Consolidation Characteristics Research Articles

Fully Coupled Model for One-Dimensional Large-Strain Consolidation and Heat Conduction in Saturated Clay

The consolidation characteristics of soils are affected by both mechanical loading and ambient temperature. However, research on this coupled theory is lacking. In this study, a fully coupled model for one-dimensional large-strain consolidation and heat conduction is established, where the influences of temperature on the physical-mechanical properties of saturated clay are considered. Based on the finite difference method, the numerical solutions for the coupled model are developed. Moreover, the correctness is validated by comparing the calculational results of the proposed model with those of the COMSOL simulation (a finite element software simulation) and the classical analytical solutions, respectively. Finally, the effects of different factors on consolidation behaviors are discussed. It is found that the increase in temperature increment ΔT generally accelerates the dissipation rate of excess pore-water pressure (EPWP) and increases the final settlement. The settlement is gradually reduced with an increasing effective yield stress σcR. A larger permeability coefficient kvr,R leads to an increasing EPWP dissipation rate. Furthermore, it is observed that the influence of σcR on the settlement is slightly enhanced with an increasing ΔT, while the effect of kvr,R on the dissipation rate of EPWP becomes less remarkable under a higher ΔT. In conclusion, the proposed coupled model can properly describe the large-strain consolidation behaviors of saturated clay when the effect of heat conduction is incorporated.

Destruction or protection? Experimental studies on the mechanism of biological soil crusts on the surfaces of earthen sites

Earthen sites are cultural and have rich historical significance. However, most earthen sites have been damaged or even destroyed during historic preservation. To reduce the damage caused by rain, snow erosion, freezing and thawing, these sites should be protected using vascular plant capping technology, which has great research value and application prospects. However, the effect of biological soil crusts (BSCs) on the shallow surfaces of these sites is scarcely understood. Therefore, this study aimed to explore the soil consolidation characteristics of BSCs on the shallow surfaces of earthen sites through laboratory experiments. First, the species, morphology and geometric characteristics of BSCs were studied using observation with a high–resolution digital microscope and analyses of the fractal and topological dimensions of rhizoids. The results showed that the dominant population of BSCs was composed of Didymodon vinealis, and the rhizoid type exhibited herringbone architecture. In addition, the effect of rhizoid anchoring was greater than that of rhizoid wedging. Second, the mechanical properties of the soil consolidation of the rhizoid–soil composite were investigated using tensile strength tests of single rhizoids and shear strength tests of rhizoid–soil composites. It was concluded that moss rhizoids could improve the shear strength of the surface soil. Additionally, the surface roughness of the rhizoids affected their anchorage characteristics. Finally, we discussed the disadvantages of generally classifying plants as “potentially harmful”, and emphasized the necessity of constructing a heterogeneous research model highlighting specific environmental factors, plants, and earthen sites.

Machine learning-based approach for predicting the consolidation characteristics of soft soil

In recent times, large-scale infrastructural projects are being constructed on varieties of soil, especially in highly compressible marine clays and soft soil. The coefficient of consolidation (cv ) is one of the most important technical parameters used to estimate the consolidation characteristics of the soil. The experimental laboratory techniques used to obtain cv are time-consuming and possess different practical limitations. In this study, a reliable method for predicting cv is presented based on machine learning (ML). The study considered 11 inherent soil variables, among which the least significant variables are discarded using univariate feature selection technique. Different ML models were developed like the random forest, artificial neural network, and support vector machine for nonlinear mapping of the cv using dimensionally reduced independent variables. Verification against experimental data demonstrates that the Random Forest model accurately predicts the cv (with MAE = 0.0231, MSE= 0.00148, and RMSE = 0.03854). Further, a comparative study of the proposed model is presented with available empirical equations and numerically simulated data. Moreover, the strengths and shortcomings of different ML algorithms are also discussed in detail.

