Simplified design of strip foundation (shallow foundation)

Codes: DS/EN 1997-1 Eurocode 7: 2005 Geotechnical design - Part 1: General Rules

DS/EN 1997-1-1 DK NA:2015

DS/EN 1997

Undrained conditions (clay), can be simplified to:

R/B = ( +2) Cd + qππππ R = load [kN/m]

B = nessesary width of foundation pr running m.

Cd = design shear strength of clay (geo-report)

q = load on soil at buttom level of foundation next to foundation (overburden)

Example:

= Density of soil (geo-report)γγγγ

Cv = Shear strength of clay(geo-report)

q1

q1 is weight of soil to the left of the foundation.

q2 is the weight of the basement floor and sand to the right of the fundation.

q2

Lowest value of q1 or q2 is used (can be omitted)

≔R ⋅200 ――kNkNkNkN

mmmmLoad at foundation level (underside)

≔Cv ⋅135 ――kNkNkNkN

mmmm2

Shear strength of the clay from geo-report

≔γγγγcccc 1.8 Safety parameter of shear strength, 1997 DK NA

≔q1 ⋅60 ――kNkNkNkN

mmmm2

≔q2 ⋅10 ――kNkNkNkN

mmmm2

≔q min ⎛⎝ ,q1 q2⎞⎠ =q 10 ――kNkNkNkN

mmmm2

≔Cd ―Cv

γγγγcccc=Cd 75 ――

kNkNkNkN

mmmm2

≔B ―――――R

+⋅(( +ππππ 2)) Cd q=B 0.506 mmmm Nessesary width of foundation

DS/EN 1997

DK NA

Drained conditions as for sand, can be simplified to

R/B = +⋅⋅⋅0.5 γγγγ B NγNγNγNγ ⋅q Nq q can be omitted

≔ϕ 35 degdegdegdeg (geo-report) ≔γϕ 1.2 Safety factor for angle of friction from DK NA

≔ϕd atan⎛⎜⎝―――tan((ϕ))

γϕ

⎞⎟⎠

=ϕd 30.264 degdegdegdeg Used to find N and Nq from tableγγγγ

≔γγγγ ⋅18 ――kNkNkNkN

mmmm3

Density of soil from geo-report

≔Nγ 15 ≔Nq 18 From tables or spread sheet

Guess a dimension ≔B ⋅0.72 mmmm Continue guessing until the numbers are almost equal or solve the equation.

=―R

B277.778 ――

kNkNkNkN

mmmm2

≔X +⋅⋅⋅0.5 γγγγ B Nγ ⋅q Nq =X 277.2 ――kNkNkNkN

mmmm2