A combination of techniques to modify and improve ground properties (permeability, strength, capacity, density…) with the objective to carry out construction
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Use of horizontal directional drilling for the construction of two subsea wastewater outfalls.
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Cost saving use of post-tensioning for the world’s tallest free standing tower when completed in 1975.
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VSL's Ground engineering services are provided by its subsidiary
Modification or improvement of the soil plays an important role in the field of foundation stability, particularly in situations such as treating load-bearing soils under new and existing buildings, changing the ground’s permeability, building tunnels or controlling the movement of impacted soil and groundwater. Over the years, Intrafor has become a recognised specialist in ground improvement techniques through the development of its in-house know-how and methods.
Temporary or permanent
The choice of ground improvement techniques depends upon the local conditions and the short-term or long-term stability requirements. The ground improvements may be temporary (as for a tunnel boring machine break-through or the construction of cross-passages between tunnels) or permanent (for situations including the compaction of reclaimed land, stabilization of weak soils, waterproofing, or the drainage of land to accelerate its settlement).
VSL’s ground improvement services
Intrafor offers most of the ground engineering techniques that may be required as part of civil engineering or building projects such as metro stations, tunnels, roads and bridges, land reclamations, dams, deep basements, car parks and high-rise buildings.
This includes :
- soil consolidation techniques such as grouting, jet grouting, vibro-compaction, stone columns, soil mixing
- environmental protection such as slurry walls, curtain grout,
- temporary consolidation such as curtain wall by ground freezing.
- Drainage and preloading, to consolidate compressive soils.
A full range of techniques to monitor the behaviour of the ground or of a structure, during underground works or afterwards
Diaphragm walls and deep foundations
A diaphragm wall is the most cost-effective retaining solution for providing strong soil and hydraulic support to control and protect the surrounding environment against settlement, water drawdown, etc.
A combination of techniques to investigate and assess the ground strata (layers, faults, voids, water level) and soil properties (chemical and mechanical) prior to starting construction works.
VSoL® Retained earth wall system
Precast concrete or preformed mesh facing panels anchored to galvanised steel mesh or polymeric strips to reinforce soil and create retaining structures with a variety of shapes, surface textures and colours. Uses include abutments, ramps and road or rail projects.
Ground anchors (or tie-backs)
Used for retaining walls, buildings, bridges, dams, unstable slopes and to prevent water-table uplift. Systems include drilled and grouted, post-tensioned (stressed) passive or active ground reinforcement to provided resistance to uplift and lateral forces. They can take the form of strands or bars and the system may be temporary (during the construction phase) or permanent. VSL has developed a complete electrical insulation system for permanent anchorages.
Advantages of VSL’s offer
Intrafor is convinced that its people are its main and most critical asset. Intrafor’s project teams are organized around a permanent core of highly experienced and mobile staff, guarantor of the highest quality and safety standards and problem solving.
Cutting edge equipment
Intrafor owns its pool of specialized equipment composed of some of the most powerful machines available on the market. This allows Intrafor to be very reactive and able to mobilize the project right upon award which often proves to be a dramatic advantage.
As experienced ground engineering specialist, Intrafor can use innovative geotechnical techniques to provide value engineering for its clients’ projects at an early stage in the design. Intrafor proposes construction schemes or alternative approaches. The project details and interfaces are then developed with the client’s team to produce the most cost effective and safe solutions. Intrafor aims to be “Your Foundation Partner”, providing clients with safe and economic ground engineering solutions.
In-house design capabilities for better optimisation and risk assessment
Intrafor’s design teams are experienced and conversant with design calculation methods and standards, as well as - and especially - with construction processes and risk management. These aspects often prove to be decisive factors in the success of a project. In addition, Intrafor’s designers work closely with estimators and operational staff at all phases of the project, from the tender to the final details of executing the work. This allows selection of the most suitable methods together with the definition and optimisation of the construction sequences and programme.
Designers remain involved in the construction processes and in the risk management throughout the execution of the work. Thus, they can refine the methods and the design as required to take into account any changes on the site, whether due to ground conditions or other factors. This makes Intrafor’s design expertise one of the company’s key strengths.
Contributing to sustainable solutions
Limiting the impact on the environment
By carefully choosing the best method to improve the soil, ground improvement contributes to limit the impact on the environment.
