Less pain with piles using Ischebeck Titan anchors

Redevelopment of properties in South Kensington, London were aided by piles created using Ischebeck Titan's 127/111 hollow self-injecting anchors.

The redevelopment of two properties near to the Old Brompton Road in South Kensington, London has benefited from the application of materials and methods more familiar to ground engineering projects than construction and temporary works.

The multi-million pound project involves the conversion of two existing end of terrace properties into a prestigious single executive residence.

In most circumstances this would have been a relatively straightforward task.

However, in this case, in addition to the normal construction work that might be expected, the developers decided to create a 13m x 8m basement beneath the end property where previously there had not been one.

The end property would, obviously, have to be demolished and rebuilt, but this left the problem of excavating the 4.5m deep basement on a site that was adjacent to the neighbouring property and bounded on the other side by a high brick garden wall, both of which were subject to local conservation/preservation orders.

Ground conditions on site were typical for the area, comprising 5-6m of dense terrace sand and gravels overlying London clay.

The water table level fell below the level of the new basement formation.

Initial considerations suggested an underpinning solution for both the adjoining property and boundary wall, with the latter also requiring a Party Wall Award.

This work would more than likely have required sacrificial earthworks support and temporary propping, possibly at several levels to resist horizontal earth pressures, as prevailing deposits would have been unable to stand unsupported during excavation.

For safety reasons, pins would have to be constructed in a minimum of two vertical lifts due to the overall depth of the excavation.

In addition, the front, central and rear walls of the adjoining property would also have required underpinning, again using transition pins due to the depth.

All in all, the underpinning solution would have been a costly and potentially risky operation, a fact recognised by temporary works consultants, Contractors Design Services (CDS) of Stanstead Abbotts, Hertfordshire.

CDS managing director, Simon Smith, explains, "Underpinning is probably the first thought when faced with a situation such as this, but with the complexities of this project, we very soon realised that this was a non-starter".

"We also had to consider the client's desire to maximise the size of the basement, which virtually ruled out the use of an inboard piling solution".

"So, working in conjunction with specialist groundworks contractors, WT Group and injection anchor supplier, Ischebeck Titan, we devised a solution using Pali Radice piles, which was accepted by all parties".

Piles were created using Ischebeck Titan's 127/111 hollow self-injecting anchors.

"Each anchor has an external diameter of 127mm and an internal diameter of 111mm through which grout is injected under pressure as drilling proceeds".

"The grout exudes from apertures in the body of the drill bit at the end of the anchor, creating a continuous low pressure scouring action against the sides of the drill hole".

"This action exposes harder parts of the hole whilst flushing and removing the softer parts".

"A repeated withdrawal and redrilling procedure reams and improves the hole, which fills with grout to create a strong irregular grout body reinforced by the steel anchor that runs through its centre".

"The piles were installed to a sequence at 450mm centres, using 225mm sacrificial drill bits, through the existing masonry party and garden walls via cored holes inclined at 15 degrees to the vertical around the entire perimeter of the intended basement area".

"The piles provided both vertical support to the walls and horizontal support to the ground below, which allowed for excavation of the basement to proceed without hindrance and without the need for further temporary works".

"A single level of temporary bracing was located at the pile heads to maintain overall horizontal stability across the excavation".

"This was removed on completion of the new lower ground floor slab".

Simon Smith concludes, "The Pali Radice technique not only provided an excellent temporary works solution, it also obviated the need for the transition pins below the front, central and rear walls of the adjoining property.

The solution delivered significantly greater savings in both time and costs than would have been achieved using underpinning and more common temporary works methods.

It has allowed the development to proceed without undue delay and should enable the developers to secure an earlier return on their investment".

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