The wind-water two-phase erosion and sediment-producing processes in the middle Yellow River basin, China

Based on data from the middle Yellow River basin, a wind-water two-phase mechanism for erosion and sediment-producing processes has been found. By using this mechanism, the extremely strong erosion and sediment yield in the study area can be better explained. The operation of wind and water forces is different in different seasons within a year. During winter and spring, strong wind blows large quantities of eolian sand to gullies and river channels, which are temporally stored there. During the next summer, rainstorms cause runoff that contains much fine loessic material and acts as a powerful force to carry the previously prepared coarse material. As a result, hyperconcentrated flows occur, resulting in high-intensity erosion and sediment yield.     

广义塑性力学的加卸载准则与土的本构模型——广义塑性力学讲座(3)

首先介绍了广义塑性力学的加卸载准则,该准则能准确判断各应变分量的加卸载状态,可以方便地应用于数值分析。然后提出了基于广义塑性力学的土本构模型。通过试验,给出了硬化压缩土和硬化剪胀土的屈服条件与计算参数,并由算例说明了其合理性。     

干旱胁迫下秸秆覆盖增强玉米耐旱性的研究

田间试验于1994- 2000年在吉林省西部半干旱地区洮南市幸福乡实施,试验田包括露地栽培和秸秆覆盖栽培两个处理,覆盖区于玉米植株5叶期用粉碎的长度为2~3的玉米和小麦秸秆全面覆盖,随机区阻设计,重复4次,试验区每年重新安排,以免上一年的覆盖物对试验结果产生影响。于5叶期在每个小区的中部连续标记10株,以后跟踪调查记录,子粒达生理成熟时收获。研究结果表明:秸秆覆盖前处理与对照的土壤含水量无差异,而5叶期实施秸秆覆盖处理的土壤含水量显著高于对照,这种效应一直持续到7月的第二周。6月10日、6月25日和7月15日秸秆覆盖处理的土壤含水量分别比对照高12.86%、7.17%和2.86%,这就保证了玉米植株的根系和地上部生长发育对水分的需求。在半干旱地区及干旱年份实施秸秆覆盖处理可提高田间土壤水分含量、促进玉米植株中后期的生长发育、提高单株叶面积和干物质重、有利于雌穗分化发育、改善穗部性状、增加单穗粒数和粒重、最终增加子粒产量。因此,可把秸秆覆盖作为玉米综合抗旱栽培措施中的一项措施加以实施。     

应变软化Tresca材料中扩孔问题解答及其应用

依据常规试验成果,对岩土材料的剪胀、剪缩和应变软化特性进行简化后,利用弹塑性理论和体积平衡原理,推导出应变软化Tresca材料中扩孔问题的一般解答,并分析了不排水饱和土扩孔问题的规律性,对解决诸如沉桩挤土效应等工程问题具有一定的应用价值。     

偏最小二乘回归神经网络的矿坑涌水量预测

影响矿坑充水的因素多且复杂,矿坑涌水量预测模型主要考虑降水、地表水、引水灌溉等影响因素,因变量和自变量的关系比较复杂。将偏最小二乘回归与神经网络耦合,建立了矿坑涌水预报模型。模型将自变量利用偏最小二乘回归处理,提取对因变量影响强的成分,既可以克服变量之间的相关性问题,又可以降低神经网络的输入维数,并能较好地解决非线性问题,提高了模型的学习能力和表达能力。以河南鹤壁八矿涌水量为例,建立了基于偏最小二乘回归和神经网络耦合的矿坑涌水量预测模型。计算验证表明,该类模型具有较高的预报精度和推广应用价值。     

Integration of remotely sensed C factor into SWAT for modelling sediment yield

The C factor, representing the impact of plant and ground cover on soil loss, is one of the important factors of the Modified Universal Soil Loss Equation (MUSLE) in the Soil and Water Assessment Tool (SWAT) to model sediment yield. The daily update of C factors in SWAT was originally determined by land use types and plant growth cycles. This does not reflect the spatial variation of C values that exists within a large land use area. We present a new approach to integrate remotely sensed C factors into SWAT for highlighting the effect of detailed vegetative cover data on soil erosion and sediment yield. First, the C factor was estimated using the abundance of ground components extracted from remote sensing images. Then, the gridding data of the C factor were aggregated to hydrological response units (HRUs), instead of to land use units of SWAT. In the end, the C factor values in HRUs were integrated into SWAT to predict sediment yield by modifying the ysed subroutine. This substitution work not only increases the spatial variation of the C factor in SWAT, but also makes it possible to utilize other sources of C databases rather than those from the United States. The demonstration in the Dage basin shows that the modified SWAT produces reasonable results in water flow simulation and sediment yield prediction using remotely sensed C values. The Nash–Sutcliffe efficiency coefficient (E_NS) and R² for surface runoff range from 0·69 to 0·77 and 0·73 to 0·87, respectively. The coefficients E_NS and R² for sediment yield were generally above 0·70 and 0·60, respectively. The soil erosion risk map based on sediment yield prediction at the HRU level illustrates instructive details on spatial distribution of soil loss. Copyright © 2011 John Wiley & Sons, Ltd.     

