[info]Both permanent and temporary techniques available for providing support at locations the shoring wall design requires.[/info]
Soil Nailing
Advantages of Soil Nailing
Advantages associated with soil nailing fall into three main categories: Construction, Performance, and Cost.
Construction
- Soil nail walls require smaller ROWs than most other competing systems. This is also true for ground anchors as soil nails are typically shorter.
- Soil nail walls are less disruptive to traffic and cause less environmental impact compared to other construction techniques such as drilled shafts or soldier pile walls, which require relatively large equipment.
- Soil nailing causes less congestion in the excavation when compared to braced excavations.The installation of soil nail walls is relatively fast.
- Easy adjustments to nail inclination and location can be made when obstructions are encountered, such as boulders, piles or underground utilities. As a comparison, adjustments in the horizontal position and orientation of ground anchors often require changes to the soldier pile layout or the addition of waler beams, making adjustments in the field costly.
- Soil nail wall installation is not as restricted by overhead limitation as in the case of soldier pile installation. This advantage is particularly important when construction occurs under a bridge.
Soil nailing may be more cost-effective at sites with remote access because the smaller equipment is more readily mobilised. - Soil nails are installed using equipment that is multipurpose and can be used for other substructure elements such as underpinning or protection of adjacent, movement-sensitive structures.
- A relatively large number of qualified soil nail contractors exists.
- A widespread knowledge about soil nailing exists among engineers.
- Soil nail walls can accommodate curves and “bends” more easily than other top-down construction wall systems, which would otherwise require straight wall segments.
Performance
- Soil nail walls are relatively flexible and can accommodate comparatively large total and differential movements.
- The measured deflections of soil nail walls are usually within tolerable limits in roadway projects when the construction is properly controlled.
- Soil nail walls have performed well during seismic events.
- Soil nail walls have more redundancy than anchored walls because the number of reinforcing elements per unit area of wall is larger than for anchored walls.
- Sculpted facings, which can be applied to soil nail walls, give a more natural appearance than other finishes, to fit in with the surrounding environment.
Cost
- Conventional soil nail walls tend to be more economical than conventional concrete gravity walls taller than approximately 4 to 5 meters.
- Soil nail walls are typically equivalent in cost or more cost-effective than ground anchor walls when conventional soil nailing construction procedures are used.
Limitations
The main limitations associated with soil nailing are:
- In projects where strict wall movement criteria exist, additional measures to limit deflections may be required. These requirements would add cost. If very strict movement criteria exist, soil nails may not be a feasible option for the project.
- The existence of utilities behind the wall will likely create restrictions to the location, inclination, and length of soil nails, particularly in the upper rows.
- Soil nail walls are not well-suited where large amounts of groundwater seep into the excavation. Soil nail walls require maintaining a temporary unsupported excavation face during construction.
- Permanent soil nail walls require permanent underground easements.
- Soil nail tendons may interfere with certain types of communication lines (e.g., optic fiber) running immediately adjacent to soil nail walls.
Ground ANCHORING
Advantages of Ground Anchoring
- Practical alternative to propping
- Versatile form of earth retention
- High loads can be obtained in relatively poor ground conditions
- Driven anchors can be used in a variety of soil conditions
- Used to install ‘active’ forces into structures
- Enhanced durability including resistance to corrosion and resistance to alkalis and solutions in soils increase their life and greatly reduce the need for maintenance, thereby decreasing life-cycle costs.
- Driven anchors create a low environmental impact
- Permanent anchors are frequently used in new ports and harbour developments, road schemes, dam refurbishments and for the tensile support of new sports stadium structures.
- Maximised working spaces can be created for deep excavations on civil engineering projects such as cofferdams, new build or extensions, cut and cover tunnels, to name a few.
- Can produce valuable savings in programme and budget.
Disadvantages
- It is necessary to use specifed equipment, exprienced professional engineers.
- It is difficult to apply anchors in weak soil and to implement anchors with great depth.
- Anchor execution would affect the land of surrounding construction works, which must be accepted by their owners.