A Guide on Structural Health Monitoring (SHM)

1. A Guide on Structural Health Monitoring(SHM)

2. 1 6 STRUCTURAL HEALTH MONITORING OF BRIDGES INTRODUCTION 2 7 WHAT IS MEANT BY STRUCTURAL HEALTH MONITORING? STRUCTURAL HEALTH MONITORING OF TUNNELS TABLE OF CONTENT 3 8 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF DAMS 4 9 ADVANTAGES OF STRUCTURAL HEALTH MONITORING STRUCTURAL HEALTH MONITORING OF BUILDINGS 5 10 HOW DOES STRUCTURAL HEALTH MONITORING WORK? STRUCTURAL HEALTH MONITORING OF NUCLEAR POWER PLANTS

3. 1 INTRODUCTION With technological advancements in the field of civil engineering and geotechnical engineering, the magnificent structures like Burj Khalifa and Gotthard Base Tunnel have been made possible. Humans have built large structures like dams, tunnels, skyscrapers, power plants etc. to make their life easier. But even a minor failure in these structures can cause loss of property as well as human life. Hence, regular structural health monitoring is a must. Let's discuss more on structural health monitoring, geotechnical instrumentation, and how it makes the world a safer place to live.

4. 2 WHAT IS MEANT BY STRUCTURAL HEALTH MONITORING? Structural health monitoring is vital to avoid sudden failures and accidents. Before proceeding with any construction activity, it's necessary to carry out the monitoring of the construction site as well as the nearby assets.

5. 2 2 WHAT IS MEANT BY STRUCTURAL HEALTH MONITORING? WHAT IS MEANT BY STRUCTURAL HEALTH MONITORING? Geotechnical instrumentation and monitoring supply quantitative data on the struc- ture's performance to aid in evaluating its safety and detecting problems at an early stage. stage. Geotechnical instrumentation and monitoring supply quantitative data on the struc- ture's performance to aid in evaluating its safety and detecting problems at an early Structures can fail due to several reasons like design error, geological instability, poor maintenance, deterioration of construction material, etc. poor maintenance, deterioration of construction material, etc. Structures can fail due to several reasons like design error, geological instability, Structural health monitoring is a process to keep an eye on all the structures and generate early warnings to avoid mishaps. generate early warnings to avoid mishaps. Structural health monitoring is a process to keep an eye on all the structures and Encardio-rite is geotechnical instrumentation and monitoring company that provides various monitoring services along with state-of-the-art geotechnical instruments. various monitoring services along with state-of-the-art geotechnical instruments. Encardio-rite is geotechnical instrumentation and monitoring company that provides

6. 3 WHY IS GEOTECHNICAL MONITORING IMPORTANT? WHY IS GEOTECHNICAL MONITORING IMPORTANT? Site investigation Site investigation is crucial before carrying out any construction activity.

7. 3 WHY IS GEOTECHNICAL MONITORING IMPORTANT? It is important to check if the land is strong enough to bear the structure. Apart from this, it's essential to check for the safety of other assets in the vicinity of the con- struction land. Several geotechnical Instruments are used to characterize and determine initial site conditions. The most common parameters of interest in a site investigation are pore pressure, the permeability of the soil, slope stability etc.

8. 3 WHY IS GEOTECHNICAL MONITORING IMPORTANT? WHY IS GEOTECHNICAL MONITORING IMPORTANT? Design verification It's quite important to verify the design of the structure. Improper designing may lead to its failure.

9. 3 WHY IS GEOTECHNICAL MONITORING IMPORTANT? WHY IS GEOTECHNICAL MONITORING IMPORTANT? Geotechnical instruments are used to verify design assumptions. Instrumentation data from the initial stage of a project may show the need or provide the opportunity to modify the design in later stages. For example, data obtained from reinforcement bar strain meters installed by Encar- dio-rite at Teesta Barrage in the left embankment led the project authorities to revise their estimates of the requirement of steel in the right embankment.

10. 3 WHY IS GEOTECHNICAL MONITORING IMPORTANT? WHY IS GEOTECHNICAL MONITORING IMPORTANT? Construction control Structural monitoring is necessary to help the engineer in determining how fast con- struction can proceed without adverse effects on the foundation soil and construc- tion materials used.

