In the field of earthquake engineering, many problems have been raised in past large earthquakes, and subsequent research and technical development are being carried out. Three important problems of ground improvement raised in recent earthquakes are introduced in this paper. Since the 1995 Hyogoken-Nanbu (Kobe) Earthquake caused a very strong shake, it was necessary to consider a new design philosophy concerning liquefaction countermeasure that can withstand extremely strong shake. Therefore, not only the occurrence of liquefaction but also a new evaluation method to estimate the deformation of the structure was introduced. The 2004 Niigataken Chuetsu Earthquake caused severe damage to residential complexes developed by artificially embanking at hills and terraces. Therefore, researches on appropriate ground improvement method to prevent slide of the embankment slope began. The 2011 Great East Japan (Tohoku) Earthquake demonstrated the need for a new concept of measures to prevent liquefaction in areas encompassing houses, roads and lifelines because liquefaction occurred in many residential areas. Then a new project to improve the liquefiable soil of an entire area by lowering water table started.
In order to dispose of dredged clay effectively, it is important to plan the dredged clay disposal based on the settlement prediction in advance and to understand accurately the acceptable quantity of dredged clay in the disposal pond. However, it is still a great challenge to understand properly the consolidation characteristics of the dredged clay for the settlement prediction. The authors have already examined, in the disposal pond at Kobe airport, the settlement of the clay was calculated using the volume ratio ƒ represented uniformly by logƒ for the consolidation characteristics of clay (compressibility, permeability and consolidation velocity) by soil improvement after dredged clay was disposed of several times, and then additional dredged clay was disposed of. And the calculation was compared to the measurements of various properties, which agree well with calculation results. After the completion of the dispose of dredged clay, the supernatant in the pond was drained, and then land forming has been done. The authors performed calculations with the proposed consolidation method against the bed of dredged clay with the complex complicated disposal history. It is reported that the results agree mostly with the measured settlement, pore water pressure and the water content at the site. In addition, it is reported that residual settlement prediction is calculated including the settlement of alluvial clay bellow the dredged clay.
A deep mixing stabilization method is often adopted as soft ground measures. For the purpose of cost reduction, the economical method is suggested, such as the floating type or low improved rate type. If we build road embankment on the soft ground at a near the house, in danger of a house inclining because the ground sinks. Therefore we need the new soft ground improvement method for the subsidence and displacement depression technique of the peripheral ground. In this report, we introduce the result of the centrifuge model test. Furthermore, we report measures effect of the road embankment on the soft ground. To obtain a satisfactory sideways flow preventive effect by effectively reinforcing the banking support ground by improving soil having a low improvement rate.
Reinforcement of superstructures and substructures is being carried out for existing bridges which are judged to have low earthquake resistance. However, reinforcement techniques are not systematized because the seismic diagnosis method and required performance are not clarified for existing pile foundations. One of the reason is that no reasonable reinforcement technology under construction constraints are established. Therefore, reinforcement technology, that ensures seismic performance by improving ground around the pile, is examined for the existing pile foundation in the soft ground against large-scale earthquakes. In this paper, its seismic reinforcement effect for the existing pile foundation in extreme soft ground and liquefiable ground is shown based on representative experimental results.
Frost heave occurs in clayey soil and the coefficient of permeability increases after thawing. It has been believed that trace of ice lens in the freeze-thawed soil formed by frost heave is a major factor to the phenomena. The purpose of this study is to identify mechanism of the permeability that is increased in the freeze-thawed saturated fine-grained soil. In our previous studies, a 1-D freeze-thaw permeability test was conducted with a ramp-type freezing, which allowed the freezing front to proceed at a constant speed. The test result revealed that the permeability was affected by overburden pressure rather than cooling rate and temperature gradient. However, it was not clear whether the permeability change was caused by a disturbance of soil structure by the ice lens (IL) or other factors. In order to clarify influences of the trace of IL, a step-type freezing was carried out to form a thick IL which occurs in soil with the freezing front fixed. In addition, the permeabilities of freeze-thawed soils of IL and IL orthogonal directions were compared by a consolidation permeability test, and no difference was recognized for both directions. However, in this laboratory finding, it was pointed out that we could not ignore the influence when a test specimen was taken out of the 1-D acrylic cylinder. Therefore, a tri-axial freeze-thaw test was conducted in which a test specimen was wrapped with a soft membrane, and the test specimens of the consolidation permeability test were easily taken. The result of the freeze-thaw experiments has led us to the conclusion that there is no difference in permeability of freeze-thawed soils between ramp-type and step-type freezing. In the consolidation permeability test, the permeabilities in the IL and IL orthogonal directions were almost equal. However, the permeability on the unfrozen side in the IL orthogonal direction which was obtained from a step-type freezing was significantly greater than other freeze-thawed soils. It has been suggested that the shrinkage cracks formed by IL formation remained as traces even after thawing and might become water passageways in the case of extremely small overburden pressure.
