Earth temperatures and underground buildings

Previous experimental studies have dealt with the earth's surface and subsurface temperature profiles. The results from these studies have been summarized and analysed jointly, making it possible to derive some generalizations. It appears that the temperature range decrement factors for the different studies fit within a narrow range, and that they suggest a classification by climatic type. The values for the time lag in the annual temperature wave were also found to fall within a narrow range. Simplified equations are presented for determining soil temperatures and time lags as a function of depth. Different approaches for estimating the surface temperature are presented and discussed.     

The frost resistance of coarse-grained soils as one of the properties determining their suitability for earth-dam constructions

The earth-dams in the mountainous regions of Poland are working under very specific, severe, climatic conditions. The daily variations of temperatures submit subsurface soil strata to frequent cyclic freezing and thawing, that leads to the destruction of the initial structure of the soil. It leads to the conclusion that we have to forecast the changes which in course of time can follow in the soil used in the structure. In the paper the methodology of frost resistance tests is described and the results obtained in course of the tests are given. These results are connected with the situation of the soil bed along the river and the level of terraces, as well as with such other properties as particle size distribution, degree of roundness, degree of weathering. The tests were carried out in two different negative temperatures, that enabled the establishment of the influence of temperature disintegration of grains. Different types of disintegration depending on the origin of the rock type are described.     

盐渍土冻结过程中的特征温度研究

盐渍土在降温冻结过程中出现过冷温度和冻结温度两种特征温度,分别表示在降温过程中孔隙溶液中晶核形成和孔隙溶液与冰晶共存时的临界温度,对判断土体的冻结状态有着重要的意义。首先,通过不同含盐量的土体冻结试验,得到了相应的过冷温度和冻结温度;然后,基于热力学与经典成核理论给出了盐渍土冻结过程中的两种特征温度的理论计算模型,并与试验结果进行对比,验证了该模型的有效性;最后,分析了盐渍土特征温度的影响因素,重点考察了孔隙溶液中结晶盐析出对冻结温度和过冷温度的影响。结果表明,提出的模型可以实现对盐渍土冻结特征温度的有效预测。通过冻结特征温度随含盐量的关系曲线,可以得到结晶盐析出时的含盐量。冻结时孔隙溶液的浓度与冻结温度存在负相关关系,结晶盐的析出引起冻结时孔隙溶液浓度下降,从而使冻结温度升高。而结晶盐析出导致孔隙溶液浓度降低和土颗粒与冰晶接触角减小的双重影响,是盐渍土过冷温度的升高的原因。     

黏土中隧道开挖引起的地表及地表以下土体长期 沉降计算方法

基于 Mair 提出的隧道开挖引起的土体瞬时沉降的理论以及进行的有限元数值模拟结果,推出地表及地表以下不同深度土体长期沉降的计算方法。首先模拟了 Ong 的离心机试验以验证数值模型的合理性,然后对隧道开挖引起的不同深度处土体长期沉降问题进行了模拟研究,建立了长期和瞬时情况下地层损失率之间的关系,并推导出长期情况下各深度处沉降槽宽度系数和最大沉降值的计算式,从而可确定沉降槽的形状。经与现场实测资料和数值模拟结果对比,验证了方法的合理性,可作为实际工程的借鉴。     

Indoor thermal conditions and thermal comfort in air-conditioned domestic buildings in the dry-desert climate of Kuwait

