Environmental Engineering Reference
In-Depth Information
rock mass ruptures in tension. The pressure required to initiate failure and the subsequent
pressure required to maintain an open hole after failure are used to calculate the magni-
tude of the
in situ
stress.
4.5
Instrumentation Arrays for Typical Problems
4.5.1
Importance
Soil Formations
Design Data Procurement
Design data are usually based on properties measured in the laboratory or
in situ
. Load
tests on piles or other types of foundations, and preloading with embankments, provide
additional design information.
Construction Control
Instrumentation is required where analytical limitations result in marginal safety factors,
if excessive deformations are anticipated or if remedial measures are to be invoked. Such
conditions exist for retaining structures constructed in soft ground, structures on shallow
foundations, embankments on soft ground, and earth dams and cut slopes.
Rock Masses
Design Data Procurement
Design is usually based on assumed properties because of the cost and limitations of the
validity of
in situ
tests; therefore, careful monitoring of construction is required on impor-
tant projects.
In situ
load tests and stress measurements require instrumentation.
Construction Control
Instrumentation is used to monitor the changes in
in situ
conditions caused by construc-
tion and to provide an early warning of impending failures. It is also used to assess the
effectiveness of the installation of supports or other changes to improve the stability of
tunnels, caverns, mines, cut slopes, and other excavations.
4.5.2
Settlement of Structures
Case 1: Structure Undergoing Differential Settlement
Problem
The structure in
Figure 4.34a
is undergoing excessive differential settlements resulting in
wall cracks, distortions of doors and windows, misaligned machinery, and floor warping,
as a result of the consolidation of a weak soil stratum.
Objectives
It is desired to determine the magnitude and anticipated rate of the remaining settlements
of the floors and structural frame. This information will provide the basis for determining
the remedial measures.
