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1.
循环孔隙水作用下混凝土动态特性试验研究Symbol`@@ 总被引：1，自引：0，他引：1
对0、10、50次孔隙水循环下不同应变速率(10 -5、10 -4、10 -3、10 -2/s)的混凝土和中低应变速率(10 -4、10 -3/s)下不同孔隙水循环次数(0、10、50、100、200次)的混凝土进行了常三轴压缩试验,试件尺寸为300 mm×600 mm。对循环孔隙水压作用后混凝土的峰值应力物理力学参数的变化规律进行了统计分析,并对混凝土在不同加载速率下的吸能变化规律进行了分析。结果表明：随着应变速率增大,混凝土的峰值应力呈增大趋势,随孔隙水压循环次数的增加,峰值应力大体呈现先增大后减小的阶段性变化;混凝土的吸能能力随加载速率的增加,表现出明显增大的趋势。混凝土的吸能能力随孔隙水压循环次数的增加表现出一定的离散性,但整体上呈先增大后减小的趋势;选用基于Weibull统计理论的混凝土材料分段式动态损伤本构模型对试验数据进行拟合,经验证,此模型与试验结果吻合较好。 相似文献
2.
原状黄土冻融过程抗剪强度劣化机理试验分析 总被引：3，自引：0，他引：3
通过对西安Q3原状黄土在封闭系统冻融作用下的电镜扫描和直剪试验,研究了冻融作用对原状黄土微观结构和强度的影响。试验表明：冻融过程中原状黄土微观结构发生显著变化,大颗粒集粒数量明显减少,小粒径土颗粒所占比重增加,孔隙面积比增加。进一步基于损伤力学理论,得到微观结构冻融损伤度随冻融次数增加呈指数增加趋势,反映出冻融作用一定程度上破坏黄土体的结构强度,但多次冻融后黄土体结构强度趋于稳定的残余强度。冻融过程土样表面结构发生破坏,且含水率越高,土体表面特征破坏越严重。粘聚力随冻融次数增加呈指数衰减趋势,且含水率越高,粘聚力衰减幅值和速率越小;粘聚力随含水率增加表现出线性衰减特征,且冻融后粘聚力与含水率的变化规律近似重合;内摩擦角无明显规律性变化。粘聚强度冻融损伤系数随冻融次数增加呈指数增加趋势,随含水率升高有增大趋势。基于试验数据规律性,进一步提出了原状黄土粘聚强度劣化模型,该模型经试验验证可较好描述原状黄土粘聚强度劣化规律。 相似文献
3.
不同氮肥水平下早熟晚粳氮和磷的吸收利用特性及相互关系 总被引：6，自引：1，他引：5
采用大田试验,以长江中下游地区具有代表性的50个早熟晚粳品种为材料,研究7个氮肥水平(0、150.0、187.5、225.0、262.5、300.0、337.5 kg hm-2纯氮)下水稻氮和磷积累量、吸收速率、利用效率的差异及其相互关系。结果表明：(1)在0~337.5 kg hm-2纯氮范围内,随着氮肥水平的增加,早熟晚粳的植株含氮率和氮积累量在拔节、抽穗和成熟期均显著增加;植株含磷率和磷积累量在拔节和抽穗期显著增加,成熟期呈先增后减变化。(2)播种至拔节阶段氮和磷吸收速率随施氮量的增加而提高,差异极显著;拔节至抽穗阶段氮和磷吸收速率随施氮量的增加呈现先增加后降低的变化趋势;抽穗至成熟阶段的氮和磷吸收速率规律不明显。(3)在0~337.5 kg hm-2纯氮范围内,随着施氮量的增加氮素籽粒生产效率和磷素籽粒生产效率均显著降低,随着施氮量的增加基因型之间的差异减小;随着施氮量的增加氮和磷收获指数都呈现抛物线关系,在施氮量为262.0 kg hm-2纯氮时出现最大值。(4)早熟晚粳对氮和磷的吸收利用具有显著的协同效应,但随生育进程的推进这种效应减弱。水稻在播种至拔节、拔节至抽穗和抽穗至成熟3个生育阶段的氮和磷吸收速率都呈二次曲线关系(r=0.892**,r=0.736**,r=0.512**)。(5)相关分析表明,产量与拔节期、抽穗期和成熟期的吸氮量和吸磷量以及播种至拔节期和拔节至成熟期的吸氮速率和吸磷速率呈极显著正相关关系。增施氮肥有利于水稻氮和磷吸收利用的提高,但氮肥过高时氮和磷吸收利用不再增加,甚至有所降低。 相似文献
4.
