A Graphical Analysis-based Method for Undrained Cylindrical Cavity Expansion in Modified Cam Clay Soil

A novel graphical analysis-based method is proposed for analysing the responses of a cylindrical cavity expanding under undrained conditions in modified Cam Clay soil. The essence of developing such an approach is to decompose and represent the strain increment/rate of a material point graphically into the elastic and plastic components in the deviatoric strain plane. It allows the effective stress path in the deviatoric plane to be readily determined by solving a first-order differential equation with the Lode angle being the single variable. The desired limiting cavity pressure and pore pressure can be equally conveniently evaluated, through basic numerical integrations with respect to the mean effective stress. Some ambiguity is clarified between the generalized (work conjugacy-based) shear strain increments and the corresponding deviatoric invariants of incremental strains. The present graph-based approach is also applicable for the determination of the stress and pore pressure distributions around the cavity. When used for predicting the ultimate cavity/pore pressures, it is computationally advantageous over the existing semi-analytical solutions that involve solving a system of coupled governing differential equations for the effective stress components. It thus may serve potentially as a useful and accurate interpretation of the results of in-situ pressuremeter tests on clay soils.

Undrained Elastoplastic Solution for Cylindrical Cavity Expansion in Structured Cam Clay Soil Considering the Destructuration Effects

Soil structure has significant influences on the mechanical behaviors of natural soils, although it is rarely considered in previous cavity expansion analyses. This paper presents an undrained elastoplastic solution for cylindrical cavity expansion in structured soils, considering the destructuration effects. Firstly, a structural ratio was defined to denote the degree of the initial structure, and the Structured Cam Clay (SCC) model was employed to describe the subsequent stress-induced destructuration, including the structure degradation and crushing. Secondly, combined with the large strain theory, the considered problem was formulated as a system of first-order differential equations, which can be solved in a simplified procedure with the introduced auxiliary variable. Finally, the significance and efficiency of the present solution was demonstrated by comparing with the previous solutions, and parametric studies were also conducted to investigate the effects of soil structure and destructuration on the cavity expansion process. The results show that the soil structure has pronounced effects on the mechanical behavior of structured soils around the cavity. For structured soils, a cavity pressure that is larger than the corresponding reconstituted soils when the cavity expands to the same radius is required, and the effective stresses first increase to a peak value before decreasing rapidly with soil structure degradation and crushing. The same final critical state is reached for soils with different degrees of the initial structure, which indicates that the soil structure is completely destroyed during the cavity expansion. With the increase of the destructuring index, the soil structure was destroyed more rapidly, and the stress release during the plastic deformation became more significant. Moreover, the present solution was applied in the jacking of a casing during the sand compact pile installation and in situ self-boring pressuremeter (SBPM) tests, which indicates that the present solution provides an effective theoretical tool for predicting the behavior of natural structured soils around the cavity.

Description of Limit States in the Subsurface Layer of Loosened Subsoil in View of Critical State Soil Mechanics

The article aims to present an effective numerical method for the behaviour analysis and safety assessment of a subsurface layer of subsoil in the existing or predicted states of mining and post-mining deformations. Based on our own analytical record, using the equations of the Modified Cam-Clay model, the description of limit states in the subsurface layer of subsoil was validated, making it consistent with in situ observations. The said effect was demonstrated by comparing numerical analyses of the subsoil layer subjected to the limit state, using the Modified Cam-Clay (MCC) model and the Coulomb-Mohr model (C-M). The article also presents the applicability potential of the numerical analysis of the loosened subsoil layer for the assessment of protection elements (e.g., geo-matresses) used under linear structures in the areas subjected to mining and post-mining impacts.

Probabilistic Failure Estimation of an Oblique Loaded Footing Settlement on Cohesive Geomaterials with a Modified Cam Clay Material Yield Function

In this work, a quantitative uncertainty estimation of the random distribution of the soil material properties to the probability density functions of the failure load and failure displacements of a shallow foundation loaded with an oblique load is portrayed. A modified Cam Clay yield constitutive model is adopted with a stochastic finite element model. The random distribution of the reload path inclination κ, the critical state line inclination c of the soil and the permeability k of the Darcian water flow relation, has been assessed with Monte Carlo simulations accelerated by using Latin hypercube sampling. It is proven that both failure load and failure displacements follow Gaussian normal distribution despite the excessive non-linear behaviour of the soil. In addition, as the obliquity increases the mean value of failure load and the failure displacement always increases. The uncertainty of the output failure stress with the increase of the obliquity of the load remains the same. The failure spline of clays can be calculated within an acceptable accuracy with the proposed numerical scheme in every possible geometry and load conditions, considering the obliquity of the load in conjunction with non-linear constitutive relations.

An extended super/subloading surface model for soft rock considering structure degradation

The strain-softening and dilatancy behavior of soft rock is affected by the loading history and the development of structure. This study regards soft rock as a structured and overconsolidated soil and develops a new elastoplastic model based on the classical super yield surface Cam-clay model. The proposed model is capable of capturing the effect of yield surface shape on the mechanical behavior of soft rock by introducing a new yield function. The proposed model is validated against the triaxial test results on different types of soft rocks under drained condition. The comparison results indicate that the proposed model is suitable for describing the constitutive behavior of soft rock.

MODIFIED CAM-CLAY MODELS FOR DYNAMIC ANALYSIS OF GRANULAR METAMATERIALS IN EARTHQUAKE ENGINEERING

the problem of protecting buildings and structures from vibrations of natural and artificial nature is im-portant for modern construction. One of such modern methods of protection is seismic pads. The purpose of this work was to study the effect of adding a layer of granular metamaterial under a slab foundation on the vibration of a building under the influence of seismic shear waves (S-waves). To achieve this objective, the finite element method (FEM) was used in combination with Cam-Clay models. The FE model consists of a ten-story superstructure rested on the slab foundation, under which there is a layer of granular metamateri-als. 16 models were created taking into account changes in the values of these parameters (pad thickness; density; cohesion; critical state strength parameter (M); Young's modulus-Poisson's ratio). The dynamic analysis performed using the software package Abaqus/CAE showed the effectiveness of granular met-amaterials in their ability to dissipate seismic energy and significantly reduce vibration transmitted from the ground to the building.

Theoretical solution for drained cylindrical cavity expansion in clays with fabric anisotropy and structure

This paper presents a novel, exact, semi-analytical solution for the quasi-static drained expansion of a cylindrical cavity in soft soils with fabric anisotropy and structure. The assumed constitutive model is the S-CLAY1S model, which is a Cam clay-type model that considers fabric anisotropy that evolves with plastic strains, structure and gradual degradation of bonding (destructuration) due to plastic straining. The solution involves the numerical integration of a system of eight first-order ordinary differential equations, three of them corresponding to the effective stresses in cylindrical coordinates, other three corresponding to the components of the fabric tensor and one corresponding to the amount of bonding and another corresponding to the specific volume. The solution is validated against finite element analyses. When destructuration is considered, the solution provides slightly lower values of the effective radial and mean stresses near the cavity wall. Besides, the specific volume is further reduced due to loss of bonding. Parametric analyses and discussion of the influence of soil overconsolidation, expansion of the cavity and initial amount of bonding are presented.