Comparison of liquid limit values determined using the hard and soft base Casagrande apparatus and the cone penetrometer

The liquid limit is one of the most commonly used index properties of soils. The study compares liquid limit values determined by the hard base and soft base Casagrande apparatus and the cone penetrometer, based on 42 natural soil samples with liquid limits varying between 30 and 105%. The results indicated that the liquid limits obtained by the soft base Casagrande apparatus are up to 5% higher than those from the hard base apparatus. Compared with the cone penetrometer, the hard base Casagrande apparatus generally gives a lower liquid limit for soils with a liquid limit of less than about 70% while the soft base Casagrande apparatus gives a higher liquid limit for soils with a liquid limit of more than some 40%.      

液限、塑限标准的选定

我国现行的液限标准与多数国家的液限标准相比,液限时土的强度偏高,因而需制定新的标准。本文根据对比试验成果,结合我国实际,提出将76g锥（锥角30°）5s时下沉深度17mm含水量定为液限;同时保留76g锥10mm含水量供过渡需要。当采用液塑限联合试验时,对于除低液限土及红粘土等一些特殊土外的细粒土,将76g锥5s时下沉深度2mm含水量定为塑限,可以与搓滚塑限相一致。     

The pre-consolidation pressure of a laterite soil

The pre-consolidation pressure of a soil is often determined in the oedometer using the Casagrande method. Recently, the trend has been to carry out this determination using the ‘Constrained Modulus’ method. The relationships between the constrained moduli, the normal pressures and the pre-consolidation pressures of temperate-zone soils have also been established. These relationships are investigated for an undisturbed tropical soil—an amphibolite derived laterite soil in the fixed ring oedometer. The pre-consolidation pressures as well as the over-consolidation ratios thus obtained are evaluated along with those obtained using the Casagrande method. The values of the pre-consolidation pressures obtained using the Casagrande and the ‘Constrained Modulus’ methods gave means of 3,8×10² and 3,5×10² KN/m² respectively. The respective coefficients of variation are 0.40 and 0.58. A test of the significance of the difference of the means shows no significance at the 1% level on the Student-t distribution. The constrained modulus method is however recommended for determination of pre-consolidation pressures of laterite soils in view of its advantages over the other method.     

土的液限塑限联合测定法的改进

按100g锥（锥角30°）进行土的液限塑限联合试验（或称联合测定）时,关键的问题是如何首先准确地确定塑限入土深度hp,然后才好从联合测定图（双对数座标）中的h-ω直线（锥入深度与含水量的关系）上读出相应于该土类的塑限值ωρ.鉴于hp是个变值,随土质而异,粉质土和粘土质土的hp值变化幅度很小,而亚砂土（或称砂质土）的hp值却变化很大,因而更关键的问题是如何准确地确定亚砂土的hp值。实践表明,对于亚砂土,用双曲线法求得的塑限值,与常规搓条法相比,稍感偏低,但根据一百多个亚砂土样品试验结果的验证,用正交三次多项式（简称三次多项式）曲线或组合曲线（由双曲线与三次多项式曲线配成）求得的塑限值则接近于搓条法塑限值。对于粉质土和粘土质土,以采用双曲线法比较合适。这样,针对不同土质情况,分别采用不同的曲线,将使测得的塑限值更符合实际。因此,三次多项式曲线的出现,是对联合测定法的进一步改进。     

液塑限联合测定法的应用与研究

本文对落锥法与液塑限联合测定法测定土的液塑限进行了对比试验研究。土样来自北京周边地区,共400余组。试验结果表明:对于粉土,误差范围大部分在-1～1之间;对于粉质粘土,误差范围大部分在-1～2之间;对于粘土,误差范围大部分在-1～5之间;两种方法液限的拟合曲线为y=1.0286x,相关系数为0.98,两种方法塑限的拟合曲线为y=1.0224x,相关系数为0.90。说明利用联合测定法取代搓条与落锥法在液塑限试验中是可行的。     

Spannbetontragwerke von Straßenbrücken – Bemessungsvergleich nach neuen Nationalen Normen und bisherigen Europäischen Normen

Prestressed concrete structures of road bridges – Comparison design of the new National and previous European Standards. With article takes a look at the final European Standards (EN), compares the calculation procedures of the new National Standards (DIN) with those of the European Prestandards (ENV) both in combination with the additional national rules and shows the e xisting differences. In a second step it contrasts the resulting effects for the ultimate and serviceability limit states and quantifies the differences using the example of a prestressed single‐span bridge with box section.     

