The displacement diagram shows a dishing effect as discussed earlier. For this exercise, the software default value for the modulus of subgrade reaction was used.

It was modeled and analyzed in STAAD Foundation as “Mat”, which is a flexible foundation the soil was defined using coefficient of subgrade reaction. Figure 1a shows a simple slab-on-grade foundation. Displacement reduces as it moves away from the center. So the displacement diagram of a footing with a load at center will have a dishing effect.Ī point at the center of the footing will experience the highest displacement. In other words, the ratio between pressure and settlement at all locations of a footing will remain constant. Vx Heavens Virus Collection more.Īs Terzaghi mentioned, proper estimation of contact pressure for a flexible foundation could be very cumbersome, so it is assumed that Ks remains constant for the entire footing. Authentication options include: 802.1x, MAC-based. Established access rights, internet safety. Download (5MB) results of designed deflections in a piled retaining wall produced by WALLAP, calculation based. Mathematically, the coefficient of subgrade reaction is expressed as: Ks = p/s (Eqn 1) where p = contact pressure intensity and s = soil settlement. Numerically, kip/in 3 is correct but does not properly represent the physical significance of the measured value and could be mistaken as a density unit or a volumetric measurement. Some express this term in kip/in 3 (or kN/m 3) which can be misleading. For the English unit system, it is often expressed in kip/in 2/in in the SI system it is expressed as kN/m 2/m. Is there any relationship between bearing capacity and modulus of subgrade reaction? Modulus of Subgrade Reaction (Ks) This term is measured and expressed as load intensity per unit of displacement. As more and more engineers will use software to design foundations, it is essential for engineers to have a fundamental understanding of this soil parameter. Many engineers are not familiar with this term and often try to compare it with bearing capacity. However, these computer programs often ask for an input called “modulus of subgrade reaction”.

Manual computation of flexible analysis could be challenging and, in almost all cases, software programs such as STAAD, SAFE, GT STRUDL etc. But for large and multi column foundations, most engineers prefer flexible analysis. That particular assumption works well in practice for small and single column footings. However, that simplicity assumes the footing will behave as a rigid body. Because of simplicity and ease of use, this method is still the fundamental soil parameter for foundation design. The obvious reason is that basic examples given in most text books almost always use bearing capacity to calculate the plan dimension of a footing. Probably the most widely used value in a soil report is soil bearing capacity.

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