Consolidation Test Results Research Articles

Experimental study on soil deformation caused by overexploitation of groundwater.

Due to the overexploitation of deep groundwater, the largest cone of depression in the world has formed in the North China Plain. This led to severe geological hazards, including land subsidence and ground fissures, and also caused economic losses. The prevention and treatment of subsidence needs to rely on the accurate prediction of subsidence amount. According to the one-dimensional consolidation theory and effective stress principle, combined with stratum structure, groundwater flow, stress distribution, and so forth, the high-pressure consolidation test results of 569.6m deep borehole soil samples are adopted; with a specific focus on stress and deformation parameters under exploitation of groundwater condition, the soil-water coupling prediction model of groundwater level lowering depth and land subsidence has been established. Verification with measured subsidence data near the study sites demonstrated that the predicted curve is consistent with the measured one and the differences between them are acceptable. The model can be applied in different areas after making adjustment based on different regional stratigraphic structures. Its key advantage lies in the ability to provide land subsidence prediction for areas lacking monitoring data, making it highly valuable for widespread application. PRACTITIONER POINTS: There is a compressible stratum structure; it is the internal factors of land subsidence. The groundwater level decline causes the soil body stress to change. It is land subsidence of the external factors. Based on the one-dimensional consolidation theory and by combining stratigraphic structures, groundwater flow, and stress distribution, a ground settlement prediction model was established.

Deep Learning Approach on Prediction of Soil Consolidation Characteristics

Artificial neural network models, crucial for accurate predictions, should be meticulously designed for specific problems using deep learning-based algorithms. In this study, we compare four distinct deep learning-based artificial neural network architectures to evaluate their performance in predicting soil consolidation characteristics. The consolidation features of fine-grained soil have a significant impact on the stability of structures, particularly in terms of long-term stability. Precise prediction of soil consolidation under planned structures is vital for effective foundation design. The compression index (Cc) is an important parameter used in predicting consolidation settlement in soils. Therefore, this study examines the use of deep learning techniques, which are types of artificial neural network algorithms with deep layers, in predicting compression index (Cc) in geotechnical engineering. Four neural network models with different architectures and hyperparameters were modeled and evaluated using performance metrics such as mean absolute percentage error (MAPE), mean squared error (MSE), root mean squared error (RMSE), and coefficient of determination (R2). The dataset contains 916 samples with variables such as natural water content (w), liquid limit (LL), plasticity index (PI), and compression index (Cc). This approach allows the results of soil consolidation tests to be seen more quickly at less cost, although predictively. The findings demonstrate that deep learning models are an effective tool in predicting consolidation of fine-grained soil and offering significant opportunities for applications in geotechnical engineering. This study contributes to a more accurate prediction of soil consolidation, which is critical for the long-term stability of structural designs.

High Temperature Effect on the Engineering Performance of Pumice Added Sand-Bentonite Mixtures

The surrounding soils at energy geo-structures must perform for a long time under high temperatures and thermal cycles. Engineering properties of soils are affected by temperature. Pumice is a thermally durable material and it may be used to increase thermal durability of soils. For this reason, it was aimed to develop thermally durable soil material by adding pumice additive to sand-bentonite mixtures. 10% and 20% pumice were added to 10% and 20% sand-bentonite mixtures and compaction, consolidation, direct shear and hydraulic conductivity tests were performed. The direct shear and hydraulic conductivity tests were performed both at room temperature and 80 °C. The consolidation test results showed that as pumice content increases the total vertical deformation decreased at room temperature. Pumice additive reduced the maximum shear stress values when temperature increased for 10B-90S mixtures. However, the pumice additive increased the internal friction angle of the mixtures at high temperature. It was observed that the hydraulic conductivity increased with increasing temperature. Thermal conductivity measurements showed that pumice additive reduced the thermal conductivity value of the mixtures.

