Experimental arrangements are described that lead to reliable stress measurements in calibration chamber tests involving steel displacement piles in dense sand. The research required: developments with the chamber and pile testing equipment; novel approaches to the calibration and modelling of soil in-situ stress sensors; special arrangements for the sensors’ deployment; and development, calibration and operation of a miniature instrumented ICP pile. Preliminary results are reported from pilot tests to demonstrate the capabilities of the resulting measurement systems.
This paper describes the potential use of miniature soil stress measuring cells in model pile tests where normal stresses up to several MPa may be expected, accompanied by unloading and multiple substantial stress reversals. Devices rated in the 0.5 to 7 MPa range are considered and it is shown that they can develop marked cell-action effects, including strong non-linearity and hysteresis. A new approach to cell calibration and characteristic modelling is presented. It is shown that measurement errors may only be kept within tolerable limits through complex calibrations involving cells with suitable boundary conditions combined with a multi-stage loading history dependent, data reduction procedure.
This paper presents a simple procedure for evaluating the coefficients of volume change of unsaturated soils from measurements of the shear and dilatational wave velocities. The procedure is based on some analytical expressions that have been derived in the present study using the theory of linear elasticity for low-frequency excitations. The soil parameters required as input are the porosity and degree of saturation of the soil, Poisson's ratio of the soil skeleton, and three physical parameters that generally assume constant values. The results of some applications of the proposed method to a set of experimental data published in the literature are also shown.
Spectral analysis of surface waves (SASW) technique is an in-situ nondestructive method used for near surface soil site profiling. In the present study experimental uncertainties related to this method are assessed in connection with test configuration specification and data quality. Field experimentations have been conducted for this purpose with various spatial configurations of source to near receiver distance and inter-receiver distance under various impact source magnitudes and heights of fall. Based on the experimental findings, a method has been proposed to identify the frequency range of interest based on a threshold minimum cross power spectrum value. Further, it is proposed to consider subset stacking combination with good data quality which can be estimated based on weighted evaluation of the coherence of each frequency and importance of different frequency ranges. A procedure of obtaining the site specific dispersion curve is illustrated with due consideration to the issues associated with data quality and power spectra.
The high-cycle accumulation (HCA) model proposed by Niemunis et al. (2005) predicts permanent deformations in non-cohesive soils due to many cycles (N>103) with relatively small amplitudes (εampl<10-3, so-called high- or polycyclic loading). This paper demonstrates the applicability of the HCA model to different sands. For this purpose, approximately 200 triaxial tests with 105 cycles each have been performed on eight different quartz sands with mean grain sizes in the range of 0.15 mm≤d50≤4.4 mm and coefficients of uniformity in the range of 1.3≤Uc≤4.5. For each sand, test series with a variation of stress amplitude, initial relative density, average mean pressure pav and average stress ratio ηav=qav/pav have been conducted. The influence of the grain size distribution curve on the rate of strain accumulation is discussed. A comparison of the measured data with predictions made by the HCA model (with different material constants) is given. Correlations of the material constants with index or granulometric properties are discussed. The correlations may be useful for a simplified procedure to determine a set of material constants.
T-bar and Ball penetration tests (TPT and BPT, respectively) were carried out at three sites consisting of soft clays. These penetration tests have several advantages over the conventional cone penetration test (CPT): much larger project area and no effects of overburden pressure for obtaining soil parameters such as undrained shear strength. Therefore, TPT and BPT are considered to be suitable in-situ tests for very soft ground. In this paper validity of the assumed mechanism of these cones are examined, using ball cones with different diameters of the ball. In addition, the cone factors for CPT, TPT and BPT are compared based on undrained shear strengths (su) measured from field vane and direct shear tests. Cyclic BPT was carried out to measure the sensitivity of soil layers. It is revealed that reduction in the tip resistance with the increase in the number of cyclic penetration can be correlated with the sensitivity measured by the field vane tests. Finally, the possibility of estimating the in-situ effective overburden pressure (σ′vo) is discussed for an artificial island filled by dredged clayey soil, where consolidation due to self weight of the filling is still continuing.
In the evaluation of the damage caused by earthquakes, particular attention has been paid until now to the unstable behaviour (the phenomenon of liquefaction) of sandy grounds during tremors. However, studies of post-seismic damage and damage to clayey grounds have also been reported. In this paper, the behaviour of an actual alternately layered sand-clay ground and embankment-coupled system before, during, and after an earthquake is investigated. The investigations were carried out by soil-water coupled finite element analysis (GEOASIA), which is capable of handling inertial forces and utilizes the SYS Cam-clay model as the elasto-plastic constitutive model of the soil skeleton. By accounting for the effects of the soil skeleton structure (structure, overconsolidation, and anisotropy) at work, the above constitutive equation is capable of expressing the reduction of shear modulus, etc. caused by disturbance in loose sands and naturally deposited clays. In the analysis, (1) the effect of the rigidity of the embankment and (2) the effect of the penetration depth of the sheet pile in a strengthened ground with retaining walls and sheet piles joined by tie rods were examined. The main results are as follows: (1) If the embankment is soft, liquefaction of the upper sandy soil layer during the earthquake causes the embankment itself to collapse. In contrast, if the embankment is relatively hard, the shape of the embankment remains stable. However, a decrease in shear rigidity occurs in the lower clayey soil layer due to degradation (disturbance) of the soil structure, resulting in increased settlement both during and after the earthquake. (2) In the case of grounds strengthened by the sheet pile method, if the tips of the sheet piles are located in a soft soil layer with a high degree of structure, large disturbance may occur at such locations during an earthquake and cause increased settlement during and after the tremors.
