The determination of optimum moisture content is very important for soil materials. Conventionally the optimum moisture content is estimated by the measurement of void ratio (or dry density) of soil samples, which is sometimes time-consuming and tedious. This paper proposes a nondestructive evaluation (NDE) technique based on the nonlinear ultrasonic theory to determine the optimum moisture content of clay. It is found the nonlinear parameter of material defined by the nonlinear ultrasonic technique presents a similar variation trend with the void ratio of clay, corresponding to the increased moisture content. The same optimum moisture content is found by observing the variation of nonlinear parameter and void ratio. The results indicate the developed nonlinear ultrasonic technique could be a fast and convenient testing method for the determination of optimum moisture content of soil materials.

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This study reports a series of triaxial compression tests on frozen clay. The tests were performed on reconstituted Kasaoka Clay frozen at -2, -5 and -10 oC from isotropic normal consolidation of 400kPa. The specimens were sheared at constant or varying strain rates and temperatures, and their observed strength and its dependence on these factors are discussed. The results show that, within the investigated range of conditions, the shear strength increases log-linearly with an increase in the strain rate. The shear strength normalized by that at a given temperature, or by that at a given strain rate formed unique relationships against the strain rate or the temperature, respectively. The stress in a temperature-varying condition can generally be predicted for a given strain if constant-temperature stress-strain curves are considered as backbone relationships. The same observation is probably true for the strain-rate, as described by the isotache rule. These effects are similar on the deviator stress for strains larger than 5% as on the strength. At these strain levels, the stress-strain curves suggest that the frozen specimens were at a sufficiently plastic stage. The above features of temperature and strain rate effects are relatively simple to formulate and will be useful in developing a general rate-dependent thermo-mechanical model for frozen clays.

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This paper firstly introduces the constitutive model considering sand crushing and the transformed stress method, and then applies the transformed stress method to generalize this constitutive model. As an example, the yield and constitutive equations of the generalized model are detailedly given, and the stress-strain relation of a rockfill material under triaxial compression and extension state is predicted.

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This paper describes the effect of the initial volume ratio f0 (or the initial water content w0) on the rate of self-weight consolidation of dredged clay as well as the effect of the expressive form of the consolidation characteristics, by examinations on results of the consolidation calculation by means of the finite deferential method. The consolidation characteristics such as the compression curve were considered to express either the arithmetic f or the logarithmic f in calculations performed with different f0 (or w0) conditions. It was found as conclusions that the faster rate of self-weight consolidation was observed in cases of the arithmetic f was considered, and the rate of consolidation became faster with an increase of f0. It is also found that the stable calculation can be performed if consolidation characteristics were expressed in log f form even though a large interval of time difference was configured. In contrast, the short interval of time difference was needed to obtain stable results from calculations with the arithmetic f expressive form.

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This paper extends a constitutive model previously developed by the authors to model the anisotropic sand behavior during cyclic rotation of principal stress axes. A new anisotropic stress tensor is defined by transforming the principal stresses during the rotation, and is then incorporated to formulate the incremental form of the constitutive relation for anisotropic soil subjected to cyclic load. All the model parameters can be conveniently calibrated by triaxial compression/extension tests. The new model is validated by simulating the behavior of Toyoura sand subjected to rotational shearing and good comparison is observed with the experimental data.

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Strong weathered granite is abundant in China and it is used extensively as a fill material. However, systematic research on this material is relatively less as compared to sedimentary type of soils like sand and clay. In this study, a series of laboratory tests were performed, including X-ray diffraction test, sieving test, liquid and plastic limit test, compaction test, and California bearing ratio (CBR) test, to study the basic characteristic of strong weathered granite. Specially, in order to evaluate the effects of clay content on the mechanical properties of the compacted weathered granite, the extra compaction test and CBR test were made by using samples with the five different clay contents of 4, 8, 10, and 12% by weight. Results of the laboratory tests indicated that the clay content of 8% could be a good indicator to determine the compaction characteristics of weathered granitic with different clay contents. Thus, clay content of about 8% would be advantageous to the compaction rate of subgrade and the stability of roads. However, The California bearing ratio of strong weathered granite with clay content of about 4% is largest, 95%. A preliminary relationship between weathering process parameters (m, r) and burying granite depth (h) was established to improve the understanding of weathering process and degree of this material. It is found in this research that as the depth h of weathered granite increases, the geological year’s parameter m becomes smaller in a power function, but the geometric progression constants r becomes larger in a power function.

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Engineering properties of local soil called ‘Polishing sand’ distributed over the southern district of Tsu-shi in Mie Prefecture was examined by performing laboratory tests. Polishing sand at natural state found as a sedimentary soft rock with average strength parameters of qu = 0.2 to 3.4MPa, ccu = 100 to 200 kPa,φcu³ 40 - 50 degrees, it transforms into a homogeneous grayish-white sand when exposed to the surface by excavation. Looking on the average strength parameters of the disintegrated sand, ccu = 10kPa, φcu = 360, a drop in qu to almost 1/10 or smaller level than that at natural state is observed. The difference in properties of these two states of the same material are considered to be due to cementation and crystallization effects between soil particles. When in a natural state, the anisotropy evaluated by triaxial tests with bender elements shows Ghh/Gvh = 1.4 - 1.5 at mean effective confining pressure, p'= 0 - 100kPa and Ghh/Gvh >>1.0 at 100 <p'£ 400kPa. This shows an anisotropic behavior at deposition because of cementation and its destructuration afterwards at higher confining pressure. Additionally, the relation between qu and G has been elaborated by comparing it with cement-treated soil and by discussing physical and chemical aspects of cementation.

