Code Combinations (Foundation Design)

The following assumptions for load combinations in foundation design have been adopted:

• In a single run of limit state verification, all effects of the same impact are multiplied by the same safety factor
• A soil load acts stabilizing on a foundation
• A dead load on the backfill acts stabilizing on a foundation.

If one limit state condition of the same impact yields simultaneously favorable and unfavorable effects, then the effects of this impact are given simultaneously the same factor. Such an assumption results in the load of a given condition being smaller (favorable) or greater (unfavorable) than the assumed condition.

Adoption of the following two assumptions indicates that for a given state it is possible to assume one safety factor for backfill loads as well as for the weight of the soil and a foundation. The maximal or minimal factor depends on the effect of these impacts in an analyzed state. For the available codes the following effect of impacts and the corresponding load factors have been adopted.

Impact Limite state	Foundation weight	Soil weight	Dead load on the backfill	Live load on the backfill	Ground water
Capacity of the soil	maximal	maximal	maximal	maximal	minimal
Sliding	minimal	minimal	minimal	0.0	maximal
Rotation	minimal	minimal	minimal	0.0	maximal
Position of a force resultant	minimal	minimal	minimal	0.0	maximal
Lifting	minimal	minimal	minimal	0.0	maximal
Average settlement	maximal	maximal	maximal	maximal	minimal
Settlement diffrence	maximal	maximal	maximal	maximal	minimal

Note: It is possible that calculations are incorrect for a load that is strongly uneven and for the varied backfill.

Regulations of code combinations (*.rgl files) are linked permanently to the geotechnical design codes:

• ACI: aci2002_geo.rgl or aci_geo.rgl.
• BS 8004:1986: bs_geo.rgl.
• CSA: csa_geo.rgl.
• DTU 13.12: Dtu13_12.rgl.
• ENV 1997-1:1994 (EC 7): EC7_geo.rgl
• EN 1997-1:2004 (EC 7): EC7_2004_geo.rgl
• Fascicule 62 Titre V: fasci62.rgl.
• PN-81/B-03020: pn84_geo.rgl.
• SNiP 2.02.01-83: snip_geo.rgl.

Both the regulation provided factors and the rules describing combination generation are user-defined.

In the regulations are the following designations of load subnatures that enable differentiation of the safety factors for the soil weight, backfill loads, foundation self-weight and the Archimedes pressure.

• FWE - self-weight of a spread footing.
• SWE - self-weight of the soil.
• BLO - loads on the backfill.
• APR - Archimedes pressure.

In the default regulations it has been assumed that factors of subnatures correspond to the natures to which the loads have been assigned.

For ENV 1997-1:1994 (EC 7) code, the table below presents the combination types available in the regulations as well as the impact types with their partial safety factors:

Combinations	Impacts
	dead		live - favorable	accidental - unfavorable
	favorable	unfavorable
ULS A	[1.0]	[0.95]	[1.5]	-
ULS B	[1.35]	[1.0]	[1.5]	-
ULS C	[1.0]	[1.0]	1.3]	-
SLS	[1.0]	[1.0]	[1.0]	-
ALS	[1.0]	[1.0]	[1.0]	[1.0]

For ENV 1997-1:2004 (EC 7) code, the table below presents the combination types available in the regulations as well as the impact types with their partial safety factors:

Combinations	Impacts
	dead		live - favorable	accidental - unfavorable
	favorable	unfavorable
ULS A1	[1.0]	[1.35]	[1.5]	-
ULS A2	[1.0]	[1.0]	1.3]	-
SLS	[1.0]	[1.0]	[1.0]	-
ALS	[1.0]	[1.0]	[1.0]	[1.0]

Note: Calculations of the factors for backfill loads, the weight of the soil, and a foundation are carried out based on the default combination rules for the combination types A, B,C, as well as A1 and A2. Modification of these rules in the regulations will not pertain to these types of loads.