What is a settlement plate and how does it work?

A settlement plate is an instrument that measures settlement of the original ground beneath a fill. It consists of a square base plate with a riser pipe fixed perpendicular at its center. The crew places the base plate on the leveled original ground surface before the first fill layer is placed. As fill is placed on top, its weight compresses the underlying soft soil, which settles, and the base plate resting on the original ground settles with it, while the top of the riser pipe always stays above the fill surface.

Surveyors carry out leveling at the pipe top in rounds, tied to a benchmark (BM) outside the fill area. The cumulative settlement at that point equals the baseline reading taken before filling minus the current pipe-top level. This data answers the two key questions of any fill on soft ground: how much the ground has settled so far, and how fast it is still settling.

Settlement plates have three advantages: low cost per point, durability, and readings taken with the level instrument already on site. The result is the settlement of all layers combined beneath the base plate, which is the value the design engineer compares with the calculations. The limitation is that it cannot tell which layer the settlement comes from; separating it by layer requires Multi-level Settlement Points as well. For an overview of all geotechnical monitoring instruments, see the geotechnical instrumentation guide.

What projects use settlement plates?

Settlement plates are used wherever load is placed on soft soil and the amount of settlement must be known. Four common groups of work are:

  • Road embankments and roads on soft ground If the pavement is laid before settlement stabilizes, it sags into depressions and needs repeated repairs.
  • Site filling and leveling for factories and warehouses Concrete floors on soft ground are sensitive to differential settlement.
  • Stockyards and large storage tanks The load is spread over the entire area.
  • Fills behind retaining walls and bridge approaches Differential settlement between the embankment and the structure creates a bump at the joint and is a cause of negative skin friction on abutment piles. Read more about this mechanism in negative skin friction in Bangkok soft clay.

Settlement plates are indispensable for settlement acceleration using preloading with PVDs. The decision to remove the surcharge must be confirmed by actual field settlement data, not by counting days on the schedule. The principle of this method is explained in how PVDs and preloading improve soft soil. If the problem is fill that settles after construction, see the remedies in how to fix settling fill.

What makes up a settlement plate and how is it installed?

A standard settlement plate set has three parts: the base plate, the riser pipe and the sleeve. The base plate is about 50-100 cm per side and must be stiff enough not to bend when the roller compacts the first fill layer. The riser pipe is a steel or PVC pipe welded or fixed perpendicular at the center of the plate. The sleeve (casing) fits over the riser pipe as an outer layer without being attached to it. SPN's detail drawing below uses a 500 × 500 mm steel base plate, 100 mm total height, with a Ø 50 mm steel riser pipe.

Settlement plate detail drawing in elevation and plan: 500x500 mm steel base plate, 100 mm high with stiffener ribs, Ø 50 mm steel riser pipe extendable 1 m at a time, and a 6 mm steel pin at the pipe top for seating the leveling staff
Settlement plate detail — 500x500 mm steel base plate stiffened with 5 mm steel ribs, Ø 50 mm steel riser pipe extendable 1 m at a time as the fill rises, and a 6 mm steel pin at the pipe top that seats the leveling staff in the same position every round (drawing: SPN Soil Engineering)

Besides SPN's design above, many project drawings use another configuration: a 0.50 × 0.50 m base plate of waterproof plywood at least 20 mm thick or steel plate at least 6 mm thick, with a 150 × 150 × 6 mm steel plate fixed at the center and 6 mm stiffener ribs welded to the measuring rod. The rod is a Ø 25 mm steel bar or Ø 38 mm steel pipe, extended with couplings or welding. Both types work on the same principle; the actual sizes and materials must follow that project's drawings and specifications. The enlarged detail below compares SPN's Type A with this Type B.