Large-Strain Nonlinear Consolidation of Sand-Drained Foundations Considering Vacuum Preloading and the Variation in Radial Permeability Coefficient

The vacuum preloading method effectively strengthens soft soil foundations with vertical drainage, which produces a smear effect when laying sand drains. Meanwhile, the seepage of pore water and soil deformation during consolidation exhibit nonlinear characteristics. Therefore, based on Gibson’s 1D large-strain consolidation theory, this paper developed a more generalized large-strain radical consolidation model of sand-drained soft foundations under free-strain assumptions. In this system, the double logarithmic compression permeability relationships for soft soils with large-strain properties, the variation in the radical permeability coefficient in the smear zone, and the effect of the non-Darcy flow were all included. Then, the partial differential control equations were numerically solved by the finite difference method and validated with existing radical consolidation test results and derived analytical solutions. Finally, the influences of relevant model parameters on consolidation are discussed. The analysis shows that the greater the maximum dimensionless vacuum negative pressure P0, the faster the consolidation rate of sand-drained foundations. Meanwhile, the decrease in the negative pressure transfer coefficient k1 will result in a decreasing final settlement amount. Moreover, the consolidation rate of sand-drained foundations is slower considering the non-Darcy flow, but the final settlement is unaffected.

Analysis of long-term settlement of road embankment on peat ground during its service period

Roads on peat grounds are subject to stringent requirements in terms of controlling the residual settlement during their service period in order to minimize the post-construction maintenance work. This paper addresses the applicability of the Finite Element Method (FEM) by incorporating a time-dependent model for peats to an evaluation of the residual settlement. The applicability of isotach viscoplasticity, used to describe the peats’ behavior under variable-rate compression, was confirmed in laboratory tests. Long-term consolidation test results and a model simulation revealed the particular importance of two mechanisms in the residual settlement in peat grounds, namely, the stress-dependency of the coefficient of consolidation, cv, and the viscosity-induced secondary consolidation. A model peat ground, capturing these mechanisms, was implemented for the FEM and applied to a case history of a high-standard road construction in Hokkaido, Japan. The viscoplastic parameters determined from standard oedometer tests successfully reproduced the observed long-term settlement in a peat-dominated section of the expressway. The analysis was extended to address the settlement in the peat ground with the installation of prefabricated vertical drains (PVDs). The results indicate that the delayed primary consolidation due to the stress-induced cv reduction can be significantly alleviated, while the settlement arising from the secondary consolidation over a longer term is little affected by the PVDs. These insights point to the importance of untangling the two mechanisms of long-term settlement for the sake of making accurate predictions of the residual settlement in different time scales.

Case Study on Tunnel Settlement Calculations during Construction Considering Shield Disturbance

Shield construction in structural soft soils inevitably disturbs the soil around the tunnel leading to tunnel settlement instead of tunnel uplift due to soil unloading rebound during construction. In this paper, tunnel settlement prediction in structural soft soils during construction has been studied by adopting Oujiang Beikou shield tunnel as an example. Firstly, disturbance degree calculation method based on effective stress was introduced and the disturbance degree due to shield construction was numerically simulated. Secondly, combined with one-dimensional consolidation test results, a “two-fold line” settlement calculation model was developed for disturbed soil. Finally, tunnel settlement during construction was predicted through one-way compression layer-summation method and compared with experimentally measured results. Research results demonstrated that the developed method was suitable for the prediction of shield tunnel settlement in structural soft soils.

Compressibility Characteristics of an Organic Soil Treated with Fly Ash and Fly Ash-Based Geopolymer

Organic soils are problematic soil for various engineering applications due to their high compressibility and low shear strength which need to be improved. For many soil improvement techniques, using waste materials, such as fly ash (FA), is a practical and sustainable process. In this research, FA and geopolymer were used e used to reduce organic soil's compressibility. A one-dimensional consolidation test was performed to evaluate the organic soil's consolidation and compressibility properties. The geopolymer was prepared using 20% FA and of sodium hydroxide ratio and sodium silicate alkali solutions. The geopolymer specimens were first cured for 2 hours at 45 and 65 oC, then cured for further 28 days at room temperature. The consolidation test results showed that FA-based geopolymer is effective in stabilizing organic soils due to the observed improvement in the compressibility, consolidation, and permeability characteristics. The compression index decreased by 98.16%, and the permeability decreased by 95%.

