The oldest and most well known form of underpinning is ‘Traditional Underpinning’.  Traditional Underpinning stabilises the existing walls by excavating beneath the existing foundations in a ‘Hit & Miss’ fashion to a depth where firm load bearing strata exists.  The excavated material is replaced with mass concrete and can be reinforced or un-reinforced depending on the application.

Traditional Underpinning is usually applied when the existing foundations are at a shallow depth.  It is economical if load bearing strata can be found at a depth up to 1.5m.  If load bearing strata is found to be at a depth greater than 1.5m then a minipiled solution will be more economical, safer, less obtrusive and faster.

Due to advances in minipiling installation and minipiled underpinning techniques traditional underpinning has become less common and is generally only used to increase the ceiling height of an existing basement.

Larsen Foundations Ltd has several cost effective minipiled underpinning solutions. We can provide a full surveying and underpinning design service. Our most popular restricted access minipiled underpinning solutions are outlined below.

sIMPLY SUPPORTED needleS

This method supports the wall / foundations by installing piles at either side of an existing wall (internally & externally) or at either side of a corner (both piles externally).

A pocket is created either in the masonry above the foundation (if site dimensions allow) or beneath the foundation (if the depth from ground level to top of foundation is shallow – less than 400mm).  A cage of structural steelwork is inserted through the pocket and placed over the piles. The needle is then cast in-situ using high strength concrete.

ADVANTAGES OF SIMPLY SUPPORTED NEEDLES

Considerably less excavation than for a traditional underpinning solution thus a reduction in material to be taken off site.

High load capacities possible depending on the diameter of the piles installed and the spacing of the needle beams.

Suitable for restricted access situations.

Quicker than traditional underpinning.  The needles are spaced at intervals and there is no requirement for a ‘hit & miss’ approach.   

Depending on the wall’s condition, the needles can be at up to 1200mm centres, this reduces site time, plant and labour costs.

CANTILEVER needleS

The construction of the cantilever needle beam is as per the simply supported needle beam. It varies however as both piles are installed either externally or internally (usually externally). The pile installed closest to the wall is a compression pile and the pile furthest away from the building is a tension pile.

ADVANTAGES OF CANTILEVER NEEDLES

Considerably less excavation than for a traditional underpinning solution thus a reduction in material to be taken off site.

Quicker than traditional underpinning.  The needles are spaced at intervals and there is no requirement for a ‘hit & miss’ approach.   

Suitable for restricted access situations.

Depending on the wall’s condition the needles can be at up to 1200mm centres, this reduces site time, plant and labour costs.

The cantilever needle can be created externally allowing the owner to remain in the property whilst works are being carried out.

ADVANTAGES OF SINGLE PILE NEEDLES

Considerably less excavation than for a traditional underpinning solution thus a reduction in material to be taken off site.

Quicker than traditional underpinning. The needles are spaced at intervals and there is no requirement for a ‘hit & miss’ approach.   

Depending on the wall’s condition, the needles can be at up to 1200mm centres, this reduces site time, plant and labour costs.

The single pile cantilever needle can be created externally allowing the owner to remain in the property whilst works are being carried out.

The single pile cantilever needle can be constructed within a space of 750mm making it ideal for highly restricted access situations.

internal piled raft

This underpinning method supports existing walls to individual rooms or entire buildings. Minipiles are installed internally using low vibration piling equipment and the piles are incorporated into a series of needles which are in turn incorporated into a new reinforced concrete structural floor slab. The needle beams project from the raft slab at intervals into the internal and external load bearing walls below ground level.

Depending on the height of finished floor level in relation to finished ground level we can offer a dropped edge raft solution that ensures the ends of the needles are not visible from outside.

For highly loaded structures the spans between the needles are reduced and the needle reinforcement increased. Multi storey buildings of solid masonry construction can be underpinned up to 6 storeys high.