Pile Design and Construction Practice, Fifth edition

510 Ground investigations, contracts and pile testing
have supervisory responsibilities (only co-ordination authority) under a JCT contract with
the Employer.
Irrespective of whether piling work is executed as a main contract or by sub-contract, in
traditional British practice tenders are invited by one of three principal methods. These are
as follows:
Method 1: The Engineer is responsible for deciding the type or alternative type of
pile, the working loads, and the allowable settlement under test load. The
Engineer specifies the material to be used, the working stresses, fabrication
methods and penetration depths. Tenders are invited on the basis of
a detailed specification and drawings, which should be accompanied by a
ground investigation report, and a site plan for contract works showing
existing structures and surface levels, proposed re-grading levels, and the
operating levels for the piling rigs.
Method 2: The Engineer invites tenders for one or an alternative system of piling
from specialist contractors. The invitation to tender is accompanied by a
pile layout showing individual pile loads or column and wall loadings, and
by a detailed specification including such items as materials, working
stresses, performance under load test, and other criteria of acceptability.
The Contractor decides on the required type (or alternative type) of pile,
the diameter and the penetration depth for the specified working loads, and
bases a tender on in-house estimates of performance. Site information as
described for Method 1 should also be supplied.
Method 3: The Engineer supplies a drawing to the tendering Contractor showing the
wall and column layout of the structure together with the loadings; the site
information as described for Method 1 is also supplied. No specification is
issued and the Contractor is expected to submit a specification with his
tender, and to guarantee the successful performance of the piles. Because
an increasing number of piling contractors are offering new types of piles,
particularly displacement piles which are designed to optimize bearing
capacity and minimize concrete usage and spoil disposal, this procurement
method can give best value to the Employer in these circumstances.
Method 1 has the advantage that the responsibility of each party is clearly defined. The
Contractor has the responsibility only of selecting the most efficient type of plant to do the
job and to install the piles in a sound manner complying with the specification. The method
has the disadvantage that the knowledge and experience of the Contractor may not be fully
utilized, since the Engineer may not always select the most suitable pile for the job. In exercising
responsibility for deciding on the pile diameters and penetration depths, the Engineer
may instruct the Contractor to install preliminary test piles before making final decisions on
the dimensions of the working piles. The liability for unforeseen adverse ground conditions
generally falls to the Employer on the advice of the Engineer.
Method 2 provides the widest choice of piling systems and utilizes the experience
of the Contractor to the fullest extent, but greater care is needed in defining responsibility.
In particular, the Engineer must specify precisely the requirements for performance under