Hydraulic conductivity test system for compacted, 2-mm-thick bentonite specimens

Both the design and safety assessment of radioactive waste disposal facilities demand an accurate evaluation of the hydraulic conductivity of the bentonite materials, especially compacted bentonite. For permeability tests of bentonite materials, the lengthy time necessary for specimen saturation and measurement may present a bottleneck. The permeability behavior of bentonite, such as the effects of the water quality and the exchangeable cations, has not been systematized sufficiently. For the present study, a hydraulic conductivity test system with 2-mm-thick specimens was developed. Its applicability was evaluated in terms of test accuracy. Six specimens of compacted Japanese sodium bentonite, with dry densities of 1.34–1.79 Mg/m3, were subjected to falling head hydraulic conductivity tests. The results showed that the hydraulic gradient set for this study did not affect the hydraulic conductivity, indicating that the macroscopic hydraulic behavior was consistent with Darcy's law. Furthermore, it was possible to reduce the test period considerably, by about one-tenth, compared to that using 10-mm-thick specimens. The obtained hydraulic conductivity was found to be similar to that in earlier studies. Furthermore, the values showed less variation particularly in terms of the consolidation test results. The results demonstrated that 2-mm-thick specimens are useful for hydraulic conductivity measurements of compacted bentonite.

Geotechnical properties of marine dredger fill with different particle size

To get a macroscopic understanding of the geotechnical engineering properties of typical marine dredger fill in coastal areas of Shandong Province, China, the mineral composition, particle size distribution, cation exchange capacity (CEC), consolidation characteristics, and strength characteristics of dredger fill in four regions, namely Rizhao, Dongying, Weifang, and Yantai, were studied and the correlation between typical indicators of dredger fills in different regions were analyzed. The results show that the difference in soil particle size distribution in Shandong province is related to the regional sedimentation type and dynamic effect and there is a significant correlation between some typical soil indicators. Vane shear strength test and consolidation test results show that the silt in Weifang has good drainage and shear strength indicating it is suitable as dredger fill. For the mucky clay in Rizhao, pharmaceutical vacuum preloading method is recommended to improve soil strength and the reasonable loading size should be less than 200 kPa. The purpose of this paper is to study typical geotechnical properties of four types of dredger fill, find and verify the correlation between some of geotechnical properties, to provide an objective scientific reference basis for the treatment of dredger fill in coastal area from the perspective of dredging and filling engineering.

Effect of Biopolymeric Stabilization on the Strength and Compressibility Characteristics of Cohesive Soil

Sustainable engineering discourages the use of conventional soil stabilizers such as lime and cement owing to their higher carbon emission rates. To address these challenges, many researchers considered biopolymer stabilization, a promising green technique in geotechnical engineering practice for treating expansive soils. This study evaluated the performance of two biopolymers, xanthan gum (XG) and guar gum (GG), in improving the unconfined compressive strength (UCS) and consolidation characteristics of an expansive soil subjected to different testing conditions. The dosage of the biopolymers (XG and GG) was maintained at 0.5%, 1%, 2%, and 4% by weight of dry mass of soil mass. Biopolymer treated samples were subjected to desiccator and natural curing conditions (i.e., specimens were exposed to different temperature and relative humidity conditions) for 7, 14, 28, 45, and 60 days. Results showed that the UCS of biopolymer-treated soil increased with increased dosage up to 2% and 1% for XG and GG, respectively; strength significantly improved during the first 28 days of curing under controlled conditions. Improvement of strength was due to increased adhesive strength between gum strands and soil particles. One-dimensional fixed-ring oedometer consolidation test results indicated that the compressibility and swelling characteristics of biopolymer-treated soil increased due to the hydrophilic nature of gum and an increase in the repulsive forces between negatively charged clay particles and the respective functional groups of XG and GG. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) were performed on both untreated and biopolymer-treated soil to evaluate the interaction mechanism between soil and biopolymer strands. The microlevel studies confirmed the crosslinking of soil particles by gum strands, which aids in the strength improvement.

Swelling and consolidation behaviour of polymerised bentonites with cation solutions

