In this study, appropriate temperature conditions and functions were examined to obtain high estimation accuracy in a method for estimating the strength of cement-treated soil at arbitrary age using the strength of early age of the soil cured at two different temperatures. This strength estimation method utilizes an equivalent age and considers the effect of temperature during curing on the strength development of cement-treated soil. Unconfined compression tests were conducted on cement-treated soils cured under six different temperature conditions in the range of 20 to 55°C. Strength estimation was performed using three different functions for a total of 15 temperature combinations, and the estimation accuracy was evaluated. The results showed that when temperature conditions of 50°C or higher were used, the accuracy tended to be poor regardless of the estimation equation. When power functions were used, the difference from the measured values was larger than in other formulas, and there were cases where a significant decrease in estimation accuracy was observed. Under the conditions of this experiment, the evaluation index I_e of estimation accuracy was within 20% when the temperature condition was set to be between 20°C and 45°C and the temperature difference was within 20°C, and when an exponential function was used in the regression equation.

Since the shear strength of cement-mixed soil is affected by cement content and mixing quality in addition to physical and mechanical properties of original soil, the in-situ strength of ground improved by cement mixing shows large spatial variation. Therefore, the amount of cement is conservatively set to satisfy the in-situ strength more than design strength considering the spatial variability in shear strength. The purpose of this study is to propose a rational method for setting the amount of cement by evaluating performance of improved ground taking the spatial variability of shear strength into consideration. In this paper, we report the results of a two-dimensional static residual deformation analysis to propose the relationship between deformation of embankment and the shear strength variability of the improved ground as an example of performance evaluation. The analysis was conducted for an embankment on a ground improved beneath the toes of slope. It was found that the settlement at the embankment top increased with the increase in the coefficient of variation for the similar average strength. The relationship between coefficient of variation and average strength for the similar settlement was further investigated, revealing that the amount of cement could be reduced by up to 11% when optimizing the number of agitations and the W/C ratio.

Steel making slag and clay mixtures (hereinafter referred to as “modified clay”), which are dredged clay mixed with steel making slag, are self-hardening, so unconfined compression strength is used for quality control as a geomaterial. The self-hardening properties of modified clay depend on the water content of dredged clay, properties of steel making slag, and mixing ratio. Therefore, mixing experiments to determine the mixing ratio of steel making slag are essential, and there is a desire to streamline these experiments. In this paper, the results of mixing experiments of improved clay mixed with different types of steel making slag using dredged clay with different water content as the base material are rearranged, and a method to evaluate the relationship between mixing ratio and unconfined compression strength in a unified manner is discussed, and the following results were obtained. 1) To achieve the desired strength as modified clay, a certain amount of modifying agent must be added. 2) The relationship between slag-clay mass ratio and unconfined compression strength was different for each condition, but the relationship between slag-clay mass ratio and unconfined compression strength normalized by unconfined compression strength for a given slag-clay mass ratio was a univocal relationship.

Cement-based materials are widely used for soil stabilization, but their high CO₂ emissions during production pose environmental concerns. This study investigates an eco-friendly soil stabilizer using waste siding cut powder (SCP) combined with an alkali activator (AA), as a substitute for ground granulated blast furnace slag (BFS). We have conducted some laboratory tests using commercially available clay with 40% water content, focusing on unconfined compressive strength (UCS) and leaching characteristics of stabilized soil specimens. The soil stabilizers which were made from SCP alone required 200 kg/m³ of dosage to meet the UCS criterion for third-class construction-generated soil, while 150 kg/m³ sufficed with AA addition. Heat treatment of SCP at 110°C or 200°C further reduced the required dosage. Blending with ordinary Portland cement (OPC) or calcium hydroxide (10–20%) improved strength, achieving target UCS at 100 kg/m³ after 28 days. Arsenic leaching exceeding environmental standards was observed in some specimens, attributed to natural arsenic in the clay and minor contributions from AA derived from waste glass. Adding sufficient calcium hydroxide effectively reduced arsenic leaching through the formation of insoluble calcium arsenate. SEM-EDS analysis confirmed the formation of hydration and geopolymer-like products. These findings demonstrate the potential of using SCP in combination with AA and calcium-based additives for sustainable and effective soil stabilization.

