This study examines how coarse aggregate volume fraction (V_a) affects the double-K fracture toughness and fundamental mechanical properties of concrete. Wedge-splitting tests were conducted on specimens with six different V_a values: 19%, 25%, 31%, 37%, 43%, and 50%. The results indicate that compressive strength (f_c) and elastic modulus (E) consistently increase with V_a, reaching 59.8 MPa and 37.9 GPa at V_a = 50%, respectively. Conversely, tensile strength (f_t), double-K fracture toughness (including initiation toughness $K_{\mathrm{IC}}^{\mathrm{ini}}$ and unstable toughness $K_{\mathrm{IC}}^{\mathrm{un}}$), and fracture energy (G_IF) initially increase before decreasing, peaking at an optimal V_a of 37%. Specifically, $K_{\mathrm{IC}}^{\mathrm{ini}}$, $K_{\mathrm{IC}}^{\mathrm{un}}$, and G_IF reached their maximum values of 0.54 MPa·m^1/2, 1.20 MPa·m^1/2, and 225.0 N/m at V_a = 37%. The tortuosity of crack paths follows a similar trend, becoming more pronounced up to V_a = 37% before diminishing. Furthermore, quantitative exponential relationships were established between f_t and $K_{\mathrm{IC}}^{\mathrm{ini}}$, $K_{\mathrm{IC}}^{\mathrm{un}}$, and G_IF. A safety warning parameter (δ), derived from the double-K fracture toughness, was proposed to quantitatively assess the pre-peak ductility, with values ranging from 0.88 to 0.72 in this study. The findings offer valuable guidance for optimizing concrete mix design, suggesting that a V_a range of 25% to 31% provides an optimal balance between high crack initiation resistance and adequate safety warning capacity for critical engineering structures.

The sedimentary laminae of Tamarix cones in arid regions are of great significance for dating and climatic reconstruction. Here, we present a multiproxy climatic record from the Tamarix cones in the southern margin of the Taklimakan Desert. Both the bivariate analysis and canonical correlation analysis were carried out for four groups of climate proxies in Tamarix cones, including organic matter content, grain size, cation content, and stable isotope content (δ¹³C, and δ¹⁸O). The temperature during the period from 1790 to 2010 AD has been reconstructed using the support vector machine optimized by the grey wolf optimizer, in which the climate proxies (TN, TOC, C/N, Mg²⁺, Ca²⁺, δ¹³C, and δ¹⁸O) were selected using the neighborhood rough set. The reconstructed values are in good agreement with the instrumental data. The regional temperature has distinct stages during the period from 1790 to 2010 AD, with cold conditions during 1790–1840 AD and 1896–1939 AD, and with warm conditions during 1841–1895 AD and 1940–2010 AD. The present work is beneficial to predict the future climate in the local area and encourage local governments to develop more effective measures to address the risks of climate change to environmental sustainability.

State-of-the-arts in the study of urban land subsidence in our country, including its occurrence mechanism, prediction and control have been reviewed in recent years. The land subsidence is a geological hazard with a reduction of regional elevation owing to the compact of soil which is given rise to the natural and human factors. It is found that the engineering construction is getting more and more impact on land subsidence. The relationship between the construction characteristics, such as the size of buildings, the volume ratio and the degree of dispersion, and land subsidence was revealed, which is helpful to the environmental protection and the sustained development of the city.