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Site investigation

NSP Foundations Ltd offers a full ground investigation service for clients. From the smallest single bore-hole project to large scale developments, our technical team has a wealth of experience of different drilling, sampling, testing, monitoring and surveying.

Our services include:

  • Underground service searches

  • Trial pitting

  • Window sampling

  • Rotary, open hole and cored drilling

  • Gas and groundwater monitoring

  • Inclinometer monitoring and data processing

  • GPS surveying


Piles can be installed with or without casing, using auger, rotary percussive or driven methods to cater for most ground conditions.



  • Rotary Bored cased cast insitu piles from 350mm to 900mm diameter.



  • Overburden Drilling System (ODS).  These are rotary percussive bored cast insitu permanently cased piles 150mm to 330mm in diameter.


  • Top Driven steel tube up from 115mm to 400mm diameter of H section up to (300 x 200kg)


  • Bottom Driven from 220mm diameter to 300mm diameter steel tube.


Contiguous Pile Walls

Structural piles are installed at close spacing,

100-150mm between piles. Soil between piles

is therefore exposed during excavation, so

suited for projects where groundwater level

lies below the maximum excavation depths.



Secant Pile Walls

A guide wall is required for this method of construction

to ensure that piles are accurately located to achieve an

interlock (or secant) cut into the adjacent pile. A secant

pile wall uses interlocking male and female cast in situ

piles to produce a retaining structure. Construction is

carried out sequentially with primary (female) piles installed

first the secondary (male) piles cut into the primary piles

forming a continuous wall.

The wall uses a weak concrete or grout for the female pile,

which is unreinforced. This wall type provides some degree

of water retention but is not watertight.


A bored pile retaining wall of any type can stand unsupported and acting in cantilever up to a limit. For deep excavations, piled retaining wall designs would require temporary propping, bracing or anchoring; all can be designed by the NSP Team.

These can be for example:

  • Braces or props across the excavation from wall to wall. These are heavy and obstruct headroom in the excavation.


  • Raking shores, founded in the excavation and propping diagonally upwards against the walls.


  • Ground anchors to tie the wall back, leaving the excavation unobstructed but there are issues for adjacent landowners.


  • Berms, or banks of earth left in place, unexcavated, acting as mass-stabilisation for the wall.



This repair process can be used to strengthen foundations which have been weakened by a variety of factors, including leaking drains or clay heave.

or if you wish to lower existing foundations adjacent to new proposed deep excavations or to increase headroom within existing basements.

In the process of underpinning, the area underneath the load of the foundation is repaired or reinforced.

Underpinning comes in many types and suits different kinds of repair projects. In order to make the right choice, it is necessary to understand the structure of the foundation, the supports which are used, and the factors that cause the foundation to become damaged.

Rock Anchoring and Soil Nailing

We can provide a range of rock anchor and soil nail solutions, for both private and commercial sector projects.

These include:

  • Full anchoring of retaining walls.

  • For the stabilisation of eccentrically loaded foundations.

  • In the stabilisation of slopes and rock walls or cuts.

  • For systematic rock stabilisation and local support for underground excavations.

  • For the stabilisation for uplift purposes as, for example, in structures in ground water.


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