The quality of soil improvement and soil cement piles is managed by measuring unconfined compressive strength. But, this method has the problem that the collected improved soil needs to be cured for a certain period of time. Moreover, if their strength were not enough, it would require a large amount of work to repair or reconstruct. To solve this problem, we examined a method of measuring the amount of cement contained in the unsolidified mixture and using the results to estimate the strength of the cured mixture.
Where soft ground is widely distributed, ground improvement is necessary to ensure safety. Generally, as ground improvement, cement soil stabilization is applied for soft ground. However, cement soil stabilization may not be applicable to peat. This is because the humus contained in peat interferes with the hydration reaction of cement. There are some methods of using special stabilizers for peat, but it may not be possible to use it because the available place is limited or expensive. To solve this problem, the technology to improve strength of soil cement mixed peat was examined. When the cause of the strength decrease was examined, it was found that humic acid inhibited the hydration reaction of cement. Therefore, a cationic insolubilizing material was added so that humic acid did not adsorb on the surface of the cement. As a result, inhibition of hydrate by humic acid is suppressed, and the strength of soil cement with peat was improved. This result showed that cement stabilization of peat is possible using Ordinary Portland cement or slag cement even in places where stabilizers are not available.
In this paper, Dynamic centrifuge model tests were conducted to understand the effects of different cross-sections and unconfined compression strength of Composite ground improvement on the deformation of embankments and surrounding ground in response to Level-2 seismic motion. The result of dynamic centrifuge model experiment, we verified that Composite ground improvement can be expected to control the deformation of the surrounding ground against Level-2 seismic motion under the experimental conditions. However, the deformation control effect of the embankment depends on the cross section and strength of the shallow improvement.
To investigate the effect of changes in chemical properties on the long-term strength of the compacted soil with stabilization by small amount of cement, specimens were cured under sealed and soaked conditions in laboratory. Unconfined compression tests and chemical analyses (XRF and XRD) were conducted periodically until 2 years. At each period of curing, the unconfined compressive strengths of the specimens soaked were lower than the strengths of the specimens sealed. The strengths of the specimens soaked for 2 years were not decreased significantly but higher than the strength of the specimens sealed at the short period such as 7 days. The difference between soaked and sealed samples for 2 years was shown by XRF and XRD in terms of the distribution of Ca ion or the existence of ettringite on the cross-section of the specimens. It was inferred that the difference in strength of the specimens soaked from those sealed at each period of curing was attributed to the dissipation of hydrates such as ettringite from the surface of specimen. On the other hand, strengths of the specimens soaked for 2 years were kept higher levels than those sealed at initial curing periods, due possibly to the existence of hydrates on the specimens soaked even after 2 years.
It is necessary to properly fill underground cavities encountered during construction works in order to eliminate the risks of subsidence and depression prior to building a sound foundation that supports structures. The most common method of filling treatment is to pour a highly fluid cement-based material over a wide area, but "plastic grout filling" is also often used, in which the grout that has been adjusted to have plasticity is pumped and supplied into flat cavities. The lateral reaches of plastic grout supplied from the inlet hole has a relative difference due to ease of spreading depending on the height of the filling space. It does not spread to concentric circles unless the condition is completely uniform height. In former studies, the author has clarified the factors that influence the progress of the filling area and the required inlet pressure through experimental studies as well as by computational fluid dynamics. In this paper, the author studied a simplified numerical analysis method that easily calculates the reaches of the grout that spreads laterally in a cavity with a height of less than about 500 mm. The focus is put on the practical utilization for the prediction and evaluation of the filling works. As an algorithm for simplified analysis, a convergence calculation was proposed on the filling experiment results that spread in two directions, left and right, while balancing the inlet pressure generated by the stepwise advancement of the filling area in both directions. The effectiveness of this method was confirmed through comparison with the results of four experiments in which the cavity filling heights were changed.
The ground solidification method, which mixes an improvement material such as cement into soft ground, is one of soil improvement technologies. This method has been widely used to improve the bearing capacity and control settlement of the foundation ground. However, there is not much research on the strength recovery characteristics of cement-treated soil that has already damaged during the curing period by external forces such as earthquakes and landslides. In this paper, the recovery characteristics of the shear strength for cement-treated Kawasaki and Kaolin clays were clarified by means of a series of box shear tests and powder X-ray diffraction analysis. As a result, the shear strength recovery depends on the soil type of base material, GGBS content, and the vertical pressure for the box shear test. Cement-treated Kawasaki clay shows a strong shear strength recovery as the range from 7.4 % to 340.8 %.
