ERSS Instrumentation & Monitoring for Deep Excavation Projects

An inclinometer measures below-ground lateral displacement with depth and can reveal where a retaining wall or adjacent soil profile is deforming. A survey prism with total station measures a discrete visible point, usually as an absolute 3D coordinate relative to survey control. Prisms are valuable at the wall head, façade or adjacent structure and can be automated, but require visibility and stable control. They are not a simple substitute: one gives a profile, the other a point or target network.

Typically preferred: use an inclinometer when deformation with depth is the risk question; use prisms when absolute movement of visible points, structures or wall heads needs frequent or remote observation. A hybrid scheme can be appropriate.

A vibrating-wire piezometer measures pore-water pressure at a selected depth and can support frequent automated readings when pressure response is important. A standpipe piezometer or observation well is commonly read as water level or hydraulic head and is simple, robust and often manual. Response time depends on installation, filter, soil permeability and water-column behaviour.

Typically preferred: select the pressure sensor and depth that answer the dewatering or basal-risk question; choose a standpipe where a simpler head trend is sufficient and access allows manual readings. Neither should be selected without checking datum, saturation, response and maintenance.

A load cell measures force at a defined interface, such as a selected anchor or strut location, and is direct for that load path. A strain gauge measures strain in a member; converting strain to force requires calibration, member properties, temperature compensation and interpretation of load sharing. Singapore BCA guidance specifically cautions that strain-gauge readings can be affected by non-uniform stress, temperature, joints, strut installation and pre-loading, and notes independent confirmation by calibrated load cell where applicable.

Typically preferred: use a load cell when the defined support force is the key question; use strain gauges when member strain behaviour is required and installation/calibration can support meaningful interpretation.

Precise levelling and settlement markers measure surface or asset elevation change with a strong point-based survey geometry. Automated survey / ATS measures visible target coordinates and can add frequency and remote access, but depends on line of sight, control and target condition. A deep settlement point or extensometer describes movement at depth or between anchors, helping distinguish shallow surface settlement from deformation in selected soil layers.

Typically preferred: use levelling for accurate arrays across roads or buildings; ATS for visible points needing repeated or automated 3D observation; deep instruments where the depth distribution of settlement matters. These are different measurement geometries.

A tiltmeter measures local angular rotation and can detect differential response even when a single displacement point appears small. A prism measures absolute spatial movement at its target. A building or retaining wall may need both: tilt describes rotation, while prisms describe translation and 3D movement relative to a network.

Typically preferred: use a tiltmeter where rotation is the risk parameter; use prisms where spatial movement and coordinate trends are required. Orientation, temperature, mounting stiffness and survey control affect both interpretations.

A manual crack gauge or tell-tale supports periodic inspection at low cost and is useful for condition records. An automated crack meter provides a time series and potential alerts where access is limited or the crack is in a sensitive asset. Automation adds mounting, wiring, calibration, environmental and data-review requirements.

Typically preferred: manual gauges for low-frequency condition checks; electronic meters when continuous change and timely review justify the additional system complexity.

A geophone or vibration monitor is commonly used for construction vibration and reports ground or structural velocity over a defined frequency range, including PPV where that is the project metric. An accelerometer measures acceleration and is more suited to dynamic structural response or higher-frequency analysis. Frequency range, sampling, coupling, filtering and reporting criteria must match the risk question.

Typically preferred: use a geophone for construction-vibration assessment when velocity-based criteria apply; use an accelerometer for acceleration or dynamic-response questions. Do not treat PPV and acceleration as the same quantity.