Amongst all existing ground improvement techniques, deep cement mixing knew a big leap forward with the emergence of new technologies in the early 21st century. One of those, called Trenchmix® technique, involves a trencher to form continuous soil-cement walls by mixing the disaggregated ground with a binder on full depth in a single pass. As shown in this paper, the binder may be introduced either as a powder or in the form of a cementitious grout. The soil mixed material then self-hardens forming a barrier with a greatly reduced permeability and enhanced strength.This paper reviews 20 years of case histories with single pass trenching technology in Europe, through a wide range of applications dealing with ground improvement, slope stability, cut-off walls, retaining walls and environmental remediation. A particular highlight is provided on the properties of the soilmix walls constructed with this technology, with a focus on laboratory results vs field results about unconfined compressive strength and hydraulic permeability.

The Cutter Soil Mixing (CSM) method has been used for ground improvement to provide seismic resilience in multiple infrastructure projects in NZ since 2019. The CSM equipment was developed around 20 years ago using rectangular panels to form insitu continuous walling, to replace the traditional methods using rotary drilling rigs that use overlapping secant piles or mixed columns to form walls. The CSM’s mechanical cutters provide construction flexibility through variable soils, with down hole sensors, and onboard computer system, to record key performance indicators. Extensive testing has been undertaken over multiple projects in NZ aimed at gaining a better understanding of the properties of the insitu mixed walls, leading to future optimization of designs, specifications, and construction, to deliver a more efficient and economical outcome. Lowering the cost base of the works can commonly be achieved by lowering cement content, minimizing waste and improving productivity. This paper sets out the design and testing processes for the upgrade of Napier Port, in a zone of significant seismic risk, and with underlying recent alluvial deposits causing a high risk of liquefaction requiring extensive ground improvement. Soil mixing was the best approach with fill and alluvial layers varying in particle size including silt, sand and gravel, overlying siltstone. The depths of pre-treatment ranged from 15m to 17m deep, using lattice walls in a closed cell system. The lattices provided approximately a 20-25% area replacement ratio. Equipment used comprised a Cutter Soil Mixing (CSM) rig for deeper mixing to 17m depth, with a batch plant supplying slurry to the rig. This paper details a practical solution to liquefaction risk and management of the wide range of variables effecting the in-situ mixing, the sampling and testing difficulties, and analysis of results. Collectively these factors all influence QA/QC outcomes, and we investigate how to provide sufficient ground improvement, without over delivering on the various quality metrics.

The CDM Association is working on the development of technologies for the use of deep mixing methods in order to create new demand, with a view to the effective use of deep mixing machinery, the maintenance of construction unit costs, and the transfer of technology. As part of the results, this paper presents two new applications. The first is a quaywall structure using the deep mixing method. In Japan, sheet pile, pier, and gravity quay structures are commonly used, and caissons are often used as the main body of gravity quaywalls. This is a technique for constructing quay walls using a single large solidified body produced by the deep mixing method as an alternative to gravity caissons. The second is a technique for strengthening coastal levees using deep mixing. In the 2011 Great East Japan Earthquake, a large tsunami overflowed coastal levees and the water flow destroyed them, and various countermeasure methods were proposed after the disaster. This technology can be used to construct a lattice of solidified bodies inside the levee, which can withstand earthquakes and tsunamis and maintain the top height of the levee.

In recent years, the Japanese construction industry has faced the challenge of improving the efficiency and productivity of construction works. Therefore, an automatic operation system for deep mixing (hereafter referred to as GeoPilot-AutoPile) has been developed using ICT. This system has been applied to several actual sites and has ensured smooth construction, high efficiency, and good quality comparable to the manual operation by experienced operators. The application of GeoPilot-AutoPile has also been extended to small-type deep mixing machines, enabling its use in a wide range of site conditions, such as narrow areas or height-restricted areas.

Reducing CO₂ emissions is a critical concern in addressing global climate change. In Japan, CO₂ emissions from cement production constitute approximately 3% of the country's total CO₂ emissions. This study investigates a technological system designed to significantly reduce CO₂ emissions in cement production. The system involves the development of blast furnace slag high-content cement and its application in concrete structures and ground improvement. This paper provides a detailed explanation of the development process of high-slag cement and presents experimental results from laboratory tests on ground improvement using this material. The developed high-slag cement was subsequently applied to ground improvement in grid-form deep cement mixing walls as a liquefaction countermeasure. The compressive strength of the ground improved with high-slag cement exceeded that achieved with an alternative type B blast furnace slag cement. Based on laboratory and in-situ results, high-slag cement was confirmed to be well-suited for ground improvement.

Shallow geothermal energy systems (SGESs) are a promising technology for contributing to the decarbonisation of the energy sector. Soil thermal conductivity (λ) governs heat transfer process in ground under steady state, thereby it is a key parameter for SGES performance. Soil mixing technology has been successful in enhancing the shear strength of soils, but is adopted in this paper for the first time to improve soils as a geothermal energy conductive medium for SGES applications. First, the thermal conductivity of six types of soils representing commonly encountered ground were systematically investigated and the key parameters analysed. Next, graphite-based conductive cement grout was developed and mixed with the six soils to demonstrate the significant increase in soil thermal conductivity. For example, the thermal conductivity of a very silty sand increased from 0.19 to 2.62 W/m·K (a remarkable 14-fold increase) when mixed with the conductive grout at a soil-to-grout ratio of 6:1. In addition, the mechanical properties of the cement grouts and cement-mixed soils were examined along with the microstructural analysis revealing the mechanism behind the thermal conductivity improvement.