Highly organic soil is widely distributed and deposited with large thickness at southeastern area of Suwa Lake in Nagano prefecture, where is known as one of Japan’s softest ground. The ground settlement has been accumulated more than 3 m in this area, hence exposed pile foundations can be found out everywhere the area. Also, it has been known that this area is much susceptible to earthquake shaking. Then, general site investigation tests were conducted on July 2015 at Konami in Suwa city, in order to evaluate the possibility of ground settlement in highly organic soil, and to discover the correlation between results of different sounding test. This paper presents results obtained from the borehole survey, Swedish ram sounding test and Swedish weight sounding test as well as the examination on the correlation between each sounding testing result. Further, the possibility of ground settlement of surveyed ground due to loading a new fill is considered, which was calculated based on results of laboratory physical, chemical and mechanical soil tests. As a result, we found that there is still the possibility of large ground settlement on this site.
It is well known that strength of cement-treated soil column by deep mixing method varies greatly, even at a single column, owing to the variability of in situ soil properties, the variability of mixing effectiveness and other factors. Such variability of strength should affect the overall behavior of the cement-treated soil column. This study presents the investigation on strength of cement-treated soil samples composed of various strength parts. Unconfined compression tests were conducted to reveal the strength of cement-treated soil with spatial variability. Cement-treated samples composed of two different strength parts were prepared in the tests. The experimental results showed that the strengths of the composite sample do not correspond to the mean strength of the composing parts. The different distribution of the composition causes the different unconfined compression behavior of the cement-treated soil samples, even though the mean strength of the parts composing the sample is the same. Moreover, finite element analysis was conducted to valid that the numerical analysis can describe the behavior of the composite samples. The simulation results agreed reasonably with the experimental results, indicating that the finite element analysis used in this study can appropriately describe the strength of the cement-treated soils composed of various strength parts.
The strength of cement treated soil by the Deep Mixing Method (Dry Jet Mixing Method) has increasedwith progress of the time. However, it is reported that the strength of cement treated soil surface parts has decreased according to a rate of square root of the period. Conversely, it is lack of information a long term properties of cement treated soil due to that the Deep Mixing Method of construction has been developed less than 40 years. The authors carried out the unconfined compression test, the needle penetration test, and the pH test for cement treated soil by DJM 30 years after construction. Here we report a long-term strength properties of cement treated soil and the deterioration condition of cement treated soil surface.
The method of estimating the unconfined compression strength of solid ground improved with permeation grouting was discussed in which the adsorption phenomena of powder material among grain particles was considered. A set of one dimensional permeation tests and unconfined compression tests on the hundreds specimens were conducted. The density of powder component of improved material in the soil was evaluated by solving the advection equation. The unconfined compression strength was found to be proportional to the density of powder component contained in the soil. The estimation procedure of the unconfined compression strength was proposed based on the test result. The model test using the drums and in-situ test of the grouting were conducted. The estimated unconfined compression strengths were compared with the results of these tests, and the estimation method was found to be promising.
