研究城乡土地利用变化规律与驱动机制,有利于实现区域土地资源可持续发展。本文以长春市为例,以监督分类与人工解译相结合的方式对1997、2007和2017年Landsat卫星影像进行分类,总体精度分别为93.06%,90.70%和94.12%。1997-2017年,草地、耕地和其他土地面积分别减少354.74、922.11和55.35 km2,建设用地、水域和林地面积分别增加1 154.14、70.38和107.54 km2,整体表现为建设用地向周边扩张,侵占其他用地类型面积。利用未来土地利用模拟（future land use simulation,FLUS）模型,以2007年分类数据为基础,结合地形、交通区位和社会经济等土地利用变化驱动因子,仿真2017年土地利用格局,仿真结果与真实情况吻合较好,仿真精度达85.10%,Kappa系数为0.821 2,验证了模型和驱动因子精度可靠,符合土地利用变化趋势。以此模型因子预测2027年土地利用格局,结果表明：在城镇周围,建设用地将持续侵占耕地、林地、草地和其他土地的面积,但趋势减缓,同时林地面积和水域面积增加。 相似文献
It is important to be fully aware of the dynamic characteristics of saturated soft clays under complex loading conditions in practice. In this paper, a series of undrained tests for soft clay consolidated with different initial major principal stress direction ξ were conducted by a hollow cylinder apparatus (HCA). The clay samples were subjected to pure principal stress rotation as the magnitudes of the mean total stress p, intermediate principal stress coefficient b, and deviator stress q were all maintained constant. The influences of intermediate principal stress coefficient and initial major principal stress direction on the variation of strain components, generation of pore water pressure, cyclic degradation and non-coaxiality were investigated. The experimental observations indicated that the strain components of specimen were affected by both intermediate principal stress coefficient and initial major principal stress direction. The generation of the pore water pressure was significantly influenced by intermediate principal stress coefficient. However, the generation of pore water pressure was merely influenced by initial major principal stress direction when b?=?0.5. It was also noted that the torsional stress–strain relationships were affected by the number of cycles, and the effect of intermediate principal stress coefficient and initial major principal stress direction on the torsional stress–strain loops were also significant. Stiffness degradation occur under pure principal stress rotation. Anisotropic behavior resulting from the process of inclined consolidation have considerable effects on the strain components and non-coaxial behavior of soft clay.
Acta Geotechnica - This work presents the results from a series of plane strain compression experiments on medium-density sands. In these experiments, a new type of plane strain experimental... 相似文献
Mathematical Geosciences - In order to speed up the development and utilization of hydrothermal energy, it is essential to assess the potential of geothermal resources in petroliferous basins. In... 相似文献
Unlike conventional grouted micropiles, screw micropiles have been recently introduced to the foundation industry. Full-scale field tests of screw micropiles were carried out at a cohesive soil site. The screw micropiles have a diameter varying from 76 to 114 mm and a length varying from 1.6 to 3 m, and spiral threads welded on the lower half of the steel tubular shaft. Site investigation from cone penetration tests (CPT) and laboratory testing implies that the soil was medium to stiff, low plasticity clay. Six axial monotonic and three axial cyclic load tests were performed on three micropiles. One micropile was instrumented with strain gauges to investigate the shaft load distribution during loading. The axial cyclic loading was intended to simulate cyclic inertia load during vertical ground motions. Results showed that the micropiles behave as frictional piles during monotonic tests; the unit shaft resistance and adhesion coefficient were calculated and compared with results in the literature. The end installation torque was estimated using CPT shaft resistance and was shown to agree reasonably with the measured torque. Under axial cyclic loading, the micropiles underwent small cumulative displacements and the magnitude of the displacement decreased with increasing pile length and diameter. Cyclic loading redistributed the load transfer along different segments of the micropile. Negative skin resistance was observed along the smooth pile shaft when the pile underwent decreasing axial loading.
An approach based on individual rainfall events is introduced to mathematically describe the hydrologic responses and estimate the stormwater capture efficiencies of permeable pavement systems (PPSs). A stochastic model describing the instantaneous dynamic water balance of a PPS is established, from which the probability distribution of the antecedent moisture content of the PPS at the beginning of a rainfall event is analytically derived. Based on this probability distribution and the event‐based approach, an analytical equation that can be used for estimating the stormwater capture efficiencies of PPSs is also derived. The derived analytical equation is verified by comparing its results with those from continuous simulations for a wide range of PPSs with different sizes and underlying soils and operating under various climate conditions. It was found that the antecedent moisture contents of PPSs at the test locations are usually fairly close to zero, suggesting that PPSs at these locations are always almost empty at the start of a rainfall event. The derived analytical equation accounts for many key processes influencing the behaviour and operation of PPSs; it may serve as an easy‐to‐use tool that is essential for the planning and design of PPSs. 相似文献
Through analysis of seismic ambient noise recorded by the GHENGIS array, we constructed a high‐resolution 3‐D crustal shear‐wave velocity model for the central Tien Shan. The obtained shear‐wave velocity model provides insight into the detailed crustal structure beneath the Tien Shan. The results obtained at shallow depths are well correlated with known subsurface geological features. Low velocities are found mainly beneath sedimentary basins, whereas high velocities are mainly associated with mountain ranges. At greater depths of ~43–45 km, high velocities were observed beneath the Tarim Basin and Kazakh Shield; these high velocities extend forward in opposite directions and tilt down towards the central Tien Shan to a depth of in excess of 50 km, most likely reflecting lateral variations in crustal thickness beneath the Tien Shan and surrounding platforms. 相似文献
