Experimental investigation into the salinity effect on the physicomechanical properties of carbonate saline soil

For engineering structures with saline soil as a filling material,such as channel slope,road subgrade,etc.,the rich soluble salt in the soil is an important potential factor affecting their safety performance.This study examines the Atterberg limits,shear strength,and compressibility of carbonate saline soil samples with different NaHCO3 contents in Northeast China.The mechanism underlying the influence of salt content on soil macroscopic properties was investigated based on a volumetric flask test,a mercury intrusion porosimetry(MIP)test,and a scanning electron microscopic(SEM)test.The results demonstrated that when NaHCO3 contents were lower than the threshold value of 1.5%,the bound water film adsorbed on the surface of clay particles thickened continuously,and correspondingly,the Atterberg limits and plasticity index increased rapidly as the increase of sodium ion content.Meanwhile,the bonding force between particles was weakened,the dispersion of large aggregates was enhanced,and the soil structure became looser.Macroscopically,the compressibility increased and the shear strength(mainly cohesion)decreased by 28.64%.However,when the NaHCO3 content exceeded the threshold value of 1.5%,the salt gradually approached solubility and filled the pores between particles in the form of crystals,resulting in a decrease in soil porosity.The cementation effect generated by salt crystals increased the bonding force between soil particles,leading to a decrease in plasticity index and an improvement in soil mechanical properties.Moreover,this work provides valuable suggestions and theoretical guidance for the scientific utilization of carbonate saline soil in backfill engineering projects.

Effects of irrigation water salinity on soil salt content distribution,soil physical properties and water use efficiency of maize for seed production in arid Northwest China

In order to explore the use of groundwater resources,field experiments were conducted for three consecutive years during 2012-2014 in the Shiyang River basin of Northwest China.Irrigation was conducted using four different water salinity levels that were arranged in a split plot design.These four water salinity levels were s0,s3,s6 and s9(0.71,3,6 and 9 g/L,respectively).The soil salt content,soil bulk density,soil porosity,saturated hydraulic conductivity,plant height,leaf area index and yield of maize for seed production were measured for studying the effects of saline water irrigation on soil salt content distribution,soil physical properties and water use efficiency.It was observed that higher salinity level of irrigation water and long duration of saline water irrigation resulted in more salt accumulation.Compared to initial values,the soil salt accumulation in 0-100 cm soil layer after three years of experiments for s0,s3,s6 and s9 was 0.189 mg/cm3,0.654 mg/cm3,0.717 mg/cm3 and 1.135 mg/cm3,respectively.Both greater salt levels in the irrigation water and frequent saline water irrigation led to greater soil bulk density,but poorer soil porosity and less saturated hydraulic conductivity.The saturated hydraulic conductivity decreased with increase in soil bulk density,but increased with improvement in soil porosity.It was noted that the maize height,leaf area index and maize yield gradually decreased with increase in water salinity.The maize yield decreased over 25%and the water use efficiency also gradually declined when irrigated with water containing 6 g/L and 9 g/L salinity levels.However,maize yield following saline water irrigation with 3 g/L decreased less than 20%and the decline in water use efficiency was not significant during the three-year experiment period.The results demonstrate that irrigation with saline water at the level of 6 g/L and 9 g/L in the study area is not suitable,while saline water irrigation with 3 g/L would be acceptable for a short duration together with salt leaching through spring irrigation before sowing.

Soil Thermal Diffusivity of a Gleyic Solonetz Soil Estimated by Different Methods in the Brazilian Pantanal

The soil temperature is an important microclimatic factor due to the interactions between soil and plant, and the energy exchange with the atmosphere. The soil energy exchange is affected by the incident solar radiation, type of coverage and mainly by the soil thermal properties. Among the soil thermal properties, the soil thermal diffusivity is highlighted because it affects the soil temperature profile and soil heat flux transport and distribution. Thus, the aim of this study was to evaluate different estimates of soil thermal diffusivity of a Gleyic Solonetz soil in the Brazilian Pantanal. The soil thermal diffusivity was determined by the amplitude, logarithmic, arctangent and the phase methods between 0.01 and 0.03 m, 0.01 and 0.07 m and 0.01 and 0.15 m depth. The soil thermal diffusivity estimated by the four methods showed significant differences and varied over the study period as a function of volumetric soil water content. The soil thermal diffusivity estimated by logarithmic methodshowed better performance at different depths, followed by the method of phase.

