Civil Engineering Reference
In-Depth Information
17
Monitoring
17.1
Introduction
Geotechnical measurements referred to as “monitoring” are conducted to assess the
stability of rock engineering structures during and after construction. Furthermore, the
measurement results are compared with the results of the stability analyses by means
of back analyses. This also allows improved rock mechanical parameters and in-situ
stresses to be evaluated.
In tunneling, these measurements are of particular importance for monitoring the stabil-
ity of the tunnel adjacent to the temporary face, monitoring the loading of the support
and, particularly in the case of tunnels with low overburden, controlling subsidence or
heaving on the ground surface. Also, in many cases the vibrations during heading need
to be monitored for reasons of protection of buildings. Monitoring results are also used
for adapting the support measures to the local ground conditions. This also applies to
large underground openings such as caverns (Section 16.7.1).
In the case of dams, monitoring of displacements, temperatures, pore pressures and
quantities of seepage serves predominantly for supervising and verifying the operating
conditions (Chapter 24). In certain cases, such as where there are adjacent buildings or
potential rock slides, construction pits and rock slopes are also equipped with monitor-
ing devices (Sections 16.7.2, 17.10.2 and Chapter 25). Monitoring of displacements due
to excavation is also carried out in exploration adits and shafts. The main purpose here,
however, is to derive the rock mechanical parameters and the in-situ stress state in con-
junction with field and laboratory testing as well as stress measurements (Chapter 19).
In all cases the monitoring results have to be interpreted by means of numerical analy-
ses to verify the rock mechanical parameters and the in-situ stress state and, if indicat-
ed, the design of the temporary and permanent support. The volume affected by the
excavation of an underground opening is considerably larger than in the case of field
tests and local stress measurements. Back analyses of monitoring results therefore allow
representative rock mechanical parameters to be determined according to the homo-
geneous model and the large-scale in-situ stress state to be evaluated. Corresponding
examples already have been given in Sections 8.8 and 16.7. Further examples from engi-
neering practice will be presented in Sections 19.2, 20.3.7, 22.10, 24.7 and 25.3.
This chapter describes the most common geotechnical monitoring methods: geodetic
measurements, monitoring of vertical displacements at the ground surface, monitoring
of rock displacements along boreholes, monitoring of relative displacements between
rock surfaces (convergence measurements), pressure monitoring, anchor force measure-
ments and the monitoring of water level and water pressure (piezometric head measure-
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