A high-performance concrete (HPC) is required to have superior performance in various aspects such as workability, strength, durability, dimensional stability, segregation stability, and passing ability. The mix design of HPC is rather complicated because the number of ingredients in HPC is usually more than those in conventional concrete and some of the required properties are conflicting with each other in the sense that improvement in one property would at the same time cause impairment of another property. However, there is still lack of understanding regarding how the various mix parameters should be optimised for achieving best overall performance. Most practitioners are still conducting mix design primarily through trial concrete mixing, which is laborious, ineffective, and often unable to timely respond to fluctuations in the properties of raw materials. To address these issues, the authors have been developing the packing and film thickness theories of concrete materials, in order to revamp the mix design philosophy of HPC in terms of the water film thickness (WFT), paste film thickness (PFT), and mortar film thickness (MFT) in the concrete. Based on the findings from an extensive experimental programme, suitable ranges of WFT, PFT, and MFT have been recommended.

Establishing an accurate in situ stress field is important for analyzing the rock-mass stability of the underground cavern at the Huangdeng hydropower station in China. Because of the complexity and importance of the in situ stress field, existing back analysis methods do not provide the necessary accuracy or sufficiently recognize nonlinear relations between the distribution of the in situ stress field and its formative factors. Those factors are related to the geological structures of high compressive tectonic stress regimes, including geological faults and tuff interlayers. The new two-stage optimization algorithm proposed in this paper is a combination of stepwise regression (SR), difference evolution (DE), support vector machine (SVM), and numerical analysis techniques. Stepwise regression is used to find the set of unknown parameters that best match the modeling prediction and determine the range of parameters to be recognized. Difference evolution is used to determine the optimum parameters of the SVM. The SVM is used to create the DE-SVM nonlinear reflection model to obtain the optimal values of the parameters from measured stress data. We compare the new two-stage optimization algorithm to other two popular methods, a multiple linear regression (MLR) analysis method and an artificial neural network (ANN) method, to estimate the in situ stress field for the actual underground cavern at the Huangdeng hydropower station. The two-stage optimization algorithm produces a more realistic estimate of the stress distribution within the investigated area. Thus, this technique may have practical applications in realistic scenarios requiring efficient and accurate estimations of the in situ stress in a rock-mass.

Piled embankments are widely used in highway and railway engineering due to their economy and efficiency in overcoming several issues encountered in constructing embankments over weak soils. Soil arching, caused by the pile-subsoil relative displacement (Δs), plays an important role in reducing the embankment load falling on weak soil, however, the fundamental characteristics (e.g., formation and features) of soil arching remain poorly understood. In this study, a series of discrete element method (DEM) modellings are performed to study the formation and features of soil arching with the variation of Δs in piled embankments with or without geosynthetic reinforcement. Firstly, calibration for the modelling parameters is carried out by comparing the DEM results with the experimental data obtained from the existing literature. Secondly, the analysis of the macro- and micro-behaviours is performed in detail. Finally, a parametric study is conducted in an effort to identify the influences of three key factors on soil arching: the friction coefficient of the embankment fill (f), the embankment height (h), and the pile clear spacing (s−a). Numerical results indicate that Δs is a key factor governing the formation and features of soil arching in embankments. To be specific, soil arching gradually evolves from two inclined shear planes at a small Δs to a hemispherical arch at a relatively large Δs. Then, with a continuous increase in Δs, the soil arching height gradually increases and finally approaches a constant value of 0.8(s−a) (i.e., the maximum soil arching height). For a given case, the higher the soil arching height, the greater the degree of soil arching effect. The parametric study shows that the friction coefficient of the embankment fill has a negligible influence on the formation and features of soil arching. However, embankment height is a key factor governing the formation and features of soil arching. In addition, pile clear spacing has a significant effect on the formation of soil arching, but not on its features.

Pressurized bentonite slurry is applied on a tunnel face to form a filter cake to stabilize the tunnel face when the slurry shield excavates through the sandy soil. Failure of the tunnel face may be caused by a high permeable filter cake, which commonly has a long penetration distance of slurry in sands. A column system with a height of 680 mm and a diameter of 300 mm was developed to model pressurized slurry infiltration in sands. Pressure transducers were installed to estimate the hydraulic conductivity of the filter cake during slurry infiltration. The electrical conductivity of the leachate of collected samples was measured. Results show that the majority of fine particles in slurry are within the range 100–300 mm into the sand specimen. The time for forming an impermeable filter cake is about 300 s, which indicates the impermeable filter cake is hard to form during the excavation.

Non-dispersive solvent extraction (NDSE) with p-xylene as extractant was employed as a novel separation method to recover both p-toluic (PT) acid and water from purified terephthalic acid (PTA) wastewater. The mass transport behavior of PT acid from aqueous solution to p-xylene was investigated by experiments and numerical simulation. Experiments showed that NDSE is feasible and effective. Residual PT acid in the raffinate can be reduced to lower than the permitted limit of wastewater re-use (100 g/m³) with extraction time longer than 60 s in industrial conditions. A mathematical model of PT acid mass transport was developed to optimize the membrane module performance. The model was validated with the experimental results with relative errors of less than 6%. Numerical analysis for mass transfer through the lumen side, the porous membrane layer, and the shell side showed that PT acid transport in the aqueous solution is the rate determining step. The effects of the membrane and operating parameters on membrane module performance were investigated by means of computational simulations. The key parameters suggested for industrial NDSE design are: fiber inner radius r₁=200–250 μm, extraction time t_e=50–60 s, aqueous/ organic volumetric ratio a/o=9.0, and temperature T=318 K.