Physical Status of Soils Developed from Loesslike Loams in the Southwest of the Central Russian Plain （the Belogor＇e Reserve）

Soils developed from the Quaternary loesslike loams have been studied in the south of the forest-steppe zone on the Central Russian Upland. A polygenetic nature of the soil profile on the loesslike loams is shown. The modem pedogenetic processes in this soil ensure its eluvial-illuvial differentiation with the development of multilayered coatings in the illuvial horizon. The middle horizons in the studied soil profiles are referred to as textural （clay-illuvial） horizons. Differences in physical soil properties （bulk density, airconductivity, texture, water content, and temperature dynamics） were studied in the soil on the loesslike loam.

Practical Engineering Behavior of Egyptian Collapsible Soils, Laboratory and <i>In-Situ</i>Experimental Study

In many sites on Egypt desert roads collapsible soils is broadly classified as a problematic soils containing silty fine sand which is cemented with low density and low degree of saturation which is susceptible to a large and sudden reduction in their volume upon inundation, with or without vibration in its stress. Four sites have been studied for new urban, roads and industry work sits, related to increase in natural water content. These soils go through radical rearrangement of their particles, causing sudden changes in the stress-deformation behavior which cause differential settlement of foundation and roads. This change in volume can lead to foundation failures and worth of damages under ground public facilities and infrastructure. In this study, the search program is developed to establish their different behavior under wetting in two phases: field and laboratory work. The obtained results are useful in mapping the trend of the factors affected in assessing soil collapsibility rate or collapse potentials which are observed in construction with volume change problems. The major factors observed are the natural structure skeleton of the soil particle and its grain size and mechanism of soil sedimentation. The field collapse potentials value assigned for these tested sites along Alexandria—Cairo desert road indicated that the field measured collapsibility potentials are smaller than those measured on the same extracted undisturbed samples in laboratory by 15%, which can be saved in coast, change in proposed collapsibility improvement method and change in select foundation type. Also, field tests evaluate the collapsibility rate with time and highlight that environmental history and natural soil structure in field are the important factors affected on these soil collapse, and also, knowledgeable by collapsible soils during wetting in these sites studied.

Hydraulic properties of typical salt-affected soils in Jiangsu Province, China

Every year about 1,500 ha of land is reclaimed from the sea along the coastline of Jiangsu Province,China.It is important to characterize the hydraulic properties of this reclaimed land to be able to predict and manage salt and water movement for amelioration of these saline soils.In this paper,we report hydraulic properties of these salt-affected soils.The pressure-plate method,constant head method,the crust method and Klute’s method were used in this study.The satu-rated hydraulic conductivities of the soils ranged from 128.66 to 141.26 cm/day and decreased with increasing soil depth.The unsaturated hydraulic conductivities followed an expo-nential function of pressure head.The soil water retention curves were similar for three soil layers in the soil.The satu-rated water content,field capacity and wilting point decreased with increasing soil depth.Plant available water contents of the three layers in the soil profile were 0.21,0.20 and 0.19 cm3/cm3,respectively.The unsaturated soil water diffu-sivity of the studied soils ranged from 0.07 to 10.46 cm^(2)/min,and was related to the water content via an exponential relationship.

