Field Instrumentation - Geotechnical Engineering Investigation - page 279

Tilt
Tilt can indicate differential settlement of a structure, impending failure of walls and
slopes, or major tectonic movements.

Lateral Displacement
Lateral surface displacements can signify slope failure or fault activity. The surfaces of tun-
nels and other underground openings undergo convergence from stress relief, which may
lead to failure.

Vibrations
Construction activity or earthquakes can induce vibrations in structures, resulting in over-
stress and failure.

Summary
Forms of surface movement, their occurrence, and applicable monitoring methods are
summarized in Table 4.4.

TABLE 4.4
Surface Movements: Forms, Occurrence, and Monitors

Movement Occurrence Monitoring Method Reference

Settlement or subsidence Fills, surcharge: buildings Optical survey nets with monuments Section 4.2.2

or settlement plates

Over tunnels, behind Settlement extensometers Section 4.3.2

walls

Heave or rebound Fills, surcharge: Optical survey nets Section 4.2.2

buildings

Settlement extensometers Section 4.3.2

Differential settlement Within buildings Optical survey nets Section 4.2.2

Water-level device Section 4.2.2

Tilt Retaining structures, Portable electric tiltmeter Section 4.2.3

buildings, rock-slope
benches

Pendulums Section 4.2.3

Terrestrial Section 4.2.2

stereophotography

Ground surface Mercury pools set in piers Section 4.2.3

Lateral Slopes Survey nets and GPS Section 4.2.2

displacement

Terrestrial photography Section 4.2.2

Wire extensometer Section 4.2.4

Precision electric strain meter Section 4.2.4

Sliding wire contact Section 4.2.4

Tension cracks, joints Simple strain meter with pins Section 4.2.4

Faults Survey nets Section 4.2.2

Precision electric strain meter Section 4.2.4

Convergence Tunnels Wire extensometer Section 4.2.4

Vibrations Blasting, pile driving, Vibration monitors Section 4.2.5

etc.