Distribution Characteristics and Prediction of Equilibrium Moisture of Non saturated Clay Subgrade

The space distribution characteristics of equilibrium moisture of non saturated clay subgrade were surveyed along the road cross section by the in situ and laboratory tests. Based on the basic theory of unsaturated soil mechanics, matric suctions of soil samples with different kinds of moisture condition were determined and the soil water characteristic curve model was calibrated to reflect a single valued function relationship between water content and matric suction of clay soils. Combining the above results, an estimation method of the equilibrium moisture of the unsaturated clay subgrade outside the affected zone of atmospheric precipitation/evaporation was established. The results show that the atmospheric precipitation/evaporation has significant effect on moisture condition of the subgrade soil located in the upper part of the subgrade near the central reserve and hard shoulders. However, equilibrium moisture of subgrade soil outside the affected zone of atmospheric precipitation/evaporation is mainly controlled by the impact of the groundwater table. Fredlund & Xing model can be used to characterize the relationship between the unsaturated clay soil moisture and matric suction, and the fitting results of model parameters have high reliability. A consistency between the predictive results and the experimental data shows the presented model is accurate and credible.     

Tests with Controlled Net Mean Stress Equaling Constant of an Remolded Unsaturated Loess

The disruption, yield and water content change of a remolded unsaturated loess is studied during the course of shear tests with controlled net mean stress equaling constant. Two types of density's triaxial drained shear tests with controlled net mean stress and suction equaling constants are conducted. The test results show that the disruption stress increases with suction. A new method to identify the field stress under triaxial drained shear tests with controlled net mean stress equaling constants is suggested, and the shape of loading-collapse yield curve are similar in q-s plane and in p-s plane. The soil-water characteristic curve is dependent on deviatoric stress, and the soil-water characteristic curve including water content, suction, net mean stress and deviatoric stress is proposed.     

Prediction Analysis on Equivalent Resilient Modulus of Clay Subgrade of Water Network Intensive Areas

According to unsaturated soil basic theories, equilibrium moisture of clay subgrade is predicted based on the updated studies of soil suction and soil water characteristic curve. Also, the bilinearity constitutive experience model of resilient modulus of clay soil is presented by triaxial repeated loading tests in laboratory. Using above mentioned results, a prediction method of equivalent resilient modulus of clay subgrade is established by comprehensively considering subgrade moisture and stress condition. Then, based on the concrete engineering, the prediction function of equivalent resilient modulus of the clay subgrade is provided by taking ground water table and subgrade height as centers. Compared with the results of other traditional testing methods on the same test road, the new prediction method may be used in practice. The results provide new perspectives and standpoints to determine the equivalent resilient modulus mechanics features of clay subgrade structure from two aspects of equilibrium moisture and stress condition.     

Probability Statistics and Sensitivity Analysis of Parameters of Soil-Water Characteristic Curves

To study the characteristic of soil-water characteristic curves (SWCC) of several different types of soils, a number of data sets of matric suction-volume water content were studied for UNSODA clay, UNSODA sand, Guangxi expansive soil and Hefei expansive soil. Three types of Fredlund-Xing models and three types of van Genuchten models were used to study the influence of SWCC models, and three types of functions in the scientific programming language MATLAB were applied to analyze the effect of different fitting methods. Through the data fitting and statistic analysis, the probabilistic characteristics of the fitting parameters of SWCCs for the four types of soils were obtained. For analyzing the relative sensitivity of the normalized volume water content to the three fitting parameters of SWCC, a formula which considers the correlation of parameters was proposed. Through the data fitting of many data sets, it is found that the fitting methods influence the value of parameters of SWCC, while the influence is less than that of fitting models from the statistical point of view. The SWCCs of all the models are nearly the same when the suction is low. With the increase of the suction, the SWCCs of FX2 and VG2 are very close, and the SWCCs of FX3 and VG3 are the same. The sensitivity analysis shows that the normalized volume water content is more sensitive to parameters n and m than to parameter a.     

降雨条件下坡积土边坡暂态饱和区形成机理及分布规律

降雨是引起坡积土边坡失稳的最常见外部因素之一。雨水的入渗在引起土体抗剪强度参数降低的同时，还将导致土体重度的增加、基质吸力的降低，最终造成边坡的失稳。开展雨水在边坡内部的渗流过程研究已成为分析边坡在降雨条件下稳定性的前提。基于有限元数值模拟方法，进行了雨水在土体中渗流过程的模拟，着眼于降雨条件下边坡暂态饱和区的形成、分布及消散特征，描述了该过程中边坡内部含水率、基质吸力、水力梯度的变化规律。结果表明：暂态饱和区形成的主要原因是土体中向湿润锋下方渗出的雨水量小于降雨入渗补给量，从而使得土体中的含水率累积升高；暂态饱和区的形成与降雨强度、降雨时间具有十分密切的关系，暂态饱和区形成时间、雨水入渗深度、土体表面体积含水率大小分别与降雨强度存在函数关系；清晰描述了暂态饱和区形成发展消散地下水位升高的全过程，从该过程看，边坡排水措施的设计值得思考。     

