Environmental Engineering Reference
In-Depth Information
(A)
(B)
(Direct readout)
(a)
(a)
Bench
mark
Remote
readout
(v)
Bench
mark
(a)
(c)
(c)
(a)
Remote readout
Fill
(k,r)
(k,r)
Weak soil
(r)
Weak soil
(r)
(r)
(d)
(r)
(L)
(d)
(L)
(d)
Strong materials
FIGURE 4.35
Instrumentation for embankment or steel storage tank over soft ground: (A) embankment over soft ground,
(B) steel storage tank over soft ground. Legend: (a) optical survey; (c) settlement plates; (d) borehole
extensometer; (k) borros points; (L) inclinometers; (r) piezometers; (v) strain gages.
Objectives
Loading rates must be controlled to prevent foundation failure. Data on the magnitudes,
rates of settlement, and on the pore pressures provide the basis for determining when the
surcharge may be removed. (After the storage tank is surcharged, it is raised, releveled,
and used for storing products lighter than water.)
Instrumentation
Precise optical surveys monitor settlements as a function of time as well as heave occur-
ring beyond loaded areas. Settlement plates, extensometers, and borros points are moni-
tored at the fill surface. Remotely read piezometers and inclinometers may be installed in
the fill and beneath the tank. (With respect to tank rupture, the critical differential settle-
ments are between the center and the bottom and along the perimeter.) Stresses in the tank
wall are monitored with strain gages; mechanical types are preferred.
The piezometers, inclinometer, and heave reference points are necessary to provide con-
trol against failure by foundation rupture. Pore-pressure data are needed to determine
when the preload may be removed. Bench marks must be installed beyond any possible
ground movements.
Case 4: Pile Load Testing
Objectives
A pile load test may be performed (1) to determine the capacity of a pile as required to
satisfy a building code, (2) to determine the proportion of the total load carried in end
bearing and that carried in shaft friction during vertical load testing, and (3) to measure
horizontal deflections during lateral load testing for the determination of the horizontal
modulus of subgrade reaction.
