The effects of sample disturbance on undrained shear strength were investigated from samples with various qualities, retrieved by different types of samplers at the Takuhoku site, Sapporo. Sample quality was evaluated by three types of shear tests: unconfined compression, fall cone and triaxial recompression tests. Similar to a previous study conducted by Horng et al. (2010), in which the sample quality was evaluated by two nondestructive tests, the residual effective stress (suction) by ceramic disc and the shear modulus by bender element under unconfined conditions, the present study shows that the small edge angle of a tube sampler is important to obtain high quality sample. In addition, the existence of a piston does not have a significant effect on the strength properties. The recompression technique in the triaxial test, where the specimen is consolidated back to the in situ stresses, was able to duplicate undisturbed soil behavior except when the structure of a soil sample was significantly destroyed. The unconfined compressive strength is apparently governed by the residual effective stress. From the two types of tests simulating sampling processes, however, it was found that a reduction in the unconfined compressive strengths of low quality sample was brought by the loss of the residual effective stress as well as destruction of soil structures.

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The 2005 Fukuoka-ken Seiho-oki earthquake caused damage to structures due to liquefaction, slope failure and strong shaking in Fukuoka City. One of the authors had conducted microzonation for liquefaction, slope failure and strong shaking about 17 years before the earthquake. After the earthquake, the authors compared the zoning map with the actual damage. The results showed that liquefied sites coincided fairly well with predicted zones in the reclaimed lands. However, they were slightly different in a big sand spit named Uminonakamichi. Failure occurred at several slopes inside the predicted areas, while damage to buildings occurred due to strong shaking along the Kego Fault. The damaged area was slightly different from the predicted area. Furthermore, a liquefaction analysis was conducted and the results of this analysis were compared with the results of microzonation in 1988. In this paper, the authors discuss the validity of microzonation based on this comparison.

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The effect of the 2008 Iwate-Miyagi Nairiku earthquake (M_J 7.2), Japan on the Aratozawa dam, which is a 74.4 m high rockfill dam with a central clay core located in the area, was studied with a main focus on the change in the vibration period, shear wave velocity, shear modulus, and pore-water pressure. In a vertical section of the central part of the dam, three sets of 3-component accelerometers and 15 pore water pressure meters were installed. During the main shock, the acceleration exceeded 10 m/s² at the gallery, inducing large shear strains in excess of 10⁻³ and a sudden build-up of the excess pore water pressure in the core. Due to the large strains, the shear wave velocity and shear modulus showed a significant decrease from their initial values and the vibration period was elongated. The decreased shear wave velocity gradually recovered toward the end of the main shock, and continued to recover with the passage of time. The full recovery of the wave velocity was found to take at least one year, while the dissipation of the excess pore water pressure proceeded more quickly than the recovery of the wave velocity.

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The in-situ deep mixing technique has been established as an effective means to effect columnar inclusions into soft Bangkok clay to enhance bearing capacity and reduce settlement. In this paper, an attempt is made to identify the critical factors governing the strength development in cement admixed Bangkok clay in both the laboratory and the field. It is found that clay-water/cement ratio, w_c/C is the prime parameter controlling the laboratory strength development when the liquidity index varies between 1 and 2. Based on this parameter and Abrams' law, the strength prediction equation for various curing times and combinations of clay water content and cement content is proposed and verified. This will help minimize the number of trials necessary to arrive at the quantity of cement to be admixed. Besides the w_c/C, the strength of deep mixing column is controlled by the execution and curing conditions. For low strength improvement (laboratory 28-day strength less than 1,500 kPa), the field strength of the deep mixing columns, q_uf, made up from both dry and wet mixing methods is higher than 0.6 times the laboratory strength, q_ul. The q_uf/q_ul ratios for the wet mixing columns are generally higher than those for the dry mixing columns. This higher strength ratio is due to the dissipation of the excess water in the column (consolidation) caused by the field stress. The water to cement ratio, W/C, of 1.0 is recommended for the wet mixing method of the soft Bangkok clay. A fast installation rate was shown to provide high quality for low strength columns. Suggestions are made for improving the deep mixing of soft Bangkok clay, which are very useful both from economic and engineering viewpoints.

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There are a number of advantages to be gained by representing the oedometric compression of a soil skeleton, during virgin loading, unloading and subsequent reloading by ‘log (v) versus log (p′)’ relationships rather than the conventional ‘e versus log₁₀ (p′)’ expression. The paper presents an augmented version of the basic, two parameter (C′_c, C′_s), ‘log (v) versus log (p′)’ model in which the addition of two further parameters (C′_r, C′_o) enables a complete, non-linear response for any load-unload-reload cycle to be reproduced. All four parameters, deduced from a single such cycle in an oedometer, can then be used to predict the response of the sample in any other unload-reload cycles. Results are presented from tests of this kind on a range of fine-grained soils to demonstrate the key attributes of the model. These include the generation of ‘log (m_v) versus log (p′)’ diagrams that furnish practically useful m_v values applicable throughout any unload-reload cycle. The model also provides a simple means of assessing the overconsolidation ratio of an undisturbed soil sample.

