CBR to bearing strength

Hennie Schoeman

unread,

Nov 26, 2001, 1:14:46 PM11/26/01

to

Anybody out there able to help me to convert CBR-values (obtained by DCP) to
bearing strength (allowable soil pressure)???

Czap Zoltan

unread,

Nov 28, 2001, 10:27:29 AM11/28/01

to

For a saturated clay in undrained conditions:
CBR=0.09*c
where c is the cohesion of the soil in kN/m2.

For a cohesionless soil you can use the bearing capacity
equation for circular foundations.

(Carter, Bentley: Correlations of Soil Properties, Pentech
Press, London, 1991)

--
CZAP Zoltan, Bp. Musz. es Gazd. tud. Egyetem (BME), Geotechnikai
Tansz.
(Mr. Zoltan CZAP, Dept. of Geotechnics, Budapest Univ. of Techn.
and Econ.)
H-1521 Budapest
T: +36-1-463-2172, F: +36-1-463-3006, E: zc...@epito.bme.hu

"Hennie Schoeman" <hn...@icon.co.za> az alábbiakat írta a
következő üzenetben: news:9tu0nm$qje$1...@ctb-nnrp1.saix.net...

Adrian Wightman

unread,

Nov 28, 2001, 1:29:33 AM11/28/01

to

You're probably better off trying to go from DCP (Dynamic Cone
Penetration??) to an SPT N value and then to bearing pressure. CBR is just
some kind of pavement design index - related to soil type and density of
course but not directly to allowable bearing for foundations.

"Hennie Schoeman" <hn...@icon.co.za> wrote in message
news:9tu0nm$qje$1...@ctb-nnrp1.saix.net...

Adrian Wightman

unread,

Nov 29, 2001, 1:20:13 AM11/29/01

to

Let's be a bit careful here now, isn't there's a scale problem ?- how much
soil are you testing with a CBR and how does that relate to the bearing
capacity and size of your footing?

"Czap Zoltan" <zc...@epito.bme.hu> wrote in message
news:9u2vp2$pq4$1...@analog.eik.bme.hu...

Hennie Schoeman

unread,

Dec 1, 2001, 10:11:38 AM12/1/01

to

I am trying to evaluate the bearing capacities of soils underneath normal
strip foundations for 2-storey housing. The strips are some 750 mm wide and
300 mm deep.
"Adrian Wightman" <awig...@dccnet.com> wrote in message
news:u0cp7ui...@corp.supernews.com...

Eric Dickner

unread,

Dec 2, 2001, 12:06:15 PM12/2/01

to

I think you are supposed to do a triaxial test and determine the angle thi,
the soil friction angle and go from there. CBRs are for designing flexible
pavement structures, i.e. ashpalt roads and nothing else.

ejd

"Hennie Schoeman" <hn...@icon.co.za> wrote in message
news:9tu0nm$qje$1...@ctb-nnrp1.saix.net...

Adrian Wightman

unread,

Dec 2, 2001, 3:03:48 PM12/2/01

to

OK, so what is needed is some way to characterize the strength and
compressibility of the soils for a depth of say two to three times the
footing width below foundation level, or about 2 to 3 metres. If the ground
floor is grade supported it would be a good idea to know what's down below
to a depth of maybe 10 metres, or more if there is any indication of softer
soils with depth. A CBR isn't going to help with this at all.

"Hennie Schoeman" <hn...@icon.co.za> wrote in message

news:9uarrb$bch$1...@ctb-nnrp2.saix.net...

JBgoode

unread,

Dec 3, 2001, 10:24:50 AM12/3/01

to

"Hennie Schoeman" <hn...@icon.co.za> wrote in message
news:9uarrb$bch$1...@ctb-nnrp2.saix.net...

> I am trying to evaluate the bearing capacities of soils underneath normal
> strip foundations for 2-storey housing. The strips are some 750 mm wide
and
> 300 mm deep.

I wouldn't sign off on a foundation designed using a CBR value. Would you?
Unless this is for just a rough estimate, I think you need borings...

Hennie Schoeman

unread,

Dec 3, 2001, 2:36:59 PM12/3/01

to

Thanks all - I got the message!

Apparently no quick fix here.

"Hennie Schoeman" <hn...@icon.co.za> wrote in message
news:9uarrb$bch$1...@ctb-nnrp2.saix.net...