Consolidation Ratio Research Articles

Elasto-plastic modeling of soft soil considering degradation of stiffness

The stiffness has a large influence on the behavior of soils. Its value is affected by some of the soils properties, such as the over consolidated ratio (OCR), the effective normal stress, and the plasticity index etc. In this paper, the numerical modeling of soft soils was carried out using an improved elasto-plastic S-clay1 model accounting for degradation of stiffness. The relation between the stiffness and the shear strain was established based on a large number of experimental data. The effects of strain-dependent stiffness of normally consolidated soils and over consolidated soils on the stress-strain behavior were studied through a comparison of the simulations with the experimental results of undrained triaxial compression tests. The results show that the behaviors of soils can be well predicted with the improved constitutive model, particularly before the peak stress.

Shear strength and compressibility behaviour of lime-treated organic clay

Apart from strength characteristics, a review of studies on the compressibility of lime-treated soils is equally important that influenced the stability of soil structures. Due to the fact that no study has been carried out, an investigation on the effects of humic acid on strength and compressibility behaviour of lime-stabilised organic clay is presented in this paper. Unconfined Compressive Strength (UCS) and oedometer tests were carried out at different curing periods of 7, 28 and 90 days. Consolidation data was analysed in terms of changes in void ratio (e), volumetric strain (ε1), compression index (Cc), and coefficient of consolidation (cv) which defines a soil's compressibility. The results showed a similar behaviour when compared to both tests. It can be conclude that the cementation bonding was associated with the fabric arrangement of soil structures.

The pore pressure model of cement soil under cyclic loading

The long-term settlement of soft soil under cyclic loading is significant, the reinforcement of cement soil can improve the dynamic characteristics of soft soil and reduce the settlement, so it has been widely applied in soft soil foundation treatment. Affected by the disturbance of metro shield tunnelling, the surrounding grout-strengthened soil possesses initial degree of consolidation and the variation pattern of pore pressure of cement soil is differentiated, which leads to differential settlement. Therefore, in this study, global digital system dynamic triaxial apparatus was used to simplify the dynamic loading of subway to biased sine wave, and the effect of initial degree of consolidation and cement ratio on the development pattern of pore pressure of cement soil was studied. Combining tests results and existing studies, pore pressure model incorporating the initial degree of consolidation, cement ratio and cyclic stress ratio was established. Results from this study showed that under cyclic load, the pore pressure increased dramatically at the early stage, then slowly and gradually became stable; the initial degree of consolidation affected the development of pore pressure to a certain extent: for specimens with low degree of consolidation, the pore pressure stabilised prior to others at high value; compared with remoulded soil, the increase in pore pressure of cement soil with a cement ratio of 15–20% was effectively reduced and so was the consolidation settlement after construction.

Automatic memory-based vertical elasticity and oversubscription on cloud platforms

Hypervisors and Operating Systems support vertical elasticity techniques such as memory ballooning to dynamically assign the memory of Virtual Machines (VMs). However, current Cloud Management Platforms (CMPs), such as OpenNebula or OpenStack, do not currently support dynamic vertical elasticity. This paper describes a system that integrates with the CMP to provide automatic vertical elasticity to adapt the memory size of the VMs to their current memory consumption, featuring live migration to prevent overload scenarios, without downtime for the VMs. This enables an enhanced VM-per-host consolidation ratio while maintaining the Quality of Service for VMs, since their memory is dynamically increased as necessary. The feasibility of the development is assessed via two case studies based on OpenNebula featuring (i) horizontal and vertical elastic virtual clusters on a production Grid infrastructure and (ii) elastic multi-tenant VMs that run Docker containers coupled with live migration techniques. The results show that memory oversubscription can be integrated on CMPs to deliver automatic memory management without severely impacting the performance of the VMs. This results in a memory management framework for on-premises Clouds that features live migration to safely enable transient oversubscription of physical resources in a CMP.

