Geological and hydrogeological environment in Tianjin with potential geohazards and groundwater control during excavation

This paper discusses the geological and hydrogeological features of Quaternary deposits in Tianjin as well as the geohazards related to groundwater hydrology in this region. The soft soil deposits, comprising silt, sand, silty clay and clay, are composed of four aquifer groups. In the first aquifer group, one phreatic aquifer and two confined aquifers have relationships with underground construction in the urban area. These three aquifers are separated by two aquitards and collectively form a multi-aquifer system. During geotechnical construction, potential geohazards present are related to the groundwater, which include water-in-rushing, quicksand and piping hazards. To prevent the aforementioned geohazards, dewatering is conducted; however, groundwater pumping may result in large settlements of the surrounding ground. To reduce pumping-induced settlement, the dewatering–waterproofing system has been adopted. According to the characteristics of the subsoil, excavation depth and the surrounding environment, the dewatering system can be divided into five patterns. In the first four patterns, when pumping is conducted in the excavation pit, the groundwater head in the adjacent aquifers outside the pit decreases due to the leakage effect of the aquitards located between the aquifers. In the fifth pattern, waterproof curtain has cut off the aquifers completely and dewatering in the pit cannot result in settlement around excavation pit. To avoid geohazards related to groundwater hydrology, countermeasures recommended include construction of an effective waterproof curtain, selection of a reasonable excavation dewatering pattern and withdrawal of required groundwater.     

Calculation of groundwater head distribution with a close barrier during excavation dewatering in confined aquifer

When pumping is conducted in confined aquifer inside excavation pit(waterproof curtain),the direction of the groundwater seepage outside the excavation changes from horizontal to vertical owing to the existence of the curtain barrier.There is no analytical calculation method for the groundwater head distribution induced by dewatering inside excavation.This paper first analyses the mechanism of the blocking effects from a close barrier in confined aquifer.Then,a simple equation based on analytical solution is proposed to calculate groundwater heads inside and outside of the excavation pit with waterproof curtain(hereafter refer to close barrier)in a confined aquifer.The distribution of groundwater head is derived according to two conditions:(i)pumping with a constant water head,and(ii)pumping with a constant flow rate.The proposed calculation equation is verified by both numerical simulation and experimental results.The comparisons demonstrate that the proposed model can be applied in engineering practice of excavation.     

Clay mineral assemblages of the oceanic red beds in the northern South China Sea and their responses to the Middle Miocene Climate Transition

Science China Earth Sciences - The Middle Miocene Climate Transition (MMCT, ～14 Ma) is the largest cooling event in the Cenozoic “Coolhouse”, which significantly impacts the...     

A glimpse into rapid freezing processes in clay with x-ray tomography

Acta Geotechnica - This short paper proposes time-series x-ray tomography as a valuable tool for quantifying freezing processes in a remoulded clay. As an example, three simple closed system...     

陕北三叠纪煤田中—特高油产率煤分布规律及成因机理

以子长矿区内分布的300余组钻孔数据为基础,研究了陕北三叠纪煤田煤炭资源的物理化学性质,按照《煤中焦油含量分级》(MT/T1179—2019),划分了中油产率煤(7.0%<ω(Tar_d)<12.0%)和高油产率煤(12.0%<ω(Tar_d)<15.0%)的分布范围,预测了中—特高油产率煤的资源量。研究了矿区主采煤层3号煤层和5号煤层的煤质、沉积环境、变质程度等,认为矿区内中—特高油产率煤具一低两高的特征:镜质体反射率高(0.61%~0.83%)、变质程度低、挥发分高(35.78%~45.64%),认为成煤环境及变质程度是影响煤层富油的关键因素,研究区内5号煤层的焦油产率略高于3号煤层。     

河西走廊产业园区集群化发展机理研究——基于扎根理论分析

基于扎根理论研究产业园区集群化发展现状与存在问题。研究发现,园区集群化发展需要园区企业有效利用其显性契约、强化关系契约,提升联合规划、联合解决问题的能力;提升河西走廊产业园区集群化发展水平要运用组织生态学中的内外因视角发现问题,使外因为内因变化提供更好的环境;依照产业园区集群化发展模型,增强企业根植性、创新性和开放性,强化园区企业契约关系,推动集群向创新集群发展。     

