Bearing capacity of strip foundation on sand with fides software
Determination of Bearing capacity of strip foundation on sandfrom bearing capacity theories and comparision with fides-bearing capacity software results
By : Reza heidari
Job : Geotechnical engineering & lecturer
Season : winter / Year : 2013
The soil must be capable of carrying the loads from any engineered structure placed upon it without a shear failure and with the resulting settlements being tolerable for that structure. Determination of the ultimate bearing capacity of foundation bed soil is an important step for evaluation safe and economy of foundation project . one of methods for determination ultimate bearing capacity foundation bed soil is static analysis that base on foundation bed soil failure analytical methods at limit state and soil shear strenght parameters. In this paper I decide that investigate about the ultimate bearing capacity of strip foundations on sand from available bearing capacity theories and comparision with fides-bearing capacity software results. There are many different important parameters that effective on bearing capacity of foundations . for example depth and width of the foundation thus I assumption that one of the parameters is variable and the other parameters are constant and comparision the results of bearing capacity from different bearing capacity theories and fides-bearing capacity software results . This research showed the best results with the minimum error between vesic bearing capacity equation and software resuls for strip foundation on sand.
Keywords : Ultimate bearing capacity – Static analysis – Analytical methods – limit state – Minimum error - Fides bearing capacity software .
Determination of geotechnical bearing capacity of foundations is the important step in foundation design . there are many different methods for determination of the ultimate bearing capacity of foundations. for example we use terzaghi and meyerhof methods with the variable bearing capacity factors ( hansen- vesic – debeer - ... ) but witch method gives the best result ? all of methods are acceptable but the best method for determination the ultimate bearing capacity of foundation is foundation load test but expensive. The other method is plate load test (PLT) but this method is expensive and may be not justifiable for all of projects . meantime plate load test can not expression of stress-strain behavior of the soil under the super structural loads (actual loads). insitu tests is the suitable method but many factors exist that effective on the tests results. thus we use the analytical methods and bearing capacity theories . the best way to check of this methods is calculate the ultimate bearing capacity from several methods and find the average of them and then comparision it with the actual result that is get from foundation load test ( verify with the actual value) . we can use the finite element method or the special software for evaluation of bearing capacity of foundation . the basic difference between the bearing capacity equations is Nγ at the third term that several investigators discrition about its . for example in table 1 we seeing the different opinions .
Table1: bearing capacity factors at the third term of bearing capacity equations
I don,t expression the other factors ( for example shape factor,inclination load factor) .
Purpose and procedure
The main purpose of this investigate is determination of bearing capacity of 40 strip foundations with properties like what in table2 . in table3 we also see the bearing capacity factors that calculates from different methods . in table4 we also see the ultimate bearing capacity that calculates with the different methods and by fides-bearing capacity software . Fides – bearing capacity software is one of softwares that able to calculate the ultimate bearing capacity of shallow foundations and rupture surface shape and dimensions . the other abilities of this software is calculation of the bearing capacity of shallow foundations with the different load conditions and surface conditions and foundation on layered soils . we caution about use of this program because we must verify the results with the actual bearing capacity that recommendation in valid refrences. I investigate the bearing capacity of strip foundation on sand in this paper. The properties of sand layer indication in table2. This investigate perform in three cases .
Case 1 : depth of foundations is constant and width of foundations is variable .
FS=Qu(max) / Qu from Vesic method
That Qu(max) is get from fides-bearing capacity software. We see that the error percent between the vesic method and fides bearing capacity software results is minimum.
Case 2 : depth of foundations is variable and width of foundations is constant
Table5: ultimate bearing capacity of foundations in case2
Case 3 : depth of foundations is constant and width of foundations is variable
Table6: ultimate bearing capacity of foundations in cas
This results indicate that there is a good agreement between the vesic method and fides bearing capacity software results. Fides bearing capacity also able to calculate the rupture surface shape and rupture dimensions .
Figure1: Dimensions and shape of the rapture surface for strip foundation with B=5m and Df=1m
Consclusions and proposals
In the present study the ultimate bearing capacity of strip foundation on sand examined with fides-bearing capacity software results . minimum error between the hansen method and fides-bearing capacity software in three case . maximum error percent is about 4% for Case 1 and case3 while the error percent is about 3% for Case 2 . so the fides bearing capacity results and bearing capacity equations have good acordance with together . also we optain the Dimensions and shape of rapture surface from fides-bearing capacity software. I consclusion that we investigate the ocassions like what indicate in table5.
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