Laboratory CBR Seating loads.
Laboratory CBR Seating loads.
(OP)
Hi everyone, i'm a soils technician from England working to BS1377 standards.
We are trying to develop a method to accurately judge the CBR value of recompacted soils to pre-determine seating loads. We have trid a hand penetrometer but found it to be too inaccurate. Any suggestions?
We are trying to develop a method to accurately judge the CBR value of recompacted soils to pre-determine seating loads. We have trid a hand penetrometer but found it to be too inaccurate. Any suggestions?





RE: Laboratory CBR Seating loads.
The surcharge for a CBR test is based on the pavement section loads. It should be the weight of the base and surface sections, but not less than 4.5kg.
RE: Laboratory CBR Seating loads.
eg: for CBR values 8%-40% using a 10KN load ring we apply a seating load equivalent to 10N (6 units).
The problem lies in accurately estimating the CBR% to determine which load ring and/or seating load to apply.
RE: Laboratory CBR Seating loads.
Material CBR Value
Sand 5-20
Clayey Sand 10-30
Silty Sand 10-25
Stabilized Sand (with gravel) 20-35
Stabilized Clayey Sand (with gravel) 30-50
Graded aggregate base 50-80
RE: Laboratory CBR Seating loads.
With respect to the surcharge load - alluded to by dirtman85, he is correct in his definition as per the ASTM/AASHTO standards. On one job I was on, we required some 34 kg to hang on the surcharge weight - and the "commercially" available equipment only allowed 10kg. So it was necessary to manufacturer specific hangers to permit the 34 kg to be placed. Now, normally, it just wouldn't be done (I presume by 90% or more of the testing companies - in this case, it was necessary to do so to achieve the CBR minimum requirements for subgrade).
RE: Laboratory CBR Seating loads.
RE: Laboratory CBR Seating loads.
Most in-situ tests are requested on the subgrade which has particles far in excess of the recommended tolerance. We always try to convince clients to go for a plate load test in these circumstances instead to allow for the particle sizes and convert it to a CBR percentage using the modulus of subgrade reaction, typically this is declined due to cost, you can but try!!!