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1.
A study was undertaken on a compacted silt to determine fabric modifications induced by suction and/or stress variations. The link between fabric and hydromechanical behaviour was also investigated. A suction-controlled oedometer, using air overpressure, was developed for this purpose and mercury intrusion porosimetry was employed to determine sample fabric. The initial samples fabric was made of macro and micropores. It was shown that suction increase produced a strong decrease in the macroporosity associated with an increase in microporosity. However, some macropores were not significantly affected by the suction increase; this phenomenon might be related to the initial fabric of the samples. Second, it appears that loading under saturated conditions also produces strong fabric modification: the higher the applied stress, the lower the macroporosity. Soil fabric depends on the maximum stress experienced by the soil. Finally, some tests have shown the influence of suction, as well as the role of the degree of saturation, on the deformation process and the mechanical behaviour. The test results show that in the case of unsaturated mechanical loading, all macropores are not destroyed by the mechanical loading. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
2.
The soil fabric plays an important role in complex hydromechanical behaviour of the expansive soils. This article addresses the influence of the wetting and drying paths on the soil fabric of compacted bentonite and silt mixtures at two different initial dry densities corresponding to loose and dense states. To obtain the hydric response of the soil, two suction imposition techniques were used: osmotic technique for the suction range less than 8.5 MPa and the vapour equilibrium or the salt solution technique for the suction range between 8.5 and 287.9 MPa. Additionally, the soil fabric analysis was performed using mercury intrusion porosimetry (MIP) and nitrogen gas adsorption (BET) techniques. The dense samples produced cumulative swelling strains during the suction cycles, while shrinkage was observed for the loose samples. The suction cycles induced an equilibrium state indicative of the elastic behaviour of the samples. The soil fabric analysis showed that regardless of the soil's initial state (loose or dense), the samples obtained the same soil fabric at the equilibrium state. The experimental results illustrated also the existence of an elastic void ratio (e0el) where the compacted soils at this state present an elastic hydric behaviour during the successive suction cycles. 相似文献
3.
C. M. O. Nwaiwu I. B. K. Alkali U. A. Ahmed 《Geotechnical and Geological Engineering》2006,24(2):283-298
A laboratory investigation was conducted to determine properties of five samples of ‘oolitic ironstone’ lateritic gravel aggregates
which are relevant to their use as road construction materials. Measured values of physico-chemical, physico-mechanical as
well as index properties and compaction characteristics are similar to those of other lateritic, gravels occurring in West
Africa which are used in road pavement applications. These lateritic clayey gravels have good workability as engineering construction
materials and are rated fair to good as road aggregates in terms of probable in-situ behaviour based on water absorption values. Relationships between maximum dry unit weight and optimum moisture content as
well as those between California bearing ratio and some derived soil parameters such as grading modulus, plasticity product
or plasticity modulus can be described using a third-order polynomial function. The maximum dry unit weight has a bimodal
frequency distribution and can be predicted from logarithm to base 10 of compaction energy with fairly good accuracy. 相似文献
4.
G. H. McNally 《Australian Journal of Earth Sciences》2013,60(6):535-547
The uses and shortcomings of duricrusts (ferricrete, calcrete and silcrete) in engineering construction (as used for road‐base, aggregate, foundation materials and aquifers) are reviewed. Australian production of these materials represents about one‐third of all unprocessed road‐base and they are especially important as pavement courses for lightly trafficked, low‐cost rural and outback roads. However, duricrusts are regarded as marginal materials at best because of their typically poor grading, particle unsoundness, high fines plasticity, and absorption of water and bitumen. These materials are used because they are available locally in areas that are otherwise lacking in hard rock materials, such as deeply weathered and sedimentary rock terrains. The weathering profiles of which they form part are characterized by high permeability (despite being clay‐rich), variable cementation, low compressibility and a tendency to become weaker with depth. Although the more indurated layers are unrippable, they are also difficult to blast. Pedogenic (nodular) duricrusts were formerly sought for natural road‐base, because they occur widely and require only rudimentary processing. However, well‐cemented groundwater (vadose) duricrusts are now the preferred deposits, even though they require crushing and screening. Ferricrete is the most widely exploited of the duricrusts for engineering purposes, especially in northern and southwestern Australia, although calcrete is important in South Australia and in the Murray Basin. Silcrete is only a minor source of aggregate and road‐base, mainly in western Queensland. 相似文献
5.
