Effects of Different Gravel Mulched Years on Soil Microbial Flora and Physical and Chemical Properties in Gravelsand Mulched Fields

Soil microbial flora and influencing factors of soil microbes in soil and gravel-sand mixed layer（ SGSML）,roots denseness layer（ RDL）,eluviate layer（ EL） and calcium accumulation layer（ CAL） in gravel-sand mulched fields（ GSMFs） with different gravel mulched years（ 1,6,12,19 and 25 years） were studied. The results showed that in the composition of soil microbes in the GSMFs,the quantity of bacteria was the largest,followed by actinomycetes,while the number of fungi was the smallest. The total quantity of soil microorganisms in the GSMFs dropped rapidly with the increase of soil depth,which was related to the sudden decrease in the quantity of bacteria. The number of microbes in the RDL was larger than that in the SGSML with few roots due to the effects of root distribution. The number of bacteria and actinomycete in the growing season was larger than that in the non-growing season,while the quantity of fungi in the growing season was smaller than that in the non-growing season. The quantity of bacteria and fungi was the largest in the GSMFs which had been mulched with gravel for 6-12 years. With the increase of mulching time,the GSMFs aged gradually,so their quantity reduced gradually. The quantity of actinomycetes was the smallest in the GSMFs which had been mulched with gravel for 6-12 years and increased with the increase of mulching time. The number of soil microbes in the GSMFs had a good correlation with soil moisture content,p H and mulching time. Soil total carbon content was an important factor restricting the quantity of soil microbes in the GSMFs.

Effect of the W-beam central guardrails on wind-blown sand deposition on desert expressways in sandy regions

Many desert expressways are affected by the deposition of the wind-blown sand,which might block the movement of vehicles or cause accidents.W-beam central guardrails,which are used to improve the safety of desert expressways,are thought to influence the deposition of the wind-blown sand,but this has yet not to be studied adequately.To address this issue,we conducted a wind tunnel test to simulate and explore how the W-beam central guardrails affect the airflow,the wind-blown sand flux and the deposition of the wind-blown sand on desert expressways in sandy regions.The subgrade model is 3.5 cm high and 80.0 cm wide,with a bank slope ratio of 1:3.The W-beam central guardrails model is 3.7 cm high,which included a 1.4-cm-high W-beam and a 2.3-cm-high stand column.The wind velocity was measured by using pitot-static tubes placed at nine different heights(1,2,3,5,7,10,15,30 and 50 cm)above the floor of the chamber.The vertical distribution of the wind-blown sand flux in the wind tunnel was measured by using the sand sampler,which was sectioned into 20 intervals.In addition,we measured the wind-blown sand flux in the field at K50 of the Bachu-Shache desert expressway in the Taklimakan Desert on 11 May 2016,by using a customized 78-cm-high gradient sand sampler for the sand flux structure test.Obstruction by the subgrade leads to the formation of two weak wind zones located at the foot of the windward slope and at the leeward slope of the subgrade,and the wind velocity on the leeward side weakens significantly.The W-beam central guardrails decrease the leeward wind velocity,whereas the velocity increases through the bottom gaps and over the top of the W-beam central guardrails.The vertical distribution of the wind-blown sand flux measured by wind tunnel follows neither a power-law nor an exponential function when affected by either the subgrade or the W-beam central guardrails.At 0.0H and 0.5H(where H=3.5 cm,which is the height of the subgrade),the sand transport is less at the 3 cm height from the subgrade surface than at the 1 and 5 cm heights as a result of obstruction by the W-beam central guardrails,and the maximum sand transportation occurs at the 5 cm height affected by the subgrade surface.The average saltation height in the presence of the W-beam central guardrails is greater than the subgrade height.The field test shows that the sand deposits on the overtaking lane leeward of the W-beam central guardrails and that the thickness of the deposited sand is determined by the difference in the sand mass transported between the inlet and outlet points,which is consistent with the position of the minimum wind velocity in the wind tunnel test.The results of this study could help us to understand the hazards of the wind-blown sand onto subgrade with the W-beam central guardrails.

Sieving Error from Dry-Separating Silt-Sand-Gravel Soils

The dry-separation method is an alternative to the wet-preparation in the current European Standard for the determination of particle size distributions by the sieving of soils. Due to the risk of error, dry-separation is cautioned against in the standard;however, there is no additional guidance as to when it is unsuitable nor for the magnitude of error that it may introduce. This study investigates the dry-separation method as an alternative by comparing with the conventional method of Wet-preparation in terms of particle-size distributions of eight cohesionless sand-gravel soils with varying amounts of nonplastic fines. The findings indicate a gradually increasing sieving error for fractions at minus 0.5 mm with the amount of fines in the soil, and depending on the fines content of the soil, dry-separation introduced errors upwards of 45% in silt-sand-gravel soils. An empirical best-fit formula is proposed for the estimation of the error using the dry-preparation method on this type of soil. Furthermore, to avoid sieving errors, the results suggest that the dry-separation method should not be used for silt-sand-gravel soils exceeding 2% silt size fractions.

