Purpose of Geotechnical Investigation
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Site Investigation |
Characterise site conditions before, during & after construction (bearing capacity, settlement, permeability, pore pressure & slope stability) |
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Design Verification |
Verify assumptions & predicted performance |
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Construction control |
Monitor the effects of construction |
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Quality control |
Enforce quality of workmanship & document work done to specifications |
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Safety |
Provide early warning signals |
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Legal protection |
Provide evidence in litigation |
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Performance |
Monitor in-service performance |
Factors Affecting the Choice of Instruments
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Critical parameters |
Identify parameters & select instruments to measure them within tolerances |
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Ground conditions |
Soil profile & strata, properties, difficulties & pore-water conditions |
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Redundant & complementary measurements |
Complex behaviour of soil/rock understood through one or multiple parameters |
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Instrument performance |
Specified by range, resolution, accuracy & precision |
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Cost-effectiveness |
Produces sufficiently reliable results within resource constraints |
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Instrument life |
Expected period of applications for each instrument |
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Environmental conditions |
Conditions of temperature & humidity |
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Resources at site |
Resources available for instrumentation |
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Data acquisition |
Real-time monitoring, remote investigation & adaptability |
Common Types of Geotechnical Instruments
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Piezometers |
Measure pore-pressure & ground water levels |
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Inclinometers |
Monitor lateral earth movements in landslide areas & embankments; monitor deflection of retaining structures & piles |
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Horizontal inclinometers |
Provide settlement profiles of embankments, foundations & other structures |
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Beam sensors & Tiltmeters |
Monitor changes in the tilt of a structure, especially due to construction activity & applied loads |
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Borehole Extensometers |
Monitor settlement, heave, convergence & lateral deformation in soil & rock |
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Settlement cells |
Provide single-cell measurement of settlement, especially where access is difficult |
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Load cells |
Proof-test & measure loads in tie-backs, rock bolts, ground anchors, & struts |
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Total Pressure Cells |
Measure the combined pressure of effective stress & pore water pressure; verify design assumptions & warn of excessive soil pressures |