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Critical State Soil Mechanics

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... Bild 5b zeigt die Ergebnisse der Drucksondierungen in Form des gemessenen Spitzendrucks q c in allen drei be- [25]. In beiden Fällen führt eine monotone Scherung asymptotisch zum sogenannten kritischen Zustand [21] und eine zyklische undrainierte Scherung zu einem Abbau der effektiven Spannungen, wobei ein vollständiger Verlust der effektiven Spannungen, eine Bodenverflüssigung, erreicht werden kann [25]. Das genannte Stoffmodell der Hypoplastizität mit intergranularer Dehnung [8] kann diese Effekte qualitativ abbilden. ...
... Zu Beginn der Aufweitung verhält sich der Boden kontraktant, was sich bei einer großen Durchlässigkeit in einer Reduktion der Porenzahl und bei geringer Durchlässigkeit in einer Spannungsrelaxation zeigt. Die monotone Hohlraumaufweitung führt asymptotisch zum Erreichen des kritischen Zustands, welcher durch den kritischen Druck p c und die kritische Porenzahl e c [21] gekennzeichnet ist. Praktisch ist dies mit einem ausgeprägten Druckanstieg verbunden. ...
... Diese Unterschiede konnten anhand von vereinfachten numerischen Simulationen gezeigt werden, siehe Bild 8 und Bild 13. Während bei einer monotonen Belastung asymptotisch der kritische Zustand[21] erreicht wird, was bei Böden mit einer relativen Lagerungsdichte I D > 0 zu einem Druckanstieg am Hohlraumrand führt, ergibt sich im Falle der zyklischen Belastung in Abhängigkeit von der Durchlässigkeit eine Reduktion der effektiven Spannungen bzw. eine Verdichtung. ...
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Die Rüttelstopfverdichtung kommt als Baugrundverbesserung weltweit in fein- und grobkörnigen Böden zum Einsatz. Jedoch sind die Zustandsänderungen des anstehenden Bodens infolge des vollverdrängenden Säuleneinbaus und der induzierten Vibration noch nicht ausreichend untersucht. Im ersten Teil dieses Beitrags werden daher in einem Feldversuch die Auswirkungen der Rüttelstopfsäulenherstellung auf den Zustand des anstehenden Bodens untersucht. Dabei zeigt sich, dass der Rüttelstopfsäuleneinbau in grobkörnigen Böden zu einer Verbesserung der bautechnischen Eigenschaften des anstehenden Bodens führen kann. Motiviert durch den Feldversuch betrachtet der zweite Teil der Arbeit anhand von simplifizierten Beispielen einen grundsätzlichen Vergleich verschiedener Hohlraumaufweitungsprozesse. Mithilfe eines hypoplastischen Stoffmodells wird dabei die Aufweitung eines Hohlraums infolge (1) einer monotonen und infolge (2) einer zyklischen Belastung betrachtet. Beide Fälle werden im Hinblick auf eine qualitative Übertragbarkeit auf die Modellierung der Säuleninstallation verglichen. Es zeigt sich ein qualitativ unterschiedliches Bodenverhalten: Eine monotone Aufweitung führt zum kritischen Zustand im Boden, während eine zyklische Aufweitung in Abhängigkeit von der Durchlässigkeit zu einer Verdichtung und/oder einer Spannungsrelaxation führt. Eine vollständige Vernachlässigung der Rüttlervibration in entsprechenden numerischen Modellen erscheint daher nicht zutreffend.
... (a) The more aspects of the constitutive response that can be accounted for by the constitutive model (e.g. the evolution of elasto-plastic models from the original Cam Clay model as an elasto-plastic constitutive law (Schofield & Wroth, 1968) to MCC (Roscoe & Burland 1968) and finally into bounding surface plasticity models with various hardening mechanisms and memory surfaces (McDowell & Hau, 2004;Seidalinov & Taiebat, 2014)), the more parameters typically need to be calibrated, leading to additional uncertainties and requirements on the laboratory testing program. (b) With an increasing number of phenomena considered, the number of state variables usually increases as well (cf. ...
... The first critical state elasto-plastic models were the series of Cam Clay formulations, developed at the University of Cambridge, UK (Roscoe & Schofield, 1963;Schofield & Wroth, 1968). The advantages of these models lie in their apparent simplicity and few parameters, which can be directly obtained from conventional laboratory tests (Borja & Seung, 1990). ...