旱区连作砂田土壤质量和土地生产力演变与调控研究进展

砾石覆盖在改变旱区水文循环和物质转化方面有着至关重要的作用。然而,长期连作给砂田土壤质量及土地生产力带来危机和不确定性。以连作砂田为研究对象,归纳总结了连作年限对砂层质地结构、土壤物理结构、土壤水盐热效应、土壤养分状况、土壤酶活性、土壤微生物特性、作物生长发育以及产量品质的影响效应和可能机制,发现砂田土壤生态环境和土地生产力在人类活动及自然侵蚀的扰动和破坏下整体呈现退化态势,但对不同覆盖条件、施肥水平和种植结构等农田管理措施的响应过程表现出差异性。继而,基于土壤质量和土地生产力的协同和互作效应深入揭示了砂田性能逐年退化机理,并简述了生物、农业及工程调控措施在砂田退化阻控和修复方面的应用进展。在此基础上,提出了砂田退化进程中急需解决的关键科学问题和未来发展方向,主要包括土壤质量演变的基本过程及其发生机制、“砾石-土壤-微生物-植物”系统的叠加和互作效应及其分子机理、土壤改良与生物防治措施的定量化及其调控机制三个方面。在气候变化、植被演替和土地退化背景下,废弃风化砾石的劣化增肥机制及其环境效应将是今后研究的重点。

袋装砂井打设深度的磁场法检测技术研究

袋装砂井的打设深度是排水固结法处理软基工程须控制的技术指标,开发原位检测已打设袋装砂井深度的有效方法,对于保障排水固结法的处理效果意义重大。研究表明,软土地基的平均固结度和袋装砂井深度近似线性正相关;在砂袋内设置人工磁场作为袋装砂井端头的检测标识具有显著的辨识度,检测靶标预置在砂袋内底端随同砂袋被打设到预定深度具有良好的成功率,控制靶标中磁芯的磁场强度和双芯的距离可以规避天然磁场和相邻靶标的影响,借助静力触探机械系统贯入磁感探头同步检测靶标的空间位置具有良好的可操作性和精度。现场试验显示,磁场法检测满足工程需要,相对于高压水冲法检测具有显著的性价比优势。

中国西北旱区砂田表层土壤养分效应对连作响应的整合分析

为明确砂田表层土壤养分对连作的响应规律,深入揭示砂田性能逐年退化机理,文章基于国内外已发表的16篇相关文献的586组有效数据,借助Meta-analysis方法进行整合定量研究,定量分析覆砂1—3年农田与其他连作年限砂田(4—6年、7—9年、10—12年、13—15年、16—20年)在表层土壤水分状况(SWC)、养分特性(有机质SOM、全氮TN、全磷TP、全钾TK、碱解氮AN、速效磷AP、速效钾AK、全盐TSS)和酸碱环境(pH)方面的差异效应,系统阐释砂田表层土壤养分特性逐年变异的发生路径及驱动因素,进而综合评估其肥力水平。结果表明:伴随种植年限的增加,砂田表层土壤水分储量和养分强度整体呈现下降态势(P<0.05),4—20年的土壤SWC、SOM、TN、TP、TK、AN、AP、AK含量分别较1—3年减少39.06%、14.21%、14.96%、10.06%、8.20%、15.87%、37.01%、18.60%(P<0.05)。表层土壤SOM、TN、TP、TK、AN、AP、AK主要于10—12年开始大幅流失(P<0.05),而4—6年土壤SOM、TP、TK、AK含量的相对变化则不显著(P>0.05)。砂田在耕作12年内具有显著压盐效果,12年以后的表层土壤TSS含量则开始呈现逐年增加的发展趋向(P<0.05),其土壤pH整体增加1.29%(P<0.05)。连作年限是砂田表层土壤TN、TP和AK变异的关键因子;SWC则为土壤SOM、AP和TSS演化的主导要素。总体而言,砂田在连作10年左右即可出现明显的养分亏缺状态。因此,亟需提出科学合理的农田管理措施,以有效提升退化砂田的土壤肥力水平。