Enlarged details of two settlement plate types: a ribbed steel base plate with a Ø 50 mm steel pipe, and a plywood or steel base plate with a 150 mm steel plate holding a steel bar or pipe The left drawing is Type A: a 500 by 500 mm steel base plate, 100 mm total height, stiffened with 5 mm steel ribs on four sides along the axes, 50 mm high at the plate edge and 100 mm at the pipe; a 50 mm steel riser pipe extendable 1 m at a time; and a 6 mm steel pin, 50 mm long, at the pipe top for seating the leveling staff. The right drawing is Type B: a 0.50 by 0.50 m base plate of waterproof plywood at least 20 mm thick or steel plate at least 6 mm thick, with a 150 by 150 mm, 6 mm thick steel plate at the center bolted or welded to the base plate; 6 mm steel ribs welded all around between the rod and the steel plate; the rod is a 25 mm steel bar or 38 mm steel pipe, extended with couplings or welding. Below each type is a dimensioned plan. The bottom strip notes that actual sizes follow the project drawings, the pipe top must be surveyed before and after every extension, and a sleeve must always be fitted so the fill does not drag the riser pipe. Two Settlement Plate types (Detail) Not to scale A Ribbed steel plate + Ø 50 mm pipe SPN detail design Original ground (leveled) 50 100 Steel pin Ø 6 mm, 50 long Same staff seat each round Steel pipe Ø 50 mm Riser pipe Extend 1 m at a time as fill height rises Steel plate 500×500 mm Total height 100 · rib t = 5 mm Plan 500 500 4 ribs along the axes Rigid, will not bend during 1st-layer compaction Units: mm B Base plate + 150 mm plate + ribs Common alternative in project drawings Original ground (leveled) Steel bar Ø 25 mm or steel pipe Ø 38 mm Coupling or welded joint Extended as fill rises 6 mm steel ribs All-round weld (orange dots) Steel plate 150×150×6 mm Bolted/welded to base plate Base plate 0.50×0.50 m Plan 175 150 175 500 Base plate material Waterproof ply ≥ 20 mm or steel plate ≥ 6 mm 4 diagonal ribs Units: mm 1 Actual size per project dwg Both types: same principle 2 Extend pipe in sections Survey top before & after each 3 Always fit a sleeve Stops fill dragging the riser
Enlarged details of two settlement plate types — Type A: 500 × 500 mm steel base plate with 5 mm ribs and a Ø 50 mm steel pipe (SPN design); Type B: 0.50 × 0.50 m base plate with a 150 × 150 × 6 mm steel plate, 6 mm ribs and a Ø 25 mm steel bar or Ø 38 mm pipe. Actual sizes must follow the project drawings
Settlement plate set with a square pyramid-ribbed steel base plate and perpendicular riser pipe, with steel extension pipes lying beside it at a fill site, an excavator and excavated pit in the background
Settlement plate set with a pyramid-ribbed steel base plate and riser pipe, plus extension pipes, ready for installation at a fill site (photo: SPN Soil Engineering)

The sleeve is the part that keeps the fill from rubbing against or dragging the riser pipe directly. Without a sleeve, settling fill pulls the riser down through skin friction along the pipe, so readings come out larger than the real value. As the fill rises, both the riser pipe and the sleeve must be extended section by section. Each time the pipe is extended, the pipe-top level must be surveyed both before and after, so the readings stay continuous with no step in the curve. The section below shows the position of each part under the embankment and the distance S that the pipe top has dropped from the baseline.

Section of a settlement plate installed under a fill embankment, with pipe-top leveling against the baseline Cross-section of a fill embankment on soft clay overlying stiff soil. The steel base plate is placed on the original ground before filling. After filling, the original ground under the embankment settles into a dish, and the base plate drops from its original level, shown as a dashed line, by a distance S. The riser pipe with its sleeve protrudes above the fill surface. A level instrument reads a staff placed on the pin at the pipe top. The current pipe-top level is lower than the baseline, the first pipe-top level, by the same S, tied to a benchmark outside the fill area. The bottom strip summarizes 3 steps. Settlement Plate installed under a fill embankment Not to scale S S Baseline = first pipe-top level Current pipe-top level Staff Level Tie to BM every round Riser + sleeve Sleeve stops fill drag Fill Orig. ground before fill Original ground dishes down Steel base plate — settles with soft soil Soft clay Stiff soil (no settlement) Benchmark (BM) Outside fill area 1 Place plate before filling Read baseline several times 2 Extend pipe as fill rises Survey top before–after 3 S = baseline − current Tie to BM every round
The base plate settles with the soft clay while the pipe top stays above the fill for leveling. The distance the pipe top has dropped from the baseline (S) equals the cumulative settlement of the base plate, tied every round to a benchmark outside the fill area.

Settlement plate installation follows five steps in order:

  1. Level the original ground surface, then seat the base plate firmly so it does not rock.
  2. Assemble the riser pipe and sleeve plumb.
  3. Place the first fill layer around the base plate by hand or with light equipment to keep the plate from tilting.
  4. Take several baseline readings before placing the next layer.
  5. Fence or put bollards around the pipe top for the whole duration of the work.

The most common cause of lost data is not instrument failure but rollers or trucks clipping the pipe top and knocking it over. When the pipe top is knocked over, the baseline for that whole point must be restarted.

How many points are needed, and how often are they read?

