. Soil nailing, grouting systems or ground freezing can be viable alternatives to traditional earth retention.
Because Moretrench is experienced in all of these techniques, we can offer the optimum solution tailored to project requirements and subsurface conditions and restraints.