Active soils existing to irreplaceable extents (both laterally and vertically) within the freshwater zone of the Niger delta
are known and have been shown to be highly undesirable in their natural forms for road construction. This is because they
swell extensively in the rainy season and shrink proportionately in the dry months together with any structure including road
pavement constructed with or placed on them. In this paper, four samples of these soils collected from across the Niger delta
were subjected to chemical stabilization with slaked-lime and calcium chloride (CaCl2) to reduce swelling potential while resulting mixtures (corresponding to tolerable swelling limits) were stabilized with
Portland cement to improve strength. First, swell indicator (i.e. 24-h free swell index) was found to diminish with increasing
stabilizer content while for combined plot (independent of location/percentage fines), about 10.7% and 6% slaked-lime and
CaCl2 were found to be required to achieve the minimum (2.5% free swell) tolerable, normal or non-swell soil condition. Under this
condition and for individual soil materials, addition of cement was found to enhance continual increase in MDD, soaked-CBR
and durability index such that the soil becomes better compactible, stronger and more durable with increasing cement content.
About 2.6% and 14.6% cement contents were found needed to respectively produce sub-base and base-course materials in roadworks
with the latter much more durable than the former. The graphs so obtain could also constitute a complete graphical model for
preparing deltaic active soils for use as road pavement materials. 相似文献
6.
应用冷却路基原理建设青藏铁路 总被引：9，自引：6，他引：3
More than half of the total length of the Qinghai-Tibet Railroad (QTR) traverses warm (0 to-1℃) permafrost areas, and about 40% of its total length is in ice-rich permafrost areas. Thc construction of the QTR also must consider the impacts of climatic warming along the QTR during the next 50～100 years. The latest projection indicates a warming of 2.2 to 2.6℃ on the Qinghai-Tibet Plateau (QTP) by the year 2050. Therefore, the key to the successful construction of the QTR is to protect permafrost from being thawed. Although railroad construction in permafrost areas has had a history of more than 100 years, the troubled sections of the railroads in permafrost areas have been greater than 30% of their total length. Based on the experiences and lessons learned from the road construction in permafrost areas, both in China and abroad, the author proposes that the principle of “active cooling” of railroad roadbed by lowering permafrost temperatures should be used in designing QTR, rather than that of “passive protection” of permafrost through increasing thermal resistance of roadway, such as increasing fill thickness and/or using insulative materials. This is especially important for the road sections in warm, ice-rich permafrost. In addition, this paper proposes several methods for “cooling the roadbcd” by controlling radiation, convection and conduction through modifying roadway structure and using different fill materials. 相似文献
7.
Scaly clays are stiff and highly fissured clays often used as construction materials. This paper presents the results of triaxial compression tests carried out on saturated and unsaturated samples of a compacted scaly clay. Complementary investigation on the microstructural features and their evolution with the amount of water stored into the material are also presented in order to shed light on the evolution of the micro- and macroporosity with suction. The water retention behaviour of the compacted scaly clay is also addressed. The results from the controlled suction triaxial tests are used to discuss the applicability of a single-shear strength criterion to compacted double-structured clays when the effective stress concept for unsaturated soils is used. The choice of the degree of saturation to be included in the effective stress definition for obtaining a satisfactory representation of the shear strength is addressed. It is shown that the best results are obtained when the macropore degree of saturation is considered along with its evolution during the applied stress path. 相似文献
8.
The potential damage to man-made structures associated with earthquake-induced liquefaction has been demonstrated in catastrophic
fashion over the past 40–50 years. The phenomenon of liquefaction of relatively clean, poorly graded, sands is well understood.