In late years, quantity of construction by-products tends to increase in our country. Therefore, dumping restraint of construction by-products and promote those recycling are the most critical issue from a viewpoint of establishing the recycling society. In the other hand, soils generated from construction generally show strong alkalinity because cements are mixed. Thus, the cost at the time of the disposal of soils generated from construction becomes expensive, and it is thought that it has a great influence on environment when the soils is disposed by no improvement. However, it is the present conditions that technique in consideration of the influence on environment with non-appropriate processing is not established. Therefore, a vegetation is applied for an index indicating a recycling potential of soils generated from construction. This paper is inspected experimentally to the potential of soils generated from construction as a planting base by mixing neutralizing agents. It was realized that the soils generated from construction had vegetation by mixing neutralizing agents.
This paper is focused on chemical diffusion parameters of soil-bentonite mixture which is one of barrier materials commonly used for containment of ground contamination. Although vertical cutoff walls using low-permeable materials, such as soil-bentonite mixture, need to prevent mobile contaminants from migrating in the aquifer for a long period, a limited number of studies have focused on chemical diffusion through hydraulic barriers, whereas factors affecting hydraulic conductivity of barrier materials have been frequently discussed. In this study, solute transport through soil-bentonite mixtures made with a bentonite powder content of 50 kg/m3 was evaluated by a laboratory experiment using an acrylic vertical column and a one-dimensional advection-dispersion finite element analysis. Two soils having different particle size distributions were used as parent soil. By fitting experimental and numerical results regarding the chloride flux, effective diffusion coefficient, De, and effective porosity, ne, of the mixtures were determined with two significant digits. Results obtained in this study indicate that soil-bentonite mixtures made with a same bentonite powder content can have a similar De value, regardless of the type of parent soil. Another important finding is that larger total porosity of mixtures led to smaller ne value probably because powder bentonite can sufficiently hydrate and swell in macropores of the mixture with a larger total porosity; therefore, pore structure of bentonite became more dominant for that of soil-bentonite mixture.
The natural resources should be utilized effectively while circulating, and regarding targeted resources the acid sulfate soil often appearing among surplus soil and tsunami deposits is no exception. As acid sulfate soil usually contains the gypsum dihydrate which is the reaction products with sulfuric acid and carbonate mineral, ettringite crystal is produced by adding hydrated lime, and the coagulation hardening of the soil is promoted. In this study, we have investigated a relation with the strength increase and ettringite production on acid sulfate soil treated using only hydrated lime and the stabilizers which include an iron oxide in raw materials through the unconfined compression test, X-ray diffraction analysis and differential thermal analysis. The iron oxide is a residue deriving from the rare earth magnet grinding waste. We have mixed unslaked lime, calcium carbonate, granulated blast-furnace slag fine powder and anhydrous gypsum fine powder into the wet or dry iron oxide under a certain proportion and have called such stabilizers the iron oxide-lime based materials. Additive contents of hydrated lime and iron oxide-lime based materials were 6 to 10 percent for dry mass of acid sulfate soil. The specimens were cured in an incubator regulated to a temperature of 20 degrees Celsius for up to 360 days. From a result of the unconfined compression test and thermogravimetry, it was ascertained that not only the strength increase but also the ettringite production rose with additive contents provided the strength increase was more than 0.5MN/m2.
Development of low-cost and environmentally-friendly techniques to treat construction wastes containing toxic substances is one of the crucial issues in construction projects. A mechano-chemical treatment technology for construction waste containing non-scattering asbestos, such as cement-asbestos slate boards, has been developed recently. This treatment process discharges high water content sludge, which is composed of fine-grained waste slate, as a residue, since slate boards are crushed and ground into fine particles under a wet condition to enhance the reactivity between a treatment agent and asbestos. Recycling this high water content residual sludge is a challenging issue to improve the environmental suitability of this treatment technology. In this study, applicability of two cement treatment techniques (i.e. granulation and liquefied stabilization) was investigated for recycling this sludge in geotechnical applications. Granulated sludge was accepted for geotechnical utilization in regards to its mechanical properties. For liquefied stabilization, workability, bleeding, unconfined compression strength and consolidation characteristics were evaluated for the sludge treated with various water-cement (W/C) ratios. Testing results indicated that these characteristics of the liquefied stabilized sludge were consistent with those of typical high water content cement-stabilized soil, and W/C is a fundamental parameter for the compressive strength.