Soft soils treated by the deep mixing method (DMM) are not always homogeneous and often consist of heterogeneous soils such as clay, loose sandy soil, and organic soil. In such cases, it is common to set the amount of binder on the safe side to avoid insufficient strength. However, this method may cause variations in the strength of the improved soil. It is also uneconomical and has a large environmental impact. In order to optimize the strength and cement content of improved bodies obtained in the improvement of heterogeneous soft ground, it is first necessary to quantitatively analyze the effects of ground characteristics and DMM application conditions on the difference between the in-situ strength of improved bodies and the design strength. Therefore, this study first identified trends in DMM construction conditions employed in road construction projects over the past 10 years. In addition, construction data for 8 representative cases were analyzed. As a result, it was found that the mechanical mixing by wet method with a construction depth of 5 to 20 m and an improvement diameter of 0.6 to 2.0 m was frequently adopted. Furthermore, it was confirmed that the higher the fine-grain content of the soft ground, the greater the in-situ strength of the improved material tended to exceed the design strength. On the other hand, there was no clear relationship between the number of improvement diameters or mixing shafts and the strength of the improved material.

The deep mixing method is the technology of improving soft ground by adding a stabilizer to soft ground and forcibly mixing the target soil and the stabilizer to create a strong foundation for relatively deep depths. Most of the improved bodies in general deep mixing methods are created using mechanical mixing methods, and the cross section of improved body (columnar improved body) has a uniform across cross section injection rate of stabilizer within the improved body. We are developing a method of constructing the cylindrical improved body with variable stabilizer injection rates within it. With this method, we can construct a column efficiently by lowering the stabilizer injection rate in the center and increasing the injection rate on the outer side. The construction of a cylindrical improved body utilizes a hybrid technology that combines the mechanical mixing method, in which high-concentration stabilizer slurry is injected under high pressure into the outer periphery of the body using special mixing blades, and the high-pressure jet grouting method. To confirm the effectiveness of the developed cylindrical deep mixing method in improving soft ground that we are developing, we conducted experimental and analytical studies, comparing it with column cross-sections of conventionally a improved body. Specifically, we performed element tests and numerical analyses using elastic-plastic FEM. This paper reports the results obtained from these tests and analysis, and discusses the improvement effect of the cylindrical improved body. Consequently, we were able to confirm that the unconfined compressive strength of the cylindrical improved body is about 20% higher than that of columnar improved body when the same amount of stabilizer was used. The superiority of the cylindrical improved body was also confirmed by the FEM analysis results.

The authors have developed a technology that involves driving biomass mixed materials into the ground as infill material using the sand compaction pile (SCP) method, thereby preventing liquefaction while storing carbon in the ground. The biomass material selected was bamboo crushed into chips, which also serves to effectively utilize abandoned bamboo forests that are causing bamboo problems (phenomenon in which bamboo proliferates abnormally, adversely affecting the natural environment and human life) in various areas. A biomass mixed material is used, which is a mixture of recycled crushed stone made from bamboo chips and concrete waste. Sand, crushed stone, and recycled gravel, which are conventional SCP infill materials, have a long history of use. However, biomass mixed materials have no history of use, and their material characteristics as SCP infill materials are unknown. Therefore, indoor tests were conducted to confirm the compaction characteristics of the biomass mixed material, its strength characteristics through CBR tests, and its liquefaction strength through repeated triaxial tests. At the same time, tests using actual equipment were conducted to confirm workability and quality (completed pile diameter, N-value at pile center) as well as improvement effects (N-value in-between piles). In addition, estimates of CO₂ emissions from construction using the infill material used in this project showed that the use of biomass mixed materials resulted in a reduction of approximately 600% compared to conventional sand piles.

Clinker ash is coal ash that has collected in the water tanks at the bottom of boilers in a coal-fired power station and is crushed to the size of sand or gravel. It has a porous and complex particle shape, is lightweight, has excellent permeability, and high shear strength. The purpose of this study is to compare the mechanical properties of clinker ash and construction-generated soil in alternating layered and mixed conditions, and to investigate the slope stability when these materials are used as embankment materials. Mechanical properties were investigated by triaxial compression tests, and slope stability was investigated by circular slip analysis. As a result, there was no difference in the consolidation termination time, and the volume change was slightly smaller for the layered structure. The shear strength was slightly higher in the layered structure at CA 10-20%, while the mixed structure exhibited less volumetric strain contraction at CA 50%. The stability analysis of the embankment slope indicated that the minimum factor of safety was slightly higher for the mixed structure, but that the mixed structure had greater resistance in the clinker ash layer, and that safety could be improved depending on its placement.