The purpose of this study is to understand the effect of drying and wetting (DW) cycle on the unconfined compression (UC) properties of the solidified geomaterials mixed with wood chips, which imitates the under-sieve residue, steelmaking slag and blast furnace slag fine powder. The experiment was carried out by changing the shape of wood chips (fibrous / granular) and the number of DW cycles (0, 2, 4 or 8 times). The following observations were made: (a) The effect of DW on UC properties differed depending on the shape of the wood chips. (b) When granular wood chips were mixed, there was almost no change in the volume of the specimen due to DW. However, when fibrous wood chips were mixed, the volume of the specimen expanded significantly due to DW. (c) When fibrous wood chips are mixed, the volume of the specimen would not expand unless either drying or wetting occurred. From these results, it is considered that the slag containing a large amount of granular wood chips can be sufficiently used at the surface layer where DW cycles are likely to happen. On the other hand, the slag containing a large amount of fibrous wood chips should be used in the ground that always contains water, not at the surface layer.
According to the mission scenario of the International Space Exploration Collaboration Group (ISECG), a "Mars sample return plan" is underway to bring the soil of Mars back to Earth by 2030. In the near future, in order to efficiently perform various operations on Mars (filling, excavation, sampling, ground improvement, etc.), pre-simulation on Earth will be important. Therefore, there is an urgent need to develop an appropriate simulated soil and to understand its material and mechanical properties. Based on this background, the authors are investigating the physical and basic mechanical properties of Mojave Mars Simulant soil (MMS-1), which has been reported as a simulated soil for Mars. This study focused on the particle shape of MMS-1 and was conducted to investigate the effect of particle shape on shear strength and volume change. As a result, it was revealed that MMS-1 has a higher shear strength than Toyoura sand and has a clear peak as the relative density increases. Moreover, MMS-1 is a material that causes volume expansion during shearing even for low stress and density states compared with artificial soil, and it was revealed that this is due to the angularity of the MMS-1 particles.
We developed a new soil washing method which can be used for silty or clayey oil-contaminated soil. The new method uses a combination of selected anionic surfactant and nonionic surfactant. This paper consists of two parts. Firstly, we describe laboratory tests to illustrate how we develop the new method and how it can significantly decrease TPH (Total Petroleum Hydrocarbon) of oil-contaminated soil by using selected surfactants. Secondly, we focused on environmental impact of recycling the washed soil since a small portion of surfactants is remained after treatment. In order to estimate the behaviour of the residual surfactants, we conduct laboratory tests and numerical analysis. The results suggested, although the movement of residual surfactants in the ground varies depending on types of soil, it is unlikely that surfactant leached from treated soil affects surrounding groundwater environment.
Using a slurry shield tunneling method, the main leaching mechanisms of arsenic naturally contained in the ground are as follows: (1) the arsenic adsorbed on iron hydroxide elutes in an alkaline pH range, and (2) arsenic adsorbed on iron hydroxide is released into a reducing atmosphere as iron hydroxide decomposes. We use the slurry shield tunneling method to supply acid agents to the slurry regulation tank of a slurry treatment system to keep the pH of the slurry at the cutter face in a weakly acidic range of approximately pH 5. We use UltraFine Bubble (UFB, a bubble of less than 1 micrometer) technology with excellent gas-dissolution efficiency to increase dissolved oxygen and promote the oxidation of the slurry. As a result of laboratory and demonstration tests, by reducing arsenic elution, surplus soil (gravel, sand, and silt) and surplus slurry (silt and clay) recovered from the slurry treatment system meet the soil leachate standard.
