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The zero load readings of cone resistance (qc) and sleeve friction (fs) measured by a piezocone (uCPT) shift with the ambient temperature. A method of correcting the effect of temperature on uCPT measurements in seabed sediments has been proposed for the case where there is no temperature sensor in the uCPT probe. This method is based on the assumption that the "actual" profile of fs of soft shallow seabed sediments linearly increases with depth, and a rate of increase of α = 0.2 kPa/m was obtained using measured ground temperatures and fs values in seabed sediments in Isahaya Bay, Japan. An "actual" fs profile can then be constructed using the measured fs value at the shallow surface and the value of α. Using the differences between the measured and the estimated "actual" fs profiles, the ground temperature profile can be obtained, and then the effect of temperature on the uCPT measurements can be corrected. The proposed method was used for temperature corrections on uCPT measurements in Isahaya Bay, Japan. The values of undrained shear strength (su) from the temperature-corrected uCPT measurements agree well with the laboratory measured values of su using the undisturbed soil samples. [ABSTRACT FROM AUTHOR]

In this study, settling tests were conducted to investigate the sedimentation and self-weight consolidation behavior of seafloor sediments from Isahaya Bay, Ariake Sea, Japan. During the tests, the density variations with depth and time were measured by a gamma-ray transmission radioisotope densitometer. The test results show that the settling process of the seafloor sediments can be classified into the flocculation stage, settling stage, and consolidation stage. The settling rate of the seafloor sediments in the settling stage is dependent on the temperature and initial water content, while the settling rate in the consolidation stage is independent of the temperature and initial water content. The density profile changes from a constant density profile to a linear density profile when the sedimentation process transitions to the self-weight consolidation process. The relations between the void ratio (e) and effective vertical stress (p') at very low pressures can be calculated from the measured density values, and this can be used for the analysis of the self-weight consolidation of seafloor sediments. For the seafloor sediments tested in this study, the undrained shear strength (su) values are almost the same when the density values are less than 1.14 g/cm3, and the su values increase linearly with an increase in density when the density values are in the range of 1.14–1.2 g/cm3. [ABSTRACT FROM AUTHOR]

Abstract To investigate the effects of different pore water environments on compressive behaviours of the deep-sea soft soil from South China Sea, four kinds of soil samples including natural sample with sea water or deionized water, remolded sample with sea water or deionized water were prepared, respectively. Then, a series of oedometer tests and scanning electron microscopy tests were performed on the above samples to examine their compressive behaviours and microscopic characteristics, respectively. Additionally, the microscopic pore distribution of natural sample with sea water was observed by mercury intrusion porosimetry tests. The effects of different water environments on macroscopic compressive behaviours and microscopic particle characteristics are analyzed. The deionized water environment increases the compressibility and decreases the consolidation coefficient for natural samples after structural breakage and remolding. The microscopic particle characteristics corresponding to the macroscopic compressibility are also qualitatively analyzed. In deionized water environment, soil particles exhibit higher roundness, more orderly and lower surface roughness than that in seawater environment. In this study, the deionized water environment has no obvious effect on the structural yield stress and secondary consolidation coefficients of deep-sea soft soil. [ABSTRACT FROM AUTHOR]

This paper describes a full-scale test on a very soft clay ground around 70,000 m2, which is conducted in Huizhou of Guangdong Province, China, to present a new method of vacuum preloading method. A novel moisture separator was developed, which can automatically regulate the vacuum pressure variation by changing the volume of the gas inside it. A large quantity of water drained by the proposed moisture separators can be directly used as a surcharge loading, which would shorten the ground improvement time and save costs as well. Three levels of silt-prevention prefabricated vertical drains were used in the treating process to accelerate the consolidation. In addition, the vacuum preloading method also included an effective radial drainage device which would strengthen the dredged soft clay fill in a deep layer. In the in situ test, tens of piezometers and settlement plates were installed to measure the variations of excess pore water pressures and settlement of two stages of observation points at different positions in the ground. The results show that the largest average consolidation settlement was 314.1 cm and made a saving of more than 66% in power consumption compared with traditional method. It demonstrates that this adopted method is an efficient, cost-effective, and environmentally friendly method for improving sites with low bearing capacity and high compressibility soils. [ABSTRACT FROM PUBLISHER]

The mechanical behavior of clay subjected to cyclic loading is important to consider in the design of the foundations of many types of structures that must resist cyclic loading, such as subgrades and offshore foundations, because clay undergoes greater settlement under cyclic loading than under static loading. The difference in settlement between these two loading patterns due to creep behavior is affected by the cyclic frequency and the cyclic stress ratio. This study investigated the effects of the frequency and cyclic stress ratio of cyclic loading on the creep behavior of a natural clay in China using stress-controlled triaxial tests. The assessed the following parameters: three frequencies, four cyclic stress ratios, and six vertical stresses. The test results indicate that the soft clay displays accelerated creep behavior under dynamic loads. A specific “limit frequency” (in this case, 0.2 Hz) and a “safe load” at which the strain of the soft clay increases very slowly were observed. The effect of the effective axial stress on the creep behavior increases with the increase in the cyclic stress ratio. Based on the tests, the critical cyclic stress ratio is 0.267 at a certain effective axial stress and frequency. [ABSTRACT FROM AUTHOR]

