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Construction Monitoring For Earth Dams 1 Fars Science and Research Branch, Islamic Azad University.
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Transcript of Construction Monitoring For Earth Dams 1 Fars Science and Research Branch, Islamic Azad University.
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Reasons for Construction Monitoring Ensure proper materials are used Ensure proper construction and design is
followed Quickly modify design and construction
practices based on encountered site conditions
IT IS IMPERATIVE TO HAVE FULL TIME SITE INSPECTION
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Inspection Requirements Must not hinder or slow down contractor Must work with contractor Must consider contractor construction
practices
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Construction MonitoringMATERIALS Grain size distribution analysis of materials
Core, filters, drains Make sure material installed meets
specifications Make sure that the borrow materials do not
change…
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Construction MonitoringMATERIAL tests Triaxial extension/shear – filter and core Consolidation – core mv
d(H)= mv*H0*d(σ΄)
Hydraulic conductivity Lab tests:
filters - Constant or falling head core – triaxial
Field clay: Centrifuge permeanometer
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Construction MonitoringProctor Tests
Source materials in borrow pit Materials hauled to site
Field Compaction Uncompacted layer thickness (300mm max) Compaction equipment is suitable Moisture content and Maximum dry density
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Goal of Compaction Place loose soil in the field and compact it
to make soil strong as possible Maximum shear strength Very little settlement Low hydraulic conductivity
Find soil lowest emin ……highest dry unit weight
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Soil Compaction Measurement
Use dry sand with known dry density and specific gravity
Use dry sand to get volume of hole
Quick and reliable method
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Soil Compaction Measurement
Use radioactive material to get moisture content and soil density
Quick method Reliable if calibrated Radioactive device
therefore special transportation and rules must be followed
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Compaction Specification
100 (Proctor)t unit weighdry Max.
tunit weighdry Insitu (%) level Compaction x
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Compaction Specification Make sure compacted
soil same as Proctor material (grain size distribution analysis)
Add water to soil if too dry
95% Field Specification
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Field Instrumentation Measure performance of structure during
construction Long-term monitoring of structure
behaviour and health Must not impact structure performance
Geotechnical instrumentation can reduce undesirable consequences from construction.
These consequences may be the results of adverse performances, damage to the adjacent
facility and/or delays.
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Engineers should developed justifications for geotechnical instrumentation program on their projects In practice such programs are used to save lives, save money and/ or reduce risk of failure
In concept, these are simple and easy to understand benefits but in practice it is
difficult to quantify
Justification for Instrumentation
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Indicate impending failures Provide a warning Reveal unknowns Evaluate critical design assumptions Assess contractor's means and methods Minimize damage to the adjacent structures Control construction Control operation Provide data to help select remedial methods to fix
problems Documents performance for assessing damages Satisfy regulators …
Reasons to Install Instrumentation
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Field Instrumentation Piezometers
Excess pwp in core during compaction Uplift pressures Foundation head loss Core phreatic surface
Inclinometers Stability of slopes and foundations
Settlement gauges Extensometers Total earth pressures
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Earth fill dam:
1- Control placement of fill, monitor pwp to find shear strength and measure uplift pressure2- Control placement of fill, monitor pwp to find shear strength and measure uplift pressure and monitor seepage3- Control placement of fill and monitor seepage.
Suggested Piezometer locations
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Monitor lateral earth movements in embankment e.g. detect movement of D/S of earth fill dam, particularly during impounding. Determine type of shear zone in foundation. Monitor stability of U/S slope during and after impounding. Determine depth, direction, magnitude and rate of movement
Inclinometers:
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• Locate shear zone and help identify whether shear is planner or circular• Measure the movement at the shear zone. Determine whether the
movement is constant, accelerating or slowing.• Inclinometer must be founded into solid foundation
Embankment:
Inclinometer:
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5- Tilt meter: Monitor changes in the tilt of the structure. Activities such as dewatering, tunnelling, excavation causes settlement or lateral deformation. Placement of surcharge and pressure may cause heaves. Dam impounding, excavation beyond diaphragm wall etc.
Monitor differential settlement
Dewatering
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6- Settlement cell: Pneumatic settlement provide a single point measurement of settlement. They can be read from central location and are particularly useful where asses is difficult. Monitor consolidation during construction and long term settlement in the foundation of the fill.
Earth fill dam
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7- Bore hole extensometer: Monitor settlement heaves, convergence, and lateral deformation in the soil and rock
For vertical settlement profile
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Earth fill dam:Monitor vertical settlement in the toe of the dam ( Magnetic extensometer)
Borehole extensometer:
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Monitor settlement to determine when construction can continue. ( Magnetic
extensometer used inside the inclinometer)
Embankment:
Borehole extensometer
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8- Total pressure cell: Measured combined pressure of effective stress and pwp
Embankment dam Verify assumptions and warn of the soil pressures in excess of
those a structure is designed to withstand. It determine distribution, magnitude and direction of the total stress.
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Rock fill dam
SM: Strong motion accelerograph ( for monitoring earth tremors) TS: temperature sensor EX: Extensometer( Identify movement of dam base and ground at base) PZ: piezometers PC: Pressure cell W: V-Notch weir SC: settlement cell WL: water level meter
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Earthfill dam
SM: Strong motion accelerograph ( for monitoring earth tremors) TS: temperature sensor EX: Extensometer( Identify movement of dam base and ground at base) PZ: piezometers PC: Pressure cell W: V-Notch weir SC: settlement cell WL: water level meter
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Key Components for Design of Instrumentation Put in redundancy
Instruments will get lost due to construction activities Equipment will stop working
Protect equipment from contractors Put in safe areas Mark equipment Protect it during installation and post installation
Spend money so can remotely monitor and collect data
Consider data analysis cost