However, the same cannot be said for cases when fine-grained materials are present within the sand matrix. A resolution of
what appears in some reported studies as conflicting observations related to the effect of fines on cyclic resistance is of
concern, particularly for land reclamation projects and sea fills where the material source is variable and may contain significant
levels of fines. The nature of the fines themselves may have a measurable effect on the matrix behavior. The work presented
herein explores the effect of silt and clay-size carbonaceous fines on the liquefaction susceptibility of sand. The choice
of fines was guided by the conditions associated with the Lebanon coastal reclamation projects, where limestone/marlstone
quarry source materials are dominant. The results obtained confirm the significant effect of fines on the cyclic resistance.
They also confirm the existence of a limit fines content and a plasticity index threshold and establish their effect on observed
behavior. 相似文献
9.
M.D. Gidigasu 《Engineering Geology》1983,19(3):213-240
The ideal standard grading specification for gravels was meant to ensure high density and stability, and specifications on maximum limits of content of fines, liquid limit and plasticity index were meant to control the magnitude of swell of materials in the pavement structure.Experience in Ghana and elsewhere in the tropics has shown that specifications based only on these index properties may be misleading. For example, the strength criterion based upon minimum soaked CBR of 80% for separating sub-base and base gravel materials has been found to be more critical and makes it possible to modify the allowable maximum fines content, liquid limit and plasticity index for the residual gravels studied.Material selection, field compaction (construction) control and long-term field performance studies on two trunk roads were analysed.Limiting values of index properties for separating these gravels into sub-base and base course materials for pavement construction in a moist sub-humid climatic environment was proposed. For example, the maximum fines content, liquid limit and plasticity index for accepting these gravels for base course construction were increased from 10, 25 and 6% to 12.5, 37.5 and 10%, respectively.The importance of using the products of fines content and plasticity parameters for selecting these gravels was also established. 相似文献
10.
On the capillary stress tensor in wet granular materials 总被引：3，自引：0，他引：3
This paper presents a micromechanical study of unsaturated granular media in the pendular regime, based on numerical experiments using the discrete element method, compared with a microstructural elastoplastic model. Water effects are taken into account by adding capillary menisci at contacts and their consequences in terms of force and water volume are studied. Simulations of triaxial compression tests are used to investigate both macro and micro‐effects of a partial saturation. The results provided by the two methods appear to be in good agreement, reproducing the major trends of a partially saturated granular assembly, such as the increase in the shear strength and the hardening with suction. Moreover, a capillary stress tensor is exhibited from capillary forces by using homogenization techniques. Both macroscopic and microscopic considerations emphasize an induced anisotropy of the capillary stress tensor in relation with the pore fluid distribution inside the material. Insofar as the tensorial nature of this fluid fabric implies shear effects on the solid phase associated with suction, a comparison has been made with the standard equivalent pore pressure assumption. It is shown that water effects induce microstructural phenomena that cannot be considered at the macro level, particularly when dealing with material history. Thus, the study points out that unsaturated soil stress definitions should include, besides the macroscopic stresses such as the total stress, the microscopic interparticle stresses such as the ones resulting from capillary forces, in order to interpret more precisely the implications of the pore fluid on the mechanical behaviour of granular materials. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
11.
The ability to model and predict the formation of desiccation cracks is potentially beneficial in many applications such as clay liner design, earth dam construction, and crop science, etc. However, most studies have focused on statistical analysis of crack patterns and qualitative study of contributing factors to crack development rather than prediction. Because it is exceedingly difficult to capture the nonlinear processes during desiccation in analytical modelling, most such models handle crack formation without considering variation of material properties with time, and are unattractive to use in realistic modelling. The data obtained from laboratory experiments on clay soil desiccating in moulds were used as a basis to develop a more refined model of desiccation cracking. In this study, the properties, such as matric suction, stiffness and tensile strength of soil, and base adhesion, could be expressed approximately as functions of moisture content. The initial conditions and the development of suction due to desiccation and the varying material properties were inputted to UDEC, a distinct element code, using its internal programming language FISH. The model was able to capture some essential physical aspects of crack evolution in soil contained in moulds with varying lengths, heights, and materials of construction. Extension of this methodology is potentially beneficial not only for modelling desiccation cracking in clay, but also in other systems with evolving material properties such as concrete structures and road pavements. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
12.
