Strip surcharge

For vertical strip loading  f_a acting parallel with structure on the ground surface along an infinitely long strip the trapezoidal increment of active earth pressure applied to the structure over a given segment h_f is assumed – see figure.

Diagram of increment of active earth pressure due to strip loading f_a

This segment is determined by intersection of the structure and lines drawn from the edge points of the strip loading having slopes associated with angles φ  and ϑ_a. The angle ϑ_a corresponding to critical slip plane follows from: 

The formula is described in detail in section "Active earth pressure – line surcharge".

Variation of pressure increment is trapezoidal; the larger intensity of Δσ_fs is applied at the upper end while the smaller intensity of Δσ_fi at the bottom end. The two increments are given by:

where:	fa	-	magnitude of strip surcharge
	b	-	width of the strip surcharge acting normal to the structure
	hf	-	section loaded by active earth pressure increment

where:	ϑa	-	angle of critical slip plane
	φ	-	angle of internal friction of soil
	δ	-	angle of friction structure - soil

The resultant of the increment of active earth pressure due to strip loading  f_a is provided by:

where:	ϑa	-	angle of critical slip plane
	φ	-	angle of internal friction of soil
	δ	-	angle of friction structure - soil
	fa	-	magnitude of strip surcharge
	b	-	width of the strip surcharge

For non-homogeneous soils the program proceeds as follows.