基于水利项目中碎石土渗透性的研究

结合国内一些研究思路及研究成果,依据多年现场实地工作经验,针对碎石土渗透性能展开研究。选取九江县戴山某滑坡的碎石土,进行样本重塑,分别改变碎石比例、空隙比、颗粒大小等条件设置多种试验样本,并设计对比试验方案。探究碎石比例、孔隙比、碎石颗粒大小对碎石土渗透性能的影响,采用对比分析的方法分析其试验数据,得到相应的函数变化关系,并分析小颗粒土流失情况。其结论可为水利工程建设及维护提供参考。

海口林场固定样地土壤渗透性能初探

在海口林场设立29块固定样地,包括12个土壤剖面47个层次,每层重复三次,进行森林土壤渗透性能测定。结果表明成土母岩不同,渗透速度不同;此外还受到土壤质地、石砾含量、土壤有机质含量的影响。

真空预压在超低渗透软粘土中的应用研究

通过现场试验探究了真空预压技术在低渗透性软粘土中的处理加固效果,设计了6组试验组次共4组对照试验,分析了膜下处理方式、排水板深度、排水板类型和排水板间距对真空预压处理效果的影响。对于该工程中的超低渗透性软粘土,试验结果表明:排水板间距为0.8 m的分布型式优于间距为1.0 m的分布型式;采用长短板相结合的分布方式较单一长度的排水板处理方式,可有效提高真空预压的处理效果;采用较大的滤膜等效孔径可有效提高排水板真空度的传递效率,从而加强真空预压效果;传统铺设砂垫层的膜下处理方式虽然效果最佳,但考虑到施工成本和时间成本的因素,可采用三维排水网+直排式处理的方式进行替代。

直排式真空预压法在高渗透软黏土地基中的应用

采用直排式真空预压法对北方某港口高渗透性软土地基进行处理,该工法取消了水平排水砂垫层,以真空排水管网与排水板直接连接,形成排水系统,真空能量更为快速有效地作用于加固土体,加固后土体的各项指标均达到了处理目标的要求,技术经济效果显著,可为类似高渗透性软土地基处理提供有益的借鉴。

土建基础施工中深基坑支护施工技术的应用

当前,深基坑支护技术具有加固结构、提高建筑工程结构安全性和稳定性的重要作用。同时,深基坑支护技术较为复杂,在实际施工过程中还存在许多问题。基于此,论文以深基坑支护技术中对砂砾土渗透性进行快速检测的设备为核心,从相应技术要求和实际施工中存在的问题出发,探讨土建深基坑支护中快速检测基坑周围砂砾土渗透性的设备的具体应用,提高土建基坑支护施工质量,确保基坑支护的顺利进行。

土建基础施工中深基坑支护施工技术应用探讨

在土建深基坑支护过程中,在基坑周边是砂砾土的情况下,土壤的渗透性具有很强的不确定性。本文以此为基础,对其渗透特性进行快速测试的装置进行了探讨。主要将深基坑支护技术的基本理念、关键技术进行概述,并对工程实践中遇到的问题进行了分析,最后给出了相应的实施对策。对基坑周边土壤特性的快速监测装置进行全面研究是很有必要性的,因为这将为今后的建筑施工提供更为可靠的技术支撑,对保证施工质量和施工安全具有重要的指导作用。

挡土墙填土的选择

在山坡地建筑,或在深基础施工中,常用挡土墙阻挡土和维持地面高差;在公路、铁路建设中,也常常需要沿挖方或填方边沿设置挡土墙或护坡。 大多数挡土墙外立面是直立的,或带有不大于20％的倾斜,挡土墙种类繁多,按材料分有砖、毛石、混凝土和钢筋混凝土挡土墙,按结构型式分,常用的有重力式、悬臂式和扶壁式挡土墙。

