Cavity Expansion Theory Research Articles

Modeling Hydraulic Fracturing and Blow-Out Failure of Tunnel Face During Shield Tunneling in Soft Soils

A common conflict of objectives for shield tunneling is to provide sufficient support pressure to maintain the stability of the tunnel face while avoiding blow-out of the tunnel face. Slurry-induced hydraulic fracturing, which is an important cause of blow-out failure in slurry-type shield tunneling, is investigated in this study. A fracture initiation mechanism for soft soils is developed and the fracturing pressure is described using a combined shear and tensile failure criteria within the cavity expansion theory framework. A slurry-induced fracture propagation model, coupled with the fracture initiation mechanism, is then proposed for predicting the fracture length and growth rate in front of tunnel face. The model is successfully applied to test data from the literature, and used in a parametric analysis. The results show that a fracture may easily extend to the ground surface when tunneling in ground with low strength parameters or shallow depth, and hydraulic fracture can be mitigated by using a high-density slurry. Finally, some design charts are provided to guide engineers in selecting a reasonable range of slurry pressure during shield tunneling, thus mitigating the risks of blow-out as well as maintaining face stability.

Dynamics Analysis of Penetration against Pebble-Concrete Target.

The classical continuum mechanics theory cannot sufficiently describe the effect of pebbles on projectile, which leads to a large calculation error. In this paper, an orthogonal curvilinear coordinate system is constructed, which effectively describes and perfects the normal cavity expansion theory. A couple stress theory based on the normal cavity expansion is proposed in which not only the tangential movements but also the rotations of the concrete medium are considered. According to the high-speed impact of pebble concrete, combined with dynamic equations and the FE simulation, the theoretical and simulation results of pebble particles scale on warhead resistance are compared. It is shown that, the larger the scale of pebble particles, the stronger the effect of rotation on the resistant force applied on the warhead.

Delineation of Soil Interfaces Using Cpt Resistance Based on Cavity Expansion Theory

Delineation of Soil Interfaces Using Cpt Resistance Based on Cavity Expansion Theory

Modelling the penetration of subsonic rigid projectile probes into granular materials using the cavity expansion theory

Typical subsurface investigation tools used on Earth are not applicable for subsurface exploration of the Moon and other extraterrestrial bodies due to payload limitations in space missions. Instead, light and compact subsonic projectile probes can be considered as an alternative subsurface investigation tool in such exploratory missions to overcome a host of challenges. Such probes can be launched from a lunar orbiter or lander to the surface of the Moon to provide the initial effective penetration from the impact. Here, we develop a model based on the spherical cavity expansion theory to predict the deceleration rate and final penetration depth of a rigid projectile probe into geological targets under the perpendicular subsonic impact. Two stress fields are assumed to propagate in the medium, plastic (near field) and elastic (far field), upon the impact. The stresses at the cavity wall are obtained by combining the Mohr–Coulomb failure criterion for the target failure (plastic region) considering two different assumptions for plastic wave propagation. Two field experiments are used to compare and assess the robustness of the proposed solutions in the subsonic range. Base on the simulation results and the experiments, it is concluded that the cavity expansion model considering the locked hydrostat assumption, with the modification here introduced for the volumetric strain, can provide us with a reasonable prediction of the projectile penetration, final penetration depth and the stresses on the probe. Thus, our proposed solution can be used as a benchmark for sophisticated and computationally-expensive numerical calculations.

A semi‐analytical solution for displacement‐controlled elliptical cavity expansion in undrained MCC soil

AbstractConventional cavity expansion theory is a one‐dimensional problem and is not applicable for the two‐dimensional cavity expansion issue, which is also required for geotechnical problems. This paper proposes a novel semi‐analytical solution for displacement‐controlled elliptical cavity expansion (DC‐ECE) in undrained soil. The displacement and strain fields for DC‐ECE are obtained from the strain path method (SPM) with the aid of conformal mapping theory. The effective stress can be subsequently obtained by the incremental stress‐strain calculation using a suitable constitutive model such as the MCC model. Then, the computed effective stress results are substituted into the stress equilibrium equation to give the pore pressure solution. The new semi‐analytical solution reveals the non‐axisymmetric characteristics of DC‐ECE and allows the elastic‐plastic (EP) boundary, excess pore pressure, stress, and displacement to be calculated. The proposed method provides a solution to non‐axisymmetric cavity expansion issues and it can be applied to geotechnical engineering problems, including vertical drain installation, flat dilatometer tests and noncylindrical pile penetration in clay.

