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 domdem (Civil/Environmental) 15 Jul 02 12:08
 Could someone please explain exactly what the modulus of subgrade reaction is and how it relates the cbr valueat the moment i cannot find any information that correlates one to the other.any help would be much appreciated
 (2)  drt (Geotechnical) 15 Jul 02 19:14
 Domdem,The modulus of sudgrade reaction is determined from a plate loading test, in which a 30 inch diameter steel plate is loading using a steel jack and beam (for reaction).  The load is applied at a predetermined rate until a pressure of 10 psi (69 kPa) is reached.  The pressure is held constant until the deflection increases not more than 0.001 inch per minute for three consecutive minutes.  The modulus of subgrade reaction (k) is calculated as:k=p/Deltawhere: p = load (10 psi)delta is total deflection of steel plate (inches)traditionally expressed in lbs/in3.The following is a rough correlation between the CBR and modulus of subgrade reaction (MSR):MSR = CBR100 = 3150 = 5.5200 = 10250 = 20500 = 50700 = 80The above information was taken from "Pavement Analysis and Design" by Yang H. Huang.
 domdem (Civil/Environmental) 16 Jul 02 3:18
 Thank youCan this relationship be correlated to other size plates (ie 300mm)i believe th army corps did something about it but here in the uk it is very difficult to get any information about itbest regards
 drfefefe (Civil/Environmental) 1 Dec 02 15:00
 The best formula for this correlation according with my experience is:K=-3.03E-05(CBR)^4+0.0069(CBR)^3-0.571(CBR)^24.305(CBR)CBR    K 0       0 3      68 5     10810     19320     30830     37735     40245     44250     46160     50070     54375     56380     58290     604
 ktw381 (Structural) 2 Dec 02 20:54
 how spt value correlate with modulus of sub-gradeappreciate if someone can help.
 Focht3 (Geotechnical) 31 Dec 02 12:58
 (Sigh.)  The modulus of subgrade reaction is not a soil property.  As a result, it cannot be "determined" using a CBR test, plate load test - or any other test, for that matter.The modulus of subgrade reaction is a calculation expedient, and nothing more.  It is the ratio of applied pressure divided by the corresponding soil or rock movement.  It is directly affected by the size of the loaded area, the soil or rock shear modulus (which is strain dependent), the direction of loading, the type of loading - and many other factors.  It is not analogous to the stiffness of a steel spring, or Young's modulus for steel.  There is no such thing as "the" modulus of subgrade reaction - and it cannot be found in some textbook or simple correlation.If I remember the definition of CBR correctly, it is defined as:CBR = ([Applied Pressure at 0.1 inch piston deflection]/1000 psi)*100Assuming this equation is correct, you can directly calculate a "modulus of subgrade reaction" k-value for the test as:k (psi) = CBR * (1000/100)/(0.1) = CBR * 100This is markedly different than the correlations proposed by drt or drfefefe.drt and/or drfefefe: Where do your correlations come from?

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