The maximum feature of the Holocene clay deposited in the eastern Osaka area is that the sensitivity is very high. In this paper, firstly the geotechnical characteristics and the regional differences of this clay are discussed by using “Kansai Geotechnical Information Database” and standard borings having detailed soil testing data due to continuous undisturbed samples. This sensitive clay is distributed in the former river channel, and it has been understood to adjust well with the distribution region of N-value (SPT) ≒ 0. Next, the cause of sensitivity is reconsidered from the aspect of the depositional environment. The formation of sensitive clay is thought to be due to not only leaching of the salinity but also low activity of benthos. So, these are thought to be caused by the depositional environment under the brackish water located the closed-off section of bay.
The role of an airport during and after a great earthquake is important because of its helpful function for emergency medical services and special activities of the transport of relief supplies to the disaster areas. In this study, the authors conducted a full-scale field experiment on liquefaction phenomena induced artificially by controlled-blast technique in the experimental site at the Ishikari Bay New Port in Hokkaido Island, in order to investigate the influence of a great earthquake on the airport's function in Japan. This experiment especially focused on the assessment of the performance of runway pavement and the effect of densification method as countermeasure for liquefaction with a cost-reduction design. This study concludes that densification method examined with cost-reduction design in this experiment keeps its effectiveness based on results of measurements of liquefaction behavior of liquefied layer and runway pavement, ground investigations after liquefaction and liquefaction-induced residual deformation analysis.
As a liquefaction countermeasure technique, lattice-type deep-mixing method restrains shear deformations of the ground induced by earthquakes and therefore is effective in controlling the generation of excess pore water pressure. In a full-scale liquefaction experiment, ground improvement by lattice-type deep mixing method was implemented in Ishikari Bay New Port where the lattice was formed by X-jet (cross jet) method which is a high-pressure jet-type deep mixing method. The effectiveness of the method as liquefaction countermeasure was confirmed from the excess pore water pressure that was generated by blast-induced shaking and the workability of the method was examined. This report focused on the data acquired from the field test, such as the excess pore water pressure generated during the earthquake, and the controlling effect on the post-earthquake subsidence at the site. Moreover, FEM analysis and simplified analysis were conducted to reproduce the above behavior. As the result of this study, it is confirmed that the lattice-type deep-mixing method using X-jet method is very effective as a liquefaction countermeasure technique.
The volume of waste tires is increasing every year and it has become a major environmental problem. In the use as a heat source which is the mainstream of recycling, there are problems, such as waste of rubber resources and generating of carbon dioxide. Therefore, increasing attention has been paid in recent years on the technology of using scrap tire derived recycled products (tire shreds and tire chips) in construction. With characteristics such as lightweight, compressible, permeable, durable and thermally insulating, this material has a myriad of applications in civil engineering. This research attempts to exploit the potentials of tire chips as a tool to attenuate the earthquake loading propagating through the foundation soils. Online testing is a method of feeding soil response characteristics directly from soil samples into a modeling algorithm. The effects of the layer thickness of tire chips, configuration and degree of mixing between tire chips and sand on the earthquake characteristics of alternating layers of sand and tire chips have been investigated. As a result, it was confirmed that tire chip layers attenuate the motions of sand layers for short period vibrations increasing strain in overlying sand layers. Moreover, tire chip layers which were closer to the bottom or greater thickness tended to decrease the surface accelerations.
As a foundation engineering technique to deal with soft ground, a rational design method involving the formation of composite ground around piles (mainly using the deep mixing method) and reflecting the increased shear strength as the horizontal resistance of piles was studied and developed. The result of combining piles and composite ground is referred to as the composite ground pile foundation. The scope of improvement for composite ground around piles is set as a range raised to the working gradient of passive earth pressure from a characteristic length of 1/β according to engineering theory. The horizontal resistance of piles is designed by converting the shear strength of composite ground into the modulus of deformation and using the elastic subgrade reaction method. The validity of the design method was confirmed empirically through an on-site horizontal loading test using actual piles. In addition, the dynamic mechanical behavior of piles and composite ground with this method in response to large-scale earthquake motion was verified through a centrifugal excitation test. The results confirmed that piles and composite ground maintained their soundness and displayed the required subgrade reaction under earthquake conditions. Dynamic nonlinear finite element analysis was also conducted on an actual site with this method as a model to confirm that pile displacement and strain were controlled and that the seismic performance of the foundation was improved by forming composite ground around piles. As it was possible to summarize basic data on the validity of this method, plans are now under way to develop guidelines for its effective use on actual sites.
