1 Scope
1.1This Standard governs the procurement, installation, baseline establishment, reading, data management, alert response, and decommissioning of geotechnical instrumentation used to monitor ground, groundwater, and structure movement during and after construction.
1.2This Standard applies to braced excavations, sheetpile and soldier-pile walls, slurry walls, tieback and anchored walls, driven and drilled deep foundations, MSE walls, embankments, slope stabilization, and structures within the influence zone of tunneling and excavation.
NOTE Geotechnical monitoring exists to verify design performance and to provide early warning of ground or structure behavior that departs from prediction, so that contingency action can be taken before damage occurs. (1.2.1)
NOTE The instruments covered here measure displacement, pore pressure, settlement, strain, load, and earth pressure, and report through manual readings or automated data acquisition systems with real-time telemetry and alarm notification. (1.2.2)
NOTE The Geotechnical Engineer of Record (GEOR) develops the Geotechnical Instrumentation Plan (GIP) that defines instrument types, locations, depths, monitoring frequency, and threshold values; this Standard is the contractual instrument that enforces that plan in the field. (1.2.3)
NOTE Threshold values, instrument locations, and monitoring frequencies stated in this Standard are illustrative starting points for the GEOR to confirm or revise per project; they are not prescriptive limits. (1.2.4)
NOTE Instrument design and selection — including selection of instrument types to address a specific geotechnical hypothesis — is the GEOR's responsibility and is not part of this Standard; this Standard governs procurement, installation, and operation of instruments that have already been specified in the GIP. (1.2.5)
NOTE Structural design of earth-retaining systems is covered by
Retaining Walls; surface and subsurface monitoring of those walls is within this Standard's scope.
(1.2.8) NOTE Geoenvironmental groundwater quality sampling wells and structural health monitoring of completed in-service structures are outside the construction-phase geotechnical scope of this Standard. (1.2.10)
2 Referenced Standards
2.1Instruments, installation, calibration, and reporting shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2Where referenced standards conflict, the more stringent requirement shall govern unless the Geotechnical Engineer of Record directs otherwise in writing.
| Standard |
Title |
| ASTM D6230 |
Monitoring Earth or Structural Movement Using Inclinometers |
| ASTM D7299 |
Verifying Performance of a Vertical Inclinometer Probe |
| ASTM D7764 |
Pre-Installation Acceptance Testing of Vibrating Wire Piezometers |
| ASTM D6598 |
Installing and Operating Settlement Points for Monitoring Vertical Deformations |
| ASTM D4750 |
Construction Monitoring of Soil Improvement Programs That Use Vertical Drains |
| ASTM D5781/D5781M |
Dual-Wall Reverse-Circulation Drilling for Installation of Subsurface Monitoring Devices |
| ISO 18674-1 |
Geotechnical Monitoring by Field Instrumentation - Part 1: General Rules |
| ISO 18674-3 |
Geotechnical Monitoring by Field Instrumentation - Part 3: Inclinometers |
| FHWA-NHI-14-007 |
Geotechnical Instrumentation for Monitoring Field Performance |
| FHWA-NHI-09-087 |
Soil Nail Walls Reference Manual |
3 Submittals
3.1Action Submittals
3.1.1The Contractor shall submit the following action submittals for review and acceptance before any instrument is installed:
- Geotechnical Instrumentation Plan (GIP) prepared and sealed by the GEOR, defining instrument types, locations, depths, monitoring frequency, and Alert/Action/Trigger thresholds
- Instrument schedule listing each instrument by designation, type, location, tip or sensor depth, measurement range, and baseline due date
- Manufacturer cut sheets and technical data for every instrument type proposed
- Installation procedures for each instrument type, including borehole drilling method, grout mix design, sand-pack and seal details, and casing orientation
- Combined utility and excavation-support layout review confirming that no instrument borehole conflicts with existing utilities or with support-of-excavation elements
- Automated data acquisition system (ADAS) architecture, including channel assignments, power source, telemetry carrier, and alarm-notification logic
- Qualifications of the instrumentation installer and the data-reduction personnel
☐ Geotechnical Instrumentation Plan (GEOR-sealed)
☐ Instrument schedule
☐ Manufacturer cut sheets / technical data
