High-density polyethylene (HDPE) is increasingly used for pipe applications owing to its lower cost and higher resistance to chemical corrosion and biological attack compared with metallic materials. Hence, HDPE with improved mechanical properties for pipe application were developed. In addition, additives are used to improve the longterm performance of PE pipes. Carbon black (CB) is one of the most widely used additives in PE pipes due to its low cost and absorption of UV which contributes to the resistance to photo degradation. However, it is difficult to achieve good homogenisation of HDPE and additives by the single-screw extrusion method. Insufficient homogenisation is observed as black (where HDPE and CB are well mixed) with white striations (only HDPE without CB); the white striations are called "windows". It has been shown that windows could lead to reduction of HDPE pipe performance and several methods have been developed to detect them. However, there is lack of study on the effect of windows on the integrity of butt fusion joints and there is only one method reported in open literatures which can quantify the window. However, this method causes material wastage.
Artificial freezing method has been widely used in various underground projects, but the development law of freezing temperature field of complex curtain is difficult to be calculated by analytical method. As a general method, numerical method is feasible to simulate the development law of horizontal freezing temperature field of complex curtain. In this paper, the development law of temperature field in the freezing process is analyzed based on the freezing method construction of a subway connecting passage. The feasibility of this method is verified by comparing with the measured data. The results can be used to guide the design and construction of artificial freezing.
The stability mechanism of large-diameter steel cylinder under fill load has not yet formed a complete theory. In order to calculate the stability of the steel cylinder island arm structure in a certain project, the limit equilibrium and finite element method are used in this paper. The limit equilibrium method is based on the limit equilibrium of the soil inside and outside the steel cylinder, taking into account the earth pressure and friction force on the cylinder, and using moment equilibrium to calculate its stability coefficient. Secondly, the finite element strength reduction method is adopted to analyze the stability of the steel cylinder island arm structure by using strength parameters to correlate with the temperature field and changing the boundary conditions of the temperature field. The results and analysis methods of this paper provide references for the construction and design of the same type of projects.
Uniaxial compressive strength is the most basic mechanical property of frozen soil and a necessary mechanical parameter in frozen soil design and construction. Therefore, uniaxial compression test of frozen soil is one of the important test contents of frozen soil test. On the basis of field sampling, this paper conducts a series of uniaxial compression tests on silty clay and silty soil in Binhai New Area under different freezing temperatures. Through analysis and research, the uniaxial compression stress-strain relationship of frozen soil with different soils is established, and the variation law of uniaxial compression strength with freezing temperature is summarized. The results of this paper provide effective guidance for frozen soil design and construction.
Freezing up is one of the problems that are paid close attention to in the construction of artificial freezing method, especially the horizontal freezing up of complex curtain is difficult to be calculated by theoretical formula. The adaptability of numerical calculation is strong. In this paper, numerical calculation method is used to simulate the horizontal freezing and freezing expansion of complex curtain. Thermophysical parameters considered in the simulation change with the change of temperature field. Thermodynamic parameters of each point in soil are given by way of field variables, which provides ideas and methods for accurately simulating the horizontal freezing and freezing expansion displacement field of complex curtain.
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