The accelerated rheological properties of natural soft clay are the external power and predisposing factors of geological and geotechnical disasters. To determine the changes in soil micro-structure for natural soft clay under accelerated creep condition, a detailed study has been carried out using consolidated undrained tri-axial tests under static and cyclic loads, as well as experimental data from mercury intrusion porosimetry and a scanning electron microscope. In the tri-axial tests, creep of the soft clay would be accelerated under dynamic loads, the sample would be destroyed faster, and the strain-rate would increase clearly along with the increase of the vibration frequency. Based on a comparison of micro-structure behaviors between the intact sample and the test soil samples under static and dynamic loads in the creep condition, an interpretation of the changes in soil micro-structure for natural soft clay under an accelerated creep condition was proposed. The research indicated that the large pores of the soil sample gradually changed into small pores, the large particles continuously changed into tiny particles, and the pore distribution gradually became uniform under dynamic loads. It was found that the fractal dimension of the pores decreased with the increase of the vibration frequency. The test results not only showed that the accelerated creep characteristics depended on the vibration frequencies of the applied dynamic loads, but the accelerated creep was actually an unceasingly self-adjusting and reengineering process of the internal structure in soil under dynamic loads. In addition, these results revealed that there was a close relationship between the vibration frequencies and the micro-structure parameters. [ABSTRACT FROM AUTHOR]

Recent research has shown that in a parallel twin-tunnel arrangement, the 2nd tunnel generates greater settlement than the 1st tunnel as the soil between the two tunnels softens. For other spatial twin-tunnel arrangements (twin tunnels with different cover depths), the pattern of settlement can be more complex and is inevitably affected by the order in which the two tunnels are constructed. Few studies have attempted to establish the relationship between the changes in soil stiffness and settlement behaviour. Hence, the settlement behaviour induced by twin tunnels is not yet well understood. A numerical model was created in this study, and a centrifuge model test was then used to verify the performance of this model. A series of comparative numerical analyses (e.g., inclined and overlapping twin tunnel arrangements) were performed to investigate the effect of the construction order and relative positions of the two tunnels. The relationship between the changes in soil stiffness and settlement behaviour was well established. The mechanisms by which the 1st tunnel affects the settlement behaviour produced by the 2nd tunnel were clarified. [ABSTRACT FROM AUTHOR]

The dynamic constitutive relationship of soil is essential for seismic dynamic calculations in geotechnical seismic engineering. Numerous experiments have demonstrated that cohesive soil exhibits cyclic strain softening characteristics under dynamic loading (equal-amplitude loading and unequal-amplitude loading) conditions. However, the Masing criteria (Masing's 2-fold method) cannot describe the cyclic strain softening behaviour of soil for equal-amplitude loading and often fail to estimate the damping ratio accurately (underestimation of the damping ratio at low strain; overestimation of the damping ratio at high strain). Furthermore, the Masing criteria are not applicable for nonequal-amplitude loading. To solve these problems, the research in this paper is based on the Davidenkov skeleton curve, and Masing's 2-fold method is utilized to establish a hysteretic curve. The cyclic strain softening coefficient and damping ratio adjusting coefficient were proposed for equal-amplitude loading to accurately capture the cyclic strain softening properties of cohesive soil. For nonequal-amplitude loading, Masing's n-fold method is employed to establish stress‒strain hysteresis curves, and using the customized constitutive interface reserved by FLAC3D, the development of this constitutive model is achieved on the Visual Studio (VS)2015 platform. The calculation accuracy of the model is verified by comparison with the theoretical values and experimental data, and the rationality of the constitutive model is verified by cyclic direct simple shear tests and cyclic torsional shear tests of soil subjected to equal-amplitude loading and centrifuge model tests of ground bearing unequal-amplitude loading, which provides effective help for the study of earthquake disasters in cohesive soil sites. • A nonlinear dynamic constitutive model of cohesive soil captured cyclic strain softening characteristics was established. • The program of this constitutive model was achieved on the visual studio (VS) 2015 platform, and model rationality was verified. • The simulation performance of this constitutive mode is superior to FLAC 3D's built-in constitutive model. [ABSTRACT FROM AUTHOR]

• Field monitoring in combination with elaborate numerical modelling. • Clear insight into settlements of pile-tip and its surrounding soil. • Two load transfer mechanisms of pile foundation due to adjacent shield tunnelling. This study investigates the response of piled buildings to shield tunnelling in soft ground based on both a case history and numerical modelling. The findings indicate that building settlement can be significantly affected by the position of the tunnel relative to the pile foundation. Basically, two different settlement patterns of the pile toe are observed when the tunnel is excavated below and to the side of the pile foundation, implying the presence of different load transfer mechanisms: when the tunnel is excavated on the side of the pile foundation, the loads carried by the raft and pile shaft are transferred to the pile toe. The foundation may settle by compressing the pile-tip soil. In contrast, when the tunnel is excavated below the pile foundation, the loads carried by the pile toe are transferred to the pile shaft and raft. Unloading in the soil above the tunnel crown gives rise to foundation settlement. Notably, the settlement of the foundation in the latter mechanism is shown to be more significant. [ABSTRACT FROM AUTHOR]