湿软土壤剪切应力—剪切速度—时间关系及其应用（第1报）：湿软土壤剪…

为了探讨湿软土壤的剪切应力－剪切位移关系，对湿软土壤的剪切变形机制进行了分析。分析结果表明，由于土壤内部颗粒排列的不规则性和缺陷的存在使得其抗剪能力大大降低。可借助位错理论的某些方法来阐述湿软土壤的剪切变形机理。     

湿软土壤的剪切应力—剪切速度—时间关系

从位错理论出发导出了湿软土壤的剪切应力－剪切应变－时间关系。理论分析和试验结果表明土壤剪切应力与剪切速度成幂函数关系；与其本身可能抵抗的最大剪应力相比的相对剪应力水只与剪切位移有关而与剪切速度无关。     

湿软土壤剪切应力—剪切速度—时间关系及其应用(第2报)——湿软土壤的剪切应力—剪切速度—时间关系

从位错理论出发导出了湿软土壤的剪切应力—剪切应变—时间关系。理论分析和试验结果表明土壤剪切应力与剪切速度成幂函数关系;与其本身可能抵抗的最大剪应力相比的相对剪应力水平只与剪切位移有关而与剪切速度无关。     

湿软土壤剪切应力—剪切速度—时间关系及其应用(第3报)——湿软土壤上履带板的推力计算

为了合理地预测湿软地上履带行走装置的推进力,对履带板的推力计算模型进行了修正。修正后的计算模型考虑了土壤受剪速度对其剪切应力的影响。实验结果表明履带板的推力介于考虑和不考虑履剌效应的两个理论值之间。     

湿软土壤上履带板的推力计算

为了合理地预测湿软地上履带行走装置的推进力，对履带板的推力计算模型行了修正。修正后的计算模型考虑了土壤受剪速度对其剪切应力的影响。实验结果表明履带板的推力介于考虑和不考虑覆刺效应的两个理论值之间。     

滑板土壤间充气层的理论计算及其试验验证

采用气幕法可以有效地减少滑板在湿软土壤上的滑行阻力,其减阻效果取决于滑板土壤间充气层的压力、厚度和宽度等状态参数。文中提出了一种数学模型,从理论上预测了充气层的诸状态参数,并对理论预测结果进行了试验验证。理论计算和试验测量结果均表明:离充气孔越远,充气层厚度越薄;而随着流量的增加,充气层厚度和压力也增加。     

草本植物根系增强土壤抗剪切强度的量化研究

通过对黄土高原丘陵沟壑区山西省河曲县砖窑沟流域内4种有代表性的草本植物进行野外剪切测试和模型预测,证实和量化了草本植物根系增强土壤抗剪切强度的作用。试验表明,在0～20cm土层4种草本植物根系均可显著增加土壤抗剪切强度,其中紫花苜蓿根系对土壤抗剪切强度的增强作用最大,其增大土壤抗剪切强度值为15．33kPa;草木樨和紫花苜蓿根系在20～40cm土层也能明显增大土壤抗剪切强度。同时,对比分析了实测结果与模型预测值间的差异,认为根系增大土壤抗剪强度的真实值应介于实测值和预测值之间。研究结果也表明这4种草本植物根系均具有较高的抗拉强度,且根系的抗拉强度与直径间存在显著幂函数负相关关系。这些研究对黄土区预测和评估草本植物根系的固土护坡作用,以及水土保持植物的选择及优化组合,更有效地发挥植物根系生物软措施的固土潜能具有重要现实指导意义。     

