微型土压力传感器标定方法研究   总被引：2，自引：0，他引：2       下载免费PDF全文

李连祥  符庆宏  张海平 《地震工程学报》2017,39(4):731-737

离心模型试验常用微型土压力传感器测量地基或土与结构接触边界上的土压力。传感器使用之前应进行标定。传统的液标或气标方法不能准确反映传感器埋置过程对土体的扰动或传感器周围人为土拱边界条件形成,导致测试结果不甚理想。故针对试验条件,设计制作一套标定微型土压力传感器的方法和装置,以水、粉质黏土和福建标准砂为标定介质,考虑有无刚性靠背两种工作状态对多个传感器进行室内标定,得到标定系数。结果表明:水标未出现卸载滞后,砂标和土标均出现卸载滞后,且表现为非线性;引入滞后比R评价微型土压力传感器的滞后性,认为标定介质和传感器类型是影响滞后比的两个主要因素;传感器自身材料特性和几何特性、地基土的制备和传感器放置、加载预压和加卸载循环等对土体密实度、土体强度等的改变、工作介质和状态等对标定结果有影响。建议尽量模拟试验工作介质和工作状态,逐个标定传感器,以得到更准确的土压力测量值。  相似文献   

Field‐scale phosphorus losses from a drained clay soil in Sweden     

Barbro Uln  Kristian Persson 《水文研究》1999,13(17):2801-2812

The objective of this study was to determine and discuss field‐scale phosphorus losses via subsurface tile drains. A total phosphorous (Tot‐P) export, which averaged 0·29 kg ha⁻¹ year⁻¹, was measured over a six‐year period from the 4·43 ha drainage system of a Eutric Cambisol in Central Sweden. The main part (63%) was in particulate form (PP) while the remainder was either in phosphate form (PO₄‐P) or in other dissolved or colloidal forms. A very small area, less than 1% of the soil surface, was demonstrated to be hydraulically active by using a staining technique in soil monoliths taken from the field. The stained macropores were few, but were continuous downward, and were relatively evenly distributed among the eight 7 dm² areas that were investigated. The transport from the field mainly occurred in episodes during which the relationship between phosphorus concentration and discharge was characterized by hysteresis loops. On average, half of the yearly P transport occurred in 140 hours. Compared with flow‐proportional and frequent sampling, manual and fortnightly sampling underestimated the transport of Tot‐P and suspended solids (SS) by 59 and 42%, respectively, during the six years studied. Amounts of different phosphorus forms exported through the tile drains were very similar to those reported from other clay soils in Northern Europe and North America. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Obstacles to long‐term soil moisture monitoring with heated distributed temperature sensing          下载免费PDF全文

John J. Sourbeer  Steven P. Loheide II 《水文研究》2016,30(7):1017-1035

The field deployment of a heated distributed temperature sensor (DTS) for over three years has revealed two obstacles to estimating soil moisture (θ) that may hamper subsurface DTS applications as well as use of other subsurface thermal probes. The first observed obstacle was a hysteretic response of the DTS sensor. The relationship between θ and the temperature response (?T) within the cable was not only dependent on θ of the soil, but also on the previous wetting and drying cycles leading to that state. The second observed obstacle was soil structure healing. Soil structure healing causes the relationship between ?T and θ to evolve through time; this calibration curve becomes flatter, or less sensitive, as the surrounding soil makes better contact with the cable. Effects of the hysteretic response of the instrument and soil structure healing are largely the result of small gaps between the cable and soil. These small gaps can be approximated by a contact resistance between the cable and soil. In this article we characterize the occurrence of hysteretic and soil structure healing effects from field data and parameterize contact resistance by simulating heat transfer using a numerical modelling approach Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Nonmonotonic moisture profile as a solution of Richards' equation for soils with conductivity hysteresis     

A. R. Kacimov  N. D. Yakimov 《Advances in water resources》1998,21(8):175

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Distinct export dynamics for dissolved and particulate phosphorus reveal independent transport mechanisms in an arable headwater catchment          下载免费PDF全文

Rémi Dupas  Chantal Gascuel‐Odoux  Nicolas Gilliet  Catherine Grimaldi  Gérard Gruau 《水文研究》2015,29(14):3162-3178

