This document discusses an elemental stiffness matrix for shallow foundations. It notes that in the elemental matrix, K1 and K2 only include the contribution of the subgrade modulus for the element. If the subgrade modulus is constant for the element, then K1 would be equal to K2, with both represented as the product of one half the element length, the subgrade modulus, and the element width.

1. From Foundation Analysis and Design,
5th edition, by Joseph E. Bowles,
McGraw-Hill, New York, 1996.

42. L1 / 2

43. Note: In this elemental
ASAT matrix, K1 and
K2 only include the
contribution of the
subgrade modulus for
the element. If ks is
constant for the
element, then:
K1 = (L1/2) ks B = K2

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