What is the modulus of subgrade reaction used for?
The modulus of subgrade reaction (k) is used as a primary input for rigid pavement design. It estimates the support of the layers below a rigid pavement surface course (the PCC slab). The k-value can be determined by field tests or by correlation with other tests.
How do you calculate modulus of subgrade reaction from bearing capacity?
k = 40 x SF x qa, where SF is factor of safety considered in bearing pressure calculation and qa is allowable soil bearing capacity. So, you could employ the above equation in determining the Soil Subgrade Modulus.
What is unit of modulus of subgrade reaction?
Modulus of Subgrade Reaction (Ks) This term is measured and expressed as load intensity per unit of displacement. For the English unit system, it is often expressed in kip/in2/in; in the SI system it is expressed as kN/m2/m.
What is soil subgrade reaction?
The subgrade reaction is the resistance from peripheral ground layers. It is a reaction force which depends on the ground displacement. It is assumed to be proportional to ground displacement with a proportionality factor that depends on the ground stiffness and lining dimensions (Fig. 3.15).
How do you measure soil modulus?
Soil elastic modulus can be estimated from laboratory or in-situ tests or based on correlation with other soil properties. In laboratory, it can be determined from triaxial test or indirectly from oedometer test.
What should be the CBR value for subgrade?
To understand the impact of CBR (subgrade strength) on the pavement, let’s look at some typical CBR values. A clayey soil generally has a low CBR value (less than 8). Sands are more granular and drain better and will generally have CBR values between 15 and 35. Gravel will have the best CBR values, generally 25 and up.
What is the K value of soil?
What is the K Factor? The K Factor is an index which quantifies the relative susceptibility of the soil to sheet and rill erosion. K Factor is used in the RUSLE2 soil loss prediction equation. Values range from 0.02 for the least erodible soils to 0.64 for the most erodible.
What is the subgrade modulus of soil?
The subgrade modulus is a function of the soil stiffness and compressible layer thickness, as well as the foundation dimensions and stiffness. The subgrade modulus is not constant underneath a foundation.
How CBR is calculated?
California Bearing Ratio Test Calculation
- Volume of mold=π4D2h.
- Volume of soil mass in mold=π4D2×Height of soil sample.
- Mass of water required=Dry volume of soil×Laboratory(OMC)100.
- CBR at 2.5mm=Test load at 2.5mm1370.
- CBR at 5.0mm=Test load at 5.0mm2025.
What is CBR method?
The California Bearing Ratio (CBR) is a measure of the strength of the subgrade of a road or other paved area, and of the materials used in its construction. The ratio is measured using a standardized penetration test first developed by the California Division of Highways for highway engineering.
What is coefficient of subgrade reaction?
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.
What is Oedometer modulus?
Nevertheless, oedometer tests are useful for determining the constrained modulus, also known as oedometer modulus (D), which is simply the reciprocal of the coefficient of volume compressibility (mv) commonly used in consolidation.
What is a standard Oedometer test?
The standard oedometer test, also referred to as consolidation test or one-dimensional compression test, is a classical laboratory test that allows characterizing the soil stress-strain behavior during one-dimensional compression or swelling.
How do you calculate CBR of soil?
CBR is the ratio expressed in percentage of force per unit area required to penetrate a soil mass with a standard circular plunger of 50 mm diameter at the rate of 1.25 mm/min to that required for corresponding penetration in a standard material. The ratio is usually determined for penetration of 2.5 and 5 mm .
How do you determine the subgrade reaction modulus?
Walker and Holland (2016) proposed the following approach to determine subgrade reaction modulus: Develop three-dimensional continuum model of the mat and the soil. Representative soil properties are assigned to the soil elements (see Fig. 1)
What is the equivalent modulus of subgrade reaction for 80 PCI?
For our example, the equivalent modulus of subgrade reaction was determined to be 80 pci. The 80 pci would have both the reduction of wide area loading and the reduction for long-term soil consolidation. The 80 psi would be 35% (80 pci/230 pci X 100%) of the plate subgrade reaction value.
What is the coefficient of subgrade reaction?
By implication, the coefficient of subgrade reaction is the unit pressure required to produce a unit settlement in a soil. In saturated clay soils, the settlement under load will take time due to consolidation, so the coefficient of subgrade reaction should be determined on the basis of the final settlement.
Can we use modulus of subgrade reaction to model raft foundations?
Modulus of subgrade reaction found from the above equation can be used to model raft foundations, footings, and combined footings. However, when we model piles, it is better to refer to some other method of obtaining the subgrade reaction even though this above method may be used for the analysis.