黑龙江省不同年代玉米杂交种产量对种植密度和施氮水平的响应 总被引：9，自引：0，他引：9
明确不同年代春玉米生产力对种植密度和氮肥水平的响应特征及其趋势,对高产高效的耐密品种选育和密植抗倒栽培具有重要的理论参考和技术指导意义。本文以黑龙江近50年来第一积温带大面积种植的8个典型春玉米品种为材料,于2009和2010年进行密度和施肥的田间试验,比较不同年代主栽品种生产力演变特征。结果显示,黑龙江省1970s—2000s玉米品种更替过程中,单株生产力与群体产量均明显提高,平均增幅分别为16.96 g 10年-1和790 kg hm-2 10年-1;植株空秆率和倒伏率显著下降,株高、穗位、单株叶面积、穗粒数、千粒重显著提高。随着密度的提高,各年代玉米的单株产量呈显著下降趋势,群体产量呈抛物线形上升,群体最高产量的理论密度增幅为3 507株 hm-2 10 年-1;空秆率显著提高,但倒伏率仅1970s和1980s的品种呈递增趋势;株高、单株叶面积、棒三叶面积、穗粒数与千粒重均呈现下降趋势,穗位随密度增加呈显著上升趋势。各年代品种株高、穗位、单株叶面积和千粒重随氮肥水平提高呈增加趋势。在150~450 kg hm-2的施氮水平范围,随着氮肥水平的提高,各年代品种增产效果不明显。各主要指标在年代、密度和氮肥水平之间存在显著的互作效应。对照东北玉米现有的品种特性、种植密度和施肥现状表明,选育耐密品种和实施密植抗倒栽培的增产潜力大,在现在的施肥水平上进一步提高种植密度是东北春玉米高产增效耕作栽培的技术创新方向。 相似文献
5.
氮肥水平和种植密度对冬小麦茎秆抗倒性能的影响 总被引：13，自引：0，他引：13
以中穗型小麦品种山农15为材料,在2个氮肥水平(180 kg hm-2和240 kg hm-2)和2个密度(150×104 hm-2和225×104 hm-2)下,研究了抗倒性能相关的形态学特征、茎基部节间化学组分、抗倒指数（茎秆机械强度/茎秆重心高度）、木质素合成相关酶活性和籽粒产量的变化特点,以及抗倒指数与形态学和生化指标的相关性。结果表明,施氮水平和种植密度间存在显著的互作效应,当施氮水平由180 kg hm-2增至240 kg hm-2或种植密度由150×104 hm-2增加到225×104 hm-2时,茎秆重心高度、基部节间长度显著提高,基部节间直径、厚度、充实度、机械强度和抗倒指数显著降低,同时茎秆基部节间纤维素含量、木质素含量显著减少,含氮量显著升高,碳氮比(C/N比)以及木质素合成相关酶活性显著降低。逐步回归分析表明,氮肥水平对小麦抗倒性的影响大于种植密度。本试验条件下,氮肥水平180 kg hm-2和种植密度为150×104 hm-2的处理穗数较低,但穗粒数和千粒重显著高于其它处理,因而籽粒产量最高。建议在降低氮肥用量至180 kg hm-2的同时降低种植密度至150×104 hm-2,可在增强植株抗倒伏能力的同时获得高产。 相似文献
6.