The objective of this study is to develop a novel method for producing polymerised bentonite (PB) that will have a high swelling capacity and low permeability when treated with aggressive cation solutions. PBs with polymer-to-bentonite ratios of 0.1 (0.1PB) and 0.2 (0.2PB) were produced using natural sodium bentonite (UB) and two monomers (acrylic acid (M 1) and acrylamide (M 2)) by a free-radical polymerisation method. The optimum conditions for polymerisation were an M 1/M 2 ratio of 0.5, initiator (I) to monomer I/(M 1 + M 2) ratio of 0.5% and a pH of 6. Instead of using nitrogen gas, a vacuum pressure was used to remove oxygen during the polymerisation process. The results of X-ray diffraction test showed that 0.2PB is an intercalated composite. The results of free swelling index (FSI) and swelling pressure tests indicated that the PBs have higher swelling capacities than UB (e.g. in 0.6 M sodium chloride (NaCl) solution, the FSIs of PBs were more than 24 ml/2 g). In terms of consolidation behaviours, the compression indexes of PBs were higher than those of UBs. For given void ratios, the permeabilities of PBs calculated from the results of consolidation tests were smaller than 10−10 m/s for 0.6 M sodium chloride solution.

Study on the Effect of Chemical Conditioning on the Consolidation Characteristics of Municipal Sludge in Landfill Depot

Vacuum preloading is one of the effective methods for in-situ dewatering and reduction treatment of municipal sludge landfill, but because the consolidation coefficient of municipal sludge is 1 or 2 orders of magnitude smaller than that of sludge, the drainage consolidation technology will face the problem of vacuum for too long. In order to improve the consolidation characteristics of sludge, combined with the chemical conditioning technology in the field of water treatment, firstly, the chemical conditioner suitable for landfill sludge was selected. The effects of different conditioning combinations on sludge dewatering characteristics were studied by microscopic testing techniques (zeta potential analysis and environmental scanning electron microscope analysis) and vacuum filtration test and consolidation test. The results show that the combination of ferric chloride and calcium oxide can significantly improve the dewatering characteristics of sludge. After conditioning with 10% ferric chloride and 10% calcium oxide (relative to sludge dry base), the specific resistance of sludge is reduced from 2 × 1013m/kg to 3 × 1012m / kg, and the consolidation coefficient is 3.5-10 times higher than that of original sludge, which lays a foundation for improving the efficiency of vacuum preloading treatment. In addition, from the results of vacuum filtration test and consolidation test of sludge, it can be found that there is a good negative linear relationship between specific resistance and consolidation coefficient of sludge. Compared with the consolidation test, the vacuum filtration test is simple and easy, so it can be used as an effective means to select sludge conditioner or test the conditioning effect.

Evaluation of Using Different Nanomaterials to Stabilize the Collapsible Loessial Soil

Construction over problematic soils is a common problem in many parts of the world, and one of the effective procedures to tackle this problem is soil stabilization. Accordingly, the current study provides the finding of a laboratory investigation into the effect of three kinds of nanomaterials, including nano-silica (NS), nano-clay (NC) and nano-calcium carbonate (NCC) on the properties of a loessial collapsible soil. To accomplish this issue, reconstituted samples of the stabilized loessial soil were prepared for unconfined compression and consolidation tests. The results illustrated that an insignificant amount of nanomaterials (less than 1% of the total dry weight of the soil when is used in as a liquid prepared solution) could considerably improve the mechanical behavior of the soil. The values of additives which gave the maximum unconfined compressive strength (UCS) were determined to be 0.1, 0.2, and 0.4% of the total dry weight of the soil, respectively, for NS, NCC, and NC. The most efficient improvement was the stabilized sample with 0.2% NCC which resulted in the highest UCS after 28 days of curing. In addition, the results of consolidation tests showed that the degree of collapse potential (CP) of the tested stabilized loess improved from moderately severe for unstabilized soil to moderate for all of the stabilized soils with different stabilizing agents. Hence, stabilization using these nanomaterials could partially improve the collapse potential of the tested loessial soil.

Mechanical and osmotic consolidation of geosynthetic clay liners: a laboratory study

This study aims to assess the effect of pore water salinity (sodium chloride (NaCL) solution) on the consolidation behaviour of GCLs (geosynthetic clay liners) using one-dimensional oedometer test apparatus. The experiments include two testing conditions: (1) an investigation of mechanical consolidation of GCL specimens saturated with water having different salinity levels, and (2) an investigation of the effect of pore water salinity on the volume change of GCL specimens under different constant vertical stress levels (i.e. osmotic consolidation). The mechanical consolidation test results indicated that the compression and swelling indices decrease as the liquid salinity increases, whereas an elastic hysteresis volume change behaviour was observed in the osmotic consolidation test results. The results of this study also show that the compression and swelling indices, and the hydraulic conductivity of a GCL specimen are almost reversible when it is subjected to an osmotic cycle.

