Page 330 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

SITE UTILITY SYSTEMS

6.52 CHAPTER SIX

TABLE 6.8 Weight of Soil

Average moisture
3
Type of soil Kg/m 3 Weight, lb/ft Correction factor content, %
Sand and sandy loam 1,600 100 0.83 15
Sand and gravel mix 1,760 110 0.90 20
Saturated topsoil 1,840 115 0.95 25
Average clay 1,920 120 1.00 30
Wet clay, peat 2,080 130 1.10 100

earth load. Table 6.9 gives the transition width for various combinations of pipe size and
depth of burial.
It is common practice to allow 1 ft (0.3 m) on either side of a pipe in a trench for work-
ing space. Figure 6.32 provides direct determination of earth load for this condition. If soil
3
3
weight is other than 120 lb/ft (1920 kg/m ), proportionally decrease or increase the result-
ing weight according to the correction factor in Table 6.8.
SUPERIMPOSED LOADS

Live Loads
Whenever pipe is buried in the ground there is always the possibility of heavy equipment or trucks
riding over the buried pipe during construction. When pipe is placed under a road or railroad, this is
a normal occurrence. This load must be added to the earth load to determine the total force exerted
on the buried pipe. The general contractor should be consulted to determine if piping will be buried
to its full depth during construction or if additional cover will be added later.
A live load consists of two separate types of loads: the actual weight of any vehicle
passing over the pipe and the impact load that places additional stress on the pipe due to
the fact the load is moving.
Live Load from Trucks. The type of road surface over the pipe may have a reducing effect
on the amount of live load reaching the pipe. A flexible surface such as light-duty asphalt
will have little or no reducing effect. A concrete road or heavy-duty asphalt will greatly
reduce the load intensity. Railroad tracks are constructed over a standard bed consisting of
rock ballast and ties, which gives a uniform distribution of load to the piping.
For calculating the live load transmitted to a pipe under a road, the following formulas
are used.
Unpaved or light-duty pavement:

L = CRPF (6.13)
t
Rigid or heavy-duty pavement:
L = CBPF (6.14)
t
where L = truck superload, lb/ft of pipe
t
C = surface load factor
R = reduction factor
P = wheel load
F = impact factor
B = outside diameter of pipe, ft

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