Lateral Earth Support Structures – Excavation Shoring

Lateral earth support structures provide side support to a shoring wall by holding the planned lateral loads during an excavation. These support structures stabilize soil and rock from erosion and downslope movement while providing support for both vertical and near-vertical grade changes.

Importance of Lateral Earth Support Structures in Excavation Shoring

In excavation shoring, the ground is excavated to the right depth with retaining walls supporting the soil at the sides. Upon completion of the excavation to the targeted depth, the base slab of the structure is placed at the bottom-most level, then followed by the side walls. The casting of concrete progresses upwards until the roof of the tunnel structure is completed and ground is then back-filled and reinstated.

The secant pile technology considered as a form of top-down construction system with the added benefit of the shoring system walls forming part of the final structure was looked at as one option. Another important aspect of secant piles is the minimum vibration and noise that the system provides. Secant piles are simply drilled shafts that interlock to make a continuous wall. The walls are formed by constructing intersecting reinforced concrete piles, with every second or third pile typically reinforced with a broad flanged steel section or a reinforcing steel cage. With proper waterproofing and finishing, this wall can then be made to form part of the final structure for the tunnel or trench.

For proper and economical design of lateral earth support structures and generally of any retaining wall, it is crucial that complete information on all prevailing site conditions that may affect the pile wall during its short term and long term conditions be obtained. In this case, the design of the shoring system must be able to withstand intensive earth pressure, hydrostatic pressures, equipment loads, applicable traffic, construction loads as well as the other surcharge loads. This way, they will allow safe construction without movement or settlement of the ground, to prevent damage or to shift the adjacent structures, streets and utilities and the design be compatible with the geologic conditions and predictable field response.

The stability of the excavation must also be maintained against sliding and bottom heave. As these walls are required to form part of the final wall system for the structure, the wall system has to be analyzed for lateral pressure loading distribution on the final structure. The pile and shoring system has also to perform as a structural element for the finished structure. The analysis of a combined system has to be carried out in order to develop a computer model that would provide the anticipated behavior of the system when subjected to the various loading and stresses during its construction as well as lifetime period.

The top down construction allows for the piles to be right on the borders or walls of adjacent properties and can usually be driven with minimal disturbances to the adjacent structures. The secant piles can be installed in difficult ground conditions with more flexibility in the construction alignment.

Conclusion

The lateral earth support structures have to be designed to safely support the ground, water pressure, existing loads, permanent loads, traffic or construction loads, while protecting utilities without permitting undesirable wall deflections and ground settlements behind the wall. The support structures can be installed in difficult ground conditions with more flexibility in the construction alignment.

 

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