## Earth pressure coefficients

EN 1997-1 Annex C provides a numerical procedure for determining active and passive earth pressure coefficients for use in retaining wall design, which is discussed in Chapter 12.

The charts that follow show the variation in KaY and KpY (denoted Ka and Kp on these charts) with angle of shearing resistance 9, for different values of interface friction 5 (0°, 5°, 10°, 15°, 20°, 25°, and 30°), for vertical walls (0 = 0°). Each figure gives curves for different slope gradients tan p (flat, ±1:10, ±1:5, ±1:4, ±1:3, ±1:2.5, ±1:2, and ±1:1.5), where available. Coefficients KaY and KpY allow the earth pressure acting normal to the all surface to be calculated (see Chapter 12 for details).

The numerical procedure on which these charts are based imposes certain limitations on the values of interface friction 5 and slope angle p that can be used. Specifically, 5 must satisfy the condition 5 < 9 and p must satisfy p > mw - mt (see Chapter 12 for the definition of these terms). For this reason, several of the lines shown on the charts are truncated and others lines are missing. If the value of Ka or Kp is not given here, then an alternative procedure must be used to obtain their values (again, see Chapter 12 for possible alternatives).

The practical consequence of these limitations is that the procedure is not valid when p < 5 for the active case and - p < 5 for the passive.

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