This paper presents an experimental program to investigate the amplitude of the effect of pile compressibility on the reduction of frictional capacity between downward- and uplift- loading of a single bored pile in sand. For this task, model pipe piles made of three different materials were used in gravity field and in centrifuge apparatus. The amplitude of the reduction was evaluated according to the compressibility parameter η defined by De Nicola and Randolph. The ratio of uplift friction resistance to downward friction resistance reached an asymptotic value as η increases. The experimental curve of the reduction of frictional capacity and η has been found to be different from the analytical one.

View full abstract

This paper proposes a back analysis method of measured displacements for predicting deformational behavior of discontinuous rock mass. The method is formulated by the adaptive filtering combined with the Backward Discontinuous Deformation Analysis formula proposed by Shi. It can estimate the present deformational behavior of discontinuous rock mass and also predict the final behavior of rock mass from measured displacements. Geometrical conditions of discontinuous rock mass, i. e. location and direction of discontinuities, are required in the method, but any mechanical constants of rock mass are not needed. In order to verify the proposed method, numerical simulations are conducted.

View full abstract

Rock mass contains many discontinuities such as joints and faults. In this paper, the effectiveness of FESM, which is an analysis method of discontinuous medium considering elemental deformations and also slips and openings at interface boundaries, was verified by means of the stress transfer in a photo-elastic experiment of discontinuous rock mass models, and by means of the deformation and fracture strength in bi-axial compressive tests of plaster samples including joints. This paper clarifies that the use of a equivalent rigidity for interface boundaries results in highly precise solutions for an analysis using polygonal shaped elements.

View full abstract

As an analytical method to solve the mechanical behavior of jointed rock mass, a micromechanics-based continuum model of rock mass (MBC model) is proposed by H. Yoshida and H. Horii. The distinctive features of the MBC model are the followings: it can grasp the behaviors of joint; the informations on dominant joint sets such as strike and dip are employed as direct input data for the analysis; the opening and sliding displacement across joints are obtained as numerical results. To examine the performance of the proposed method, the excavation of the Okawachi power station cavern constructed by The Kansai Electric Power Co., Ltd. is analyzed and results are compared with measurement data in the present study.

View full abstract

The settlement of the oil storage tank during liquefaction, is the most serious problem for the engineers and company owners. In this paper, one of liquefaction-resistant methods which constrain the soil under the oil tank by a sheet pile wall is used. Some series of model tests using centrifuge are carried out to evaluate the liquefaction-resistant method from a settlement point of view. The effects of the sheet pile wall and mass of an oil tank are tested, respectively. The results show that the settlements of the oil tank depend on the mass of the oil tank, and on the type of sheet pile wall, and also show that the closed type wall is more useful against liquefaction than the open type wall.

View full abstract

To estimate the bearing capacity of the piles during driving, both of the dynamic resistance of the soil against penetration of the pile and the setup factors of the each soils should be determined. In this paper, the method to measure the dynamic resistance of the ground working along the pile shaft and beneath the pile base based on the stress wave theory and so callled re-driving method to determine the setup foctors of soil layers are presented. And the fact that the estimated bearing capacity of the test pile from the dynamic measurement and it determinted by the static loading test are very close is shown in this paper.

View full abstract

The freeze-closure phenomenon, under the ground water flowing the space between thickly formed frozen walls, is studied and the formula, represented frozen soil rate, is conducted.
The closure condition of each frozen wall is clarified by numerical analysis.
The existence of two equilibrium frozen fronts is indicated if the freeze-closure condition is not satisfied.
An example of this theory applied to real work is showed in this paper.

View full abstract

The two-dimensional laboratory tests have been studied and have obtained the useful data to design the tunnel construction methods. This paper introduce the both two and three dimensional laboratory tests by using X-ray Radiography method under the condition of small strain and tunnel face supporting pressure control tests. From the experiments, the supporting pressure required to maintain the tunnel face is approx. 20% compare with the value which is obtained Terzaghi theory. And, the supporting pressure of both the bench and the cross section heading model is approx. half value of full section model. X-ray radiography method is useful to clear the behavior around the tunnel face.

View full abstract

To use effectively soft clays in construction works with high water content, a way which estimates the degree of strength increasing is suggested. As a strength of improved soft clays with pozzolanic materials depends on kinds of pozzolanic materials, to estimate the characteristic of strength increasing due to chemical reaction of silica and alumina which are chemical component of pozzolanic materials was tried. As a result, it is found that strength increasing can be expressed by the amount of (silica+alumina). Further, it is pointed out clearly that a degree of pozzolanic reaction and a improved strength differs from the amount of chemical component.

View full abstract

The paper reports the results of centrifuge shaking table tests to study the stability of embankment on liquefiable sand layers during the earthquakes. On basis of the results of 1/37.5 and 1/50 scaled models, the residual deformation of embankments subjected to both sinusoidal wave and earthquake motion was studied. The conclusions obtained from this study are as follows: (1) The residual deformations of different scaled model converted to prototype scale were well consistent. (2) Liquefaction of base ground considerably affected the stability of embankments. The soil mass enclosed by the circular arc did not behave like a rigid body, but like a flow type failure. (3) A method of circular arc analysis taking into account the seismic force and the excess pore pressure gave a reasonable explanation of the test results.

View full abstract

Resistivity-based high-density prospecting methods have recently increased to be applied to tunnel, landslide and other ground investigations. Therefore, it is essential to establish the rock classification technique by resistivity-based high-density prospecting data. In this paper, the authors try to propose a tunnel rock classification technique, in which the converted seismic wave velocity based on resistivity-based high-density prospecting data can be used for classifying tunnel rock mass. Furthermore, the applicability of the proposed tunnel rock classification technique is discussed, by comparing estimated support patterns with actually performed ones.

