In this paper, some results from an on-going project regarding long-term properties of in situ lime-cement stabilized columns of clay, are presented. In the field, core sampling and pillar sounding were performed on 30 years old columns at the test site Håby in Sweden. In the laboratory, strength tests and accelerated leaching tests on the core samples were conducted. For the leaching tests and the strength tests respectively, newly developed equipment was used. The results show a possible strength increase with time and the new equipment seem to work well.

This communication presents the results of four static load tests carried out on Soil-Cement columns realized using the wet Deep Mixing Method. After a short introduction, the geological and geotechnical context is presented, as well as the tool used to execute the columns. The instrumentation is then described into details. Then, the main results of the four load tests are presented, such as the bearing capacity and creep load. The base resistances and shaft resistances derived from the extensometers installed in the columns are then pared to each other. Finally, results are compared to past experiences realized in soils of comparable nature, and to calculated values according to different standards.

As a part of creating new living zones by using abandoned industrial areas in Stockholm, new residential areas will be built both on land and at sea. Due to the difficult soil conditions under the seabed, where silt and soft clay are present, a design is being developed with soil improvement to ensure the stability of the natural soil and the embankment of reclamation fill. Cement columns are pre-designed to improve weak soil layers ranging from 10 meters to approximately 25 meters in depth, underlain by moraine layers, while the water depth is approximately 10 meters. The decision on how to construct the cement columns will be taken and the design will be finalized based on the results of the test field. While dry deep soil mixing is the predominant and widely accepted soil improvement method in Sweden, the test field was carried out using wet deep soil mixing (wet DSM). Nonetheless, prior laboratory investigations involved both dry and wet soil mixing techniques. In the project, 37 columns with a diameter of 2.4 meters were constructed using a 130-tonne rig standing on the barge under challenging weather conditions and the dynamic impacts of the sea. Cement and cement/slag (30/70) were used as binders at different dosages. Column verticality was controlled during installation using a verticality sensor mounted on the mixing tool. Wet grab and core sampling was carried out to inspect the quality of mixing along the columns and within the clay/moraine transition zone. This project is known as the first wet DSM application in Sweden, proving the future of this technique in Scandinavia.

Soil columns cemented by in-situ mechanical mixing were investigated for 15 years to demonstrate the long-term strength development and durability of cement-treated soil. The soil was a volcanic cohesive clay called Kanto-loam. The cement used was two special types of cement for general purposes. One type of cement was for soft soils and the other was for special soils (hexavalent chromium (Cr(VI)) elution reduced type). Both cement-treated soils increased in strength over the long term, maintaining more than doubling the 28-day strength after 15 years. The cement hydrate contributing to the strength development was identified as ettringite by powder X-ray diffraction (XRD). The ettringite was produced from an early age and was stable over the long term. C-S-H is also one of the major cement hydrates, but could not be identified by XRD due to its amorphous nature. The durability of the cement-treated soils was also verified by measuring changes in calcium content and pH. All measurements showed no tendency to decrease over time, confirming the long-term durability of the cement-treated soils. In addition, to investigate the impact of the cement-treated soils on the surrounding environment, the groundwater concentrations and surrounding soil elution of hexavalent chromium (Cr(VI)) were measured. Measurements were implemented several times from immediately after construction up to 15 years. None of the results exceeded the environmental standards, confirming that the cement-treated soil does not pollute the surrounding environment.

The CDM (Cement Deep Mixing Method) is a method of consolidating soft ground by mixing a stabilizing material, such as cement slurry, with the subsoil. In Japan, it has been widely used in the port sector, mainly with special working vessels. It is applied to the foundation soils of breakwaters, quays, and revetments. Our deep mixing vessel "Koukaku" can improve up to 5.47 m2 per cycle and 52 m below sea level, which is more than three times the capacity of land-based soil improvement machines (improvement area of 1.5 m2 and application depth of 45 m). In recent years, there has been a need for productivity improvement of the entire construction production system through the full implementation of ICT (Information and Communication Technology). Therefore, we have developed an automated construction system and a 3D construction management system using "Koukaku" and implemented them on site. In this paper, we describe the results of Koukaku's ground improvement work, including stabilizing quality through automated construction, achieving worker training and early independence, the real-time 3D construction management system, and the automated creation of forms and BIM/CIM (Building/Construction Information Modelling) models.