Analytical Solutions for Radial Consolidation of Soft Ground Improved by Composite Piles Considering Time and Depth-Dependent Well Resistance

Composed of a stiffer core with gravel shell, composite pile is a new pile technology with a variety of shapes and sizes to improve soft soils. Compared with piles with single materials, composite ground improved by composite piles avoids some drawbacks with slow consolidation and limited increase in load bearing capacity. After converting unit cells with noncircular composite piles into cylindrical ones using an annular conversion method, based on an equal strain assumption and the hypothesis that water volumes flowing into and out of the gravel shell are equal, an analytical model is proposed to investigate consolidation characteristics of soft ground improved by composite piles. Furthermore, the hypothesis that the discharge capacity of the composite pile is exponentially decreased with time owing to clogging, and linearly varied with depth is employed in the derivation. In addition, detailed solutions subjected to an instantly applied load are obtained using a Bessel function, and the degeneration of this answer is calculated to verify its accuracy. Then, some comparisons between this method and previous studies including mathematical methods and a case are made to verify the feasibility and applicability of the presented solution. Finally, a parametric study is conducted to find detailed effects of time-dependent clogging and depth-dependent well resistance on consolidation. The results show that consolidation rate is proportional to B1, while it is negatively correlated with B2, α3, and H.

Investigating the Consolidation Behaviour of Cement-Bentonite Barrier Materials Containing PFA and GGBS

Cement-Bentonite (CB) barriers are expected to become a sustainable and reliable engineering solution. The deformation of CB is of interest to engineers to comprehend, particularly how CB responds to changes in loading during its construction and service life. The purpose of this study was to examine how samples of CB mixtures behaved during consolidation. This study investigated: (1) the influence of curing time and constituent materials on the consolidation properties of CB samples, (2) the volumetric change and the rate of volumetric change in response to a specific loading condition via consolidation tests. For this purpose, a laboratory consolidation test with a load range of 50 to 3200 kPa was carried out in accordance with BS 1377-7:1990 using the oedometer apparatus. This study discovered that the consolidation characteristics of CB samples are similar to those of overconsolidated soil. The CB sample became more resistant to consolidation under varying loads as curing progressed. The presence of more bentonite resulted in an increase in the recompression index. The inclusion of GGBS contributed to the consolidation characteristics of CB through the following mechanisms: (1) the significant decrease of the degree of consolidation with a curing period longer than 28 days, despite the slow strength development of the early-age curing; (2) the increase of the preconsolidation pressure; and the addition of GGBS was found to be more effective than the addition of more bentonite in increasing the preconsolidation pressure. Doi: 10.28991/CEJ-2023-09-03-02 Full Text: PDF

Modification of Highway Sub-Grade Black Cotton Soil by using Nano Chemical: Terrasil Mixed with Fly-Ash and Rice Husk Ash

Abstract: As the population grows daily, the amount of excellent, solid ground available for development decreases, necessitating the use of weaker or softer soil for the construction of buildings and other civil engineering projects. The building of structures built on the problematic broad black cotton soil is fraught with difficulties. It has poor geotechnical subgrade features, including swelling and imperviousness. In this study, an attempt is made to improve the different geotechnical characteristics of black cotton soil by mixing it with waste products like river sand, fly ash, and marble dust. These properties include index properties, swelling characteristics, consolidation characteristics, hydraulic conductivity characteristics, and strength characteristics. Due to the best possible use of these waste materials in the enhancement of various aspects of black cotton soil, these techniques therefore minimised the impact of waste materials on the environment. There are many different types of soil stabilisation, but typically, mechanical, and chemical stabilisation procedures are used to accomplish traditional soil stability. Stabilizers are the additives that are used to stabilise substances. For stabilisation, a variety of stabilisers are utilised, including fly ash, bitumen, rice husk, lime, cement, and other chemicals. When dry, black cotton soils are extremely hard; yet, when wet, they entirely lose their strength. Widespread issues with expansive soils provide a number of difficulties for civil engineers. Numerous techniques are used to enhance the expanding soils' engineering properties. The study's findings are summarised as follows. By raising the percentage of Terrasil and maintaining the values of rice husk ash and fly ash, which are 10% and 20% respectively, unchanged, the liquid limit percentage lowers by 0% to 0.08% and grows. When Terrasil is changed while leaving the values of rice husk ash and fly ash, which are 10% and 20% respectively, unchanged, the plastic limit percentage falls from 0% to 0.10 percent. When rice husk ash and fly ash are kept at their constant values of 10% and 20%, respectively, the plasticity percentage drops from 0% to 0.04% and then rises to a high of 0.06% at 30.07. The maximum value is reached before the optimal moisture content (OMC) first increases, then declines. achieved after 0.10% addition of Terrasil while maintaining the 10% and 20% values for rice husk ash and fly ash, respectively, and were equivalent to 27.64%. The compressive strength first increases and then decreases, the maximum value obtained was at 0.06% addition of Terrasil keeping constant value of rice husk ash and fly ash, i.e., 10% and 20% respectively, and were equal to 1.69 gm/cm2. The maximum dry density (MDD percentage) first increases up to 0.06% of Terrasil and then decreases.. The greatest value achieved was at 0.06% addition of Terrasil retaining constant value of rice husk ash and fly ash, i.e., 10% and 20% respectively, and were equal to 0.861kg/cm2. The shear strength initially increases and subsequently drops. As Terrasil's percentage rises while the amounts of fly ash and rice husk ash remain constant at 10% and 20%, respectively, the permeability commonly drops.

