When Should You Request a Cross Hole Sonic Logging Test? A Structural Engineer’s Checklist

In the world of structural and geotechnical engineering, the integrity of deep foundations is non-negotiable. When it comes to cast-in-place concrete piles, undetected flaws can compromise an entire structure’s stability and longevity. That’s where cross-hole sonic logging (CSL) comes into play—a powerful non-destructive testing (NDT) method that provides insight into the internal quality of concrete piles. 

But how do you know when to request a cross hole sonic logging test? This guide offers a practical checklist for structural engineers, outlining the scenarios where CSL is not just recommended, but essential. 

What Is a Cross Hole Sonic Logging Test? 

Cross hole sonic logging is a non-destructive testing technique used to evaluate the integrity of drilled shafts or bored piles. It involves installing access tubes—typically PVC or steel—within the rebar cage of the pile before concrete is poured. Once the concrete cures, a transmitter and receiver are lowered into the tubes to send ultrasonic waves across the pile. Variations in wave speed, energy, and arrival time help identify internal defects such as: 

• Voids 

• Honeycombing 

• Cracks 

• Necking 

• Water penetration  

This method complies with global standards, including ASTM D6760, making it a reliable and widely accepted technique for pile integrity testing. 

If you’re looking for industry-leading equipment, the CHUM system by Piletest is one of the most advanced tools available, offering precise results and intuitive data interpretation. 

Why CSL Testing Matters in Pile Construction 

Pile foundations carry massive structural loads. Any flaw in the construction or material quality can lead to long-term structural issues, increased maintenance costs, and in worst cases, catastrophic failures. Cross-hole sonic logging tests help ensure piles meet design specifications and safety standards. 

The use of CSL isn’t just about compliance—it’s a proactive measure to confirm quality, increase accountability, and reduce risk. Moreover, its precision makes it ideal for high-stakes environments where foundational integrity is critical. 

Trusted globally, Piletest has become synonymous with high-performance testing systems like CHUM, helping engineers safeguard complex foundation projects. 

A Structural Engineer’s Checklist: When to Request CSL 

Knowing when to use a cross-hole sonic logging test for piles can make the difference between structural certainty and unknown risk. Below are the key scenarios where CSL is essential. 

1. Large-Scale or Critical Infrastructure Projects 

Projects involving bridges, tunnels, dams, high-rise buildings, and power stations demand the highest levels of reliability. In these cases, failure is not an option. 

CSL is often mandated by regulatory authorities or included in project specifications. Its ability to detect minute anomalies in foundation piles makes it a critical tool in major civil engineering works. 

Structural engineers should always request CSL testing when working on critical infrastructure—even if it’s not explicitly required—because the cost of failure far exceeds the cost of testing. 

2. Complex Soil Conditions or Uncertain Geotechnical Profiles 

When the soil beneath a site is difficult to classify or has unusual load-bearing characteristics—such as expansive clay, soft silt, or unpredictable fill—foundation performance can vary. 

Cross-hole sonic logging offers reassurance that the piles poured under challenging conditions are structurally sound. It acts as a backup to geotechnical assumptions and mitigates risk when subsurface data is incomplete or inconclusive. 

3. Deep or High-Capacity Bored Piles 

Any pile deeper than 20 meters or designed to carry high axial or lateral loads should be tested with CSL. The deeper the pile, the more difficult it is to assess visually or through surface methods. That's why a cross hole sonic logging test for piles becomes essential in such cases. This can also be described as the diameter to length ratio pf the pile as described here. 

Defects that occur at depth—such as inclusions or necking—can’t be detected without a subsurface method like CSL. Engineers should consider CSL not just as a compliance step, but as a critical quality control measure for deep foundations. 

4. Design-Build or Fast-Track Construction Schedules 

In design-build or fast-track projects, construction often progresses while the design is still evolving. This overlap increases the likelihood of missteps or communication gaps. 

By incorporating CSL testing into the schedule, engineers gain real-time assurance that each pile meets the project’s evolving demands. The CHUM system by Piletest is particularly useful in these settings due to its fast deployment and efficient reporting features. 

5. Unexpected Events During Pile Installation 

Not every pour goes according to plan. Issues such as: 

• Collapse of boreholes 

• Slurry loss 

• Cage misalignment 

• Delays in concrete pouring 

can all introduce risks that go undetected without testing. In these instances, requesting a cross hole sonic logging test is essential to assess potential damage and take corrective action before superstructure work begins. 

