Cellulose nanofiber (CNF) is a biomass material made from wood fibers that have been refined to the nano-order. Currently, CNF is being developed for a variety of applications in various industries by taking advantage of its characteristics (large specific surface area, light weight, high strength, low thermal expansion, and biodegradability). On the other hand, in the field of geotechnical engineering, technological development using CNF has just begun. The authors investigated the quality of cement treated soil by the addition of CNF in terms of increased strength and improved dispersion. In laboratory mixing tests, the addition of ACC-CNF to the cement-treated soil showed that the strength development was equivalent to that of the specimens prepared by standard methods, even at shorter mixing times.

A modernized city like Tokyo has a weakness in that its aging buildings lack seismic resistance. Cement-based ground improvement, which provides a high degree of flexibility in strength, has been used for a variety of purposes, including temporary applications such as tunneling support, excavating support, and permanent applications such as liquefaction countermeasures, a spread foundation, a foundation reinforcement for damaged piles. The design and evaluation of ground improvement have been investigated and researched by various researchers and engineers, for the understanding of physical and mechanical properties. In such efforts, unconfined compression strength has been used as a criterion for design and evaluation for quality of ground improvement. However, there is not enough knowledge of the dynamic properties (shear wave velocity) of cement-mixed soils and scale effect in the strength of small specimens and full-scale large specimens. From the above background, we discuss the dynamic properties and scale effect of cement-mixed soils prepared in a laboratory with reference to previous findings and the data obtained in this study.

Typical techniques used to make soil-cement columns for quay wall structures include the DM (mechanical mixing) and jet grouting methods. In this study, borehole samples were taken from sites where both the DM method and jet grouting method were applied, and mechanical tests such as unconfined compression tests and flexural tests were conducted to investigate the differences in strength development between the two methods on the same soil type. The results showed that both methods achieved sufficient improvement effects; however, when comparing the two, the DM method tended to exhibit less variability in strength.

Quality evaluation of the jet grouting method is normally performed based on the unconfined compression strength of specimens taken from the constructed ground improvement by core boring. The core strength data is the sample data representing the strength of the ground improvement. The core strength varies spatially even under the same soil and construction conditions. Therefore, statistical variables such as mean values and standard deviations of the core strengths are used for the evaluation of the quality of the improved ground. This paper reports the results of an analysis of core strength data obtained from cement-treated soil columns by the jet grouting method. The mean value, standard deviation, and autocorrelation distance of the unconfined compressive strength were evaluated based on the core strength obtained at construction sites. Autocorrelation distance is a variable that allows for the quantitative evaluation of the spatial correlation of strength. The autocorrelation distance was calculated using the maximum likelihood method, assuming that the core strength follows a normal distribution. The Kolmogorov-Smirnov (K-S) test was performed to confirm that the probability distribution of the core strength follows a normal distribution. Based on the K-S test result, the goodness-of-fit for the normal and lognormal distribution against the probability distribution of the core strength was examined. Finally, the autocorrelation distance of the core strength data obtained from soil-cement columns by mechanical mixing method was compared with that evaluated in this study.

Deep soil mixing is a soil mixing technique with a binder, which has numerous applications and is constantly evolving. The study focuses on the influence of different low-carbon binders on the soil composition. Despite their significance, our understanding of soil-binder interactions remains relatively limited. Several binders, ranging from clinker-rich cements to ternary binders, are used at various dosages and with different soils. The impact of binder composition is assessed through physical properties (porosity, density, permeability), mechanical properties (compressive strength, dynamic elastic modulus), and durability tests. This study primarily focuses on the durability aspect of soil-cement mixtures with tests for carbonation and resistance to sulfate attack. The study indicates a partial incompatibility between clinker-rich binders and the clay present in the soil. Binders with latent hydraulicity exhibit better performance, as demonstrated by their mechanical properties. The distribution of pore sizes and the formation of different bonds during hydration also appear to vary depending on the different components of our binder. The results demonstrate that using clinker is not the optimal choice for our application, and the development of binders based on pozzolanic products seems promising.

This paper presents an innovative contra-rotational shear deep soil mixing (CS-DSM) technology for ground improvement. The CS-DSM system features a coaxial dual-barrel design with independently controlled internal and external mixing blades rotating in opposite direction. This contra-rotational shearing mechanism enhances degree of mixing, prevents surface spoil, and improves construction efficiency. Field investigations involving coring, visual inspection, and unconfined compressive strength (UCS) testing validated the technology's effectiveness in achieving high-quality deep mixing columns with core recovery over 85% and UCS meeting design requirements. A small-scale model testing system was developed to address technical challenges for building the full-scale system. It served several goals: 1. verified the contra-rotational mixing feasibility, 2. optimized the mixing tool structure, 3. guided control system development, and 4. reduced research costs and time. Crucially, model tests established equation for computing the blade rotation number of CS-DSM column, and quantified the linear relationship between the blade rotation number T and UCS. This T-UCS correlation enables estimating the minimum blade rotation number for target strengths, optimizing quality and costs. In all, the CS-DSM technology integrated with the model-based design approach and robust process control demonstrates tremendous potential for efficient, high-quality ground improvement worldwide.

In ground improvement works underground, if the auger trajectory deviates from the correct position, there is a risk that not only the final shape but also the intended purposes of ground improvement such as bearing capacity, deformation control, and water shielding may not be achieved. Therefore, ensuring vertical accuracy is a crucial challenge. However, the current commonly used method for managing vertical accuracy assumes the rod to be always rigid and is controlled using inclinometers on the construction machinery above ground, making it unclear what the actual position of the rod tip underground is. To address this issue, a system has been developed to monitor vertical accuracy in real-time during construction by combining a gyro sensor with a wireless communication pipe. In this development, a gyro sensor is installed near the mixing blade at the end of the rod, and the sensor is connected to the surface using a dedicated wireless communication pipe. This allows for real-time measurement of vertical accuracy during construction and its incorporation into the construction process. This report applies the developed system to a 2-axis deep mixing machine and demonstrates the effectiveness of the developed system by comparing the real-time vertical accuracy obtained during construction with the actual measured vertical accuracy of the rod position after bottoming of the ground improvement.

This paper provides an idea of statistics approach about the quality control for Cement Deep Mixing (CDM). Patimban Port Development Project (I) has a large construction area, then total 1.4 million m3 of CDM was installed. In addition, it was observed that the seabed profile could be clearly separated into 3 different types of soil layers and there was the organic clay in the middle layer. Considering the unique soil profile and the presence of the organic soil, the slag cement was selected for CDM construction. The cement factor was varied toward the depth direction for the economical construction purpose. In the middle of construction period those cement factors were adjusted after reviewing the result of Unconfined Compressive Strength (UCS) Test and the summary of percent failure. Percent failure means the percentage of specimens out of all tested ones whose the strength is less than the design. Not only histogram but also this percent failure helped us to decide the cement factor during the construction.