氮钾配合施用对短季棉光合特性和产量品质的影响 总被引：7，自引：3，他引：7
大田条件下,采用施尿素225 kg·hm-2、300 kg·hm-2两个水平和施氯化钾0 kg·hm-2、120 kg·hm-2、195 kg·hm-2三个水平,研究了不同组合对短季棉光合特性和产量品质的影响。结果表明,在相同施钾水平下,高氮比低氮的叶片光合能力和产量略有提高,高氮比低氮的增产效应随钾量的增加而增加,氮肥的肥效随钾肥的增加而明显提高;在相同施氮水平下,2个施钾的比不施钾的光合能力、产量和纤维品质均显著提高;不同施钾处理间子棉产量差异极显著;本试验条件下,以尿素300 kg·hm-2、氯化钾195 kg·hm-2组合产量最高。在充足的氮肥条件下,保证适量钾肥的供应,维持氮钾平衡对提高短季棉的氮肥利用效率、产量和纤维品质极为重要。 相似文献
7.
河南植棉区施氮量对麦棉两熟产量及氮肥利用率的影 响简 总被引：3，自引：2，他引：1
研究了河南植棉区麦棉两熟施氮量对两季产量和氮肥利用率的影响。结果表明,施氮能显著提高小麦产量、总有效穗数和穗粒数,籽粒千粒重随施氮量增加而降低;商丘和内黄试验点小麦最高产量所需的施氮量分别为201.4 kg·hm-2和187.2 kg·hm-2,经济最佳施氮量分别为163.0 kg·hm-2和134.9 kg·hm-2。施氮也能显著提高棉花产量和单株成铃数;适量施氮可提高铃重;商丘和内黄试验点棉花最高产量所需的施氮量分别为244.4 kg·hm-2和224.2 kg·hm-2,经济最佳施氮量分别为225.9 kg·hm-2和207.0 kg·hm-2。小麦氮肥利用率以施氮量180 kg·hm-2最高。麦棉两季氮肥利用率,商丘试验点随施氮量增加而降低;内黄试验点以施氮量390 kg·hm-2最高。小麦、棉花氮肥偏生产力、农学利用率均随施氮量增加而降低。 相似文献
8.
春玉米叶面积系数动态特征的密度效应 总被引：17，自引：0，他引：17
为进一步明确春玉米不同密度群体叶面积系数(LAI)特征参数的密度效应,以吉单209和郑单958为材料,于2005年和2006年在东北春玉米区(吉林)分别设置4.5~10.5万株 hm-2 5个密度和3.0~12.0万株 hm-2 7个密度处理试验,应用作物高产群体相对LAI动态普适模型方程y= (a+bx)/(1+cx+dx2)模拟分析不同密度对LAI动态特征参数的影响。结果表明,春玉米群体最大LAI在3.0~12.0万株hm-2范围内随密度增加呈近似直线增大趋势,而最大LAI出现的时间随密度增加而提早;将LAI数据相对化处理后,不同密度群体的LAI差异在最大LAI之后较之前表现明显,高密度群体较低密群体LAI衰减迅速。全生育期平均LAI随密度增加呈显著线性增大趋势,而平均LAI与最大LAI的比率则随密度增加呈显著线性减小趋势。密度对模拟方程各参数均有不同程度的影响,相邻密度差异不明显,间隔3.0万株 hm-2的差异显著;不同参数变化趋势不同,其中参数a接近“0”,受密度影响不大;b、c均随密度的增加而减小,d随密度的增加而增大。全生育期群体LAI变化速率呈“N”形变化趋势,且与群体LAI变化及生育期对应,高密度群体LAI增加及衰减的速率均大于低密度群体,拔节期和大喇叭口期为密度响应敏感期。由此可见,密度对春玉米全生育群体LAI动态具有调节作用,尤其群体LAI变化速率、最大LAI及其到达的时间、平均LAI及其与最大LAI的比率等重要特征参数对密度响应较为敏感,可作为对春玉米群体密度调控的参考指标。 相似文献
9.
