Trenchless technology is a widely used term to describe a range of relatively modern engineering methods, that are employed to either install new services or replace/upsize existing ones without resorting to conventional open-cut methods. Some trenchless techniques are relatively new to the South African market place.

Pipe jacking was the original trenchless technique and dates back to the early 1960's where overseas it rapidly became a widely accepted method for installing concrete pipelines and sleeve pipes with the minimum of surface disruption.

PIPE JACKING

• Concrete pipes from 840mm I. D. to 2,35mm I. D.
• Box culverts including bridge structures
• Rehabilitation of corrugated steel stormwater culverts
• Inverted 'D'sections for jacked bridge foundations.

WKSA has installed many kilometres of pipes in all geological conditions including rock, up to distances of 250m. The company was a pioneer in successfully achieving underground junctions with total accuracy.

SLIPLINING

This technique involves rehabilitating pipelines by inserting a smaller pipe (usually HDPe) inside the existing structure. The company was largely responsible for pioneering the technique in South Africa when two 16 ton x 900mm O.D. HDPe pipes were pulled 120m into a failing 1,Om concrete sewerage pipe on the Bluff in Durban.

MOLING

This non-steerable, percussive, displacement tool is used to install small diameter PVC or HDPe pipes and pipe sleeves under roads and rail-lines. The tool of choice selected by WKSA is a Grundomat which is imported from Germany. Diameters from 75mm to 110mm have been installed to date, up to a maximum distance of 20-25m. By using a winch and enlarging tool, the 110mm diameter can be up-sized further to 160mm if prevailing geological conditions permit. Soils information (trial pits) at tender stage is essential as moling is unable to penetrate rock and boulders and also cannot advance itself in wet saturated conditions

PIPE-BURSTING

This technique is widely used to upgrade existing pipelines that are failing and/or no longer have adequate capacity. It is essential to detect existing pipeline problems early (via CCTV) as once advanced failure has occurred, severe misalignment means the technique cannot be used successfully.

GROUTING

With experience gained in the grouting of pipe jack "over­break" voids, the company has carried out bulk/mass grouting using locally manufactured equipment. Large voids under roads that have been formed by corrugated steel culvert failure have been successfully stabilised by the company.

HORIZONTAL DIRECTIONAL DRILLING (H.D.D.)

This 'state of the art' technology is imported from overseas where hundreds of kilometres are installed annually. WKSA has a small HOD rig capable

of installing pipe sleeves up to 150mm to generally accepted tolerances. Distances up to 80 metres can be achieved with the WKSA machine on condition that the insitu geology is soft to intermediate and devoid of rock, boulders and similar obstructions.

STORMWATER CULVERT REHABILITATION

The company has developed expertise over the last 20 years that involves refurbishment of corrugated steel storm water culverts. Techniques available include 'sliplining' the existing culvert using concrete pipes that are grouted into place to ensure the continued integrity of the original structure. Another method involves pipejacking a new concrete pipe (Class 100 D) over the existing culvert and dismantling the failed steel product as the tunnel shield advances. Finally very large diameter culverts have been successfully repaired using a combination of pre-cast concrete (low flow) channels and a cement: sand grout. It is expected that many kilometres of this work will need to be done in the next few years, especially in the 50km 'coastal' zone of South Africa.To date over 20 culverts have been replaced using one of the above non-disruptive methods. Early detection of failed culverts is critical.

SUMMARY

WKSA is South Africa's first trenchless company capable of installing pipes/ pipe sleeves from 75mm I.D. to 2,35mm I.D. For trenchless work it is crucial that pertinent geological information is made available at pre-tender stage so that the correct technique is applied to achieve the most cost­effective solution. This is particularly important for all jacking, moling and HDD work.

Finally, while Trenchless techniques may appear costly, (imported equipment and expensive pipe materials) it is incorrect to compare costs directly with open-cut alternatives. When the indirect costs of open-cut are factored into the cost comparison these far outweigh the direct costs of Trenchless methods.

NOTABLE ACHIEVEMENTS

• Installation of over 50kms of small diameter pipelines/pipesleeves for the Durban AC water main replacement project. (Techniques included moling, HDD and pipebursting)
• Successful underground mid-junction of 1600mm I.D. concrete pipe jack to form a 250m long pipe sleeve in solid rock: Port Shepstone.
• A 680 tonne bridge-jack at Queensmead industrial area Durban.
• The first HDPe-lined pipejack (1500mm diam.) in South Africa at Umkomaas (Sappi-Saiccor).
• The longest (and largest) HDPe slipline contract in S.A. (Bluff Treatment Works).
• Caisson sinking at Amanzimtoti. Several concrete caissons were constructed using 1500 ID Class 100D jacking pipes to a maximum depth of 12m in dune sa