The need for "self-use" as a means of recycling construction sludge is increasing. Methods for improving construction sludge include using dedicated treatment plants and soil improvement machines. However, in confined sites, it is difficult to install treatment plants and soil improvement machines, and there are challenges such as the need for dewatering operations for high-moisture sludge. On the other hand, backhoes can be used in confined sites and can improve various types of sludge, but ensuring the quality of the improved soil, which tends to be inconsistent, has been a challenge. Therefore, the authors have developed a quality control method focusing on the uniformity of the improvement effect using infrared thermography.This report discusses the usefulness of the quality control method for indoor experiments mixed manually with a spatula and full-scale experiments mixed with a backhoe.As a result of the full-scale mixing experiment, it was found that surface temperature could be measured in real-time and evaluation based on standard values could be applied. Additionally, it was possible to confirm the variation in surface temperature of the improved soil during mixing from the infrared thermography images, confirming the usefulness of the devised quality control method.

In the construction planning of cut-off wall, hydraulic conductivity (k) is a crucial parameter. There are various construction methods for cut-off walls, and the effectiveness is compared by k listed in the technical documentation for each method to select the most suitable method. However, these k lack clarity regarding construction conditions, ground conditions and evaluation methods, and there are very few cases where different methods have been compared at the same site. Additionally, when construction space is limited, methods are restricted to those using small machinery such as steel sheet piles, jet grouting and chemical grouting. Therefore, we constructed cut-off walls using these methods in the same ground conditions and evaluated their k. As a result, we found that some methods showed higher values than those in technical documents, some showed lower values, and some methods showed different values between in-situ tests and laboratory tests. Consequently, it is necessary to consider safety factors for k in technical documents, and field verification is deemed necessary.

The objective of this study was to clarify the effect of lattice-arranged gravel on the liquefaction characteristics of sandy soil because it was considered that the liquefaction strength increases when gravel is placed vertically into sandy soil. Liquefaction tests by torsion shear tests and two-dimensional liquefaction analysis were carried out at various gravel insertion rates. From a series of tests and analyses, as the gravel insertion rate increased, the occurrence of double amplitude shear strain and residual excess pore water pressure ratio was suppressed. When the number of cycles was small, the amount of shear strain and residual excess pore water pressure increased per a wave decreased as the gravel insertion rate increased, and there was no significant difference in the amount of these increases when the number of cycles increased. For the gravel insertion rates greater than 10%, the liquefaction strength increased proportionally with increasing gravel insertion rate. These results suggest that placing gravel in a grid pattern within sandy ground can be an effective countermeasure against liquefaction, improving the ground.

Plasticity behavior of the foam-conditioned soil in the chamber is critical in the earth pressure balanced shield tunneling operation. An experimental study was conducted to evaluate the factors affecting the plastic fluidity of the air-foamed sand under pressures close to the actual field, and to clarify the relationship with that under atmospheric pressure. Plastic fluidity of the air-foamed sand was highly dependent on the difference between the overburden pressure and foam injection pressure, which is normalized by the overburden pressure. Another critical factor was the foam expansion ratio (FER). Foam-conditioned sand with FER = 16 maintained higher plasticity than that with FER = 8, when subjected to an equivalent increment of effective stress. However, the higher FER led to the larger residual volume change after a loading-unloading cycle. The table flow test is widely employed as an index of the plastic fluidity of foam-conditioned soil. The table flow values measured under atmospheric pressure do not completely correspond to the plastic fluidity under high-pressure conditions.

The mattress ground reinforcement method is characterized by simplicity, a well-established design procedure, and relatively low cost. Thus, it is widely adopted in practice, and its effectiveness is confirmed. However, the existing method does not consider the tensile stiffness of geotextiles in the design. In this paper, a series of model loading tests was conducted using aluminum rod laminates and two types of geotextile with different tensile stiffnesses. The tensile forces on the geotextiles and the strain distribution in the ground were measured to examine the effect of the geotextile tensile forces on the bearing capacity of the mattresses. It was found that the larger the tensile stiffness of the geotextile, the more effective the generated tensile forces, resulting in a greater restraining effect within the mattress. Consequently, this enhances the bearing capacity of the ground and results in a less immediate settlement.

The ground freezing method is a construction technique used to support earth pressure and hydraulic pressure during excavation. It is crucial that this method ensures adfreeze―the adhesion between the frozen ground and the structure ―in order to prevent gaps from forming. However, the adfreeze mechanism is not yet fully understood or widely applied in practical construction. Additionally, some factors that affect the strength of adfreeze remain unclear. In this study, we conducted direct shear test to evaluate the adfreeze strength. Eight with different surface roughness levels ware used. The adfreeze occurred between the iron disk and the soil, and the shear strength at their interface was measured using the direct shear test. As a result, it was found that the shear strength of the adfreeze increased with greater surface roughness.