成层土中长桩竖向承载激发规律研究

针对成层土中长桩承载问题,结合试桩数据建立了成层土中长桩-土相互作用特性分析模型,基于分析模型研究了上砂下黏和上黏下砂中砂-黏占比对长桩竖向荷载-位移曲线的影响,分析了成层土中长桩侧阻和端阻承载分担比,揭示了达到极限承载力时成层土中桩基侧阻、端阻激发规律,即黏土层侧阻可完全激发、砂土层侧阻未完全激发,桩底端阻完全激发,为实际工程中长桩承载力计算选取合理参数提供依据。

砂砾石地层渗透注浆扩散规律模型试验研究

为探究水泥浆液在砂砾石地层中的运移扩散规律,结合正交设计开展了9组室内渗透注浆模型试验,研究了不同注浆压力和水灰比影响下级配组成各异的砂砾石料试样中浆液的扩散特性,并在此基础上进行了多元线性回归分析,结果表明:受土骨架渗滤影响,水泥浆液在砂砾石孔隙中的扩散速度逐渐减缓,并扩散形成近似球形的结石体;注浆压力与渗透系数分别是影响渗透注浆量及浆液扩散半径的主要因素;结合试验结果拟合得到了注浆量、浆液扩散半径与渗透系数、水灰比、注浆压力之间的幂函数经验方程,分析发现浆液扩散半径随渗透系数的增大呈指数增大,增大注浆压力能有效克服水泥颗粒惯性力和吸附力的不利影响,使浆液的可注性显著提升。试验所得结论较为全面地记录了水泥浆液在砂砾石中的渗透扩散变化,可为砂砾石渗透注浆理论的进一步研究提供参考。

轴压荷载对胶凝砂砾石材料渗透性能的影响

胶凝砂砾石作为一种新型环保的建筑材料,在其实际服役状态下坝体承受各种荷载作用,为研究轴压荷载对于胶凝砂砾石渗透性能的影响,选用工程中常用的4种配合比,进行轴压加载试验、渗透试验、超声波速监测试验、核磁共振试验。针对试验数据分别分析了不同轴压荷载对胶凝砂砾石渗透性能的影响,得出以下结论:试件的渗透系数与孔隙率随轴压荷载水平呈正相关;渗透系数与孔隙率服从指数函数关系。采用孔径分布的回归模型能够较好的适用于胶凝砂砾石渗透系数的预测。

新疆叶尔羌河某水电站深厚砂卵砾石层坝基承载力及变形特性原位试验研究

针对新疆叶尔羌河某水电站深厚砂卵砾石覆盖层坝基,采用刚性承压板法开展原位承载力及变形试验研究,采用直径为50 cm和75 cm的承压板分别开展试验,试验结果表明:冲积形成的深厚密实砂卵砾石层具有相当高的承载能力,加载至3 MPa以上仍未出现较明显的破坏现象,且比例界限并不明显,判断其承载力特征值需要结合试验曲线及沉降与承压板直径之比即S/d值进行选取。采用不同直径的承压板试验所得到的加载曲线未表现出明显不同,获得的变形模量在同一水平,表明在一定尺度范围内承压板直径对试验结果影响不大。

地聚物对风积沙砾石混合料力学性能影响

为实现地聚物胶凝材料在公路路面基层的应用,研究不同物料配比对地聚物稳定风积沙砾石混合料力学性能影响。采用正交试验,探究钢渣微粉与粉煤灰质量比例2∶8、3∶7、4∶6,碱含量6%、8%、10%,碱激发剂模数1、1.2、1.4时对地聚物稳定风积沙砾石混合料抗压强度与劈裂强度影响,并通过极差分析明确各因素对风积沙砾石混合料强度影响关系。结果表明:钢渣微粉与粉煤灰质量比例对混合料强度影响最大,碱含量次之,碱激发剂模数最小。当钢渣微粉与粉煤灰质量比例为3∶7,碱含量8%,碱激发剂模数1.4时混合料力学性能最佳,7 d、28 d龄期下混合料抗压强度达到1.89 MPa与4.89 MPa,劈裂强度达到0.43 MPa与0.85 MPa,研究结果可作为水泥替代胶凝材料应用到公路路面基层建设当中。

