Cathedral Street Timberheading

The Challenge

City College Glasgow has gone from strength to strength since being founded and specifically since a merger in 2010 which has turned this Scottish institution into an educational powerhouse. It has grown to accommodate over 27,000 students, studying on over 2000 different courses.

Of course, with growth comes the need for expanded infrastructure. When our client needed to make a connection to a sewer at the College’s Cathedral Street campus- requiring a tunnel be constructed large enough for engineers to enter- they enlisted the help of the Trenchless Experts- Terra Solutions. That this tunnel was to be built under one of the busiest roads in Glasgow was not an issue for Terra, who specialise in non-disruptive tunnelling techniques, including Timberheading.

The sheer volume of traffic using Cathedral Street, an arterial route in Glasgow, meant that an open cut requiring mass diversions would be unworkable. A cluster of existing services grouped close to this sewer further exacerbated this, making Timberheading the most logical choice of technique to use.

The Solution

Without the option to utilise Open Cut, our client engaged Terra Solutions- The Trenchless Experts- to develop a trenchless solution which would enable a ‘blind’ connection to be made without exposing the existing sewer from ground level. Terra Solutions formed a method statement which would fulfil this whilst avoiding services & ensuring constructability in potentially challenging ground conditions. A timber heading was constructed in the gravelly clay, launch was at a depth of 4.5m and once it crossed over an existing storm sewer the heading was stepped down to meet the existing foul sewer at a depth of 7m. Using a heading to achieve this provided adaptability for changing ground conditions. As the heading progressed kick boards were installed, the frames tied together and overcut grouted to ensure stability. When the heading met the existing foul sewer a saddle connection was made & a 300mmø pipe connected, the heading was then packed with concrete & the pipe laid to a fall. Once fully backfilled, the pipe was laid the required gradient, additional grout was pumped along the heading via grout tubes installed at 1.8m centres

The Result

Terra Solutions completed their contract, bringing their expertise in trenchless technology to bear for the client. The high standards to which Terra operate prompted a senior engineer at Sir Richard McAlpine Ltd. to comment:

Timberheading Testimonial

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