The soil-water characteristic curve (SWCC) is the basis for describing seepage, strength, and constitutive model of unsaturated soil. The existing SWCC models do not work accurately for evaluating loess, because they do not consider the pore deformation that is induced by wetting. The present study develops a new SWCC model for unsaturated loess. The model considers the effect of wetting-induced pore deformation (WIPD) on the SWCC. The new model includes 6 parameters, which could be confirmed by laboratory tests. The pore volume function (PVF) was described by the WIPD. The shift factor ξ1i and the compression factor ξ2i were introduced into the model. The relationship between the void ratio e and ξ1i and ξ2i was established using the average pore radius. The new SWCC model for saturated loess was improved based on the classical van Genuchten (V-G) model. If the WIPD had not been considered, the new model would regress into the classical V-G model. SWCC tests of unsaturated loess with different void ratios were carried out to verify the new model. The model parameters were calibrated in the original state, and the SWCCs of different void ratios were predicted by the new model and found to be in good agreement with the test results.
The collapsibility is one of the key properties for loess. Harmful impacts on the metro tunnels could be obviously subjected to the soaking collapsibility in collapsible loess. However, loess soaking cannot be effectively modeled by the existing centrifugal test equipment (CTE) due to its inherent limitations. In the present paper, a water soaking system (WSS) was improved based on the existing CTE for simulating various loess soaking conditions. The WSS was made of a water storage subsystem and a water distribution subsystem. Some tests were conducted to show the capability of the improved WSS in centrifugal model tests firstly, then it was used to carry out centrifugal model tests on a metro tunnel under full-range and half-range foundation soaking conditions with different soaking depths. The impacts of various soaking conditions on the mechanical properties of the metro tunnel were discussed in detail.
In order to investigate the actual health condition of asphalt concrete pavements on widened road embankments, a full-scale model test study was conducted. A fiber Bragg grating–based sensor network was developed to monitor the strain distributions within the pavement structure, which was subjected to differential settlements. An improved packaging and installation method of the quasi-distributed sensor system was utilized, which not only ensured a high sensor survival rate but also achieved accurate measurement of axial strains in longitudinal and transverse directions. Based on the monitoring results, the strain characteristics of the pavement structure under different settlements were analyzed in detail. It is found that in general, the top layer of the asphalt pavement structure was subject to tension stress due to the differential settlement of the embankment. Plastic deformation of the pavement was observed when the differential settlement increased to 22 cm. The base layer of the pavement had the most significant response in comparison with the top and middle layers. The geogrid reinforcement in the embankment had a positive effect to alleviate the tension stress in the pavement. This experimental study also indicates the capability of fiber optic sensor networks to monitor the performance of pavements with a high degree of accuracy.
To evaluate the performance of supercapacitor objectively and accurately, it is critical to develop an electrode with a thickness in the hundred-micrometer range and commercial-level mass loading of active material. In this work, for the first time, high mass loading CuO as active material (10 mg cm −2 ) is supported on La 1-x Sr x CoO 3-δ (LSC, 0 ≤ x ≤ 0.8) substrate (thickness: ∼ 500 μm) and used as a cathode for asymmetric supercapacitor. The novel and binder-free CuO/LSC73 (i.e., x = 0.3) electrode shows high areal (C a , 5.45 F cm −2 ) and specific (C s , 545 F g −1 ) capacitances. The packaged quasi-solid-state asymmetric supercapacitor with PVA/KOH gel as an electrolyte and carbon cloth as an anode, delivers an ultrahigh volumetric energy density of 4.92 mWh cm −3 at 10 mA cm −2 in a wide potential window of 1.4 V, which is comparable to those of lithium batteries (∼0.3−10 mWh cm −3 ). In addition, power density of the assembled device can reach 727 mW cm −3 at 80 mA cm −2 with a high energy density of 3.03 mWh cm −3 . The remarkable electrochemical performance is attributed to high conductivity of the porous LSC73 substrate and uniform distributions of CuO nanoparticles, which are favorable for the rapid electron transport and effective ions diffusion.
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