Quantification of peatland water storage capacity using the water table fluctuation method

Peat specific yield (S_Y) is an important parameter involved in many peatland hydrological functions such as flood attenuation, baseflow contribution to rivers, and maintaining groundwater levels in surficial aquifers. However, general knowledge on peatland water storage capacity is still very limited, due in part to the technical difficulties related to in situ measurements. The objectives of this study were to quantify vertical S_Y variations of water tables in peatlands using the water table fluctuation (WTF) method and to better understand the factors controlling peatland water storage capacity. The method was tested in five ombrotrophic peatlands located in the St. Lawrence Lowlands (southern Québec, Canada). In each peatland, water table wells were installed at three locations (up‐gradient, mid‐gradient, and down‐gradient). Near each well, a 1‐m long peat core (8 cm × 8 cm) was sampled, and subsamples were used to determine S_Y with standard gravitational drainage method. A larger peat sample (25 cm × 60 cm × 40 cm) was also collected in one peatland to estimate S_Y using a laboratory drainage method. In all sites, the mean water table depth ranged from 9 to 49 cm below the peat surface, with annual fluctuations varying between 15 and 29 cm for all locations. The WTF method produced similar results to the gravitational drainage experiments, with values ranging between 0.13 and 0.99 for the WTF method and between 0.01 and 0.95 for the gravitational drainage experiments. S_Y was found to rapidly decrease with depth within 20 cm, independently of the within‐site location and the mean annual water table depth. Dominant factors explaining S_Y variations were identified using analysis of variance. The most important factor was peatland site, followed by peat depth and seasonality. Variations in storage capacity considering site and seasonality followed regional effective growing degree days and evapotranspiration patterns. This work provides new data on spatial variations of peatland water storage capacity using an easily implemented method that requires only water table measurements and precipitation data.     

Did annual run‐off and low flow decrease with reduced forestry practices in Japan?

Japan developed large areas of coniferous plantations for timber production between the 1950s and 1970s; however, forestry practices such as thinning, pruning, and harvesting in most of the plantations have declined since the 1980s. Researchers speculated that reduced forestry practices could reduce run‐off and therefore available water resources. As a countermeasure to this potential risk, many local governments have introduced local taxes to stimulate forestry practices in the plantations. However, no studies have presented evidence for decreased annual run‐off and/or low flow in watersheds where forestry practices have declined. As a starting point for assessing this risk, this study examined potential changes in the annual run‐off and low flow in the Terauchi watershed. A large area of this watershed was covered with coniferous plantations. We first surveyed the annual investment in forestry operations and the number of forest owners in the city of Amagi. (Note that Amagi includes the Terauchi watershed.) Both decreased during the period 1979–2007, indicating reduced forestry practices. The frequency distribution of plantation tree ages in the watershed also suggested reduced forestry practices. After excluding the effect of precipitation, we examined potential changes in the annual run‐off and low flow during the period 1979–2007. We did not observe significant decreases in the annual run‐off and low flow during the period. Thus, the risk of decreased water resources might be less than expected, and countermeasures to the risk should be reconsidered. Copyright © 2010 John Wiley & Sons, Ltd.     

Kinematic analysis of pile behavior for improvement of slope stability in fractured and saturated Hoek–Brown rock masses

Because of a multitude of steep slopes being constructed adjacent to roadways, there is greater concern of landslide occurrence, particularly in instances where poor geomaterials are present. Installation of piles along the slope is one commonly adopted method. This paper presents the assessment of the stability of a rock slope with stabilizing piles based on kinematic analysis. The pile effect is introduced with a resultant lateral force and a moment. Upper bound solutions of the pile's lateral force are derived with a log‐spiral rotational failure mechanism. The slope performance based on the bearing capacity of surcharge loading is also discussed with consideration of pore water pressure. In order to substantiate the derived theoretical solutions, numerical analysis with optimization technique is carried out. Results demonstrate that rock materials with high quality are conducive to ensure slope stability. Reduced lateral force on the pile is produced with lower rock weight, slope height, and surcharge loading. Finally, the safety factor and stability coefficient are discussed to complete the evaluation of the slope stability. Copyright © 2016 John Wiley & Sons, Ltd.     

Analysis of piles subjected to lateral soil movements using a three‐dimensional displacement approach

An analytical approach using the three‐dimensional displacement of a soil is investigated to provide analytical solutions of the horizontal response of a circular pile subjected to lateral soil movements in nonhomogeneous soil. The lateral stiffness coefficient of the pile shaft in nonhomogeneous soil is derived from the rocking stiffness coefficient that is obtained from the analytical solution, taking into account the three‐dimensional displacement represented in terms of scalar potentials in the elastic three‐dimensional analysis. The relationship between horizontal displacement, rotation, moment, and shear force of a pile subjected to lateral soil movements in nonhomogeneous soil is obtainable in the form of the recurrence equation. For the relationship between the lateral pressure and the horizontal displacement, it is assumed that the behavior is linear elastic up to lateral soil yield, and the lateral pressure is constant under the lateral soil yield. The interaction factors between piles subjected to both lateral load and moment are calculated, taking into account the lateral soil movement. The formulation of the lateral displacement and rotation of the pile base subjected to lateral loads in nonhomogeneous soils is presented by taking into account the Mindlin equation and the equivalent thickness for soil layers in the equivalent elastic method. For lateral movement, lateral pressure, bending moment, and interaction factors, there are small differences between results obtained from the 1‐D and the 3‐D displacement methods except a very flexible pile. Copyright © 2015 John Wiley & Sons, Ltd.