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Direct assessment

Direct assessment of soil parameters is typically only possible on the basis of laboratory tests. For example, derived values of strength, permeability, and stiffness (drained or undrained) may be determined directly from appropriate triaxial tests. Such direct assessment must, however, take appropriate account of any sample disturbance that could influence the derived value.

### 5.2.6 Symbols

Symbols used in Eurocode 7 Part 1 for geotechnical parameters include c' for cohesion (in terms of effective stress), cu for undrained shear strength, Kg for the coefficient of earth pressure at rest, y for weight density, and 9' for the angle of shearing resistance (in terms of effective stress) - with X being used as a general symbol for an unspecified material property. [en 1997-1 §1.6(1)]

A longer list of symbols for geotechnical parameters is given in Eurocode 7 Part 2. [EN 1997-2 §1.8(1)]

In our opinion, the failure of Eurocode 7 to provide a more comprehensive list of 'standard' symbols is a lost opportunity to remove confusion between engineers who have to check each other's calculations or work together on the same calculations. In addition, the opportunity to standardize symbols common to both geotechnical and structural engineering has not been grasped, except at the highest level of abstraction, where, for example, E is used for effects of actions and R for resistance, etc.

Throughout this book, we have adopted a set of symbols that follows the notation used in many of the non-geotechnical Eurocodes. In particular, we have used simple capital letters to denote major variables, for example: F for a general force V for a vertical force H for a horizontal force M for a bending moment q for surcharge u for pore pressure

To each of these symbols we then attach subscripts that provide the necessary additional information that the Eurocodes require in order for the appropriate combination and partial factors to be applied. For example: VGk = characteristic (k) permanent (G) vertical force (V) MQ,rep = representative (rep) variable (Q) moment (M) uAd = design (d) accidental (A) pore pressure (u)

Furthermore, we identify design effects of actions and design resistances by using the subscripts 'Ed' and 'Rd' attached to the main symbol, rather than use the symbols Ed and Rd alone; e.g. MEd rather than plain Ed; MRd rather than plain Rd.

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