室外盆栽条件下盐胁迫对甜高粱光系统II活性的影响 总被引：3，自引：0，他引：3
室外盆栽条件下, 设置2个NaCl浓度(100 mmol L–1和200 mmol L–1), 调查盐胁迫对甜高粱光合特性和光系统II (PSII)活性的影响。结果表明,叶片Na+离子含量与Na+/K+比随盐浓度增加和处理时间延长而增加。净光合速率(Pn)、光系统II开放反应中心天线转化效率(Fv¢/Fm¢)、光化学猝灭系数(qP)和光系统II实际光化学效率(ΦPSII)随盐浓度的增加而降低,非光化学猝灭(NPQ)随盐浓度增加而增加;100 mmol L–1处理组的Pn、Fv¢/Fm¢、qP和ΦPSII随处理时间延长有所恢复,但200 mmol L–1处理组无此现象。光系统II (PSII)最大光化学效率(Fv/Fm)在100 mmol L–1 NaCl处理时影响较小,但在200 mmol L–1 NaCl处理时明显下降。短期盐胁迫未影响荧光诱导动力学曲线,而200 mmol L–1 NaCl处理5 d后荧光诱导动力学曲线O-K和O-J相上升。进一步研究证明,PSII的失活速率在两个盐浓度下均无明显变化,而修复速率在200 mmol L–1盐浓度处理5 d后降低明显。因此,认为室外盆栽条件下盐胁迫造成甜高粱碳同化能力降低并改变PSII激发能分配;叶片Na+离子含量的大幅增加会导致PSII活性下降及光抑制,这与PSII失活速率无关,主要是失活PSII修复速率受抑制的结果。这对理解户外盐胁迫条件下C4作物的光抑制机制具有一定意义。 相似文献
10.
研究了降雨雨型、雨强和持时对边坡孔隙水压力分布的影响以及降雨入渗条件下饱和渗透系数的空间变异性对孔隙水压力、含水率、抗剪强度参数、局部安全系数等参数空间分布的影响。研究结果表明,降雨特性对边坡孔隙水压力的影响较大;受渗流主方向影响,降雨条件下饱和渗透系数的水平波动尺度对孔隙水压力及含水率的变异性影响小于竖向波动尺度,降雨致滑坡的临界滑面基本与坡面平行且深度较浅;随着饱和渗透系数水平波动尺度的增加,滑坡深度随之增大,从总体上坡体上部局部安全系数随饱和渗透系数竖向波动尺度的增加而减小。 相似文献
11.
To explore the characteristics of deformation of sandstone under cyclic pore water pressure, the experiments with different axial stresses (60%, 70% and 80% of peak intensity) of sandstone subjected to cyclic pore water loading are investigated by using MTS815 rock mechanics testing system, and irregular small deformation in deformation curve of sandstone are also processed by wavelet transformation of Matlab. The results show that with the increase of constant axial stress, fatigue deformation under cyclic pore water pressure will accelerate the failure of the sandstone. With the increase of the number of cyclic pore water pressure, the deformation evolution of the plastic-loop is illustrated as sparse-dense-sparse. The deformation curves of sandstone under cyclic pore water pressure affected by many factors are decomposed, reconfigurable processed and evaluated by using wavelet transformation, which indicates that the basic curve with optimal decomposition scale fits well with the experimental curves and reveals the deformation evolution of sandstone. 相似文献
12.
An indoor experiment on explosive compaction of saturated sand has been done.The changes of pore water pressure during blasting are measured and the laws of pore water pressure increment and dissipation are analyzed.It indicates that the processes of increment and dissipation of pore water pressure have particularity along the depth and radial.At the same time,the development rule of liquefaction under explosive loading is also analyzed;these conclusions obtained in the experiment,may provide some useful references for the engineering design and the theoretic study of explosive compaction for water-saturated granular foundation. 相似文献
13.