Analytical solution for one-dimensional nonlinear consolidation of double-layered soil with improved continuous drainage boundary

Following the assumptions proposed by Davis and Raymond, an analytical solution for one-dimensional nonlinear consolidation of double-layered soil under constant loading is derived by introducing an improved continuous drainage boundary condition. The effectiveness of the present solution is assessed by comparing against other existing analytical solutions and laboratory consolidation test results. A parametric study is then conducted to investigate the consolidation behaviour of double-layered soil for different interface parameters or stress ratios (i.e. final effective pressure over initial effective pressure, Nσ ). The results show that, the average consolidation degree defined by soil settlement U s increases with the increase of N σ, and the average consolidation degree defined by excess pore water pressure U p decreases with the increase of Nσ . The magnitude of U s is always larger than U p, and the difference between U s and U p increases with the increase of Nσ . Compared with the Xie's solution, the stress ratio Nσ has little effect on U p in the solution with continuous drainage boundary condition.

Variation of swelling pressure, consolidation characteristics and hydraulic conductivity of two Indian bentonites due to electrolyte concentration

The hydro-mechanical properties of the buffer material play an important role in the design of deep geological repositories. This paper presents the effect of various electrolyte concentrations on swelling pressure, consolidation characteristics and hydraulic conductivity of two different Indian bentonites. Constant volume swelling pressure tests on compacted bentonite specimens as well as consolidation tests on saturated bentonite specimens were carried out by supplying 0, 0.1, 0.5 and 1.0 N NaCl and CaCl2 solutions. The change in morphology and microstructure of bentonite specimens were examined by Scanning Electron Microscope (SEM) and XRD analysis. The hydraulic conductivity was calculated based on consolidation test results. At a dry density of 1.4 Mg/m3 both swelling pressure and hydraulic conductivity of divalent bentonite were found to be approximately 2.9 and 7.3 times higher than that of monovalent bentonite when saturated with deionized water. The electrolyte solutions altered the morphology, microstructure and hydro-mechanical properties of the monovalent bentonite significantly; however, the effect was found to be negligible for divalent bentonite. An empirical equation is proposed to predict the hydraulic conductivity of the bentonites. A good correlation between experimental and predicted hydraulic conductivity of bentonites is obtained. The divalent bentonite was found to be better suitable engineered barrier material in the electrolyte environment, whereas monovalent bentonite was found preferable at low salinity conditions.

Mechanical properties of calcareous silts in a hydraulic fill island-reef

The mechanical characteristics of calcareous silt interlayers play an important role in the stability of island-reef foundations. Direct shear and consolidation tests were performed to study the relationship between the mechanical properties and the physical parameters of calcareous silt. Based on the consolidation test results and analysis of the settling examples, different calculation methods for soil settling were compared. The results show the following. (1) The relationship between the cohesion and water content of calcareous silt can be represented by an M-shaped curve. The water contents corresponding to the two peaks of the M-type curve increase with increasing dry density. (2) When the dry density is less than 1.33 g/cm3, increasing the density significantly improves the internal friction angle of calcareous silts. When the dry density of the calcareous silt is greater than 1.33 g/cm3, the internal friction angle is affected by both the dry density and the water content. (3) The shear strength decreases when the water content exceeds the optimum level. (4) The compressive modulus of calcareous silt is larger than that of terrigenous silt. Specifically, it decreases with decreasing dry density and increasing water content. (5) The stepwise loading method should be used to estimate the soil settling before fill engineering construction.

Comprehensive monolayer two-parameter isotherm and kinetic studies of thiamine adsorption on clay minerals: Experimental and modeling approaches