Founded on safety
Intrafor’s employees demand, and actively participate in, the establishment of a safe environment. They are proactive in identifying and communicating their concerns. All employees are given the authority and responsibility to stop works if they feel safety compromised.
Identifying hazards ahead
Hazards need to be carefully managed. Intrafor is well versed in safe working methods and makes safety a top priority, as demonstrated by gaining OHSAS 18001 certification in 2003.
Good practice in environmental impact assessment
The Lok Ma Chau Spur Line is a 7.4km railway from the existing Sheung Shui station on East Rail to a new terminal at Lok Ma Chau. A tunnelled alternative was developed to pass beneath the Long Valley without disturbing an environmentally sensitive wetlands habitat, which is home to a number of rare bird species.
After the construction of 3.2km of twin-bored tunnels 8.75m in overall diameter, 12 cross-passages were then built to connect the two tubes at regular intervals and allow passenger evacuation from one tunnel to the other. These were built in saturated, mostly decomposed, rock and were therefore very unstable, requiring ground treatment to ensure safe excavation. Construction of three of the passages had to be carried out from the tunnel without any access from the surface. Intrafor worked with the contractor and engineers to develop a ground treatment scheme based on ground freezing to stabilise the ground during excavation. It was Hong Kong’s first use for tunnelling works of this environmentally friendly technique, which does not introduce any foreign materials into the ground, nor does it require any work above ground.
Soil freezing actually involves artificial freezing of the groundwater in order to create a resistant and impervious soil mass. It increases the strength and reduces the permeability of the surrounding treated ground. Used as a temporary measure it allows for safe excavation in water-bearing granula materials to enable installation of the permanent structure to proceed. Intrafor successfully implemented ground freezing to construct three cross-passages between twin-tube tunnels. No access from ground level was possible and use of the technique protected the environment above. The soil freezing was fully executed from inside the tunnels with no impact above ground.
The process involved pumping coolant through a series of pipes installed in the soil to chill it to -30°C. The ground freezes at this very low temperature, gaining a significant increase of strength as well as becoming watertight, thus making it completely safe for excavation.
How it works
Ground improvement is about changing the properties of the soil with various techniques depending on the ultimate objectives.
Compaction consists in rearranging the soil particles in order to reduce the voids and increase the density. This translate into a ground that has better mechanical properties and that can bear higher loadings.
Techniques includes :
- Vibro-compaction : Generally used for reclamation areas. Vibro-compaction is carried out in order to consolidate granular soil. The compaction is achieved by vibrations, which are generated by a vibro-probe and create an optimum rearrangement of the soil particles. This increases the density of the soil in situ and ultimately increase the loading capacity.
- Drainage and preloading : Used to consolidate compressive soils before building construction. Vertical drains eliminate water and gas and a certain height of fill acts as a preload, which is removed after consolidation. Atmospheric consolidation is when the fill load is replaced by application of a vacuum between a membrane and the soil to create the necessary pressure.
- Stone columns : Columns made of compacted gravel to reinforce and drain a cohesive soil. Compaction is not the primary goal. Two techniques are implemented: Wet stone columns: Flushing a hole with a vibro-probe and then creating a column by pouring gravel from the top. A widely used, fast and low-cost soil improvement method. Dry stone columns. Introduction of gravel at the bottom of the hole through a separate gravel duct alongside the vibro-probe. This technique is also used in combination with the preloading technique.
- Soil mixing : Mixing in-situ existing soil with additives (cement-lime) to obtain semi-rigid inclusions to improve the compressive strength.
- Injection grouting : Controlled injection of a self-hardening mix through drilling rods to fill cavities and cracks, as well as to strengthen and/or waterproof the soil.
- Jet grouting : A high pressure jet, which restructures the soil by introducing a cement grout that forms a hardened mix with the soil.
- Ground freezing : Generally used as temporary measure to improve soil strength and water tightness when excavating beneath the water table; uses brine or nitrogen.
The technique of soil freezing actually involves artificial freezing of the groundwater in order to create a resistant and impervious soil mass. It increases the strength and reduces the permeability of the surrounding treated ground.
Used as a temporary measure therefore allows for safe excavation in water-bearing granular materials to enable installation of the permanent structure to proceed.
Intrafor successfully implemented ground freezing to construct three cross-passages between twin-tube tunnels. No access from ground level was possible and use of the technique protected the environment above. The soil freezing was fully executed from inside the tunnels with no impact above ground.
XRL 820, Hong Kong