11. 3 WHY IS GEOTECHNICAL MONITORING IMPORTANT? WHY IS GEOTECHNICAL MONITORING IMPORTANT? The instruments are installed to monitor the effects of construction. For example, the temperature rise in concrete due to the heat of hydration was moni- tored at Sardar Sarovar Dam on the Narmada River with Encardio-rite’s temperature meters to determine the pouring temperature of mass concrete. By mixing ice flakes, the temperature of the concrete to be poured was brought down to around 15°C. This resulted in the temperature of the setting concrete not exceeding the critical 29°C, as specified and required by the Central Water and Power Research Station (CWPRS), Pune.

12. 3 WHY IS GEOTECHNICAL MONITORING IMPORTANT? WHY IS GEOTECHNICAL MONITORING IMPORTANT? Safety Instruments can provide early warning of impending failure. Safety monitoring requires quick retrieval, processing, and presentation of instrument data so that analyses and decisions can be made promptly. An effective action plan for implementing corrective measures can then be prepared.

13. 4 ADVANTAGES OF STRUCTURAL HEALTH MONITORING Structural health monitoring (SHM) is critical because: • • • • • • • • • • It can provide early warning to the concerned authorities so that they can take actions well before any casualties. It keeps a regular check on the health of structures so that sudden failures can be avoided. It safeguards human life as well as the loss of property. It also protects the surrounding structures in the vicinity. It increases the life span of the structures. It reduces the long-term and short-term costs related to structural maintenance. It monitors the performance for safety during the life of the structure. It evaluates the effect of the operation of the structure on parameters like stress, strain, water, pressure, inclination, deflection and water seepage. It compares the observed data with design assumptions. It helps with the data to plan and schedule predictive and preventive maintenance programs for the structure.

14. 4 ADVANTAGES OF STRUCTURAL HEALTH MONITORING • • It provides data to determine the effects of natural calamities such as earthquake, flooding etc. on the structure. Compilation of long-term and reliable data on the various elements of the plant especially foundations, anchoring systems and containment structures.

15. 5 WHY IS GEOTECHNICAL MONITORING IMPORTANT? HOW DOES STRUCTURAL HEALTH MONITORING WORK? Structural health monitoring requires several geotechnical instruments installation. The instruments like strain gauges, piezometers, tilt meters, temperature sensors, pressure cells, load cells etc. measure the crucial parameters affecting the struc- tures. These instruments are installed on dams, tunnels, nuclear power plants, buildings, monuments to measure the important parameters. The measured data is logged in real-time through data loggers and displayed via a PC/laptop/mobile device at any remote location. The data loggers are capable of generating early warnings such that the concerned person can take actions accordingly.

16. 6 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF BRIDGES There are numerous rail and road bridges built across the globe. They are an essen- tial component of transportation networks and, hence, structural health monitoring of bridges is crucial.

17. 6 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF BRIDGES Any damage or collapse of bridges due to their deteriorating performance disrupts transportation systems and may result in the loss of life as well as property. The railway bridges are well documented and have a laid down system for checking and maintenance. Bridges must function safely at all times. A large number of bridges are quite old and not designed for the heavier and faster-moving vehicular loads that they are cur- rently subjected to.

18. 6 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF BRIDGES Online cloud-based web data monitoring service Encardio-rite offers public cloud-based online web data monitoring services for the safety of existing rail and road bridges. The heart of the online structural monitoring instrumentation system is a web data monitoring service (WDMS) offered by Encardio-rite. The service forms an important part of the Bridge Management System. It is a web-based data-management and presentation tool for retrieving data from the sensors through Encardio-rite range of automatic data loggers. WDMS consists of Drishti, data management software that acts as a data collection agent, a database server and a web server hosted on a high-reliability server computer.

19. 6 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF BRIDGES The host computer periodically collects data from the remote data logger over cell phone networks. Users interact with the software using their web-browser when connected to the Internet. The only requirement is that the data logger site is covered by a cell phone service provider who can provide reliable GSM/GPRS enabled cellular data connection locally. Multiple authorized users at different locations assigned with an individual password are allowed to view any data or report from the structure simultaneously. Graphs & reports can be viewed using popular web browsers like Microsoft internet explorer or Mozilla Firefox amongst others.

