IN-SITU CALIFORNIA BEARING RATIO (CBR) TEST (Method Based On BS 1377 Part 9 – 4.3 1990) INTRODUCTION General This method is to determine the California Bearing Ratio (CBR) of a soil tested in situ, with a selected overburden pressure, by causing a cylindrical plunger to penetrate the soil at a given rate and comparing the relationship between force and penetration into the soil to that for a standard material . At certain values of penetration the CBR is defined in the form of a percentage, as the ratio of the force exerted on the soil to a standard force that would be exerted on a specified crushed rock compacted and confined in a given manner. Test Procedure Remove which is not representative soil of the area to be tested, and make sure that the area is flat and horizontal. The position of reaction load and its supports, such as the jacks when using a vehicle, so that the cylindrical plunger after assembly is directly over the area to be tested. Fit the jack (in the fully retracted position), extension rods, force measurement device and cylindrical plunger on to the reaction load frame such that the whole assembly hangs vertically with the lower face of the plunger above 25mm above the soil surface to be tested than lower the cylinder plunger so that its lower surface comes into contact with the soil. Place a sufficient number of surcharge dics, one top of top another, around the test point than apply a seating force to the plunger, record the reading of the force-measuring device as the initial zero reading.

In-situ Cbr Test

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IN-SITU CALIFORNIA BEARING RATIO (CBR) TEST(Method Based On BS 1377 Part 9 – 4.3 1990)

INTRODUCTION

General

This method is to determine the California Bearing Ratio (CBR) of a soil tested in situ, with a selected overburden pressure, by causing a cylindrical plunger to penetrate the soil at a given rate and comparing the relationship between force and penetration into the soil to that for a standard material . At certain values of penetration the CBR is defined in the form of a percentage, as the ratio of the force exerted on the soil to a standard force that would be exerted on a specified crushed rock compacted and confined in a given manner.

Test Procedure

Remove which is not representative soil of the area to be tested, and make sure that the area is flat and horizontal. The position of reaction load and its supports, such as the jacks when using a vehicle, so that the cylindrical plunger after assembly is directly over the area to be tested. Fit the jack (in the fully retracted position), extension rods, force measurement device and cylindrical plunger on to the reaction load frame such that the whole assembly hangs vertically with the lower face of the plunger above 25mm above the soil surface to be tested than lower the cylinder plunger so that its lower surface comes into contact with the soil. Place a sufficient number of surcharge dics, one top of top another, around the test point than apply a seating force to the plunger, record the reading of the force-measuring device as the initial zero reading.

Results Calculations

Calculate the force applied to the plunger from each reading of the force-measuring device observed during the penetration test to plotting the force-penetration curve.Penetration of 2.5mm and 5mm are used for calculating the CBR value. From the test curve, read off the force corresponding to 2.5mm and 5mm penetration. Express these as a percentage of the standard forces at these penetration. i.e. 13.2KN and 20.0KN respectively. Take the higher percentage as the CBR value.