Drilled shafts in sand: failure pattern and tip resistance using numerical and analytical approaches

ABSTRACT Drilled shafts are one of the most important types of pile foundations. Several researchers have suggested different soil failure patterns for driven piles; however, for drilled shafts, this issue is inadequately addressed in the literature. In this paper, a numerical approach was pursued to obtain the location and dimensions of plastic zones around the tip of drilled shafts. The dependence of the suggested failure pattern size on the soil properties and drilled shaft dimensions was investigated. Based on several analyses, a soil jug-shaped failure pattern around the tip of drilled shafts was proposed, and its dimensions were determined using the regression-based and trial and error analyses. A c Comparison of is made between the proposed failure pattern obtained in this study for drilled shafts with the ones reported in the literature that were based on the logarithmic spiral curve and also cavity expansion theory showed that. This study shows that the suggested failure pattern hasd some similarities with the one proposed based on the cavity expansion theory. Finally, based on the suggested plastic zone, an analytical approach was used introduced to estimate the tip resistance for drilled shafts in sand. Good agreement between the analytically predicted results and measured values of tip resistance reported in the literature was found.

Research progress of target resistance model of cavity expansion theory and its application

The cavity expansion theory is one of the main basic theories for the theoretical analysis of penetration problems. It is mainly used to analyze the failure response characteristics of typical target materials under impact load, and then to determine the penetration resistance of the target. It is widely used in the analysis of high-speed impact penetration and failure problems. Domestic and foreign scholars have made abundant research achievements on plastic and (quasi) brittle materials based on the theory of cylindrical and spherical cavity expansion. Starting from the theoretical system of the static/dynamic cavity expansion model, the results of the cavity expansion model in different directions are introduced, mainly involving the cavity expansion pressure theoretical calculation model and numerical simulation method under ideal penetration conditions, and the application of cavity expansion model to typical penetration problems and complex missile target conditions. The theoretical calculation model under ideal penetration conditions based on cavity expansion theory mainly discusses the influence aspects of target material, yield criterion and equation of state on target resistance and the applicability of the cavity expansion model. According to the different initial conditions in the numerical simulation, two numerical simulation methods of cavity surface constant velocity/constant pressure are introduced, and the reliability of the numerical simulation method is proved. The basic assumptions, application scope and engineering application characteristics of the cavity expansion model are summarized, and its applications in typical penetration problems and complex missile targets such as multilayer composite target plate, constrained target, projectile grooves and projectile body with special cross-section are listed. Based on the current status of the cavity expansion model, we summarized the current cavity expansion model application direction in the field of impact dynamics, and the problems existing in the application of the cavity expansion model, as well as the key development direction in the cavity expansion model.

Behavior of oil-based modeling clay at medium strain rates

The modeling clay is an oil-based soft, flowable, and pliable material made from waxes and oils. Besides its primary use for making sculptures, the modeling clay is commonly used to evaluate bulletproof vests and simulate metal manufacturing processes by conformation. In ballistic tests, the clay is used to retain the deformation of the rear face of body armors; and in the study of metal forming processes, it is used as a physical model to provide information on the plastic flow. However, its mechanical dynamic behavior is not entirely understood. In this study, Plastilina Roma No. 1 modeling clay was mechanically characterized using the power-law constitutive model at medium strain rates [Formula: see text]. The material parameters were determined using a penetration model based on the Cavity Expansion Theory and an inverse technique involving the comparison of the model with experimentation. The optimum set of constitutive parameters was found by reducing the difference of the calculated penetration profile and the measurements from a drop test. This optimization process was programmed on the MATLAB–Simulink environment. The determined material parameters were validated by comparing the results from a computational model with three test set-ups. Finite element model results show good concordance with experimental measurements.

