Determination of in-situ undrained strength of soft clay deposits is discussed based on their stress history (engineering geological history). First, classification of soft clay deposits is shown and the importance of understanding the stress history for evaluating undrained strength characteristics of soft clay deposits is demonstrated for an alluvial marine clay. The method for obtaining in-situ undrained strength of soft clay deposits are then discussed for each clay classified with brief review on past studies. A method for obtaining in-situ undrained strength is proposed for normally consolidated aged clay which is the most common type of soft clay deposits and its validity is proved by various tests results. Characteristics of unconfined compression and in-situ vane strengths are also discussed based on their comparison with the in-situ undrained strength obtained from the proposed method. Further, field behaviour and stability analysis of five embankments constructed on a normally consolidated aged clay under very low factor of safety are shown. The results of stability analysis strongly demonstrated the efficiency of the method proposed in this paper.

抄録全体を表示

In order to investigate the influence of seepage flow on active earth pressure, the authors performed earth pressure tests under the condition that rainfalls seeped into the backfill and ran slowly through it and then drained into a filter located between the wall and the backfill. It was found that the resultant force of the active earth pressure acting on the wall increased due to the influence of the seepage flow and the influence became more pronounced as the slope of the backfill surface increased.The values of the active earth pressure calculated by the logarithmic spiral method taking into account the seepage flow in the backfill, agreed with the observed values. It has been proved that the calculation method developed by the authors is reasonable.The authors compared the coefficients of horizontal component of the active earth pressure proposed by Terzaghi and Peck for clean sand or gravel with the values calculated by the authors. It was estimated that Terzaghi and Peck had taken into account two thirds of the increase of the earth pressure due to seepage flow.

抄録全体を表示

An increasing attention has been given to clarifying the mechanism of negative friction on piles and to developing a method of reducing it. In spite of many related studies, however, several unknown points still appear to remain as to the group action of downdrag forces on vertical piles and the flexural behaviour of batter piles subjected to surrounding ground settlement. In this paper, a program of model tests has been performed to investigate the characteristics of negative friction on both vertical and batter pile groups, and to assess the efficiency of bitumen coatings in reducing these frictions. The main results obtained can be summarized as follows : Firstly, a method of estimating the group action of negative friction has been derived for vertical pile groups, and the validity of proposed method has been confirmed based on available data of laboratory and field tests. Secondly, it was shown that the theoretical model advocated by Broms and Fredriksson (1976) can give good insight into the overall flexural behaviour of batter piles when subjected to the surrounding ground settlement. Lastly, the model tests have demonstrated that the negative friction on vertical piles can be reduced to an acceptably low level if the piles are provided with a slip layer of bitumen.

抄録全体を表示

A use of constant rate of strain consolidation tests for determining the consolidation constants of very soft soils was previously proposed together with a new interpretation of the test results. Using this method and a sedimentation test method, the consolidation and settling characteristics of various marine bottom sediments taken from several harbors in Japan and evaluated and comparatively examined. In addition, analytical results on the self-weight consolidation observed in a model landfill composed of marine bottom sediments are presented and discussed from a view point of verifying the validity of the laboratory testing procedure proposed.

抄録全体を表示

In the first part of the article a review of laboratory cyclic undrained test methods is presented. The features of the cyclic torsional simple shear device which was newly developed to assess the resistance of saturated dense sand against cyclic undrained loading are described. The test results are represented by the relationship between the relative density D_γ and the cyclic shear stress amplitude normalized by the effective mean principal stress at consolidation τ_cy/σ'_mc for which a certain value of double amplitude shear strain is observed at a certain number of loading cycles. Cyclic undrained tests were performed for 1) isotropically and anisotropically consolidated specimens, 2) specimens initially sheared and not sheared during consolidation and 3) specimens prepared by different methods, using two different sands, Toyoura Sand, a clean, uniform, fine sand having no fine particles and Sengenyama Sand, a medium fine sand including fine particles to some extent. For any test condition, specimens denser than some critical densities showed extremely high resistances which were much larger than expected from the concept that the cyclic undrained strength be proportional to relative density. For identical values of relative dinsity, loose Sengenyama Sand specimens had strengths similar to loose Toyoura Sand specimens, while dense Sengenyama Sand specimens had strengths much less than dense Toyoura Sand specimens. Loose specimens prepared by the air pluviation method had strengths similar to ones prepared by the wet tamping method, while air-pluviated dense specimens had strengths much lower than wet tamped dense specimens. Other factors affecting the cyclic undrained strength of sands were also investigated. Effects of any factor investigated on the cyclic undrained strength were very large for dense specimens, but only slight for loose specimens.

抄録全体を表示

One of the most important points to be solved on passive piles may be to accurately estimate the lateral pressure acting on piles due to soil movements. The authors have already presented a theoretical equation to estimate the lateral pressure on piles in the previous paper, considering the pile interval as accurately as possible.In this paper, to check the validity of the theoretical equation presented, a series of model tests are carried out for various conditions of the pile and the soil. First, based on the experimental results, the validity of an assumption on the plastic state of soil made in the theoretical derivation and the significance of the presented theoretical equation are clarified. Then, both the experimental and theoretical values of the lateral pressure on piles are compared for both clay and sand specimens, followed by their very good agreements for various kinds of soil strength, pile diameters and intervals between piles. Consequently, it is concluded that the theoretical equation due to the authors' theory can estimate the lateral pressure on passive piles in a row when the soil just around piles becomes a plastic state, with a sufficient reliability over a wide range of the interval berween piles. Finally, a method to approximately estimate the ultimate lateral pressure is also shown.

抄録全体を表示

Using a simple displacement field the vertical uplift behaviour of a single rigid pile (or pier) embedded in a frozen sandy soil is analyzed. Results of the analysis are represented by curves from which the magnitude of the butt movement can be estimated for given uplift forces. The procedure outlined in the paper is directly applicable to piles embedded in moderately to heavily overconsolidated clay deposits.

抄録全体を表示

In the load testing of a foundation or any other ground structure, the method of defining ultimate failure load depends on many factors which include the design criteria and the soil stress history. Some of the more commonly used methods are noted in this technical note. A graphical method is presented which harmonises three of these methods and thus makes it easier to make comparable safety factors between different loading test results.

抄録全体を表示