Severe collapse settlements in fill of stiff clays or weak rocks can occur several times due to inundation. This paper shows a method used for controlling the placement of stiff clays to reduce collapse settlement in a residential development. An in-situ compression test developed by the authors was used to observe the settlement of trial fills compacted by three types of rollers. The results of the in-situ tests were compared with those of the laboratory compression tests conducted on undisturbed samples taken from the test site, and it was shown that the vertical strains in the both cases coincided. Guide indices for the control of the placement of fill previously presented, such as the density, air void ratio or strength of the fill, have been re-evaluated following the results of the in-situ compression tests according to a current code for the maximum incremental inclination of houses by Architectural Institute of Japan. It was found that the following procedures should be adopted at the site as guidelines for placement of the stiff clays : (1) The soil should be spread in layers less than 30 cm thick and compacted by two passes of a vibrating roller of 9.8 tons at least, (2) The relative density of the fill should be greater than 98%, (3) The strength as measured by a dynamic cone test should be greater than 5 blows per 30 cm, (4) The air void ratio should be less than 12%, and (5) Water should be spread before compaction when fill-materials lose more than 1.5% of water content due to drying.

View full abstract

A generalized method has been proposed to analyze the stability of embankments constructed over soft subsoil reinforced with granular piles. The problem of determining the critical slip surface and the corresponding minimum factor of safety has been formulated as a constrained minimization problem. The shear strength of the improved subsoil has been estimated using both the conventional and the equivalent anisotropic concepts. The proposed method has been validated comparing the results obtained with solutions available in the literature. With reference to a typical problem, limited results are presented to highlight the influences of the various parameters on the stability of an embankment.

View full abstract

It is imperative to examine the properties of soils eroded due to acid rain in order to increase our understanding of the influence of acid rain on geotechnical engineering. Two test methods were employed, the infiltration method and the soak method, to investigate the physico-chemical and engineering behavior of soils eroded due to acid rain. Significant effects of artificial acid rain on the physico-chemical properties were observed compared to engineering properties. The variations of the physico-chemical properties of eroded soils such as an increase in the pH value of outflow and soaked water, an increase in the cation concentration of the outflow and soaked water, a decrease in the pH value of a specimen, and a decrease in the exchangeable cation concentration of the specimen were examined. These variations were caused by an ion-exchange reaction between the exchangeable cations in soil specimens and the H⁺ ions in acid rain. The concentration of water-soluble cation and the electric conductivity increased by continuing to infiltrate or soak, showed a larger increase in Kanto Loam than that in alluvial clay and decomposed granite soil. These physico-chemical behaviors were strongly affected by the pH level of artificial acid rain, and a more significant change was observed under a higher acid condition than under a weaker one. For engineering behavior, an increase in the sensitivity ratio and in the liquid limit was detected when alluvial clay was soaked in the higher acid rain.

View full abstract

This paper focuses on the patterns of deformation of the wall and the soft clay foundation beneath the reinforced soil mass based from the results of full-scale field tests and finite element analyses. The performances of two reinforced soil test wall-embankment systems constructed on soft clay foundation with different reinforcement types but have the same backfill soils were used in the investigation. One test facility used steel grid reinforcements (higher stiffness or rigidity) and the other used polymer grid reinforcements (lower stiffness). Measurements from the instrumentations of these test facilities were compared with the results from numerical simulations based on a finite element solution in which reasonable agreement were obtained. Parametric studies were then carried out to examine the effects of the stiffness of the reinforced soil system and the foundation on the overall deformation characteristics of reinforced soil wall. Results indicated that increasing the stiffness or rigidity of the reinforced soil system led to lower lateral spreading of the soft clay foundation owing to more lateral confinement of the underlying soil as compared with less stiff reinforced soil system. However, increasing the system stiffness had the tendency to settle more below the toe because a more stiff reinforced soil system tended to rotate more about the toe compared to that which has lesser system stiffness. Consequently, the pattern of foundation movements associated with system stiffness affected also the outward facing movement of the reinforced soil wall. It was found that the increase in reinforced soil system stiffness does not necessarily result to the reduction of the outward lateral wall deformation.

View full abstract

In order to clarify the behavior of loose sandy and non-plastic silty soils, which are the most susceptible to liquefaction, a multiple series of tests were undertaken, concentrating on the effects of fabric. For this purpose, three distinctively different specimen preparation methods were chosen, and two or three were used for each of the materials, to prepare specimens with a very loose structure. The loosest state of packing was found to exist, for each of the preparation methods with different void ratios. In the loosest state, the normalization of the undrained stress∼strain curves and stress paths to the initial confining pressure, can provide a meaningful interpretation of the soil behavior. This procedure is similar to the one adopted for normally consolidated clays. Regarding the effects of fabric on the undrained behavior, it was found that they are negligible up to the peak strength. However, once the shear straining reaches the state beyond the peak, the fabric becomes a very important factor governing the undrained response of non-plastic soil, which includes the minimal or residual shear strength. When the soil is largely sheared to reach the steady state, gradual remoulding erases the initial fabric and ultimate stress state is, governed by the void ratio only, once again not affected by the initial fabric.

View full abstract

An estimate of bearing capacity coefficient N_γ for a strip footing is made using the kinematical approach of limit analysis. This approach leads to an upper bound on the true limit load when the calculations of the three terms in the bearing capacity formula are consistent with one collapse mechanism. However, as accepted in other proposals, the estimate of the influence of the soil weight is calculated here separately from the terms dependent on the cohesion and the footing depth (overburden). It is conservative to take the minimum of each term in the bearing capacity formula, rather than minimum of the sum of the three terms. Coefficient N_γ from such calculations becomes increasingly conservative (underestimated) with the increase in the soil cohesion and the footing depth. In view of using the upper-bound approach, such "all-minimum" procedure is prudent and appropriate for design. Results are given for both rough and smooth footings. A substantial influence of the dilatancy angle on N_γ was found, and this is a reason for concern, since the non-associativity of plastic deformation of soils is usually not accounted for in design. Although calculations are numerical in nature, with optimization of the failure mechanism to obtain the best estimate, closed-form approximations are suggested for practical purposes.

