The weak point of cast-in-place bored piles is that nobody can see what happens underground while the concrete is placed. The shaft may neck in a soft soil layer, soil or slurry may get mixed in, or the cage may drift against the borehole wall so that the cover on one side is too thin. TIP is one method that answers these questions while the concrete is still curing, without waiting for it to gain strength.

What is TIP, and what does it measure in a bored pile?

Thermal Integrity Profiling, or TIP, is an integrity test for cast-in-place concrete piles under ASTM D7949-25. It measures temperature versus depth along the pile, generated by the heat the concrete releases on its own during hydration (Heat of Hydration), so no waves or other energy need to be put into the pile.

The interpretation principle is simple: the amount of concrete at any point is proportional to the temperature measured at that point.

🔥 Basic principle

More concrete = more stored heat = higher temperature · Less concrete or inclusions = less heat = lower temperature

Plotting temperature against depth gives a profile that reflects the shape of the pile. Zones where the temperature drops clearly below the average are suspected necking or inclusions, while zones that are warmer than normal usually mean the concrete has bulged into the soil. A bulge is not a defect, but it means more concrete was actually used than calculated.

The figure below places a pile section next to the temperature profile at the same depths. Note that the temperature drops at the neck, rises at the bulge, and falls naturally at the pile head and toe because heat escapes through the ground surface and the pile toe, so these two end zones should not be read as defects straight away.

Thermal Integrity Profiling (TIP) principle — bored pile shape compared with the temperature profile versus depth The left panel is a section of a bored pile through fill, soft clay, stiff clay, a loose soil layer and dense sand. Temperature sensor cables are fixed to the reinforcement cage along its full length and connected to a data logger at the ground surface. The concrete releases heat as it sets. The pile necks in the soft clay and bulges in the loose soil layer. The right panel is the temperature profile at the same depths: the temperature falls below average at the neck because there is less concrete, and rises above average at the bulge because there is more concrete. At the top and bottom ends the temperature drops naturally because heat is lost through the ground surface and the pile toe. The strip at the bottom summarizes that the test is done while the concrete releases heat, covers the cover concrete outside the cage, and references ASTM D7949-25. TIP principle: reading pile shape from heat Not to scale Fill Soft clay Stiff clay Loose soil Dense sand 42.6 °C Recorder Thermal cable Fixed to cage, full length Neck / inclusion Less concrete → cooler Bulge More concrete → warmer Temp. profile Temp. → ← Depth Average Temp. drop Temp. rise Ends cool naturally (roll-off) 1 Measured during hydration No need to wait for curing 2 Sees cover outside cage incl. off-center cages 3 Reference standards ASTM D7949-25
TIP principle — left: section of a bored pile with a neck and a bulge, and temperature sensor cables fixed to the cage along its full length. Right: the temperature profile at the same depths. Temperatures clearly below average indicate suspected necking or inclusions, temperatures above average indicate a bulge, and the pile head and toe cool naturally (roll-off). (Conceptual diagram: SPN Soil Engineering)

Why can TIP check the concrete outside the reinforcement cage?

TIP can check the concrete outside the cage because heat radiates from the whole cross-section in every direction; it does not travel only along the paths between tubes, as sound waves do. A sensor tied to the cage can therefore tell how thick the concrete is on its outer side.

If one side of the cage sits close to the borehole wall so that the cover is thin, heat on that side dissipates into the soil faster, and the temperature measured on that side is systematically lower than on the other side.

As a result, TIP can assess two things that cross-hole sonic methods cannot: the thickness of the concrete cover over the reinforcement (Concrete Cover) and the eccentricity of the cage. Both directly affect the long-term durability of piles in corrosive environments.

By contrast, Cross Hole Sonic Logging (CSL) sends sound waves between tubes embedded in the cage, so it checks the concrete along the paths between tubes, which is mainly inside the cage. Concrete outside the cage is a blind spot for this method. Read more about CSL at Cross Hole Sonic Logging (CSL)

The 2D drawing below is a side section of the pile with cross-section B–B on the right. Note that when the cage is off-center, the sensors on the thin-cover side read lower than those on the thick-cover side. The 3D view that follows shows thermal cables tied around all sides of the cage and the heat radiating into the soil around the pile.