Predicting Soil Moisture Characteristic Curves from Continuous Particle-Size Distribution Data

Soil moisture characteristic curve （SMC） is a fundamental soil property and its direct measurement is tedious and time consuming. Therefore, various indirect methods have been developed to predict SMC from particle-size distribution （PSD）. However, the majority of these methods often yield intermittent SMC data because they involve estimating individual SMC points. The objectives of this study were 1） to develop a procedure to predict continuous SMC from a limited number of experimental PSD data points and 2） to evaluate model predictions through comparisons with measured values. In this study, an approach that allowed predicting SMC from the knowledge of PSD, parameterized by means of the closed-form van Genuchten model （VG）, was used. Through using Mohammadi and Vanclooster （MV） model, the parameters obtained from fitting of VG to PSD data were applied to predict SMC curves. Since the residual water content （Or） could not be obtained through fitting of VG-MV integrated model to PSD data, we also examined and compared four different methods estimating 0r. Results showed that the proposed equation （MV-VG integrated model） provided an excellent fit to all the PSD data and the model could adequately predict SMC as measured in forty-two soils sampled from different regions of Iran. For all soils, the method in which Or Was obtained through parameter optimization procedure provided the best overall predictions of SMC. The two methods estimating Or with Campbell and Shiozawa （CS） model resulted in less accuracy than the optimization procedure. Furthermore, the proposed model underestimated the moisture content in the dry range of SMC when the value of 0r was assumed to equal zero. 0r could be attributed to the incomplete desorption of water coated on soil particles and the accurate estimation of 0r was critical in prediction of SMC, especially for fine-textured soils at high suction heads. It could be concluded that the advantages of our approach were the continuity, robustness, and independency of model performance on soil type, allowing to improve predictions of SMC from PSD at the field and watershed scales.

Effects of regulated deficit irrigation on soil salinity,physiological processes and fruit quality of gray jujube under desert conditions

Regulated deficit irrigation(RDI)was applied to gray jujube trees in an oasis region,to determine the effects of this irrigation system on soil salinity,gray jujube physiological processes,fruit yield,and fruit quality.Treatments consisted of severe,moderate and low deficit irrigation(irrigated with 85%,70%and 55%of CK,respectively)at the flowering stage to fruit set stage.During the other growth stages,all treatments were irrigated with 80%of pan evaporation,which was the same as that in control.The results indicated that soil salinity was enhanced during the periods of water stress,but the high value of soil salinity declined by 3.48%-37.27%,at each depth,after irrigation was resumed.RDI caused a decline in the photosynthetic rate,transpiration rate,and stomatal conductance,but enhanced the water use efficiency of the leaves.However,the leaf photosynthetic rate was effectively enhanced after the recovery of irrigation,especially in the moderate deficit irrigation treatment,which exceeded the control.This led to an improved fruit yield,which was 9.57%higher than that of the control.The deficit treatments caused a significant increase in the soluble solid content,soluble sugar content,single fruit weight and sugar/acid ratio.Enhanced vitamin C content,resulting from deficit treatments,has also been observed in the gray jujube.Therefore,this research shows that RDI provides some benefits in the production of gray jujube trees in desert conditions.

冻融循环及含水率对冰碛土力学特性影响

处在季节性冻土区的冰碛土受冻融循环作用影响显著,极大地影响工程的稳定和安全。为了探究冻融循环作用及初始含水率对冰碛土静力学特性的影响,以川西甘孜州海螺沟的冰碛土为研究对象,通过开展不同冻融循环次数及初始含水率条件下冰碛土不固结不排水三轴试验研究冻融循环作用对冰碛土力学参数的影响。试验结果表明:冻融循环作用下冰碛土应力-应变曲线为弱应变软化型;随冻融循环次数增加,冰碛土弹性模量、抗剪强度均呈现出先快速衰减后趋于稳定的变化趋势,且初始含水率越大其力学指标衰减程度越大,黏聚力呈负指数型函数降低,而内摩擦角无明显变化;采用指数型函数对抗剪强度、弹性模量试验值进行多元非线性拟合,建立冰碛土力学参数与围压、含水率及冻融循环次数的关系表达式,拟合效果理想,可用于推算经历冻融循环后土体力学参数值;冻融循环作用会使冰碛土力学性质显著劣化,且劣化程度与含水率呈正相关。研究成果可为高寒山区工程设计与建设提供科学支撑。