On-device synaptic memory consolidation using Fowler-Nordheim quantum-tunneling.

For artificial synapses whose strengths are assumed to be bounded and can only be updated with finite precision, achieving optimal memory consolidation using primitives from classical physics leads to synaptic models that are too complex to be scaled in-silico. Here we report that a relatively simple differential device that operates using the physics of Fowler-Nordheim (FN) quantum-mechanical tunneling can achieve tunable memory consolidation characteristics with different plasticity-stability trade-offs. A prototype FN-synapse array was fabricated in a standard silicon process and was used to verify the optimal memory consolidation characteristics and used for estimating the parameters of an FN-synapse analytical model. The analytical model was then used for large-scale memory consolidation and continual learning experiments. We show that compared to other physical implementations of synapses for memory consolidation, the operation of the FN-synapse is near-optimal in terms of the synaptic lifetime and the consolidation properties. We also demonstrate that a network comprising FN-synapses outperforms a comparable elastic weight consolidation (EWC) network for some benchmark continual learning tasks. With an energy footprint of femtojoules per synaptic update, we believe that the proposed FN-synapse provides an ultra-energy-efficient approach for implementing both synaptic memory consolidation and continual learning on a physical device.

A Study on the Consolidation Characteristics of Sleep on Memory of Different Intensity

A Study on the Consolidation Characteristics of Sleep on Memory of Different Intensity

Numerical Simulation of Vacuum Preloading for Chemically Conditioned Municipal Sludge

Municipal sludge is a sedimentation waste produced during the wastewater process in sewage treatment plants. Among recent studies, pilot and field tests showed that chemical conditioning combined with vacuum preloading can effectively treat municipal sludge. To further understand the drainage and consolidation characteristics of the conditioning sludge during vacuum preloading, a large deformation nonlinear numerical simulation model based on the equal strain condition was developed to simulate and analyze the pilot and field tests, whereas the simulation results were not satisfactory. The results of the numerical analysis of the pilot test showed that the predicted consolidation degree was greater than that measured by the field tests, which is attributed to the relatively low permeability layer formed during the preloading process of the prefabricated vertical drain. To better reflect the consolidation process of the conditioned sludge, a simplified analysis method considering the low permeability layer around the prefabricated vertical drain was proposed. The initial permeability coefficient of the low permeability layer is determined via numerical simulations using finite difference method. The predicted settlement curve was in good agreement with the measured results, which indicated that the numerical simulation based on the equal strain condition considering the relatively low permeability layer can better analyze the consolidation process of ferric chloride-conditioning sludge with vacuum preloading.

Geotechnical performance of combined stone columns and piles capped with reinforced concrete raft foundation in soft clay soil

Stone columns consist of granular material compacted in long cylindrical holes. They are used for improving the strength and consolidation characteristics of compressible soils. However, they are still less effective at supporting heavy loads, since they still cannot transfer applied stresses to deeper layers of soil. The main objective of this numerical study was to investigate the geotechnical performance of a combined foundation system composed of stone columns and piles grouped together under a rigid raft foundation in compressible soil. The failure mechanism of this hybrid foundation system was examined, and configurations optimizing the performance of the combined foundation system were explored. An analytical model was developed for predicting the ultimate carrying capacity of the combined system in compressible soils. It was deduced that combining stone columns and piles in one foundation system improved considerably the system’s carrying capacity. Moreover, the uppermost improvement was observed when the piles were installed on the periphery or edge of the raft foundation, while stones columns were placed at the center area of the raft. The failure of the combined foundation system started from the center of the raft and noticeably extended to its edges. Due to the presence of stone columns in the combined foundation system, the piles did not interact. The areas affected or influenced by the soil–pile interaction also did not overlap.

