A performance-based design concept has recently been employed to ground structures in Japan. Reliability analysis method is one of the most compatible approaches to a performance-based design. It is widely known that reliability analysis has three methods: Level-I, Level-II, Level-III. These three methods are based on failure probability, but it is difficult to decide a criterion of failure probability and the probability distribution of input parameters should be assumed. In this study, we suggested a framework of reliability based design of ground improvement from "robust control approach", which is able to solve these problems. It is realized that this design method enables an owner to decide the specifications of ground improvement rationally.
In order to simulate aging effect on the relationship between penetration resistance qt and liquefaction strength RL in a short time, miniature cone penetration tests and subsequent cyclic triaxial tests are carried out in sand specimens containing fines added with a small amount of cement to make an accelerated test. In contrast to a unique cone resistance (qt) versus liquefaction strength (RL) relationship for specimens without cement despite large difference in relative density and fines content, higher fines content results in higher liquefaction strength for the same cone resistance for sand with cement, which is consistent with the trend found in the field investigation. Thus, it is revealed that the reason why higher fines content leads to higher liquefaction strength does not depend on fines content itself but aging (bonding) effect by fines, which tends to be pronounced as fines increase.
Bentonite mixed soil is commonly used as soil liner in landfill. In this paper, a simple method that can determine the critical content of the bentonite is presented. The critical content of the bentonite is defined as the ratio over which addition dose not contribute to decrease the permeability considerably. For this, a concept of macro void ratio that consider the particle pore and swelling ratio of bentonite is described. Then the calculated critical content of the bentonite for four parent soils with different amount of particle pore are compared with the measured critical content of the bentonite from permeability tests. As the results, it is found that the calculated critical contents of the bentonite are well coincident with the measured ones. In the paper, the reason why the value of macro void ratio shows negative for bentonite addition beyond critical content is also discussed based on the results of water absorption tests for compacted bentonite mixed soil.
Both of NATM and shield tunnelling method can be applied to Diluvial and Neogene deposit, on which mega cities are located in Japan. Since the lining design method for both tunnelling methods are much different, the unified concept for tunnel lining design is expected. Therefore, in this research, a frame structure analysis model for tunnel lining design using the ground reaction curve was developed, which can take into account the earth pressure due to excavated surface displacement to active side including the effect of ground self-stabilization, and the excavated surface displacement before lining installation. Based on the developed model, a parameter study was carried out taking coefficient of subgrade reaction and grouting rate as a parameter, and the measured earth pressure acting on the lining at the site was compared with the calculated one by the developed model and the conventional model. As a result, it was confirmed that the developed model can represent earth pressure acting on the lining, lining displacement, and lining sectional force at ground ranging from soft ground to stiff ground.
In order to introduce the performance based design of pile foundation, vertical stiffness of pile is one of the important design factors. Although it had been es timated the vertical stiffness of pile had the displacement-level dependency, it had been not clarified. We compared the vertical stiffness of pile measured by two loading conditions at pile foundation of the railway viaduct. Firstly, we measured the vertical stiffness at static loading test under construction of the viaduct. Secondly, we measured the vertical stiffness at the time of train passing. So, we recognized that the extrapolation of the displacement level dependency in static loading test could evaluate the vertical stiffness of pile during train passing.
This paper investigates a method for ob taining the probable freezing index for n -years from past frostaction damage and meteorological data. From investigati on of Japanese cold winter data from the areas of Hokkaido, Tohoku and south of Tohoku, it was found that the extent of cold winter had regularity by location south or north. Also, after obtaining return periods of cold winters by area, obvious regional characteristics were found. Mild winters are rare in Hokkaido. However, it was clarified that when Hokkaido had cold winters, its size increased. It wa s effective to determine the probable freezing indices as 20-, 15- and 10-year return periods for Hokkaido, Tohoku and south of Tohoku, respectively.
The purpose of this paper is firstly to simulate the tunnel face failure in laboratory with four cases of model tests by pulling out tunnel model from a sandy ground that are without using auxiliary method nor facebolts and using facebolts with three different lengths of bolts, and secondary, to investigate the behavior of model ground using X-ray computed tomography (CT) scanner to visualize the failure zone in three dimensions. In addition to those results, a series of centrifuge model tests are conducted to confirm the results of X-ray CT test and also to discuss the ground behavior under full scale stress level. Finally, the effect of face bolting method is evaluated based on all the test results.
