Construction Monitoring For Earth Dams 1 Fars Science and Research Branch, Islamic Azad University

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 2

Inspection Requirements  Must not hinder or slow down contractor  Must work with contractor  Must consider contractor construction practices 3

Construction Monitoring MATERIALS  Grain size distribution analysis of materials Core, filters, drains Make sure material installed meets specifications Make sure that the borrow materials do not change… 4

Construction Monitoring MATERIAL tests  Triaxial extension/shear – filter and core  Consolidation – core m v d(H)= mv*H0*d(σ΄)  Hydraulic conductivity Lab tests:  filters - Constant or falling head  core – triaxial Field clay:  Centrifuge permeanometer 5

Construction Monitoring Proctor 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 6

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 e min ……highest dry unit weight 7

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Knead Clay Chunks Sheepsfoot roller 10

Soil Compaction Measurement 11

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 12

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 13

Compaction Specification 14

Compaction Specification  Make sure compacted soil same as Proctor material (grain size distribution analysis)  Add water to soil if too dry 95% Field Specification 15

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. 16

 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 17

 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 18

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 19

Earth fill dam: 1- Control placement of fill, monitor pwp to find shear strength and measure uplift pressure 2- Control placement of fill, monitor pwp to find shear strength and measure uplift pressure and monitor seepage 3- Control placement of fill and monitor seepage. Suggested Piezometer locations 20

Piezometer 21

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: 22

Inclinometer system (Courtesy of N. Sivakugan, James Cook University, Australia) 23

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: 24

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 25

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 26

Monitor long term settlement and consolidation in the foundation of embankments Settlement cell 27

Settlement cell 28

7- Bore hole extensometer : Monitor settlement heaves, convergence, and lateral deformation in the soil and rock For vertical settlement profile 29

Earth fill dam: Monitor vertical settlement in the toe of the dam ( Magnetic extensometer) Borehole extensometer: 30

Monitor settlement to determine when construction can continue. ( Magnetic extensometer used inside the inclinometer) Embankment: Borehole extensometer 31

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. 32

Earth pressure cell (Courtesy of N. Sivakugan, James Cook University, Australia) 33

Total pressure cell 34

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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 36

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 37

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 38