Consolidation calculation of a foundation partially penetrated by concrete‐cored gravel (CCG) columns

AbstractA concrete‐cored gravel (CCG) column is composed of a precast concrete pile inserted at the center of sand or gravel materials. This technique has been experimentally adopted to support the soft soils in China. However, there has been limited investigation on the consolidation characteristics of a CCG column improved foundation under embankment loading. This study develops analytical solutions for the consolidation of a composite foundation partially penetrated by the CCG columns. The rigid pile's upward and downward piercing effects were considered to improve CCG column‐soil equal strain relationship. The partially penetrated consolidation problem was addressed by assuming the seepages in the unpenetrated layers to be vertical or horizontal and vertical combined. A simplified approximate method was also provided, enabling the users to quickly evaluate the consolidation process of a foundation partially penetrated by the CCG columns. The proposed solution was applied to a case history of an anti‐flood embankment on soft soil with partially‐penetrated CCG columns, and a good agreement was found between predictions and the field measurements.

Secondary consolidation characteristics of organic soil modified by bio-enzyme based on the Gibson model

In order to study the secondary consolidation characteristics of organic soil improved by bio-enzyme, the secondary consolidation test was carried out. First, the Gibson rheological model parameters were fitted according to the experimental results. Then, the relationship between rheological model parameters, Ca/Cc value, secondary consolidation coefficient Ca, and load was analyzed for different ratios of bio-enzyme. The results showed that: 1) the rheological model parameters were negatively correlated with the ratios of bio-enzyme and positively correlated with the load value. The rheological model parameters E1 (Kelvin elastic modulus) and η (Kelvin viscosity coefficient) reached the maximum value when the ratio of bio-enzyme was 0.01%. 2) The secondary consolidation coefficient was related to the load and showed a certain law. At 100 kPa, the secondary consolidation coefficient of samples reached the peak. When it was less than 200 kPa, the secondary consolidation coefficient changed obviously with the increase in load. When the load was greater than 200 kPa, the variation trend of the secondary consolidation coefficient tended to be gentle with the increase in load and finally tended to be constant. With the increase in load, the secondary consolidation coefficient Ca finally approached to a stable value. 3) The value of Ca/Cc of improved organic soil varied from 0.042 to 0.1 under various loads. In this article, the secondary consolidation characteristics of organic soil modified by bio-enzyme were studied. The secondary consolidation strain can be predicted by the established rheological model parameter equations.

Experimental study on consolidation characteristics of deep clayey soil in a typical subsidence area of the North China Plain

Land subsidence is an important environmental problem in the North China Plain (NCP). A typical subsidence area mainly located on adjoining areas of Beijing and Hebei provinces was selected to study the consolidation characteristics of deep clayey soil. Clay samples were collected from 14 boreholes at different depths, and the compression and consolidation behavior of the soil was analyzed by high-pressure oedometer tests. Results show that the deformation amount and deformation stabilization time in the primary consolidation stage increase with the load but decrease with the sampling depth. The nonlinear compression model of e-log(p) does not fit well for deep normally-consolidated clayey soil, the log(e+ec)–logp model fit the shallow clayey soil better than the deep clayey soil, and the hyperbolic model fits almost all soil samples well. Based on statistical theory, the soil consolidation equation CE_NCP was established for calculating the relationship between the degree of consolidation and the time factor in subsidence areas. The equations were fitted with the data obtained from high-pressure consolidation tests to obtain three parameters a, b and c, which are applied to the consolidation calculations for soil samples at depths of 0–100 m, 100–200 m, 200–300 m and 300–400 m, respectively. The applicability of CE_NCP equation was evaluated by comparing it to the analytical solution of Terzaghi’s consolidation equation, results showing that CE_NCP equation is more suitable for the calculation of the consolidation in the study area than the Terzaghi’s analytical solution. Eventually, the CE_NCP equation was successfully used to estimate the degree of consolidation in a subsidence area of Lang Fang City in the NCP.