The summer season in the state of Kuwait is long with a mean daily maximum temperature of 45 °C. Domestic air conditioning is generally deployed from the beginning of April to the end of October. This accounts for around 75% of Kuwaiti electrical power consumption. In terms of energy conservation, increasing the thermostat temperature by 1 °C could save about 10% of space cooling energy 1 and 2. However, knowledge of indoor domestic temperatures and thermal comfort sensations is important to aid future advice formulation and policy-making related to domestic energy consumption. A field study was therefore conducted during the summers of 2006 and 2007 to investigate the indoor climate and occupants' thermal comfort in 25 air-conditioned domestic buildings in Kuwait. The paper presents statistical data about the indoor environmental conditions in Kuwait domestic residences, together with an analysis of domestic-occupant thermal comfort sensations. With respect to the latter, a total of 111 participants provided 111 sets of physical measurements together with subjective information via questionnaires that were used to collect the data. By using linear regression analysis of responses on the ASHRAE-seven-point thermal sensation scale, the neutral operative temperatures based on Actual Mean Vote (AMV) and Predicted Mean Vote (PMV) were found to be 25.2 °C and 23.3 °C, respectively, in the summer season. Findings from this study provide information about the indoor domestic thermal environment in Kuwait, together with occupant thermal comfort sensations. This knowledge can contribute towards the development of future energy-related design codes for Kuwait.     

Phosphorus losses in subsurface flow before and after manure application to intensively farmed land.

A study was conducted to examine the loss of P in subsurface flow from three cultivated soils of varying soil P concentrations. Measurements were made in flow waters from the soils before applying manure and then 3 weeks after sowing the soils to grass. An additional measurement of P in flow waters was made 1 year later. Dissolved reactive P (DRP) concentrations measured in flow water before (0.15-0.20 mg l(-1)) and after (0.39-0.51 mg l(-1)) manure application exceed current estimates of those required to promote surface water eutrophication (0.05 mg l(-1)). Concentrations of DRP1 year after manurial application increased compared to 3 weeks after application and was attributed to the slow movement of P down the cultivated soil. Concentrations of soil P were significantly increased down the soil profile and attributed to the P saturation of soils before manurial application. The results suggest that despite the establishment of fast growing grass, P concentrations would not be mitigated in the short-term (= 1 year), due to the large contribution of P in subsurface pathways.     

Causes and consequences of desertification in Kuwait: a case study of land degradation

Desertification in Kuwait is a process of environmental degradation under fragile ecological conditions and intensive human activities and the consequences of Gulf War. In Kuwait, very severe desertification prevails, due to increasing formation of new active sandy bodies, deterioration of many areas of natural vegetation cover to less than 10%, and limited water resources for large-scale forage production. Average annual desertified land in Kuwait is estimated to be 285 km². In Kuwait, three indicators of land degradation are encountered. These are vegetation, soil, and surface hydrological changes. Based on field measurements of soil compaction and vegetation changes, in the west Jahra area in the northern part of the country, degradation levels were assessed. Results of these measurements show that the average infiltration rate in compacted soil decreased by 53.8% in comparison with non-compacted soil, while the average soil penetration resistance in compacted soil increased by 154.1% in comparison with non-compacted soil. The bulk density in open sites was 23.4% higher than that in protected sites. The percentage of litter in open sites decreased by 77.3% in comparison with protected sites, while the percentage of total vegetation in open sites decreased by 6.1% in comparison with protected sites. Electronic Publication     

Reconstruction of the thermal environment evolution in urban areas from underground temperature distribution

It is possible to estimate the ground surface temperature (GST) history of the past several hundred years from temperature profiles measured in boreholes because the temporal variation in GST propagates into the subsurface by thermal diffusion. This “geothermal method” of reconstructing GST histories can be applied to studies of thermal environment evolution in urban areas, including the development of “heat islands.” Temperatures in boreholes were logged at 102 sites in Bangkok, Jakarta, Taipei, Seoul and their surrounding areas in 2004 to 2007. The effects of recent surface warming can be recognized in the shapes of most of the obtained temperature profiles. The preliminary results of reconstruction of GST histories through inversion analysis show that GST increased significantly in the last century. Existing temperature profile data for the areas in and around Tokyo and Osaka can also be used to reconstruct GST histories. Because most of these cities are located on alluvial plains in relatively humid areas, it is necessary to use a model with groundwater flow and a layered subsurface structure for reconstruction analysis. Long-term records of subsurface temperatures at multiple depths may demonstrate how the GST variation propagates downward through formations. Time series data provide information on the mechanism of heat transfer (conduction or advection) and the thermal diffusivity. Long-term temperature monitoring has been carried out in a borehole located on the coast of Lake Biwa, Japan. Temperatures at 30 and 40 m below the ground surface were measured for 4 years and 2 years, respectively, with a resolution of 1 mK. The obtained records indicate steady increases at both depths with different rates, which is probably the result of some recent thermal event(s) near the surface. Borehole temperatures have also been monitored at selected sites in Bangkok, Jakarta, and Taiwan.     