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Fire occurred in underground engineering such as tunnel will cause the change of the temperature field in the surrounding soil. The study on thermal conductivity of soils in fire environment is very important. This paper focuses on the experimental study on heat transfer characteristics of soft clay in Shanghai in high temperature environment over 100°C. The test results show that the change of internal temperature of initial saturated soils can be roughly divided into four stages, namely rapid heating stage I, constant temperature stage II, the second rapid heating stage III and the final constant temperature stage IV, when the drainage and exhaust are allowed in the high temperature environment. There is a peak value in the high temperature curve, the higher the temperature the bigger the peak value. According to comprehensive analysis of the heating curves under different temperature, high temperature has significant influence on thermal conductivity of soils and causes the increasing of thermal conductivity for wet soil and dry soil. The thermal conductivity of dry soil is relatively smaller than that of wet soil.

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Here we hoped to understand loess dynamic deformation through analyzing the physical process and mechanical mechanism. Therefore, we introduced a concept of stress ratio and proposed its mathematical formula to disclose the three-stage feature of loess dynamic strain hiding inside a series of laboratory data. By applied Mohr-Coulomb failure criterion, the stress ratio could consider three aspects of influence factors, i.e. structure strength of soil, consolidation pressure in actual field and seismic loading onto the soil. To a certain extent, the stress ratio could reveal the relative tolerability of loess soil under seismic loadings. Based on three-stage features of loess dynamic deformation, we obtained an empirical relation between stress ratio and compression value of void ratio. Then combined with a theoretical relation of dynamic residual strain, initial void ration and compression value of void ratio, we provided a semi-empirical model to estimate the dynamic residual strain of unsaturated loess.

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Many of geotechnical engineering problems arising from particle crushing have been identified under high earth dams and the tips of pile foundations where extremely high pressures exist. Particle crushing causes a change in initial soil structure, resulting in remarkable influence on the compressive and shear behavior of granular materials. In order to investigate the soil behavior associated with the particle crushing in detail, three types of tests were carried out using newly-designed high pressure true tri-axial compression apparatus with capacity of maximum stresses up to 200MPa. High pressure compression test was conducted on Toyoura sand with a variety of stress paths taking into account of an assumption of the actual stress state under the tips of pile foundations. The occurrence of particle crushing was confirmed by showing the particle size distribution curve derived from the sieving test before and after three types of tests. The crushing degree after the shear compression test was found to be significantly higher than other tests. The plastic work calculated from the results of stress-strain relationship and the relative breakage, Br, can be approximately linearized. Furthermore, particle shape analysis was carried out using digital microscope and image analysis software. The difference in appearance and shape of sand before and after test was remarkable.

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On basis of the analysis on results of laboratory test, the field vane shear test and the static cone penetration test of different types of soil in Tianjin, it is proposed that there is significant positive linear correlation between the static cone penetration tip resistance and the vane shear strength. Moreover, for clay a more distinct linear correlation exists than that for mucky soil and silty clay. Therefore the results of static cone penetration test can be applied to the stability calculation.

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A theoretical study of the behavior of structured soil is presented in this paper. By introducing the influence of soil structure and loading history into the Cam Clay model, a new model is formulated. The concept of the difference of void ratios is modified to combine the structure parameter and the overconsolidation ratio and the evolution law is proposed. The new model is a two yield surface model by introducing the concept of the subloading yield surface. By making comparisons of predictions with experimental results, it is demonstrated that the new model provides satisfactory qualitative modelling of many important features of the behavior of structured soils.

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Drained and undrained shear strength and creep characteristics of saturated Hokota sand were evaluated by triaxial compression (TC) tests. Among the specimens, the degree of compaction Dc = ρd/(ρd)max x100 %, where ρd is the dry density and (ρd)max is the maximum dry density for the compaction energy level (CEL) equal to the standard Proctor (1.0Ec), and the degree of saturation, Sr, were changed. Compressive strength qmax in undrained TC increases significantly with Dc, becoming significantly higher and lower than drained qmax as Dc increases and decreases from about 90 %. This result indicates that, despite that the drained strength is often used irrespective of drain condition in seismic design, the undrained strength should be used where relevant. For the same Dc, the effects of Sr at compaction on qmax are insignificant. In practice, CEL used in a laboratory test is often equal to 1.0Ec (Ec is compaction energy) and the field compaction is done at a water content higher than its optimum value for 1.0Ec, (wopt)1Ec. However, the actual CEL in the field is variable and usually unknown. CEL in the modern earthwork can easily exceed 1.0Ec. In that case, w higher than (wopt)1Ec may become too high in that, despite an increase in CEL, ρd may not increase noticeably while the strength and stiffness may not increase efficiently. Besides, Sr may become too high and the risk of over-compaction becomes high. On the other hand, "the optimum degree of saturation (Sr)opt" defined as Sr where (ρd)max is obtained at a given CEL is independent of CEL. So, it is recommended to control the field Sr to be equal to (Sr)opt so that (ρd)max is obtained for the current unknown CEL, while ensuring the (ρd)max value to be high enough to achieve the design drained or undrained qmax value.

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Crushed granular materials have been considered as different materials compared with original one, which can be described by new compression parameter and peak stress ratio. Based on experimental results, the movement laws of compression line and critical state line of the original and crushed granular materials were investigated in this paper and two basic formulas were given: one formula describes the relationship between compression parameter/rebound parameter and broken indexes; the other formula describes the change about stress ratio at critical state when grain crushing occurs. A constitutive model is proposed by combining the above two formulas and the unified hardening model. The new model can not only consider particle crushing, but also describe shear dilatancy, strain-hardening and softening. In addition, the validity of this new model was confirmed by test data.

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