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Unconfined compression tests and suction measurements were carried out in the present work on sandy specimens with distinct Class F fly ash amounts, lime contents, porosities and curing periods to assess key parameters controlling strength of fly ash-lime amended soil. A special effort has been allocated in order to develop a dosage methodology for fly ash-lime improved soils based in a rational criterion, as it exists in the concrete technology where the water/cement ratio plays a fundamental role in the assessment of the target strength. The results show that the unconfined compressive strength (UCS) increased linearly with the amount of lime for soil-fly ash-lime mixtures at all curing time periods studied. A power function fits better the relation UCS-porosity for soil-fly ash-lime mixtures. The bigger the amount of fly ash and the curing time, the larger the UCS for any given porosity and lime content. Finally, the porosity/volumetric lime content ratio, in which volumetric lime content is adjusted by a coefficient (in this case a unique value-0.12-was found for all soil-fly ash-lime mixtures and all curing periods studied) to end in single correlations for each curing period, show to be a good parameter in the evaluation of the unconfined compressive strength of the soil studied (UCS varies non-linearly with the porosity/volumetric lime content ratio in the case of fly ash-lime addition).

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To determine the properties of bentonite in an unsaturated condition, which is typically used in the initial placement of the clay liners in landfills, the effect of the soil fabric on the mechanical properties of unsaturated compacted Kunigel-V1, a bentonite clay, and NSF Clay, a non-swelling clay, were investigated. Samples were prepared at varying gravimetric water contents, ranging from natural to 70%, with the use of distilled water. The soil fabric was studied using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The mechanical behaviour was studied by constant rate of strain (CRS) consolidation testing and constant volume direct shear (CVDS) testing. The results indicate that while an increase in water content resulted in the formation of aggregates and an increase in shear strength, it was the dilatancy behaviour that was most affected. The saturation of Kunigel-V1 resulted in a decrease in the friction angle, from 40.4° to 20.4°, while the saturation of NSF Clay resulted in a decrease in friction angle from over 40° to 32.3°.

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Compacted soils are widely used in engineering work and engineers often specify that cohesive soils be compacted either around or on the wet side of optimum water content. In general, at the corresponding degree of saturation values, water component in soil voids is continuous but the air phase is not. The modelling of the infiltration process through compacted soils requires that unsaturated hydraulic functions be defined. A theoretical soil water retention function for soils with a discontinuous air phase is derived using the theory proposed by Schuurman (1966). Data from the test results provide encouraging evidence of the validity of the proposed theory. An empirical hydraulic conductivity function where the air is present in the form of occluded bubbles is also determined by curve fitting to the experimental measurements. A numerical solution of Richards' equation for one-dimensional flow, which incorporates the experimental findings, was used to simulate the measured transient water flow. The results show that the proposed constitutive relationships are capable of producing simulations of the measurements of the unsaturated flow that are both qualitatively and quantitatively realistic.

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A rainfall simulation device was developed to realize uniform rainfall at high g-levels in centrifuge model tests. A series of centrifuge model tests was conducted on cohesive soil slopes during rainfall, and the displacement and suction of the slopes were measured. The slope exhibits a relatively shallow slide after a heavy rainfall, and exhibits a shear zone with significant deformation in the interior of the slope. The vertical displacement is significantly larger than the horizontal displacement of the slope during rainfall. The rainfall-induced displacement process can be divided into three phases: (1) small displacement, (2) rapid increase, and (3) large displacement with minor rate of increase. Strain analysis was conducted on the basis of the measured displacement, and the results showed that the rainfall-induced deformation of the slope is governed by two types of mechanisms: increasing overburden weight and softening of soil. For a point in the slope, the first mechanism occurs from the beginning of rainfall; and the second mechanism occurs only when the water infiltrates there, which is described using the wetting front. Accordingly, another term, stable front, describes a boundary of zero increment of deformation. These two fronts gradually advance into the slope with increasing rainfall and divide the slope into three zones. The middle zone exhibits the most significant deformation.

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A new kind of Deep Cement Mixing (DCM) pile called Stiffened Deep Mixing Pile (SDCM) is introduced to mitigate the low flexural strength and unexpected failures of DCM piles. A jet grouting method with a jet pressure of 22 MPa, was utilized in the installation of DCM piles. The SDCM pile consists of a DCM pile with a precast reinforced concrete core pile inserted at its center. Pile and embankment load tests were conducted, and then the results of the field load tests were simulated by a 3D finite element method (FEM) to back-analyze and confirm the related design parameters. These parameters were then used further in numerical experiments. The field test results showed that the settlements and lateral movements of the SDCM pile using a prestressed concrete core pile with area ratio (A_core/A_DCM) of 0.17 and a length ratio of 0.85 was less than those of the DCM pile by 40% and 60%, respectively. Moreover, the SDCM pile foundation increased the bearing capacity by as much as 2.2 times. The average lateral pile capacity of the SDCM piles was 15 times higher than the DCM piles. A strength reduction factor of 0.40 was obtained at the concrete core and the DCM interface from the full scale pullout test. The behavior of both the DCM and SDCM piles was confirmed from the subsequent 3D FEM simulations. From the 3D FEM simulations, the length of the concrete core pile had more influence on the settlements of the SDCM pile than its cross-sectional area. However, both the length and cross-sectional area of concrete core pile affected the lateral resistance of the SDCM pile.