View full abstract

A case study on the measurement of lateral movement of an abutment supported by pile groups constructed in a cohesive soil is reported in this paper. Based on prediction at the design stage and observational construction control, the abutment was successfully constructed within the range of allowable lateral movement. After the completion of construction, the 3D elasto-plastic coupled FE analysis based on the Cam-clay model was applied to the problem. Although the analysis overpredicted the lateral movement, it was indicated that such analysis is useful for evaluating the mechanism of lateral movement of such an abutment and the effect of the weak surface soil, replaced by more "competent" material.

View full abstract

A new concept for the calculation of the bearing capacity of shallow foundations is presented. The Terzaghi-Buisman equations was transformed and extended to include all possible load cases. The shape ratio was rigorously defined. Torsional moment factors considering eccentric horizontal loads were proposed and defined for the first time, in order that complete 6-dimensional interaction diagrams could be derived. The effect of embedded depth was also investigated and considered for special factors. The influence of cohesion was derived from Caquot's theorem of the corresponding states of stress. Experimental investigations with some interesting results are presented. A new calculation scheme is presented at the conclusion of the paper.

View full abstract

A series of undrained cyclic triaxial tests were performed on various types of high-quality undisturbed gravelly samples recovered by the in-situ freezing method. The undrained cyclic shear strength obtained from these tests was reviewed and related to shear wave velocity measured in the field. Similar test results determined by other investigators were also adopted for establishing a correlation. Based on the review of these test results, the following conclusions were drawn. For the case of gravels of Holocene Epoch, a fairly good correlation could be found between the undrained cyclic shear strength and shear wave velocity, in such a way that the undrained cyclic shear strength increases with an increase in the shear wave velocity. The data for Pleistocene gravel, however, indicated two separate groups. One basically coincides with the correlation of Holocene gravel. The data from the other group indicated that the liquefaction strength is much higher than that of Holocene gravels for the same value of shear wave velocity. In order to correct the effect of confining stress on this correlation, a normalized shear wave velocity, V_S1, in terms of the effective vertical stress was introduced. Similar good correlations were found between V_S1 and the undrained cyclic shear strength. These correlations can be well expressed with empirical equations proposed by the authors. In the case of Pleistocene gravel, however, these equations indicate the lower boundary of undrained cyclic shear strength.

View full abstract

A series of triaxial compression tests on soil-cement mixture samples has been made in order to investigate its mechanical properties. The test results show that as the confining pressure increases, the strength and the strain at peak stress of this soil-cement mixture increase drastically and the initial modulus changes very little. The failure mode is a plastic-shearing one imposed by the confining pressure. These results are different from the previous ones for a soil-cement mixture being brittle and of low strength obtained based on unconfined compression tests, where the condition does not satisfy the actual in situ stress condition for the cutoff wall. The study suggested an important idea of using a soil-cement mixture instead of common concrete to construct a deep cutoff wall under high earth-rockfill dams. This has been proved by the stress-displacement analysis by FEM for a high earth-rockfill dam with a cutoff wall in deep alluvium.

View full abstract

SPT N-value and S-wave velocities for gravelly soils with widely varying grain size distribution were measured in a large container test and formulated as functions of gradation, relative density and confining stresses. These values have been found to be very sensitive to the difference in gradation. It has also been found that well-graded gravelly soils, despite the much smaller void ratio than sand, can have an N-value and shear wave velocity as low as loose sand if it is loosely deposited. It has also been found that the formulae can readily estimate N-values with the factor of 1.5∼1/1.5 and S-wave velocity with that of 1.2∼1/1.2 for a wide range of gravelly soils and can give a direct relationship between the two variables which is consistent with previous research based on field data.

View full abstract

Surge waves often form on the free surface of debris flows. These surge waves have the form of a hump that moves down slopes at speeds that are greater than those recorded for the free surface and the front of the debris flows. Surge waves can be very destructive. In the present study, a theoretical analysis is proposed to explain the formation and the velocities developed by these surge waves. The analysis models the debris flow material as one having a frictional-viscous resistance to flowing down slopes. Using this model, it was determined that surge waves travel on the free surface of debris flows at a speed that is two times greater than that recorded for the free surface and three times greater than the mean velocity of the debris flow. The theoretical findings were substantiated by velocity measurements on a debris flow in Sakurajima, Japan.

View full abstract

The design implication of stress-confinement effect of nonwoven geotextile is addressed. The unconfined and confined strengths of a selected needle-punched nonwoven geotextile are used to conduct a comparative design of a granular soil retaining wall based on a limit equilibrium approach. A higher wall may be allowed when considering the confined strength as compared to the unconfined strength. For a selected wall height, confined strength allows for fewer geotextile layers when compared to that designed using unconfined strength. It is recommended that stress-confinement test procedure should be standardized so that confinement effect of some nonwoven geotextiles may be incorporated into an individual wall design procedure.

View full abstract

Based on the assumption that an inward- or outward-directed flow perpendicular to a slope exists, this paper describes an experiment and test results. The results are compared with both traditional continuum and single-grain theories presented for the relationship between hydraulic gradient and slope angle. For the case of outward flow, the continuum theory governs the failure mechanism of the Shirasu talus deposit. The single-grain theory controls the failure process for inward flow.

View full abstract