Our underpinning works range from subsidence work to deep bases in granular soils for retaining purposes. Although we are competitive in winning work which is relatively uncomplicated we possess the in-house skills both on site and from an engineering point of view to carry out the most complex of schemes. This can involve ground enhancement and/or preloading the bases by jacking.

Ground Conditions

As we offer a complete range of pile types we are able to study the ground conditions and choose the type of pile which is most practical, economic and rapid to construct. We are not restricted in our choice by a limited range. We design the piles in-house so if the ground conditions change unexpectedly on site whilst carrying out the work then we can respond in the minimum of time.

Pile Diameter and Load Capacity

Typically this will range from anything from 100mm diameter to 450mm diameter. Load capacity will of course depend on the soil characteristics but normally loads up to 850kN can be achieved with a single pile.

Types of Piles

Typical types of pile are as follows:-

• Bottom Driven drop hammer (220m diameter)
• Bottom Driven Pneumatic (150 x 100mm diameter)
• Bored, Cased cast Insitu up to 450mm diameter using concrete or grout.
• Hollow stem technique (cfa) for a bored cast insitu system.

Ground Conditions

When the ground conditions consist of predominantly of Clay it is a case of attention to safety and then a question of achieving the most economic and most competitive system for underpinning. When the ground conditions are more difficult i.e. loose granular soils we can offer a closed board system or a system of ring shores as the excavation progresses. In cases of running sand a jacked shield system can be used.

Ground Enhancement and Jacked Underpinning

When underpinning works is being carried out, for example, to create a room below ground it is sometimes apparent that the bearing capacity of the ground at depth is less than that at the original founding level. This can of course lead to settlement of the building if the right techniques and precautions are not taken. We can enhance the ground at formation level by driving 100mm diameter piles. This not only enhances the bearing capacity of the ground but provides a shear key in the case of a retaining structure. Granular soils can be pre-consolidated by hydraulically jacking the primary bases using sacrificial stools similar to those used for high level beams.

Retaining Structures

For basements and similar retaining structures reinforced underpinning bases are often required. These sometimes have a toe to prevent forward sliding. We can create this type of underpinning base.

Deep underpinning and Work Below The Water Table

Underpinning bases some 6-7m depth have been formed in one operation. For works below the water table a system of well pointing can be used. To minimise the possibility of settlement to adjacent buildings a pre-grouting technique can also be used.