Surface/Structural movement points

Survey points set in pavement, soil, or structures and read with precise leveling or a total station. Under pavement, a deep point is used: a small-diameter pipe driven below the pavement section inside a larger grouted casing. The annulus between the two pipes is kept free of grout so the point moves with the soil, not the pavement. Building points typically use a stainless steel bolt in an expansion anchor with an identification tag.

Utility monitoring points

Used where excavation, dewatering, tunneling, or trenching could move a buried utility. A single point rod extensometer is installed in a riser down to the top of the utility and read at a traffic rated monument at the surface. This measures the utility itself rather than the ground above it.

Deformation monitoring prisms

Reflective targets mounted on structures, walls, or tunnel linings with a swivel bracket and an anchor bolt with at least 8 in. of embedment into concrete or rock. They are read by a total station, often a robotic unit running on an automatic schedule. Reference prisms must sit outside the zone of influence of the work so they provide a stable baseline.

Inclinometers

Inclinometers measure lateral movement with depth in slopes, retaining walls, and excavations.

1. A grooved guide casing is grouted into a borehole and founded in stable ground below the expected movement.
2. A probe with a gravity sensing transducer is lowered along the grooves and read at fixed intervals, commonly 2 ft or 0.5 m.
3. At each interval the probe measures tilt
4. Summing from the fixed bottom upward gives the displacement profile.
5. Comparing each survey to the baseline profile shows where and how much the ground is moving.

Settlement plates

A base plate set on the compressible foundation soil with a riser pipe extended up through the fill. The top of the riser is surveyed against an external benchmark. An optional PVC isolation casing keeps the fill from dragging on the riser. Settlement plates are common on embankments, foundations, and landfills to track consolidation.

Extensometers

Extensometers measure the change in distance between anchors at different depths and a reference head at the surface. A multipoint rod extensometer above a tunnel might have anchors at 5 ft, 10 ft, and 15 ft above the extrados. Comparing anchors shows where in the soil column the movement is happening, which surface points alone cannot tell you.

Tiltmeters

Mounted on structures with a bracket to measure rotation, usually on two axes. Small rotations can reveal differential settlement or foundation distress well before cracking appears.

Standpipe piezometers

A slotted well screen surrounded by filter sand, sealed above with at least 2 ft of bentonite and then cement grout to the surface. The water level is measured manually with a dip meter. They are simple, inexpensive, and easy to verify, but readings are manual and response is slow in low permeability soils such as clay.

Vibrating wire piezometers

Water pressure deflects a diaphragm, which changes the tension in a steel wire and therefore its resonant frequency. The readout converts frequency to pressure using the manufacturer calibration factor with a temperature correction. They respond quickly, work well with data loggers, and are stable over the long term. Several sensors can be placed at different depths in one borehole backfilled with cement bentonite grout.

Load cells

Load cells are hollow cylinders placed between the bearing plate and anchor nut of a rock bolt, tieback, or strut. They confirm that loads stay within design limits and show load loss over time.

Pressure cells

Pressure cells are two thin plates welded together with fluid between them. Earth pressure on the plates is read by a transducer. In shotcrete or concrete linings, a pinch tube is used after curing to restore contact between the cell and the concrete.

Strain gauges

Strain gauges measure strain in beams, columns, struts, and tunnel linings. Foil resistance gauges work well on steel. For concrete and long term monitoring, vibrating wire strain gauges are more common. Stress is estimated from strain using the material modulus.