Sand-clay Mixtures Research Articles

Shear strength characteristics of a sand clay liner

This study investigated shear strength behaviour of compacted sand–clay mixtures used as liners, with 10%, 20%, and 30% clay contents. A natural high-plasticity and highly expansive clay found in the eastern province of Saudi Arabia was used. A series of consolidated undrained triaxial tests and pore water pressure measurements of saturated samples with various clay contents and confining pressures was conducted using a computer-controlled Bishop and Wesley triaxial cell. The unit was equipped with pressure volume controllers and a pressure transducer for measuring sample volume changes and excess pore water pressure. The experimental test results indicate that clay content and confining pressure significantly affect stress strain response curves, pore water pressure generation curves, and steady-state shear strength. Sand–clay mixtures with clay content less than 10% showed a tendency toward contractive behaviour. The failure line slope increased in accordance with clay content increase. The deviator stress versus axial strain of saturated sand–clay mixtures indicated a hyperbolic trend. The stress ratio versus axial strain representation was more informative for the shear strength behaviour assessment. Clay content did not significantly affect critical-state friction angle. Scanning electron microscope images of the sand-clay mixtures with different clay contents are presented.

Pengaruh Penambahan Semen Sebagai Bahan Stabilisasi Tanah Terhadap Kecepatan Permeabilitas Pada Tanah Pasir Kelempungan

Sand loamy soil is often used as construction material for buildings and highways. The disadvantages of this soil are low density and high permeability that can reduce the quality ofroad construction. One way to improve thequality of the soil is to stabilize it with cement added material. This study aims to determine how much the velocity of permeability of subgrade and to the addition of the Portland Cement Composite (PCC) mixture with variationsof 2%, 4%, and 6%. Calculation analysis method uses SNI M.22-1990-F. From the permeability test with the variation of native soil without cement mixture, the coefficient value is 10.025 cm/hour, with the addition of 2% cement the coefficient value is 7, 132 cm / hour, the addition of 4% cement is obtained coefficient of 6.245 cm /hour, the addition of 6% a value of 5.208 cm / hour was obtained. So it can be concluded that along with the increase in cement content for the clay sand mixture, the coefficient value is getting smaller

Research on microstructure properties of clay-sand mixtures studied by ipp and mip methods

The clay-sand mixtures with diferent partcle sizes were prepared to investgate partcle and pore characteristcs. The microstructure characteristcs of the sand-clay mixtures were studied by the Mercury Intrusion Porosimetry (MIP) test and Scanning Electron Microscopy (SEM). Image-Pro Plus (IPP) image processing sofware was used to quantfy SEM images which investgated the micro-mechanism of structural evoluton of mixtures under diferent gradatons. The research results indicate that the units of mixtures develop from platelets and honeycomb to agglomerated and granular with the increase of sand content. The contact between partcles transits from face-face contacts to edge-face and pointface contacts. This artcle evaluated the fractal characteristc of partcle and pore structure based on the fractal theory. With the increase Circularity of the partcles, the ordered arrangement of the partcles in the mixed soil is further reduced. In general, the distributon of pores changes from intergranular pores to pores in aggregate, which provides a theoretcal basis for further study on the micro-macro correlaton of mixtures.

Observations and findings on mechanical and plasticity behavior of sand-clay mixtures

This paper presents effects of particle size distribution and plasticity on geotechnical properties of sand-clay mixtures. Two different clay types (kaolinite and bentonite) were mixed with different-sized clean sand at mixture ratios of 0 to 100% with increasing 10% by dry weight. An intensive series of standard compaction, Casagrande, fall cone, and plastic limit (wP) tests were performed on specimens. Experimental results showed that the maximum dry density (ρdmax) values of the mixtures increased up to 10% clay content (threshold clay content) then decreased with increasing clay content. Besides, optimum water content (ωopt) values of the mixtures decreased up to around 10–20% of clay content and then increased continuously. It was found that fall cone liquid limits were 2–4% higher than obtained from the Casagrande device. The undrained shear strength at liquid limit is approximately 2.19 kPa, but, though the undrained shear strength at plastic limit has a wide range in comparison with liquid limit (17–636 kPa), as its recommended value, 143.95 kPa was proposed by the researchers. Moreover, results also reveal that consistency limits of specimens are governed by the content and type of clay and grain size distribution of the sand-clay mixtures. Finally, some equations were proposed between various findings (i.e., optimum water content-maximum dry density, plasticity index (PI)-optimum water content, undrained shear strength (Su)-liquid limit (wL)) that were derived from the test results.