To investigate the monotonic and cyclic shear characteristic of the tire chips and the tire chips-sand mixture, a series of monotonic and cyclic triaxial tests were performed under CD and CU conditions using the three kinds of tire chips. From the results of monotonic triaxial tests, in spite of the different particle size of the tire chips, the deviator stress showed linear behaviour with loading up to 20 % axial strain. And during unloading, a hysteresis curve was drawn and some residual plastic strain was induced. The volumetric strain showed a contract trend during loading, and it was restored after unloading tests. The strength of sand mixture was smaller than that of the pure sand, and drastic decrease in strength appeared when the tire chips fraction is more than 0.5. From undrained cyclic triaxial tests, in the case of a tire chips fraction of 0 and 0.3, the material shows almost liquefaction at the final stage of the cyclic loading, whereas in mixtures with tire chips fraction of more than 0.5, no liquefaction occurred.
The method proposed here attempts to modify consolidation characteristics of cohesive soils by chemical action at the interface between soil particles and pore water. In this paper, a series of laboratory experiments was carried out using dredged clay with dispersing agents to evaluate the potential as a volume reduction technique. The experimental work shows that (1) liquid limit wL of the modified soil falls by up to 15% compared to wL of the original soil; (2) ƒ - logp curves of the modified soil are plotted below ƒ - logp curves of the original soils, which means the volume of the modified soil is smaller than the original soils under the same overburden pressure; (3) volume ratio ƒ at the consolidation yield stress pc decreases by 4.7~6.7%. In addition, a trial calculation was carried out based on one-dimensional consolidation theory to simulate the amount and the process of settlement at a hypothetical disposal site. The calculation indicates the volume of the modified soil is reduced compared with the original soil, and therefore the work life of the disposal site becomes longer.
We have developed a method for making effective use of unused small-diameter thinned wood as a ground reinforcement material for small buildings. The results of evaluations including materials testing of the reinforcement material, full-scale plate load testing of the reinforced ground, and static axial compressive load testing of the standalone reinforcement material showed that: (1) the reinforcement material had sufficient strength to support the building load, (2) settlement of the reinforced ground was reduced, and the reinforcement material was effective in controlling differential settlement of the building, (3) the reinforcement material was able to secure the allowable ground bearing capacity required for small buildings (30-50 kN/m2). This method reinforces the ground to a depth of 2 m below the foundation (reinforcement material length: 2 m), which is considered to be the most important part of the foundation ground for small buildings, and allows the foundation ground to be designed as composite ground.
Jet grouting is a technique for ground improvement which employs high pressure cement slurry and high pressure air. This technique has been applied in various types of work, such as excavation support and the protection of departure and arrival shafts in tunnels. However, after the 2011 Great East Japan Earthquake, applications for liquefaction mitigation through a lattice- or wall-form arrangement of columns have increased. Until now, the lattice- and wall-form improvements were constructed with round columns generated by jet grouting. Because the columns were round, more soil was improved than what was actually required. Therefore, round column are not acceptable with respect to cost and environmental factors. Consequently, the MultiFan jet grouting method of ground improvement was developed in order to reduce the amount of redundantly improved soil. This method is comprised of partially formed, fan-shaped columns. In this paper, we geometrically examined the effectiveness of the MultiFan shape column for lattice- or wall-form ground improvements. The effectiveness of the MultiFan column was verified by comparing it with round and oval columns. Consequently, when the wall-form improvements were constructed, the MultiFan and oval columns demonstrated a smaller value of redundantly improved soil body than the round columns. On the other hand, when the same thickness of wall-form ground improvement was constructed, the spacing of each oval column was less than that of the MultiFan and round columns. In other words, more oval columns were required than the MultiFan or round columns. This revealed that improvement work could be carried out more effectively with MultiFan columns than with oval or round columns. Furthermore, we developed new equipment for this work, and carried out field tests to confirm its workability. Consequently, we were able to confirm our assumption that it is possible to construct the MultiFan shape columns for ground improvement work.