2D model (side section) of Thermal Integrity Profiling (TIP) with temperature sensor cables tied to the reinforcement cage A bored pile has temperature sensor cables tied to the reinforcement cage, with the cable ends connected to a data logger at the pile head. Heat from hydration radiates from the concrete in every direction. The necked section in the loose sand layer has less concrete, so its temperature is low, while the bulged section in the soft clay layer has more concrete, so its temperature is high. Cross-section B–B on the right shows an off-center cage: the side with thin cover reads a lower temperature than the side with thick cover. Side section (2D) Not to scale Fill / stiff clay Loose sand Soft clay Dense sand °C °C B B Thermal data logger Linked to each cable at pile head Thermal cable Tied to cage, sensors along cable Necking Less concrete → cooler Bulging More concrete → warmer Hydration heat Radiates all ways Pile toe Section B–B Cage offset to the right Thick cover Thin cover Thick-cover sensor → reads high Thin-cover sensor → reads low Systematic difference = offset
2D model (side section) — thermal cables are tied to the cage and record values while the concrete is still releasing heat. The neck gives low temperatures and the bulge gives high temperatures. Section B–B shows that the sensor on the thin-cover side reads lower than the one on the thick-cover side, so TIP can assess cover thickness and cage eccentricity. (Image: SPN Soil Engineering)
3D model of Thermal Integrity Profiling (TIP) showing a soil cut-away and a transparent pile The 3D view cuts away one corner of the soil to show the whole bored pile. Four thermal cables are tied to the reinforcement cage, each with sensors at intervals and connected to a data logger at the pile head. Hydration heat radiates into the soil around the pile. The necked section in the loose sand layer is shown in blue because it is cooler, and the bulged section in the soft clay layer is shown in dark orange because it is warmer. Detail C shows a thermal cable tied to a longitudinal bar. Not to scale Detail C — thermal cable Temp. sensor Equal spacing Tied to main bar Main bar Alternative: tubes cast with the cage and a probe lowered into each tube C 4 thermal cables Tied around cage before pour Heat radiates to soil while concrete hydrates Neck Less concrete → cooler Bulge More concrete → warmer Bored pile Transparent view Thermal data logger Linked to each cable Loose sand Wall caves in Soft clay layer Concrete bulges Rebar cage
3D model — thermal cables are tied to the cage on every side of the section, revealing both the pile shape with depth and the cover thickness all around. Blue marks the cooler neck and dark orange marks the warmer bulge. Detail C shows a cable with sensors at intervals along its length. (Image: SPN Soil Engineering)

What defects can TIP detect?

TIP detects anomalies that change the amount of concrete in the cross-section, in six main categories:

  • Necking — a zone where the concrete is narrower than designed, usually where the borehole wall has caved in or soft soil has squeezed in.
  • Bulging — a zone where the concrete has expanded into a soft soil layer, so the actual concrete volume exceeds the calculated volume.
  • Inclusions in the concrete such as soil, slurry or bentonite trapped during the pour, which reduce both the concrete and the heat at that point.
  • Uneven concrete cover caused by the cage shifting to one side.
  • Average pile radius versus depth, when calibrated against the actual concrete volume placed.
  • Continuity at the pile head and toe — temperatures naturally drop here because heat is lost through the ground surface and the toe (roll-off), so the interpreter must separate this effect from real defects.

Common defects and their causes are explained in Pile defects: causes and detection

How does TIP differ from CSL and the Seismic Integrity Test?

The main differences among the three methods are the signal used and the zone each can check. TIP uses heat and sees the concrete outside the cage. CSL uses sound waves between tubes, so it mainly checks inside the cage. The Seismic Integrity Test uses a wave from tapping the pile head, needs no embedded equipment, and can be used on piles that have already been cast.