高分子活性剂改良盐渍土力学特性及机理研究

基于三轴剪切试验与可溶盐含量测试,探究高分子活性剂掺量与养护时间对硫酸型盐渍土力学性能与可溶盐含量的影响,揭示土体微观特性及其改良机理.结果表明:CLI型高分子活性剂的掺入能有效提升硫酸型盐渍土的力学强度和抗变形能力,其最佳掺量为8%;活性剂与盐渍土发生置换反应,从而增强盐渍土的保水性能,有效降低盐渍土的可溶盐含量,CLI型高分子活性剂掺量越大,改良效果越好;养护时间达到7 d时,盐渍土的可溶盐含量趋于稳定.

植烟区烟叶氯含量风险评估及影响因素分析

为进一步明确植烟区影响烟叶氯含量的环境因素及其可能的影响路径,于2021年在云南采集7个乡镇植烟区的烟叶及对应的土壤和灌溉水样品,系统评估该植烟区烟叶的氯含量状况,并探讨其与植烟土壤和灌溉水之间可能存在的联系。结果表明,该植烟区烟叶、灌溉水和土壤均存在不同程度氯含量超标风险,其中28.79%的烟叶中氯含量超过优质烟叶标准。Mantel-Test分析表明,烟叶氯含量与烟叶品质整体呈负相关,且与土壤主要理化性质、灌溉水氯含量密切相关。结构方程模型(structural equation model,SEM)分析表明,灌溉水氯含量对烟叶氯含量具有极显著直接正向效应(影响系数为0.459),对土壤化学特性有显著直接负向效应(影响系数为-0.225);而土壤物理特性对化学特性具有极显著正向效应(影响系数为0.370)。综上所述,该植烟区存在较高氯含量超标风险,灌溉水氯含量和土壤物理性状是重要影响因素,它们通过影响土壤化学性状及土壤含氯量共同引起烟叶氯含量超标,并最终降低烟叶品质。

高钾型氮磷钾水溶肥对核桃生长发育和土壤理化性质的影响

为了研究不同时期及不同次数施用高钾型水溶肥对核桃叶片、果实品质及土壤理化性质等的影响,以“辽宁1号”核桃品种为试材,在树体萌芽期、果实膨大期、果实硬核期施入高钾型水溶肥,测定核桃叶片、果实和土壤相关指标。结果表明,在萌芽期、果实膨大期及果实硬核期3次施用高钾肥对叶片叶面积、叶绿素、可溶性糖、光合作用及全钾含量提高最多;果实膨大期及果实硬核期、萌芽期和果实膨大期的2次施肥处理下,叶片全氮和全磷含量最高;全磷含量在3次施肥与2次施肥处理下无显著性差异;在萌芽期、果实膨大期、果实硬核期3次施用高钾肥对坚果单果质量、脂肪含量及产量提高最多;果实硬核期1次施用高钾肥处理下黄酮、多酚含量提高最多,但多酚含量在果实膨大期、果实硬核期1次施肥,果实膨大期和果实硬核期2次施肥处理下差异不显著;在果实膨大期和果实硬核期2次施用高钾肥能有效提高土壤速效钾和全钾含量,有机质、全氮、全磷含量均在果实萌芽期和硬核期2次施肥处理时效果较好。综合各项指标,萌芽期、果实膨大期及硬核期3次施肥处理对叶片品质和坚果质量、脂肪含量提高最多,然而产量与2次施肥处理间无显著性差异;2次施肥处理下土壤有机质、速效钾、全氮、全钾含量较高。本试验表明,对于提高核桃仁品质而言,3次施肥效果较好;而对核桃产量及土壤理化性质来说,建议2次施肥。