Experimental Analysis of the Water Weaken Effect on Gravel Soil Roadbed Locating in the Reservoir Region with Different Compactedness

It is vital to get the accurate data of the shear strength parameters of gravel soil with different water content and compactedness before they conduct the stability analysis for gravel soil roadbed. Under several test conditions, a series of direct shear tests were performed by using some gravel soil samples obtained from a selected roadbed which is under the influence of water level fluctuation. The corresponding results show that the gravel soil cohesion increased as the water content of fine soil increases till it meets its peak value, then it will decrease as the water content keeps increase. However, the internal friction angle will decrease slowly with the increase of water content of fine soil in the initial phase, and then it will decrease rapidly as the water content keeps increase. And on the other hand, the fitted shear strength parameters calculated from the test data has been influenced by the pre-load values that used to prepare soil samples, especially for the condition that the pre-load value less than the normal stress value applied in the direct shear test. All in all, the fitted shear parameters will be controlled by the relationship among water content, pre-load value and normal stress.     

Analysis of the Lateral Deformation of Structural Soft Dredger Fill with True Triaxial Test

In order to study the mechanical properties and structural properties of soft dredger fill under lateral deformation. Based on true triaxial and WF stress path apparatus, lateral unloading undrained tests were carried out. The results derived from true triaxial test, WF stress path test and routine triaxial shear test were analyzed. The contrastive conclusions are as follows: The stress-strain curve of true triaxial unloading test shows a softening behavior, which is different from the hardening behavior for that of conventional triaxial shear test. With the increase of initial confined pressure, the dilatancy of soil transfers from shrinkage to expansion. The structural yield stress of the unloading soil with true triaxial test method is dramatically larger than that with the latter two tests due to the effect of intermediate principal, which exhibits a nonlinear growth as the coefficient of intermediate principal bd stress jumps. The shear strength indexes of unloading soil with true triaxial test is larger than that with WF stress path test. Compared with the results of routine triaxial test, the internal friction angle of true triaxial test is bigger while the cohesion is smaller.     

不同耗水强度下节水灌溉稻田土壤含水率与非饱和土层厚度关系研究

为了探索基于土壤非饱和层厚度指导水稻节水灌溉的可能性,研究节水灌溉稻田土壤含水率与非饱和土层厚度的关系非常必要。本文通过设计盆栽试验,针对不同耗水强度开展连续观测,根据实时观测的土壤含水率与非饱和土层厚度,建立起两者之间的定量关系。结果表明：稻田日耗水强度越大,其非饱和土层厚度随时间增加的速率越大,达到最大值所需的时间越短。非饱和土层随时间增加时对应的土壤含水率则随时间下降,两者之间成负相关关系。通过建立土壤含水率与非饱和土层厚度的二次抛物线关系,结果显示将非饱和土层厚度作为水分控制指标指导灌溉精度高、切实可行。最后,将土壤含水率与非饱和土层厚度关系曲线运用到水稻控制灌溉的实践中,推算出土壤含水量下限对应的非饱和土层厚度值,确定以非饱和土层厚度为指标的控制灌溉方法,为黑龙江地区水稻节水灌溉管理技术提供参考,为下一步的水分运动模型率定及模拟更多土质和更多耗水情形下的土壤水分提供依据。     

Soil‐Based Vegetation Technique to Quantify Effects of Rhizospheric Soil Osmotic and Matric Water Potentials on Crop Salt Tolerance

In saline soils, plant water supply is the most critical growth factor. To better understand water supply and growth of soil‐grown crops, research should focus on root water uptake in saline soils. Plant water supply and growth is complex. One has to consider, simultaneously, soil and plant parameters: (i) the soil physical parameters texture; pF curve; osmotic, matric and total water potential; salinity at the soil/root interface; and bulk soil salinity; and (ii) the plant parameters root mass and rooting density; root morphology; transpiration; and shoot growth. Technical devices for direct and simultaneous measurement of all parameters are not yet available. This study presents a vegetation technique (VeTe) that permits to determinate required data from continuous measurement of pot water losses and by indirect calculation. The VeTe was tested using young rape (Brassica napus, cv. Lingot) as the model plant, growing in a silty soil. Rape was selected for its efficient root system to explore soil determined growth factors. Basically, the VeTe requires two vegetation phases: a pre‐cultivation phase, and an experimental phase. The objective of the first phase is to grow young plants that are homogenous in their shoot and root development through well‐controlled water management. Varying rooting densities of soils are performed when plants are pre‐cultivated in different soil volumes. The experimental phase starts when plants are irrigated with water of different salt concentrations up to soil water contents of 30 vol.%. During the experiment, plants were grown under well‐controlled, climatic conditions, and pot water losses were measured bi‐hourly. Measurement of continuous water losses serves to calculate soil moisture contents, derive osmotic and matric heads and their impact on plant transpiration. The proposed technique provides a means for quantitatively studying the combined impacts of soil osmotic and matric stresses on water uptake by crops differing in their root morphologic traits at different rooting densities.     