Think of CSL as your diagnostic tool when red flags arise during installation. 

6. Mandatory Requirements in Specifications or Contracts 

In many projects—especially public infrastructure or government contracts—CSL is listed as a mandatory step in the quality control process. ASTM and ACI guidelines often make direct or indirect references to sonic logging when it comes to assessing pile integrity. 

Structural engineers should always check the specifications. Even when CSL is not explicitly listed, it may be required to meet broader non-destructive testing standards. The Piletest CHUM system fully complies with international testing requirements and offers easy integration into contractual QA/QC workflows. 

7. Post-Construction QA or Legal Disputes 

Sometimes issues arise long after construction is complete. Perhaps there’s unexpected settlement, a nearby excavation, or legal scrutiny of construction practices. 

In such cases, CSL serves as forensic evidence. Engineers can use it to confirm the condition of existing piles and protect themselves against liability. 

Having a record of cross hole sonic logging tests completed during or after construction provides documentation that can make or break a legal defence or warranty claim. 

How to Prepare for a Cross Hole Sonic Logging Test 

Preparation is critical for accurate CSL results. Here’s what engineers need to keep in mind: 

Access Tube Installation 

• Install tubes during cage fabrication 

• Use 4 tubes for circular piles; more for larger diameters (the ASTM recommends every 30 cm) 

• Tubes must be watertight, securely tied to the rebar, and reach the full length of the cage 

Tube Material 

• PVC tubes are widely used for their corrosion resistance and ease of handling 

• Steel tubes are better as they bind better with the concrete, and therefore are more common in use, but must be free of debris and welded smoothly  

Concrete Pouring Best Practices 

• Use vibration to minimize segregation and ensure homogeneity 

• Ensure proper head coverage above the tube tops 

Testing Window 

• Optimal testing is typically done between 4–10 days after concrete pouring 

• This window allows sufficient curing for signal transmission but is early enough to act on results 

If you’re using advanced equipment like the CHUM by Piletest, preparation also includes software setup, calibration, and data management plans. 

Choosing the Right CSL Equipment 

Not all testing equipment is created equal. When selecting CSL gear, engineers should prioritize: 

• Signal precision 

• Ease of use in the field 

• Fast and efficient operation to allow minimal test time on site 

• Clear data visualization 

• Compliance with ASTM D6760 and other global standards 

• Capable of supporting 3D Tomography  

The CHUM system from Piletest checks all these boxes. It’s designed for field engineers, offering rapid setup, robust performance, and accurate detection of even subtle defects. Its intuitive interface allows engineers to quickly interpret results and generate professional reports. 

Common Mistakes to Avoid 

Even with the right equipment, poor preparation or execution can compromise test results. Here are common pitfalls to avoid: 

• Improper tube installation: Misaligned or collapsed tubes can block signal transmission. 

• Dry tubes: CSL requires tubes to be filled with clean water to facilitate sound wave travel. 

• Testing too early: Testing before curing can yield false negatives, as concrete did not fully hardened and behaves more like water. 

• Ignoring anomalies: Engineers sometimes overlook minor signal disruptions. All anomalies should be investigated further. 

By avoiding these mistakes, you increase the reliability of your cross-hole sonic logging tests and build a solid foundation—literally and figuratively—for your project. 

Summary: Know When to Test and Why It Matters 

Cross hole sonic logging is one of the most effective methods for validating the structural integrity of drilled shafts and bored piles. For structural engineers, knowing when to request CSL is a matter of both professional responsibility and project success. 

Here’s a recap of when to use CSL: 

• Critical infrastructure and high-risk projects 

• Uncertain geotechnical conditions 

• Deep or load-intensive piles 

• Fast-track construction 

• Installation anomalies 

• Contractual mandates 

• Post-construction QA and legal defence. 

Tools like the CHUM system from Piletest are trusted worldwide for accurate, efficient CSL testing. As a structural engineer, integrating CSL into your QA/QC processes ensures better outcomes, higher client trust, and greater long-term stability for the structures you design. 

For more about the latest in pile testing technology, visit Piletest.com and explore their full range of non-destructive testing systems.