Micro-mechanical study of stress path and initial conditions in granular materials using DEM

The macroscale response of granular materials under different loading conditions stems from the alteration of micromechanical properties during loading. Previous studies have used either physical experiments or discrete element method simulations to explore the effect of initial conditions and stress path on granular materials. However, microscale studies are not sufficient, especially for various loading paths. We study micromechanics of granular materials using the stress-force-fabric (SFF) relationship for a better understanding of the behavior of granular materials. Triaxial compression and extension tests are conducted on samples containing 1000 spherical particles, with periodic boundaries, and the effect of initial porosity is studied. In the next step, using the SFF relationship, we study the effect of anisotropic consolidation ratio. In addition to providing an appropriate explanation for shear strength out of evolution of anisotropy coefficients, our results show that anisotropic consolidation does not affect the micromechanical properties of granular materials in a way to change mobilized friction angle of sample at failure point.

1D-consolidation analysis based on UH model considering time effect

The soil stress-strain relationship under 1D consolidation condition was derived from the unified hardening( UH) model considering time effect. Based on this,a governing differential equation of 1D consolidation was established,which could simultaneously describe the deformation behavior of both primary and secondary consolidation. The one direction drainage consolidation problem was analyzed by the differential method. Since there is the phenomenon of relaxation that the effective stress pressure near the impermeable layer would decrease during the initiation of loading,a formula that can reflect the decrease of effective stress by time was deduced. Then,numerical analysis of the influence of secondary consolidation parameter,over consolidation ratio and the consolidation and swelling index was made and the results prove the conclusion of the formula. Besides,the laboratory tests were used to confirm the numerical prediction results of the governing equation. Depending on the condition that when the primary consolidation was almost finished,the main deformation was produced by secondary consolidation,a relationship between average degree of consolidation and time was deduced,which could be used to predict the time when primary consolidation would be finished.

Dynamic Strength and Accumulated Plastic Strain Development Laws and Models of the Remolded Red Clay under Long-Term Cyclic Loads: Laboratory Test Results

Abstract The dynamic strength and accumulated plastic strain are two important parameters for evaluating the dynamic response of soil. As a special clay, the remolded red clay is often used as the high speed railway subgrade filling, but studies on its dynamic characteristics are few. For a thorough analysis of the suitability of the remolded red clay as the subgrade filling, a series of long-term cyclic load triaxial test under different load histories are carried out. Considering the influence of compactness, confining pressure, consolidation ratio, vibration frequency and dynamic load to the remolded red clay dynamic property, the tests obtain the development curves of the dynamic strength and accumulated plastic strain under different test conditions. Then, through curve fitting method, two different hyperbolic models respectively for the dynamic strength and accumulated plastic strain are built, which can match the test datum well. By applying the dynamic strength model, the critical dynamic strength of the remolded red clay are gained. Meanwhile, for providing basic datum and reference for relevant projects, all key parameters for the dynamic strength and accumulated plastic strain of the remolded red clay are given in the paper.

One dimensional thaw consolidation behaviors with periodical thermal boundaries

In this paper, one dimensional thaw consolidation behaviors with periodical thermal boundaries were studied. A new numerical simulation method was proposed to implement thaw consolidation calculation. Thaw consolidation tests were conducted to verify the validity of new proposed method. It was proved that the simulated data have a good agreement with tested results. Due to the influence of periodical thermal boundary, Thaw Consolidation Degree (TCD) changes periodically, which is the most significant difference from that of constant thermal boundary problems. At the same time, peak values of TCD in each freeze-thaw cycle decreases continuously with time and tends to be the value of TCD0 obtained from constant thermal boundary, which is equal to the corresponding average temperature of periodical thermal boundary. The attenuation process of TCD is proportionally related to thaw consolidation Ratio (R).