The number and location of monitoring points are set by the design engineer; there is no fixed number. Three factors govern it: the size of the fill area, the fill thickness, and the variability of the soft soil layers from the soil investigation results. The layout must cover both the critical points, usually the embankment centerline where the soft soil is thickest or the fill is highest, and reference points where the soft soil is thinner, to show how much settlement varies along the work. Long road embankments usually use monitoring sections at intervals along the route rather than randomly scattered points.

The model below shows the section layout commonly used for road embankments. Each section has a point at the embankment centerline, which settles the most, and a point at the shoulder, and every round of readings is tied to the same benchmark outside the fill area.

3D model of settlement plates placed in monitoring sections along a road embankment 3D view of a fill embankment on soft clay overlying stiff soil. The front cut face shows a monitoring section with two settlement plates: one at the embankment centerline, where the fill is highest and settlement greatest, and one at the shoulder for comparing differential settlement. Each point has a steel base plate on the original ground and a sleeved riser pipe protruding above the fill. The red dashed outline marks the base plate position before settlement; the green dashed line is the original ground level before filling. The original ground under the embankment settles into a dish. Further along the embankment is the next monitoring section with pipe tops in the same positions, and a benchmark outside the fill area is used to tie levels every round. 3D model — monitoring sections along the embankment Not to scale Next monitoring section Spaced along the embankment Benchmark (BM) Outside fill · tie every round Fill Soft clay — dishes under embankment Stiff soil (no settlement) Shoulder point Compare differential Critical: embankment center Highest fill, most settlement Orig. ground before fill Plate before settling
3D model — settlement plates placed in monitoring sections at intervals along a road embankment. Each section has a centerline point, the critical point that settles most, and a shoulder point for comparing differential settlement. Every round of readings is tied to a benchmark outside the fill area.

Reading frequency follows the settlement rate and is not constant throughout the project. Readings are most frequent during filling and just after the final layer is placed, because stress rises quickly and the ground settles fastest. As the settlement rate begins to drop, the frequency is reduced to weekly or monthly until the criteria in the project specification are met. The actual reading schedule is stated in the project's monitoring specification, so there is no single value that applies to every project.

Projects with thick soft soil or preloading should install a piezometer to measure excess pore water pressure alongside, because settlement and the dissipation of excess pore pressure are two sides of the same consolidation process. When both curves point the same way, the engineer can decide with more confidence. Some projects also add an observation well to track the groundwater level.

How do you read a time–settlement curve?

A time–settlement curve has time on the horizontal axis and cumulative settlement on the vertical axis, with fill height plotted above on the same time axis, so the reader sees the relationship between the load applied and the ground's response. A normal curve has three stages: rapid settlement during filling, a gradually decreasing settlement rate once filling stops, and then a curve that flattens toward a constant value. The chart below is an illustrative example, not measured data.

Chart of fill height and cumulative settlement versus time from a settlement plate, with how to read it Illustrative chart. The horizontal axis is time from the start of filling, 0 to 300 days. The upper plot is fill height rising in steps of 1, 2, 3 and 4 m on days 0, 34, 67 and 103. The lower plot is cumulative settlement from each round of readings. Settlement is rapid during filling. The final layer is completed at about day 103, with settlement of about 250 mm and still continuing. After filling stops the settlement rate decreases and the curve flattens toward the final settlement S infinity of about 540 mm, estimated by the Asaoka or Hyperbolic method. Around day 215 the settlement rate is below the criterion and steady for several consecutive rounds. The right panel summarizes three things read from the chart: settlement rate, final settlement and degree of settlement achieved. The bottom strip summarizes three abnormal patterns. Time–Settlement Curve Conceptual graph · Not measured data 0 2 4 0 50 100 150 200 250 300 0 200 400 600 Time from start of filling (days) Fill (m) → ← Cumulative settlement S (mm) Design fill height reached Filling · fast settlement After filling · rate decreasing S∞ = final settlement (estimated from trend) Δt ΔS Final layer placed Still settling — read often ΔS/Δt = settlement rate Slope of the curve Rate < criterion Stable over rounds What the engineer reads 1 Settlement rate Slope below criterion over several rounds 2 Final settlement S∞ Asaoka Method or Hyperbolic Method 3 Degree of settlement U = S ÷ S∞ Basis to remove preload Actual criteria per project spec ! Faster after filling stops Check embankment stability ! Erratic up-down readings Pipe top hit / different BM ! Step jump on extension day Incomplete tie at extension
Normal curve shape — rapid settlement during filling, then a settlement rate that decreases toward a constant value after filling stops. The right panel summarizes what the engineer reads from the chart, and the bottom strip shows abnormal data patterns that must be checked.

