FLOOD10139

• County: Statewide
• Basin: Statewide
• Title: Users Instructions for SAMM
• Date: 9/1/1990
• Prepared By: Simpson Gumpertz & Heger, Inc.
• Floodplain - Doc Type: Educational/Technical/Reference Information

The lateral pressure ratio, K, is the ratio of the unit lateral soil
pressure to unit vertical soil pressure or commonly referred to as
the Rankine's coefficient of active earth pressure. For positive
projecting embankment installations, a value of 0.33 is usually
sufficiently accurate for design.

The lateral pressure fraction, m, is the fractional part or ratio of
the outside diameter of the pipe over which the lateral pressure is
effective,

Since the fill material can be compacted more readily in embankment
installations, the effect of active lateral pressure in a positive
projection condition is considered in evaluating the bedding factor.
The supporting strength of the pipe is a function of the
distribution of the vertical load, the class of bedding, the
magnitude of the active soil pressure against the sides of the pipe,
and the area of the pipe over which the active lateral pressure is
effective.

2,3 TURDeled ADd Jacked InstallatioD

Two types of loads are imposed upon concrete pipe installed by the
tunneling and jacking methods: the axial load due to the jacking
pressures applied during installation and tbe earth loading due to
tbe overburden, witb some possible influence from live loadings.

Axial loadings are not considered by tbe program in tbe design
analysis, SAMM will only calculate tbe loads due to eartb and live
loadings,

Major factors influencing tbe vertical earth load on pipe installed
by jacking are:

o Weigbt of tbe prism of eartb directly above tbe bore.

o Upward sbearing or frictional forces between the prism of
eartb directly above tbe bore and tbe adjacent earth.

o Cohesion of soil.

The vertical earth load on tbe borizontal plane at tbe tip of the
bore, within the widtb of tbe excavation, is equal to tbe weigbt of
the prism of earth above tbe bore minus the upward frictional forces
and minus the coheaion of the soil along the limits of the priam of
the soil over tbe bore. Tbe user must select an appropriate value
for cobesion for tbe type of soil being jacked through, These
values range from 0 to 1000 pounds per square foot (0 - 47.88 kPa)
for soils classified as loose dry sand to hard clay, respectively,

Since tbe jacking metbod of construction affords positive contact
around tbe lower exterior surface of the pipe and the surrounding
earth, an ideal bedding condition is provided, This positive
contact can be obtained by close control of the bore excavation to
the outside dimensions and Shape of the pipe or, if the bore is

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