水泥-碱渣固化高含水率海相软土力学性质试验研究

为了解决低剂量水泥单独固化高含水率海相软土早期强度不足及固废碱渣资源化利用率低等问题,采用水泥、碱渣联合固化高含水率软土。通过30种不同质量配比的无侧限抗压强度试验得出,水泥-碱渣固化高含水率海相软土试样的无侧限抗压强度不仅与水泥、碱渣的掺量有关,还受到软土含水率的控制。在无侧限抗压强度研究基础上,推荐优选配比(碱渣、软土、水泥质量比为30∶70∶6),其7 d无侧限抗压强度为682.7 kPa。优选配比固化土的加州承载比(CBR)和回弹模量满足各级公路路基填料的指标要求。通过对高含水率软土中水的影响以及固化土级配和微观结构分析得出,水泥-碱渣固化高含水率软土的力学强度主要来源于碱渣吸水作用、碱渣骨架作用以及各组分材料化学反应的作用。化学作用产生的C-S-H,C-A-H和Aft等凝胶物质共同密实结构,提高固化土强度。研究结果可为固废物固化高含水率软土在路基中的应用提供理论支持。

黑水虻虫沙对普通白菜产量品质及土壤水溶性盐含量的影响

为明确黑水虻虫沙在蔬菜生产中的实际应用效果,采用盆栽方式,以不添加黑水虻虫沙为对照,研究添加不同比例黑水虻虫沙对普通白菜生长、产量、品质以及土壤肥力、水溶性盐含量的影响。结果表明:黑水虻虫沙施用量为2.5%、5.0%处理对普通白菜生长、产量总体上表现为促进作用;除施用量为2.5%外的其他处理VC、可溶性糖含量均显著低于对照,且硝酸盐含量显著高于对照。随着黑水虻虫沙施用量的增加,土壤p H值呈下降趋势,有机质、碱解氮、有效磷、速效钾和水溶性盐含量总体上均呈上升趋势。综合来看,本试验条件下2.5%黑水虻虫沙对普通白菜的施用效果最佳。

不同含水率与剪切速率下超固结红砂岩粗粒土的剪切特性研究

为研究不同含水率和剪切速率下超固结红砂岩粗粒土剪切特性,利用Shear TracⅢ大型直剪仪对其进行固结排水剪切试验,研究含水率和剪切速率对不同超固结比土体剪切特性的影响规律。结果表明,不同超固结比的红砂岩粗粒土剪切特性在初始剪切阶段有很大的不同,正常固结土会先产生剪缩,而超固结土会产生不同程度的剪胀。随着含水率的增加,超固结土体的剪切变形特性由不同程度的剪胀现象转为剪缩;随着剪切速率的增加,土体的剪切变形特性由剪缩转变为剪胀;随着超固结比的增大,土体会逐渐产生剪胀现象。超固结比越大的土体,其抗剪强度越大,含水率和剪切速率对土体的剪切特性影响越小。在相同的超固结比下,随着含水率的升高,其抗剪强度呈先增后减的趋势,当含水率为8%时,抗剪强度最大;随着剪切速率的增加,剪胀效应越明显,抗剪强度呈先减小后增大的趋势。在剪切过程中,土颗粒间不同的移动方式,会影响剪切带的形成,从而导致产生不同的剪切特性。

