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Ground investigation

Ground investigation is based on a combination of techniques aiming to investigate and assess the underground properties (chemical, mechanical…) prior to starting construction works.

  • Tseung Kwan O to Lam Tin Tunnel
    Site investigation using horizontal directional coring (HDC) techniques and in-situ testing.
    Hong Kong - 2015 read more

    Tseung Kwan O to Lam Tin Tunnel

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  • Perth City Link Rail Project
    VSL Intrafor / Avopling JV were subcontracted for a multi-faceted range of ground engineering solutions on this complex project..
    Australia - 2012 read more

    Perth City Link Rail Project

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  • KCRC East Rail Extension
    Ground investigation, jet grouting, ground freezing and construction of diaphragm walls for a major railway.
    Hong Kong - 2004 read more

    KCRC East Rail Extension

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VSL's Ground engineering services are provided by its subsidiary

Investigate and assess ground properties

Ground investigation is based on a combination of techniques aiming to investigate and assess the underground properties (chemical, mechanical…) prior to starting construction works. Successful project execution relies on the quality of information provided to clients, consultants, contractors and subcontractors and the information is needed as early as possible in the construction process. This is crucial for projects with high loading (such as high-rise towers) and also for tunnelling schemes facing extremely difficult ground conditions such as changing faces and faults that will be encountered along the route. It is therefore of vital importance to know in advance the ground conditions ahead and, more importantly, the locations of faults, groundwater and large fissures with soft infill materials. This information dictates the choice of methods, which in turn defines the programme, the resources needed and the project costs.

Intrafor, VSL’s ground engineering division, proposes all ground engineering techniques applicable to

  • retaining structures (diaphragm walls, sheet piling, contiguous and secant pile walls),
  • foundation (barrettes, bored piles, continuous auger piles, micropiles, h-piles, pre-bored hè-piles
  • soil improvement (grouting, jet grouting, vibro-compaction, stone columns, soil mixing…)
  • environmental protection (slurry walls, curtain grout, curtain wall by ground freezing…),
  • soil investigation (sub-horizontal and directional drilling and coring, ground investigation, laboratory testing…)

as part of civil engineering or building projects such as metro stations, tunnels, roads and bridges, reclamations dams, deep basements, car parks, high rise building, etc.

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VSL Services

Ground investigation

Planning and implementation of destructive and non destructive techniques to penetrate into the underground to :

  • establish water table level, water flow…
  • indentify presence of faults, voids in the underground
  • assess ground layer thickness, mechanical properties, material.
  • extract soil and ground samples for further testing and analysis in laboratories

Investigation techniques include seismic investigations, penetrometers, drilling, cross-holes and in-situ tests (pressuremeters, inspections, gamma density, permeability etc).

Soil testing

A full range of laboratory techniques to measure the properties of a soil sample after it has been extracted. This information is then used for designing the underground structures.

Directional coring

Directional coring allows ground investigation following a predetermined path. For example, it allows accurate and thorough ground investigation along a future tunnel route.

Directional drilling

To maintain and expand the utility infrastructure around the world is a challenging task. As an alternative to the traditional open trench construction method, the Horizontal Directional Drilling (HDD) has emerged as a preferred method in many situations for the installation of oil and gas pipelines as well as other utility pipes under watercourses, roads, railway lines, steep slopes and other obstacles.

Intrafor has introduced this trenchless technology to Hong Kong and has developed a local expertise in this field. Intrafor’s HDD specialists are in a position to offer clients and engineers the appropriate technical and financial solution to suit the specificities of all ground and environment conditions.

Associated Services

Monitoring

All techniques available to monitor the behaviour of the ground or of a structure, during underground works or after.

Diaphragm walls and piles

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Construction of underground walls and piles from the surface using grab or cutter machines under bentonite protection. VSL has available some of the most powerful worldwide cutter capable of trenching and building walls at depth of up to 120 meters.

Ground improvement

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Lok Ma Chau, Hong Kong, soil freezing to construct cross-passage between the 2 tunnels

This is a combination of techniques to improve the ground properties for both temporary and permanent works to enable construction of underground or elevated structures. VSL can implement a wide variety of these techniques including soil freezing, dynamic compaction, vibro-flotation, grouting, jet-grouting…

Ground anchors (or tieback)

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Drilled and grouted, post-tensioned (stressed) passive or active ground reinforcement system providing resistance to uplift and lateral forces, used for retaining walls, buildings, bridges, dams, unstable slopes and to prevent water table uplift. Taking the form of strands or bars, the system can be temporary (during the construction phase) or permanent. VSL has developed a complete electrical insulation system for permanent anchors.

Dewatering

Ground water lowering to guarantee either a maximum water flow inside a deep excavation or maximum draw down outside and excavation to control settlements.

VSoL® Retained earth system

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Pre-cast concrete or pre-formed mesh facing panels anchored to galvanised steel mesh or polymeric strips to reinforce soil, and create retaining structures including abutments, ramps and roads with a variety of shapes, surface textures and colours.