软土地基路堤施工控制的离心模拟试验研究 总被引：1，自引：0，他引：1
软土路基上快速填筑路堤时的稳定控制是非常重要的。为此在现行规范中,采用了一些位移或位移速率的控制标准。但实践表明,采用现行的标准仍然出现一些地基失稳的事例,说明这些标准需要进一步求证和改进。除了继续收集、分析失效事例之外,通过离心模型试验也可以进一步理解堤基失稳的机制。离心模型试验结果表明：路堤快速填筑使得地基破坏时,地基变形略呈马鞍形,坡肩处沉降比道中处沉降略大,坡脚水平位移增加较快;破坏时的位移速率与现有规范建议的控制标准基本符合,但地基内的孔隙水压力是在地基进入破坏状态并发生较大变形之后才有突然增加的趋势;此外,坡脚水平位移和道中沉降的速率比,可能是一个较好的稳定性控制的指标。 相似文献
13.
Mababa Diagne 《Geotechnical and Geological Engineering》2012,30(6):1303-1309
A large network of paving blocks has been initiated in some districts of the region of Dakar (Senegal) within the framework of the Urban Program of High Intensity Manpower (PUHIMO). The purpose of this study is to explore the process of production of paving blocks to be used for roads and sidewalks. The study also seeks to investigate the materials used for the formulation of hydraulic concrete for the manufacturing of paving blocks that are H-shaped. The blocks made are 20?×?10?×?6?cm3 of size. The originality of this paper is the complete substitution of crushed basaltic sand by the fines of alumina phosphate that are stored for a long time over large areas. These fines particles of phosphate are generated by the physical processing (crushing, transportation and screening) of the raw alumina phosphate material. This paper deals with how to make good paving blocks out of crushed basaltic sand on the one hand and on the other hand with how to substitute basaltic sand for fines of alumina phosphate as waste for their recycling. The finished products are tested, for their resistance to splitting rupture, for their abrasion and for their water content, to see their compliance with the European standard EN 1338, which defines, according to the results obtained, their use or not in road pavement and in sidewalks. The standard values must be below 23?mm for abrasion, 3.6?MPa for the tensile rupture strength and 6?% for the percentage of total water content. Average abrasion values of 20.71 and 22.67?mm, 5 and 3.46?MPa of splitting rupture strength, 5.26 and 7.73?% of average water content are obtained in paving blocks made respectively out of crushed basaltic sand and out of fines of alumina phosphate. These results obtained testify good physical and mechanical characteristics of the paving locks made out of fines of alumina phosphate compared to the standard, if tolerance values are taken into account. 相似文献
14.
M. D. Gidigasu 《Geotechnical and Geological Engineering》1991,9(3-4):219-260
Summary Road transportation is increasingly becoming one of the key factors for promoting economic growth in most developing countries. However, transport and road research in the tropics has received relatively little attention. Experiences in road construction in the tropics within the past 50 years or so have established that local materials specifications and pavement construction technologies have to be developed in relation to the climatic conditions. This would involve knowledge of the processes of formation as well as genetic characteristics of the local gravels. Genetic characteristics exert considerable influence on the geotechnical properties and engineering behaviour of local gravels under pavement. The construction technology of the road pavement should take cognizance of the compositional variabilities of the gravel deposits. Construction studies of pavement sections (as well as assessment of the performance of existing roads) built with different gravels formed over different geological formations in specific climatic, and drainage conditions would provide useful data for evolving local gravel specifications for constructing stable and durable pavements. Stage construction of pavements involving the exposure of the various layers to traffic loading and seasonal climatic influences appears to hold promise for formulating strategies for constructing stable, and long-term durable tropical roads. The problem of achieving reproducible laboratory test data under field conditions is perhaps the most challenging aspect of utilizing local gravels for pavement construction in tropical and sub-tropical conditions. It is noted that the stability of pavements in tropical environments depends not so much on the geotechnical properties of the available gravels as on the appreciation by the designers and construction engineers of the relationship between the genetic and laboratory determined characteristics of the gravels on the one hand and the pavement construction technology and local climatic and drainage conditions on the other. This paper is a contribution to development of highway geotechnics for tropical and sub-tropical conditions. 相似文献
15.