The soil improvement technique called as microbially induced carbonate precipitation (MICP) is recognized to be more environmentally friendly than traditional techniques using piles or cement milk. The soil particles bind by precipitating calcium carbonate on particles or in pores, depending on microbial activity. Although the binding structures such as active and inactive bonds have been numerically simulated from chemical-based modelling, the simulation of carbonate precipitation taking into account microbial growth has not been carried out. In addition, the relationship between the spatial precipitation pattern and improvement of mechanical properties remains ambiguous. In this study, a novel MICP simulation scheme dealing with microbial growth is proposed, and the impact of carbonate precipitation on the mechanical properties of the MICP-treated materials is discussed. In this scheme, a reaction-diffusion system and a homogenization method are used for microscale bacterial growth and for multiscale stress and strain analysis, respectively. The results of the calcium carbonate precipitation were 4.5 μmol/mm3 at 10.3 hour, which is slightly higher than the experimental data. Furthermore, the homogenization simulations indicated that soil stabilization could be attributed to the formation of a novel skeleton structure comprising soil particles and calcium carbonate-filled soil pores.
This study focused on the in-situ mixing process of middle-pressure jet grouting method of 20 MPa or less and aims to establish a computer-aided engineering (CAE) system that can simulate the performance on a computer from the planning/design stages. This ground improvement method is the combination of a jet grouting method and a jet grouting with mechanical agitation and mixing method having been put into practical use. These two ground-improvement processes were computationally reproduced here using the moving particle semi-implicit (MPS) method which is capable of handling ground failure phenomena and high-velocity fluids and construction specifications were examined according to the ground conditions. In order to confirm its effect, a comparative analysis was performed with different jet pressures, development situation was visualized, and its performance was evaluated. The results show that the cement slurry jet ratio in the planned improvement range, including the periphery of the mixing blade was increased and a high-quality columnar soil-improved body was obtained. It is expected that the introduction of CAE will contribute to the visualization of the ground, and that CAE will be an effective tool for the visual management of ground improvement method during and after the construction.
The compaction method, such as the sand compaction pile (SCP) method, is a method to increase the strength of the ground by installing the material into the ground to be improved. However, in the standard penetration test (SPT) and cone penetration test (CPT) of the in-situ sounding test to confirm the improvement effect, the effect of density increase has been sufficiently evaluated, but the effect of lateral stress has not been evaluated. The authors investigated the effect of the lateral stress ratio, Kc-value and presented a relationship between the normalized N-value, N1 of the standard penetration test and cyclic strength based on the results of soil chamber tests and hollow torsional shear tests under anisotropic condition of clean sand. This relationship was analyzed using the same method that led to this relationship against sands containing fines. As a result, a design chart of the ground (recommended chart), which is the relationship between the two considering the fine content, was presented.
In the conventional ground improvement method, the strength is exhibited by stirring and solidifying the solidifying material in the ground, so it is difficult to expect a strength higher than the solidifying potential of the solidifying material. In addition, because the soil is directly agitated with solidifying material in the in-situ, there is a concern that the strength may decrease due to the soil quality (physical and chemical properties) of the in-situ ground. In order to solve the above problems, the authors respected the basic principle of soil mechanics that soil becomes hard if voids between soil particles and water are eliminated. That is, the authors thought that the soil would harden by mixing particles of different sizes and compressing each other's particles with a strong force. Then, an original SST method was developed that allows the column to be constructed while compacting. The feature of the SST method is that it is possible to construct high quality columns on the ground where humus soil, that is unsuitable for applying the conventional ground improvement method, is deposited. In this study, the authors will take up two cases where the SST method is applied. As a result, it was clarified that high quality columns can be constructed by the SST method at two sites with different soil characteristics.
This study focuses on the effects of temperature on the consolidation property and consistency limit of clay for thermal improvement of soft clay ground. Although it is already known that an increase in temperature can accelerate the consolidation of clay, the degree of the temperature effect has not yet been generalised between various clays. A series of one-dimensional consolidation tests at different temperatures (17, 23, 35, 50, and 65°C) using 2 processed clays and 3 natural clayey soils dredged at ports are presented in this study. To evaluate the temperature effect on soil consistency, which might affect the consolidation behaviour, consistency limits of the clays were also evaluated at different temperatures. In addition, the effect of the difference in pore water on the consolidation properties was evaluated by a consolidation experiment using a CaCO3 solution and artificial seawater. As a result, it was confirmed that the consolidation coefficient could be estimated using the activity regardless of the type of clay. However, the influence of temperature on the consistency limit is different between general clay and swelling clay.
