September_1971 — Page 30

against the slope in the direction most appropriate to a safe response of the soil. In the worst soil condition, these forces from the building even could act in the direction perpendicular to the slope.

Geological conditions: Through time, erosion has caused the weaker strata of soil at the top of the slope and at the steepest sections to be de- posited at the foot. Consequently, more resistive strata of soil are nearer to the surface at the top and steep sec- tions of the slopes and can be exploit- ed advantageously for structural pur-

poses.

The parts of the building located on the slope will not require deep foundations since the resistive strata are nearer to the surface of the slope. On the other hand, the resistive strata which are much deeper at the foot of the slope can be dealt with in a con- ventional manner since heavy equip- ment has easy accessibility to this level area. Piles are the most common type of footing for this type of situation.

=

angle ✪ = angle of the slope with the horizontal angle ẞ the possible angle of deviation from

the perpendicular to the slope

when ẞ= 0, poor soil conditions

B=, good soil capacity

Vpl

Vsl

5=

= the ratio of the base volume

to the slope volume

1.6

1.5

C

an

Vsl Vpl

1.4

tan

1.3

1.2

1.1

1.0

0.9

Vsl

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

Vil ≥(4-tan α)

tan -tan B tan2+1

0.0

0.0 0.2

0.4

0.6 0.8 1.0 1.2

1.4

1.6

1.8 2.0

tan ♂

Force distribution

poor soil

good soil

The above formula and the ad- jacent diagram are derived from the as- sumption that the vertical component of the force transmitted to the founda- tion under Vpl should be more than four times greater than the horizontal component resulting from the protec- tion of slippage of Vsl.

The graph represents the required Vpl and Vsl ratio as dependent on the function of the inclination of the slope (angle) and the relative soil capacity on the slope which is expressed as an- gle ẞ, the deviation from the most effi- cient response of the soil, perpendicu- lar to the surface.

The bulk of the building is com- posed of two volumes. The volume Vpl is based at the bottom of the slope; the triangular volume Vsl is positioned only on the slope.

Vertical loads coming from the structure of the building to the soil on the slope are supported by two inter- related systems:

(1) A system where the load from the building is resisted by the soil of the slope according to its capacity: The loads are resisted vertically with high capacity soil and in the worst case with poor soil capacity, the loads from

24

Vpl

711

Vsl

Load Vpl

Load V

d

Angle B

:

Bi

force diagram

The gravity load due to the volume of the base plane mass

The gravity load due to the volume of the mass on the dope

Based on the soil capacity, the angle between the line perpendicular to the slope and the direction of the possible response of the subsoil

The angle is small for conditions of pour soil response. The angle is zero when the ground response is perpendicular to the contour of the slope.

Angle ẞ = ♬ for the condition of stable slopes composed of highly resistive material fa vertical responset

The compressive component which absorbs the inclined reaction in the foundation strip where it is transferred to the base mass supports

For good mechanical properties of the soil, C is small and vice vers

Far East BUILDER, September 1971

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