灌浆期叶面喷施不同硒源对水稻主要性状、硒含量和根际土壤理化性质的影响

【目的】探索灌浆期叶面喷施不同硒源对水稻生长、品质、硒含量和根际土壤理化性质的影响,为外源硒肥的选择及富硒水稻安全生产提供参考依据。【方法】以水稻品种鄂中5号为试验材料,设5个硒含量梯度(15.0、22.5、30.0、37.5和45.0 g/ha,以硒计),水稻灌浆期叶面喷施对应的生物纳米硒[3.0 L/ha(N1)、4.5 L/ha(N2)、6.0 L/ha(N3)、7.5 L/ha(N4)和9.0 L/ha(N5)]和亚硒酸钠[32.61 g/ha(Y1)、48.91 g/ha(Y2)、65.22 g/ha(Y3)、81.52 g/ha(Y4)和97.83 g/ha(Y5)],以喷施等量清水为对照(CK)。成熟后分别调查各处理水稻的农艺性状、经济性状、品质性状、精米硒含量及根际土壤理化性质。【结果】与CK相比,生物纳米硒处理的每穗总粒数、每穗实粒数、结实率和千粒重有不同程度提高,亚硒酸钠处理则出现一定程度降低。外观品质方面,2种硒源对稻米的粒长、粒宽、粒型和透明度影响不显著(P>0.05,下同),但显著降低垩白度和垩白粒率(P<0.05,下同),最大降幅分别为23.13%(N2处理)和39.60%(N5处理);N2处理显著提高稻米的碾磨品质,精米率和整精米率分别提高3.07%和5.89%。在蒸煮品质方面,除Y2处理外其余处理均降低稻米直链淀粉含量,且Y5处理降幅最大(12.56%),施硒对胶稠度和碱消值影响不显著。施硒能提高稻米的蛋白质含量(4.76%~30.98%),且在Y3处理时增幅最大。硒对根际土壤有机质含量影响不显著,但一定程度提高碱解氮、有效磷和速效钾含量,最大增幅分别为3.86%(N1处理)、18.86%(Y5处理)和5.57%(N4处理),且喷施亚硒酸钠后均显著降低根际土壤pH。施硒能提高稻米硒含量,生物纳米硒处理的稻米机硒占比均大于95.00%,而亚硒酸钠处理的大米有机硒占比均在85.00%以下。【结论】叶面喷施不同用量的生物纳米硒和亚硒酸钠均会影响水稻的千粒重、整精米率、垩白粒率、垩白度、直链淀粉含量、蛋白质含量和硒含量。综合分析,水稻灌浆初期叶面喷施22.5或30.0 g/ha的生物纳米硒可生产出同时符合国家标准和湖北省食品安全地方标准的富有机硒大米。

基于分层土壤的水土调控方法试验

以土壤物理学原理为指导,充分利用土壤基本物理性质,提出一种通过调整土壤剖面的分层组合方式,达到调控水土过程的技术,命名为人工分层配土(artificially layered soil,ALS)工程。为验证人工分层配土工程在水土调控方面的作用,开展室内积水入渗试验、植被蒸散发试验和野外干旱区土壤水分观测试验。结果表明:室内试验中,通过调整土壤剖面结构,人工分层配土显著提高了土壤的入渗能力,初始入渗速率提高3倍以上,平均入渗速率提高67.57%,土壤累计入渗量增加47.14%,同时降低了表层土壤含水量,减少38.39%土壤的无效蒸发量;野外试验中,分层配土处理组土壤含水量主要储存在地表下31~50 cm处,而野外原状土土壤含水量主要位于表层土壤,且相较于原状土壤,人工分层配土耗水量减少13.32%,耗水速率降低12.90%。因此,人工分层配土工程实现了水土调控的目的,对干旱区水土资源调控和荒漠化防治具有重要的意义。

新型水溶性保水剂改良盐渍土保水特性试验研究

针对我国西部存在的水资源匮乏及高强度蒸发作用而导致的土地盐渍化问题,现选择一种新型水溶性保水剂对盐渍土进行生态改良,提升其水分保持能力。开展室内保水性试验,并根据试验结果,选择适宜的新型水溶性保水剂浓度应用于现场试验;同时监测、分析土壤湿度、温度以及电导率变化,探究新型水溶性保水剂对盐渍土壤水分保持能力的影响。结果表明:(1)新型水溶性保水剂溶液与土颗粒反应形成乳白色的弹性黏膜,可存储土壤中的部分水分,达到延缓蒸发作用的目的。(2)保水剂溶液浓度为0.5%时即可显著提升土壤的保水能力,且土壤保水能力与保水剂溶液的浓度呈正比。(3)新型水溶性保水剂溶液可在一定程度上提升盐渍土的温度与湿度,减少土层表面盐分的析出。