← Scroll to see the full table →

IssueTIPCross Hole Sonic Logging (CSL)Seismic / Low Strain Integrity
Reference standardsASTM D7949-25 (Active)ACI PRC-228.2 guidance · ASTM D6760-16 (withdrawn 2025)DPT 1551-51 primary · ASTM D5882-16 (withdrawn 2025)
Signal usedHeat of hydrationSound waves between embedded tubesWave from tapping the pile head with a hand hammer
Equipment cast in before pourYes (cables or probe access tubes)Yes (steel or PVC tubes)Not required
Sees concrete outside the cageYesNoNo detail
Testing windowWhile hydration still releases heat (hours to a few days)Once concrete has hardened enough, typically several days or moreOnce concrete reaches specified strength
Usable on piles cast long agoNoYes, if tubes are embeddedYes
Cost per pileHighModerate to highLowest
📌 Note on standards

ASTM D6760-16 (CSL) and ASTM D5882-16 (Low Strain Integrity) were withdrawn in 2025, so CSL work also references the ACI PRC-228.2 guidance. Low-strain integrity testing in Thailand uses DPT 1551-51 as the primary criterion, while TIP can cite ASTM D7949-25 directly because it remains Active.

The most widely used low-strain integrity test in Thailand is explained at Seismic Integrity Test

What are the limitations of TIP?

TIP has three main limitations: the equipment must be installed before concreting, the data-collection window is limited, and it cannot test piles cast long ago. It is therefore not a replacement for other methods in every case.

  1. Equipment must be installed before concreting. Thermal cables or probe access tubes must be tied to the cage before it is lowered into the borehole; nothing can be added once the concrete is placed. TIP must therefore be part of the quality control plan before piling starts.
  2. Limited time window. The signal is hydration heat, which rises and then gradually falls to the temperature of the surrounding soil. If data are collected too late, no signal remains, so the test team must time the work to when the concrete is still releasing heat.
  3. Cannot test piles cast long ago. Old piles or the existing piles of a building are at the same temperature as the surrounding soil, so there is no signal to measure. In these cases use CSL if tubes are embedded, or a low-strain method per DPT 1551-51.
⚠️ TIP does not give bearing capacity

TIP tests only the integrity of the pile shaft; it does not tell how much load the pile can carry. Capacity requires actual loading, such as a Static Load Test per ASTM D1143/D1143M-20e1 and DPT 1251, or a Dynamic Load Test (PDA) per ASTM D4945 and DPT 1252-51.

When should you choose TIP?

TIP is worthwhile when damage to a single pile has a large impact on the project and the cables can be planned in before piling starts. Cases where the benefit justifies the advance preparation include:

  • Large-diameter or very deep bored piles where a single defective pile has a large impact on the project
  • Piles through thick soft soil, where the borehole wall is at risk of caving and the concrete may neck or bulge away from the design
  • Projects that need to verify the concrete cover over the reinforcement, such as structures in highly corrosive or coastal areas
  • Projects that need fast results, since data can be collected from the day of the pour without waiting for the concrete to gain strength
  • Projects that use it alongside CSL to cover both inside and outside the cage

For typical buildings with normal-size bored piles, the most widely used and cost-effective combination is still integrity testing with the Seismic Integrity Test together with capacity testing by PDA. For an overview of each test method, see Pile testing services

Summary

Thermal Integrity Profiling uses the heat of hydration of concrete as the signal to check the integrity of bored piles under ASTM D7949-25. Its key advantage is that it assesses the concrete across the whole section, including the cover concrete outside the reinforcement cage that CSL cannot reach.

The trade-off is that the cables must be installed before concreting, and data must be collected within the hours to few days when the concrete is still releasing heat. TIP therefore requires advance planning, cannot be used on piles cast long ago, and does not give the bearing capacity of the pile.

⚠️ Scope of this article

This content is general information for understanding only. It is not design advice or a quality control plan for any particular project. The choice of test method, the number of piles to test and the acceptance of results must be made by the project's responsible engineer holding a Council of Engineers Thailand (COE) license, together with the actual construction drawings and project specifications.