☐ Installation procedures (drilling, grout, seals, orientation)
☐ Combined utility / support-of-excavation layout review
☐ ADAS architecture and alarm logic
☐ Installer and data-reduction qualifications
3.2Informational Submittals
3.2.1The Contractor shall submit the following informational submittals before instruments are accepted on site:
- Factory calibration certificates for every instrument with a measured output (piezometers, strain gauges, load cells, pressure cells, inclinometer probes)
- Inclinometer probe verification record per ASTM D7299
- Vibrating-wire piezometer pre-installation acceptance test record per ASTM D7764
- Grout mix design test data confirming target stiffness and bleed
- ADAS communication test record demonstrating end-to-end telemetry and alarm delivery
☐ Factory calibration certificates
☐ Inclinometer probe verification (ASTM D7299)
☐ VW piezometer acceptance test (ASTM D7764)
☐ Grout mix design test data
☐ ADAS communication / alarm test record
3.3Closeout Submittals
3.3.1The Contractor shall submit the following closeout submittals before final acceptance:
- Full as-installed instrument record with surveyed coordinates and elevations
- Complete reading history in non-proprietary digital format (CSV) plus the native data files
- Final interpretive monitoring report prepared by the GEOR
- Instrument decommissioning records, including abandonment and grouting of boreholes left in place
☐ As-installed instrument record (surveyed coordinates/elevations)
☐ Complete reading history (CSV + native files)
☐ Final interpretive monitoring report (GEOR)
☐ Decommissioning and borehole abandonment records
4 Quality Assurance
4.1Instruments shall be installed by personnel experienced in geotechnical instrumentation of the specific types deployed on the project.
4.2Each instrument with a measured output shall be furnished with a current factory calibration certificate traceable to a recognized standard.
4.3Inclinometer probes shall be verified per ASTM D7299 before the baseline reading and at intervals not exceeding the manufacturer's recommended recalibration period.
4.4Vibrating-wire piezometers shall pass pre-installation acceptance testing per ASTM D7764 before installation.
NOTE Acceptance testing confirms that the sensor reads correctly and responds to a known pressure change before it is sealed permanently below ground, where it can never again be checked against a reference. (4.4.1)
4.5The instrumentation installer shall hold a pre-installation coordination meeting with the GEOR, the excavation-support contractor, and the survey crew before the first borehole is drilled.
NOTE The most common cause of lost data is not instrument failure but physical conflict: a borehole drilled into a utility, a casing installed where a strut or waler will land, or a monument set where equipment will run over it. A combined layout review prevents these conflicts before drilling. (4.5.1)
4.6Calibration certificates and acceptance test data shall be reviewed and accepted before an instrument is accepted on site.
NOTE Instruments installed without verified calibration produce readings that cannot be defended if a threshold exceedance is later disputed. (4.6.1)
5 Geotechnical Instrumentation Plan
5.1A Geotechnical Instrumentation Plan (GIP) prepared and sealed by the GEOR shall govern all instrument types, locations, depths, monitoring frequencies, and threshold values.
NOTE Instruments installed without a GEOR-sealed plan are routinely placed in the wrong location or at the wrong depth relative to the failure mechanism they are meant to detect, rendering the data uninterpretable. The GIP ties every instrument to a specific design concern. (5.1.1)
5.2The GIP shall identify the failure mechanism or performance question each instrument addresses.
5.3The GIP shall define Alert, Action, and Trigger threshold values for each monitored quantity, with the calculation basis stated.
NOTE Generic threshold numbers carried into the contract without project-specific calculation are either overly conservative, producing constant false alarms that desensitize the team, or unconservative, missing real movement. The GEOR must calculate thresholds for the actual ground, structures, and tolerances. (5.3.1)
5.4The GIP shall define the monitoring frequency schedule as a function of excavation stage and proximity to active work.
5.5The GIP shall define the response protocol for each threshold tier, including who is notified, within what time, and what action follows.
6 Instrument Types
6.1Inclinometers shall measure lateral ground and wall movement along a cased borehole.
