Soldier beams or soldier plies are used to prevent excavation from collapsing; by preventing the lateral movement of the soil and hence, stopping the soil from entering into the excavated area.
Figure 1: Soldier Beam Wall
Soldier beams are H-section or W-section steel or reinforced members and in some cases, prestressed members as well. They can be installed for temporary support of the excavation or as a permanent support as well.
Soldier beams are usually drilled, driven or vibrated into their fixed places at intervals of up to 10 to 12 feet however, their spacing depends on several factors such as:
Table of Contents
Height of the Retaining Wall:
Soldier beams are required to be spaced closely with the increase in height of the retaining walls in order to provide stability and avoid deflections.
Type of Soldier Beam Used:
Type of soldier beam here refers to whether a steel or a reinforced one is used. More spacing can be provided if steel soldier beams are used in comparison with the reinforced type.
Surcharge Loads and Geotechnical Analysis:
from the geotechnical report we get the necessary loads, and we plan the spacing accordingly keeping in view the lateral pressure. Similarly, if there are any additional loads (surcharge loads) that are being applied on top of the retained soil then we have to decrease the spacing between the soldier beams in order to provide stability.
Codes and Specifications:
Obviously, the codes and specifications provide the basic guide for the design and spacing of soldier beams. (the codes will be listed further along)
Components of Soldier Beam Wall
The entire structure of a soldier beam wall includes the following components:
Soldier Beams
Vertical beams that are the primary support of the wall, installed at regularly spaced intervals.
Walers
These are the beams that are provided in between the soldier beams to provide additional lateral support to the wall and evenly distribute the load as well. Walers are of two types:
Ø Internal walers, which are present inside the excavated area and are in direct contact with the lagging or facing.
Ø External walers, which are provided on the other side of the soldier beam wall i.e. outside the excavation area. They are connected with the soldier beams to enhance their lateral load resisting ability.
Figure 2: Walers
Tiebacks or Anchors
Tiebacks or anchors may be used in a soldier beam wall in order to provide additional support to the wall against the lateral forces. They are installed approximately at an angle of 45 degrees.
Lagging
This is the material that is placed between the soldier beams to prevent the soil from sliding inside the excavated area. If soldier beams are provided for permanent support, generally concrete lagging is used and if they are provided for temporary support then wooden lagging is used.
General Steps in Installation of Soldier Beams
Installation of soldier beams and construction of a traditional soldier beam wall typically constitute of the following steps:
- After the site visit and the layout of the construction site, several necessary tests including soil tests are carried out.
- Excavate the area between the places where soldier beams will be installed.
- Soldier beams are either driven or vibrated in the ground, if incase that cannot be done holes are drilled and soldier beams are installed in those pre-drilled holes. The soldier beams are to be installed as per the code requirements.
- Horizontal connections, walers, are provided between the soldier beams.
- Tiebacks or anchors are installed if required.
- Lagging is installed within the soldier beams to provide lateral support against the soil and form a stable wall structure.
- Then we gradually, behind the soldier beam wall we backfill the area while compacting it layer by layer in order to reduce settlement.
- For some cases, facing material which maybe shotcrete or precast concrete panels may be installed in order to provide further stability to the soldier beam wall.
Types of Soldier Beams Wall
Different types of soldier beam walls are provided in accordance to our requirements and site limitations. Some of the main types of soldier beam walls are as follow:
Traditional Soldier Beam Wall
This type of wall is used when we have normal retaining wall height. Steel or reinforced soldier beams are either drilled, driven or installed in pre-drilled holes. Walers are provided for lateral support along with lagging.
Cantilever Soldier Beam Wall
This type of soldier beam wall is used when excavation depths are to be less than 15 feet. In this case, some part of the soldier beam is extended above the excavated portion forming a vertical cantilever type beam.
However, it is not feasible to provide a cantilever soldier beam wall when the water table is present above the excavation subgrade.
Tieback or Anchored Soldier Beam Wall
Tensioned tiebacks or anchors may be used in soldier beam wall when there are challenging soil conditions. In this case, the tensioned anchors are extended into the soil behind the wall to improve stability of the soldier beam wall.
Benefits of Using Soldier Piles or Soldier Beams
1.Cost Effective
As compared to other retaining structures such as sheet piles or concrete piled walls, this is a much more economic option.
2.Less Noise Pollution During Installation
As compared to other retaining methods, the vibrations and noise caused by installing this type of retaining structure is very minimal due to which it is a go-to option for construction in a residential area.
3.Time Effective Installation process
If the soldier beam wall is to be used as a temporary support structure, the installation of wooden or timber lagging consumes very less time and labour.
4.Preferable Option When Dealing with Challenging Soil Type
Soldier beam wall is a good option when the site of excavation consists of consolidated clay.
5.Flexibility
Different kinds of support systems can be used for additional support such as tieback or braced system etcetera, to support deep excavations. Furthermore, keeping in view the guidelines, the layout and spacing of soldier piles can be altered according to the situation.
Codes and Standards Used for Soldier Beam Installation
Following are some of the codes for this type of retaining structure or shoring:
- International Building Code (IBC)
- American Concrete Institute (ACI 318)
- American Society of Civil Engineers Standards (ASCE 7)
- Eurocode 7: Geotechnical Design
- British Standards (BS 8002:1994)
- Australian Standards (AS 4678:2002)