Erosion damage and expansion evolution of interfacial transition zone in concrete under dry-wet cycles and sulfate erosion

Interfacial transition zone (ITZ) is of paramount importance to the durability of concrete. However, the evolution of damage characteristics and mechanical properties of ITZ under dry-wet cycles and sulfate erosion were not fully investigated in the literature. Therefore, this paper presents the expansive model of ITZ based on cylindrical cavity expansion theory, following by calculation of mechanical properties evolution of ITZ under sulfate erosion. The expansion ratio, Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) were utilized to analyze the internal erosion and expansion characteristics of concrete with the water-cement ratio (w/c) of 0.3, 0.4 and 0.5. The results indicate that the expansion ratio of concrete increases with the erosion age and w/c. The new diffraction peaks appear in the XRD pattern after sulfate erosion. As compared with Poisson's ratio (γ) and internal friction angle (φ), cohesive force (C) has the largest influence on the internal stress and plastic zone width. The final internal stress and plastic zone width are affected by w/c, and the damage degree of concrete with 0.4 w/c is the minimum. This study provides new insights into damage mechanism of concrete and ITZ under dry-wet cycles and sulfate erosion, the results of which provide new perspectives for improving the durability of concrete.

A method of calculating the bearing capacity of sand pile composite foundations in a mucky soil layer considering consolidation

In engineering practice, the measured bearing capacity of a sand pile composite foundation in a mucky soil layer is much larger than the design value. Based on the sand pile construction and the load application process, a method of calculating the bearing capacity of the foundation based on the effective stress was proposed. Cavity diameter expansion in sand pile construction was simplified into a planar problem, and the cavity expansion theory was used to establish the expression of the rate of displacement and the horizontal stress increase. Based on the e–p curve and the calculation of the degree of consolidation, the relationships between the horizontal and vertical effective stress and the void ratio were obtained. According to the close relationship between the bearing capacity of the foundation in a mucky soil layer and the water content, an expression describing the relationships between the bearing capacity of the foundation, effective stress, void ratio, and water content was established. For the temporary engineering foundation treatment project, which needs a high bearing capacity but allows large foundation deformation, the design of sand pile composite foundations uses these relationships to take the consolidation effect of mucky soil into consideration, thereby reducing the replacement rate and lowering the construction cost.

Theoretical prediction models for ground settlement during box jacking

Box tunnels, compared with circular tunnels, can increase the space utilization ratio by approximately 20% and have been increasingly used in urban underground space. Box jacking generates more ground loss due to its special geometric shape, inducing larger ground settlement, compared with circular pipe jacking. Accurate prediction of ground settlement during box jacking is a key aspect for the success of a project. This paper proposes the ground settlement prediction models during box jacking based on stochastic medium theory and cavity expansion theory, and compares the applicability of the models. The comparison shows that the modified Verruijt model based on the cavity expansion theory can provide a relatively accurate prediction for the magnitude and trough width of the ground settlement. The analytical model is validated through numerical simulation and field instrumentation using the project of Shilianjie Station of No. 5 metro line in Suzhou, China as a testbed. The validation shows that the analytical predictions compare reasonably well with the numerical simulation results and field measurements with a maximum error within 13%. The analytical model in this paper can provide a quick estimate on the ground settlement during box jacking.

Experimental and Numerical Investigation of the Effect of Projectile Nose Shape on the Deformation and Energy Dissipation Mechanisms of the Ultra-High Molecular Weight Polyethylene (UHMWPE) Composite.

The effect of projectile nose shape on the ballistic performance of the ultra-high molecular weight polyethylene (UHMWPE) composite was studied through experiments and simulations. Eight projectiles such as conical, flat, hemispherical, and ogival nose projectiles were used in this study. The deformation process, failure mechanisms, and the specific energy absorption (SEA) ability were systematically investigated for analyzing the ballistic responses on the projectile and the UHMWPE composite. The results showed that the projectile nose shape could invoke different penetration mechanisms on the composite. The sharper nose projectile tended to shear through the laminate, causing localized damage zone on the composite. For the blunt nose projectile penetration, the primary deformation features were the combination of shear plugging, tensile deformation, and large area delamination. The maximum value of specific energy absorption (SEA) was 290 J/(kg/m2) for the flat nose projectile penetration, about 3.8 times higher than that for the 30° conical nose projectile. Furthermore, a ballistic resistance analytical model was built based on the cavity expansion theory to predict the energy absorption ability of the UHMWPE composite. The model exhibited a good match between the ballistic resistance curves in simulations with the SEA ability of the UHMWPE composite in experiments.