基于数字图像测量技术的豆粕剪切变形特性

为了研究豆粕在剪切过程中的变形特性,利用基于数字图像测量技术的三轴仪,开展了豆粕三轴剪切试验。考虑了围压(25~100 kPa)、孔隙率(44.8%~50.9%)及颗粒破碎对豆粕强度及变形的影响,分析豆粕的不同变形发展阶段,并提出对应的应力应变模型,获得相关的强度和变形参数。试验结果表明,豆粕试样的应力应变曲线为软化型,随着围压增大,其强度软化性增大,剪胀性却逐渐减小。相同围压下,随着试样孔隙率减小,豆粕的峰值强度逐渐增大,剪胀角也逐渐增大,剪胀性表现越明显。不同破碎程度的豆粕颗粒分析结果对比发现,破碎后的豆粕峰值剪切强度增大,体变呈完全剪缩,围压越大剪缩现象越明显,这表明颗粒破碎对强度和变形影响很大,且围压对颗粒破碎的影响比孔隙率对颗粒破碎的影响大。最后,基于局部变形结果分析,将豆粕的应力应变曲线划分为3个阶段,即破坏前、破坏和残余阶段,提出了不同阶段对应的应力应变模型,获得了其强度和变形参数,得到破坏比为0.701 6。通过研究豆粕的剪切变形特性试验结果,获得了豆粕的强度、变形规律及其本构模型,可为粮仓结构的安全设计、优化分析及粮仓储粮等进一步数值仿真建模提供基础参考数据。     

反复剪切作用下砒砂岩土壤力学性能试验

为分析砒砂岩土壤的力学性能,该文根据砒砂岩土壤的粒径分布特点,对比分析3种不同粒径（≥0.5～1 mm、≥0.25～0.5 mm、＜0.25 mm）,4种不同含水率（5%、8%、11%、14%）土壤试样在法向压力50~300 kPa作用下反复直剪的力学性能,得出以下结论：1）不同粒径的砒砂岩在第1次剪切中剪应力出现峰值,第2、3、4次的剪应力与剪切位移关系曲线呈微硬化型。粒径范围为≥0.25～0.5 mm的砒砂岩峰值强度和残余强度均最低;2）砒砂岩随含水率增加,峰值强度和残余强度均有所降低。粒径范围为≥0.5～1 mm的峰值强度和残余强度受含水率影响最显著;3）进一步拟合得到了砒砂岩法向位移和剪切位移的函数关系,可以较好地反应砒砂岩剪切过程的剪胀规律。该研究为砒砂岩区水土流失及边坡稳定问题的防治提供力学依据。     

石匣小流域整地措施对土壤剪切性质的影响

为了解坡面整地措施对坡体稳定性的影响和土壤物理性质对土壤抗剪强度的差异性,选取石匣小流域4个标准样地,通过测量多个土壤物理性质指标(土壤容重、土壤含水率、总孔隙度、毛管孔隙度、非毛管孔隙度、紧实度和液限),研究不同坡面整地措施的土壤临界剪切力随深度的变化,以及土壤抗剪切破坏能力的强弱关系和影响因素。结果表明:原状土的临界剪切力随深度的增加而增加;通过库伦公式得出的土壤抗剪强度与土壤临界剪切力的回归方程为σ=0.0123τf+0.6308。土壤物理性质对抗剪强度的影响不同,紧实度、容重与含水率对抗剪强度的影响相对较大。对于不同的坡面整地措施,土壤抗剪切能力强弱顺序为梯田水平条裸地,其中,在水平条上种植针叶树,土壤抗剪切能力优于种植阔叶树。在北京石匣地区,布设坡面整地措施时,需因地制宜地增加田面宽度,并种植针阔混交林以增加土壤抗剪强度。     