NOTE An inclinometer detects horizontal displacement of the casing relative to a fixed datum, profiling how a wall or slope deflects with depth. It is the primary instrument for verifying excavation-support performance. (6.1.1)
6.2Vibrating-wire piezometers shall measure pore water pressure where a fast, stable response is required.
NOTE Vibrating-wire piezometers respond to pressure change in seconds and remain stable for years, making them suitable for time-critical construction monitoring and for low-permeability soils where a standpipe cannot keep up. (6.2.1)
6.3Standpipe (Casagrande) piezometers may be used for long-term post-construction monitoring in granular soils.
NOTE A standpipe piezometer is a low-cost open well read with an electric water-level indicator; its response lag of days to weeks disqualifies it for time-critical construction monitoring but suits long-term observation in permeable ground. (6.3.1)
6.4Settlement monuments and liquid-level systems shall measure vertical movement of the ground surface and adjacent structures.
6.5Extensometers shall measure relative vertical or axial movement between subsurface anchor points.
6.6Tiltmeters and crack meters shall measure rotation and crack-width change of adjacent structures within the influence zone.
6.7Strain gauges, load cells, and total pressure cells shall measure force and pressure in support-of-excavation members and anchors.
NOTE Strain gauges on struts and sheetpiles, load cells on tiebacks, and pressure cells behind walls confirm that the support system is carrying the loads the designer assumed. (6.7.1)
7 Inclinometers
7.1Inclinometer casing shall be installed to a depth that extends below the anticipated zone of movement into stable ground that serves as the fixed reference.
NOTE If the casing toe is not embedded in ground that does not move, the entire profile floats and apparent displacements are referenced to a moving base, corrupting the reading. (7.1.1)
7.2Inclinometer readings shall be taken in all four orientations (A+, A-, B+, B-) at each survey.
NOTE Four-orientation (two-pass, both grooves) readings cancel sensor bias and detect casing rotation; a single-axis or single-pass reading cannot distinguish real oblique movement from instrument error. (7.2.1)
7.3A minimum of three baseline readings shall be established before excavation begins, taken on three separate days or over a minimum of 72 hours.
NOTE Without a stable pre-construction zero, every subsequent reading is uninterpretable because there is no reference against which to measure change. Repeating the baseline confirms the casing and probe are stable before work disturbs the ground. (7.3.1)
7.4Casing shall be grouted in with a cement-bentonite mix proportioned to approximate the stiffness of the surrounding soil.
NOTE Neat cement is too stiff and shrinks: it constrains the soil so the casing understates true movement, and the shrinkage cracks let it move independently. A cement-bentonite mix matched to soil stiffness lets the casing deflect with the ground. (7.4.1)
● ABS plastic
○ Aluminum alloy
● 70 mm (2.75 in) standard
○ 48 mm (1.9 in) tight boring
● Portable servo-accelerometer probe (periodic manual)
○ In-place inclinometer string (continuous telemetry)
● Grouted-in (cement-bentonite)
○ Backfilled (sand/native)
8 Piezometers
8.1Piezometer tip elevation and the soil layer monitored shall be set by the GIP to address the specific pore-pressure concern.
8.2Vibrating-wire piezometers shall be used where pore-pressure response must be tracked in time with active construction or in low-permeability soils.
NOTE In silts and clays a standpipe lags reality by days to weeks, so by the time the well registers a pressure rise the excavation stage that caused it is long past. A vibrating-wire sensor responds immediately. (8.2.1)
8.3Each piezometer shall be isolated within its monitored zone by a sand pack at the tip and a bentonite seal above to prevent vertical migration of water along the borehole.
NOTE Without an effective seal the borehole short-circuits the natural stratigraphy, and the instrument reads a blended pressure that belongs to no real layer. (8.3.1)
● Vibrating-wire (fast response, long-term stable)
○ Standpipe / Casagrande (long-term, granular soils)
● 0-350 kPa (0-50 psi) shallow
○ 0-700 kPa (0-100 psi) intermediate
● 50 mm (2 in) PVC
○ 25 mm (1 in) PVC
9 Settlement and Heave Monitoring
9.1Surface settlement monuments shall be installed and read by precise differential leveling referenced to a benchmark outside the zone of influence.