水平地埋管冬季土壤温度场及换热性能研究

以土壤源热泵水平地埋管为研究对象,建立了水平地埋管的二维数学模型,采用边界离散、保形变换方法对模型进行求解,采用VB编制了水平地埋管及其周围土壤温度场计算软件。运用模型和软件,模拟冬季工况下,水平地埋管及其周围土壤温度场和热流量分布情况。冬季水平地埋管周围土壤温度纵向呈不对称单峰状分布,横向呈完全对称的单峰状分布。地埋管外土壤沿与地埋管同圆心的圆周上温度呈正弦曲线分布。随着位置远离地埋管,土壤温度变化幅度减小。地埋管上部热流量较高,下部热流量较低。给定工况下水平地埋管单位管长换热量模拟值与实验值比较,误差为6.2%,可靠性较高。     

Detecting urbanization effects on surface and subsurface thermal environment--a case study of Osaka

Tremendous efforts have been devoted to improve our understanding of the anthropogenic effects on the atmospheric temperature change. In comparison, little has been done in the study of the human impacts on the subsurface thermal environment. The objective of this study is to analyze surface air temperature records and borehole subsurface temperature records for a better understanding of the urban heat island effects across the ground surface. The annual surface air temperature time series from six meteorological stations and six deep borehole temperature profiles of high qualities show that Osaka has been undergoing excess warming since late 19th century. The mean warming rate in Osaka surface air temperature is about 2.0 °C/100a over the period from 1883 to 2006, at least half of which can be attributed to the urban heat island effects. However, this surface air temperature warming is not as strong as the ground warming recorded in the subsurface temperature profiles. The surface temperature anomaly from the Osaka meteorological record can only account for part of the temperature anomaly recorded in the borehole temperature profiles. Surface air temperature is conventionally measured around 1.5 m above the ground; whereas borehole temperatures are measured from rocks in the subsurface. Heat conduction in the subsurface is much less efficient than the heat convection of the air above the ground surface. Therefore, the anthropogenic thermal impacts on the subsurface can be more persistent and profound than the impacts on the atmosphere. This study suggests that the surface air temperature records alone might underestimate the full extent of urban heat island effects on the subsurface environment.     

Evaluation of subsurface spatial variability in site characterization based on RCPTU data

The resistivity piezocone penetration test (RCPTU) does not only include a conventional piezocone penetration test, but also provides a continuous profile of electrical resistivity. Therefore, RCPTUs have the potential for wide application in environmental geotechnics. Electrical resistivity is a fundamental parameter characterizing soil conductivity, one of the inherent physical properties of soil. The objective of this study was to evaluate subsurface spatial variability using RCPTU data and laboratory tests. Normalized electrical resistivity was proposed for developing the relationships between electrical resistivity and soil behavior type index, relative density and cyclic resistance ratio. These relationships are used for evaluation of subsurface spatial variability. The soil behavior type index can be represented by the function of normalized electrical resistivity R and normalized cone tip resistance. Additionally, there is a positive correlation between relative density and normalized electrical resistivity. The evaluation of cyclic resistance ratio adopting the normalized electrical resistivity and normalized cone tip resistance was effective.     