View full abstract

Various cyclic plasticity models have been proposed in the past. Among them only the subloading surface model fulfills the continuity condition, the smoothness condition and the work rate stiffness relaxation, obeying the associated flow rule, and describes the Masing effect pertinently so that it would be applicable to the prediction of the cyclic loading behavior of materials. The constitutive equation of soils is formulated by introducing the subloading surface model and formulating the rotational hardening rule for the description of the induced anisotropy. Its applicability is verified by predicting monotonic and cyclic loading behavior of sands under drained and undrained conditions and comparing them with test data.

View full abstract

In order to graspe the distribution of rock joint and to construct the jointed rock mass model, we have carried out the borehole survey through the Borehole Scanner System and have analyzed the image data so as to obtain a location, orientation, aperture etc. of rock joint. Based on the analyzed joint data, we have constrcuted two kinds of jointed rock mass model; namely a discontinuous model and an equivalent continuous model. The former is based on the cluster analysis in addtion to the relative importance which is our concept and considers of joint frequency, joint area, joint aperture. The latter consists of the joint frequency map which considers of geological structure and joint aperture and takes an advantage of not only the mechanical numerical simulation but also the application of geotomography analysis.

View full abstract

A series of triaxial compression tests, plane strain tests and cyclic undrained triaxial tests on several volcanic coarse-grained soils were performed to understand the physics of the mechanical behavior of soils with particle crushing. Volcanic coarse-grained soils were taken from natural deposits, produced by fall deposition in Hokkaido, Japan. Test results showed that anisotropy in mechanical properties of volcanic soils is observed more clearly than that of clean sand. It was also found that the stress-strain-strength properties of granular materials are strongly influenced by their particle breakage, when the test is performed under stress system with the increase of effective mean principal stress.

View full abstract

During the 1995 earthquake, the vertical array observation system installed by Kobe City recorded accelerations over 0.5g. Using the records observed by the system, the authors have estimated average stress-strain relationships in the ground at Kobe Port Island. The stress was directly estimated from earthquake acceleration records. The strain was estimated from the relative displacement divided by the distance between adjacent observation points. The hysteretic deformation properties were analyzed from the following points of view: (1) Softening of the ground stiffness during the earthquakes, (2) Nonlinear property changes during the main shock and the aftershocks and (3) Liquefaction process of the reclaimed ground during the main shock.

View full abstract

By employing a 19cm cubic granite specimen with a 2cm diameter hole, hydraulic fracturing experiments are conducted to clarify the viscous effect of fracturing fluid. The viscosity is varied by 1cP water and 80cP oil. The fractures are measured by acoustic emission, pressure and strain. It is elucidated that viscous oil tends to create thick and plane cracks with few branches, while water tends to generate thin and wavelike cracks with many branches of a network. This suggests a possibility to control the fracture patterns by changing viscosity of fracturing fluid in the hydraulic fracturing.

View full abstract

At present, the treatment of construction waste soil is becoming a large scale environmental problem. The soil improvement method of using the construction waste soil instead of sand for sand compaction pile is expected to encounter above situation.
This paper reveals that the increase of shear strength on the surrounding clay takes place both when sand pile is driving and embankment load is applying independently, by model tests and numeical analyses. Based upon the experimental results, it is also investigated to apply the plastic boad drain for drainage.

View full abstract

The thermal behavior of rock mass around openings when low temperature material are stored, will be different with each type of rock. In this study, Affect of the difference of water content in each rock on physical properties in wet state under low temperature were investigated by experiment. From results, it was found that the physical properties of rocks which have large porosity, were affected by pore water. Then, temperature distribution and behavior around openings were analyzed and the results which were discussed for mechanism of crack development are described. In the case of granite and sandstone, it was found that cracks were caused by tensile stress. On the other hand, in the case of tuff and mudstone, cracks were caused by shearing stress.

View full abstract

This paper presents the results of an experimental investigation on three different volcanic coarse-grained soils in the cyclic undrained triaxial tests varying both maximum past consolidation pressure and the overconsolidation ratio (OCR). Test results showed that the variation in cyclic deformation-strength behaviors due to overconsolidation was observed more clearly in the volcanic soils with which particle breakage had been induced during consolidation process and their variation characteristics relate uniquely to the OCR value. Therefore, the cyclic undrained triaxial strength of overconsolidated volcanic soils can be determined only by OCR. It was also considered that strength increase by overconsolidation is attributed mainly to the fabric change with significant particle breakages.

View full abstract

Recently there has been increasing public interest in the disposal of low-level radioactive nuclide waste and energy storage. Underground rock caverns have been considered as possible repository sites. This paper presents a new grouting method which uses a suspension of liquefied ultrafine clay in fractured rock masses. In order to demonstrate the effect to block open cracks, two experiments were carried out on large-sized granite samples with open cracks. The experiments proved the method to be highly effective. Furthermore, experimental results were compared with those from a mathematical model based on successive blocking in parallel walls.

View full abstract

The NATM has developed as the standard tunnelling method in Japan. In this situation K. Kovari criticized that the concept and methodology of NATM have been misled, and we are also aware of these partialy because of our own experiences last 20 years.
This note, firstly, reviews a developping process of tunnel engineering as a science methodology and it's positioning of NATM, and, secondary, proposes some subjects which should be taken into consideration to establish new tunnelling concepts.

View full abstract