Page 27 - Trenchless Technology Piping Installation and Inspection

2 Cha pte r O n e

drawing flat strips of hot iron through a bell-shaped die. Then came
the Bessemer process for making steel, and the open-hearth furnace
for production of large quantities of steel. Steel pipes became reality.
The urban way of life changed. Community expanded into metrop-
olis. The “guts of the city” became steel pipes for water and clay
pipes for sewage.

1.1.1 The Pipe-Soil Interaction
The evolution of pipes was by trial and error. How many lives were
lost in cave-ins when the Persians excavated tunnels ahead of rock
lining? How could Romans predict that lead pipes would poison
them? Evolution of pipes proceeded empirically—not by design.
Design of buried pipes started in 1913, when Anson Marston became
the dean of engineering at Iowa State College. He noted, with con-
cern, how transportation bogged down during every rainstorm and
every spring thaw when “dirt” roads became quagmires of mud. The
dean sought a remedy. He called for action with publicized resolve:
“Let’s get Iowa out of the mud.” He recognized that to get Iowa out
of the mud, he had to get the water out of the roads. His remedy was
buried drainpipes along the roads. It worked. The nation was
impressed. A Federal Highway Research Board was formed with
Marston as the first director. Marston came out with the first engi-
neered design of buried pipe, an equation for soil load on pipe. In those
days, drainpipes were clay or concrete—both rigid. He left design of
the pipe up to the manufacturers to make pipe strong enough to with-
stand his Marston load. The idea was radical—performance specifica-
tion, not the traditional procedure specification. The test for pipe
strength was a three-edge-bearing (TEB) load. A pipe was supported
on two wooden 2 × 4’s close together and one 2 × 4 on top onto
which load was applied. The load at failure, divided by a safety fac-
tor, was to be greater than the Marston load. Clearly, design was
conservative.
The Armco Company had developed flexible pipe of corrugated
steel. Steel was available in coils from which corrugated pipe could
be fabricated. But the flexible pipe could not support a Marston
load under a three-edge-bearing test in the yard. When buried,
however, flexible pipe worked. Armco sponsored a research project
at Iowa State College. The project was assigned to a young faculty
member, M. G. Spangler. Using a soil box, Spangler showed that
flexible pipe deflects under soil load and develops horizontal soil
support on the sides of the pipe. Corrugated steel pipe could be
used as culverts and drain pipes. Spangler derived the Iowa formula
for predicting the horizontal expansion of buried, flexible pipe
based on a horizontal soil modulus of elasticity, E’. The derivation
was elegant and correct, except for the definition of E’. The soil
modulus was corrected by Spangler’s student Watkins and the