历史城区旅游化：时空过程、功能转换及关联协调——以甘肃省天水市历史城区为例

借助史料、历史地图及谷歌POI数据,运用空间句法和GIS空间分析探讨天水古城自明清以来空间和功能的演化过程及其内在关联。研究发现：① 明清以来,天水古城的旅游化经历了传统游憩的普及（明清）、衰落（民国）、停滞（1949—1987年）阶段,现代旅游兴起与传统游憩恢复（1988—2000年）及融合创新（2001年至今）阶段。古城传统格局逐渐消失,但是历史轴线的主轴线地位延续,可达性、穿越性最好,协同度最高,“空间结构惯性”规律作用明显。② 在不同施动主体的共同作用下,天水古城由安全防御、军事政治、集市商贸等传统功能向工业生产,进而向现代旅游、居住功能转变,游憩休闲功能显著增强。③ 居民和游客共享公共活动空间,但服务功能相互分离。游客活动空间与功能服务协调性较好,居民公共活动空间与服务设施一致性较差。     

中国城市生活垃圾处理能力的时空格局及影响因素

基于2003—2017年中国30个省份的数据,探究城市生活垃圾处理能力的时空格局,并构建动态面板数据模型实证检验中国城市生活垃圾处理能力的影响因素。研究结果表明,考察期内城市生活垃圾处理能力存在空间发展不平衡问题;进一步利用Dagum基尼系数测算城市生活垃圾处理能力的空间差距并将其进行分解,其中,东部地区的地区内差距最大,地区间差距则以东部地区和西部地区之间最大,而超变密度则是空间差距的主要来源;此外,通过回归模型发现人均GDP、专利授权数、城镇化水平以及无害化处理厂数目的提升将促进城市生活垃圾处理能力的提高。     

中国主要城市技术创新影响环境污染的空间分异与机理

基于中国285个地级及以上城市的数据,利用空间自相关模型,在全域和局域尺度分析技术创新与环境污染的空间关联,在此基础上,使用地理加权回归模型分析技术创新对环境污染影响程度的地区差异,并借助地理探测器分析其影响机理。研究结果表明:① 技术创新与环境污染均存在显著的空间集聚性,二者在全域尺度上存在正向的空间关联,在局域尺度上正向和负向关联并存,具有高创新-高污染、低创新-低污染、高创新-低污染、低创新-高污染4种集聚类型。② 所有城市的技术创新对环境污染均存在负向影响,影响程度呈现出由东向西渐次递增的空间分异格局,现有样本计算结果有条件地支持EKC曲线,技术创新能够促进经济与环境的良性发展。③ 环境污染是多种因素共同作用的结果,经济发展、产业结构、人力资本、外商直接投资、环境规制均能强化技术创新对环境污染的改善作用,技术创新对环境污染的影响更多的是通过技术进步优化产业结构,从而减少环境污染。     

Distribution and accumulation of soil carbon in temperate wetland,northeast China

Estimating carbon sequestration and nutrient accumulation rates in Northeast China are important to assess wetlands function as carbon sink buffering greenhouse gas increasing in North Asia. The objectives of this study were to estimate accreting rates of carbon and nutrients in typical temperate wetlands. Results indicated that average soil organic carbon(SOC), total nitrogen(TN) and total phosphorus(TP) contents were 37.81%, 1.59% and 0.08% in peatlands, 5.33%, 0.25% and 0.05% in marshes, 2.92%, 0.27% and 0.10% in marshy meadows, respectively. Chronologies reconstructed by 210 Pb in the present work were acceptable and reliable, and the average time to yield 0–40 cm depth sediment cores was 150 years. Average carbon sequestration rate(Carbonsq), nitrogen and phosphorus accumulation rates were 219.4 g C/(m~2·yr), 9.16 g N/(m~2·yr) and 0.46 g P/(m~2·yr) for peatland; 57.13 g C/(m~2·yr), 5.42 g N/(m~2·yr) and 2.16 g P/(m~2·yr) for marshy meadow; 78.35 g C/(m~2·yr), 8.70 g N/(m~2·yr) and 0.71 g P/(m2·yr) for marshy; respectively. Positive relations existed between Carbonsq with nitrogen and precipitations, indicating that Carbonsq might be strengthened in future climate scenarios.