Temporary shoring is a construction technique used to support a building, structure, or trench to prevent a collapse. This method is essential in various construction scenarios, particularly during repairs, renovations, or when an existing structure is being modified. The primary purpose of temporary shoring is to provide stability and safety until the permanent structure can take over these responsibilities. Let’s delve into its key aspects
This method is used when:
Table of Contents
a)The Structural Integrity of a Building is Lost
This may be due to:
- Any natural disaster such as flood or earthquake
- Any man-made disaster such as a fire
- Differential settlement of one portion of a structure, which may lead to cracks resulting in loss of load bearing capacity
- Bulging of walls, which may be due to constant heavy vibrations or due to excessive loads, leading to a significant decrease in the bearing capacity of walls
b)Before Starting the Construction
Shoring may be provided when there is deep excavation when the soil is cut vertically therefore, in order to provide slope stability while constructing the foundation of the structure and for safety of workers as well. Otherwise, the excavation is likely to collapse.
It may also be provided to a structure when there is deep excavation being carried out in the premises of that structure or adjacent to it or when the adjacent structure is to be demolished.
c)Construction of a Bridge
Shoring is also provided during construction of a bridge in order to support the beams, girders and other elements of a bridge and evenly distribute the load safely onto them.
Shoring does not fix the problem permanently hence it is removed once permanent supports are installed or when the construction is completed.
Types of Shoring for Buildings
There are different types of temporary shoring which are provided to existing structures which are generally unsafe otherwise.
a)Horizontal Shoring or Flying Shoring
This is provided between two adjacent buildings when one of them is being restructured or reconstructed.
It may also be used inside the structure between walls to hold the weak walls in place.
There are generally three ways to provide horizontal or flying shoring:
1.Normal horizontal shoring
2.Single flying shoring
3.Double flying shoring
Single shoring is used when the distance between the adjacent walls, between which the shoring is being provided, is 9 meters. However, when that distance exceeds 9 meters, double shoring is used.
b) Vertical Shoring or Dead Shoring
This type of shoring is used when:
i.We have to rebuild the lower part of a load bearing wall which has lost its structural integrity due to some defect.
iiWe have to provide a wider opening under a wall.
iii. We have to reconstruct the foundation to either enhance its structural capacity or when it has become unsafe
Figure 5: Dead shoring for strengthening foundation or replacing defective walls
c) Inclined Shoring or Raking Shoring
This type of shoring is generally provided to unsafe walls for lateral support.
Figure 6: Raking shoring provided to an unsafe load bearing wall
Types of Shoring in Excavation
Shoring provided for stabilizing the slope of an excavation depends on soil characteristics and ground conditions. For instance, if the excavation is being done where the soil is mostly sandy, it becomes crucial to provide shoring in order to prevent failure.
Some of the methods are:
a)Soldier Piling
These are H-beams that are temporarily installed to prevent the soil from collapsing in medium or deep excavations. However, it is not a suitable type of shoring when there is a water table present.
Figure 7: Soldier piles
b)Secant Pile Wall
This type of shoring does not allow water to pass through and can be used in areas where there are boulders etc. It is available with and without reinforcement, non-reinforced secant piles are installed before the reinforced ones.
It provides lateral support and considerably reduces the effect of vibrations during construction.
Figure 8: Secant Pile Wall
c)Soil Nail Shoring
This type of shoring is suitable for loose soil types. It is a fast and an effective way for excavation shoring.
For soil nail shoring, holes are drilled into the vertical or nearly vertical excavation. After that, long slender reinforcement or “nails” are inserted and the holes are filled with grout. An angle of about 10 degrees to 20 degrees is kept between the nails with the vertical.
Figure 9: Soil Nail Shoring
Types of Shoring for Bridge Construction
a) Falsework
Falsework provides temporary support to the span of a bridge while it is being constructed, by transferring the loads to the soil and to maintain the shape. It is only a temporary prop for an incomplete structure, therefore it is removed when the bridge can support the loads.
Figure 10: Falsework for motorway bridge in Rio Sordo, Portugal
b) Scaffolding
Although the primary objective of a scaffolding is to provide a platform for workers for construction. However, in rare instances it may be used to provide a temporary support to the structure as well but it is not preferred.
Shoring Material
Usually timber is used for different kinds for shoring, especially for providing support to structures with reduced load bearing capacities. Steel may also be used where it is necessary however, using timber is much more economical.
Codes and Limitations for Temporary Shoring
ACI 562-19 “Code Requirements for Assessment, Repair and Rehabilitation of Existing Concrete Structures” can be used as a guide for providing temporary shoring to structures and AASHTO Standard Specifications for Highway Bridges or AASHTO LRFD Bridge Design Specifications may be consulted in order to provide adequate shoring for bridges.
A Comprehensive Overview for ACI 562-19 Guidance for Temporary Shoring
According to chapter 9 of ACI 562-19 temporary shoring requirements for stability purposes are:
- While designing a temporary shoring of any type loads such as wind, seismic, snow, live and construction loads shall be considered.
- Preferably a licensed design professional should design the shoring, and the installation process can be carried out by a contractor.
- Shoring should be able to maintain the global structural stability of a structure before and during the renovation process
- Shoring should be designed such that it maintains stability of the structure even when some component of the building is removed.