Engineers read three things from the curve:

  1. Settlement rate per unit time (ΔS/Δt) is the slope of the curve. When the slope falls below the criterion in the project specification and stays steady over several consecutive readings, the ground is considered to have entered the slow-settlement stage.
  2. Final settlement (S∞) is estimated from the data trend by analytical methods such as the Asaoka method, which plots each current settlement reading against the previous one at equal time intervals and finds the intersection with the 45-degree line, or the Hyperbolic method, which linearizes the data to estimate the end value.
  3. Degree of settlement achieved (U = S ÷ S∞) is the figure used to decide whether the preload can be removed or pavement work can begin.

The curve also reveals three abnormal patterns that need prompt checking:

  • A settlement rate that increases even though filling has stopped usually means an embankment stability problem, not normal consolidation.
  • Readings that jump up and down with no trend usually come from the pipe top being hit, a tilted pipe, or a different benchmark from the previous round.
  • Readings that jump in a step on the day the pipe was extended indicate that the tie-in at extension was not done completely.

How does a settlement plate differ from a settlement marker and a deep settlement point?

All three measure settlement, but at different locations and to answer different questions. A settlement plate measures the original ground beneath a fill; a surface settlement marker measures a visible ground or road surface; and a deep settlement point measures settlement separately by depth. They are therefore often used together on the same project. For a real job using deep settlement points to measure settlement layer by layer, see the Deep Settlement Point case study, Grandio Bang Na Km 5. For settlement points on adjacent buildings, read Settlement points and tiltmeters for monitoring settlement and tilt of adjacent buildings.

← Scroll to see the full table →

TopicSettlement PlateSurface Settlement MarkerDeep / Multi-level Settlement Point
What it measuresSettlement of the original ground under the fill (all layers below the plate combined)Settlement of a visible ground or road surfaceSoil settlement separated by depth
When installedOnly before the first fill layerAny time, on an existing surfaceInstalled in a borehole, before or after filling
Shows which layer settles?No — total value onlyNoYes — layer by layer
Reading methodLeveling of the pipe top with a level instrumentLeveling of the marker with a level instrumentProbe lowered in a pipe, or data logger
Pipe extended with fill?Yes, every time the fill risesNot requiredDepends on the type
Cost per pointLowLowestHigher, because drilling is required
Best forFills, road embankments, preloadingRoad surfaces, adjacent buildings, deep excavationsWork needing to know which layer settles, or multiple soft layers

Large fill projects therefore often have all three types in one layout: settlement plates as the main instrument under the embankment, surface settlement markers spread around the site boundary to check effects on neighboring areas, and deep settlement points only at critical sections where the settling layer must be identified. Deep excavations use a different set of instruments; compare them in deep excavation monitoring in Bangkok soft clay. If you are planning filling for a whole project, see the overview in planning site filling and grading.

What standards does SPN's service follow, and what does it cost?

The international standard that directly covers this work is ASTM D6598-19 (Standard Guide for Installing and Operating Settlement Points for Monitoring Vertical Deformations), a guide to assembling, installing, operating and reading settlement points under fill or embankment loads. In Thailand there is no DPT standard that specifically sets out the method for this work, so the accuracy of the work depends on two further parts together:

  • Leveling follows precise leveling practice, tied to a benchmark located outside the influence of the fill.
  • Project-specific monitoring specification sets the monitoring point locations, reading schedule, settlement-rate criteria and report format.

Projects that install other instruments as well involve additional standards, such as ASTM D7764 for pre-installation acceptance testing of vibrating wire piezometers and ASTM D6230 for movement monitoring with inclinometers.

SPN provides a complete settlement plate service: planning the monitoring layout with the design engineer, supplying and installing the instrument sets, reading the baseline, extending pipes as the fill rises, taking scheduled readings, processing them into time–settlement curves with fill height, and analyzing the trend of final settlement. Reports are signed and certified by a licensed civil engineer (COE license) with signature and registration number, and can be submitted to the relevant authorities. See the full scope of services on the geotechnical instrumentation and monitoring page. If soft soil improvement is needed as well, see ground improvement methods.

Fees depend on the number of points, the fill thickness (which sets how many pipe extensions are needed), the monitoring period and the number of reading rounds, so they are assessed per project. Contact us for a free quotation within 24 hours. Prices exclude travel and equipment mobilization, which are charged according to the site distance.

⚠️ This article provides general information

This content explains the principles of settlement monitoring with settlement plates for general understanding. The number and location of monitoring points, the reading schedule, the acceptable settlement-rate criteria, and the decision to remove the surcharge or start pavement work must be set by the design engineer and the responsible engineer based on the specific conditions of each project.