Reconversion CBR, M1, Ev1, Ev2
Important comment
All sorts of methods are used in different countries to quantify the bearing capacity of soil. Theories, published in many parts of the world, use the local measuring method and unit as default values.
Texion tries to reconvert different units into others, knowing that theoretically it is not possible, because the values are the outcome of very different test methods. Therefore, especially this calculation module should be used with care. The output results have to be treated with vigilance, naturally, because the conversions take place between significantly different measuring procedures.
Texion welcomes comments and new formulae that will improve and/or correct the existing version.
Measuring methods and devices
Plate test (M1) in MN/m2
The plate test is performed, by loading the surface of the soil to be tested, using a rigid steel circular plate of either 200 cm2 or 750 cm2, depending upon the soil’s particle size distribution. The load is applied vertically at the centre of the plate, and the central vertical deflection is calculated from the readings from three symmetrically arranged measuring gauges. The vertical load is applied at a fixed, predetermined rate of settlement. The load / deformation curve is used to calculate the compression coefficient. Typical values the first load cycle (M1) for a road construction should be:
Base layer: 110 MN/m2
Sub base layer: 35 MN/m2
Formation level: 17 MN/m2
First layer of embankment: 11 MN/m2
Base of embankment: x MN/m2
CBR in %
The California Bearing ratio (CBR) test is a penetration test for the valuation of the mechanical strength of road sub-grades and base courses. It was developed by the California Department of Transport. The test is performed, by measuring the pressure required to penetrate a soil sample with a plunger of standard area. The measured pressure is then divided by the pressure required to achieve an equal penetration into a standard crushed rock [multiplied by 100 to produce a percentage.] The harder/stronger the material being tested, the higher the CBR rating will be. A CBR of 3 equates to tilled farmland; a CBR of about 5 equates to turf or moist clay; moist sand may have a CBR of 10.
Ev1 and Ev2 in MPa
Being easy to handle and being capable of providing immediate results, the light Drop-Weight Tester (LDWT), also known as the Lightweight Deflectometer (LWD), or the Portable Falling Weight Deflectometer (PFWD), is a practical device for quantifying the bearing capacity of a soil.
Ev1 and Ev2 are deformation moduli and indicate, together, the bearing capacity of a soil and it’s plastic properties. Their coefficient quantifies its compaction quality.
