In his Terzaghi Lecture t o the American Society o f Civil Engineers in 1975, G.G. Meyerhof introduced the concept of critical depth for a pile foundation: if the base of the pile is above the critical depth, the pile capacity is a function of the penetration depth, but if below the critical depth the capacity is constant and independent of the penetration depth.

This program has been written in BASIC language, to use Meyerhof's methods for calculating the ultimate load capacity of single piles, as set out in that lecture. The program will work with any kind of pile: end-bearing and/or frictional; driven or bored; straight or belled; and of any common cross-sectional shape, in up to six layers of any soil except unsaturated cohesive soil. Immediate or long-term loading may be selected, and provision is made for the calculation of negative friction effects when an endbearing pile passes through soft cohesive soils.

Because of the large amount of data that may have to be entered, the program has built-in cross-checks wherever possible, which detect conflicting data, warn the operator, and allow amendment. Means have also been provided for easy correction of errors in input at the end of each block of data entered. Prompts are liberally used, to make the program as "user-friendly" as possible.

The ultimate end-bearing capacity of piles in layered soils may be limited by the proximity of the pile base to the underlying and/or the overlying layer boundary, and these conditions are fully checked by the program. The ultimate bearing stress of frictional piles is obtained from one or more of several equations, depending on the soil type and its consistency, but the bearing strength of unsaturated cohesive soils is ignored.

After the bearing capacity of the pile has been calculated and displayed, options are given of repeating the calculations with a change of pile function, or of pile type, or of penetration depth, or with different soil properties, and without loss of any of the other data.

The method relies heavily on the evaluation of critical depth ratios and bearing capacity factors, given in graphical form in Meyerhof's paper. It was found to be impossible to curve-fit these relationships, so the curves on the graph were digitised by measurement of ordinates. These were stored in a virtual array, and smoothed out by differencing the values using a subsidiary program. The digitised values are read from the array and interpolated if necessary by a sub-program within the main program.

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