The paper proposed a new method to calculate a liquefaction strength curve with a single specimen using the two unique relationships between the normalized cumulative dissipation energy and excess pore pressure ratio, the increment of the normalized dissipation energy and the shear stress ratios defined at each cycle. The method was verified from the liquefaction strength tests using the reconstituted specimens with various relative density made by wet tamping (WT) and air pluviation (AP) method. In the specimens for AP, the liquefaction resistance was increased by small cyclic loads during the undrained cyclic test. The different liquefaction strength curves were obtained depending on the amplitude of cyclic load tests. Applying the small drained cyclic loads to the specimens for AP prior to liquefaction strength tests, the liquefaction strength became higher and the increase of liquefaction resistance during load tests was not observed. As the results, the almost same liquefaction strength curve was obtained from many specimens without depending on the amplitude of cyclic loads.

Cyclic and post-cyclic undrained triaxial tests were conducted on undisturbed volcanic cohesive soils taken from residential sites in Mashiki Town, Kumamoto, which were struck by and severely damaged by the 2016 Kumamoto earthquake. Special emphasis was placed on elucidating the degradation of the undrained strength and stiffness of volcanic cohesive soils based on test results used for predicting earthquake-induced settlement and displacement of residential foundations. Results of laboratory tests and analyses of instability of residences and foundations that had experienced the Kumamoto earthquake indicate the points listed below.
i) Decreased strength and stiffness as well as strength parameters were observed after cyclic loading. Particularly, the post-cyclic stiffness reduction was more marked than strength reduction.
ii) Strength parameters, cohesion c, and internal friction angle φ, were reduced both on a total stress and an effective stress basis after undrained cyclic loading.
iii) Instability and residual deformation of residences on volcanic ash cohesive soils were verified using both strength and stiffness degradation and a decrease in strength parameters.

To evaluate undrained shear strength of saturated soil during undrained cyclic loading without performing a large number of laboratory tests, simple methods for prediction of undrained cyclic strength and strength reduction characteristics were proposed. Analyses of the relationships between properties of soil which is commonly obtained when seismic capacity of irrigation earth dams is evaluated and the characteristics of undrained cyclic strength and strength reduction showed key parameters governing above characteristics. Undrained cyclic strength of gravelly soil and sandy soil increases with an increase in degree of compaction, while that of cohesive soil increases with an increase in clay content. For gravelly soil and sandy soil, when degree of compaction is used as one of explanatory variables, strength reduction characteristics predicted from the model proposed in this paper have good correlation with that obtained from laboratory tests. In contrast, strength reduction characteristics of cohesive soil can be predicted from the model which incorporates dry density, fines content, mean diameter and cohesion as explanatory variables.

When laying water pipelines, excavated soil is generally disposed and replaced with commercially available sandy material. Reuse of the excavated soil yields reduction of both the environmental loads and the construction costs. Although “The guideline for use of excavated soil” by Ministry of Land, Infrastructure and Transport, specifies reusable soil types, it is not common practice to use the excavated soil for the laying of water pipeline because the specification requires complicated laboratory soil tests for the judgement. In this study, the applicability of the on-site simple method, called the “FK method”, is evaluated through a series of laboratory tests and model tests by using soil samples collected from various regions in Japan. As a result, the FK method successfully indicated compaction characteristics and bearing capacity of excavated soil. Hence, the method can be used on-site to judge the availability of excavated soil for water pipe laying works.

The soundness of the pier may be evaluated using the natural frequency of the pier, because it is not easy to visually confirm the scour condition of the ground around the pier directly after the river level rise. In this study, to investigate the influence of local scouring directly on the vibration characteristics of the foundation pier model, an experiment in which the model ground supporting the model pier is excavated in stages and a local scouring experiment using an open channel model are conducted. The microtremor measurement of the model bridge pier was carried out at the time of those experiments. As a result, it was revealed that the damping constant of the soil-structure system tends to increase when the range of local scouring reaches the bottom of the pier. In addition to the natural frequency, it is considered effective to evaluate also the damping constant in the assessment of the soundness of the bridge pier.

