Shigeo Sasahara’s research while affiliated with Fuji Xerox Co.,ltd. and other places

There is no unified view on the strength development mechanism of chemically grouted sand, which has not been clarified yet. This study investigated the cohesion and friction angle, which are the shearing strength components of the chemical grouted sand, using a consolidated drained triaxial compression test. The microscopic molecular structure of the hydrogels in which the grout gelled itself was analyzed using a small angle x-ray scattering. In the experiment, we used a type of chemical grout that gelled in the non-alkaline region and caused macro volumetric shrinkage. As a result of the triaxial compression test until 300 days, the strength development of the grouted sand added cohesion and increased friction angle because of the fixed soil particles. And these values did not decrease. In the void of soil particles, neither volumetric shrinkage nor peeling of the hydrogel occurred. These suggest that the effect of fixing the soil particles continues. On the other hand, it was confirmed that the aggregation structure became smaller in microscopic molecular structure.

The chemical injection method is one of the ground improvement methods used to stop water and increase strength. It is essential for soft ground improvement. Although the chemical injection method is a proven technique, it still faces technical challenges. The improved area and strength are generally non-uniform because the area to be improved cannot be controlled artificially due to the nature of the method. This study aims to identify and evaluate three causes of infiltration behavior. Firstly, the effects of different viscosities of various types of chemicals and different ground permeability on chemical infiltration behavior were evaluated through infiltration flow analysis. Secondly, the effects of ground uncertainty on infiltration behavior were assessed through infiltration flow analysis and Monte Carlo simulation. Lastly, the influence of rheological properties of the chemical solution on infiltration behavior was evaluated using a coupled MPS-DEM analysis. By presenting these three evaluation procedures, this study proposes a new method to evaluate the performance of chemical injection methods.

For years, the chemical injection process has aided construction works by increasing the strength and water-sealing efficiency of sandy soil. Despite its growing popularity in projects, such as seismic strengthening and liquefaction mitigation, a unified understanding of how chemically treated soil develops its strength, especially under static conditions, remains elusive. Some studies have proposed that strength is derived from the tensile effects of dilatancy, where shearing of the sandy soil causes expansion, creating tension in the interstitial hydrogel and resulting in negative pressure that consolidates the soil particles. Other studies, however, attribute this strength development to the volumetric shrinkage of the hydrogel, which the authors argue confines and compresses the sandy soil particles. Challenges are encountered with this theory, particularly with respect to the consistency of the volumetric shrinkage measurements and the timing of these measurements in relation to changes in soil strength. The aim of the current research is to shed light on this mechanism by using consolidation drainage triaxial compression (CD) tests to measure the cohesive strength and internal friction angle of chemically enhanced soil. By eliminating the dilatancy-induced negative pressure effects and coupling this with an analysis of the molecular structure of the hydrogel, the present study provides an in-depth look at the strength development mechanism and its durability. This holistic approach not only fills in the existing gaps in the understanding of this mechanism, but also paves the way for optimized construction techniques.