Many tide breakwaters had been damaged by the impact of a tsunami that occurred due to the Great Tohoku Earthquake in 2011. As a restoration works, a tide breakwater with the length of about 800m and the height of T.P. +14.5m is being constructed in the coast of Katagishi in Iwate prefecture. In which, a special deep-mixing method with large diameter and great depth (DCS method) was applied to the ground that is sandwiched by hard soil layers in order to construct foundation of the tide breakwater. In addition, a real-time contrition management and work completion progress/quality control system is introduced in this paper. As examples of the result obtained in this paper, it was confirmed that the deep-mixing method with the diameter of φ = 2.0 m and the depth of 33.6 m can be performed by applying the DCS method. The introduction of the real-time construction management and work completion progress/quality control system enabled it to ensure shape and quality of improved soil with high accuracy and it was confirmed that information sharing is promptly possible.
In the press and injection hybrid molding of GFRTP, short or long fiber reinforced thermoplastics or thermoplastics are injected on the continuous fiber reinforced thermoplastics, which allows us to obtain light weight structures with excellent strength and stiffness. In previous studies, it has been reported that the interfacial bonding strength between laminates and ribs was improved by supplying fiber of laminates to the interface. Although the interfacial bonding strength of the hybrid molded product was improved, its fracture occurred at the injected material or the interface between laminates and ribs. In the case of the fracture at the injected material, it is expected to improve the interfacial bonding strength by using fiber reinforced thermoplastic with higher mechanical properties as injection material. For the injection molding, forming a V-shaped interface by moving the melted resin was reported to improve the weld strength. This technique can be applied to the press and injection hybrid molding and may improve the interfacial bonding strength. In this study, GFRTP were molded by press and injection hybrid molding under different injection volumes using PP and the short glass fiber reinforced thermoplastics and the effect of injection material and injection volumes on the interfacial bonding strength was clarified by the tensile tests using T-shaped specimens cut out from the molded products. When larger volume of the short fiber reinforced thermoplastics was injected, fracture occurred mostly at the injected material and higher interfacial bonding strength was obtained.
In the press and injection hybrid molding of CFRTP, short or long fiber-reinforced thermoplastics are injected on the continuous fiber-reinforced thermoplastics that are used for the outer shell material. In a previous study, the interfacial bonding strengths between the injection material and the continuous fiber-reinforced thermoplastics were evaluated; it has been reported that the interfacial bonding strength was improved by inflowing the continuous fiber into the rib structure, however, the strength of the outer shell laminate was lowered due to the waviness of the continuous fiber that was inflowing into the rib structure. In the paper-type intermediate materials, reinforcing fibers and matrix resin fibers are dispersed by the paper-making method. By supplying the paper-type intermediate material into the interface between the injection material and the continuous fiber-reinforced thermoplastics, the paper-type intermediate material comes to inflow into the rib structure; and the improvement in the interfacial bonding strength, and the reduction of the waviness of the continuous fiber can be expected. In this study, to clarify the effects of the quantity of the paper-type intermediate material on the mechanical properties of the press and injection hybrid molded CF/PA6, T-shape tensile tests for interfacial bonding strength, and in-plane tensile tests for the strength of the outer shell laminate were conducted. Supplying the paper-type intermediate material into the interface between the injection material and the continuous fiber-reinforced thermoplastics resulted in higher interfacial bonding strength and higher tensile strength of the outer shell laminate due to smaller waviness of the continuous fiber.
Post-installed anchors are used in many existing concrete structures to construct additional members. The purpose of this study is to investigate the pull-out behavior of a post-installed adhesive anchor under pull-out load. The post-installed adhesive anchor, which is employed with the epoxy resin to obtain the chemical bonding, has been newly developed. In this study, the single adhesive anchor was installed into concrete which was cast in steel pipes and into concrete slabs. The test parameters were the embedment length and concrete strength. From the results of the pull-out test, the bond strength related to the concrete strength without the embedment length. As the mechanical and chemical resistances of the adhesive anchor, the bond strength was highly obtained in comparison with the common adhesive anchors. Furthermore, the pull-out and torque tests were carried out on concrete slabs. From the test results, the ultimate tensile load linearly related to the torque. This relation can be employed for the inspection of the post-installed adhesive anchor after construction.