Proactively Breaking Large Pages to Improve Memory Overcommitment Performance in VMware ESXi

VMware ESXi leverages hardware support for MMU virtualization available in modern Intel/AMD CPUs. To optimize address translation performance when running on such CPUs, ESXi preferably uses host large pages (2MB in x86-64 systems) to back VM's guest memory. While using host large pages provides best performance when host has sufficient free memory, it increases host memory pressure and effectively defeats page sharing. Hence, the host is more likely to hit the point where ESXi has to reclaim VM memory through much more expensive techniques such as ballooning or host swapping. As a result, using host large pages may significantly hurt consolidation ratio. To deal with this problem, we propose a new host large page management policy that allows to: a) identify 'cold' large pages and break them even when host has plenty of free memory; b) break all large pages proactively when host free memory becomes scarce, but before the host starts ballooning or swapping; c) reclaim the small pages within the broken large pages through page sharing. With the new policy, the shareable small pages can be shared much earlier and the amount of memory that needs to be ballooned or swapped can be largely reduced when host memory pressure is high. We also propose an algorithm to dynamically adjust the page sharing rate when proactively breaking large pages using a VM large page shareability estimator for higher efficiency. Experimental results show that the proposed large page management policy can improve the performance of various workloads up to 2.1x by significantly reducing the amount of ballooned or swapped memory when host memory pressure is high. Applications still fully benefit from host large pages when memory pressure is low.

A Qualitative and Quantitative Analysis of Multi-core CPU Power and Performance Impact on Server Virtualization for Enterprise Cloud Data Centers

Cloud is an on demand service provisioning techniques uses virtualization as the underlying technology for managing and improving the utilization of data and computing center resources by server consolidation. Even though virtualization is a software technology, it has the effect of making hardware more important for high consolidation ratio. Performance and energy efficiency is one of the most important issues for large scale server systems in current and future cloud data centers. As improved performance is pushing the migration to multi core processors, this study does the analytic and simulation study of, multi core impact on server virtualization for new levels of performance and energy efficiency in cloud data centers. In this regard, the study develops the above described system model of virtualized server cluster and validate it for CPU core impact for performance and power consumption in terms of mean response time (mean delay) vs. offered cloud load. Analytic and simulation results show that multi core virtualized model yields the best results (smallest mean delays), over the single fat CPU processor (faster clock speed) for the diverse cloud workloads. For the given application, multi cores, by sharing the processing load improves overall system performance for all varying workload conditions; whereas, the fat single CPU model is only best suited for lighter loads. In addition, multi core processors don’t consume more power or generate more heat vs. a single-core processor, which gives users more processing power without the drawbacks typically associated with such increases. Therefore, cloud data centers today rely almost exclusively on multi core systems.

Discussion of ‘Soil creep effects on ground lateral deformation and pore water pressure under embankments’

Settlement analysis of field cases is normally studied based on parameters interpreted from laboratory samples influenced by varying degrees of sample disturbance. Such disturbance is more pronounced in natural soft clays and could significantly affect the engineering properties of the soil, e.g. the over consolidation ratio (OCR) and compressibility index (Cc). Hence, it is vital to understand the role of sample quality in relation to soil characterisation for long-term settlement analyses. In this work, this is numerically illustrated by use of a simple creep model along with realistic parameter selection. This work takes its starting point on critical discussion of the work presented by Fatahi et al. (2013) and uses the opportunity to further clarify some important aspects of settlement/creep analyses in light of sample quality and parameter interpretation valid for the corresponding constitutive model.