Spudcan-pile interaction in thick soft clay and soft clay overlying sand: A simplified numerical solution

A drilling jack-up is often deployed to perform drilling activities or well intervention at an existing fixed jacket platform. Depending on the clearance distance between the aft spudcan and the nearest pile, the installation of the spudcan may have an adverse effect on the platform pile which in turn could compromise the integrity of the jacket structure. This paper presents a simplified method for assessing the effect of spudcan installation on the pile foundation of a jacket platform in thick soft clay and soft clay overlying sand layers. Adopting a two-stage uncoupled approach, in which predetermined free-field lateral soil displacements are applied to a beam-column model with soil modelled using p-y curves, the soil displacements around a penetrating spudcan is estimated by an analytical solution derived from spherical cavity expansion theory. With appropriate consideration for the volume of soil displaced by the penetrating spudcan for the cases of thick soft clay and consideration for soil squeezing for soft clay overlying sand, the computed free-field lateral soil displacements are in fair agreement with the measured profiles in centrifuge tests and can be used in a beam-column model to estimate the induced bending moment in the pile in practice.The pile response to the free-field lateral soil displacements is assessed using a beam-column model incorporating p–y curves, considering the effect of soil remoulding caused by the installation of the spudcan where appropriate. A numerical model which considers the evolving lateral soil displacements due to the progressive advancement of the penetrating spudcan is also studied. The computed pile bending moment profiles are consistent with the measured profiles in the centrifuge tests and those computed by 3D large deformation finite element (LDFE) model. The proposed practical method is simple but yet effective to assess the influence of the installation of a spudcan foundation on an adjacent pile of a jacket platform in thick soft clay and soft clay overlying sand.

Study of the Bearing Capacity at the Variable Cross-Section of A Riser-Surface Casing Composite Pile

Reducing the cost of offshore platform construction is an urgent issue for marginal oilfield development. The offshore oil well structure includes a riser and a surface casing. The riser, surface casing and oil well cement can be considered special variable cross-section piles. Replacing or partially replacing the steel pipe pile foundation with a variable cross-section pile to provide the required bearing capacity for an offshore oil platform can reduce the cost of foundation construction and improve the economic efficiency of production. In this paper, the finite element analysis method is used to investigate the variable cross-section bearing mode of composite piles composed of a riser and a surface casing in saturated clay under a vertical load. The calculation formula of the bearing capacity at the variable section is derived based on the theory of spherical cavity expansion, the influencing factors of the bearing capacity coefficient Nc are revealed, and the calculation method of Nc is proposed. By comparing the calculation results with the results of the centrifuge test, the accuracy and applicability of the calculation method are verified. The results show that the riser composite pile has a rigid core in the soil under the variable cross-section, which increases the bearing capacity at the variable cross-section.

Experimental and analytical study on soilbag and encased sand columns in loose sand

It has been shown that wrapping granular soil with geotextile significantly increases its bearing capacity. This finding, recently, has extended the use of soilbags to construct permanent structures. This paper investigates the compressive behavior of a new geo- column called the soilbag column. Several compression tests were performed for both end-bearing and floating columns with different diameters and lengths in a testing tank filled with loose sand. To compare the effectiveness of this method with other common techniques of soil improvement, the compressive behavior of encased sand columns was also studied. In both scenarios, induced additional confining pressure provided by the encasement is the most important factor in increasing the bearing capacity. The results indicated that the soilbag columns provide much stiffer compression behavior than the encased sand columns. Compared to an encased sand column, the superiority of using a soilbag column is more evident for the end-bearing type. The values of bearing capacity of the physically modeled encased sand columns agreed well with the values estimated by an analytical approach using cavity expansion theory. Besides, an analytical approach developed to predict the stress-strain response of the soilbags under the uniaxial compression test.

Numerical Simulation of the Construction Process of Long Spiral CFG Piles

A numerical model for the construction process of long spiral CFG piles is established based on the coupled Eulerian–Lagrangian method. The construction process is divided into drilling process and concrete pouring process for modeling. The influence of long spiral CFG piles construction on saturated sand foundation is studied, and dynamic responses, changes of pore water pressure, and void ratio of saturated sand foundation are obtained. The rationality and accuracy of the simulation results are proved by comparing with the field test data and calculation results of the theory of cylindrical cavity expansion. The presented numerical results prove that the vibration load generated during the construction acts on saturated soil in the form of irregular reciprocating shear forces, which leads to a large excess pore water pressure in the soil and an increase in soil void ratio. Both the excess pore water pressure field generated during the construction and the soil pore ratio after the construction show a parabolic distribution in the vertical direction. The research results can provide reference and theoretical basis for future research and engineering practice.

