Decision making, planning and design for the conservation of indigenous vegetation within urban development

Utilization of indigenous vegetation as parts of the urban landscape is still a problematic matter in decision making and planning. On one hand, there are many activities in cities and towns aimed at providing more green areas. On the other hand, there is an increasing destruction of indigenous vegetation, not only for building purposes, but also partly by extreme maintenance of urban open spaces and an increasing number of recreation activities. Despite there is a considerable amount of scientific knowledge on indigenous plants in urban and sub-urban areas, the use of this knowledge is still low. The socio-economic knowledge about such vegetation (acceptance, utilization, economic value, etc.) is mostly non-existent in many regions.The indigenous vegetation has to become an important aspect of urban biodiversity as well as part of the living space of the urban dwellers. This links two important subjects: the specific nature of the original biomes in which the urban region is situated, and the cultural aspect of acceptance of various kinds of nature. The nature preservation strategies, especially of Central European cities, show a lack of willingness to preserve indigenous vegetation sites. But there are instruments of planning and methods which allow better preservation of these areas.Furthermore, it must be determined whether it is possible to reduce the human impact on open spaces by reintroducing indigenous vegetation, and under what circumstances this works. The cost reduction of maintenance of urban green areas is seen as one major factor linking to this target. Human acceptance is still an uncertam factor which has to be investigated and will, in the long term, be improved by education and evaluated under different cultural and social aspects.The management of the classical conflict between pure species or habitat preservation in open urban spaces of untouched nature and the high pressure of recreation on the same sites, is explained by example. An important question follows: will it be possible to establish “new” indigenous nature in the urban and sub-urban spaces?     

植被护坡在路基边坡水土流失治理中的应用

从水土流失的诱发原因和危害入手,分析了在路基工程中植被护坡技术的作用机理、具体特点、实施方法,指出该方法在达到防护要求的同时可兼顾经济、生态环境效益,值得推广。     

Establishing North American prairie vegetation in urban parks in northern England: Effect of management and soil type on long-term community development

The effect of management and soil type on the development of an experimental prairie plant community was investigated over a 4-year period. Soil type had a greater affect than management treatment, with poor persistence of the prairie community on topsoil plots largely irrespective of management. On sand mulched plots, prairie persistence was high. Burning was the most successful management technique for maintaining prairie plant cover and facilitating recruitment of prairie seedlings. The most successful treatment combinations were generally sand mulching plus spring burning. Sand mulching was successful because it minimised weed germination and competition in the first growing season hence allowing prairie species to dominate and compete effectively with invading weeds in subsequent years. Sand mulching also minimised slug grazing in spring, hence mortality of adult prairie plants was reduced and seedling recruitment facilitated. Although seedling recruitment occurred within the experiment, no seedlings of prairie plants were observed to establish outside the experiment. This, in combination with the observation that where not managed by spring burning, prairie communities declined or disappeared, strongly suggests that the species used in the study do not pose a naturalisation threat to native vegetation in northern England. The management techniques used in the study vary considerably in terms of efficacy and energy consumption and are discussed in relation to practice in public parks and other urban landscapes.     

基坑支护结构土压力与抗力研究

探讨了基坑支护结构上主被动土压力的确定方法,通过具体的工程实例,比较了我国相关设计规程对m值取值的差异,并归纳了m法用于基坑支护计算的局限性,为基坑支护的设计提供了借鉴。     

砂土介质中薄膜压力传感器的标定试验研究

土压力的精确测量在岩土工程领域有重要作用。传统土压力盒体积大,对土体完整影响较大,薄膜压力传感器是一种新型测量土压力的仪器,厚度薄、灵敏度高。薄膜压力传感器应用过程中需要根据实际使用情况进行标定。本文通过自主研制的标定筒研究薄膜压力传感器在砂土介质中的标定效果,并将砂标结果与厂标结果进行对比。采用同一薄膜压力传感器对不同相对密度的砂土进行了标定,结果表明,砂标结果值大于厂标结果值,砂土的相对密度越大,标定系数越小。     

Uncertainties of thermal boundaries and soil properties on permafrost table of frozen ground in Qinghai-Tibet Plateau

In the permafrost regions of the Qinghai-Tibet Plateau(QTP),the permafrost table has a significant effect on the stability of geotechnical engineering.The thermal boundaries and soil properties are the key factors affecting the permafrost table.Complex geological environments and human activities can lead to the uncertainties of thermal boundaries and soil properties.In this paper,an array of field experiments and Monte Carlo(MC) simulations of thermal boundaries and soil properties are carried out.The coefficient of variation(COV),scale of fluctuation(SOF),and autocorrelation distance(ACD) of uncertainties of thermal boundaries and soil properties are investigated.A stochastic analysis method of the probabilistic permafrost table is then proposed,and the statistical properties of permafrost table on the QTP are computed by self-compiled program.The proposed stochastic analysis method is verified with the calculated and measured temperature observations.According to the relationship between ACD and SOF for the five theoretical autocorrelation functions(ACFs),the effects of ACF,COV,and ACD of soil properties and the COV of thermal boundaries on the permafrost tables are analyzed.The results show that the effects of different ACFs of soil properties on the standard deviation(SD) of permafrost table depth are not obvious.The SD of permafrost table depth increases with time,and the larger the COVs of thermal boundaries and soil properties,the deeper the SD of permafrost table;the longer the ACD of soil properties,the shallower the SD of permafrost table.This study can provide a reference for the stability analysis of geotechnical engineering on the QTP considering the uncertainties of thermal boundaries and soil properties.     