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Huafan University is located on the slope of the Ta-Lun Mountain area. The slope surface in this area is a colluvium soil cover layer with loose non-uniform particles, with high permeability. Because it is situated above a rapidly changing water table, the pore water pressure varies dynamically, depending on the weather conditions. In the dry season, most of the topsoil behaves in the unsaturated condition such that the matrix suction in the soil increases its shearing strength. In contrast, when heavy rainfall occurs, the seepage by precipitation tends to destroy the existing matrix suction. This reduction in soil strength frequently results in slope failure. This study, focuses on the variation of matrix suction of the colluvium soil in different precipitation conditions with varying vegetation at the campus of Huafan University. The analysis of the in-situ monitoring results and the laboratory test results for the undisturbed specimens taken from the field, with shearing strength and matrix suction taken into account. It is expected the results to be a useful reference for disaster protection on slopes.

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This paper reports and discusses the results of a field survey conducted by a joint scientific group from Japan and Indonesia to assess the geotechnical aspects of the Sumatra earthquake (M_w=7.6) of September 30, 2009. The studied area included the Padang and Pariaman cities, where a number of buildings collapsed as a result of strong shaking, and a mountainous part of the Pariaman district, a place where massive landslides buried several villages, claiming more than 400 human lives. The main objective of the survey was to investigate the causes and mechanisms of catastrophic landslides; however, other geotechnical problems such as lateral spread and liquefaction were also addressed. Field observations indicated that the catastrophic landslides occurred on relatively gentle slopes, then mobilized into debris flows, and traveled several hundred meters from their points of origin. The failure surfaces developed along the boundary of highly weathered pumice tuff with more intact and less weathered bedrock. Data from a portable cone penetration test showed that the sliding material was rather weak, having SPT N-values in the range of 5-10. The results of the field survey suggested that the main cause of slope instability was high pore-water pressures that generated in the soil mass during the earthquake.

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The building complex of the Beisheim Center at the Potsdamer Platz in Berlin has recently been completed. Different building parts had to be founded partially on the existing tunnel structures and partially on a system of piled-raft and raft foundations. The combined foundation was designed so as to minimize sectional forces due to the different foundation stiffnesses that were the unknowns in the analysis. Based on pile load tests the nonlinear stiffness of piles has been determined. For the design, both foundation components have been first decoupled and analysed separately. Subsequently, the interaction effects have been estimated by a simplified procedure. The pile configuration has been optimized by considering its effects on the superstructure. The performance of the combined foundations has been checked by comparing computed deformations with actual measurements at relevant points. Parallel to this, the system has been analysed by a 3D finite element model. The concept and the key design items of the combined foundation are presented, and a comparison is made between the estimated deformations and the measurements. The methodology for the analysis of building response to train induced vibrations is outlined.

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The influence of curing stress on the one-dimensional compression characteristics of cement-admixed clay at high water content is investigated by oedometer tests, with special attention paid to the primary vertical yield stress. From the test results, the stress acting during the formation of cementation plays an important role in the one-dimensional compression characteristics of cement admixed clay. The stress compresses the treated clay and results in an increase in the vertical yield stress. For the cement-admixed clay studied, the effect of the curing stress inherently reflects on the after-curing void ratio. Therefore, the primary vertical yield stress in one-dimensional compression is a function of the after-curing void ratio and the ratio of the clay water content to the cement content ratio.

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This paper presents the effects of dilute polyelectrolyte solution used in combination with aluminum sulfate on the geotechnical properties of a homogeneous high-plasticity organic clay derived from the purification of turbid water. Apart from the chemical additives, the alum-polyelectrolyte clay (APC) and untreated clay were similar in composition, comprising 41% micro-fibrous amorphous organic solids by dry mass. However, the geomechanical behavior of the APC material was enhanced by polymer-particle bridging phenomenon, which contributed to higher stress-strain modulus, 10-20% greater shear strength in undrained triaxial compression, a higher effective angle of shearing resistance value, reduced compressibility and a slower rate of consolidation compared to the untreated clay. Hence, this study raises the possibility of using dilute polyelectrolyte solution in combination with aluminum sulfate as an alternative soil improvement measure for organic residues and ultra-soft organic clay deposits.

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