Cyclic triaxial tests: Evaluation of liquefaction resistance in chemically treated soils

Soil liquefaction can be a major threat to the infrastructure and built environments in an earthquake-prone area. This happens due to substantial loss of soil stiffness and strength due to applied stress. Loose, moderately granulated, sandy soil is more prone to soil liquefaction.

Recognizing the urgent need to enhance urban resilience in seismic-prone regions, particularly in rapidly urbanizing areas vulnerable to such hazards, scientists are focusing on different mitigation techniques. Soil compaction technique is one of the effective methods developed to enhance the liquefaction resistance of the soil.

However, developing a proper evaluation method is also of the utmost importance. Traditionally, stress-controlled cyclic triaxial tests are done for the evaluation. However, the results are often inconsistent and this can lead to an overestimation of the resistance capacity.

Also, focusing on sustainable options is an inevitability in present times. So, the scientists are also trying to focus on formulating and testing environment-friendly grouting substances.

To bridge the methodological gaps and promote safer, eco-friendly ground improvement for the global infrastructure, Professor Shinya Inazumi from College of Engineering, Shibaura Institute of Technology (SIT), Japan, along with a small team of researchers, developed a strain-controlled testing method using cyclic triaxial.

“We pursued this research after recognizing the urgent need to improve urban resilience to earthquakes,” mentions Prof. Inazumi, talking about the motivation for the study. The findings were published in the journal Results in Engineering.

As a grouting solution, an environment-friendly formulation of colloidal silica (CS) and geothermal-recycled sodium silicate were used. Compared to conventional grouting solutions, this reduces carbon-dioxide emissions during production by approximately 60%. Three different concentrations of CS–6%, 8%, and 10% were tested.

The stress-controlled test was conducted following previously established protocol. For the strain-controlled cyclic triaxial test, double-amplitude axial strain was maintained constant at 5%, simulating large cyclic deformations from earthquakes. Cumulative dissipated energy was evaluated as an alternative indicator of liquefaction potential.

The phase transformation angle was evaluated. Cumulative dissipated energy as a unified evaluation index was also evaluated. Pore pressure-based criterion, strain-based criterion, and energy-based criterion were assessed to evaluate the resistance.

The test result revealed that a higher concentration of CS increases the resistance, with 10% concentration yielding the best result. Analysis of the cumulative dissipated energy confirmed that energy-based evaluation is a viable approach for assessing liquefaction resistance.

“This new method is superior to the present evaluation methods,” mentions Prof. Inazumi. “It reduces the need for multiple specimens, which makes it cost-effective and produces consistent, reproducible results.”

The team also observed a linear relationship between dissipated energy and liquefaction resistance ratio (R_{L20, 5%}) which can be a potential calibration path for integrating strain-controlled results into existing stress-based design charts. This can save time and improve previous test results significantly.

The new method’s potential of being integrated into energy-based designs supports its use in performance-based seismic design frameworks, as proposed in recent studies.

“The research has profound real-world applications, especially in earthquake-prone regions,” says Prof. Inazumi.

“One key application is retrofitting existing structures, based on the updated test results. Chemical grouting with CS can be used to mitigate liquefaction hazards in waterfront projects, such as expanding school buildings, residential complexes, and medical facilities near seawalls.”

Furthermore, this method can stabilize loose sands against lateral spreading. The eco-friendly nature of the silica formulation can also ensure the safety of marine environments. Additionally, owing to the low-vibration nature of this method, it could be ideal for crowded urban areas, aiding in the development of bridges, ports, and dams in regions such as Japan and California.

Taken together, integrating this new method of testing into global standards could save lives, minimize economic losses by providing precise, cost-effective liquefaction mitigating strategies.

In the future, the testing method could be used to evaluate other types of soil, other grout types, and testing methods. The study hugely contributes to the development of performance-oriented ground improvement design under seismic loading conditions.