The purpose of this study is to understand the soil properties of grounds which contain shallow type gas hydrates. For this purpose, the surveys were conducted in Lake Baikal, Russia from 2005 to 2007, where shallow gas hydrates existed. For the lake-bottom sediments, physical and mechanical properties were tested (on-board and laboratory tests). The tested samples were retrieved from the mud volcano ground which contains the shallow gas hydrates, and reference ground at the same area. From these results, it was found that the gas hydrates distribute in large amounts in the lake-bottom sediments of Lake Baikal, and that form of the gas hydrates are varied. In addition, the reference samples in Lake Baikal have no marked differences in the soil properties of the sediments obtained from other sea-bottom grounds. On the other hands, the strengths of the mud volcano samples were lower than those of the reference samples. It would seem that these results are due to the effect of the disturbance of sedimentary layers by upwelling of gas and water from underground and the pressure release during the sampling.
The viscous properties of air-dried relatively poorly-graded granular materials having different particle shapes were evaluated by performing a series of direct shear (DS) tests. The applied loading histories include repeated step changes in the shear displacement rate (s) or repeated sustained loading stages during otherwise monotonic loading (ML) at a constant s under constant vertical stress. Test results of an angular gravelly soil (i.e., Chiba gravel-a) obtained from the present study and those of a wide variety of poorly-graded granular materials (i.e., glass beads and natural sands including Toyoura, Hostun, Silica No. 6a, Ticino, Silver Leighton Buzzard, Ottawa, Albany and Monterey sands) previously obtained by the authors are analysed. The viscous properties of granular materials can be adequately described by three basic parameters: i.e., the rate-sensitivity coefficient, the residual rate-sensitivity coefficient (or their ratio, i.e., the viscosity-type parameter) and the decay parameter. These parameters, as well as the viscosity type (i.e., Isotach, Combined, TESRA and P&N), are strongly affected by particle shape as quantified in terms of the degree of particle angularity while being rather independent of particle size. The creep deformation that takes place by sustained loading increases with an increase in the shear stress level, and it also increases with changes in the viscosity type associated with an increase in mainly the particle angularity and partly the coefficient of uniformity. The various viscous property types and transitions among them can be described by a single general equation incorporating these parameters. A non-linear three component model incorporating this general equation can simulate very well all of the various viscous responses observed in the DS tests referred to in the paper.
Typhoon No. 14 in 2005 caused significant rainfall in Yamaguchi Prefecture of Japan, and, due to this, an embankment of Sanyo Expressway at Hataki in Iwakuni city failed. Detailed investigation was conducted after this event in order to identify the mechanism of this failure, which consisted of the field studies as well as laboratory tests and numerical analyses. It was consequently shown that the combined effects of heavy rainfall and the local geological and topographic conditions as well as the reduction of drainage capability due to the breakage of perforated pipe in the underdrainage system were the causes of the failure.
Matric suction is an important stress state parameter in unsaturated soil mechanics. Many studies have been carried out in the past to determine the matric suction through direct and indirect methods. Direct measurement of matric suction has been proven possible with high-suction tensiometer; however high-suction tensiometers are still susceptible to cavitation. The axis translation technique developed by Hilf (1956) has been employed in many laboratory tests for unsaturated soils to avoid problem of cavitation in the water pressure measurement system. However in laboratory testing of unsaturated soils, air and water pressures are usually independently controlled and there is no need for a feedback control. The matric suction of soil can be measured using a modified pressure plate apparatus by actively changing the air pressure to maintain the water pressure to be close to zero thus imposing negligible water content change in the soil. A major setback of the existing practice is the need to manually adjust the air pressure of the modified pressure plate in response to the changes in the water pressure. This paper presents an active control system for the modified pressure plate apparatus for matric suction measurement. The experimental results obtained from modified pressure plate apparatus with active control system show good performance as compared to the high suction tensiometer.
In this study, the possibility of wet compaction method to reduce swelling potential of high plasticity (active) clayey soils has been investigated and compared with lime stabilization method. Swell (and shrink) potential tests were performed using an oedometer apparatus on sand-bentonite mixtures which were compacted immediately after mixing with water. Tests were then repeated on different samples of the same composition after allowing 3-day free swelling prior to compaction. This method of sample preparation is herein referred to as “wet compaction”. Additional tests conducted on lime stabilized samples with and without wet compaction enabled comparison of the wet compaction and lime stabilization methods. Test results showed that wet compaction reduces the swelling potential of sand-bentonite mixtures and can thus work as a mitigation technique to reduce swelling potential of high plasticity (active) soils. However, as expected, lime treatment was found to be superior, especially if the dose corresponded to or was higher than lime fixation point. In addition, the volumetric change of both untreated and treated samples after drying at 40°C in an oven (during drying, shrinkage deformations were measured) as well as the effect of cyclic wetting and drying on the unconfined compression strength (UCS) of lime-stabilized samples were investigated.