Analysis of Memory Ballooning Technique for Dynamic Memory Management of Virtual Machines (VMs)

Memory ballooning is dynamic memory management technique for virtual machines (VMs). Ballooning is a part of memory reclamation technique operations used by a hypervisor to allow the physical host system to retrieve unused memory from certain guest virtual machines (VMs) and share it with others. Memory ballooning allows the total amount of RAM required by guest VMs to exceed the amount of physical RAM available on the host. Memory overcommitment enables a higher consolidation ratio in a hypervisor. Using memory overcommitment, users can consolidate VMs on a physical machine such that physical resources are utilized in an optimal manner while delivering good performance. Hence memory reclamation is an integral component of memory overcommitment. In this paper, we address that the basic cause of memory that ballooning is memory overcommitment from using memory-intensive virtual machines. We compared to others reclamation technique and identify Cost Associate with Memory Ballooning in state of Memory Overcommitment. The objective of this paper is to analyse memory ballooning technique for dynamic memory management of VMs. For this analysis, VMware based virtualization software, e.g., ESXi Server, vCenter Server, vSphere Client are installed and configured on the Centre for Innovation and Technology (CIT) Lab, DIU; for monitor and analyze VM performance for memory ballooning technique. The performance of memory ballooning technique is evaluated with two different test cases. The purpose is to help users understand, how this technique impact the performance. Finally, we presents the throughput of heavy workload with different memory limits when using ballooning or swapping; and analyse VM performance issue for this technique.

Experimental Study on the Dynamic Characteristic of Soft Soil under Cyclic Loads

To study the change law of the dynamic characteristics of soft soil, particularly the inadequate bearing capacity of highway and railway roadbeds induced by traffic loads, the soft soil in Yingkou area was taken as the research object. A series of dynamic strength and dynamic modulus tests were performed under different dynamic stress amplitude amplitudes, consolidation ratios, confining pressures, dynamic stress amplitudes, consolidation confining pressures, consolidation ratios, vibration frequencies, soft soil dynamic strains, dynamic strengths, dynamic backbone curves, dynamic moduli, and dynamic damping ratios. The results show that (1) Yingkou soft soil has a significant structural property. A strain turning point was found in the εd-N and dynamic curves. The deformation of soil increases rapidly when the strain is larger than this turning point. (2) Dynamic strength increases as consolidation confining pressures increase, but the influence of consolidation ratio and vibration frequencies on soft soil dynamic strength is not limited to an increase or decrease. (3) The dynamic modulus increases as consolidation confining pressure, consolidation ratio, and vibration frequencies increase, whereas dynamic damping ratio decreases with increasing pressure and ratio but increases with increasing vibrational frequency. The above results provide a theoretical basis for studying the insufficient bearing capacity of highway and rail roadbeds caused by long-term cyclic loads.

Analysis of virtualized cloud server together with shared storage and estimation of consolidation ratio and TCO/ROI

Purpose – The physical server transition to virtualized infrastructure server have encountered crucial problems such as server consolidation, virtual machine (VM) performance, workload density, total cost of ownership (TCO), and return on investments (ROIs). In order to solve the problems mentioned above, the purpose of this paper is to perform the analysis of virtualized cloud server together with shared storage as well as the estimation of consolidation ratio and TCO/ROI in server virtualization. Design/methodology/approach – This paper introduces five distinct virtualized cloud computing servers (VCCSs), and provides the appropriate assessment to five well-known hypervisors built in VCCSs. The methodology the authors proposed in this paper will gives people an insight into the problem of physical server transition to virtualized infrastructure server. Findings – As a matter of fact, VM performance seems almost to achieve the same level, but the estimation of VM density and TCO/ROI are totally different among hypervisors. As a result, the authors have the recommendation to choose the hypervisor ESX server if you need a scheme with higher ROI and lower TCO. Alternatively, Proxmox VE would be the second choice if you like to save the initial investment at first and own a pretty well management interface at console. Research limitations/implications – In the performance analysis, instead of ESX 5.0, the authors adopted ESXi 5.0 that is free software, its function is limited, and does not have the full functionality of ESX server, such as: distributed resource scheduling, high availability, consolidated backup, fault tolerance, and disaster recovery. Moreover, this paper do not discuss the security problem on VCCS which is related to access control and cryptograph in VMs to be explored in the further work. Practical implications – In the process of virtualizing the network, ESX/ESXi has restrictions on the brand of the physical network card, only certain network cards can be detected by the VM. For instance: Intel and Broadcom network cards. The newer versions of ESXi 5.0.0 and above now support parts of Realtek series (Realtek 8186, Realtek 8169, and Realtek 8111E). Originality/value – How to precisely assess the hypervisor for server/desktop virtualization is also of hard question needed to deal with it crisply before deploying new IT with VCCS on site. The authors have utilized the VMware calculator and developed an approach to server/desktop consolidation, virtualization performance, VM density, TCO, and ROIs. As a result, in this paper the authors conducted a comprehensive approach to analyze five well-known hypervisors and will give the recommendation for IT manager to choose a right solution for server virtualization.