原状黄土冻融过程抗剪强度劣化机理试验分析

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。     

非饱和土本构模型中考虑含水率的应力-应变曲线的构建方法

非饱和土的变形除受应力影响外,还与土中含水率及其变化有关。在非饱和土计算模型中引入含水率,虽然建立的是经验公式,但非常直观,作为一种近似而实用的处理方法值得深入研究和进一步发展。分别从加工硬化曲线的试验参数与含水率的关系和加工硬化曲线的割线模量与含水率的关系两个不同的角度出发,提出了考虑含水率的应力-应变关系曲线的构建方法。结合具体试验展示了2种方法的实现过程,并对模型的合理性进行检验。检验的结果表明2种方法的计算值均能于试验值较好吻合。依据试验结果对2种模型进行了比较。结果表明方法1的计算值要比方法2的计算值稍小。     

花期干湿交替对玉米干物质积累与再分配的影响

通过干湿交替处理模拟花期季节性干旱,研究了不同的土层厚度、干旱强度对不同基因型玉米干物质积累与再分配的影响。结果表明,花期严重干旱促使叶片急剧衰老,但根系发育相对稳定,以尽可能地维持茎秆正常生长,从而导致叶片（根）所贮藏干物质转移至果穗的百分率比轻度干旱增加8.48个百分点,茎秆原贮藏干物质转移至果穗的     

Die kohäsion ungesättigter sandböden und deren beeinglussung durch organische substanz

It is well known in soil science, that organic matter contributes considerably to the stability of soil structure. There are also many methods to determine this stabilizing effect of soil organic matter. But as a matter of fact those methods are mostly developed under chemical or colloido-chemical aspects and do only satisfy the demands of special purposes. The physical and mechanical aspects are often neglected. In this work, however, the mechanical parameter “cohesion of soils” c is selected to describe the stabilizing effect of organic matter on soil structure of sandy soils.Organic matter (black peat) was mixed with a fine sand in gravimetric proportions of 0:100, 1:100, 3:100, 5:100, 8:100. The mixtures were then wetted with distilled water and left undisturbed for a few weeks. A natural sandy soil (Haplo-humod) was also taken, part of the sample was treated with H₂O₂ to destroy the organic matter, so the stabilizing effect of organic matter could be evaluated. The cohesion of all the samples was determined with an annular shearing apparatus under a constant soil water suction between 0 and 300 cm H₂O. Results were calculated using the Coulomb equation τ = c + σ_n tan ϕ⁰, where τ shear strength, c cohesion, σ_n normal stress, and ϕ⁰ friction angle respectively. The results show,

1. 1.1. all samples have no cohesion under saturated conditions (water suction = 0 cm H₂O);
2. 2.2. with all samples the cohesion at first increases with increasing soil water suction, reaches a maximum under a soil water suction of about 40 to 70 cm H₂O, and then decreases with further increasing soil water suction;
3. 3.3. organic matter enhances the cohesion of both the artificial mixtures of sand and organic matter as well as the natural sandy soil, the increase being the higher, the higher the content of organic matter.
4. 4.4. no difference between the artificial mixtures of sand and organic matter and the natural sandy soil was found.

     

Influence of Ca(OH)2 on Strength of Low Proportional Cemented Soil

Laboratory experimental research is performed by strengthing three different types of soil with low proportional cement to test the unconfined compressive strength of such cemented soil under different dosages of Ca(OH)2 and the different ages. The variation rules and causes of the unconfined compressive strength of these three types of age-different cemented soil with increasing the dosage of Ca(OH)2 are analyzed. The results shows that the intensity of red clay cement improves most obviously with Ca(OH)2 content increased, followed by silty clay, and sand is the weakest. The reason is that the fineness of the soil affect the strength of the cement greatly. The finer the soil, the more clay minerals in soil. The increase in Ca(OH)2 content promotes the ion exchange and the occurrence of volcanic ash, which improves the strength of cemented soil. Among the three types of soil in this experiment, the fineness of red clay particles is the best, so the intensity of red clay cement improves most obviously with Ca(OH)2 content increased.     

