When performing a slurry shield excavation in the shallow earth cover under a waterway, the support pressure is difficult to calibrate. If not carefully monitored, slurry fracturing or even slurry breakout can occur; water from the river can rush into the slurry circulating system, threatening the security of the project. In this study, an in-situ slurry fracturing apparatus was created to analyze the phenomena of slurry fracturing and fracture propagation. First, the fracturing test procedures and the method of identifying slurry fracturing are introduced. Then, mechanical models of the slurry fracturing and fracture propagation are described and validated with in-situ tests. The models provide fairly good predictions: the driving pressure is related to the properties of both the soil and slurry. Slurry with large parameters for bulk density and viscosity is beneficial for preventing slurry fracturing propagation. However, such parameters have little influence and can be neglected when determining the initial fracturing pressure. Preventing slurry fracturing and breakout is important for not only shield tunnel preparation, but also shield tunneling under dangerous conditions. A crucial factor is setting and limiting the maximum support pressure values. These pressures can be obtained through the in-situ tests and mechanical models described here. These results provide useful references for the Weisan Road Tunnel to be built under the Yangtze River in Nanjing, China.

The ultimate load and collapsing modes of steel frames under combined vertical and horizontal forces are investigated through finite element (FE) modelling and limit analysis. Consideration is given to a frequently overlooked problem which is the kinematics arising from the actual rotation of the plastic hinges under axial force and bending moment. This fact draws attention to the necessity of a careful assessment of the limit analysis approaches, a fact that might be seen as somewhat in line with the outcome from famous paradoxes, such as the one by Stüssi and Kollbrunner (1935), which can only be solved by making reference to both elastic and plastic deformations. As a result, it can be shown that in such a manner, it is possible to obtain a handy tool capable of competing with much more computationally expensive methodologies. The approach may be relevant to practising engineers dealing with code prescriptions and standardization committees.

A new cover cracking model is proposed for rebar corrosion. Rebar corrosion involves rust, which contributes to an expansive radial pressure at the concrete-steel interface and hoop tensile stresses in the surrounding concrete. Once the stress state exceeds a certain limit, anisotropic damage occurs. First, we establish an anisotropic damage model for concrete, which fully reflects the unilateral effect. Then an analytical model is proposed to calculate the displacement and the stress in a corroded reinforced concrete (RC) structural member based on that anisotropic damage. In this study, a concrete-rust-steel composite model is considered as a circular cylindrical concrete cover and a coaxial, uniformly-corroded, steel rebar, where the steel rebar and the mechanical properties of rust can be fully taken into account. At the same time, the influences of the steel-concrete interface pores and the cracks in concrete on the rust expansion pressure value are modeled. Finally, some experiments are made for comparison with the analytical results and good agreement indicated the proposed model could be used to predict both the variation of strain fields in structures during the corrosion process and the cover cracking time.

The efficiency of 4 K Stirling type pulse tube cryocoolers (SPTCs) is rather low due to significant regenerator losses associated with the unique properties of helium around 4 K and the high operating frequencies. In this paper, regenerator performance at liquid helium temperature regions under high frequencies is investigated based on a single-stage SPTC precooled by a two-stage Gifford-McMahon type pulse tube cryocooler (GMPTC). The 4 K SPTC used a 10 K cold inertance tube as phase shifters for better phase relationship between pressure and mass flow. The effect of the operating parameters, including frequency and average pressure on the performance of the 4 K SPTC, was investigated and the first and second precooling powers provided by the GMPTC were obtained. To reduce the regenerator heat transfer losses, a multi-layer regenerator matrix, including Gd₂O₂S (GOS) and HoCu₂, was used instead of a single-layer HoCu₂ around 4 K. A theoretical and experimental comparison between the two types of regenerator materials was made and the precooling requirements for a regenerator operating at high frequencies to reach liquid helium temperatures were given, which provided guidance for the design of a three-stage SPTC.

Using large cross-sectional datasets that were collected in the Osaka metropolitan area (OMA), Japan, this study systematically analyzes the structural changes in car ownership and usage in the OMA from 1970 to 2000. A simultaneous equations model system is developed for individuals that considers age, household lifecycle stage, built environment of the household location, car ownership levels, proportion of car trips on a given day, and total car travel duration. The estimation results show that private car ownership and car usage for the residents in OMA have expanded over time. Each residential area, each lifecycle stage, and each age group has their own unique characteristics of car ownership and car usage. The results further indicate that this expansion is largely due to changes in their structural relationships, while the changes in demographic factors play a relatively small and contradictory role.

Traditional crash frequency modeling uses crash frequency data averaged across multiple years. When data size is small, crash data in each year are used in the modeling to extend the size of the samples. The extension of sample size could create a temporal correlation among crash frequencies of the different years, which could affect the modeling accuracy. The primary objective of this study is to evaluate the application of the generalized estimating equation (GEE) procedures to account for the temporal correlation in the longitudinal crash frequency data. Four-year crash data at exit ramps on a freeway in China were collected for modeling. Based on the same data, traditional generalized linear models (GLMs) were estimated for model comparison. Results showed that traditional GLM underestimated the standard errors of coefficients for explanatory variables. The GEE procedure with an exchangeable correlation structure successively captured the temporal correlation among the crash frequencies of the different years. The GLM with GEE outperformed the traditional GLM in providing a good fit for the crash frequency data. Results of this study can help researchers better understand how various factors affect the crash frequencies at freeway divergent areas and propose effective countermeasures.

The mass transfer and reaction kinetics of sulfuryl fluoride (SO₂F₂) absorption with aqueous sodium hydroxide (NaOH) solutions were studied in an experimental double-stirred cell. Results showed that SO₂F₂ absorption with NaOH was followed by a reaction model employing a fast pseudo-first-order. The second-order rate constant for SO₂F₂ absorption with aqueous NaOH solutions was determined to be 1.44 m³/(mol路s) at 298 K. Three models were used in this chemical absorption process, and in each case, the same expression of enhancement factor was obtained. A comparison was made between the experimental enhancement factor and the value calculated from the model, and the maximum relative deviation was less than 4.2%. The proposed model expression gave a reasonable fit with the experimental values, indicating that mass transfer correlations are valid for scaling up design.