土壤基质吸力与土壤微生物活性关系的研究(英文)

研究了土壤微生物活性与土壤基膜吸力的关系 ,将土壤发泡点 ,即土壤导气率由 0突变为非 0时的基质吸力 ,与微生物的最高呼吸活性相联系 ,试图证明土壤微生物的最高活性发生于略高于土壤发泡点的基模吸力。对粗沙土、细沙土和砂壤土三种轻质地土壤的测定表明 ,土壤微生物的最高呼吸活性发生在略高于土壤发泡吸力的基质吸力。土壤基模吸力较小时微生物活性到达最高值的速度较慢 ,土壤基模吸力在发泡点附近时 ,微生物活性到达最高值的速度较快。

土壤进气值和发泡点测定方法的研究

应用土壤电导率与基模吸力的关系,判断和测定了土壤的进气值,采用改进后的砂型漏斗装置测定了土壤的发泡点。对脱水过程中3个不同剖面层次土壤进气值和发泡点的测定结果表明,耕作表层(A p)土壤的进气值和发泡点分别为1.343和5.880 kPa;淋溶淀积过渡层(AB)土壤的进气值和发泡点分别为2.597和4.116kPa;埋藏表层(A b)土壤的进气值和发泡点分别为0.451和6.076 kPa。由此可见,土壤的进气值与发泡点的数值明显不同,进气值与发泡点是2个不同的概念。

新型土壤负压剖面张力计测量装置的研究

本文介绍一种新型的剖面多点土壤基模吸力测定设备——土壤负压剖面张力计测量装置的结构及工作原理,详细阐述了影响张力计测量精度,如直管式水银压力表毛管影响的修正、瓷头测值的代袁性、连通导管气泡形成规律、制作高质量无气水的技术以及长期使用中的保养维修技术等问题。所介绍的方法可供室内及野外试验应用张力计进行量测时参考。

Forming condition of transient saturated zone and its distribution in residual slope under rainfall conditions

Rainfall, as one of the most significant factors triggering the residual soil slope failure, leads to not only the reduction of soil shear strength, but also the increase of soil weight and the decrease of matric suction as well. All these modifications in soil properties have important influence on the slope stability. The water infiltration and redistribution inside the slope are the preconditions of the slope stability under rainfall conditions. Based on the numerical simulation via finite element method, the water infiltration process under rainfall conditions was studied in the present work. The emphases are the formation, distribution and dissipation of transient saturated zone. As for the calculation parameters, the SWCC and the saturated permeability have been determined by pressure plate test and variable head test respectively. The entire process(formation, development, dissipation) of the transient saturated zone was studied in detail. The variations of volumetric water content, matric suction and hydraulic gradient inside the slope, and the eventually raise of groundwater table were characterized and discussed, too. The results show that the major cause of the formation of transient saturated zone is ascribed to the fact that the exudation velocity of rainwater on the wetting front is less than the infiltration velocity of rainfall; as a result, the water content of the soil increases. On the other hand, the formation and extension of transient saturated zone have a close relationship with rainfall intensity and duration. The results can help the geotechnical engineers for the deeper understanding of the failure of residual slope under rainfall condition. It is also suggested that the proper drainage system in the slope may be the cost-effective slope failure mitigation method.

Unsaturated Creep Behaviors of Weak Intercalated Soils in Soft Rock of Badong Formation

The cutting slopes in soft rock of redbed appeared in Yichang-Badong highway often suffer from the instability along weak intercalations, so the creep behaviors of weak intercalated soils are crucially important for the stability of cutting slopes. Because the deformation of weak intercalated soils is significantly affected by water content due to the strong water sensitivity, it is necessary to study the influence of matric suction on the creep behaviors of weak intercalated soils. In order to find out the unsaturated creep characters of weak intercalated soils, a GDS unsaturated triaxial apparatus was used. Then the triaxial creep experiments on weak intercalated soil samples under varying matric suction were conducted to obtain the unsaturated creep curves. The results show that the weak intercalated soils have obvious creep behaviors, and the creep strain is in nonlinear relationship with stress and time. When the matric suction is constant, a larger deviator stress will lead to a larger creep strain; When the deviator stress is constant, a smaller matric suction will lead to a larger creep strain. Based on the Mesri creep model, an improved creep model for weak intercalated soils under varying matric suction was established, in which the relationship of stress-strain was expressed with a hyperbolic function, and the relationship of strain-time was expressed with power functions in stages. Then an unsaturated creep model including stress-matric suction-strain-time for weak intercalated soils was established based on the power function relationship between matric suction and Ed(a parameter of the improved creep model). The comparison of the calculated values of creep model and the experimental values shows that the creep behaviors of weak intercalated soils can be predicted by the unsaturated creep model by and large.

Adsorption Behavior of Methyl Orange onto Modified Ultrafine Coal Powder

The adsorption of methyl orange onto ultrafine coal powder （UCP） and modified ultrafine coal powder （MUCP） from aqueous solutions were studied, in which the influence of contact time, dosage, temperature, pH, and methyl orange concentration in the solution were investigated. The adsorption kinetics of methyl orange by UCP and MUCP can be described by the Lagergren first-order and pseudo second-order kinetic models, respectively. The adsorption isotherms of methyl orange onto MUCP at 303, 313 and 323 K follow the Freundlich and Langmuir isotherm equation. Values of △G^0 for methyl orange adsorption onto MUCP are -22.55, -23.10 and -23.79 kJ·mol^-1 at 303, 313, and 323 K, respectively. The values of △H^0 and △S^0 are -3.74 kJ· mol^-1 and 61.99 J·mol^-1, respectively. The adsorption process is spontaneous and exothermic.

Estimation of spatiotemporal response of rooted soil using a machine learning approach

In this study,a machine learning method,i.e.genetic programming(GP),is employed to obtain a simplified statistical model to describe the variation of soil suction in drying cycles using five selected influential parameters.The data used for model development was recorded by an in-situ experiment.The image processing technology is used to quantify several tree canopy parameters.Based on four accuracy metrics,i.e.root mean square error(RMSE),mean absolute percentage error(MAPE),coefficient of determination(R2),and relative error,the performance of the proposed GP model was evaluated.The results indicate that the model can give a reasonable estimation for the spatiotemporal variations of soil suction around a tree with acceptable errors.Global sensitivity analysis for the statistical model obtained using limited data of a specific region demonstrates the drying time as the most influential variable and the initial soil suction as the second most influential variable for the soil suction variations.A case study was conducted using a set of assumed input variable values and validated that the simplified GP model can be used to estimate and predict the spatiotemporal variations of soil suction in rooted soil at a certain range.