This study was prompted by the massive and unprecedented failure experienced within a very short time after construction of
“Ada-George Road” which had deltaic lateritic sub-base stabilised with undisclosed but most probably uncontrolled (scientifically) proportions
of cement and geosta (a relatively new chemical stabiliser). Samples of the deltaic laterite were taken from two of the borrow-pits
within Port Harcourt metropolis from which materials were quarried for the construction of the sub-base. The results showed
that although geosta addition to deltaic laterite mixed with cement gives considerable improvement on the strength of the
resulting mixture, this stabilisation is only effective at very low geosta content not exceeding 2% depending on the optimum geosta content (OGC) which in turn is a function of the percentage of fines of the soil. But the Ada George road project appeared to be politically
rather than scientifically motivated. Consequently, the OGC must have been grossly exceeded in the construction of this geosta
stabilised sub-base. As a result, the as-built CBR must have been much lower than expected hence the massive failure that
resulted. Even for 2% geosta content, this composite stabilisation was also found to be most effective at 4% cement content. 相似文献
16.
An experimental study on the thermo-hydro-mechanical behaviour of two heavily overconsolidated clays is presented. Laboratory tests have been conducted on a Spanish bentonite (FEBEX bentonite) and a Belgian kaolinitic/illitic clay (Boom clay), statically compacted at different initial dry densities and water contents. Volume change behaviour of the soils during suction reduction paths at different temperatures and during heating-cooling cycles at constant water content or suction have been investigated through the use of suction and temperature controlled oedometer cells. In addition, the volume change response under unconfined conditions and constant water content has been measured to determine thermal expansion coefficients. The results show similarities and differences between the observed behaviour of the two types of clays that have been interpreted on the basis of their different structures and regarding their proportion of intra-aggregate water. 相似文献
17.
Dominique Ngan-Tillard Johan Haan David Laughton Arno Mulder Art Nooy van der Kolff 《Engineering Geology》2009,108(1-2):54-64
Carbonate sands undergo degradation when transported hydraulically from a dredging vessel to the reclamation site. Risks involved in the production of fines during hydraulic transport are a deterioration of the mechanical properties of the fill in certain areas of the reclamation area where these fines concentrate. In order to assess sand degradation in the concrete and road construction industry, the Micro-Deval test for fine aggregates was developed in France and Canada. During Micro-Deval testing, aggregates degrade when tumbled in a rotating steel drum with water and steel balls. In the Canadian standard, the steel charge is lower than in the French standard and balls have the diameter of the smallest balls used in the French test. During testing, the quantity of fines produced is measured. This makes the Micro-Deval test an option for assessing the degradation of sand during hydraulic transportation of slurries in the dredging industry. Three sands are tested: two shelly carbonate sands and one quartzic river sand for comparison. The carbonate sands were sampled on reclaimed land and had been subjected to hydraulic transportation in pipeline before artificial deposition. Due to differences in particle shape, the carbonate sands and the quartz sand have a different number of contacts with the steel charge in the drum of the Micro-Deval and are not exposed to the same degradation forces during testing. It was found that the quartzic sand suffers relatively much degradation as compared to the carbonate sands, despite its greater hardness and resistance to crushability. The French test appears to create turbulence that promotes floatation of the curved shells of the carbonate sands instead of shell grinding at the bottom of the drum by contact with the steel balls. Microscopic observations of sand samples before and after testing showed that the French Micro-Deval test is too destructive. The test leads to the fragmentation by impact of the quartz sands and the destruction of certain particle types that had survived hydraulic transportation. With respect to the Canadian test, microscopic examination of sand grains before and after testing shows there is still much fragmentation of quartz grains. A lower rotational speed combined with a limited steel charge made of uniform balls of a smaller diameter, reduces turbulence, shell floatability and last but not the least, impact forces. It produces the desired result: a high Micro-Deval loss for the carbonate sands in comparison to that for the quartz sands and a very limited fragmentation of the quartz grains. Once the slurry reaches its destination, the grain size distribution of the fines fraction will influence the mechanical behaviour of mixed sands. A procedure is proposed to measure the particle size distribution of the fines fraction produced during Micro-Deval testing.Field validation is needed to validate preliminary laboratory results. 相似文献
18.