基于振冲碎石桩现场试验的软土坝基处理工艺研究

振冲碎石桩是软弱土坝基重要的加固手段,在实际的工程实践中,振冲碎石桩加固手段对于软弱坝基的处理是否有效需要基于现场试验进行检测。针对非洲卢旺达Nyabarongo II HPP工程的坝基振冲碎石桩加固措施难题,在国内选址了地质条件相似的温州仙湖试验区进行振冲碎石桩的现场试验,验证了振冲碎石桩加固深厚软土层的有效性。采用孔压静力触探试验、十字剪切板试验、动力触探试验、载荷试验检测振冲碎石桩的加固效果和地基承载力。相关研究可丰富软弱土坝基的振冲碎石桩施工处理工艺,为后续类似工程加固实践提供参考。

挤密碎石桩处理场地液化砂土研究

砂土液化作为地震灾害的一种,会导致出现地基喷砂冒水、地基破坏等问题。文章依托月亮湾海堤工程,采用规范方法对场地填砂进行液化判别。为消除填砂液化沉降,提出了挤密碎石桩的处理措施。通过标准贯入试验、重型动力触探试验及复合地基荷载试验,评估了挤密碎石桩的处理效果,并复核处理后的地基承载力。研究表明,挤密碎石桩处理对地基深层土体的标准贯入击数改善效果更好,场地填砂层由轻微液化变为不液化;三根试验桩大部分桩身的锤击数均超过七次,可见大部分桩身均处于密实状态;经挤密碎石桩加固后的土层,地基承载力显著提升,满足设计要求。

含砂层软土地基真空预压二维有限元分析

采用真空预压处理含砂层软土地基时,受现场试验环境的限制,无法定量分析含砂层会对地基形变产生的影响。以温州某围海工程为例,针对粉砂含淤泥、淤泥等物理力学性质差异明显的土样,通过有限元模型对真空预压加固过程进行数值模拟计算。将模拟分析结果与现场实测数据进行对比分析,明确了含砂层对软土地基排水的促进作用,揭示了在砂层厚度不变的条件下,含砂层埋设深度越深,软土地基的分层沉降及侧向位移越大的规律。研究验证了有限元模型的合理性,可为真空预压技术处理类似地质条件提供有效参考。

A laboratory test of the electrification phenomenon in wind-blown sand flux

The measured data in the wind-tunnel tests show that the wind-blown sand particles acquired a negative charge when their diameters are smaller than 250 μm and positive charge when their diameters are larger than 500 μm, which confirms Latham’s assumption that the large particles in wind-blown sand flux acquired positive charge while negative charge developed on small ones. In the meanwhile, the measured data also show that the average charge-to-mass ratio for wind-blown sand particles decreases with the increase of the particle diameter and the wind velocity, and increases with the rise of height. The electric field in wind-blown sand flux is mainly formed by the moving charged sand particles. Its direction is vertical to the Earth’s surface and upward, which is opposite to that of the fair-weather field. The electric field increases with wind velocity and height increasing. These experimental results will lay the foundation for developing the theoretical analysis of the electrification phenomenon in

微咸水补灌年限对压砂地水盐分布及西瓜产量和品质的影响

【目的】探讨微咸水补灌年限对压砂地土壤水盐分布特征及西瓜产量和品质的影响。【方法】采用田间定位调查方法,研究了微咸水补灌年限为2、4、7、10、14 a的压砂地0~60 cm土壤水盐动态分布及西瓜产量和品质。【结果】西瓜伸蔓期和收获期土壤饱和电导率随微咸水补灌年限增加而增加,荒地土壤20~40 cm土层饱和电导率最高,而压砂地在40~60 cm土层饱和电导率最高;微咸水补灌增加了开花坐瓜期土壤体积含水率,但随微咸水补灌年限增加呈先增加后减小的趋势;压砂地表层(0~10 cm)土壤体积含水率最高,而荒地10~20 cm土层的土壤体积含水率最高;与荒地相比,土表覆砂增加了0~40 cm土层土壤体积质量及0~8 cm土层的土壤紧实度,而8 cm以下土层土壤紧实度小于荒地;西瓜产量和瓜周可溶性固形物量随微咸水补灌年限增加分别呈降低和先增加后降低的趋势。【结论】长期微咸水补灌提高了压砂地上层土壤体积质量和紧实度,同时也增加了土壤含水率和土壤盐分,西瓜产量随微咸水补灌年限增加呈下降趋势,而西瓜品质则有先提高后降低的趋势。

