临界状态滑坡土层参数反演在工程中的应用

针对芜湖至铜陵高速K51+354～K51+500段出现的裂缝及下挫现象,分析了其产生变形的原因,通过不平衡推力法算出滑坡剩余下滑力,提出了采用抗滑桩结合挡土墙支护边坡的方案,并在工程运用中得到了很好的效果。     

土力学在工程项目中的应用分析

对土力学作了简要的论述,介绍了土力学理论在土的变形及地基沉降计算、天然地基承载力计算、挡土墙等工程项目中的应用情况,并对土力学的工程应用前景进行了分析,以不断地补充和完善土力学的理论知识。     

A unified critical state model for geomaterials with an application to tunnelling

This paper is prepared in honour of Professor E.T. Brown for his outstanding contributions to rock mechanics and geotechnical engineering and also for his personal influence on the first author's research career in geomechanics and geotechnical engineering. As a result, we have picked a topic that reflects two key research areas in which Professor E.T. Brown has made seminal contributions over a long and distinguished career. These two areas are concerned with the application of the critical state concept to modelling geomaterials and the analysis of underground excavation or tunnelling in geomaterials.Partially due to Professor Brown's influence, the first author has also been conducting research in these two areas over many years. In particular, this paper aims to describe briefly the development of a unified critical state model for geomaterials together with an application to cavity contraction problems and tunnelling in soils.     

Application of fractal theory to unsaturated soil mechanics

The mechanical properties of unsaturated soils are a function of the saturation degree or matric suction, and can be obtained based on currently available procedures. However, each procedure has its limitations and consequently, care should be taken in the selection of a proper procedure. The fractal approach seems to be a potentially useful tool to describe hierarchical systems and is suitable to model the structure and hydraulic properties of unsaturated soils. In this paper, the soil-water characteristics, unsaturated hydraulic conductivity function, unsaturated shear strength, swelling deformation and compression were derived from the fractal model for the pore-size distribution, and were expressed by only two independent physical parameters, the fractal dimension and the air entry value. The predictions of the proposed soil-water characteristics, unsaturated hydraulic conductivity, unsaturated shear strength, swelling deformation and compression were in good agreement with published experimental data. Comparisons between the experimental results of unsaturated hydraulic conductivity and the predictions of the both fractal model and the van Genuchten-Mualem model were also performed, and it was found that the predictions of the fractal model were better than that of the van Genuchten-Mualem model. __________ Translated from Chinese Journal of Geotechnical Engineering, 2006, 28(5): 635–638 [译自: 岩土工程学报]     

A pore crack model for the mechanical behaviour of porous granular rocks in the brittle deformation regime

A model is developed for predicting and simulating the mechanical behaviour and failure mode of brittle porous granular rocks loaded in compression. It is based on a fracture mechanics analysis applied to cracks emanating from the surface of cylindrical pores in two-dimensional, which is well suited to the microstructure of such rocks. It is also consistent with the usual experimental procedure used for biaxial compression tests since the numerical scheme is implemented under the assumption of imposed axial strain. The model takes into account interactions between neighbouring cracks, which grow when their stress intensity factor reaches the fracture toughness of the rock. The simulation of crack growth from cylindrical holes, associated with a failure criterion based on the coalescence of interacting cracks, allows one to calculate the critical stress at rupture and to derive theoretical stress–strain curves.The present model is then used to compare theoretical results with laboratory data obtained on four sandstones with porosity ranging between 13% and 25.5% which were deformed under conventional triaxial compression conditions at confining pressures between 0 and 35 MPa. The comparison shows that by using a small number of parameters (pore size, pore density, fracture toughness, and elastic moduli), the model is able to predict the rock behaviour during the compression tests and the stress level at rupture in a quite accurate way, when the microstructural parameters introduced are consistent with the observations.     

Poroelastic behaviour of physical properties in Rotliegend sandstones under uniaxial strain

Laboratory experiments simulating reservoir depletion and reinjection of fluids have been conducted on Rotliegend reservoir sandstones. Pore pressure dependence of petrophysical properties have been measured under uniaxial strain boundary conditions, i.e., zero lateral strain at constant overburden pressure. Permeability, formation resistivity factor, and compressional as well as shear wave velocities were recorded simultaneously and continuously during deformation in direction of maximum principal stress. The results show that the stress development is specific for different sandstones depending on the efficiency of pore pressure. The stress anisotropy increases with decreasing pore pressure, leading to stress-induced anisotropy of pore structure with preferred closure of horizontally oriented pore space. Permeability decline of initially lower permeability sandstones indicate the opening of axially oriented pores at lower pore pressure.     

活性粉末混凝土的纤维力学机理分析

从钢纤维的增强机理、活性粉末混凝土的增韧机理、活性粉末混凝土的力学性能等方面阐述了钢纤维对活性粉末混凝土的增强机理,以达到提高RPC的高力学性能和耐久性的目的。     

断裂力学和损伤力学在混凝土中的应用

叙述了断裂力学和损伤力学的形成、应用及发展过程，并将断裂力学和损伤力学引入到混凝土的研究中，探讨了断裂力学和损伤力学在混凝土中的应用。     

土力学教学方法的思考

土力学是土木工程、岩土工程以及地质工程等专业很重要的一门专业基础课,为这些领域其他后续专业基础课的学习提供了必要的理论知识。土力学教学不仅要侧重于基本概念及基本理论,同时更应注重与实际工程问题相结合。结合多年的教学经验,以及工程建设的不断发展带来的新问题、新技术对土力学教学方法进行了一些探索和思考。     

