Secant Pile Walls

Shotcrete is a mortar or concrete that is pneumatically projected or sprayed by a nozzle with high velocity on the prepared surface. The whole system is also known as spraycrete.

Spraying shotcrete walls.

Types of Shotcrete Walls

There are basically two types of shotcreting processes

  • Dry-mix process and
  • Wet-mix process.

Advantages

Shotcrete is very useful and has great advantages over conventional concrete in a new variety of construction and repair works.

  • Excellent bonding in nature makes the concrete layers very strong.
  • It is more economical than conventional concrete and requires less formwork.
  • The Concrete can be applied by a nozzle from a safe distance.

Disadvantages

  • The production cost is very high.
  • Dusting problems.
  • So many wastages of concrete.

Applications

  • Thin overhead vertical or horizontal surfaces.
  • Curved or folded sections like tunnels, canals, reservoirs, or swimming pools, and pre-stressed tanks.
  • Stabilized rock slopes.
  • Restoration and repairing of old building and fire-damaged structure.
  • Waterproofing walls etc.
Both permanent and temporary techniques available for providing support at locations the shoring wall design requires.

Soil nailing and ground anchoring.

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.
Combinations of techniques or composite profiles can provide the right economical solution, when geotechnical conditions and shoring requirements demand more complex solutions.

Mixed pile walls produced by Ausipile.

Ausiple can design the best way of delivering mixed pile walls that meet your requirements and budget.

Ausipile will design a system that meets your requirements we can do up to 36 meters length of sheet pile walls in various grades of steel or polymer, depending on the application and use.

Building site showing sheet piling.

Providing stock or lead times allow, this is one of the easiest and quickest shoring systems available. The quality of sheet pile chosen is paramount to the quality and expectation of shoring requirement.

Advantages of Steel Sheet Pile Walls

The advantages of steel sheet piling construction are as follows.

  • Steel sheeting provides resistance during installation stresses. The sheets must be driven into the ground and they have high resistance to the force of being driven down.
  • It is extremely light weight and makes it easier to lift and handle.
  • Steel sheeting is reusable and recyclable.
  • There is a long life for it both above and under water. It only requires light protection to keep it maintained.
  • The pile length is easily adaptable and can be welded or bolted to make it work.
  • They have stronger joints that can withstand the force of being driven into place.

Disadvantages of Steel Sheet Pile Walls

The main disadvantages of steel sheet pile construction are listed below.

  • The sections are rarely able to be used as part of a permanent structure. Permanent sheet piles will stay in the ground and act as a long-lasting retaining structure. Most are used as temporary structures and are used to provide safe access roads or paths for construction projects. They are removed once the project is completed.
  • It is extremely difficult to install steel sheeting in soil that is rocky or has large boulders. Many times the sheeting cannot be installed to the required depth.
  • Driving the sheets may cause neighbourhood disturbance. The vibrations from driving the sheets can make the close properties settle and cause problems.
Sheet pile walls - installation of piles.
Further spacing out of the pile centres produce soldier pile walls. Based on a competent geotechnical profile, such that the piles stand alone and panels or arches between the piles transfer loading to these soldier piles provide the shoring restraint.

A system of soldier pile walls by Ausipile.

Ausipile can design a system for your next project this type of wall is not suitable for high water table installation as it is very hard to install with out major dewatering system present.

When the piles no longer need to intersect based on the geotechnical profile it allows a small ‘gap’ between the piles that can be closed, if necessary, during excavation.

Contiguous pile walls.

Bored Piles are circular piles made of concrete and steel being installed in the soil by various drilling
methods.

When the piles are side by side and not linked together they form a retaining wall for excavation pits or terraces. Depending on the application of the contiguous pile walls, the length, diameter, material, formation, and placing of the individual piles can be adapted to meet many different requirements.

This can be done via:

  • Kelly Method
  • Continuous Flight Auger
  • Rotary Twin System

Each one has it own advantages and disadvantages.

The premium piled wall solution for retention structures. Secant pile walls require a specific technique and quality control to ensure the correct secant interlock for water retention and positional tolerances at depth.

Secant pile walls installed by Ausipile.

Ausipile will make sure our design meets the requirements of your project, and deliver the best results given budget and time frames.

We can do up maximum of 827mm diameter and depth of 30 meters.

The main advantages of Secant Pile Walls are:

  • Increased construction alignment flexibility.
  • Increased wall stiffness compared to sheet piles.
  • Can be installed in difficult ground (cobbles/boulders).
  • Less noisy construction.
  • The main disadvantages of secant pile walls are:
  • Verticality tolerances may be hard to achieve for deep piles.
  • Total waterproofing is very difficult to obtain in joints.
  • Increased cost compared to sheet pile walls.

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