A series of undrained triaxial cyclic tests was conducted to evaluate multiple-liquefaction properties of mixtures of Toyoura sand and non-plastic silt called ‘‘DL clay’’ with fines content ranging from 0 to 45%, and undisturbed and reconstituted non-plastic silty sands retrieved from road embankments. In the tests, liquefaction histories after the respective consolidation stages were applied three times to a single specimen. The test results showed that: 1) the liquefaction resistance decreased with increasing fines content irrespective of the number of liquefaction histories; 2) the specimen density increased with an increase in the number of liquefaction histories while its increment tended to be larger for samples with higher fines content; 3) the liquefaction resistance and small strain shear modulus decreased largely in the second cyclic loading stage in spite of an increase in the specimen density caused by the first liquefaction history, while they slightly increased in the third stage; 4) the liquefaction resistance and small strain shear modulus of the undisturbed specimens were larger than those of the reconstituted ones due to ageing effects; and 5) a good correlation between the liquefaction resistance and small strain shear modulus was observed for each material irrespective of the number of liquefaction histories and the sample condition (i.e., undisturbed and reconstituted).

The purpose of this article was to clarify the bearing properties when the piled-raft foundation was applied onto the single layer of the loose sand ground and clayey ground respectively. The static load test was performed using the three kinds of foundation: the spread foundation, the pile alone and the piled-raft foundation that was a combination the spread foundation and the pile located in the center of the spread foundation. Compared the pile alone with the pile of the piled-raft foundation and the spread foundation with the raft of the piled-raft foundation, it was confirmed that the interaction between the pile and the raft in the piled-raft foundation had a huge effect to the bearing capacity. Particularly, the bearing capacity of the pile of the piled-raft foundation was increased most effectively and the effect was appeared more markedly in the loose sand ground. Although the settlement restraint effect of the piled-raft foundation was obtained because the bearing capacity of the pile was added, the impact on the raft varies according to the soil; the bearing capacity decreased because of the suppression of the progressive failure in the loose sand ground, on the other hand, the bearing capacity increased by suppression of the amount of compression in the clayey ground. Especially, when put the piled-raft foundation of which the length of the pile was shorter than the short side of the raft onto the loose sand ground, the bearing capacity was lower than that when used the spread foundation. One of the reasons for this result includes the settlement restraining structure of the piled-raft foundation. On the other hand, the confining pressure to the pile was increased when used the piled-raft foundation because contact stress arose from the raft, and which may lead to increased bearing capacity. Furthermore, the depth of the influence range affected to the pile was estimated about 2 times of the width of short side of the raft.

Using the vacuum consolidation method, a soft ground is consolidated without the shear deformation of the ground, and the combination of this method along with embankment loading enables the stable construction of the embankment and the suppression of the displacement of the surrounding ground. In this study, numerical analyses are conducted to investigate the effect of the construction speed of an embankment and the period of vacuum consolidation preceding the embankment construction on the stability of the foundation ground and the displacement of the surrounding ground during the embankment construction. The analytical object is a 10-m-high embankment, and it is assumed that the embankment is constructed with the vacuum consolidation method to stabilize the foundation ground. The results indicate that it is more effective to reduce the construction speed of the embankment than to provide a preceding period of vacuum consolidation in order to obtain the effect of suppressing the pore water pressure. On the other hand, the preceding period of vacuum consolidation effectively suppresses the displacement of the surrounding ground.

In a geotechnical investigation for detached houses, preliminary surveys and the Sweden weight sounding test are commonly used. When considering consolidation subsidence, it is preferable to perform a consolidation test to accurately grasp various consolidation constants. However, it is rarely carried out for economic reasons. Therefore in this paper, we evaluated the soil test results which conducted using shallow alluvial clay samples collected at several sites and examined the results of their comparison. And we presumed the physical and mechanical properties schematically by using their moisture content, and finally we proposed a method of predicting consolidation subsidence. Moreover, we considered its usefulness by comparing the predicted values with the measured values of consolidation subsidence in actual properties, then we revealed that the prediction method can obtain the same or more amount of subsidence as that obtained from consolidation test results.

We conducted an survey on fractures of the ground anchors caused by inland earthquakes which are seismic intensity 5+ or more in Japanese earthquake scale. As a result, the failure of the anchor was confirmed not only on the collapsed slope but also on the slope without noticeable damage. The failure mode was mainly tensile failure, but some shear failure was confirmed. We also found out that it is possible that the ground anchors were damaged with less displacement than the theoretical value of tensile failure. By observing the anchor load after the earthquake, there was no increase or additional breakage due to aftershocks. This confirmed that the slopes with ground anchors maintained certain stability even after the earthquake. Regarding the relevance between earthquake motion and anchor breakage, fractures were found on the slope that had estimated acceleration of 580 cm/s² or more at max.