裂土路基处理的几点意见

裂土路基的处理,过去曾积累了不少的经验与教训,本文拟在此基础上对今后的裂土路基处理提出几点探索性的意见,以供参考。1、路堑一般裂土垄岗缺水,土渗透性差,但是长路堑(还有地下水位高的浅路堑)通车后却受地下水困扰。铁路曾在南阳开挖长逾1公里深约12米的路堑,开挖期间仅南端路堑出口处局部边坡渗水,道心见过一个小泉眼。附近单位打40米深井未见水。从勘察乃至施工资料看,

Laboratory study for effects of vacuum preloading on physical and mechanical properties of soft clayey soils

A new triaxial apparatus was designed and manufactured. It is able to applysurcharge and combined vacuum-surcharge pressures on soil samples, and allows for monitoring ofexcess pore-water pressure, axial strain or settlement, and volumetric strain during the process ofconsolidation. Tests were performed using the apparatus on undisturbed soft clayey soil samples,which were collected from Wenzhou, Zhejiang Province, China, at average natural water content 72. 5%. The consolidation behavior of theclay has no rigorous difference, whether it is consolidatedunder the vacuum, surcharge, or combined vacuum-surcharge preloading. The study shows that somephysical properties of the soft clayey soils are changed and mechanical properties are improved tosupport excessive loads transferred to the soil foundation due to construction.

Relationships Between Permeability and Erodibility of Cultivated Acrisols and Cambisols in Subtropical China

The relationships between soil erodibility factor （K） and soil saturated permeability （gfs） for cultivated Acrisols derived from Quaternary red clay and Cambisols derived from red sandstone were studied and quantified using a rainfall simulator and Guelph permeameter in a hilly area of subtropical China. A negative correlation existed between Kfs of the topsoil （0-5 cm） and K. The empirical expression K ≈ α × Kfs^-b＋c, where a, b and c are the structural coefficients related to soil properties, such as soil type, soil parent material, organic matter, pH and mechanical composition, best described the relationship between soil saturated permeability and soil erodibility.

Influences affecting the soil-water characteristic curve

The soil-water characteristic curve (SWCC) is the primary partially saturated soil information as its behavior and properties can be derived from it. Although there have been many studies of unsaturated soils and the SWCC, there is still no combined constitutive model that can simulate soil characteristics accurately. In cases when hydraulic hysteresis is dominant (e.g. under cyclic loading) it is particularly important to use the SWCC. In the past decades, several mathematical expressions have been proposed to model the curve. There are various influences on the SWCC as a source of information, so the curves obtained from conventional tests often cannot be directly applied; and the mathematical expressions from one scenario cannot be used to simulate another situation. The effects of void ratio, initial water content, stress state and high suction were studied in this work revealing that water content and stress state are more important than the other effects; but that the influences tend to decrease when suction increases. The van Genuchten model was modified to simulate better the changes in the degree of saturation at low values of suction. Predictions were compared with experimental results to determine the simulation capability of the model.

Water and Heavy Metal Transport in Roadside Soils

Roads with very high traffic loads in regions where soils are low in both pH and sorption capacity might be a source of percolation water loaded with heavy metals. Looking at some "worst case" scenarios, this study focused on the input of traffic related pollutants and on Pb, Cd, Cu, Zn, Ni and Cr concentrations in the soil matrix and soil solution, respectively. The analysis also included pH and electrical conductivity and at some sites DOC. The investigations were carried out on sandy soils with more or less low pH values at four motorway sites in Germany. The average of daily traffic was about 50 000 up to 90 000 vehicles. Soil pore water was collected in two soil depths and at four distances from the road. The pH in general decreased with increasing distance from the roadside. The elevated pH near the roadside was presumably caused by deposition of dust and weathering residues of the road asphalt, as well as by infiltration of salt that was used during winter time. At these road sites, increased heavy metal concentrations in the soil matrix as well as in the soil solution were found. However, the concentrations seldom exceeded reference values of the German Soil Protection Act. The soil solution concentrations tended to increase from the road edge to 10 m distance, whereas the concentration in the soil matrix decreased. Elevated DOC concentrations corresponded with elevated Cu concentrations but did not substantially change this tendency. High soil water percolation rates were found near the roads. Thus, even low metal concentrations of percolation water could yield high metal loads in a narrow area beside the road.