This paper describes the outline newly developed mixing machine which is equipped with a cortra-rotational mixing head. The machine is a sort of the deep mixing stabilization apparatus. That is mixing head of this machine consists of a pair of basket -like mixing wings and a flat excavating & mixing head located at the end of rotary shaft. Outer and inner wings have the same shape, but those diameters are different. The diameter of former wing is Dmax = 2.5m and it has 4 small blades inside of wing. According to the inspection of the mixed situation with the three-dimensional motion in the model ground, it is ascertained that the kneading effect of the contra-rotational mixing head is so much higher in terms of mixing quality than the flat blades mixing head. The upper and lower mixing blade were connected mutually and formed the rigid basket-like mixing wing. It is remarkably proved that the contra-rotational mixing head with high rotary torque could install to the hard sandy soil layer of N = 30∼50. In case of ground PC piles were pre-installed beforehand, it was also proved that the contra-rotational mixing head can install to the ground with obstacle such as PC piles. Existing PC piles were crushed to a large number of pieces and homogeneously-premixed. As results of the investigation in actual work in several sites with existing PC piles, it was also ascertained that the coefficient of variation of the unconfined compressive strength of stabilized soil cement columns by the contra-rotational mixing head is smaller than that by flat blade mixing head.
A combined technology of shallow stabilization and floating-type deep mixing wall has been developed as method with acceptable settlement for maintaining the function of the high standard roads or high embankments on soft ground. As for this method, shallow stabilized ground has relatively low bending strength and shows very brittle behavior. Therefore it is important to evaluate bending stress acting on the shallow stabilized ground in considering distribution of subgrade reaction from deep soil stabilization portion. In this paper, at first, in order to evaluate bending stress of shallow stabilized ground with floating type deep mixing wall under uniform vertical stress conditions, bending stress model is proposed based on the idea of stress distribution ratio in relation to the skin friction applied around the surface of the deep mixing wall. In order to confirm the validity of this proposed model, loading model test of the improved ground was performed using loading device for applying uniform vertical stress corresponding embankment load. Finally, the validity of the calculated values obtained from this proposed model was confirmed from the results of full scale analysis.
Cement-mixing method is gaining popularity as a method for stabilizing soft soils in applications ranging from the improvement of foundation properties to mitigation of liquefaction. However, spatial variability in the shear strength of the cement-treated ground introduces uncertainties in estimating the bearing capacity for design. This paper presents a reliability assessment for the bearing capacity of cement-treated ground based on the results of a probabilistic study in which the shear strength of the cement-treated ground is represented as a random field in Monte Carlo simulations of undrained stability for a surface foundation using numerical limit analyses. A statistical interpretation of the bearing capacity is based on Monte-Carlo simulations using the Random Field Numerical Limit Analyses. The results show how the bearing capacity is related to the coefficient of variation and correlation length scale in the shear strength of cement-treated ground. Based on the result, an overdesign factor and percent defective for the bearing capacity are proposed to obtain a target probability of failure.
At the moment, there are 210,000 reservoirs in Japan, and 70% of them have already aged more than 100years. Consequently, it becomes serious problems such as the decline of usable capacity due to deterioration, declining quality of reservoir water, and alluvial bottom sludge. Therefore, it is imperative that the improvement of reservoirs. Especially, bottom sludge is difficult to transport to outside of reservoir because it has high water content and high organic matter. Since it becomes difficult to secure the landfill recently. Bottom sludge is really required to utilize effectively on site. In this research, ancillary material is utilized to decrease water content from bottom sludge and the development of repairing material for embankment has attempted. In this research, blast-furnace type B and stabilized soil with cements which is effective to the highly organic soft clay were utilized as a solidification material. Then, plaster powder (milled plaster board), paper sludge ash and bamboo powder (milled bamboo) were used as an ancillary material. In order to develop a new repairing material for embankment, unconfined compression test and cone index test were carried out. As a result, it was revealed that the additive rate of solidification material for required strength could be decreased effectively by using above-mentioned ancillary materials.
Though the sediments dredged from floors of lakes and ports are beneficial earth materials, the utilization is still stagnant due to continuing restraint of construction investment. On the one hand, plasterboard wastes occurring abundantly with the renovation and demolition works of building are recently bringing the stringency of a residual capacity at controlled type landfill site. In the present study, we have investigated the California bearing ratio (hereinafter referred to as “CBR”), unconfined compressive strength, resilient modulus and constant pressure shear strength after having stabilized the base material which was composed of lake mud, sea sand and waste plasterboard powder with equivalent quantities in dry mass. According to the results obtained from CBR-test and unconfined compression test, the mixing of a waste plasterboard powder reduced apparent water content in base material, and as an effect by this, the hardening progress with the passage of time certainly exceeded a difference of the stabilizer amount added. Successively, having examined the resilient moduli concerning mixtures with a material age of 28days, it was found that these values were equal to or greater than the existing granular base course materials. Secondly, we have examined relation between shearing stress and displacement for specimens (a diameter of 100mm and a height of 50mm) which were made by wrapping the stabilized base material in geotextile and have compared the strength parameter to specimens without covering. As a consequence, it was ascertained that the angle of shear resistance in specimens with geotextile became 10 to 25degrees larger than that in specimens without covering and that meanwhile the cohesion generally tended to become largish in the latter.