In the heavy rainfall in the district of Chugoku, north Kyushu,Japan on July 21, 2009, a lot of debris flows occurred around the boundary between Yamaguchi City and Hofu City. Observing such debris flow occurrence slopes, granite hard rock layer exposed, and marsified weathered residual soil is thinly distributed at source heads and the difference in permeability between the granite hard rock layer and the weathered residual soil was observed.　In this study, we performed FEM analysis that reproduced these characteristics. In addition, a full-size experimental model slope was created, and a rainfall experiment was conducted under the conditions where a bare ground surface slope and the multi -function filter were laid.　A comprehensive examination of the two results shows that the presence of a high permeable coarse grained layer between the weathering granite layer and impermeable bed rock layer causes a sharp rise in pore water pressure at lower part of the slope due to the effect of underground penetration and groundwater funnel flow. The flow has become clear that the occurrence of boiling causes the collapse. Moreover, the expected effect of multi function filter which control the seepage in heavy rain was confirmed.

In this paper, a series of laboratory tests using a total of seventeen sandy fill materials was carried out in order to discuss the effects of the degree of compaction, initial water content, overburden pressure and the stress history on the behavior of one-dimensioal subsidence when the soil is submerged. As a result, it was manifested that the subsidence was greatly influenced by four factors; i.e., the degree of compaction, Fine fraction content, the initial water content and the overburden pressure. In addition, The total volume strain when the degree of compaction of the initial is the same and the overburden pressure and the water content each monotonically increase to approach the saturation state do not depend on the initial water content of the specimen, the history of water immersion and overburden pressure, The final overburden pressure turned out to be uniquely determined.

Despite the occurrence of various problems, such as the remaining of existing piles due to existing pile extraction work, subsidence of the surrounding ground, and deterioration of the ground environment when using the former site, it is injected into the extraction holes formed after extraction of the existing piles. There is no provision in the filler and the drawing method itself. Therefore, in this study, the pile tip chucking type pulling method (power chucking method; PG method), which is one of the existing pile pulling methods, is characterized visually and quantitatively using MPS-CAE. Evaluation was performed. As a result, simulation of existing pile drawing work by the PG method can be performed in advance, and the amount of filler that meets the target strength can be selected.

In April 2016, earthquakes occurred in Kumamoto prefecture that recorded a maximum magnitude of 7.3, causing the ground subsidence of river reeve caused by the liquefaction of river reeve body and its foundation ground. A steel sheet piling method has been widely used as a reinforcement for river levees in Kumamoto prefecture to reduce the ground settlement and lateral displacement of soft ground. In the steel sheet piling method, there are a conventional method penetrating sheet piles to support layer, a floating steel sheet piling method (called “the FL method”) not penetrating them to support layer, and partial floating steel sheet piling method (called “the PFS method”) that is combined with the FS method and the conventional method. The objective of this study is to investigate the damage of river levee caused by the 2016 Kumamoto earthquake and to evaluate the effectiveness of the steel sheet piling method as a countermeasure against earthquake. The seismic damage of the river levee reinforced with the steel sheet piling methods was analyzed in terms of both liquefactions of foundation ground and river levee body.

The sand drain (SD) ships for offshore driving disappeared in Japan due to reduced demand, and the sand compaction pile (SCP) ships have been used for the construction of sand piles for SD method. In the quay construction project at the Nakano district in the Port of Sakai, the SD drains were constructed by SCP ship into the offshore alluvial clay layer. As there was a delay in the measured settlement compared to the prediction in the design, it is assumed that the diameter of the sand drain 120 cm caused the larger disturbance in the ground than that in the normal SD method. In this study, the decrease of the consolidation coefficient due to the ground disturbance was investigated from the analysis of measured settlement data at the site and the laboratory tests. It was found that, when the diameter of the sand drain is larger than that in the normal sand drain works, the settlement rate may be overestimated in the conventional design where the vertical coefficient of consolidation obtained by the laboratory consolidation test is used as the horizontal coefficient of consolidation in the field.