Why Coulomb's Wedge Theory Ignores Earth Pressure at Rest

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SUMMARY

Coulomb's Wedge Theory primarily addresses limit active (k_a) and passive (k_p) lateral earth pressures, neglecting the concept of earth pressure at rest (k_o). The discussion highlights that k_o, which for non-compacted dense sand with an internal friction angle of 30 degrees is approximately 0.5, receives less attention in literature compared to k_a (0.33) and k_p (3.0). This oversight is attributed to the fact that small deflections in retaining walls or foundations lead to k_a and k_p dominating the behavior of lateral loads, thus minimizing the relevance of k_o in practical applications.

PREREQUISITES
  • Understanding of Coulomb's Wedge Theory
  • Knowledge of lateral earth pressure coefficients (k_a, k_p, k_o)
  • Familiarity with soil mechanics and internal friction angles
  • Basic principles of retaining wall design
NEXT STEPS
  • Research the derivation of earth pressure at rest coefficients (k_o)
  • Study the implications of lateral earth pressures on retaining wall design
  • Examine case studies involving non-compacted dense sand and its behavior under lateral loads
  • Explore advanced soil mechanics concepts related to earth pressure theories
USEFUL FOR

Civil engineers, geotechnical engineers, and students studying soil mechanics who are interested in understanding the nuances of earth pressure theories and their applications in foundation design.

whammy123
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Hi! Can someone tell me why Coulomb in his Wedge Theory of Earth Pessure didn't take into considertion Earth pressure at rest? He cosnidered only limit active and passive pressures, but why didn't he write anything about pressure at rest? I 've looked up some books, but there is only the derivation of formulas for active and passive pressure, without any note about pressure at rest. Thanks for help in advance!
 
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It's been awhile since I have looked at my aging foundation texts, but it is true that 'at rest' lateral Earth pressure coefficients (k_o) are not given as much attention as 'active' (k_a) and 'passive' (k_p) lateral Earth pressure coefficients. For a non compacted dense sand (in place) with an angle of internal friction of 30 degrees, K_o is about 0.5, k_a = 0.33, and k_p =3.0. The respective Earth pressures are these coefficients times the vertical soil pressure at a given point. When a retaining wall or other foundation is subject to lateral loads, small deflections result in k_a and k_p governing, which is probably why you don't hear too much about k_o.
 

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