This paper investigates particulate phosphorus (PP) and soluble reactive phosphorus (SRP) concentrations at the outlet of a small (5 km²) intensively farmed catchment to identify seasonal variability of sources and transport pathways for these two phosphorus forms. The shape and direction of discharge‐concentration hystereses during floods were related to the hydrological conditions in the catchment during four hydrological periods. Both during flood events and on an annual basis, contrasting export dynamics highlighted a strong decoupling between SRP and PP export. During most flood events, discharge‐concentration hystereses for PP were clockwise, indicating mobilization of a source located within or near the stream channel. Seasonal variability of PP export was linked to the availability of stream sediments and the export capacity of the stream. In contrast, hysteresis shapes for SRP were anticlockwise, which suggests that SRP was transferred to the stream via subsurface flow. Groundwater rise in wetland soils was likely the cause of this transfer, through the hydrological connectivity it created between the stream and P‐rich soil horizons. SRP concentrations were the highest when the relative contribution of deep groundwater from the upland domain was low compared with wetland groundwater. Hence, soils from non‐fertilized riparian wetlands seemed to be the main source of SRP in the catchment. This conceptual model of P transfer with distinct hydrological controls for PP and SRP was valid throughout the year, except during spring storm events, during which PP and SRP exports were synchronized as a consequence of overland flow and erosion on hillslopes. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Co-sequestration of SO2 with supercritical CO2 in carbonates: An experimental study of capillary trapping,relative permeability,and capillary pressure     

《Advances in water resources》2015

In this study we performed three categories of steady- and unsteady-state core-flooding experiments to investigate capillary trapping, relative permeability, and capillary pressure, in a scCO₂ + SO₂/brine/limestone system at elevated temperature and pressure conditions, i.e., 60 °C and 19.16 MPa. We used a Madison limestone core sample acquired from the Rock Springs Uplift in southwest Wyoming. We carried out two sets of steady-state drainage-imbibition relative permeability experiments with different initial brine saturations to study hysteresis. We found that the final scCO₂ + SO₂ drainage relative permeability was very low, i.e., 0.04. We also observed a rapid reduction in the scCO₂-rich phase imbibition relative permeability curve, which resulted in a high residual trapping. The results showed that between 62.8% and more than 76% of the initial scCO₂ + SO₂ at the end of drainage was trapped by capillary trapping mechanism (trapping efficiency). We found that at higher initial brine saturations, the trapping efficiency was higher. The maximum initial and residual scCO₂-rich phase saturations at the end of primary drainage and imbibition were 0.525 and 0.329, respectively. Each drainage-imbibition cycle was followed by a dissolution process to re-establish S_w = 1. The dissolution brine relative permeabilities for both cycles were also obtained. We characterized the scCO₂ + SO₂/brine capillary pressure hysteresis behavior through unsteady-state primary drainage, imbibition, and secondary drainage experiments. We observed negative imbibition capillary pressure curve indicative of possible wettability alteration throughout the experiments due to contact with scCO₂ + SO₂/brine fluid system. The trapping results were compared to those reported in literature for other carbonate core samples. We noticed slightly more residual trapping in our sample, which might be attributed to heterogeneity, different viscosity ratio, and pore-space topologies. The impact of dynamic effects, i.e., high brine flow rate imbibition tests, on trapping of the scCO₂-rich phase was also explored. We performed two imbibition experiments with relatively high brine flow rates. The residual scCO₂ saturation dropped to 0.291 and 0.262 at the end of the first and second imbibition tests, i.e., 11.5% and 20.4%, respectively, compared to 0.329 under capillary-dominated regime.  相似文献   

Storm event sediment fingerprinting for temporal and spatial sediment source tracing     

Simon S. Vale  Ian C. Fuller  Jonathan N. Procter  Les R. Basher  John R. Dymond 《水文研究》2020,34(15):3370-3386

Sediment fingerprinting has been widely used to distinguish discrete sediment sources; however, application to intra-storm sediment source variability has received relatively little focus despite the benefit being long recognized. In this investigation, sediment fingerprinting was applied to a 53-hr storm event sampled hourly to determine sediment source dynamics throughout the event. Sediment sources were differentiated using 16 variables, and source contribution determined using Bayesian and Frequentist mixing models for comparison. Both models provided comparable source predictions for the dominant source estimates and the general temporal pattern. The Frequentist model appeared to exhibit some unreliable values coinciding with low GOF and attributed to inherent model structure. The Bayesian model showed higher uncertainty, likely due to the “process error” utilized associated with single sample mixtures. High variability in sediment source contribution was observed between hourly time steps; however, local smoothing reveals temporal trends during the event. A higher average proportion of mudstone is found in the falling limb (0.544) compared with the rising limb (0.464), and the reverse is observed for mountain range (0.218 vs. 0.283) and unconsolidated (0.073 vs. 0.055). In the initial hours of the storm, mudstone source contribution significantly drops, whereas mountain range and unconsolidated contributions peak. The SSC-Q clockwise hysteresis indicates proximal sediment sources, suggesting the mudstone sediment is stored channel sediment and easily entrained. This sediment flushes through, coinciding with a drop as the distal mountain range and unconsolidated sources arrive to peak contribution. The wider Manawatū discharge and sediment load then arrive, delivering increasing levels of mudstone throughout the remainder of the event while mountain range sediment diminishes. Spatial representation of the sediment source contribution was derived from distributing sediment source loads to the spatial extent of the source material according to sub-catchment sediment loads and was weighted according to slope. This provided an effective means to visualize the origin of the sediment and a better spatial interpretation of sediment fingerprinting results, which is typically limited by poor spatial resolution.  相似文献