冻结饱和标准砂压缩性试验研究

在寒区进行高速公路和高速铁路等对变形要求严格的工程时,必须考虑冻土的压缩性。以冻结饱和标准砂为研究对象,利用自主研发的冻土侧限压缩仪开展不同温度下的分级加载试验。试验采用-0.5,-1.0,-2.0,-3.0和-5.0℃五级温度,压力分为1,2,3,5和10 MPa五级。根据试验结果得到e–σ_z和e–lgσ_z曲线,求得压缩系数和压缩指数,比较分析室温下的融土试样与不同温度下冻土试样的压缩系数和压缩指数随温度的变化,得到从正温到负温完整温度序列的试验规律。根据前人的模量公式得出相关参数,从而建立公式中参数与温度之间的关系。试验表明:饱和冻结标准砂压缩曲线与常温土相似;在高温条件下冻土的压缩性比较可观;冻土的压缩性受温度的影响十分显著,即压缩系数随温度的升高而增大,呈现指数函数的形式;模量公式中的参数与温度之间可建立一定的定量关系。     

宁波轨交沿线不同深度土体温度变化规律观测

通过对宁波平原轨交沿线不同地段的7处土体地温观测点研究,得到宁波平原不同深度土体温度的变化规律及地层的恒温层位置,并初略确定气温对土体温度的影响下限深度。观测结果表明:宁波平原地表以下5 m范围内土体温度受气温影响很敏感,5~10 m影响不敏感,10~25 m影响很小,一般10 m以后趋于稳定,土体温度范围为18.3~19.7℃之间。观测研究结果,可为宁波轨交车站和区间隧道设计时结构温度应力、暖通设计等提供所需参数。     

淤泥质黏土火灾高温下导热系数的试验研究

对火灾高温下隧道衬砌结构周围饱和软黏土的热传导特性进行了试验研究,旨在进一步探讨作用于隧道结构上的荷载变化,以便准确评价其安全状态.采用热探针程序法(美国材料与试验协会(ASTM)确定土体和软岩导热系数的标准方法),应用自行研制的高温土体导热系数测定仪测定了上海淤泥质黏土在高温下的导热系数.试验分别测定了不同温度及不同含水率条件下土样的导热系数,并以KD2导热系数测定仪作为校准仪器对试验结果进行了校正.试验结果表明导热系数随着温度的升高而增大,且其增大的速率随温度的增加而减小,特别是对含有机质的淤泥质黏土因有机质的高温分解而使得这种降低更加明显;此外,在不同高温下土体导热系数随含水率的增加而增大.     

环境湿度与温度对压实膨胀土裂隙发育影响试验研究

裂隙是影响膨胀土工程性质的重要因素。以南阳某高速公路膨胀土为对象,采用大尺寸压实膨胀土试样进行不同环境湿度与温度下的裂隙发育试验,通过数码相机摄影并基于自编程序进行土样表面图像的定量化分析,获得裂隙率、均宽及总长等典型特征参数,进而探讨环境湿度与温度对膨胀土裂隙发育规律的影响。结果表明:大尺寸土样裂隙发育特征相较环刀样和薄层饱和泥浆样更接近路基与边坡等工程实际;环境湿度越高,初期裂隙发展越慢,发育持续时间越长,后期裂隙特征统计参数反而越大;环境温度越高,初期裂隙发展越快,但裂隙回缩稳定速度也越快,后期裂隙特征统计参数反而越小;低湿度或高温度使土样表面易于产生更多肉眼不可见的微裂隙,是裂隙特征统计参数与理论分析相比偏小的重要原因,而高湿度与低温度则有利于收缩应力向深层土体传递,促使裂隙偏向数量更少但更宽和更深方向发展。     

The potential role of urban green areas for controlling ground surface and subsurface warming

Subsurface warming in urban areas is higher in magnitude than increases in surface air temperatures. However, little evidence exists on the effects of urbanization on subsurface environments, and there are few quantitative estimates of the effectiveness of adaptation measures. We analyzed the relationship between ground surface warming and the extent of landscape change using subsurface temperature anomalies as an indicator of surface warming in five urban areas in Japan. To interpret these results for urban planning, we presented the percentages of green areas that would be needed to achieve certain reductions in ground surface temperatures for areas with different urbanization levels. Accordingly, a 0.5 °C reduction in average ground surface temperatures can be achieved by an increased Normalized Difference Vegetation Index (NDVI) value of 0.035, which accounts for approximately a 17% increase in natural green areas in an area with 75% urbanization. This study provides quantitative estimates to cope with urban warming at the local scale in the face of climate change.     