电阻率静力触探测试技术与分析

 首先,简要回顾土的电阻率理论及影响因素,介绍电阻率静力触探测试技术。然后,在归纳相关文献与基于电阻率静力触探现场试验工作的基础上,对电阻率静力触探所测电阻率与土性变化、探头参数及土的其他特性指标进行对比分析。提供的资料表明,电阻率静力触探作为一种快速、经济、可靠的原位测试工具,在评价土的工程特性和预测一些岩土参数是可行的,尤其适用于软土工程的勘察。最后,讨论应用电阻率静力触探测试技术存在的问题,展望电阻率静力触探的研究与应用前景。     

用圆锥试验确定粘性土性质指标的新方法

本文用圆锥试验和常规试验对原状土和重塑土的物理力学性质进行了大量的对比试验,根据这些试验成果提出了确定粘性土性质指标的新法。这个方法十分简捷,一个试验人员在一小时内可完成一个土样的液限、塑限、天然稠度、渡性指数、灵敏度等试验,并得出原状土和重塑土的无侧限抗压强度和不排水抗剪强度。如果采用常规试验,将要许多天才能完成。此外,本文还分析了圆锥入土深度和抗剪强度之间的关系,并给出了液塑限和不同稠度的抗剪强度。     

Geotechnical characterization of geomaterial blends with zeolitic tuffs for use as landfill liners

Mixtures of volcanic and zeolitic tuffs from Jordan with other natural materials such as marl, sand, kaolinite and bentonite were prepared and tested for Proctor compaction in order to determine the best blend to achieve the highest dry density for use in a landfill liner. Compaction tests indicate that volcanic tuffs have higher dry densities than the zeolitic tuffs. The presence of zeolitic tuff in a mix decreases the dry density and increases the optimum moisture content. The study indicated that two mixtures of zeolitic tuff, marl, bentonite, kaolinite and sand gave the highest dry densities which, combined with the high cation exchange capacity of zeolitic tuff and bentonite, provide mixtures suitable for potential low cost landfill liners, if the shrinkage tests confirm that they are appropriate. The liquid limits measured using the cone penetration method of the volcanic tuffs were higher than those obtained using the Casagrande method except for the Rmah Tuff (RT) which showed the reverse. This needs further investigation.     

高液限黏土作路基填料改良方案现场试验研究

通过对掺石灰、掺水泥以及水泥和粉煤灰联合三种改良方法的现场试验研究分析,并进行CBR检测试验,结果表明采用水泥和粉煤灰联合法改良高液限黏土作为路基填筑材料是一种较为经济有效的改良方法。     

Etude des caractéristiques hydrodynamiques des sols par la méthode TDR (time domain reflectometry)

The object of this laboratory study was to determine any relationship between the soil volumetric water content θ, the dielectric constant (permissivity –ε), and the impedance of the same soil (R₁). Time domain reflectometry (TDR) allows the measurement of material dielectric constant and impedance by determining electromagnetic pulse transit time and pulse attenuation. Using the established relations of the TDR method, it is possible to trace the volumetric water content and electric conductivity (or the impedance) of the soil simultaneously in a continuous manner. It was hoped that, thereafter, it may be possible to calculate the soil suction using soil permissivity and impedance. TDR measurements were carried out for different leachates and soils. Relationships found in previous work by the authors were used to compare water contents given by the TDR method with water contents obtained by drying the soil samples. The test results showed a relationship between water content and soil type and the electrical conductivity of the liquid when the TDR parameter was soil impedance. It was concluded that permissivity could be used to characterise the soil's water content. This relationship is used to study the changes in bentonite water content during air drying. Volumetric water content and impedance vs time curves allows the determination of shrinkage limit.     

中国细颗粒土的统一分类体系初步研究

当前中国工程界对细粒类土的分类存在两种不同标准,一种是按液限w_L和塑性指数I_p构成的塑性图进行分类,一种是按单一塑性指数I_p进行分类,并且这两种分类方法的分类指数I_p的确定标准也不相同,造成了使用上的混乱。对中国细粒类土的两种分类标准的历史由来进行了探寻,并与国际上通行的细粒类土的分类标准进行了分析比较,最后对中国细颗粒土分类标准的统一途径提出了建议。     

新旧软粘土路基原位固结压缩特性数值分析

针对新旧软粘土路基固结压缩沉降变形的特点,通过对试验路段新旧路地基进行钻探取样和原位试验及室内物理力学试验,通过土体固结压缩试验求取土体的压缩系数和先期固结压力,用以判断土的压缩性和计算路基沉降。基于卡萨格兰德法,用多项式拟合e-lgp曲线,分析比较后确定曲线的拟合数学模型,然后根据先期固结压力的数值分析,应用Matlab软件实现其数值求解,反演新旧路基软粘土路基原状土固结现状。     

