How Do You Assess Whether a Project Needs Instrumentation?
Deciding whether a project needs instrumentation means assessing risk from several factors at once, not comparing a single depth or number of stories. Project owners often ask "Do we need to install monitoring instruments?" and expect a numerical answer, such as how many meters deep the excavation is or how many stories the building has. In engineering, there is no single threshold like that. A shallow excavation in soft clay right next to an old building can be riskier than a deeper excavation in dense soil on an open site.
In practice, engineers work through these six questions before deciding whether a project needs a monitoring plan.
- What is outside the site boundary that could be damaged? Adjacent buildings, fences, public roads, water mains, gas pipes, underground power cables or utility structures. The closer and the more sensitive they are to differential settlement, the greater the need.
- Does the work disturb the equilibrium of the soil or groundwater? Excavation, groundwater lowering, added fill surcharge and pile driving all change the stress state in the surrounding soil. Work that merely places a structure on the ground without disturbing anything has less need.
- Does the next stage have to wait for real data? Work designed to be confirmed by monitoring results before proceeding, such as removing a preload surcharge, excavating the next level or removing struts, requires data, because counting days against the schedule is not proof that the soil is ready.
- How uncertain are the soil conditions? If the soil investigation results show soil layers that vary greatly between boreholes, or a soft layer thicker than expected, the design parameters carry a wide range of uncertainty. Monitoring is how that gap is closed during construction.
- If damage occurs, can you prove what caused it? On sites with close neighbors, pre-construction data is the only thing that can show whether a crack is new or already existed.
- Has someone already specified it? The designer's drawings and specifications, EIA mitigation measures, conditions from the authority that owns the area, or contract conditions may already define the instrument types and reading frequency. In that case no reassessment is needed, but the requirements must be followed in full.
If the answer is "yes" to two or more questions, discuss a monitoring plan with the design engineer during the design stage rather than waiting until work starts, because many instruments cannot be installed retroactively. For an overview of each instrument type, see the geotechnical instrumentation guide
Which Projects Should Have It, and What Should Be Measured?
Projects in Thailand that should have a monitoring plan fall into seven work groups, each with its own questions and instrument set. The principle is to start from "the question that needs an answer" and then choose the instruments that can answer it, not to start from a list of instruments and pick according to budget. The table below summarizes the common work groups and the instrument sets typically used.
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| Type of work | Question to be answered | Typical instrument set |
|---|---|---|
| Urban deep excavations | How far the retaining wall moves, how much the ground around the pit settles, how much load the struts carry | Inclinometer · Surface Settlement Marker · Piezometer · Tiltmeter · Strain Gauge on struts |
| Earth fill, embankments and preloading on soft ground | How much the soil has settled, how much longer it will keep settling, whether the surcharge can be removed yet | Settlement Plate · Multi-level Settlement Point · Piezometer |
| Slopes and hillside cuts | At what depth the slope is moving, whether the water level in the slope is rising | Inclinometer · Standpipe / Vibrating Wire Piezometer · Surface Settlement Marker |
| Construction next to existing buildings | How much additional settlement or tilt the adjacent building shows, in numbers | Settlement Point · Tiltmeter (combined with a pre-construction building condition survey) |
| Construction dewatering | How far the groundwater drawdown extends around the site, and who is affected | Observation Well · Piezometer · Surface Settlement Marker |
| Pile tests that require load distribution | How much load transfers to each soil layer, how much end bearing the pile toe carries | Strain gauges embedded in the pile, combined with a static load test |
| Embankments, reservoirs and large earthworks | What the water level within the embankment is, whether the slope moves over the service life | Piezometer · Observation Well · Inclinometer · Settlement Marker |
The most common group in Bangkok and its vicinity is deep excavation, because Bangkok soft clay lets the soil around an excavation move significantly even while the retaining system is still far from failure. Details of what to measure and how often to read are in deep excavation monitoring in Bangkok soft clay. For earth fill and preloading, see how to interpret results in Settlement plates: monitoring fill settlement
Pile driving near existing buildings is another case that needs monitoring, but it uses a different instrument group from the table above, because the issue is vibration rather than soil movement. Details are in vibration monitoring for pile driving and pre-construction condition surveys of adjacent buildings
The 3D view below places five work groups from the table in the same area to show how each one disturbs the ground differently and which instrument set it uses. The deep excavation ① sits next to the existing building ④, so both the retaining wall side and the building side must be measured. For the building side, read Settlement points and tiltmeters for monitoring settlement and tilt of adjacent buildings. For slopes ③, see the principles in Preventing landslides and slope failure. The right-hand panel lists the six questions from the previous section. The actual instrument types and quantities for a project are as specified by the design engineer.
Does Thai Law Require Instrumentation?
No single central law states that every type of project must install any particular instrument. The most directly relevant law is the Soil Excavation and Filling Act B.E. 2543 (2000). Section 17 requires anyone intending to excavate deeper than 3 meters below ground level, or with a pit opening area larger than 10,000 square meters, or with a depth or area as announced by the local official, to notify the local official with a site plan, a plan showing the land boundary and adjacent land, the excavation method and the soil haulage method. The essence of the law is notification and having measures to prevent damage to adjacent land; it does not specify which instruments must be used.
In practice, instrumentation requirements therefore come from these four sources instead.
- The design engineer's drawings and specifications are the most common source, setting out instrument types, locations, number of points, reading frequency, trigger levels and report format in the project monitoring specification.