水肥耦合对土壤碳氮储量、理化性质及三七产量和皂苷含量的影响

【目的】探究不同水肥耦合条件对土壤碳氮储量、理化性质及三七产量和皂苷含量的影响,为三七水肥调控及土壤碳氮固定潜力研究提供理论依据。【方法】2019—2021年在云南省泸西县三七种植基地进行试验,选取3年生三七为研究对象,设3个灌水水平[W1(5 mm)、W2(10 mm)和W3(15 mm)]和4个按生育期(根增期—苗期—花期—果期)配比的施肥水平[F1(360-360-360-360 kg/ha)、F2(288-360-432-360 kg/ha)、F3(216-432-432-360 kg/ha)和F4(144-576-288-432 kg/ha)],以不进行灌溉施肥为对照(CK)。测定各生育期不同处理的土壤碳氮储量及理化性质,并于2021年11月采集新鲜三七植株测定其产量和皂苷含量,采用主成分降维分析方法探讨土壤碳氮储量与各因子的关系。【结果】相同水肥耦合条件下土壤碳氮储量随土层深度增加而减少,随生育期推进基本呈先增后减的变化规律,其中以花期最高,最大值分别为82.07 t/ha(W1F4处理)和4.41 t/ha(W2F3处理),土壤有机碳储量积累关键期在苗期—花期,全氮储量积累关键期在根增期—苗期。各土壤养分含量以W2F3和W3F4处理较高,降低根增期施肥比例并增加苗期施肥比例能提高土壤养分含量。土壤碳氮储量变化主要依赖于全磷、全钾、速效钾、速效磷、硝态氮及铵态氮含量,碳氮储量增加能提高三七产量及三七皂苷R1含量。主成分降维分析结果表明,全磷、全钾、铵态氮及硝态氮含量对碳氮储量具有显著正向影响(P<0.05)。【结论】土壤碳氮储量与养分含量变化具有趋同性,其中以W2F3和W3F4处理有利于土壤碳氮累积与养分增加,适当增加苗期施肥比例有助于增加土壤碳氮储量并提高三七产量。

斥水膨胀土的水力稳定性

由于对斥水性黏土的斥水稳定性缺乏认识,斥水土应用仅针对斥水干砂,而干砂的力学性质较差,应用范围非常有限。为充分扩展斥水土的应用范围,该研究用十八胺对吸附性较强的膨胀土进行斥水改性,并分析不同斥水度的松散膨胀土吸附水蒸气后的斥水稳定性,在此基础上进行5种膨胀土击实试样(亲水膨胀土、亲水膨胀土+亲水砂、亲水膨胀土+斥水砂、斥水膨胀土、斥水膨胀土+斥水砂)的水力稳定性研究。结果表明:水气吸附试验前不同斥水度(包括轻微斥水)的膨胀土在吸附稳定后都变成了极度斥水,且各测试点都均匀斥水。击实后的斥水膨胀土与斥水膨胀土+斥水砂试样,在较大的含水率变化范围内均表现出了斥水性。与其他试样相比,斥水膨胀土+斥水砂的水力性能最好,可使膨胀土的膨胀率从33.9%下降为3.45%,收缩裂隙度从18.75%下降为3.6%,与亲水膨胀土相比,斥水膨胀土的基质吸力与强度参数并没有出现明显的改变。膨胀土较强的吸附性及斥水团聚体的存在是斥水膨胀土产生特殊的斥水性与水力特性的主要原因。研究可为斥水性黏土在农业工程中的应用及推广提供思路,同时也为扩展斥水性土壤的应用范围提供相应的理论参考。