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Solutions

Liquefaction Mitigation

Overview

Teretek resin injection is a ground improvement technology that can be used to mitigate liquefaction with minimal disruptions.

There is a growing demand for liquefaction mitigation beneath existing structures. Resin injection is one of only a few practical and non-invasive methods that are currently available.

After a decade of researching and developing Teretek resin injection, Mainmark can claim a high level of accuracy in its design. Mainmark has also worked with international experts throughout the development of this technology. The performance of the resin injection has thus been tested across a wide range of geotechnical conditions.

Mainmark uses Teretek resin injection for ground improvement applications such as increasing bearing capacity and liquefaction mitigation.

Development of Teretek Resin Injection

In 2013, Mainmark took part in industry-leading research to test shallow ground improvement methods. These research trials attracted practicing engineers and academics from all over the world. During the course of this research, Mainmark trialed and tested Teretek Resin Injection technology.

There has also been a commercial application of Teretek for ground improvement.  From 2015-16, three adjoining large format retail buildings were re-levelled and repaired. These buildings had suffered liquefaction-related damage caused by the Canterbury Earthquakes (up to 160mm of differential settlement across the 5400m2 combined building footprint).

Teretek resin injection was used to improve soil density and stiffness and mitigate liquefaction.

The results showed that Resin Injection was one of the best ground improvement techniques from the trial and significant improvement can be achieved with Mainmark’s methods

 

 

The resin injections resulted in increases in qc1ncs (i.e. the clean sand equivalent of the corrected CPT tip resistance) in the order of 40%, and decreases in calculated settlements in the treated zones of 40-80% at 100-year return periods of shaking (Traylen et al. 2016, Hnat et al. 2017).

The project therefore demonstrated that resin injection is a viable technology for ground improvement, and is particularly useful for liquefaction mitigation or ground densification beneath existing structures. Furthermore, the low level of intrusion required to carry out the process was a particular advantage for this operation, as the three retail outlets (including a large supermarket) were able to continue trading uninterrupted through the busy Christmas trading period.

In the research trial, there was on average, there is a 65 to 75% increase  across all three sites.

After four years of development and international peer-reviewing processes, the development of Teretek as a ground improvement technology was complete.

Proven Results

Due to the proven results of this testing, our technology features in Module 5 — a guide for engineers on best practice and consistency in ground improvement design.

These guidance modules were co-developed by the Ministry of Business, Innovation & Employment (MBIE) and the New Zealand Geotechnical Society (NZGS).

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How we work with clients

Mainmark works with client engineers to align the design requirements with achievable improvement targets.

The design is determined by the initial soil properties and the desired target outcome for the overall performance of the structure.

This influences the injection depths and extent of improvement required. Following the site application, the design is then validated using standard geophysical tests.

Key Benefits

There are only a few practical methods available to mitigate liquefaction potential beneath existing structures; particularly buildings that must remain occupied and operational during any mitigation.

Mainmark solutions are non-disruptive and allow maintenance of building occupancy.
Our technology increases stiffness and shear strength while reducing earthquake-induced lateral spreading.
These methods are also versatile, and permit construction on filled soil as well as shallow footing construction.
Reduction in footing size is also possible due to the increase of bearing capacity.
Mainmark works alongside client engineers to align design requirements with achievable improvement targets.
When designing, we look at initial soil properties as well as the target outcome for the overall performance of the structure. This influences the injection depths and extent of improvement required.
Following the site application, the design is then validated using standard geophysical tests.

Improvement Mechanism

Resin injection strengthens the ground primarily through the densification of soil using an expanding polyurethane resin.

The process starts with the installation of small injection tubes, spaced evenly in the target improvement zone. At each point, low-viscosity resin is injected into the ground at controlled pressures, forming a resin-soil matrix. 

The resin penetrates the soil mass along pre-existing planes of weakness or through fracturing of the soil mass. The resin also permeates the soil mass to a limited extent depending on the porosity of the soil.

The resin mixture undergoes a chemical reaction soon after injection, changing from a fluid to an (inert) solid. The material is cured within seconds, and is 90% cured within an hour of injection. The mixture will expand up to several times its original volume. 

This expansion results in compaction of the surrounding soils as the new material is introduced. Alongside soil densification, secondary ground improvement benefits include an increase in composite stiffness and particle cementation. 

Testing and Validation

Resin injection projects are often within or in close proximity to existing structures and ongoing building operations. Following an engineering design, ground improvement targets are set, which are then validated through pre- and post-geotechnical tests.

The Cone Penetrometer Test (CPT) is predominantly utilised in this context due to its precision in determining essential soil parameters like tip resistance, soil strength, and liquefaction potential. When operating beneath existing structures or in confined spaces, miniaturised CPT rigs become invaluable, navigating restrictive sites and basements.

When required, the Direct-Push Cross-Hole (DPCH) test offers a broader perspective on larger projects, particularly for determining soil’s shear wave velocity of the soil. This is typically used on liquefaction mitigation projects as the results can determine the soil stiffness and liquefaction triggering potential.

The DPCH is often utilised in conjunction with CPT testing on larger-scale projects. Using two forms of validation provides a wider understanding of soil improvement. For example, CPT testing is a point test, meaning it only measures the soil profile in its vertical line of injection. This provides a conservative measurement of the improvement in-between the resin veins. The DPCH test measures horizontally across a 1-2m span. This then provides an average value with the composite stiffness of the material included.

Stone Columns vs Resin Injection

Similarities

Both ground improvement methods provide liquefaction mitigation as a result of soil densification. They also both provide added benefits such as increase in composite stiffness.

Differences

Either ‘top down’ or ‘bottom up’ methods can be employed for resin injection, while only the ‘bottom up’ method is used for stone columns.

Another difference is that for stone columns, solid aggregate is pumped into the ground using compressed air. For resin injection, a low-viscosity resin mix is used. This chemically reacts shortly after injection and rapidly expands in the soil.

Effectiveness in various soils

Both methods were effective in clean sand soil profiles. Stone columns are a less effective ground improvement method in silty soil profiles with high fines content (over 50%). 

 

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Whitepapers

Liquefaction mitigation resources & downloads

Liquefaction Mitigation of an Existing Waste Water Treatment
Large Scale Field Testing of Resin Injection As A Ground Improvement Method for Mitigation of Seismic Liquefaction
Comparison of Soil Stiffening from Stone Column and Engineered Resin Installation
Red Zone Trials Resin Injection Research Report

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