NOTE A settlement monument is only as good as its reference benchmark; if the benchmark itself settles, the apparent movement is wrong in an undetectable way. The benchmark must sit on stable ground well outside the construction influence zone. (9.1.1)
9.2Liquid-level settlement systems may be used where leveling access is obstructed, such as beneath existing structures or active traffic.
9.3Multi-point borehole extensometers shall be used where settlement of specific subsurface layers must be separated from total surface settlement.
9.4Monuments and instrument heads in trafficked or active-work areas shall be protected by a traffic-rated cover; monuments in unpaved areas shall use an above-grade protected pipe.
NOTE Surface-exposed instrument heads are routinely destroyed by construction equipment, which is the leading cause of data gaps. Traffic-rated flush covers in paved areas and protected above-grade pipes elsewhere keep the instrument alive through the work. (9.4.1)
● Surface monuments (precise leveling)
○ Liquid-level settlement system
○ Multi-point borehole extensometer (MPBX)
● Traffic-rated flush monument (paved areas)
○ Above-grade protected pipe monument (unpaved areas)
Per drawings
10 Load, Strain, and Pressure Instruments
10.1Vibrating-wire strain gauges shall be installed on support-of-excavation members where member force must be verified against design assumptions.
10.2Center-hole load cells shall be installed on tieback and anchor tendons where anchor load must be monitored over time.
NOTE Anchor load cells confirm that a tieback is holding its lock-off load and reveal load loss from creep or relaxation before it becomes a stability problem. (10.2.1)
10.3Total pressure cells may be installed behind walls or beneath embankments where earth pressure must be measured directly.
10.4Each force or pressure instrument shall be installed with a baseline reading taken before the member is loaded.
○ Vibrating-wire sister bar (embedded)
● Vibrating-wire surface-mount (steel members)
● Vibrating-wire center-hole
○ Hydraulic center-hole
● Vibrating-wire
○ Potentiometer
11 Automated Data Acquisition
11.1Where the GIP requires continuous monitoring, an automated data acquisition system (ADAS) shall be provided with multichannel dataloggers, telemetry, and automatic alarm notification.
NOTE Automated acquisition with telemetry turns a periodic snapshot into a continuous record and delivers an alarm within minutes of a threshold exceedance, which is decisive on urban excavations adjacent to sensitive structures. (11.1.1)
11.2The ADAS shall be provided with a power source and telemetry path sized to remain online through the full monitoring period, including a backup power provision.
NOTE Automated systems fail most often not in the sensor but in the support utilities: a depleted battery or a dropped cellular link takes the system offline precisely when active construction makes the data most valuable. (11.2.1)
11.3The ADAS shall deliver alarm notification by SMS and email to the designated recipients within the time stated in the GIP after a threshold is exceeded.
11.4Instrument data shall be exportable in a non-proprietary format and the Owner shall have read access to the live data and dashboard.
NOTE Proprietary-only data delivery locks the Owner out of monitoring records they paid for and need for the life of the structure. A CSV or open-API export keeps the data portable and auditable. (11.4.1)
11.5Monitoring data shall be retained in accessible form for a minimum period after project completion as stated in the datasheet.
○ Automated (ADAS, continuous telemetry)
● Manual periodic readings
☐ CSV / non-proprietary file
☐ Owner-accessible web dashboard
☐ Open API
12 Monitoring Frequency and Thresholds
12.1Construction-phase monitoring frequency shall increase with proximity to active excavation per the GIP schedule.
NOTE Movement is fastest and least predictable next to the active excavation face, so reading frequency must rise as work approaches an instrument and relax as it moves away. Tying frequency to excavation stage rather than the calendar keeps effort where the risk is. (12.1.1)
12.2Instruments within one wall-panel or pile spacing of active excavation shall be read daily.
12.3Instruments within two wall-panel or pile spacings of active excavation shall be read two to three times per week.
12.4Instruments beyond two wall-panel or pile spacings of active excavation shall be read weekly.