20. 6 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF BRIDGES Details like sensor identification tag, last recorded sensor reading and values of pro- grammed alert levels can be viewed on the first page of the site that shows the loca- tion of installation. If anyone of the alarm level exceeds, the sensor location turns to a red dot. Clicking the pop-up table brings up an associated data window where the sensor data can be seen either as a table or as a graph. Site administrators can set alarm limits which are generally considered as “alert level” and “action level”. WDMS can also be programmed to send SMS alert messages or e-mail to selected users as soon as any sensor data crosses its predefined alarm levels, either while going above or going below the alarm level.

21. 6 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF BRIDGES Bridge Monitoring Instrumentation Scheme There are two types of instrumentation schemes to monitor the health of the bridges. The figure above shows online web based monitoring of surface parameters like tilt, crack, load, strain, vibrations and subsurface parameters like lateral movement, set- tlement and piezometric pressure.

22. 6 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF BRIDGES The above figure shows online web based monitoring of lateral movement and settlement using robotic total stations and prism targets.

23. 6 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF BRIDGES The picture on the left is a typical installation of a robotic total station installed to automatically gather data from prism targets installed on the structure of a bridge. The picture in the middle is that of a mini prism target. The figure on the right shows points at which prism targets may be installed on a typical bridge. More than one robotic total station may be required for proper moni- toring of a structure.

24. 6 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF BRIDGES Screenshots of some sample long term monitoring data The figure above shows structural crack monitoring over a period of one year using Encardio-rite Model EDJ-40V crack meter. Crack opening is in blue and variation in temperature is in red. The initial opening of the crack gauge was set at 5.12 mm

25. 6 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF BRIDGES The above image shows the structural tilt monitoring of the bridge from September 12, 2015 to December 8, 2016 using Encardio-rite Model EAN-92M biaxial tilt meter. Tilt variation in the two directions is shown by the blue and black lines. The maxi- mum change in tilt recording during this period is 0.04 deg. The two horizontal red lines at the top and bottom are the alarm limits set at ± 0.1 deg. The red line gives the temperature variation during this period.

26. 6 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF BRIDGES The above image shows monitoring of ground water level along with daily rainfall for a period of five years.

27. 6 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF BRIDGES Piezometric pressure is in blue and daily rainfall is in purple. Maximum rainfall re- corded on any day during this period is 157 mm. Ground water table variation during this period has been between 34 and 43 m of water column. Sensors used are Encardio-rite piezometer Model EPP-30V and Rain Gauge model ERG-200 tipping bucket type.

28. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS Encardio-rite offers a comprehensive web-based monitoring solution for the long-term safety monitoring of tunnels.

29. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS It manufactures a wide range of sensors which have a proven track record for reli- ability and long-term performance under harsh conditions. It also offers advanced monitoring technologies such as automatic 3D deformation monitoring using ATS, laser scanning and aerial survey using drones for keeping a tab on the structural health of tunnels and appurtenant structures. Structural monitoring solution for tunnels WDMS – Web-based Data Monitoring Solution Web-based data monitoring solution for any type of tunnel construction such as NATM, TBM tunnelling, cut & cover, micro-TBM/pipe jacking, etc. essentially com- prises of the following:

30. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS • • • • Model EAN-92M-B or EAN-93M-B biaxial tilt meter with SDI-12 output mounted at one or more locations on the structures within the zone of influence to record changes in tilt. • Model EDJ-40V vibrating wire crack meter (with ESVI-01-01 SDI-12 interface box) for monitoring displacement/opening of existing cracks in structures within the zone of influence. Model EAN-52M vertical in-place inclinometer system with several biaxial probes with SDI-12 output mounted vertically in a borehole. These are connected in a daisy chain manner with a single output cable for continuously monitoring sub-surface lateral movements. Model EPP-30V vibrating wire piezometer with model ESVI-01-01 or ESVI-10VB SDI12 interface box for monitoring pore pressure variations. Model EDS-70V vibrating wire type multiple point borehole extensometer (with ESVI-01-04 SDI-12 interface box) for monitoring sub-surface settlement and lateral movement at specified depths.

31. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS • • • • Model EBS-16 building settlement points for monitoring settlement of structures using a digital level. • Model ESMP-10C2 or EPS-12-60 surface settlement points for monitoring settlement of ground above the tunnel. • Encardio-rite Model EAN-26-MV manual inclinometer system comprising of a bi-axial digital inclinometer probe, operating cable on a reel with Bluetooth transceiver and a smartphone data logger with inclinometer application Model ELC-30S/ELC-30SH resistive strain gage type centre hole load cell (with ES BI-10 SDI-12 interface box) for monitoring tension in anchors and rock bolts. Model ESC-30V vibrating wire shotcrete pressure cell or model EPS-30V vibrating wire concrete pressure cell (with ESVI-01-01 SDI-12 interface box) for monitoring radial and tangential stress in shotcrete lining or concrete pre-cast segments. Model EDS-20V-E/EDS-20V-AW vibrating wire strain gauges (with ESVI-01-01 SDI12 interface box) for monitoring strains in tunnel linings and concrete pre-cast segments.

32. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS • • • These could be single & multichannel. RF Gateways with integrated GSM/GPRS modem for enabling cable-free wireless transmission of data. Refer to the figure below showing installed sensors in a typical tunnel section with RF data transmission. Encardio-rite Model ESDL-30 data logger for the SDI-12 output sensors, with integral GSM/GPRS for wireless data transmission. Encardio-rite Online Web Data Monitoring Service (WDMS) that provides data access (with alarms) to authorized users at different geographical locations, on their computer/laptops.

33. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS Laser Scanning Laser scanning is an advanced method of surveying and conducting geometric doc- umentation of buildings, architectural and archaeological monuments, engineering projects or other construction works and objects which require a high degree of analysis, are difficult to reach or gain access to, or are not to be touched.

34. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS Recent developments, especially in the software, have made it a very convenient and cost-effective tool to accurately monitor structural deformations in 3D. Accuracy of up to 2-3 mm is possible using the method. Due to the lighter nature of the new software, it takes significantly lesser time to pro- cess the results and make the same available online, almost in real-time. It is based on exceptionally dense mapping of 3D coordinates of the points on the surface that is to be surveyed, taken at speeds ranging from a few thousand up to a million points per second. Depending on the object (size, shape, desired accuracy), laser scanning may be air- borne or terrestrial, static or mobile, autonomous or in combination with other stan- dard topographic methods.

35. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS Completion of the fieldwork results in a geo-referenced point cloud which, due to its great density and its ability to bear information on the reflectivity and/or the colour of each point, comes close to the term, “virtual reality”. Depending on the case and on the user’s needs, horizontal, vertical or diagonal sec- tions, aspects, images, videos, ortho-photographs, surface expansions, interval curves, 3D models, determination of distortion as well as a number of other analysis derived from the scanner’s operations in the non-visible spectrum, can be produced.

36. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS The results of laser scanning give us: • • • • • • • Surveying of current state or ‘as constructed’ state Virtual reality creations; Virtual tour videos Geometric documentation of the structure Quantitative calculation Inspection of free passage space – determination of bottlenecks Creation of 2D & 3D products (sections, facets, 3D models, etc.) Identification of deformations – discrepancies

37. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS Aerial Mapping using Unmanned Aerial Vehicles (UAV/Drone) Inspection of huge and complex structures like tunnel construction sites requires a high degree of analysis but at times is difficult to reach or gain access to. Use of Unmanned Aerial Vehicles (UAV)/Drones is best suited for such applications. UAVs/Drones are unmanned and remotely-piloted aircraft that follow a pre-pro- grammed path for takeoff, flight and landing.

38. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS These aircraft are equipped with HD/IR/Thermal cameras that compute aerial images and videos over a defined area at a specified height. Using UAVs/drones to video, model and scan for cracks, erosion, corrosion and defects in areas, that would otherwise require the inspector to use a rope/harness or erect access scaffolding, is a safer, faster and smarter choice. Large sites with complex structures necessitate aerial photogrammetry avoiding ex- pensive ground-based surveys. This technology is useful during the construction process also- as the development occurs, managers have difficulty maintaining a true picture of the site.

39. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS Automatic 3D deformation monitoring system The real-time 3D deformation monitoring system is a systematic tracking of any al- teration that may take place in the shape or dimension of the tunnel as a result of stress, load, ageing etc. or of any structure located within the zone of influence of the tunnel construction. The above deformation monitoring system consists of a high accuracy automated total stations (ATS) that have the ability of auto-target recognition (without any human interference).

40. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS Each ATS has a dedicated control box that includes a computer running special software. This control box manages the total station and schedules the frequency of the measurements, the addition or subtraction of monitor benchmarks, the filters of acceptance or repetition of each measurement, the atmospheric corrections in distance measurements, the calculation and repositioning of the total station etc. The whole system can be controlled/re-configured remotely after installation at site. The on-site system transmits the collected raw data to a remote server/computer via GSM/GPRS. Raw data is processed into meaningful results and presented in the WDMS. The system has the facility of alert notifications through SMS and (or) e-mail to the authorized team for any result exceeding present alarm and critical levels.

41. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS The system provides an accurate, continuous, real-time data, eliminating any human error/delay in manual data. The raw data is processed, analysed and the result is majorly used for predictive maintenance, alarming for safety.

42. 7 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF TUNNELS Tunnel Monitoring Instrumentation Scheme

43. 8 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF DAMS Dam monitoring instrumentation plays a key role in safety monitoring for dam and people, providing necessary information on the performance of the dam and detect problems at an early and preventable stage.

44. 8 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF DAMS The extent and nature of instrumentation depend not only on the complexity of the dam and the size of the reservoir but also on the potential for loss of life and property downstream. This information is critical for the dam’s owner who is directly responsible for any consequences of its failure. Instrumentation includes different type of sensors used for measuring pore pres- sure, water flow, lateral movement, deformation, stress, strain and temperature, in- stalled in the dam and its auxiliary structures. It also includes geodetic targets measured using surveying techniques.

45. 8 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF DAMS Monitoring solutions for dam Following solutions are available with Encardio-rite for online monitoring: • • • • • • Geotechnical sensors to measure all relevant parameters required to monitor different types of dams Automatic monitoring of geotechnical sensors with SDI-12 digital interface using SDI-12 data logger with GSM/GPRS telemetry Automatic monitoring of geotechnical sensors using nodes and gateways Geodetic monitoring with automatic total stations (ATS) with GSM/GPRS telemetry Laser scanning Survey by UAVs (unmanned aerial vehicle) or drones

46. 8 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF DAMS Public cloud-based web data management service (WDMS) that provides data online (with alarms) to authorised users at different locations on their computers/mobile devices.

47. 8 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF DAMS Dam Monitoring Instrumentation Scheme Concrete Dam

48. 8 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF DAMS Purpose Instrument Location Monitor pore pressure or seepage of water through the cross-section of the dam Pore pressure meter Dam blocks at different elevations Monitor stresses in the concrete of the dam body Stress meter Near foundation where the height of the dam is maximum (can be just below the gallery) Monitor pore pressure to adjust it from stress meter readings to get true stress Pore pressure meter Near stress meters Monitor joint opening between the blocks Joint meter – Uniaxial and triaxial Between the concrete blocks Monitor tilt of the dam Tilt meter Dam block, at the top Monitor deformation due to all causes – including those due to stress Strain meter rosette In dam body – in a group of five-four strain gages at angles of 0°,45°,90°, 135° in one plane and one strain gage at right angles to this plane

49. 8 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF DAMS Purpose Instrument Location Monitor deformation due to changes in temperature, moisture or autogenous growth in the mass concrete of the structure. Adjusting this from strain meter readings gives strain due to stresses in the dams No-stress strain meter Near strain meter rosette -inside the no stress container Monitor water level in the reservoir Automatic water level recorder The upstream side of the dam Monitor temperature of concrete during the casting of the concrete blocks to prevent undesirable micro-cracks. Temperature variation is also one of the major factors causing stress on the surfa- ceof the dam that results in material fatigue Temperature meter Dam blocks and spillway

50. 8 WHY IS GEOTECHNICAL MONITORING IMPORTANT? STRUCTURAL HEALTH MONITORING OF DAMS Purpose Instrument Location Monitor water pressure on the base of the dam caused due to water seepage from the reservoir to the foundation. This pres- sure exerts a vertical upward force on the base of the dam and tries to lift it up Uplift pressure meter In the dam Gallery – downwards – with a stop valve on the uplift pressure pipes, which is opened to release the water and reduce pressure on the base of the dam. Monitor tilt of dam – caused by thrust applied by water pressure on the dam Normal plumbline (telecoordinometer) Blocks Monitor relative displacement between the dam bottom and the foundation base rock Inverted plumbline (telecoordinometer) In the same block as that of the Normal plumbline Monitor lateral movement of the foundation Digital inclinometer or in-place inclinometer Dam foundation with top in cross or transverse gallery