Short Fiber-reinforced soil is effective in enhancing strength, toughness and erosion resistance to rain and water currents. To bring such effectiveness to its full extent, it is important to disperse the bundled Fibers uniformly in the soil. In the conventional method, however, the technology of disentangling and dispersing the bundled Fibers has not yet been fully established. This study report refers to discussions on how to disentangle and disperse the bundled Fibers using the rotary crushing and mixing (Twister) method that does crushing and mixture at the same time and also refers to confirmation regarding the enhanced strength and toughness of the relevant short Fiber-reinforced soil when mixed with cement. Consequently, it has been confirmed that the bundled Fibers, if combined with gravel, make it possible to uniformly mix with other soil materials through disentanglement and dispersion and that the strength and toughness of the relevant short Fiber-reinforced soil mixed with cement are better in mechanical characteristics than those of other improved soil not mixed with short Fibers. The mechanical characteristic of the short Fiber-reinforced soil when mixed with cement will be investigated in the future. And, the erosion resistances etc. are scheduled to examine it.
Recently, light weight soil made of dredged slurry with cement and air foam has been used for waterfront constructions. The characteristics of this material can be influenced by seawater when it is used in coastal areas. There is a risk that some air in the light weight soil may be replaced with water over time. These phenomena are affected by the absorption properties of the material. The purpose of this study is to evaluate absorption properties of light weight soil with air foam due to different mixing condition using an industrial X-ray CT scanner. In this paper, a series of absorption tests were conducted for specimens of 24 mixing conditions which were different quantity ratios of cement, water and air foam. And then, the CT scanning was also examined the process of absorption test for all specimens. Here, the density distribution change and water absorbed zones of the specimens were estimated by an X-ray CT data. And the absorption expansion velocities during absorption test of all specimens were obtained. According to these results, the effect of the mixing condition on the characteristics of absorption of light weight soil was evaluated. Especially, the absorption velocity of the light weight soil with air foam was influenced by the quantity ratios of cement and air foam.
This paper shows impermeable properties of H-jointed steel pipe sheet piles (SPSPs) with H-H joints under soil coexistence on impermeable walls used in coastal landfills. The authors have developed a number of technologies such as developing the H-jointed SPSPs and H-H joints for SPSP joint sections aimed at improving performance and widening application areas of SPSPs. Equivalent hydraulic conductivity of the H-jointed SPSPs with H-H joints under several soil coexistences was evaluated by experimental studies and it was clarified experimentally that H-jointed SPSPs with H-H joints can demonstrate the equivalent hydraulic conductivity of the 1 × 10-8cm/s order. This is because the coexistence soil particles are covered by the swelling of swellable waterproof materials inside the H-H joints.
This study aimed to investigate the effective area where the air saturation and the dissolved oxygen concentration after air sparging can be enhanced using electrical resistivity tomography (ERT). Two soil tank tests were conducted. One was that air was injected to fresh soil model saturated with tap water, and this was control for the other test. The other was that air was injected to oil-contaminated soil model saturated with bacterial solution. Air was directly injected into each model for an hour, then the change of the air saturation and dissolved oxygen in the soil after that was measured. The air saturation after air sparging was related to the dissolved oxygen concentration. In conclusion, the air saturation distribution evaluated by ERT was an effective information to estimate the effective area where the dissolved oxygen concentration is enhanced after air sparging.
Containment with soil-bentonite (SB) cutoff walls has been proved to be a valid method to prevent the contaminants in subsurface from migrating in the aquifer. Previous researches by the authors concluded that SB was able to maintain its hydraulic barrier performance even when exposed to various types and concentrations of chemicals (calcium chloride, heavy fuel oil, ethanol, and/or seawater) in the permeant and/or in the pore water of original soil, if a certain degree of bentonite hydration was expected to occur by the first wetting liquid. However, SB is a rather flexible material compared with other typical barrier materials. Thus, static/dynamic stability is another important issue. In this study, centrifuge model tests were performed to evaluate the seismic performance of the vertical SB cutoff wall, which is usually installed in a permeable aquifer with liquefaction potential during the earthquake. In addition, the deformation property of the SB against dynamic loading was examined by conducting the conventional cyclic triaxial test. SB maintained its elasticity until the axial strain reached 1%, and then the SB was subjected to large plastic deformation (5% in axial strain) against the cyclic loading. In centrifuge model tests, although vertical settlement of the SB cutoff wall in liquefied ground reached 300 to 400mm in prototype scale even against the earthquake with only 200gal in acceleration but relatively longer duration, its integrity was maintained for a range of earthquake motion applied in this study (max. 500gal in acceleration or 60second in duration).