Thaw consolidation behaviours of embankments in permafrost regions with periodical temperature boundaries

A modified simulation method based on large strain thaw consolidation theory was proposed for the thaw consolidation behaviours of permafrost embankment. It was verified using monitored data that the new method has a good performance in simulating seasonal changes of thaw settlement. For permafrost embankment with different thermal and mechanical properties, the consolidation process in the post-thawed layer of top ground surface will accomplish during initial operating period. After that, thaw consolidation degree will decrease continuously. The decreasing rate of thaw consolidation degree (Dr) is proportional to thaw consolidation ratio (R) of deep permafrost layer. Regression analysis indicates that Dr is a power function of R.

Study on Static Strength of Aeolian Sand before and after Cyclic Loading

Aeolian sand is one commonly used subgrade filling in Xinjiang Oasis-desert region, engineering practices also proved its applicability as subgrade filling. In order to find the law of Aeolian sand subgrade static strength after cyclic loading, the paper studied the static strength of Aeolian sand before and after cyclic loading through the dynamic and static triaxial tests. It is concluded that the greater cyclic loading is, the more Aeolian sand static strength peak decreases. When cyclic loading is small, the bigger confining pressure and consolidation ratio are, the static strength peak increases more after cyclic loading. The bigger initial static deviator stress is, the more Aeolian sand static strength peak reduces. The frequency of cyclic loading has little effect on static strength. In order to keep the stability of low embankment, we should restrict overload , ensure subgrade and foundation consolidation adequately, at the same time using gravel or geosynthetic materials to package edge of roadbed, so as to increase confining pressure. The research results can provide reference for the design and construction of Aeolian sand low subgrade in Xinjiang Oasis-desert region.

Survival of 1737 lobectomy-tolerable patients who underwent limited resection for cStage IA non-small-cell lung cancer†

A precise preoperative diagnosis of 'very early' lung carcinoma may identify patients who can undergo curative surgery with limited resections. Data from a multi-institutional project were collected on 1737 patients who had undergone limited resections (segmentectomy or wedge resection) for T1N0M0 non-small-cell carcinomas. As it was expected, this study was predominantly including ground glass nodules. Computed tomography was used to obtain the ratio of consolidation to the maximal tumour diameter to determine invasive potential of the tumours. Overall and disease-free survivals and recurrence-free proportions were analysed. Median age was 64 years. Mean maximal diameter of the tumours was 1.4±0.5 cm. Overall and recurrence-free survivals after limited lung resection were 94.0 and 91.1% at 5 years, respectively. Recurrence-free proportions were 93.7% at 5 years. Unfavourable prognostic factors in overall survival were lymph node metastasis, interstitial pneumonia, male gender, older age, comorbidities (cardiac disease, diabetes etc.) and consolidation/tumour ratio (C/T)≤0.25. C/T≤0.25 predicted good outcomes especially in cT1aN0M0 disease. In a subclass analysis of cT1N0M0 squamous cell carcinomas, wedge resection was the only unfavourable prognostic factor in both overall and disease-free survivals. If the patient was 75 years old or younger and was judged fit for lobectomy, limited resection for cStage I non-small-cell lung cancer (NSCLC) showed excellent outcomes and was not inferior to the reported results of lobectomy for small-sized NSCLC. The carcinomas with C/T≤0.25 rarely recur and are especially good candidates for limited resection.