This paper presents a probabilistic method for assessi ng the liquefaction risk of cement-treated ground, which is an anti-liquefaction ground improved by cemen t-mixing. In this study, the liquefaction potential of cement-treated ground is analyzed statistically using Monte Carlo Simulation based on the nonlinear earthquake response analysis consid ering the spatial variability of so il properties. The seismic bearing capacity of partially liquefied ground is analyzed in order to estimat e damage costs induced by partial liquefaction. Finally, the annual li quefaction risk is calcu lated by multiplying the liquefaction potential with the damage costs. The results indicated that the proposed new method enables to evaluate the probability of liquefaction, to estimate the damage costs using the hazard curv e, fragility curve induced by liquefaction, and liq uefaction risk curve.
The effect of partial soil improvement by the Chemical Grouting Method (called as CGM) is investigated for liquefiable runway ground in this paper. Especially, the partial soil improvement by CGM is proposed as a countermeasure against lateral flow of liquefiable runway ground. The effect of the countermeasure is verified by the laboratory experiment, in which the behavior of lateral flow is simply assumed as a static sliding problem, under 1G gravitation condition. In addition, a parametric study conducted for a model runway ground in numerical analysis. As a result of analytical examination, it is clarified that the inclination of pavement side have significant influence on occurrence of lateral flow. Moreover, the lateral flow can be mostly restrained using partial soil improvement, and it can be prevented completely by making on the both ends of an improvement layer to non-liquefiable layer.
From the results of site observations, granulated bl ast furnace slug (GBFS) is solidifying w ith time. It takes a long time to solidify the whole of GBFS, b ecause GBFS observed was no t fully solidified in 18 months. It means if GBFS is used with relied on its solidification, a treatment for acceleratin g the solidification of GBFS is needed. For discus sing this point, the condition for solidifying GB FS is checked in series of laboratory experiments. It was clarified that adding micro powder of furnace slag to GBFS is effective for accelerating the solidification of GBFS unde r sea water. Failure crite ria of solidified GBFS are explained with internal friction a ngle and cohesion intercept. Failure criteria for residual condition of GBFS are explained by internal friction angle only. These parameters can be estimated from a single triaxial experiment.
Slope failure resulting from heavy rainfall on rail road lines is a common occurrence, making it essential to minimize the phenomenon in the interests of maintaining safe, punctual train operation. It is also necessary to evaluate disaster risk of individual slopes by considering the probability and potential cost of rainfall-related slope failure. We developed a method to evaluate disaster risk for slope failure using a risk estimation technique. This paper describes this developed method, and the method of priority determination for investment to prevent slope failure caused by intense rainfall using this developed technique.
In this paper, we conducted a centrifuge model test on earthquake-induced rock slope failure, and the test results were compared with safety factors (SF) of the sliding surface obtained by the limit equilibrium method, where the stresses on the sliding surface were estimated by the equivalent linear analysis. A dip slope model for the centrifuge model test was made from cement, sand, iron powder and water, and discontinuities were imitated by Teflon sheets. In the test, the centrifugal acceleration was 30G, and the acceleration amplitudes of input sin waves were increased gradually at every step. As a result, the slope model collapsed when it was excited by the sine wave of 3.5m/s2, which was converted to real field scale. The artificial discontinuities considerably affected the collapse, and the type of collapse was plane failure. And moreover the trends of the computed SF showed that the threshold amplitude of the failure was lower than the actual amplitude that induced the failure, implying that the computed SF was conservative.
Design method for reinforced chain wall has been de veloped even though the mechanisms that generate pullout force of chain are not clear. In order to evaluate the pullout mechanism, a series of pullout test were conducted on chains of varied configurations. Assuming that the total pullout resistance consists of three components which are bearing resist ance, shearing resistance of the tr apped soil inside each loop and the frictional resistance between the chain and soil, test results showed that the bearing resistance accounts for about 90 % of the total resistance. In addition it was found that the shearing resist ance of the soil enclosed in the inside loop is too small and therefore can be neglected when computing the pullout force of steel chain.