花岗岩残积土的土-水特征曲线参数概率

土-水特征曲线（SWCC）用于描述非饱和土中含水量与基质吸力的关系，在非饱和土力学中具有重要的作用。在SWCC拟合模型中有多个拟合参数，各值通过实验方法获得且具有很大的不确定性。采用贝叶斯理论对拟合参数的不确定性进行分析，将SWCC拟合参数作为随机变量，采用Van Genuchten模型拟合花岗岩残积土的土-水特征曲线试验数据。以马尔可夫链蒙特卡罗方法的延迟拒绝适应性算法获得模型参数后验分布抽样，获得了不同置信区间的SWCC及其对应参数值。     

污水环境对水泥土力学性能的影响试验研究

由于多数地下水泥土工程直接与地下腐蚀性介质环境接触,必将导致水泥土材料的逐步劣化甚至失效破坏。以某市区工地附近明渠排放的污水作为侵蚀性介质,制作了不同水泥掺量的水泥土试件,通过对比试验,研究了污水环境和清水环境下不同水泥掺量、不同龄期的水泥土抗压强度和抗剪强度。结果表明,在污水或清水环境下,相同水泥掺量水泥土30 d龄期的抗压强度几乎相等,随着龄期的增加其抗压强度均逐步增大,但污水环境下其抗压强度增长的幅度明显小于清水环境,90 d后清水环境的水泥土抗压强度不再增长,而污水环境的抗压强度开始降低;污水环境和清水环境下的水泥土内摩擦角和黏聚力随龄期、水泥掺量的增加均逐步增大,污水环境下龄期90 d后的内摩擦角和黏聚力均开始降低。     

Test on engineering properties of unsaturated undisturbed loess Q2

A series of triaxial shear tests with controlled constant confining pressure are conducted to study the failure modes, effects of deformation, strength and yield properties of unsaturated undisturbed loess Q2, with improved SJ-1A triaxial shear equipment. The test results show that the failure mode of unsaturated undisturbed loess Q2 is shear failure with the rupture angle between 55 and 61 degree; Shear dilatancy is shown under low confining pressure, and shear shrinkage is shown under high confining pressure; The stress-strain curves of undisturbed loess Q2 will change from perfectly plastic to weak strain softening as the confining pressure increases; A effective method is suggested to identify the field stress of undisturbed loess Q2 under triaxial shear condition with the curves of - q/p ; when the confining pressure increases, the deviatoric yield stress qy has a logarithmic relationship with net mean yield stress py .     

基于摩尔库仑准则的膨胀土弹塑性本构模型及其数值实现

膨胀土的应力应变关系与含水量的变化有关，通过室内试验对膨胀土的变形、强度以及膨胀参数与含水量之间的关系进行研究，以湿度应力场理论为基础，提出了一个具有工程实用价值的基于摩尔库仑准则的膨胀土弹塑性本构模型。依据FLAC3D数值模拟软件所提供的二次开发程序，给出了该膨胀土弹塑性本构模型二次开发程序过程的基本原理以及模型的程序框图。结合渗流软件计算的湿度场分布，进行膨胀土基坑边坡实例验算，验证了该本构模型的正确性。     

河道淤泥气泡混合轻质土剪切流变特性及模型

利用剪切流变试验对以水泥为固化剂的河道淤泥气泡混合轻质土的流变特性进行了试验研究。试验结果表明，经固化处理的河道淤泥气泡混合轻质土在荷载作用下具有类似于硬粘性土的流变特征。剪切流变可以分为3个阶段：在剪应力水平较低时，剪切流变曲线呈衰减稳定型；随着剪应力水平的提高，剪切流变曲线呈非稳定的等速型；当剪应力水平增大到一定程度时，剪切流变曲线呈加速型。河道淤泥气泡混合轻质土的流变性随着混合轻质土强度的提高而降低。根据试验所呈现的剪切流变规律，可以发现河道淤泥气泡混合轻质土的剪切流变符合七元件黏弹塑性剪切流变模型，模型能够比较好地描述河道淤泥混合轻质土在各种剪应力水平下的衰减、等速以及加速流变过程。     

Experiment Study on Soil Properties of Shennv Stream Landslide in Wu Gorge

Accurate obtainting soil parameters of landslide is the key links for landslide stability evaluation and project management . This article takes Shennv Stream landslide in Chongqing Wushan County as an example, implementing unconsolidated and undrained shear test and mineral composition analysis by X ray diffraction for soil in different elevations of landslide ,conducting sensitivity test for various soil parameters of reservoir landslide change with different water level.Study shows that : Mineral composition of soil mainly contains Calcite, Quartz and clay mineral. Hydrophilic minerals in clay mineral have great effect on stability of landslide. Shear strength decreases by influence of water content on cohesion. Cohesion decreases sharply in a quadratic function relation with water content increasing .When water content comes to 18.21% ,change of cohesion tends to be stable.But the internal friction angle of landslide soil decreases linearly in small amplitude with an increase of water content. Research results may provide some important references for rationally choosing strength parameters of soil in similar landslide.