基于PPR数据建模技术的砂砾石料应力应变规律拟合

土的本构关系是岩土工程界备受关注的重要理论之一,其应力应变关系的准确描述是本构模型的关键问题。本工作基于大型静三轴试验,研究了两种不同级配砂砾石料的应力应变关系,采用PPR无假定数据建模技术对试验结果进行了建模拟合,并与邓肯-张E-B双曲线模型进行对比分析。结果表明:PPR数据建模技术能够较好地拟合砂砾石料在三轴试验下的应力应变关系,计算值与试验值的相对误差小于6%时的合格率达到90%以上,偏应力与体应变的最大相对误差分别为13.2%和20.9%,相较邓肯-张双曲线模型具有更高的精度;PPR模型能准确描述砂砾石料受剪切过程中的体胀特性,并且对三轴试验结果具有较好的预测功能。本工作提出了一种数据建模方法来表示土体应力应变关系,研究结果为岩土工程材料的应力应变关系描述提供了新的思路。

耐高温一体化乳液型压裂液研究与应用

乳液型一体化压裂液体系被当做滑溜水在非常规油气储层改造中得到广泛应用,但其高温(大于120℃)静态悬砂能力弱,在高温深井较低排量加砂风险高。为此,以丙烯酰胺单体为主,引入抗高温功能团,合成一种耐高温一体化压裂液乳液型稠化剂。乳液稠化剂性能稳定,室温存放60 d无沉淀分层;按一定比例加水,10~15 s即达到最高黏度的50%以上,3~5 min后达到最高黏度;具有自交联性能,1.6%以上乳液质量分数配制的压裂液,在160℃条件下,170 s-1剪切120 min后,黏度大于150 mPa·s;30/50目陶粒160℃条件下,静态悬砂120 min沉降5 cm;加入破胶剂2 h后,破胶液黏度小于5 mPa·s,破胶液岩心伤害率24.6%。现场应用井储层最高温度153℃,1.5%乳液稠化剂用量,施工排量8~11 m^(3)/min,最高砂浓度480 kg/m^(3),与相同黏度羟丙基瓜尔胶相比,降阻率提高10%左右,应用井改造后产量稳定。

滴头流量对压砂土壤水盐分布及西瓜生长、产量的影响

【目的】探明微咸水灌溉条件下滴头流量对压砂地土壤水盐分布及西瓜生长和产量的影响。【方法】通过田间试验,设置Q1(2 L/h)、Q2(3 L/h)、Q3(4 L/h)3种滴头流量,研究滴头流量对灌水前后土壤水盐分布特征、西瓜生长、产量、果实品质及水分利用效率的影响。【结果】滴头流量越大,土壤水平湿润范围越大,膜间土壤含水率越高,滴头下方垂直湿润深度越浅。各处理0~100 cm土壤盐分经过一个全生育期均呈下降趋势,盐分减少量随滴头流量增大而增加。果实可溶性糖量随滴头流量增大呈先增大后减小趋势,Q2处理最大,分别较Q1、Q3处理提高了54.3%和22.3%;维生素C量随滴头流量增加呈先减少后增加趋势,Q3处理最高,较Q2处理提高了53.7%。西瓜产量与灌溉水利用效率均随滴头流量增大而增加,Q3处理产量分别较Q1、Q2处理提高了6.20%和3.56%,Q3处理的灌溉水利用效率分别较Q1、Q2处理提高了6.49%和3.72%。【结论】综合考虑土壤水盐再分布形式与西瓜产量、品质,适用于压砂地西瓜微咸水滴灌流量为Q3(4 L/h)。

不同微咸水灌溉方式对压砂地土壤水盐及pH空间变异的影响

掌握不同灌溉方式下压砂地土壤水盐及pH的空间分布规律可以有效提高微咸水的利用效率。利用田间取样、经典统计学、地统计学以及克里格插值法对比分析了滴灌和微喷灌0~40cm土层土壤含水率、电导率和pH值的空间变异特征。结果表明:微喷灌的土壤含水率略低于滴灌,0~40cm土层土壤含水率属于中等变异性,且具有中等强度的空间相关性。微喷灌0~20cm土层土壤平均电导率和离散化程度小于滴灌,同时,2种灌溉方式下0~20cm和20~40cm土层电导率的空间分布均表现出中等变异且具有较强的空间相关性;20~40cm土层的平均电导率小于0~20cm土层。无论微喷灌还是滴灌,调查地块的土壤电导率表现为中间位置低而地边较高,土壤含水率则在中间位置高而地边低。灌溉方式对土壤pH值的影响不显著,其空间变异性属于弱变异,但微喷灌条件下pH值具有较强的空间相关性。微咸水灌溉条件下压砂地抑制了表层土壤盐分累积,并存在向未覆砂的地块边缘聚积的现象。不同灌水方式下压砂地土壤水分和盐分均存在中等的空间变异性和空间自相关性,而pH值空间变异性较弱。研究结果可以为压砂地的微咸水合理利用提供理论依据。