In recent years, Japan has been facing a labor shortage due to a declining population. Greenhouse gas emission measures are required to achieve carbon neutrality by 2050. This paper introduces newly installed systems on a deep mixing barge to deal with these problems. (1) Eco-friendly energy-saving engines have been installed. The hydraulic drive systems have been converted to the electric drive systems. The energy transfer efficiency has been improved because the only energy transfer medium is electricity. The drive unit of the lifting winch of the mixing machine has been replaced with an inverter-controlled electric motor. Energy conversion and CO2 reduction has achieved by installing a regenerative power system. This system can store the excess power generated during the downstroke of the mixing machine and make effective use of it during the upstroke. (2) 4D (3D + time axis) construction management system utilizing ICT has been installed. By utilizing this system, even young engineers with limited on-site experience were able to perform high-quality construction, leading to early independence of operators. Since it visualizes the construction history and construction status in 3D and allows the construction status to be monitored from various perspectives. (3) Automated normal construction. Fine-tuning of the mixing machine to match the construction conditions required experience, knowledge, and skill of the operator, and it took time to learn the operation. By programming the knowledge and skills of skilled operators, one cycle of creating a soil cement column was fully automated. Since it is not affected by the operator’s proficiency level, quality is stabilized, and human errors are prevented. Safety is ensured by a fail-safe foolproof function that can pause construction or perform an emergency stop in the event of irregular or unset operations.

Deep Mixing Methods (DMMs) are a versatile solution for ground improvement that can be used to increase bearing capacity, reduce settlement, and mitigate liquefaction. However, DMMs are cement-intensive, as a single project can consume over 100,000 tons of ordinary portland cement (OPC). This makes DMMs carbon-intensive, as OPC production has been estimated to contribute to 8% of the world’s annual CO2e production. New technologies, including calcium-silica-hydrate nanoparticles and Type IL cement, can be used to reduce the carbon footprint in DMMs by reducing the amount of OPC that is required to achieve equivalent strengths. A laboratory study was conducted using Type IL (10) cement grout with and without dosing of a calcium-silica-hydrate nanoparticle blended with a clayey sand (SC). Unconfined compressive strength (UCS) testing revealed late strength gains in excess of 60% over the baseline. UCS testing was performed on specimens after up to one year of curing to determine long-term strength gain. Scanning electron microscopy (SEM) was also performed on specimens during peak strength gain. Initial testing indicates that CSH nanoparticles can be used with Type I-L cement to reduce binder factors in DMM applications while yielding higher than baseline conditions. Additionally, a roadmap to implementation is provided with stakeholder involvement. Stakeholders are critical in the process of carbon reduction and have key roles as collaborators in the roadmap to implementation.

Recent research in Norway focuses on understanding the strength and deformation characteristics of soft soils stabilised with the dry deep mixing method, aiming for more sustainable design and practice. The present paper summarizes the carried-out work and important findings obtained during the last 10 years of research in this topic. Experience with reducing the content of traditional binders, such as cement and quicklime, to less than 80 kg/m3 is presented. The performance of industrial by-products and biochar to replace traditional binders is discussed. Innovative monitoring solutions including fibre optic sensing and geophysics are described. Recent efforts in developing new binders are reported. The paper concludes with the application of data mining techniques to soil stabilisation and provides guidance on upscaling laboratory results to field scale.

Within the framework of sustainability, the United Nations' Sustainable Development Goal 13 (SDG 13) is to limit and adapt to climate change. The Deep mixing methodology by itself can reduce the climate impact for producing geotechnical works in ground conditions and boundaries where a classic method based on excavation and backfilling with concrete would otherwise have a larger carbon footprint. However, this paper presents another beneficial use of a soil mixing application where such retaining walls become a permanent and integral part of a sustainable building concept. A case study in Bavaria, Germany, demonstrates that the mixed-in-place method is a preferred sustainable technique for harnessing geothermal energy due to favorable heat transfer properties. In this way, the supporting structures, which are often used temporarily, become an integral part of the building and contribute significantly to its energy demands. If such a “geothermal option” is implemented, the CO2 emissions saved can be recorded as the contractor’s handprint on the client’s sustainability account.