冻土断裂力学破坏准则及其在工程中的应用

考虑冻土自身存在的各种缺陷及冻胀力的作用和影响,应用断裂力学理论与方法,研究冻土破坏的机理,建立了冻土断裂力学破坏准则。该准则适用于脆性破坏并在小范围屈服条件下的冻土。对于冻土地基临塑荷载的确定以及在较低负温下的地基基础的破坏问题,该准则也是适用的。通过实际冻土工程问题的应用表明,冻土断裂破坏准则符合冻土的实际和特点,是有效的。     

本科土力学课程教学改革探讨

为了响应国家卓越工程师教育培养计划,对土木工程专业的土力学课程做了教学改革,在理论教学,实践教学,课程考核方式方面做了探索,收到了较好的教学效果。     

土力学试验教学改革探索

分析了土力学试验教学中存在的问题,从利用教学实验周,分层教学内容,建立多媒体教学、管理平台和合理的考核制度四方面做了教学改革探索,达到了较好的教学效果。     

夯实水泥土受力性能试验研究及工程应用

通过对水泥土试块无侧限抗压强度的试验研究,分析了含水量、水泥掺量和养护龄期对黄土状粉质黏土水泥土桩无侧限抗压强度的影响,建立了水泥土试块无侧限抗压强度与养护龄期和水泥掺量的关系式,为寻求更加经济、合理的施工配合比和参数提供了理论依据。用试验成果指导某工程实践,取得了较好的经济效益。     

Experimental observations of the mechanics of borehole failure in porous sandstone

To investigate borehole failure under hydrostatic stress in sandstone of varying porosity, experiments were conducted on three sandstone varieties with 2–5 mm bores. Tennessee, Darley Dale, and Penrith sandstone-types were selected to represent most of the spectrum of sandstone porosity variations (respectively, 0.07, 0.12 and 0.28). Confining pressures ranged up to 500 MPa, and pore fluid volumometry was used to detect bore failure. Failed samples were studied microstructurally using optical and scanning electron microscopy.Each rock type failed with the development of oriented breakout features normally seen to develop around boreholes loaded under non-hydrostatic stress, and in Tennessee sandstone at least, these developed in a consistent orientation with respect to an external reference frame (dip-direction of foreset beds). All of the rock types showed strength and/or elastic anisotropy, thus the formation of oriented breakouts under hydrostatic loading is attributed to the effects of anisotropy.Two modes of breakout development were observed. In Darley Dale and Penrith sandstones, a combination of intergranular shear and extensional fracture produced broad and shallow features with breakout width unaltered during growth. In Tennessee sandstone a purely extensional mode of intragranular fracture was observed, leading to deeper breakout features.The samples tested showed higher failure pressures for smaller bore sizes. When failure pressure is normalized with respect to grain crushing pressure P^*_i, and bore diameter with the product of porosity with grain size, all data lie on a single master curve, with bore failure pressure approximately 0.15 P^*_i in the regime of bore size-independent behaviour.     

土力学实验教学改革初探

针对土力学实验教学中存在的各种问题,在明确土力学实验教学改革目标的基础上,结合工作实践,提出了土力学实验教学改革的具体方法和措施,对于提高教学质量有着重要意义。     

Model for the mechanical stress due to the salt crystallization in porous materials

This paper deals with the experimental investigation and the mathematical modelling of crystal growth in porous materials and resulting mechanical stress due to the crystallization pressure.

Crystallization of potassium nitrate and of sodium sulphate was induced in two bricks by cooling down at constant rate. The measured temperatures describe indirectly the crystallization and the dissolution rates. Thus, the time-dependent amount of crystallized salt can be estimated by means of an energy balance in the reaction sample (impregnated with salt solution) and in the reference sample (impregnated with water). Therefore, the supersaturation ratio of the solution is also obtained at each point of time.

The sample strain is measured continuously during crystallization. The results show that the mechanical stress due to the salt crystallization depends on both salt and pore structure.

A mathematical model for the mechanical stress due to crystallization pressure was developed based on crystal growth kinetics considering the influence of pores with different size (called pore classes). The model considers that nucleation and crystal growth take place in large and small pores simultaneously and calculates the distribution of salt crystals in pores of different size and the resulting load surface of the crystals under stress. The estimation of two model parameters is necessary for the proposed computation model.

It is assumed that the mechanical stress is caused by the crystallization pressure that crystals exert on the pore wall when growing in a supersaturated solution. Thus, the crystallization pressure is calculated as a function of the solution supersaturation. Finally, the average mechanical stress is obtained by means of a uniform section force in a defined volume.

The results show that the material strain owing to the crystallization of KNO₃ and Na₂SO₄ can be approximately estimated in the selected bricks by means of this new model.

An improvement of the model is necessary for a better prediction of the mechanical stress, e.g., at drying conditions or for the simulation of the re-allocation of salt crystals from pores under stress into stress-free pores.

In this work, the required properties of the salt solution are calculated using a thermodynamic model according to Steiger [Steiger M, Kiekbusch J, Nicolai A. An improved model incorporating Pitzer’s equations for calculation of thermodynamic properties of pore solutions implemented into an efficient program code. Constr Build Mater 2007, accepted for publication], which is based on the Pitzer model [Pitzer KS. Ion interaction approach: theory and data correlation. In: Pitzer KS, editor, Activity coefficients in electrolyte solutions. Boca Raton: CRC Press; 1991. p. 75 [chapter 3]].