再生混凝土与锈蚀钢筋间的粘结性能试验研究 总被引：4，自引：0，他引：4
为了探究再生混凝土结构的耐久性能,对5组不同钢筋锈蚀率(0~9%)的再生混凝土梁式试件进行加载试验。分析不同钢筋锈蚀率对再生混凝土梁式试件的钢筋应变、局部粘结应力、粘结滑移和极限粘结应力的影响。结果表明：钢筋锈蚀率大于3%时试件底部开始有细微锈胀裂缝出现;锈蚀率越大,荷载作用下钢筋应变沿锚固位置的变化曲线越平缓;局部粘结应力沿锚固段呈现出双峰分布,峰值主要集中在加载端和自由端附近;加载端附近位置滑移现象最先发生,远离加载端滑移现象延后;随着钢筋锈蚀率的增大,极限粘结强度先增加后降低,极限荷载下的滑移值增大。 相似文献
14.
To analyse size effect of high-strength concrete column under small eccentric loading, experimental analysis was carried out on 3 categories of different sizes of high-strength concrete columns under small eccentric loading. The columns' section size was 200 mm × 200 mm, 400 mm × 400 mm and 800 mm × 800 mm, respectively. Failure mode, ultimate strength, deformation capacity and cross-sectional strain distributing rules were compared to get the size effect law. The results show that the compressive failure mode and cross-sectional strain distributing rules of HSC column under small eccentric loading are basically the same, and the size effect isn't obvious. Ultimate strength and deformation capacity of HSC column under small eccentric loading have size effect obviously. With increase of section size, safety reservation of ultimate strength is reduced and deformation capacity also reduces. 相似文献
15.
《Netherlands Journal of Sea Research》1994,32(1):1-11
We have examined the effects of changing the flow velocity and the oxygen concentratin in the water overlying a muddy sediment on the flux of oxygen across the sediment-water interface and on the distribution of oxygen within the pore water. The experiment was carried out on an intertidal sediment from the western Wadden Sea, using a cylindrical microcosm with a calibrated flow regime. Steady-state and transient-state models were used to estimate the values of the effective diffusion coefficient for oxygen in the pore water.Increasing the flow velocity caused a significant though small increase in the oxygen concentration in the pore water, but had little effect on the concentration gradient at the sediment-water interface. The concentration gradient in the boundary layer was too small at any of the flow velocities to account for the oxygen flux into the sediment via molecular diffusion. This is ascribed to a pressure gradient which exists in rotating flows, disrupting the diffusive boundary layer and augmenting the flux via advection. Model calculations indicate that about 25% of the flux can be attributed to irrigation by burrowing organisms, but in contrast to previous results with sandy sediments, irrigation of the pore water caused by the radial pressure gradient can be considered to be negligible. The effective diffusion coefficient ranged from 4·10−9 m2·s−1 at a depth of 1 mm below the sediment-water interface to 1·10−9 m2·s−1 deeper in the sediment. These estimates are within a factor of 1 to 3 of the modelular diffusion coefficient for oxygen, which is suprisingly close in view of the high numerical densities of meiofauna and macrofauna in this sediment. 相似文献
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17.
Aiming at evaluating the effects of vibration history on dynamic characteristics of normally consolidated clay, a series of multi-cycled cyclic shear tests were conducted on 16 soil samples under consolidation pressure of 50 kPa, 100 kPa, 300 kPa and 500 kPa respectively. The experimental results reveal that, on the stage of drainage and consolidation, with the development of duration shear modulus curve ascends while damping curve descends; this trend became significant as consolidation pressure increased. The variation tends to be stable in 25 hours. When subjected to cyclic loading controlled by constant strain amplitude, both the modulus and damping of soil samples change significantly during the first 50 cycles, and then the differences become moderate afterwards, in which the damping curve acts in hyperbolical type. It is also found that there exists a clear sign of pre-straining that affects damping more significantly than modulus. 相似文献
18.