12.5Post-construction monitoring shall continue at the reduced frequency in the GIP until readings demonstrate that movement has stabilized.
12.6Alert, Action, and Trigger thresholds shall be applied as a three-tier system, with a defined response at each tier.
NOTE A three-tier scheme (Alert, Action, Trigger) escalates the response as movement grows: Alert raises attention and verification, Action initiates predetermined mitigation, and Trigger stops work and convenes the GEOR. The numbers below are illustrative starting points the GEOR must confirm per project. (12.6.1)
12.7If an instrument malfunctions during a critical excavation stage, the Contractor shall repair or replace it within the response time in the GIP and shall provide redundant coverage where the GIP requires it.
NOTE A blind spot at a critical stage is as dangerous as a threshold exceedance; the specification must require a defined repair time and redundancy at the highest-risk locations so monitoring is never silently lost. (12.7.1)
● Tied to excavation stage and proximity (GIP table)
○ Fixed calendar interval
13 Installation
13.1Instrument boreholes shall be drilled by a method compatible with the ground and the instrument, maintaining hole stability for casing or tip placement.
13.2Borehole locations shall be cleared of subsurface utilities and confirmed against the support-of-excavation layout before drilling.
NOTE A casing borehole drilled into an unlocated utility or into the line of a strut, waler, or soldier pile both damages the work and loses the instrument; the cleared, coordinated layout from the pre-installation review prevents both. (13.2.1)
13.3Inclinometer casing shall be installed with one set of grooves oriented parallel to the expected direction of movement.
NOTE Orienting the A-axis grooves toward the expected movement direction puts the primary deflection on the principal axis and keeps the cross-axis correction small, improving the accuracy of the reported profile. (13.3.1)
13.4Each instrument shall be uniquely tagged at the surface with a durable identifier matching the instrument schedule.
13.5Instrument heads, cables, and casing left above grade shall be protected against construction traffic, weather, and vandalism for the full monitoring period.
● Hollow-stem auger
○ Mud rotary
○ Sonic
○ Dual-wall reverse circulation
Per drawings
Per drawings — A-axis toward expected movement direction
14 Decommissioning
14.1At the end of the monitoring period, instruments and their boreholes shall be decommissioned in accordance with the GIP and applicable well-abandonment regulations.
NOTE A piezometer or casing left open after monitoring ends is an uncontrolled vertical conduit between aquifers and a surface hazard; proper abandonment grouting restores the ground to its pre-installation condition. (14.1.1)
14.2Boreholes left in place shall be filled with grout from the bottom up to prevent voids and cross-contamination between layers.
14.3Surface monuments and protective covers shall be removed and the surface restored to match surrounding finishes unless the Owner directs that selected instruments remain for long-term monitoring.
14.4Decommissioning records shall document each instrument abandoned, the method used, and the final surface condition.
● Tremie grout bottom-up (cement-bentonite)
○ Pull casing and grout
● None - decommission all
○ Retain designated piezometers / monuments
Per drawings
15 Warranty
15.1The instrumentation installer shall warrant materials and workmanship of the installed instruments and data acquisition system for the period stated in the datasheet from the date of acceptance.
NOTE Because a failed instrument below grade cannot simply be reopened and repaired, the warranty must cover replacement of an instrument that fails to perform within its specified accuracy during the monitoring period. (15.1.1)
15.2The warranty shall cover replacement of any instrument that drifts outside its specified accuracy or fails to communicate during the monitoring period.
16 Spare Parts
16.1The Contractor shall furnish spare readout, telemetry, and sensor components sufficient to maintain continuous monitoring through the project without interruption for procurement lead time.
NOTE On a continuous-monitoring project the lead time to procure a replacement sensor or datalogger module can exceed the response time the GIP allows, so critical spares must be on hand before monitoring begins. (16.1.1)
16.2A spare portable readout unit shall be available on site whenever manual readings are the primary data collection mode.
☐ Spare vibrating-wire sensors (each type in use)
☐ Spare datalogger / telemetry module
☐ Spare inclinometer probe or readout
☐ Spare portable readout unit
☐ Spare cable and connectors