Clay-rich fault rocks have long been recognized to host distinctive fabric elements, and fault rock fabric is increasingly thought to play a fundamental role in fault mechanical behaviour in the brittle regime. Although the geometries of fabric elements in fault gouges have been described for almost a century, the genesis and evolution of these elements during shear, and their links to bulk mechanical properties, remain poorly understood. We characterize the development and evolution of fabric elements with increasing shear in a variety of clay-rich experimental gouges over shear strains of <1 to >20 and at normal stresses of 2–150 MPa in the double-direct shear configuration. In addition to SEM observations of experiment products at a variety of shear strains, we quantified clay fabric intensity and the degree of grain size reduction using X-ray Texture Goniometry (XTG) and particle size distribution (PSD) measurements. We also measured P- and S-wave velocities during shear to further probe the evolution of shear fabric and gouge properties. We find that clay fabric elements develop in a systematic manner regardless of the gouge material. Riedel shears in the R1 orientation and boundary-parallel shears are the dominant fabric elements. Riedel shears nucleate at layer margins and propagate into the layer shortly after reaching yield stress. Clay particles rotate into the P-orientation shortly after Riedels propagate through the layer. The Riedel shears are through-going, but are >10× thinner than similar zones observed in coarser granular materials. Our results suggest that the weakness of clay-rich fault gouge may be less a function of anisotropic crystal structure, as has been suggested previously, and more a consequence of very thin shear surfaces permitting deformation in clay-rich materials with minimal dilation or cataclasis. The very thin shear surfaces are a function of the fine grain size of the materials and possibly polymodal PSD's. 相似文献
19.
Transportation is vital for the economic and social development and prosperity of every country. Weather phenomena can significantly affect transportation, having huge impacts on the economy and transport user safety. Research indicates that the road transportation system is the most vulnerable system to weather effects. Results from a nine-year period in Cyprus showed that extreme weather conditions resulted in a 5.8 % increase in fatalities on the roads. On the other hand, there is pressure to develop more environmentally sustainable materials to be used in roads, considering the availability of natural aggregate resources and the amount of waste concrete material arising from construction and demolition. This paper describes the use of recycled aggregate concrete (RAC) as a paving material in roads and its properties related to weather effects. Eight different concrete mixtures containing recycled concrete aggregates (RCA) were tested for the weather-related parameters of sorptivity, porosity and permeability. Results showed that the use of RCA and eventually RAC will affect the behaviour of road pavements, due to their higher sorptivity, porosity and permeability. However, it is believed that this will not be detrimental to the quality of road surfaces. 相似文献
20.
This paper analyses the influence of grain shape and angularity on the behaviour of granular materials from a two‐dimensional analysis by means of a discrete element method (Contact Dynamics). Different shapes of grains have been studied (circular, isotropic polygonal and elongated polygonal shapes) as well as different initial states (density) and directions of loading with respect to the initial fabric. Simulations of biaxial tests clearly show that the behaviour of samples with isotropic particles can be dissociated from that of samples with anisotropic particles. Indeed, for isotropic particles, angularity just tends to strengthen the behaviour of samples and slow down either local or global phenomena. One of the main results concerns the existence of a critical state for isotropic grains characterized by an angle of friction at the critical state, a critical void ratio and also a critical anisotropy. This critical state seems meaningless for elongated grains and the behaviour of samples generated with such particles is highly dependent on the direction of loading with respect to the initial fabric. The study of local variables related to fabric and particle orientation gives more information. In particular, the coincidence of the principal axes of the fabric tensor with those of the stress tensor is sudden for isotropic particles. On the contrary, this process is gradually initiated for elongated particles. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献