Pile Platform Design

Pile Platform Design

Piling Mat Design

A piling mat is a type of working platform used for piling rigs to travel on, providing a stable base on which they can move around the site and operate.  Many working platforms are used in subsequent constructions phases, so the design should be checked to ensure it is appropriate for these uses and conditions.

Piling mats are typically constructed using well-graded stone, clean-crushed concrete, or crushed hard rock.  In some circumstances recycled demolition material can be used if the metal and timber debris are removed.

Piling mats will need to be compacted in layers and should be free draining to prevent any build-up of water or slurry on the surface.  On sites with a high water table, a membrane should be used to prevent the migration of fine-grained soils.

If a piling mat is too thick it will be incurring unnecessary costs, whilst if it is too thin it may require repair, resulting in lost time and financial cost; a soft spot in the surface of just 1sq meter can be enough to unbalance a rig!

The thickness of a piling mat depends on four factors:

• Quality of the subgrade – an appropriate site investigation must be carried out across the likely area of the platform. Strength determination could be carried out by either plate load tests, CBR tests or vane tests.
• Quality of the platform material – The specification of the platform material should be such that the performance requirements in term of compaction, durability, trafficking and drainage will be met.
• Strengthening material – in some cases the use of Geogrid layer may prove economical to reduce the thickness of piling mat.
• Loading – It is important to assess the size of the plant which will be using the piling mat, as well as distinguishing the different loadings between plant moving across the mat and plant in its operations state (e.g., cranes and piling rigs)

The design of piling mats should be undertaken in line with BR470, “Working Platforms for Tracked Plant”.

It is mandatory that every site with an operational piling rig has a Working Platform Certificate (WPC) that states the piling mat has been correctly designed and installed.  The WPC must be signed by the principal contractor and provided for the piling contractor before any piling commences on the site.

Piling mats should be inspected daily to ensure they are in proper working condition. If any excavations, trenches or holes have formed in the surface, they must be properly backfilled to ensure they are as stable as the rest of the mat.

GES can undertake the site investigation and design works required to assess the thickness and dimensions of a piling mat.

As mentioned above there are several methods that can be used but the most typical method of determining the ground’s ability to accept a piling platform is that of a Plate load Test (PLT).

Plate Load Testing (or Plate Bearing Testing) is an in-situ field test used to determine the ultimate bearing capacity of predominantly soils, but also rock and man-made materials such as concrete and macadam.

Plate Load Testing requires an a imposed load to be applied through a plate of known diameter, typically 300 mm, 450 mm and 600 mm. Load applied in kilonewtons per metre squared (KN/m2 ) making use of a hydraulic jack is measured through UKAS calibrated dials measuring the deflection to 0.01 mm. the deflection of the plate measured in millimetres can identify the settlement within a soil with a known forced load whilst for more ridged materials a shear strength can be identified assuming the capable load applied is enough to shear the material.