- Mitigation measures in the Environmental Impact Assessment (EIA) report for projects that are required to prepare one. Construction-phase measures usually require monitoring of impacts on adjacent areas and periodic reporting.
- Conditions from the authority that owns the area or from adjacent utility owners, for example when the work is within a distance that could affect another agency's structures, that agency usually sets monitoring conditions in its permit.
- Contract conditions and contractor's all-risk insurance policies, which may require pre-construction and during-construction data to be kept as evidence.
Wherever the requirement comes from, work related to structural and soil safety is a controlled engineering profession. The person who certifies the results must be an engineer holding a professional engineering license (COE) from the Council of Engineers Thailand. Read more about the scope of work that requires an engineer in Engineering licenses and the Building Control Act and Summary of the Ministerial Regulation on foundations
At What Stage of the Project Should Installation Start?
Instruments must be installed and baseline readings completed before ground-disturbing work begins. The most meaningful value in monitoring is not today's reading but the change from the baseline taken while everything was still in its original condition. Without a baseline, the readings have nothing to be compared with, and it is impossible to tell whether what you see is caused by construction or existed beforehand.
Some instruments cannot be installed retroactively at all. A settlement plate must be placed on the original ground before the first fill layer; once the fill is placed, the chance is gone. An inclinometer installed after excavation has started will miss the early movement, which in excavations is usually the largest part. Likewise, an observation well or piezometer must have water level readings before pumping or excavation begins, so that you can tell how far the groundwater has dropped from its original condition.
An often overlooked point is that the baseline must be read more than once. Taking a single reading as the baseline makes it impossible to separate real change from the measurement error itself, whether from instrument setup, temperature or different people taking readings. Repeating readings several times while there is still no disturbing work is how you find the range of "natural stability" of that particular measuring system.
What Happens If No Instruments Are Installed?
A project without instrumentation loses three things: early warning, evidence to prove causes, and data for decisions. These effects do not show up immediately, which is why many projects cut this item to save money.
First, there is no early warning. Movement of soil and structures happens continuously before it can be seen by eye. By the time cracks appear on an adjacent building's walls or the road starts to sink, the accumulated movement has already reached a level the materials cannot withstand. The only options left are to stop work and repair, which costs more than adjusting the construction sequence when the numbers first started to move.
Second, you cannot prove who caused it. This cuts both ways. A project owner without pre-construction data will find it hard to refute claims about cracks that already existed, while a neighbor who has genuinely suffered damage also lacks numerical evidence. Having baseline and during-construction data therefore benefits both sides. For guidance on handling cracks, see crack assessment and monitoring. The outcome of any dispute depends on the facts and process of each case; monitoring data is only supporting evidence.
Third, decisions have to be made by guessing. Without real data, those responsible face two equally bad options: adding excessive safety margins so that work is slower and construction costs higher than necessary, or pressing ahead with the plan without knowing whether the design assumptions match reality. In work designed using the observational method, having no data makes that approach unusable from the start.
How Detailed Does Monitoring Need to Be?
The right amount of monitoring is to measure only what will change a decision. Over-monitoring is also a problem. A project that installs many instruments and reads them frequently without anyone analyzing the data ends up with a pile of data no one reads, wasting both money and site time. If a reading leads to no action regardless of the value, that monitoring point is unnecessary.
Conversely, once you have decided to monitor, what you always need is a person responsible for reviewing the results with the authority to act when values approach the limits. A monitoring system without clear responsibility becomes paperwork, not a safety tool. Trigger levels and each level of response must be set by the design engineer according to that project's conditions; there is no universal number that applies to every job. How trigger levels work is explained in the deep excavation monitoring article
Another point to decide at the outset is the reading method. Most jobs use manual readings at set intervals, which are flexible and low-cost, while jobs that need immediate results or have difficult access use automatic recording systems connected to a data logger. This choice affects both cost and cabling from the time of installation, so it should be decided together with the monitoring point layout, not later. Compare the two approaches in Manual vs automatic monitoring: what is the difference?
How Can SPN Help, Which Standards Apply, and How Much Does It Cost?
SPN provides end-to-end performance monitoring services, from planning the monitoring program with the design engineer to define instrument types and point locations, through drilling and instrument installation, baseline readings before work starts, periodic readings during construction, and processing into graphs and reports compared with the specified criteria, to alerts when readings approach the limits. See the list of instruments we offer on the instrumentation and performance monitoring page.
The reference standards depend on the instrument type. Movement monitoring with inclinometers follows ASTM D6230, while pre-installation acceptance testing of vibrating wire piezometer sensors uses ASTM D7764. For instruments that measure settlement by leveling, accuracy comes from high-precision leveling practice tied to benchmarks outside the zone of influence of the works, together with the project-specific monitoring specification. Every report is certified by a civil engineer licensed by the Council of Engineers Thailand (COE), with signature and registration number, and can be used for submission to the relevant authorities.
Fees are assessed from the type and number of installation points, the drilling depth for instruments embedded in the ground, the monitoring duration, the number of reading rounds, and whether readings are manual or automatic, so pricing is project by project. Contact us for a free quotation within 24 hours. Prices exclude travel and equipment mobilization costs, which are charged extra according to the distance to the site. Our team has worked in geotechnical engineering for more than 20 years, covering projects nationwide.
This content explains the principles for assessing the need for performance monitoring for general understanding. Decisions on which instruments a particular project must install, how many points, what reading frequency and which trigger levels are appropriate must be made by the design engineer and the engineer in charge according to that project's specific conditions.