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Coefficient of Subgrade Reaction?

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Asked: September 27, 20202020-09-27T16:15:37-07:00 2020-09-27T16:15:37-07:00In: Transportation
Neenu S K
Neenu S K

Neenu S K

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Neenu S K

What is the Coefficient of Subgrade Reaction?

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  1. AdityaBhandakkar

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    AdityaBhandakkar User
    2020-09-28T13:59:35-07:00Added an answer on September 28, 2020 at 1:59 pm

    Hi, In simple words coefficient of subgrade reaction is the function of stiffness and compressibility of soil.

    It is also known as Modulus of subgrade reaction. It is pressure sustain by a sample of soil under a rigid plate of std diameter/unit settlement measured at a specified pressure.

    According to IRC, Value of  K should be measured at the 1.25 mm settlement.

    Its value is in the range of 0.05 to 0.15.

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  2. aviratdhodare

    aviratdhodare

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    aviratdhodare
    2020-10-03T11:27:46-07:00Added an answer on October 3, 2020 at 11:27 am
    Coefficient of Subgrade Reaction?

    K = Pressure / Deflection

    p ∞ Δ

    p = KΔ

    Where, p = reaction pressure, Δ = deflection, K = mod. of subgrade reaction

    MODULUS OF SUBGRADE REACTION

    In simple, it is a measure of grounds ability to resist immediate elastic deform under load. It is defined as the pressure needed to deform the subgrade by a given unit dist. SI expression is Mpa/m, & that is the unit used. Americans used pci.

    The modulus of subgrade reaction describes the soil’s short-term, elastic response to loading. That is the subgrade property we need to know to determine slab thkness in most design methods.

    100pci = 27.2Mpa/m

    To calculate the Mod of Subgrade Reaction, Plate bearing test is conducted. A graph is plotted with the mean settlement (mm) on x axis & load (kg/cm2)on y-axis. The pressure p corresponding to settlement of 1.25mm is obtained from the graph. The mod. of subgrade reaction K is calculated from the relation given below.

    K = P/0.125 Mpa/cm 

    Relation betn k value & CBR

    An existing correlation betn k-value (k in pci) & CBR, used in FAA airfield pavement thkness design (Advisory circular 150/5320-6E, FAA 2009) is k = (1500 CBR/26)0.7788 Where k is in pci or lb/in3

    Soaked CBR (%) 2 3 4 5 7 10 15 20 50 100
    k-value (MPa/m) 21 28 35 42 48 55 62 69 140 220

    Note: 100pci = 2.77 kg/cm3 = 27.2 MPa/m

    On the other hand, a commonly used conversation formula developed by Packard (Barker & Alexander, 2012) for the Portland Cement Association (PCA): k = 53.438 CBR0.5719

    Design of Rigid Pavement

    Based on K- value

    Axle load (Single & Tandem)

    Max temp differential in °C variation during day & night time.

    Flexural strength

    Slab thkness is decided with the help of chart given by IRC 58-2015 P 36-72

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  3. nikeetasharma

    nikeetasharma

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    nikeetasharma Guru
    2020-11-10T19:41:23-08:00Added an answer on November 10, 2020 at 7:41 pm

    The coefficient of subgrade reaction is referred as the ratio between the pressure against the footing or mat and the settlement at a given point expressed as the coefficient of subgrade reaction which is defined as the ratio between the pressure against the footing or mat and the settlement at a given point which is expressed as ;
    ks = q/S

    where,
    ks = coefficient of subgrade reaction
    q = pressure on the footing or mat at a given point
    S = settlement of the same point of the footing or mat in the corresponding unit of length

    i. The value of k is independent of the magnitude of pressure.
    ii. The value of s has the same value for every point on the surface of the footing.

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