A Dynamic Model for Simulating Atmospheric, Surface and Soil Water interactions in Hillslope of Loess Area Under Natural Conditions and Its Application

The mechanism of atmospheric, surface and soil water interactions (water transformation) in hillslope under natural conditions was analyzed, and a dynamic model was developed to simulate infiltration, overland flow and soil water movement during natural rainfall in hillslope, by bringing forward concepts such. as rainfall intensity on slope and a correction coefficient of saturated soil water content for soil surface seal. Some factors, including slope angle, slope orientation and raindrop inclination, which affect the rainfall amount on slope, were taken into account while developing the dynamic model. The effect of surface seal on infiltration and water balance under a boundary condition of the second kind was also considered. Application of the model in a field experiment showed that the model simulated precisely the infiltration, overland flow and soil water movement in hillslope under natural rainfall conditions.

Some Physiological Responses of Chinese Iris to Salt Stress

Chinese iris （Iris lactea Pall. var. chinensis （Fisch） Koidz.）, a robust iridaceous plant, is widespread in arid and semiarid regions with high salinity. However, the mechanism of its salt tolerance is not well understood. In this study, plant growth, water status, content and distribution of inorganic ions, cell membrane permeability, and proline content of I. laetea under salt stress were investigated using nutrient solutions with six NaCl concentrations ranging from 0 to 350 mmol L^-1. The results indicated that the biomass, height, fresh weight, K^＋ content, and K^＋/Na^＋ and Ca^2＋/Na^＋ ratios decreased with increasing NaCl stress, whereas plant water deficit and contents of Na^＋ and Cl- increased with increasing NaCl stress. In all salt treatments, water deficit of shoots was found to be higher than that of roots and had a positive correlation with salt concentration. When the NaCl concentration was less than 280 mmol L^-1, the ion absorption selectivity ratio and the transportation selectivity ratio sharply increased with increasing NaCl stress. Under medium salt stress, I. lactea exhibited a strong K^＋ selective absorption and the transportation of K^＋ from roots to shoots increased, whereas Na^＋ was not transported and was mostly retained in roots. The plants were able to maintain osmotic adjustment through the accumulation of Na^＋, Cl-, and proline. On the basis of its biomass production under salt stress, I. lactea could be considered as a facultative halophyte.

Nonlinear analysis of consolidation with variable compressibility and permeability

Terzaghi gave a theory of soil consolidation based on the effective stress principle, which was derived on several ideal assumptions to get a simplified theory. To avoid the limitations involved in Terzaghi’s theory, many efforts are being made by scholars to solve the problems in practical engineering situations. This paper presents a generalized theory for one dimensional consolidation of saturated soft clay with variable compressibility and permeability. The semi-analytical solution presented here takes into account the well known empirical e-logk and e-logp′(σ′) relations under instantaneous loading. Study of the consolida- tion behaviors showed that the ratio of Cc and Ck (the slope of e-logp and e-logk respectively) govern the ratio of consolidation. A simulative laboratory investigation with GDS advanced consolidation system was made to analyze the clay consolidation process and compare the results with the semi-analytical solution.

An Improved Frequency Domain Technique for Determining Soil Water Content

For many years a soil water content sensor with low cost, reliability and sufficient accuracy has been desirable. Thus, an improved measurement method based on the frequency domain (FD) principle for determining soil water content was considered. Unlike other measurement principles, a new measurable index, η, which was independent of the output impedance and the amplitude of the oscillator while relying on the electrical impedance of a multi-pin probe, was pro- posed. Moreover, a model for processing the impedance of the multi-pin soil probe was developed, and several important electrical parameters for establishing their operating ranges applicable to this probe were evaluated. In order to confirm the theoretical analysis, an experiment was conducted with a 4-pin probe. Using the developed model, the relationship between the proposed index η and soil volumetric water content was shown to be linear (R2 = 0.9921). Thus, as the measurable index, η seemed satisfactory.