Muskat express way, Oman, VSoL®
wall, the highest wall ever built by VSL

Advantages of VSL’s offer

Experienced staff

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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 prove to be a dramatic advantage.

Value engineering

As an 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.

Using a risk management approach in deep cofferdam construction

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In 2009, Intrafor was awarded the subcontract to design and construct a four-storey basement in the heart of Kwun Tong town centre adjacent to an MTRC mass transit station. It was considered to be one of the deepest cofferdams ever built for a private sector development in Hong Kong. Construction has involved demolition of the existing basement, diaphragm wall installation, excavation and lateral support for the diaphragm wall and the construction of footings.

For this project, Intrafor was the first contractor in Hong Kong to use the approach described in CIRIA Report C580 for the design of excavations and lateral support. The approach requires the analysis of a progressive failure of the struts, unless a risk management plan is implemented to reduce the risk of strut damage. The project is the first private development scheme of its kind in which the risk management approach has been adopted as an alternative to strut failure analysis. It has been found to be much more cost-effective than using more and heavier struts to prevent progressive failure.

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Integrated service

Intrafor integrates the full range of underground service from underground investigation to underground structure construction and delivery. This is backed by a strong technical department that is capable of designing and optimizing the permanent structure and the construction methods.

Contributing to sustainable solutions

Cost effective

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Ground investigation helps to assess the ground properties prior to starting extensive works. Issues can be addressed before heavy and costly equipment is implemented.

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.

How it works

Sub-horizontal directional coring: new technologies for ground investigations

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In its quest to push the limits of construction, Intrafor undertook some years ago to go beyond the traditional soil investigations carried out vertically (or sometimes inclined) from ground level. Intrafor has already become a renowned expert in this field and has gone on to develop and successfully complete projects using sub-horizontal directional coring. It has used this technique to achieve directional sub-horizontal coring lengths of more than 1,100m along the routes of tunnels.

Technique provides the level and quality of information required to complete successfully and safely the construction of tunnels in complex ground conditions:

  • Geological conditions are known along the whole tunnel route before the excavation process starts;
  • No sections of the tunnels are left unknown: traditional vertical ground investigations at specific spacings always miss elements of the geological conditions;
  • Problems can be anticipated and appropriate solutions developed before the difficult geological areas are reached;
  • The amount of coring is minimised by targeting the exact tunnel route rather than carrying out the unnecessary boring usually required just to reach the tunnel section if the ground investigation is done from ground level.

Traditional investigation methods provide only a few sets of localised information along the tunnel path, which may prove to be insufficient once tunnel excavation is under way.

Intrafor is one of the world’s leading specialists in this innovative ground investigation technique.

Main components

Higher accuracy

As part of an R&D project, Intrafor has successfully developed its own steerable core barrel. This proprietary equipment used together with a wireline drilling system produces the best core quality without affecting productivity.

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Core box ground sample extracted for further testing

Development of a commercial version of Intrafor’s own directional coring system started in September 2009 following the delivery of an Atlas Copco BQ wireline drilling system and Reflex EZ-AQ EMS borehole survey instrument.

The steerable core barrel was modified slightly to accommodate the wireline and survey systems. Preliminary testing using the wireline technique on Intrafor’s own steerable core barrel system has proved very successful and larger scale testing will be performed to confirm the properties of Intrafor’s commercial system.

Intrafor Hong Kong’s new proprietary directional core barrel is at work on its first project. Maeda-Crec-Seli JV awarded Intrafor the contract for ground investigation along a drainage tunnel. The new barrel developed in 2009 is being used for a 160m-long hole with two horizontal curves. The hole will also be used for rock fissure grouting to treat a known fault zone.

Air-lifted drilling rigs for Liantang

The works Intrafor carried out on behalf of LAM Geotechnics involve drilling one vertical and one inclined hole to obtain geological and geotechnical information for the design of a traffic tunnel in Hong Kong. Intrafor is drilling 315m down to the invert level of the future traffic tunnel.

Record drilling at Eagle’s Nest Tunnel

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In 2004, Intrafor was awarded a challenging subcontract to create a 2km horizontal investigation hole with directional control. The work involved the drilling with full coring of two horizontal directionally guided holes, 1,150m and 950m in length, as well as permeability tests and real-time monitoring of the net water outflow. The allowable drilling tolerance was a maximum inclination of 1% and with a target at the drilling end within a semi-circle of 8m radius. The record-breaking hole was successfully completed in October 2004.

The investigations were part of the Eagle’s Nest Tunnel project, the longest tunnel on Hong Kong’s Route 8 from Shatin to Cheung Sha Wan. The two long horizontal holes were needed to obtain geological and hydro-geological information along the alignment.

Horizontal directional drilling under Hong Kong Seabed

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Intrafor Hong Kong has completed a Horizontal Directional Drilling (HDD) contract for the Government of the Hong Kong S.A.R. (Drainage Services Department). The works included the directional drilling of two holes located near two small villages in Lamma Island (South West of Hong Kong Island), as well as the installation of HDPE pipes in those holes, for the construction of two submarine outfalls from a sewage treatment plant.

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