Info

Since the building is relatively low-rise, select a low number between these limits, say n = 12©

Depth of investigation points for individual shallow foundations Assume individual shallow foundations will be bf = 2m wide

Minimum depth of investigation is zspread = max(6.0m, 3 x bf) = 6 m if using spread footings©

Depth of investigation points for raft Assume raft will be braft = 60m wide

Minimum depth of investigation is zraft = max(6.0m, 1.5 x braft) = 90 m © Depth of investigation points for pile foundations

Assume individual piles will have base diameter Dp = 600mm and the minimum overall width of the pile group is bg = L = 60 m

Minimum depth of investigation is Zpile = max(5.0m, 3 x Dp, bg) = 60 m © Summary

Allowing for competent stratum at t = 15m, proposed maximum depth of investigation is Zmax = t + 5m = 20 m

4.11.2 Borehole log

Example 4.2 presents a typical borehole log from the hotel site, prepared according to BS 5930. The notes that follow discuss the changes necessary to bring the log into line with EN 1997-2 and EN ISO 14688.

Notes on Example 4.2

O This description remains the same after the introduction of Eurocode 7 and its associated standards, in particular EN ISO 14688.

© According to BS 5930, the term 'stiff' implies the clay has an undrained strength cu between 75 and 150 kPa. Under EN ISO 14688, the term 'stiff' refers solely to the soil's consistency as assessed by field inspection of the clay samples. Where measurements of undrained strength are made, an additional term may be added to the description, e.g. 'medium strength' for cu = 40-75 kPa. Two triaxial compression tests gave undrained strengths of 59 and 72 kPa. Hence a Eurocode 7 compatible soil description in this instance would be 'Stiff brown medium strength sandy becoming gravelly CLAY', where the CLAY may be abbreviated to 'Cl'. The terms 'stiff' and 'medium strength' are not inconsistent.

© This description remains the same under EN ISO 14688, but could be abbreviated to 'Dense brown clSa and Gr'.

© This description remain the same under EN ISO 14688.

© According to BS 5930, this sand is described as 'dense' because the measured standard penetration test (SPT) blow count is in the range 30-50. However, Annex F of Eurocode 7 Part 2 correlates blow counts corrected for rod energy and depth, the (N1)60 value, with the relative density descriptive terms. The range of corrected blow counts are different from BS 5930. However, it has been recommended17 that the descriptive terms for relative density continue to be based on the uncorrected N-value and the ranges given in BS 5930.

© The description remains the same under EN ISO 14688. See © above.

Example 4.2 Borehole log

Decoding Eurocode 7

by Andrew Bond and Andrew Harris

Chapter 4 Ground investigation and testing

Borehole NO

0 -1

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