The confirmation of the volume of the improved body formed by chemical grouting method is usually performed using the uniaxial compressive strength. However, because the target strength of the improved body is not so high, it is difficult to evaluate the difference in strength before and after the improvement. Therefore, it is required to introduce another indicator representing the difference before and after the improvement more sensitively instead of uniaxial compressive strength. In this study, we focused on the change in resistivity before and after the improvement. In this paper, we report the results of small soil tank experiments and field demonstration experiments conducted in order to clarify the electrical resistivity characteristics of improved sand and the scope of application by the proposed method
Heavy Dynamic Cone Penetration Test (H-DCPT) was carried out to study penetration mechanism by measuring impact acceleration and force during blows of the hammer at the top and bottom of the driving rod. First, the driving efficiency was estimated from measured acceleration and force. Then, the number of blows, Nd, was corrected based on the driving efficiency and comparably studied with the conventional correction based on torque. The driving efficiency at the top of the driving rod was constantly approximately 80%, while they at the bottom of the driving rod differed in kinds of soil, almost 80% in sandy soil and ranged from 5 to 10% in clayey soil. These were concluded from measurements; the driving energy was dissipated significantly affected by skin friction of the driving rod, particularly in clayey soil. The NdE, which is the number of blows corrected by the driving efficiency at the bottom, was well agreed with the SPT-N value. However, the conventional Nd was excessive compared to the SPT-N value, particularly in clayey soil. In addition, the verticality of the driving hole was surveyed. The inclined angle of the driving hole was measured by using a cone installed 2-axis inclinometer. The measurements revealed that the driving hole was not always drilled vertically, inclined angle changed in complexity depending on kinds of soil or ground hardness, and had sometimes a sizable horizontal displacement.
A cement-based stabilizer is effective in stabilizing the peat soft ground with extremely high compressibility and low shear strength for road construction. Moreover, the stabilized peat soil is occasionally fractured and reused in embankments, depending on the construction site conditions. In such circumstances, the stabilized peat soil is subjected to stress history owing to stabilization, crushing, and reconstitution. In this study, to evaluate the implication in engineering, the fractured stabilized soil sample was used to conduct unconfined compression (UC), mercury intrusion porosimeter (MIP), and scanning electron microscope (SEM) tests to measure the strength and microscopic structural characteristics. Additionally, the peat characteristics of the stabilized fractured soil that had undergone the stress history of “stabilization, crushing, and reconstitution” were analyzed. The results indicated that the period from immediately after the stabilization treatment to crushing and reconstitution and the curing period after crushing and reconstitution influenced the unconfined compressive strength of the soil. In addition, the strength of the stabilized fractured soil was higher than that of the soil that underwent regular stabilization. The outcomes of this study are beneficial for construction sites where it is desirable to minimize the environmental impact by reducing the amount of cement-based stabilizer added or where quality control and a good workability of solidified soil are required.
Ground improvement using lime or cement is popular because of the speed, adaptability, and profitability of this method. However, pollution due to alkaline water from lime or hexavalent chromium from cement may occur as a result. To avoid these issues, some studies have been carried out in India and a few African countries on the use of molasses for the improvement of clays. The increase in mechanical strength was demonstrated using the unconfined compressive strength or California Bearing Ratio (CBR) value. However, a sufficient value for ground improvement has not been achieved yet. In the present study, acetic acid and calcium oxide were added into molasses solution to increase the mechanical properties of clay specimens. Throughout the curing period, air temperature was set at 25°C and the specimens were placed in a drying furnace. 1, 3, 7 and 28 days were chosen as the curing periods. The Brazilian test was used to obtain the tensile strength value for evaluation of the mechanical properties of the specimens. The tensile strength obtained through this procedure was twice that than from specimens with distilled water and 1.5 times that from specimens treated with a 10% molasses solution. Furthermore, the dry density achieved through this procedure was larger than that of specimens with distilled water because of the surface activity of molasses. At the same time, it was shown that the pH value of Kaolin clay treated with the solution proposed in this study is in the range of weak acidity. Therefore, the solution proposed in this study is expected not only improvement in mechanical properties of Kaolin clay but also little load to vegetation in ground improvement.