Article
A critical investigation of three constitutive models for clay by means of analyses of a sophisticated laboratory testing programme and of centrifuge tests on monopiles in clay subjected to (cyclic) lateral loading is presented. Constitutive models of varying complexity – namely, the basic modified Cam Clay model, the hypoplastic model with intergranular strain (known as the clay hypoplasticity model) and the more recently proposed anisotropic visco-intergranular strain anisotropy (AVISA) model – are considered. From the simulations of the centrifuge tests with monotonic loading it is concluded that all three constitutive models give satisfactory results if a proper calibration of constitutive model parameters and proper initialisation of state variables is ensured. In the case of cyclic loading, the AVISA model is found to offer superior performance over the hypoplastic model with intergranular strain.
... Note that the κ and λ values were not reported in Hight et al. (2002). Therefore, these values were estimated from the reported plasticity index as follows (Schofield and Wroth 1968;Wood 1990): where C c is the compression index and I p is the plasticity index in percent. Using the results presented in Table 3, the numerically predicted (from this study) versus reported (from previous studies) values of q c are plotted in Fig. 3. ...
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This paper presents a finite difference-based analysis of the cone penetration test (CPT) in saturated intact clays. The modified Cam clay (MCC) model was used to capture the undrained behaviour of the saturated clays. The cone tip resistance values obtained from the numerical analyses were validated against those obtained from field and calibration chamber tests, as well as numerical analyses reported in the literature. The effect of the MCC parameters on tip resistance was investigated through sensitivity analyses. Based on a large number of numerical analyses of CPT with different MCC parameters performed in this study, a relatively comprehensive database of CPT results was obtained. Relative weight analysis was then used to determine the relative effect of each MCC parameter on the tip resistance. Using nonlinear regression analysis of the obtained database, a relationship between tip resistance and soil properties was developed. Finally, the application of the proposed equation in estimating the overconsolidation ratio and effective friction angle is illustrated with useful charts, numerical examples, and comparisons with different case studies.
... To answer the question, let us focus on the mechanical soil behavior. Soil undergoes both elastic and plastic deformation when load is applied to and reaches "critical state" under large shear deformation at constant volume and constant shear/normal stress conditions [27]. This mechanical behavior of soil can be well explained by the critical state constitutive models. ...
Chapter
Full-text available
This chapter presents an application example of a nonlinear Kalman Filters (KFs), i.e., Particle Filter (PF), for state (or parameters) estimation and prediction of a dynamical system in geotechnical engineering. First key characteristics of dynamical systems in geotechnics, which need to be considered in filtering, are described by showing some figures, and why PF is necessary for geotechnical applications is explained. Then, a detailed algorithm and implementation of PF for geotechnical problems are presented with key equations. The PF is demonstrated through a case history focusing on deformation behavior of a ground due to embankment construction. The PF is applied to estimation of geotechnical parameters and predictions of future settlement behavior of the ground to discuss the effectiveness of the PF in geotechnical engineering. The results of the case history have shown that PF has presented great promise as an accurate parameter identification for a nonlinear dynamic model. The simulation with the identified parameters predicts the actual measurement data with high accuracy even though a limited amount of measurement data was used in identification stage. The PF provides more information on estimates than optimization methods because the estimates are obtained in the form of probability density functions (PDFs). This characteristic can contribute to risk analysis and reliability-based decision-making in geotechnical practice.
... This flow rule has Degree 1 in η, as others such as the original cam clay flow rule (Schofield and Wroth 1968). Thus, the relationship between η max and D P min also is of Degree 1, because the peak points still must obey the defined flow rule. ...
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Soil mechanics traditionally have focused on studying pure clays and clean sands. However, natural soils and other geomaterials usually do not fall into these two classes. Most geomaterials are a complex matrix of fines and coarser particles, with distinct shapes and mineralogy interacting. This paper studied iron ore tailings over a broad range of pressures and stress histories to investigate the mechanical behavior of this nontextbook geomaterial. A thorough experimental program was conducted, and aspects of the stress-strain response, yielding, hardening, and critical state were evaluated. The state boundary surface of iron ore tailings also was investigated. The results demonstrated that the stress history of tailings affects the tailings' behavior only at elevated stress levels. The existence of particles with distinct mineralogy in the iron ore tailings (mainly iron oxide and quartz) could have induced different breakage patterns, with an evolving particle morphology being the dominant mechanism up to the pressures achieved.
... The strength of granular materials is influenced by the confining pressure (Schofield andWroth, 1968, Hardin, 1989). Extensive experimental and numerical studies have been carried out in past decades to investigate the behavior of granular soils under the confining pressure r c over 50 kPa, while fewer studies can be found under the lower confining pressure (Yamamuro and Lade, 1998, de Bono and McDowell, 2018. ...
