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Geotechnical investigation and design show that when evaluating the settlement of ground with soft soil ground, the use of a single stress path results in a larger error than in the case of a multistress path. To understand the influence of a multistress path on the deformation properties and microstructure characteristics of soil, a two-stage stress path (corresponding to three stress states: the in situ state, unloading-loading state, and grouting pressure state) of soil was examined by analytical solution. Then, a series of triaxial tests was conducted to analyze macroscopic deformation properties considering four influencing factors, i.e., the relative distance between the soil and tunnel, stress paths, type of silty clay, and drainage conditions. The results show that axial strain of silty clay caused by the two-stage stress path increases by 31.6% with the relative distance decreasing from 1.67R (R means tunnel radius) to 1.25R on tunnel side, while the volume strain increases by 80% with the relative distance decreasing from 1.21R to 1.06R on tunnel bottom. In addition, the deformation caused by the two-stage stress path (or reconstituted soil or undrained condition) is larger than that caused by the one-stage stress path (or undisturbed soil or drained condition). Finally, through scanning electron microscopy and mercury intrusion porosimetry, the pore size, distribution, shape, and arrangement of silty clay on the bottom and sides of the tunnel were investigated. The research shows that under the two-stage stress path, the number of large pores decrease and that of small pores increase. The probability entropy of pore orientation ranges from 0.834 to 0.971 when silty clay is subjected to a two-stage stress path. This illustrates that the pore order of the soil on tunnel side is better than that on the tunnel bottom.

Ground treatment via the vacuum preloading technique has been extensively used in coastal belts worldwide in the field of civil engineering. However, due to the poor effect of traditional ground tr...

In recent years, the artificial ground freezing (AGF) method has been widely used in subway construction, and the engineering properties of soil have changed significantly after freezing and thawing. In this paper, a series of dynamic triaxial tests were used to investigate the pore pressure development of freeze-thaw soft clay under different cyclic dynamic stress ratios, loading frequencies and freezing temperatures. The test results show that the types of normalization pore pressure development include developmental and stable. An empirical model, considering the effects of cyclic dynamic stress ratio, loading frequency, freezing temperature and number of cyclic loading, was proposed and compared with three representative models proposed by the predecessors to validate that the proposed method has the best estimation on the development of the pore pressure.

Vacuum preloading technology can effectively reinforce the soft ground in coastal areas of China, which provides support for the safe construction and normal operation of transportation engineering. However, the conventional vacuum preloading technology has the limitations of ground reinforcement due to the clogging of the prefabricated vertical drain (PVD). This paper was based on the fact that elevated temperature could improve soil permeability and shear strength. Thermal consolidation vacuum preloading technology was proposed to analyze the ground reinforcement effect. To understand the reinforcement effect, the model experimental case of thermal consolidation vacuum preloading was designed to compare and analyze the temperature distribution, the development of water discharge, surface settlement, average consolidation degree, pore water pressure, water content and undrained shear strength at 25 °C, 50 °C and 70 °C in the laboratory-scale investigation. The research results presented that thermal consolidation vacuum preloading technology could significantly improve water discharge, surface settlement, average consolidation degree, undrained shear strength and reduce pore water pressure, water content, which illustrated that this technology was capable of significantly improving the effectiveness of soft ground. The research results could provide a reference for the soft ground treated by novel vacuum preloading technology to accumulate data.

The dynamic constitutive relation of soil is widely applied to the ground design of marine structure and infrastructure in offshore geotechnical engineering. Increasing evidence from marine geotechnical design has shown that the traditional dynamic constitutive model has uncertain theories, many parameters, and complexity. Therefore, it is urgent to overcome these limitations and develop a simple and practical elastoplastic dynamic constitutive relation for the saturated structural soft clay. A simple dynamic constitutive relation with 5 parameters was proposed in this study, which can reflect the strain accumulation, hysteretic characteristics and cyclic degradation of the stress-strain for structural soft clay. First, the Drucker-Prager model was selected as the bounding surface, hardening modulus equation was established by the hardening law, interpolation function and structural strength coefficient. Then, the incremental stress-strain relationship was derived based on the incremental theory. The UMAT subroutine was compiled by FORTRAN language. Finally, the cyclic triaxial test and numerical simulation were carried out, and the stress-strain relationship was analyzed. The research results showed that the test results were in good agreement with the prediction results of the model.

The permeability and deformation characteristics of Tianjin clays under coupled dynamic stress and seepage fields is a major concern in the geotechnical engineering field. In this study, a group of samples were tested in the laboratory using cyclic triaxial tests considering different parameters, including the number of cycles, cyclic stress ratio (CSR) and back pressures. The frequency of cyclic loading was kept constant at 1 Hz. The laboratory results show that the hydraulic conductivity is correlated with the void ratio by a unique curve under the same value of the CSR. The void ratio decreases with an increase in the number of cycles, which in turn decreases the hydraulic conductivity. In addition, an empirical equation for the degradation index is investigated. The hysteretic curves of the soil are also analysed to evaluate the size of the energy accumulative consumption and dynamic deformation characteristics. The results of this study illustrate that the deformation of Tianjin clays subjected to cyclic loading and seepage permeability should be determined in engineering practice.

A series of laboratory tests were carried out to evaluate the effectiveness of polyacrylamide (PAM) on dredger fill combined with the vacuum preloading method. Five groups of vacuum preloading model tests were conducted, and the groups were mixed with 0, 15, 30, 60, or 90 mg/L PAM. The test results indicated that the optimal dosage of PAM is 30mg/L for the Tianjin Binhai dredger fill with a water content of approximately 300%. The optimal dosage of PAM can not only considerably shorten the consolidation time of the dredger fill but can also notably increase the rate of dissipation of excess pore pressure. An approximately 70% increase in the vane shear strength was also observed. Mercury intrusion porosimetry was performed to analyze the pore characteristic parameters of the soil samples after vacuum preloading combined with PAM, and the results revealed that an excessive dosage of PAM can lead to relatively bigger pore diameter in the soil samples.

Deep foundation pit will cause settlement of surround buildings in the process of excavation. When the settlement is excessive, it will give rise to safety issues. Subsidence monitoring has become an important measure to ensure the safety of deep foundation pits. But in current subsidence monitoring engineering, the costs of wiring, unwiring and installation are particularly high. This paper proposes a portable wireless data transmission device in forecasting and early warning of settlement deformation of soils around deep foundation pits. We solve the problem by adopting the means of wireless communication to replace the cable transmission link part. The device does not rely on any personal computers. Instead, it can directly deal with the collected data through grey prediction GM (1, 1) mathematical model, neural network and interpolation model to give short-term, medium- term and long-term forecasts, respectively. Additionally it is able to set a threshold value. Once the forecast data reach the threshold, the device can issue alert and achieve the target of reminding technicians, so as to provide reliable basis to prevent and reduce disasters.