Talk:California bearing ratio

What it measures
At university (geotechnics course) we are told that this measures bearing capacity and that is related to stiffness and not mechanical strength directly... I propose changing that sentence in the intro. —Preceding unsigned comment added by Edwardando (talk • contribs) 01:59, 17 January 2008 (UTC)

Removed Text
I removed the "Origin of the CBR" below, it is unreferenced and is in conflict with the referenced claims in the article. It is also hard to beleive that American military engineers in WW2 developed and named a process called the CALIFORNIA BEARING RATIO (CBR). I believe that there was probably something similar to the CBR used as described below, so if someone could find references, for the claims and put it back in the article that would be great. Jeepday (talk) 13:48, 11 May 2007 (UTC)

This is somewhat correct as the USAAF pushed this research through to provide their construction teams an easier construction process. USAAF airfields in the US were used for testing. Grant 15:14, 10/10/08, AEST —Preceding unsigned comment added by 203.9.185.137 (talk) 05:15, 10 October 2008 (UTC)

See http://gsl.erdc.usace.army.mil/gl-history/Chap3.htm. Porter completed his research at the insistence of the Corp of Engineers as they required it for airfield design. Grant 08:00, 22/06/09 —Preceding unsigned comment added by 203.9.185.137 (talk) 22:01, 21 June 2009 (UTC)

Origin of the CBR
The CBR test was developed in World War 2 by american military engineers. As US forces captured pacific islands held by the Japenese new airfields were constructed hurriedly to bring american airpower closer to the main Japenese islands. The CBR test gave engineers instantaneous results allowing the amount of aggregate used in runway construction to be calculated to the minimum requirements, thus ensuring rapid construction. The rapid advancement of US airpower was one of the factors that lead to the surrender of the Japanese.

The CBR test was originally devised by O.J.Porter, then of the California State Highway Department, but it since been developed and modified by other authorities in the USA., notably the US Corps of Engineers.....see Porter O.J. The preparation of subgrades. Proc.Highw.Res.Bd, Wash., 1939, 18 (2), 324-31 —Preceding unsigned comment added by 62.240.47.249 (talk) 13:38, 29 March 2009 (UTC)

what are the factors affecting cbr value —Preceding unsigned comment added by 124.43.60.195 (talk) 07:04, 21 August 2009 (UTC)

A 1960 reference for CBR
Some material that might be suitable for inclusion in the article:

Operations from Unprepared and Semi-Prepared Airfields, AGARDograph 45, September 1960, http://www.dtic.mil/docs/citations/AD0255177 "Soil conditions are of great Importance to the airplane designer as well as to flight operations, with reference to the trafficability of unprepared landing areas. The soil bearing capacity for smallest deformations ranks first. The bearing capacity influences especially the choice of tire dimensions, wheel loads and tire pressure, whilst the deformations produced are decisive for the number of passes the area may be used for. The moisture content of the soil is of great influence on its bearing capacity.

There exist several methods for determining the soil bearing capacity. In this report the CBR-method (California Bearing Ratio) is primarily referred to. The so-called CBR-value represents the ratio of the percentage of the loads required to press a punch of certain dimensions first into a well compacted sample of soil and then into a standard sample of compacted gravels, to a depth of 0.1 inch.

In any case, it is necessary to classify the soil type with reference to the Unified Soil Classification System as a test of the soil bearing capacity only with regard to the CBR-method does not give an exhaustive picture of its reaction to static and traffic loads, the influence of the moisture content being too varied. This system has been used by the Army Corps of Engineers for many tests of the bearing capacity of airfields."

"In the twenties, the American Society of Civil Engineers started extensive experiments with the aim of determining the bearing capacity and the suitability of various types of ground surfaces for the construction of highways. From these tests, the so-called CBR-method (Callfoniia Bearing Ratio) originated.  This uses a standardized test procedure to examine the ground In question.  It would exceed the purpose of this paper to describe this method in detail. Those particularly interested in it are referred to the condensed brochure.

The evaluated CBR-value represents the bearing capacity of the tested surface as a percentage of the bearing capacity of hardcore road-stones taken as 100%. Several years of testing roads yielded layout diagrams, thus making possible the estimation of the road layer thickness as well as the packing for any ground, together with the resulting stresses. The CBR-method is applicable to the so-called 'flexible pavement', in which a relatively thin wearing course transfers the load to the base. It is specially mentioned here as it comes close to the conditions of unprepared areas."

Development of CBR Flexible Pavement Design Method for Airfields. American Society of Civil Engineers, Paper No. 2406, 1950.

This reference is not available in electronic form. Some ASCE references for the symposium:

http://cedb.asce.org/cgi/WWWdisplay.cgi?291984

http://cedb.asce.org/cgi/WWWdisplay.cgi?291986

http://cedb.asce.org/cgi/WWWdisplay.cgi?291989

http://cedb.asce.org/cgi/WWWdisplay.cgi?291994

http://cedb.asce.org/cgi/WWWdisplay.cgi?291988

http://cedb.asce.org/cgi/WWWdisplay.cgi?291989

http://cedb.asce.org/cgi/WWWdisplay.cgi?291997

http://cedb.asce.org/cgi/WWWdisplay.cgi?292012

http://cedb.asce.org/cgi/WWWdisplay.cgi?292018

An excellent history (7.5 MB) by the Army Corps of Engineers:

Richard G. Ahlvin, Origin of Developments for Structural Design of Pavements, Technical Report GL-91-26, December 1991, http://www.dtic.mil/docs/citations/ADA245673

"The Corps of Engineers' concern for pavement design for heavier loadings began in November of 1940. Responsibility for design and construction of military airfields was then assigned to the Corps. War was threatening and the military air arm was still within the Army.

A flexible pavement design method was required. Promising methods used bearing capacity of the subgrade as the basic design input, but means for determination of the bearing capacity remained in question. Initial studies and field investigations indicated that the time to develop independently a satisfactory test procedure was not compatible with the war emergency faced. Also, it was concluded that a plate-bearing test was not suited to military field needs nor to the assessment of subgrade shear which was considered of primary interest in flexible pavement behavior.

With recognition that a rational method for design, based on limiting stress-strain, was beyond reasonable promise within the foreseeable period of need, it was concluded that an established empirical highway design method should be adopted and further developed. It was considered that such an empirical method could be made to serve the pressing short-term needs. Far from abandoning concern for a rational design method, work on both theoretical and actual stress and strain induced in flexible pavements was planned to continue parallel with the more immediate functional method development.

Investigation of possible methods led to selection of California's CBR method for the following reasons: a. The CBR method had been correlated with service behavior and construction methods (1928-1942). b. The CBR method could more quickly be adapted to airfield pavement design for immediate use. c. The method was thought to be as reasonable and as sound as any of the methods investigated. d. Two states, other than California, had similar methods that had been successful. e. The subgrade strength (CBR) could be assessed using simple portable test equipment in the laboratory or in the field. f. Testing could be done on samples of soil in the condition representative of the foundation-moisture state commonly existing under pavements."

Much more in the document.

Banchang (talk) 00:26, 10 May 2015 (UTC)