Malminkenttä, in the northern part of city of Helsinki, will be a new residential area. The surface area is about 2.4 km2. The soil conditions of the area are mainly soft sensitive clay that requires intensive ground improvement actions for the development of the residential project. Dry deep mixing (DDM) has been planned as one of the key ground improvement methods. The preliminary preconstruction plan made in 2017 showed that if lime-cement were used as binder material for DDM in Malminkenttä the CO2 emissions would be vast. Therefore, low-carbon binders have been studied widely to reduce emissions. This paper presents performance comparison of laboratory test results for different binders. The aim is to show that low-carbon binders are a real solution for DDM and that they can perform even better than traditional lime-cement. The laboratory tests include characterization, uniaxial compression and triaxial tests. Another aim is to analyze the differences of shear strength, yield stresses and deformation moduli determined by uniaxial compression and triaxial test.

Malminkenttä is an old airfield covering an area of around 2.4 km2. Area is on soft subsoil which consists mainly of 5 to 20 m deep clay layers. The amount of required column stabilization is estimated to be about 10 million meters in total. The clay layer is a challenging task for deep mixing. The uppermost clay layer is sulphate clay where the pH value is even at level 4 at the oxidized layer. The water content of the clay layer is up to 160 %. The City of Helsinki has decided to discontinue the use of lime cement in column stabilisation due to its high carbon dioxide emissions. The city has decided to use low-carbon binders, only some of which the city has previous experience, in column stabilisation in the future. One aspect at the construction at Malminkenttä area is the creek Longinoja, which is located next to the construction area and is an important living area for threatened trout and thus any negative effect to water quality of the creek is not allowed. All this together means that laboratory testing, test stabilization and environmental monitoring are very appropriated.

Carbon capture and storage (CCS) technology has been actively developed in recent years, primarily in the concrete sector, through carbonation curing and use of CO2-fixed materials. In the cement-based ground improvement sector, if the volume of cement-treated soil can be used to fix carbon dioxide in the ground, this would contribute to recent societal initiatives for carbon neutrality. In this study, the strength development characteristics of cement-treated soils mixed with carbon dioxide were investigated. Unconfined compression tests on cement-treated soil showed that a certain level of strength development was possible up to a carbon dioxide/cement ratio of approximately 10% over 224 days. The sequestration characteristics of carbon dioxide in cement-treated soils were investigated in this study. The carbon content of the cement-treated soil increased by almost the same amount as the carbon content derived from the mixed carbon dioxide compared to that of the cement-treated soil without carbon dioxide containment, indicating that carbon dioxide was sequestered in the cement-treated soil.

Towards the realization of a low carbon society, the authors have devised a system in which CO2 separated and recovered from the emissions of work vessels is fed into cement slurry in the form of dry ice and fixed in the ground by using it as a solidifier in ground improvement by deep mixing treatment methods. In this study, the feeding methods of dry ice, such as feeding amount, form and addition method, were investigated to find the method with the highest fixation amount and the least loss. The amount of CO2 fixation in the indoor and full-scale experiments was confirmed using the Gasometric Method and TC analysis, and it was confirmed that the fixation amount in the full-scale experiment was maintained at the same level as in the indoor experiment. A simple and quick method of measuring the amount of CO2 fixation is desired as part of the daily management of the CO2 fixation system devised by the authors. Therefore, a measurement method with high analysis accuracy was investigated, focusing on the Gasometric Method, in which hydrochloric acid is added to a sample and the CO2 gas generated by the chemical reaction is measured as pressure. In this study, the optimal measurement method was investigated with regard to the stirring method of the sample and hydrochloric acid and the environment during the preparation of the analysis sample. TC analysis was also carried out and the validity of the measured values was evaluated.