KlimaGrunn – One step closer to precise measurement method for achieved stability in quick clay

– Currently, we do not have an accurate method for measuring and predicting the achieved strength and homogeneity of lime cement piles, which is why we often use more binder than necessary in construction projects. We are trying to solve this challenge by developing better measurement methods, explains project manager Eivind Schnell Juvik from the Norwegian Public Roads Administration.

The challenge of overuse of binder is common to the Norwegian Public Roads Administration, Bane NOR and Statsbygg, Norway's three largest construction clients who lead the innovation partnership KlimaGrunn.

Precise knowledge of the achieved strength in lime cement piles, which are used to stabilize the ground in areas with quick clay, will be of great importance to the entire construction and civil engineering industry – it means that the amount of binder can be reduced – which will result in a significant reduction in CO2 emissions. 

– KlimaGrunn has come a big step closer to developing a more accurate measurement method where temperature sensors are installed and seismic is performed inside the lime cement piles themselves, says Juvik.

Tonje Eide Helle from Multiconsult is the project manager for the suppliers in KlimaGrunn, she emphasizes that they have come a long way:

– We have taken the experience from the first field test in August and have thus achieved a more efficient installation of the temperature sensors and casings for the cross-hole seismic. The temperature inside the pile is measured continuously and transferred digitally so that we can follow the curing process and use these measurements to predict the strength development in the pile. In this round, the seismic is carried out inside the piles themselves and data from the field measurements are correlated with laboratory tests. In this field test, we would also like to extend special thanks to Dmix AB, Skanska and Marthinsen and Duvholt for their good cooperation with the preparation and installation of the lime/cement piles, says Helle.

She continues:

– We are working closely with Dmix AB to investigate how the installation method affects the quality of the piles. Together with DmixAB, we are testing KlimaGrunn's technology to measure the strength and homogeneity of piles and comparing it with measurement methods that have been in use for a number of years. If we are to succeed in reducing the amount of binder and thus greenhouse gas emissions, we must be sure that the piles are as homogeneous as possible in the field, i.e. that the binder is mixed evenly into the clay. That is why we want to investigate whether there is a match or discrepancy in the results between new and "old" technology.

Innovation in being able to measure achieved strength over time

In this latest field trial, which is being carried out at the construction site of the E18 West Corridor at Lysaker in Oslo, KlimaGrunn is now setting down 11 lime/cement piles. The piles have different amounts of binder and different mixing work has been used during installation. The mixing work will probably affect the quality of the pile.

Norcem is the supplier of the binder Multicem, which consists of CKD and cement. By choosing Multicem over a similar mixture of lime and cement, the CO2 footprint has already been significantly reduced.

– More knowledge about the temperature achieved is interesting to analyze in order to predict the strength development in the pile, points out Atle Gerhardsen from Cautus Geo. He says that in this field trial they have used a different type of temperature sensor than in the first field trial.

– We have further developed the method, and installing temperature measurement from the inside of the piles gives us a more accurate result than in the first field trial, he says.

– In the previous field trial, the seismicity was measured through the piles from points outside the lime-cement piles, while now we have further developed the method, so that each lime-cement pile can now be analyzed using seismicity from the inside. Measurements of the shear wave velocity give us knowledge about how strong the lime-cement piles are, says Thorbjørn Rekdal from Argeo.

– Using existing methods, the strength of the pile is most often measured during the first week after installation. This is early in the curing process, and we know that the strength increases significantly in the first four weeks after installation. With KlimaGrunn's method, we will be able to perform measurements at various times throughout the curing process, even several months after the piles have been installed. The lime cement piles we have installed in this field trial will be left standing for 2-3 months to get the longest possible time series into the correlation model to predict the strength, says Juvik.

– The fact that we can measure the degree of stability we achieve – from the inside of each pile is an innovation in the Norwegian context, when we can perform tests further into the curing process we will be able to document higher strength. Reliable documentation of the achieved strength will thus make it possible to reduce the amount of binder, he says.

The “finality” will come in the fall

The 11 lime/cement piles will be left to "cure" for several weeks to come. Seismic measurements will be carried out along the way and the temperature will be logged continuously. In the autumn, KlimaGrunn will conduct a final field test to quality-assured the methodology.

– We will get the "final verdict" on whether these measurement methods are suitable for measuring the achieved strength in lime-cement piles in the autumn, when we will conduct a final verification. This will be carried out in connection with Statsbygg's ongoing project at the Viking Age Museum on Bygdøy.

Until then, we will work intensively both in the field and in the laboratory and further fine-tune the measurement methodology towards the final verification. Once the tests have been carried out and the results evaluated, our measurement method will be able to become a service that will be available on the open market, concludes Juvik.

Brief history of the phases of the KlimaGrunn project

In the first phase of the project, KlimaGrunn worked on improving the test methods used in the laboratory, where the purpose was to create consistency between results from the field and in laboratory tests.

Read more in the article Lower CO2 emissions with better testing method

The results from the first phase were tested in a field study in August 2021, where the newly developed method for predicting the achieved strength in lime cement piles was tested. Cautus Geo and Argeo used sensor technology and seismic to monitor the hardening process in the piles in the field, and measure parameters that could be correlated to the achieved strength and stiffness. In addition, they used seismic to examine the homogeneity of the pile over the entire depth. The measurement results were compared with laboratory results from tests conducted on binder-stabilized clay at Multiconsult's laboratory in Skøyen.

More information about the first field trial in the article Now we are testing new technology for climate-friendly ground stabilization

Facts about KlimaGrunn

KlimaGrunn is an innovation partnership between the Norwegian Public Roads Administration, Bane NOR and Statsbygg. Together, they will further develop technology and methods for measuring strength in ground stabilization in the construction industry. The aim is to reduce CO2 emissions by avoiding overuse of ground stabilizing materials, such as lime and cement, in connection with development projects.

The innovation partnership is funded by Innovation Norway, and is carried out in collaboration with the companies Multiconsult, Cautus Geo and Norcem, with Argeo as sub-consultant.