考虑黏聚力及放坡角度的土钉墙侧土压力计算

基于极限平衡理论及平面滑裂面假定,在考虑土黏聚力及放坡角度的基础上,推导了平面滑裂面剪切破坏角的数学表达式。结果表明:平面滑裂面剪切破坏角与土的黏聚力、计算深度无关,与放坡角度和土的内摩擦角均成线性关系。在剪切破坏角计算的基础上,建立了一个符合实际的土钉墙侧向土压力计算公式。实例计算结果表明:建立的土钉墙侧向土压力计算公式适用于不同放坡角度的土钉墙,不但适用于无黏性土,同样适用于黏性土。     

液化土振动过程中孔隙水压力变化分析

针对液化土受振后孔隙水压力变化的情况进行了研究，通过模型试验，分析并比较了液化土模型地基加固前后在地震波水平循环荷载下的振动特性。     

黏性土中单桩贯入桩–土界面超孔压和土压测试现场试验

黏性土地基中静压桩沉桩过程桩–土界面受力变化是岩土工程中常见的问题。在东营某工地黏性土地基中进行了足尺静压桩的贯入试验,重点监测了桩身不同h/L位置处桩–土界面超孔隙水压力和土压力随入土深度的变化规律,并分析了桩身不同h/L位置处桩–土界面超孔隙水压力与上覆土体有效压力的关系,在同一入土深度桩–土界面土压力的变化特性,重点研究了影响桩–土界面有效土压力分布的原因。测试结果表明:沉桩引起的桩身不同h/L位置处桩–土界面超孔隙水压力与上覆土体有效压力比值最大是1.08,且该比值沿桩身向上逐渐减小;同一入土深度桩身不同h/L位置处桩–土界面土压力存在"侧压力退化"现象,且随着h/L的增加,该退化现象会越发明显,h/L=11/12位置处桩–土界面土压力仅约为10 kPa;除h/L=11/12位置处,桩身其它不同h/L位置处桩–土界面有效土压力是桩–土界面超孔隙水压力的1.88～2.20倍。研究成果对黏性土地基中静压桩施工和承载力确定具有一定的工程指导意义。     

土体旋转流变仪开发与土压平衡盾构改性土体塑性流动特性实验

为了研究土压平衡式盾构机（ EPBS ）密封仓及螺旋输送机内改性土体塑性流动特性,开发了一种土体旋转流变仪。该装置属于可变围压式控制应变型旋转流变仪,通过测量标准十字叶片在给定围压及转速条件下的旋转扭矩,获得被测介质的表观动力黏度。对某地铁施工标段的砂土进行实验测量,实验砂土均采用泡沫改性且改性配比相同,而初始含水率不同（ 5% , 10% 和 15% ）。测量条件包含 4 个不同围压等级（ 100 , 200 , 300 和 400 kPa ）和 7 个不同的叶片转速（ 1/3.4 , 1/4.1 , 1/5 , 1/6.4 , 1/9 , 1/15 和 1/30 RPM ）。实验结果表明,泡沫改性砂土的剪切应力与剪切速率之间满足 Bingham 流体模型,属于一种黏塑性非牛顿流体。其黏度系数和屈服应力均随围压的增大而增大。该装置不但可作为一种比较改性土体塑性流动特性优劣的工具,而且可以为仿真获取密封仓及螺旋输送机内压力场分布和研究密封仓压力平衡控制提供实验支撑。     

杭州文化创意产业区的空间发展格局及空间影响

在我国城市化发展转型的大环境下,随着城市新区的开发以及城市中心区传统产业的外迁和置换,文化创意产业区建设正日益受到城市决策者和研究者的关注。本文以杭州为例,在分析目前城市文化创意产业区建设现状的基础上,探讨了其在城市宏观层面的空间发展格局与发展的基本模式。     

Effect of different types of wetting fluids on the behaviour of expansive soil during wetting and drying

This paper presents the results of an experimental investigation into the mechanical behaviour of an expansive soil during wetting and drying cycles. The experimental tests were conducted in a modified oedometer under two different surcharge pressures (10 and 20 kPa). During the tests, the samples were inundated with different types of wetting fluids (distilled water, saline water and acidic water). The volumetric deformation, void ratio and water content of the samples were determined during cycles of wetting and drying. The results show that the swelling potential increases with an increasing number of wetting and drying cycles. The effect of the distilled water on the swelling potential is not the same as that of the saline water or the acidic water, particularly for different surcharge pressures. The variations in void ratio and water content show that, at the equilibrium condition, the wetting and drying paths converge to nearly an S-shaped curve. This curve consists of a linear portion and two curved portions, and the majority of the deformation is located between the saturation curves of 90% and 40%.     