Simplified mathematical modeling to plane strain consolidation considering unsaturated and saturated conditions for ground with anisotropic permeability

Road embankment where the unsaturated soil layer lies above the saturated soil layer is often encountered in geotechnical engineering, but the analytical models for evaluating the plane stain consolidation characteristics of an unsaturated–saturated ground are limited. With a combination of the consolidation theories for saturated and unsaturated soils, this paper thus develops a plane strain consolidation model for exploring the transient behavior of unsaturated–saturated soils subjected to instantaneous loading. A semi-analytical solution, which is a simple tool for assessing unsaturated–saturated soil consolidation, is proposed by making use of decoupling strategy, Fourier expansion as well as Laplace transformation. Further, the proposed solution in this paper is validated by the published analytical or semi-analytical solutions in some specific cases. By implementing the proposed solution into a computation, the consolidation behavior of an unsaturated–saturated subgrade is presented, and the effects of important factors, including the anisotropic permeability ratio and interlayer permeability ratio, are studied. The anisotropic permeability ratio and interlayer permeability ratio are significant indexes to change the consolidation rate of lower soils so that the prefabrication of lateral drainage boundary on both sides of the unsaturated–saturated subgrade would accelerate its consolidation.

Consolidation Assessment of Marine Clay Using Electrokinetic Coupled with Constant Load

In Marine clays, the consolidation phenomenon is a significant issue of concern. For this, an innovative electrokinetic consolidation method was adopted by coupling the conventional consolidation technique with a constant voltage gradient. A series of tests were performed on reconstituted marine clay samples for constant loading intensity of 4kg/cm² coupled with a constant DC voltage of 2, 4 and 6V. Various parameters such as deformation, void ratio, current, pH, voltage and moisture content were continuously monitored to compare with test results of conventional Incremental loading (IL) and constant loading (CL) techniques. In the case of electrokinetic (EK) coupled loading, with an increase in voltage gradient, the values obtained for voltage and current were also increased to maximum and then decreased afterwards. Microfabric changes were also visible in soils collected at anode and cathode, which were evidenced with the images of scanning electron microscopy (SEM) data obtained before and after EK consolidation tests when compared with original marine clay. The constant loading intensity of 4kg/cm² with a 4V electric gradient resulted in higher compression and better consolidation characteristics than other loading conditions.

GEOMETRY ASSESSMENT ON THE SLOPE STABILITY OF MANYAR POND

Lateritic soil was treated with 0%, 4%, 8%, 12%, and 16% Rice Husk Ash (RHA) by dry soil weight to determine its consolidation properties. Test carried out include particle size distribution, specific gravity, compaction test with varying compactive efforts (British Standard Light (BSL), West African Standard (WAS) as well as British Standard Heavy (BSH)) and consolidation test. Samples for consolidation test were compacted and then cured for 7, 28 and 56 days; then subjected to one dimensional consolidation testing to observe the influence of curing period and compactive effort on its consolidation characteristics. Index tests showed improved geotechnical properties. The Maximum Dry Density (MDD) for BSL compaction decreased with a rise in RHA content from 1.72 to 1.42 Mg/m3 while optimum moisture content (OMC) increased from 16.5% to 27.3% with rise in RHA doses from 0% up to 16%. Similar trend was observed for WAS and BSH energies. Pre-consolidation pressure rise with increment in RHA content and also with increase in both compactive efforts and curing period with few exceptions. At 12% RHA content, Pre-consolidation pressure increased from 65 to 66.5 kN/m2 at 7 days and 56 days respectively. Increase in RHA content caused a decrease in Compression Index and Swelling Index. Compression Index also decreased with increase in both compactive efforts and curing period. There was no observed trend in the Swell Index with curing period. As the compactive efforts increased, the swell index decreased. The RHA reduced the Coefficient of Volume Compressibility (Mv) and the Coefficient of Consolidation (Cc). Curing period and compactive effort have no effect on Mv and Cc. Based on the results obtained, curing period at least 28 days using up to 12% RHA compacted at energy level of BSH improved the properties of the treated soil and can be used for geotechnical engineering applications like embankment or rural roads.