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Particle shape irregularity is a notable feature of granular materials that exerts a profound influence on their mechanical behavior. This study examines the effects of particle overall regularity and surface roughness on the fabric evolution of granular materials using the Discrete Element Method (DEM). By connecting multiple spheres with varying sizes and positions, a diversity of clump particles characterized by distinct overall regularity () and surface roughness () are generated. A series of DEM simulations on drained triaxial compression tests have then been performed on granular assemblies with varying shapes, whereby their characteristics of contact intensity and the anisotropy of various fabric entities defined by contact normal, branch vector, and particle orientation, have been thoroughly investigated. The results show that increasing particle shape irregularity, indicated by smaller values of and , is generally associated with an enhanced internal structure within the granular assembly, exhibiting a higher mechanical coordination number and a greater fabric anisotropy. Conversely, in granular assemblies with relatively high overall regularity, the fabric anisotropy is notably reduced, and this reduction cannot be compensated by enhancements in particle surface roughness. The evolution of two contact-related fabric anisotropies is analyzed in relation to particle orientation-based fabric anisotropy, which is more profoundly influenced by particle overall regularity, underscoring its significant role in fabric evolution of granular materials.
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Full-text available
Shear strength is a classical topic in Soil Mechanics and generally there is little concern about the inconsistencies behind the theories used to predict its value. In fact the debate on this issue is rather limited as the geotechnical community considers this a well-established concept. This note intends to highlight the difficulties that arise when teaching that concept in an undergraduate Soil Mechanics course. Those difficulties are related to the drained/ undrained behavior of soils, but also to the fact that cohesion is a tricky parameter, with a misleading physical meaning, depending not only on the properties of the contacts between particles, but also on external conditions (i.e., saturation or unsaturation). All these aspects are not analyzed in detail in many textbooks, but they should be considered in a modern Soil Mechanics course.
Chapter
As it is well known, soils are particulate materials where grains are the elementary bricks of their micro-structure. Thus, at the macro-scale, the mechanical behaviour of soils is ruled by grains’ shape, texture, deformability and strength. The mechanical behaviour of soils is fascinating for many reasons.
Article
One of the main criticisms of the triaxial test is the nonuniformity of stress and deformation at all but small strains. The main cause of this nonuniformity is friction at the end platens, which causes both the barrelling effect and the concentration of dilation in local zones which in turn results in the premature development of a failure surface. These disadvantages are largely overcome by the use of lubricated end platens which, by removing the dead zones, allow the use of shorter test samples. Short samples with lubricated end platens have proved an advantage in triaxial research on particulate matter for a number of years. Use of this technique has the consistency of the test results. Preliminary tests on clays indicate that this is a promising method of reducing the testing time necessary for accurate pore pressure measurement. An additional benefit from their use is the reduction of piston friction. The use of electrical pressure transducers for measuring pore pressures is also described; this system is particularly suitable if automatic recording is required.
Article
Soils having cohesion and internal friction are often considered to be perfectly plastic solids. A consistent approach has been proposed on the basis of the mathematical theory of perfect plasticity, and several interesting results were obtained. However, such an idealized treatment will often result in a marked difference between prediction and experimental fact. In particular, the strong dependence of the volume change under shearing action on the prior history of the soil cannot be properly taken into account. It is suggested herein that soil be treated as a work-hardening material which may reach the perfectly plastic state. A remarkable qualitative agreement is then obtained with the known behavior of soils in triaxial tests; additional study along similar lines appears most promising.
Article
A test which originated in Brazil for determining the tensile strength of concrete involves applying a compressive load to opposite generators of a cylindrical specimen. The specimenfaiL~ in tension along the diametral plane containing the load. Experiments with this teot have shown that: (1) Packing strips of relatively soft material are necessary between the specimen and the platens of the testing machine. Plywood strips ½ in. wide and ⅛ in. thick are satisfactory for the purpose, but the material and dimensions of the strips have little effect, provided they can conform to small irregularities in the surface of the specimen. (2) Cylinders 6 in. in diameter by 6 in. long may be usedfor concrete containing aggregate up to ¾ in. maximum size. Longer specimens may tend to give more uniform results, while smaller specimens may give higher average values. (3) The new test gives results higher than those given by a direct tensile test, but lower than the modulus of rupture of beams. It tends to give more uniform results than the direct tension or transverse test, but less uniform results than a compression test on cubes.