Microstructural insight into permeability and water retention property of compacted binary silty clay

The durability of silty clay embankments is partially controlled by the moisture migration, which depends on soil hydraulic properties. This paper presents an experimental study of hydraulic properties of compacted binary silty clay. Specimens with different mixing ratios and dry densities were prepared. Scanning electron microscopy and mercury intrusion porosimetry were used to characterise the microstructure of silty clay. Thereafter, falling-head permeability tests and water retention tests were conducted to study the permeability and water retention property, respectively. The results demonstrate that clay particles are dispersed and show preferred arrangements after compaction when the clay content is 100%. As the clay content decreases, the arrangement of clay particles is gradually disturbed because of the existence of silt particles, causing the formation of large pores around silt particles. When the dry density increases, the pores around silt particles significantly decrease. Moreover, the permeability of silty clay decreases but the water retention capacity increases with increasing clay content and dry density. This is because the silty clay with larger clay content and dry density has fewer large pores, which greatly restrains the flow of water. Both the permeability and water retention property of silty clay can be predicted from pore size distribution parameters.

Study on the creep permeability of mining-cracked N2 laterite as the key aquifuge for preserving water resources in Northwestern China

This research focused on the impact of mining on the permeability of key aquifuge （N2 laterite） that is widespread in the arid and semi-arid areas of northwestern China and is critical for preserving water resources. The impact of mining stress recovery on the permeability of cracked N2 laterite was assessed for parts of northwestern China that included the Jingle laterite and Baode laterite. The mineral compositions and swelling properties of the laterite at both locations were examined, and analytical results showed that the laterite contained abundant clay minerals. The Baode laterite exhibited higher expansibility than Jingle laterite. The triaxial creep permeability performance of laterite specimens with a prefabricated crack width of 1.0, 1.5, and 2.5 mm were tested. The results indicated that strain of cracked laterite all exhibited transient creep following each level of loading, and then unstable creep and stable creep. With the increase of loading, the transient creep deformation corresponding to each level of loading decreased, the unstable creep deformation produced by identical loading gradually and incrementally increased. The nonlinear power function equation was selected to fit creep grading curves which have high precision. The cracks within the laterite gradually closed with the stress recovery, and permeability gradually recovered. During the stress recovery, the narrower cracks exhibited a smaller change in permeability. However, for narrow cracks in mining soil, permeability recovered after mining stress when permeability was closer to initial permeability, and the Baode laterite showed greater recovery than that of the Jingle laterite.

Experimental study on preferential solution flow during dump leaching of low-grade ores

The phenomenon of preferential solution flow during dump leaching of low-grade ores was studied.The formative mechanism of preferential solution flow was investigated through analyzing the relationship between permeability and ore diameter,and the relationship between surface tension and ore diameter.The preferential solution flow happened within the fine ore area when the dump was unsaturated.And it could happen within the coarse ore area when the dump became saturated.The results of experiment show that the outflow of coarse ore area increases sharply with higher applied rate.The outflow of fine ore area is greater than that of coarse ore area when the applied rate is below 3.2 L/min,and the preferential solution flow happens in fine ore area.But the preferential solution flow happens in coarse ore area when the applied rate is higher than 3.2 L/min.The result of the experiment is consistent with the mechanism analyzing.

Theoretical Permeability of Two-layered Nonwoven Geotextiles

The two-layered nonwoven geotextile, which consists of a layer constructed with fine fibers for providing optimal filtration characteristics and another layer constructed with coarse fibers for providing the required mechanical properties, is desirable for drainage and filtration system. Based on Darcy’s law and drag force theory, a mathematical model on vertical permeability coefficient of two-layered nonwoven geotextile is estabilished. Comparison with experimental results shows that the present model possesses 83.6% accuracy for needle-punched two-layered nonwoven geotextiles. And experimental results also show that with the increasing of needle density the vertical permeability coefficient of two-layered nonwoven geotextiless firstly decreases and then increases, reaching the smallest value at 470 p/cm2.