Abstract One of the main reasons for shale swelling is the interaction between the montmorillonite (Mt) and water molecules. Using shale inhibitors is a principal method for preventing shale swelling when drilling shale formations with water-based drilling fluids. In the present study, for the first time, thiamine is introduced as a new shale inhibitor and as an ecofriendly substance in water-based drilling muds. The adsorption amount of the shale inhibitor onto the shale formation is an important parameter affecting the performance of the shale inhibitor. In the present study, firstly, the adsorption of thiamine onto shale formation is investigated. Batch experiments were carried out to investigate the adsorption of thiamine on sodium bentonite. The critical micelle concentration (CMC) of thiamine in the aqueous solution was obtained as 2.3 g/L. Various isotherm and kinetic adsorption models have been fitted to the experimental data and the parameters of the models have been determined. Results showed that the Jovanovich isotherm adsorption model with squared correlation coefficient of R2 = 0.96 and pseudo-second order kinetic model with contribution of intraparticle diffusion can predict the adsorption of thiamine on montmorillonite. The inhibitory properties of thiamine were investigated by various dynamic tests such as particle size measurement, consolidation test, cutting dispersion test and dynamic linear swelling test. The particle size of clay in the presence of thiamine increased from 574 to 7920 nanometer (nm) in comparison with deionized water. The consolidation test results showed that in the presence of thiamine, the compression index decreases from 0.2681 to 0.2172 and the swelling index decreases from 0.0954 to 0.0389. In the presence of thiamine, the reduction in the indices is higher than that in the presence of potassium chloride. The results indicated that the amount of recovered shale cuttings in the presence of thiamine with the concentration of 10 g/L is larger by 24.19% and 7.41% in comparison with that in deionized water and potassium chloride, respectively. The linear swelling of thiamine is lower than the potassium chloride and deionized water. In addition, thiamine enjoyed marked morphological characteristics, elemental analysis and specific surface area revealed via scanning electron microscopy, energy dispersive X-ray and Brunauer-Emmett-Teller method. In addition, the artificial neural network (ANN) was used to model the adsorption experimental data. The developed ANN model with R2 = 0.97 is accurate enough to predict the kinetic adsorption behavior of thiamine onto montmorillonite. Hence, 10 g/L is the optimum and economical concentration of thiamine as the shale inhibitor. Based on the results obtained in this study, thiamine has a high potential to prevent swelling and hydration of water sensitive shale. Also, the results from this study are applicable in determining the optimum concentration of thiamine in drilling fluids and selecting the best shale inhibitor concentration in drilling operations.

Swell and compressibility characteristics of expansive clays in north Cyprus

Expansive clays in semi-arid regions are known as problematic soils especially for low weight civil structures. Volume change is a critical issue, therefore determining expansive clays and quantifying their expandability, retractility and strength is a major step to be considered in geotechnical engineering. This research provides a study on the behaviour of expansive clays done under different geotechnical laboratory experiments on four different types of expansive clayey soils brought from various areas in Northern Cyprus, aiming to prepare a soil-properties map in these regions. Fundamental assessments were performed for determining soil index properties. Swell and consolidation behaviours were determined using one-dimensional oedometer apparatus. The results showed that the rate of the expansiveness of sample the bentonitic clay samples were the highest for the predicted ultimate swell with expandability index categorized as very high. Also, these samples showed the largest compressibility upon the consolidation test results. The results obtained were used to construct a relationship between compression and plasticity Index.

Comparative Study of Compressibility and Deformation Properties of Silt Stabilized with Lime, Lime, and Cement, and SEU-2 Binder

The compressibility and deformation of stabilized silt are important engineering characteristics. In order to study the compressibility and deformation of silt stabilized with lime, lime and cement mixture (LC), and a self-developed binder named SEU-2, the one-dimensional consolidation tests were conducted on stabilized silt cured for 7, 28, and 90 days. Meanwhile, the consolidation-undrained triaxial shear (CU) tests were conducted on the lime-, LC-, and SEU-2-stabilized silts at 28 days of curing to study deformation behavior of stabilized silt. The one-dimensional consolidation test results showed that the SEU-2-stabilized silt had better anti-compressibility performance in comparison with lime- and LC-stabilized silt. The evolution of compression modulus of lime-, LC-, and SEU-2-stabilized silt with the binder dosage was related to curing time. The compressibility coefficient of 6% and 8% lime-, LC-, and 4% and 8% SEU-2 binder-stabilized silt decreased at first and then increased with the increase in curing time. The CU tests revealed that the deviatoric stress–axial strain curves of SEU-2-stabilized silt exhibited a more obvious strain-softening behavior in comparison with lime- and LC-stabilized silt. In addition, the internal friction angle, cohesion, and brittleness index of SEU-2-stabilized silt were larger than that of lime- and LC-stabilized silt, and SEU-2-stabilized silt had a better anti-compression performance.