The water retention capacities of commonly used roof greening matrices, concluding ceramsite, peat and super absorbent polymer, under fully saturated, cyclic wetting-drying and natural evaporation conditions were studied. The saturated water retention capacity of matrices were obtained by vacuum saturated test. It showed that the fully measured saturated degree of saturation of mixed matrix was greater than that calculated by the combination of all components. The reason which increases the water contents to porous skeleton was analysed. In cyclic wetting-drying tests, the water retention capacities of ceramsite and peat were almost unchanged. However, due to the main molecular chain broken under drying in relatively high temperature, the water retention capacity decreased rapidly after several wetting-drying cycles. In natural evaporation tests, the evaporation rates of ceramsite, peat, super absorbent polymer and free water were almost identical in the condition of high water content. As the water content decreasing, the evaporation rate of the matrix which had lower water retention capacities decreases faster. The matrix with a reasonable proportion of super absorbent polymer can remarkably improved its water retention capacity. 相似文献
19.
The frost resistance of steel fiber reinforced concrete (SFRC) was studied based on the fast freeze thaw tests in water and in a 3.5% sodium chloride solution, with different mass fraction of steel fiber in concrete at 0%, 0.5%, 1.0%, 1.5% and 2.0%, respectively. The effects of the number of freeze thaw cycles and the volume fraction of steel fiber on the mass lose rate, the splitting strength loss rate and the dynamic modulus of elasticity of SFRC were analyzed. The reinforcement mechanism of the steel fiber under the action of freeze and thaw was also discussed. Moreover, mercury intrusion method and SEM analysis were carried out to study the pore size distribution features and the performance of microstructure on the impact of frost resistance of SFRC. The results show that adding an appropriate amount of steel fiber into concrete can reduce the pore porosity and improve the compactness of concrete. Furthermore, the presence of steel fiber proves to shrink the porosity and improve evidently the frost resistance of concrete. It is also shown that the steel fiber content has a great influence on the frost resisting property of SFRC. The best performance of SFRC can be achieved when the volume fraction of steel fiber is 1.5%. 相似文献
20.
水分胁迫及复水条件下外源Ca2+对玉米幼苗根系水力导度及生长的影响 总被引：1，自引：0，他引：1
利用10%PEG-6000模拟–0.2 MPa的水分胁迫,研究了外源Ca2+(在1/2 Hoagland营养液中添加10 mmol L-1 CaCl2)对水分胁迫7 d后及复水2 d,玉米幼苗整株根系水力导度(Lpr)、根系生长及叶水势(ψw)的影响。结果表明,正常水分条件下,外源Ca2+处理降低了Lpr,但对叶水势无影响;水分胁迫条件下,外源Ca2+显著提高了Lpr、叶水势,减缓了水分胁迫对植物的伤害;复水1 d,两种钙水平下Lp均无明显恢复,但Ca2+处理的Lpr显著高于对照,而叶水势无显著差异且均能恢复至正常供水时的水平;复水2 d,Ca2+处理的Lpr即能恢复至正常供水时的水平,对照仅恢复为正常供水时的59.06%。进一步用HgCl2检测表明,正常水分条件下外源Ca2+对水通道蛋白(AQP)活性没有影响;而水分胁迫下,外源Ca2+提高了AQP活性,对照AQP活性下降,说明水分胁迫时外源Ca2+促进了水分跨膜途径运输;复水2 d,外源Ca2+处理AQP活性恢复至正常供水时的水平,对照AQP活性未能恢复。另外,外源Ca2+处理减缓了水分胁迫对植物生长发育的抑制作用,促进了复水时侧根发育,增加根系吸水面积,为植株迅速恢复供水提供了形态学基础,增加了复水后的补偿效应。 相似文献