鄂东南崩岗区花岗岩风化岩土体抗剪强度的异向性

旨在从岩土力学性质的角度为崩岗侵蚀提供理论依据,采用直接剪切实验,对鄂东南崩岗区典型花岗岩风化岩土体剖面不同方向上原状土的抗剪强度进行测定,并分析了花岗岩风化岩土体抗剪强度在剖面尺度上的异向性及其影响因素。结果表明,饱和条件下,花岗岩风化岩土体黏聚力和内摩擦角的变化范围分别为3.19～19.26 kPa和26.50°～32.42°,其中B_2层黏聚力最大,而各层次间内摩擦角的差异并不明显(p0.05);黏聚力和内摩擦角均存在明显的异向性,其中水平方向总体大于垂直方向,且黏聚力的异向性较内摩擦角更明显。不同方向上抗剪强度的影响机理不同,其中,垂直于剖面方向上,黏聚力主要受毛管孔隙度(r=-0.97,p0.01)和粉粒含量(r=0.94,p0.05)的影响,而水平方向上仅与粉粒含量(r=0.91,p0.05)显著相关;而液限对水平方向上的内摩擦角影响显著(r=-0.99,p0.05)。对于花岗岩风化岩土体抗剪强度的异向性而言,其主要受自然含水率(r=-0.98,p0.01)、有机质(r=-0.93,p0.05)和塑限(r=-0.97,p0.05)影响。研究结果对于从力学稳定性角度揭示崩岗的发生机理具有重要意义。     

Critical state parameters from intact samples of two agricultural topsoils

The critical state parameters of intact samples of a sandy loam (Eutric Cambisol) and a clay loam (Gleysol) were estimated in a constant cell volume triaxial apparatus. Samples were taken under wet and dry conditions. The parameters describing the clay loam were the more variable. This was true of both its initial condition and its response to deformation. Under dry conditions, the sandy loam was less sensitive to increasing stress but compacted more at low stress than the clay loam. Isotropic stress compacted the wet soils until the percentage saturation reached about 85–95% and axial loading caused little further compaction. The difference in strength between soils was greater for the wet samples, whereas the corresponding compactibility differences were greater under dry conditions. The sandy loam was stiffer than the clay loam and the shear modulus decreased exponentially with increasing specific volume before deformation. The rebound slope was about one-twentieth of the compression index for the dry soils and about one-third of the compression index for the wet soils. A simple model of recompression accounted for plastic deformation below the virgin compression line, where the critical state model usually assumes elasticity. The proposed model reproduced the main observed features of repeated isotropic loading.     

Characterization of cohesion, friction and sensitivity of two hardsetting soils from Zimbabwe

Hardsetting soils are defined as those which develop very high strength with little observable structure when they dry, but lose much of their strength when wet. Sandy loam soils (haplic lixisol) which showed typical hardsetting behaviour in the field were identified in a small-scale farming are in Zimbabwe. They were too hard to cultivate when dry, and produced a cloudy structure when plowed by a tractor in a slightly moist state. Samples of two sandy loam topsoils were collected, prepared at different water contents varying from saturated to field-dry and tested for stress-deformation and shear strength behavior in a direct shear box. For both soils at water contents above 10 g 100 g⁻¹, the stress-deformation curves are of the plastic material type with continually increasing shear stress with deformation. At water contents less than 10 g 100 g⁻¹, curves associated with more brittle material behavior resulted, with a peak shear stress reached at 3–4 mm deformation followed by a considerable loss in strength. At nearly all of the water contents, the angle of friction was 34–37° for both soils, but cohesion changed from nearly zero at saturation to well over 100 kPa in the field-dry state. The contribution of matric tension alone to soil cohesion is more than enough to account for the observed increases in strength on soil drying, and the potential role of soluble silicate cementing agents does not appear to be a factor in the case of these two soils.     