Influence of column yielding on degree of consolidation of soft foundations improved by deep mixed columns

Laboratory and field data showed that deep mixed (DM) columns accelerated the rate of consolidation of the soft foundations. Most analyses of consolidation of DM column-improved foundations so far have been based on the elastic theory. In reality, the DM columns may yield due to the stress concentration from the soft soil and its limited strength. The influence of column yielding on the degree of consolidation of the soft foundation improved by DM columns has not been well investigated. A three-dimensional mechanically and hydraulically-coupled numerical method was adopted in this study to investigate the degree of consolidation of the DM column foundation considering column yielding. A unit cell model was used, in which the soil was modeled as a linearly elastic material. For a comparison purpose, the DM column was modeled as an elastic or elastic-plastic material. This study examined the aspects of stress transfer, settlement, and degree of consolidation of the foundations without or with the consideration of the yielding of the DM column. A parametric study was conducted to investigate the influence of the column yielding on the stress concentration ratio, settlement, and average degree of consolidation of the DM column foundation. The stress concentration ratio increased and then decreased to reach a constant value with the increase of the column modulus and time. A simplified method was proposed to calculate the maximum stress concentration ratios under undrained and drained conditions considering the column yielding. The simplified method based on a composite foundation concept could conservatively estimate the consolidation settlement. An increase of the column modulus, area replacement ratio, and/or column permeability increased the rate of consolidation.

Dynamic shear modulus of undisturbed soil under different consolidation ratios and its effects on surface ground motion

The dynamic shear modulus for three types of undisturbed soil under different consolidation ratios is presented by using the resonant column test method. Its effects on surface ground motion is illustrated by calculation. The test results indicate that the power function is a suitable form for describing the relationship between the ratio of the maximum dynamic shear modulus due to anisotropic and isotropic consolidations and the increment of the consolidation ratio. When compared to sand, the increment of the maximum dynamic shear modulus for undisturbed soil due to anisotropic consolidation is much larger. Using a one-dimensional equivalent linearization method, the earthquake influence factor and the characteristic period of the surface acceleration are calculated for two soil layers subjected to several typical earthquake waves. The calculated results show that the difference in nonlinear properties due to different consolidation ratios is generally not very notable, but the degree of its influence on the surface acceleration spectrum is remarkable for the occurrence of strong earthquakes. When compared to isotropic consolidation, the consideration of actual anisotropic consolidation causes the characteristic period to decrease and the earthquake influence factor to increase.

Dynamic strength characteristics and failure criteria of anisotropically consolidated silt under principal stress rotation

In order to identify the critical properties and failure criteria of in-situ silt under vehicle or wave loading, anisotropically consolidated silt under undrained cyclic principal stress rotation was studied with hollow cylinder dynamic tests. The results show that for the slightly anisotropically consolidated samples with consolidation ratios no larger than 1.5, the structure collapses and the deviator strain and pore pressure increase sharply to fail after collapse. For the highly anisotropically consolidated samples with consolidation ratios larger than 1.5, the strain increases steadily to high values, which shows characteristics of ductile failure. 4% is suggested to be the threshold value of deviator stain to determine the occurrence of collapse. The normalized relationship between pore pressure and deviator strain can be correlated by a power function for all the anisotropically consolidated samples. Based on it, for the highly anisotropically consolidated samples, the appearance of inflection point on the power function curve is suggested to sign the failure. It can be predicted through the convex pore pressure at this point, whose ratio to the ultimate pore pressure is around linear with the consolidation ratio in spite of the dynamic shear stress level. And the corresponding deviator strain is between 3% and 6%. The strain failure criterion can also be adopted, but the limited value of stain should be determined according to engineering practice. As for the slightly anisotropically consolidated samples, the turning points appear after collapse. So, the failure is suggested to be defined with the occurrence of collapse and the collapse pore pressure can be predicted with the ultimate pore pressure and consolidation ratio.