Investigations on air pressure and air losses in compressed air tunneling through saturated clayey soil

Determination of air pressure and assessment of air losses in clayey soil are of great importance to implementation of compressed air tunneling. In the present work, a series of air flow tests were performed to provide a more reasonable method based on flow characteristics of snap-off pressure and the dissolution/diffusion. Results showed that, the nonlinear air flow behavior and gas breakthrough were presented with the increase in air pressure. After that, the excessive pressure decreased continuously to reach an equilibrium termed as the snap-off. For the tested clayey soil, snap-off pressures around 250 kPa could be adopted as the air pressure, which was significantly lower than the gas breakthrough pressures. Diffusion coefficient of 1.5 × 10^-11 m²/s could be determined in the followed dissolution/diffusion stage, which bring 3 orders of decreasing magnitude in air losses compared to the capillary flow occurred after gas breakthrough. As a conclusion, the adoption of snap-off pressure in compressed air tunneling could effectively prevent the continuous air/water flow in clayey soil and create a more human-friendly environment. Additionally, less air losses could be presented compared to that using gas breakthrough pressure, indicating tremendous energy savings in field implementation.     

卵石地层土压平衡盾构施工土体改良试验研究

卵石地层摩擦性高,塑流性差,在土压平衡盾构施工过程中遇到了许多困难,通过对其进行土体改良改善土层性能成为不可缺少的辅助施工措施。但是,卵石地层土体改良缺乏系统研究,添加剂配比多依靠工地摸索或工程经验,容易造成添加剂使用不合理,直接影响到盾构施工效率。为此以北京地铁10号线2期隧道区间卵石地层土压平衡盾构施工为案例,进行了一系列土体改良室内试验,研究、评价常用添加剂及改良渣土性能,得到理想改良渣土的添加剂配比参数为泡沫注入比为30%,泥浆注入比为10%,最佳坍落度范围为150～200 mm。利用上述添加剂配比方案进行了盾构掘进试验,显著提高了盾构施工效率。试验结果可为类似地层盾构施工土体改良提供参考。     

Effects of soil on the energy response of equipment–structure systems with different connection types between the equipment and structure

In equipment–structure systems, the soil–structure interaction and connection types between the equipment and structure significantly affect the seismic response. To understand this effect, in this study, the motion equation of an equipment–structure–soil system was derived, and energy balance equations for each part of the coupled system were obtained. Further, the effects of the soil on the energy response were analyzed based on the results of shaking table tests of an equipment–structure system and real‐time substructure shaking table tests of equipment–structure–soil systems with different connection types. The energy response of the equipment–structure system with a rigid ground was compared with that of the equipment–structure–soil systems. The analysis results showed that the energy response of the equipment–structure–soil system with different connections was quite different from that of the system with a rigid ground. The soil decreased the total energy input to the equipment and structure and significantly changed the time distribution characteristics of the input energy. Additionally, the soil weakened the energy consumption of the connections. Therefore, the influence of the soil should be considered in the design of equipment–structure systems with connections.     

软土地区某深大基坑承压水突涌分析处理

基坑的突涌与承压地下水息息相关。软土地区某基坑下部存在承压含水层,经验算基坑底板不稳定易产生突涌现象,采用深井管井降水降压,有效地控制了⑤2层承压地下水,消除了地下水突涌隐患,保证了基坑坑底、周边环境的稳定及基坑开挖工程的正常进行,取得了满意的工程效果。     

考虑流-固耦合效应的基坑水土压力计算

深基坑开挖基坑内外产生水位差,地下水绕过围护墙底部向基坑内渗流影响围护墙上的水土压力分布.本文总结了基坑围护墙上水土压力的计算方法,针对基坑周围土体成层分布的特点.分析了传统的水土压力分算、合算以及考虑渗流影响的水土压力分算方法.利用岩土工程有限元方法,通过渗流-应变耦合来计算渗流条件下的水土压力,结合工程算例,比较了...     

上海地区软土旁压加卸载变形特性试验研究

软土具有强度低、压缩性高的特点,在不同应力状态、应力路径下其变形呈现明显不同的非线性特征,研究软土的原位变形特性对各类地下工程土体变形的控制具有重要意义.通过对上海地区不同深度土体进行原位旁压加卸载试验,从加载及卸载两个维度对原位土体的变形特性进行描述.通过旁压加载试验结合室内小应变三轴试验,获取了土体剪切模量G随剪应...     

CDIO模式下农林院校城乡规划专业实践教学体系改革

文章借鉴国外CDIO工程教育模式,针对农林院校城乡规划专业实践教学现状,以华南农业大学为例,提出构建多层次理论知识体系、注重综合实践技能训练和培养良好职业道德素养的农林院校城乡规划专业CDIO模式开放式实践教学体系。