1

Construction Monitoring

For Earth Dams

Fars Science and Research Branch, Islamic Azad University

2

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

3

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

practices

4

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…

5

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

6

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

7

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

8

9

10

Knead Clay Chunks

Sheepsfoot roller

11

Soil Compaction Measurement

12

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

13

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

14

Compaction Specification

100 (Proctor)t unit weighdry Max.

tunit weighdry Insitu (%) level Compaction x

15

Compaction Specification Make sure compacted

soil same as Proctor material (grain size distribution analysis)

Add water to soil if too dry

95% Field Specification

16

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.

17

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

18

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

19

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

20

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

21

Piezometer

22

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:

23

Inclinometer

system (Courtesy of N.

Sivakugan,

James Cook University, Australia)

24

• 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:

25

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

26

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

27

Monitor long term settlement and consolidation in the foundation of embankments

Settlement cell

28

Settlement cell

29

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

For vertical settlement profile

30

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

Borehole extensometer:

31

Monitor settlement to determine when construction can continue. ( Magnetic

extensometer used inside the inclinometer)

Embankment:

Borehole extensometer

32

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.

33

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

34

Total pressure cell

35

36

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

37

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

38

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