Subsurface ground movements due to circular shaft construction

The rapid development of modern metropolises has led to a shortage of surface space and, in response, engineers have pursued alternatives below ground level. Shafts are commonly used to provide temporary access to the subsurface for tunnelling and, as permanent works, are utilised for lifts or ventilation purposes. The construction sequence of axisymmetric shafts makes them a dramatically simple solution. In addition, circular shafts are inherently stiffer than other plan geometries. Those are perhaps the reasons why circular shafts are preferred in situations of restricted space or unfavourable ground conditions. However, due to the lack of case histories reporting ground movements induced by shaft construction, no empirical prediction method for subsurface soil displacements exists. The work presented here seeks to provide clearer insights into surface and subsurface soil displacements induced by circular shaft construction by means of an analysis of measurements obtained from centrifuge tests and available field data. Novel empirical equations and procedures are then suggested for practical use.     

Estimation of soil temperature profile in Hong Kong from climatic variables

A correlation study of the ground temperatures up to a soil depth of 3 m (for lawn condition) with the weather parameters has been performed making use of the observed data in the 4-year period 2006-2009. It is found that within the soil depth of 3 m, which belongs to the surface and shallow zones, the ground temperature is strongly correlated to the dry bulb air temperature whereas its dependence on the relative humidity, rainfall, global solar radiation or wind speed is weak. A multivariable nonlinear regression model was then developed based on the soil temperature and weather data within the same four-year period. This model can be utilized to predict soil temperature at various depths underground. The required inputs of the model are the day number of the year, soil depth and dry bulb air temperature. The model has been validated by the data records of the same site in the previous years, as well as the data record from another site in more recent years. This regression model provides a simple, fast and accurate alternative method for the estimation of natural ground temperature.     

冻土冻胀融沉的微观分析

从冻土微观结构分析了其冻胀、融沉发生机制,结果表明：随着温度的变化,冻土会出现冻胀和融沉现象,这些破坏的出现与其微结构随温度的变化密切相关,温度的变化诱发微结构内部颗粒间连接刚度的变化,正是这些变化导致了冻胀、融沉现象的出现。     

Thermal comfort in air-conditioned mosques in the dry desert climate

In Kuwait, as in most countries with a typical dry desert climate, the summer season is long with a mean daily maximum temperature of 45 °C. Centralized air-conditioning, which is generally deployed from the beginning of April to the end of October, can have tremendous impact on the amount of electrical energy utilized to mechanically control the internal environment in mosque buildings. The indoor air temperature settings for all types of air-conditioned buildings and mosque buildings in particular, are often calculated based on the analytical model of ASHRAE 55-2004 and ISO 7730. However, a field study was conducted in six air-conditioned mosque buildings during the summers of 2007 to investigate indoor climate and prayers thermal comfort in state of Kuwait. The paper presents statistical data about the indoor environmental conditions in Kuwait mosque buildings, together with an analysis of prayer thermal comfort sensations for a total of 140 subjects providing 140 sets of physical measurements and subjective questionnaires were used to collect data. Results show that the neutral temperature (T_n) of the prayers is found to be 26.1 °C, while that for PMV is 23.3 °C. Discrepancy of these values is in fact about 2.8 °C higher than those predicted by PMV model. Therefore, thermal comfort temperature in Kuwait cannot directly correlate with ISO 7730 and ASHRAE 55-2004 standards. Findings from this study should be considered when designing air conditioning for mosque buildings. This knowledge can contribute towards the development of future energy-related design codes for Kuwait.