土石坝坡极限抗震能力的下限有限元法

基于极限分析下限定理,假设材料严格服从Mohr-Coulomb屈服准则,同时考虑了堆石料内摩擦角较大以及抗剪强度具有非线性的特性,提出了一个用于求解土石坝坝坡极限抗震能力的有限元计算方法。该方法通过静力平衡条件、应力间断面连续条件、边界条件、屈服条件以及所求极限荷载,形成标准的二次锥规划数学模型,并用内点法进行优化迭代求解,得到土石坝坡极限抗震能力的下限值。对一条形基础地基承载力进行下限极限分析,通过与已有计算结果比较表明所提方法的具有很高的计算精度。运用所提方法对一典型心墙土石坝进行抗震极限分析,其计算结果符合土石坝坡在地震作用下的一般破坏规律,证明此方法具有很高的实用价值。     

基于土极限应变的建筑物纠倾方法模拟与工程应用

水平掏土法是建筑物纠倾常用方法之一,确定临界掏土孔间距是建筑物安全平稳回倾的关键,其与土体性质、上部荷载等因素有关,目前主要依靠工程经验确定.针对建筑物掏土纠倾法,采用有限元极限分析方法,将土体极限应变作为破坏准则,并通过立方体模型数值分析得到土体极限应变值,超过极限应变定义为土体破坏.在此基础上,通过数值分析研究了工...     

南宁高液限土路基石灰改良试验研究

以南宁市友爱路高液限土为研究对象,针对我国南方多雨地区的实际情况研究了此类高液限加固土的长期水稳定性。通过改变击实含水量,分别在不浸泡、浸泡4d和浸泡45d的情况下进行CBR试验,然后与未加固土进行对比,研究分析加固土在不同浸泡时间、不同击实含水量条件下的长期水稳定性规律。研究发现:加固土的强度相对于未加固有了很大的提高;在击实含水量高于最优含水量的4%时,长期浸泡条件下强度最大,水稳定性最好。土体破坏时表现出一定的脆性,击实含水量越低土体的脆性越大,在含水量为24%时脆性最小,在选择击实含水量时应考虑土体脆性的影响。一定时间内随时间的增加CBR值会增大,石灰加固高液限土长期水稳定性是能得到保证的。这些结论对南方多雨地区高液限土路基工程建设具有一定的参考价值。     

福建沿海地区土层的静力触探参数

通过对福建沿海地区土层静力触探测试成果进行数理统计分析,得到该区软土、粘性土、砂类土静力触探参数的统计值。根据静力触探参数绘制的福建沿海地区土层分类图,可快速确定、划分土类,直接应用于工程实践,从而减少钻探工作量、加快勘察工作进度,对该地区工程建设具有重要的实际意义。     

谈谈塑性图及其在我国的应用问题

本文讨论了在塑性图问题上我国专家们的两种意见,即细粒土不用塑性图按塑性指数单一指标分类,还是用塑性图按液限和塑性指数两个指标分类。分析了塑性图及其在我国应用中存在的问题。细粒土用塑性图分类是国际主流,在国家标准《土的分类标准》修订时,对是否将其列入的问题主张采取慎重态度。《土的分类标准》是岩土工程的基础性技术标准,影响很大,宜立足国内,面向广大工程技术人员,优先考虑采用我国工程界习惯采用的分类方法。     

On the thermo-mechanical properties of unsaturated soils

The establishment of energy balance equation is necessary to study the thermo-mechanical properties of unsaturated soils.To solve this equation,the determination of two fundamental parameters as volumetric specific parameter and thermal conductivity coefficient is essential.In this paper,the effective thermal conductivity coefficient of dry soil grain is analyzed for soils with different compositions,and the thermo-mechanical properties of porous media with water and gas are studied by considering the soil water retention curve（SWRC）.Different methods,i.e.volumetric average method,self-consistent method,Hashin-Strikman method,are employed to calculate thermal conductivity coefficients,and a new method is proposed to determine the thermo-mechanical parameters.Comparison of the results obtained by different methods shows that the proposed method is in a good agreement with the experimental results and is suitable for describing the main properties of the thermo-mechanical behaviors of soils.The relationship between the SWRC and the seepage curve is further studied by the natural proportional rule.The characteristics of the SWRC,its differential coefficient and the seepage curve,are investigated by considering the physico-mechanical mechanism;the limit scopes of the indices of the SWRC and the seepage curve are also given.     

基于小波分析和神经网络的静力触探土类划分

利用小波分析和BP神经网络,建立一种用于基于静力触探数据进行土类划分的神经网络模型。该方法基于实测数据,利用小波分析获得不同土层触探参数的特征值,并用BP神经网络建立特征值与土类之间的映射关系,从而得到BP神经网络分类模型。结果表明,该方法可以有效地进行土类划分。