Analytical modeling on consolidation of stiffened deep mixed column-reinforced soft soil under embankment

Stiffened deep mixed (SDM) column is a new ground improvement technique to improve soft soil, which can be used to increase bearing capacity, reduce deformation, and enhance stability of soft soil. This technique has been successfully adopted to support the highway and railway embankments over soft soils in China and other countries. However, there have been limited investigations on its consolidation under embankment loading. This paper developed an analytical solution for the consolidation of embankment over soft soil with SDM column in which core pile is equal to or shorter than outer DM column. The consolidation problem was simplified as a consolidation of composite soil considering the load shear effect of core pile. The developed solution was verified by a comparison with the results computed by three-dimensional (3-D) finite element analysis. A parametric study based on the derived solution was conducted to investigate influence factors—length of core pile, diameter of core pile, diameter of SDM column, modulus of DM column, and permeability coefficient of DM column—on the consolidation behavior of SDM column-supported embankment over soft soil. The developed solution was applied to a case history of SDM column-supported embankment, and a good agreement was found between the predictions and the field measurements.     

Water uptake of riparian plants in the lower Lhasa River Basin,South Tibetan Plateau using stable water isotopes

Riparian plants can adapt their water uptake strategies based on climatic and hydrological conditions within a river basin. The response of cold-alpine riparian trees to changes in water availability is poorly understood. The Lhasa River is a representative cold-alpine river in South Tibet and an under-studied environment. Therefore, a 96 km section of the lower Lhasa River was selected for a study on the water-use patterns of riparian plants. Plant water, soil water, groundwater and river water were measured at three sites for δ¹⁸O and δ²H values during the warm-wet and cold-dry periods in 2018. Soil profiles differed in isotope values between seasons and with the distance along the river. During the cold-dry period, the upper parts of the soil profiles were significantly affected by evaporation. During the warm-wet period, the soil profile was influenced by precipitation infiltration in the upper reaches of the study area and by various water sources in the lower reaches. Calculations using the IsoSource model indicated that the mature salix and birch trees (Salix cheilophila Schneid. and Betula platyphylla Suk.) accessed water from multiple sources during the cold-dry period, whereas they sourced more than 70% of their requirement from the upper 60–80 cm of the soil profile during the warm-wet period. The model indicated that the immature rose willow tree (Tamarix ramosissima Ledeb) accessed 66% of its water from the surface soil during the cold-dry period, but used the deeper layers during the warm-wet period. The plant type was not the dominant factor driving water uptake patterns in mature plants. Our findings can contribute to strategies for the sustainable development of cold-alpine riparian ecosystems. It is recommended that reducing plantation density and collocating plants with different rooting depths would be conducive to optimal plant growth in this environment.     

Composition and flux of suspended organic matter in the middle and lower reaches of the Changjiang (Yangtze River) — impact of the Three Gorges Dam and the role of tributaries and channel erosion

To investigate the sources of particulate organic matter (POM) and the impact of Three Gorges Dam (TGD), two large lakes and erosion processes on determining the composition and flux of POM in low water discharge periods along the middle and lower Changjiang, suspended particulate samples were collected along the middle and lower reaches of the Changjiang (Yangtze River) in January 2008. Organic geochemistry of bulk sediment (particulate organic carbon, organic carbon to nitrogen molar ratio (C/N), stable carbon isotope (δ¹³C) and grain size) and biomarker of bulk sediment (lignin phenols) were measured to trace the sources of POM. The range of C/N ratios (6.4–8.9), δ¹³C (?24.3‰ – ?26.2‰) and lignin phenols concentration Λ8 (0.45 mg/100 mg OC‐2.00 mg/100 mg OC) of POM suggested that POM originated from the mixture of soil, plant tissue and autochthonous organic matter (OM) during the dry season. POM from lakes contained a higher portion of terrestrial OM than the mainstream, which was related to sand mining and hydropower erosion processes. A three end‐member model based on δ¹³C and Λ8 was performed. The results indicated that soil contributed approximately 50% of OM to the POM, which is the dominant OM source in most stations. POM composition was affected by total suspended matter (TSM) and grain size composition, and the direct OM input from two lakes and channel erosion induced OM. The lower TSM concentration in January 2008 was mainly caused by seasonal variations; the impact from the TGD in the dry season was relatively small. A box model indicated that more than 90% of the terrestrial OM transported by the Changjiang in January 2008 was from the middle and lower drainage basins. Channel erosion induced OM, and contributions from Poyang Lake were the major terrestrial OM sources in the dry season. Copyright © 2012 John Wiley & Sons, Ltd.     

The interaction between surface water and groundwater and its effect on water quality in the Second Songhua River basin,northeast China

The relationship between surface water and groundwater not only influences the water quantity, but also affects the water quality. The stable isotopes (δD, δ ¹⁸O) and hydrochemical compositions in water samples were analysed in the Second Songhua River basin. The deep groundwater is mainly recharged from shallow groundwater in the middle and upper reaches. The shallow groundwater is discharged to rivers in the downstream. The runoff from upper reaches mainly contributed the river flow in the downstream. The CCME WQI indicated that the quality of surface water and groundwater was ‘Fair’. The mixing process between surface water and groundwater was simulated by the PHREEQC code with the results from the stable isotopes. The interaction between surface water and groundwater influences the composition of ions in the mixing water, and further affects the water quality with other factors.     

新疆东天山地区土屋和延东铜矿床斑岩叠加改造成矿作用

土屋和延东铜矿床位于东天山大南湖-头苏泉岛弧带南部,是中亚成矿带的重要组成部分。文章根据脉次穿插关系、蚀变矿物组合及矿物共生关系,将土屋和延东铜矿床均划分为斑岩成矿期、叠加改造期和表生期3个期次。土屋铜矿床的铜矿化形成于斑岩成矿期和叠加改造期,而延东铜矿床的铜矿化主要形成于叠加改造期;土屋和延东铜矿床伴生的钼矿化主要形成于叠加改造期。因此,笔者认为前人获得的辉钼矿Re-Os年龄(326.2~322.7 Ma)代表叠加改造期的成矿年龄,该期矿化与石英钠长斑岩((323.6±2.5)Ma)的侵入相关,而斑岩成矿期的矿化与斜长花岗斑岩(339~332 Ma)相关,成矿年龄为341.2~333.9 Ma。叠加改造期的存在,使得斑岩成矿期的蚀变分带可能受到了叠加和破坏。