Dear Eng-Tips members,
Could someone help me in clarifying the following input data Y (fsoil’s weight) in the Soil bearing resistance in shallow-foundations calculations, concerning soil-types and water-table influence?:
For non-cohesive soils (permeable sands or in over-consolidated clays) the calculations should de done in drained-conditions (effective stresses) using the formula
qud=(cd·Nc·sc·ic+q'·Nq·sq·iq+0.5·Y’inf,k·B·Nγ·sγ·iγ)/γqu , where
Y’inf,k is the foundation-soil’s weight ; q'=Y’sup,k·D ; Y’sup,k is the superior-soil’s weight to calculate q surcharge
Considering the nature of foundation-soil equal to the superior-soil (granular):
- If Water-Table is below a depth of B (foot width) underneath foundation-level, Y to be inputted would be Ydry (either for foundation-soil and upper-soil)
- If Water-Table is in the depth of B, Y to be inputted would be: for the foundation-soil Ysub=Ysat-9.81 ; for the upper-soil Ydry (*)
- If Water-Table is above the foundation-level, Y to be inputted would be: for the foundation-soil Ysub=Ysat-9.81 ; for the upper-soil Ysub=Ysat-9.81 (*)
(*): Cause several calculation-software only use one soil-type (foundation-soil=upper-soil), and for sands I’ve learned that it should be used
Ys=Ydry if there isn’t WT influence and Ys=Ysub if there is WT influence
Could you please clarify if I’m correct in this simplification?
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For cohesive soils (normally-consolidated impermeable clays) the calculations should be done in undrained-conditions (calculations in total stresses at short-term) using the formula
qud=[(π+2)·cud·sc·ic+q]/γqu , where
q=Ysup,k·D ; Ysup,k is the superior-soil’s weight to calculate q surcharge
The calculations only depends on the upper-soil's weight and Water-Table position in it, so:
- If Water-Table is below foundation-level, Y to be inputted would be Ysat if a clay ; Ydry if a sand (*)
- If Water-Table is in the D height, Y to be inputted would be: Ysat if a clay ; Ysat if a sand (*)
- If Water-Table is above the D height, Ys to be inputted would be: Ysat+Yw.dw if a clay ; Ysat+Yw.dw if a sand (*)
(*): Could you please clarify if I’m correct in these assumptions?
-------------------------------------------------------------------------------------
Thank you for your help and regards.
Could someone help me in clarifying the following input data Y (fsoil’s weight) in the Soil bearing resistance in shallow-foundations calculations, concerning soil-types and water-table influence?:
For non-cohesive soils (permeable sands or in over-consolidated clays) the calculations should de done in drained-conditions (effective stresses) using the formula
qud=(cd·Nc·sc·ic+q'·Nq·sq·iq+0.5·Y’inf,k·B·Nγ·sγ·iγ)/γqu , where
Y’inf,k is the foundation-soil’s weight ; q'=Y’sup,k·D ; Y’sup,k is the superior-soil’s weight to calculate q surcharge
Considering the nature of foundation-soil equal to the superior-soil (granular):
- If Water-Table is below a depth of B (foot width) underneath foundation-level, Y to be inputted would be Ydry (either for foundation-soil and upper-soil)
- If Water-Table is in the depth of B, Y to be inputted would be: for the foundation-soil Ysub=Ysat-9.81 ; for the upper-soil Ydry (*)
- If Water-Table is above the foundation-level, Y to be inputted would be: for the foundation-soil Ysub=Ysat-9.81 ; for the upper-soil Ysub=Ysat-9.81 (*)
(*): Cause several calculation-software only use one soil-type (foundation-soil=upper-soil), and for sands I’ve learned that it should be used
Ys=Ydry if there isn’t WT influence and Ys=Ysub if there is WT influence
Could you please clarify if I’m correct in this simplification?
-------------------------------------------------------------------------------------
For cohesive soils (normally-consolidated impermeable clays) the calculations should be done in undrained-conditions (calculations in total stresses at short-term) using the formula
qud=[(π+2)·cud·sc·ic+q]/γqu , where
q=Ysup,k·D ; Ysup,k is the superior-soil’s weight to calculate q surcharge
The calculations only depends on the upper-soil's weight and Water-Table position in it, so:
- If Water-Table is below foundation-level, Y to be inputted would be Ysat if a clay ; Ydry if a sand (*)
- If Water-Table is in the D height, Y to be inputted would be: Ysat if a clay ; Ysat if a sand (*)
- If Water-Table is above the D height, Ys to be inputted would be: Ysat+Yw.dw if a clay ; Ysat+Yw.dw if a sand (*)
(*): Could you please clarify if I’m correct in these assumptions?
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Thank you for your help and regards.