Estimating Hydraulic Conductivity of Overconsolidated Soils Based on Piezocone Penetration Test (PCPT)

Overconsolidated (OC) soils may develop a low or negative pore pressure during PCPT. Thus, it is challenging to develop an “on-the-fly” estimation of hydraulic conductivity from PCPT results. This study presents a method to estimate the hydraulic conductivity of OC soils from PCPT results based on a previously developed method for normally consolidated (NC) soils. To apply the existing method, PCPT pore pressure in OC soils is adjusted by using a correction factor. An equation for the correction factor is derived based on the concepts of critical state soil mechanics, cavity expansion, and consolidation theories. Then, it was reformulated so that traditional cone indices could be used as input parameters. It is shown that the correction factor is mainly influenced by the cone tip resistance, pore pressure, and the rigidity index. The comparison of predicted, which is based on corrected pore pressure and measured hydraulic conductivity showed a good match for four well documented data sets. With the findings of the study, it is expected that an “on-the-fly” estimation of hydraulic conductivity of overconsolidated soils is possible.

Calculation method for the vertical bearing capacity of a riser-surface casing composite pile

ABSTRACT The variable cross-section structure (comprising a riser, surface casing and cementing cement ring) of an oil well associated with an offshore oil platform is similar to that of a steel pipe pile foundation. If a well structure with variable cross-section characteristics can be used to provide bearing capacity, the construction cost of platforms will be reduced. In this paper, the finite element analysis method is used to study the vertical bearing mechanism of composite piles composed of a riser and a surface casing in saturated clay and sand. Based on the theory of spherical cavity expansion, the calculation methods of end resistance and skin friction resistance of composite pile are established. Finally, based on a field test of the bearing capacity of composite piles, the accuracy of the proposed calculation method is verified.

Influence of blunt-nose and conical fragment on domino accident probability in spherical-tank area

Considering wind-speed influence, a new acceleration model is established, and a trajectory equation is obtained. The impact-depth models of a cone and end-cover debris are also established based on the cavity expansion theory. Combined with the residual strength theory, a new spherical-tank failure-probability model is established, and the probability model of a domino accident caused by the debris is obtained. Additionally, the influence of different fragment shapes on the domino accident probability in spherical tanks is analysed, and minimum penetration rate of the spherical-tank failure caused by different fragment masses is calculated. Subsequently, using statistics, the correlation between failure-probability and distance between spherical tanks and shape parameters was determined. The results indicate that the debris shape significantly influences the impact-depth of the spherical-tank wall, and impact-depth of the conical-nose geometry is significantly greater than that of the blunt-nose geometry. Moreover, the minimum velocity of the conical-nose geometry penetrating the target is significantly less than that of the blunt-nose geometry. The shape change of the conical-nose geometry has almost no influence on the probability of the domino accident, whereas, that of the blunt-nose geometry significantly influences the domino accident probability.

Theoretical Investigation on Failure Behavior of Ogive-Nose Projectile Subjected to Impact Loading.

Experimental and theoretical investigations on the failure behaviors of projectile during high-speed impact into concrete slabs were performed in this study. The ogive-nose projectiles after impact experiments were recovered and their microstructures were observed by scanning electron microscope and metallographic microscope. Mass abrasion and nose blunting are the typical failure models of steel projectile. Furthermore, thermal melting and cutting are the two main failure mechanisms. Based on the microscopic experimental results, a theoretical model of ogive-nose projectile subjected to impact loading considering the melting and cutting mechanisms was proposed. A modified cap model is introduced for describing the failure behavior of concrete targets, and then the dynamic cavity expansion theory is used to determine the resistance of projectiles during penetration. Besides, combining with the two-dimensional heat conduction equation and abrasive wear theory, the two main abrasion mechanisms of melting and cutting are included in the proposed model, which breaks through the framework of previous abrasion models with single abrasion mechanism. The predicted results of the present abrasion model are in good agreement with the experimental data, which indicates that the proposed model can effectively predict the failure behavior and penetration performance parameters of high-speed projectiles during penetration into concrete targets, such as mass loss, nose blunting, and depth of penetration.