In English only
||||
 Topic: Geotechnical design and analysis Subject: subgrade modulus
 Author: Nejat Ozcimen 2001-07-12 hidoes anybody has info. about the subgrade modulus coefficient, k (t/m3) can be used for the settlement amount?if the mat foundation system is rigid and the layer below it is sandy silty clay; as far as i know it can not be used for the settlement calculations. it is only used for differencial deformations.?empric correlations recommended for the k coefficient is 1500-2000 t/m3 for this soil structure.But if you calculate that from the formula (Braja Das. "princ. of foun. engng.)it will be app. 150-200 t/m3.and consequently:if you use emprical values the settlement value is 1-2 cm.and if the other, the sett. is 12-13 cm. if i calculate the settlement by classical stress distribution method, it will be 15 cm. i use this modulus as a soil parameter to the SAP2000 programme.would you tell me that which value is reliable? and can i calculate the settlement amount by this way?..thanks.. Reply to this posting
Follow-up:
 Author: Paul W. Mayne 2001-07-12 Well, this has been subject of discussion for some time. What kind of data do you have to assess the stiffness of theground? You can represent the ground stiffness by anequivalent elastic modulus (E'), or alternate shear modulus(G') whereby E' = 2G(1+u') both in tonnes/m2, or by spring constant k' or subgrade coefficient (kh in tonne/m), or by subgrade reaction modulus (Kh in tonnes/m3).Only the E' (and G') are true soil parameters (see recentarticle by Briaud in Geotechnical News). The other k', kh, and Kh values are derived from soil + foundation geometry.For example Kh (tonnes/m3) you want comes from elasticcontinuum theory for deflection (w) of circular foundationof diameter (d) on a semi-infinite elastic medium: w = q d (1-u2)/E where u = Poisson's ratio and q =applied surface stress. For finite layer and nonhomogeneousE with depth, as well as flex vs. rigid footings, see Mayneand Poulos (ASCE JGGE June 1999).Then the definition of Kh = q/w which from above elasticsolution, give Kh = E/[d(1-u2)] for simple case (has unitsof tonnes/m3). Thus depends on foundation size & soil deformation characteristics.

Follow-up:
 Author: Nejat Ozcimen 2001-07-13 thank you Paul,i have two things that i need more info?1st as far as i understand, the subgrade reaction coefficient Kh (t/m3) can not be used for the setllement analysis. it is only used for deflection of the foundation.?is settlement only determined by E (t/m2) layer by layer?2ndif i derive Kh (t/m3) by Kh=E/b(1-u2) it is app. 100-150 t/m3 but emprical correlations give 1500-2000 t/m3. in addition, 1st value represents very soft and slime soil condition? but it is not really. what is the difference betw. them.?thanks..

Follow-up:
 Author: Maryam Akbarzad 2005-01-19 Dear sirMy name is Maryam Akbarzad and I am doing an MS in Geotechnical Engineering at the University of Tabriz. My subject of thesis is Investigaion about equations and the methods of estimation of the coefficient of subgrade reaction and analysis of the sensitivity of it in design of foundations and retaining walls. that would be very kind of you to provide me with any more lectures, books and etc. best regardsAkbarzadUniversity of Tabriz - IRANFaculty of Civil Engineering - Department of Geotechnical EngineeringMaryam Akbarzad

Follow-up:
 Author: chai 2005-02-03 I think the subgrade modulus of soil should be 1500-2000 t/m3 .