Consolidation Characteristics of Surface Soil Deposits in Kuwait

Understanding the characteristics of arid surface soil deposits leads to increasing the confidence level before stabilizing and to applying such materials in the field. Two types of surface soil deposits in Kuwait, sabkha soil and dune sand, have been examined by series of intensive laboratory testing reported in this paper. The chemical, the physical, and the compressibility characteristics of the two soils have been examined and evaluated. A single oedometer test has been carried out in order to obtain the compressibility characteristics and the collapse behavior. This paper has concluded that the samples from sabkha soil have a lower initial void ratio than the samples from dune sands. The lower compressibility parameters values of surface soil deposits and slightly higher collapsibility values of sabkha soils are encouraging that surface soil deposits can be used for construction purposes after the suitable stabilizing technique. Despite their low compressibility, the stabilizing of arid soils should concentrate on reducing salts’ dissolution in these soils during saturation.

Theoretical analysis and experimental verification of large deformation electro-osmosis consolidation treatment of dredged slurry

Electro-osmosis (EO) can be used to rapidly treat large areas of dredged slurry. At present, the theory of electro-osmosis consolidation (EOC) needs to be further developed to fit actual dredged slurry treatment scenarios. In this study, governing equations of EOC considering the large deformation constitutive relationship were derived with excess pore water pressure (EPWP) as a variable, and a concise EOC model was established for dredged slurry. Together with boundary conditions and initial conditions, the numerical method was adopted to obtain the finite difference solution for the EOC model. Then, EO experiments with different voltage stages were conducted using a self-designed and large-diameter EOC device, where the variations in current, drainage volume, EPWP, water content and vane shear strength were measured. Moreover, the phenomena of soil cracks, heat release, and electrode corrosion as well as the formation of Fe(OH)3 were recorded during the EO process. Additionally, nonlinear variation laws for effective stress, hydraulic permeability coefficient (HPC) and electro-osmosis permeability coefficient (EOPC) with void ratio of dredged slurry were obtained through indoor tests, in which a self-designed device for testing EOPC was used. Finally, the correctness of the proposed EOC model was verified by comparison with the results of the experiments and Esrig's analytical solution considering the small-strain constitutive relationship, where the consolidation characteristics were analyzed. In conclusion, the large deformation EOC model deduced in this paper could provide a more accurate prediction of the consolidation behavior of dredged slurry.

Characteristics of Elastoplastic Consolidation by Compaction and Its Effects on Coal Permeability

This paper presents a combined experimental–analytical investigation of coal strain development under fluctuating applied hydrostatic stress. The laboratory setup mimics the isotropic volumetric compaction of coal under burial–uplift cycles in the absence of tectonic stress. Special emphasis is placed on the corresponding permeability evolution of the coal strata. Our results show that the stress–strain path is exponential, approaching a linear relation in the logarithmic stress–strain space with the monotonic increase in stress. A similar behavior is found for the strain–permeability path in the logarithmic strain–permeability space. The permeability recovery undergoes hysteresis with respect to the stress in a stress loading–unloading cycle, but the hysteresis is not manifest with respect to the strain. A theoretical geomechanical consolidation analysis was performed using an elastoplastic modelling framework. The analysis suggests that plastic strain is the cause of the hysteresis of the strain recovery in a stress loading–unloading cycle. The closed hysteresis loops manifested in stress loading–unloading–reloading cycles are promoted by the plastic strain during stress unloading and the difference in evolution rates of the elastic core between loading and unloading. The results of this study are helpful for understanding the mechanism of permeability evolution and optimizing water and coal seam gas production.

Crustacean polysaccharides for the geotechnical enhancement of organic silt: A clean and green alternative

Biopolymer-based soil stabilization offers a clean alternative to conventional stabilizers like cement and lime. This study investigates the possibility of using shrimp-based chitin and chitosan for stabilizing low plastic silt with organic content by investigating their effect on pH, compaction, strength, hydraulic conductivity (HC) and consolidation characteristics. X-ray diffraction (XRD) spectrum shows that no new chemical compounds were formed in the soil on additive treatment; however, results of scanning electron microscope (SEM) analysis indicate the formation of biopolymer threads that bridge the voids in the soil matrix leading to a stiffer soil matrix, with increased strength and lower HC. Chitosan showed nearly 103 % strength enhancement after 28 d of curing with no degradation. However, chitin failed as a soil stabilizing additive as it showed degradation owing to fungal bloom after 14 d of curing. Chitosan can therefore be recommended as a non-polluting and sustainable soil additive.