不同类型土壤－柠条根系复合抗剪力学特性的比较

为揭示柠条根系固土抗蚀机理,以柠条锦鸡儿与低液限粘土、砒砂岩风化土、含细粒土砂3种土壤类型的根土复合体做为对象进行室内直剪试验,研究3种土壤类型的柠条根土复合体抗剪强度及强度指标,分析其差异性。结果表明:3种不同土壤类型下柠条根土复合体剪切规律均服从摩尔－库仑强度破坏准则。0.05显著水平下,12.5 kpa下根系提高土体抗剪强度优于25 kpa。抗剪强度、残余抗剪强度及二者的强度指标均为柠条根与3种土壤类型根土复合体优于相应素土。抗剪强度、残余抗剪强度、粘聚力及残余粘聚力大小排序为:低液限粘土根土复合体 > 砒砂岩风化土根土复合体 > 含细粒土砂根土复合体,内摩擦角和残余内摩擦角大小排序为:含细粒土砂根土复合体 > 砒砂岩风化土根土复合体 > 低液限粘土根土复合体。粘聚力、残余粘聚力的增长率区间为9.97% ~ 45.78%,内摩擦角和残余内摩擦角的增长率区间为?4.09% ~ 2.40%。根会增强土壤抗剪强度及残余抗剪强度。柠条根系对提高低液限粘土的抗剪特性作用效果最明显,提升效果最好。粘聚力在根土复合体抗剪强度、残余抗剪强度的增加中起主要作用。     

重庆缙云山典型植被原状土与重塑土抗剪强度研究

为了从土壤力学方面探索防治水土流失的途径与措施,该文采用直剪仪对重庆缙云山5种典型植被的原状土和重塑土抗剪强度进行试验测定。通过比较相同植被同干密度、同含水率的原状土与重塑土在同一垂直荷载下的剪切差异,分析了根(极细根)在土壤－根系复合体(原状土)中的作用。研究结果表明：原状土剪切位移小于重塑土;在相同垂直荷载作用下,同一植被原状土的抗剪强度大于与其同干密度、同含水率的重塑土。原状土的剪切破坏近似于塑性破坏,而重塑土则属于弹性破坏;原状土的抗剪强度与含根量呈正相关,并以此建立关于原状土的抗剪强度回归模型。     

Strength and deformation of agricultural soil: measurement and practical significance

Abstract. Soil has a finite strength to resist permanent volume change and permanent shear deformation. When the stresses imposed on the soil are of a sufficient magnitude to overcome the strength, then the deformation falls into one of two regimes. At low stress ratios (ratio of normal stress to maximum past stress) the soil expands when sheared and at high stress ratios it compresses. The maximum past stress in a field soil is the pre-consolidation stress. The pre-consolidation stress is the compressive stress greater than which compression is considerable and permanent.
These regimes of soil deformation behaviour are consistent and predictable under a wide range of conditions. They are described by the critical state concept, which can usefully be applied to soil management. Management decisions can be based on whether the stresses imposed by a particular operation result in high or low stress ratios. This governs whether the soil will deform permanently or not (for compaction damage), expand on shear (tillage) or compress on shear (preparation of rice paddy soils). The change in permeability and structure can also be predicted from the deformation regime.     

重塑黄土抗剪强度的环剪试验研究

[目的]研究大应变条件下黄土强度的影响因素及规律,为黄土地区发生滑坡等大变形破坏提供理论依据。[方法]利用环剪仪对重塑黄土进行大剪切位移下的剪切试验,探究不同正应力及剪切方式对不同含水率的重塑黄土其残余强度的影响。[结果]正应力越大,残余强度越大,达到残余强度所需的剪切位移越小;随着含水率的增大,残余黏聚力浮动值不大,残余内摩擦角逐渐减小,并据此拟合出残余内摩擦角与含水率的参考公式;从脆性指数的角度得出所研究的重塑黄土的应变软化都不明显,且脆性指数随着正应力和含水率的增加而降低。[结论]重塑黄土的峰值强度和残余强度受含水率、正应力的影响规律相似,可通过含水率对残余强度进行估算。     

盐渍土的增湿剪切变形特性

盐渍土在浸水后由于盐分的溶解,对土体的强度产生较大的影响。在以往的研究中,主要以饱和与非饱和土体的强度比较来说明水对强度的影响,没有研究在部分浸水后土体的变形和强度的变化规律。针对这一点,在参考黄土增湿剪切方法的基础上研究了盐渍土的增湿剪切变形特性,探讨了垂直压力、干密度和剪应力水平对剪切变形量的影响规律。