Relating shaft friction of buried piles and CPT resistance in clayey sands

This paper examines factors controlling the ultimate shaft friction developed on buried piles in normally consolidated clay–sand mixtures and explores the relationship between this friction and the cone penetration test (CPT) end resistance. Results from tension load tests on buried piles in a laboratory pressure chamber and geotechnical centrifuge are presented. Variable rate CPTs combined with Rowe cell, undrained simple shear and interface direct shear tests are used to characterise the mixtures. It is shown that the measured drained CPT end resistances could be predicted using parameters assessed from the laboratory tests and a simple expression derived from cavity expansion theory in an elastic Mohr–Coulomb soil. The tension pile tests indicate how changes in radial effective stresses during loading can be inferred from interface shear tests and these combined with the cavity expansion analysis allow derivation of a relationship between shaft friction (τf) and CPT end resistance (qt). This expression reveals the significant effects on the qt/τf(= βc) ratio of soil stiffness, stress level, dilation and drainage during cone penetration and is shown to be consistent with a recently proposed empirical formula for bored piles.

Physicochemical changes of lead(II) contaminated sand–clay mixture

In this study, the influence of lead nitrate as a hazardous environmental pollutant was studied through experimental tests to assess its physicochemical effects in soils. Artificially contaminated soil specimens were prepared using sand and two kinds of clays. Direct shear, consolidation, electrical resistivity and unconfined compression tests were conducted. In addition, the influence of lead cation on atterberg limits, pH and particle size distribution of soils was evaluated. Overall, the presence of lead ion in mixtures including bentonite increased the shear strength due to a flocculated structure and replacement of sodium cations by hydrogen ions which is along with the reduction of double-layer thickness. However, due to the broken bonds and rearranging of kaolinite particles to a weaker form, the strength of sand–kaolinite mixtures decreased with the increase of lead concentration. Based on the obtained results, with the addition of lead concentration, the compression index and electrical resistivity of all specimens decreased. Due to the acidic nature of positively charged lead cations, pH of the specimens directly affected and tended to a more acidic range. These findings indicate that the presence of lead ion improves the strength of some kinds of soils including bentonite and decreases the strength parameters of soils with kaolinite.

Effect of Adding Sand on Clayey Soil Compressibility

The effect of adding sand on clayey soil compressibility is investigated in this study. Four different percentage of clay-sand mixtures are used; 100% clay with 0% sand named 100C, 30% clay with 70% sand named 30C-70S, 15% clay with 85% sand named 15C-85S, and 100% sand named 100S. The used clay was obtained from Baghdad city in Iraq and classified as CH soil, while the used sand was taken from the sand quarry in Al-Khider area from Al-Muthana Governorate in Iraq and classified as SW soil. The initial dry unit weight for all mixtures is 18 kN/m3. The results show that the variations of the soil compressibility properties with soil components content changes almost linearly The results show that the preconsolidation stress (Pc) decreases with 19% and 38% and the rebound index (Cr) decreases with 4 and 53% and the compression index (Cc) decreases with 39 and 68% as the sand percentage increases with 70 and 85% respectively. Finally, predicted (fitting) Equations are achieved for the change of the soil compressibility properties with clay content with good agreement.

Experimental insights into consolidation rates during one-dimensional loading with special reference to excess pore water pressure

Consolidation rate has significant influence on the settlement of structures founded on soft fine-grained soil. This paper presents the results of a series of small-scale and large-scale Rowe cell consolidation tests with pore water pressure measurements to investigate the factors affecting the consolidation process. Permeability and creep/resistance structure factors were considered as the governing factors. Intact and reconstituted marine clay from the Polish Carpathian Foredeep basin as well as clay–sand mixtures was examined in the present study. The fundamental relationship correlating consolidation degrees based on compression and pore water pressure was assessed to indicate the nonlinear soil behaviour. It was observed that the instantaneous consolidation parameters vary as the process progresses. The instantaneous coefficient of consolidation first drastically increases or decreases with increase in the degree of consolidation and stabilises in the middle stage of the consolidation; it then decreases significantly due to viscoplastic effects occurring in the soil structure. Based on the characteristics of the relationship between coefficient of consolidation and degree of dissipation at the base, the consolidation range that complies with theoretical assumptions was established. Furthermore, the influence of coarser fraction in clay–sand mixtures in controlling the consolidation rates is discussed.

Microscale analysis to characterize effects of water content on the strength of cement-stabilized sand–clay mixtures

Cement stabilization is a useful and widely adopted method to improve the engineering properties of soils. However, characterization of the unconfined compressive strength, a simple and useful design property, is not straightforward due to complex interactions of various influence factors. This study investigated the effects of water content on the unconfined compressive strength of cement-stabilized clayey sands. The results show that the strength of the cemented binary mixtures increases with water content and water-to-cement ratio until a threshold value is reached and then decreases with further increase in water content and water-to-cement ratio. The unconfined compressive strength is correlated with ultrasonic wave velocity and shear wave velocity, respectively, showing two nearly unique correlations. Microscale analysis based on the coated sphere model revealed that the strength of the sample is affected by the bonding area and the strength of the binder material (cement–clay mixture). An empirical equation is also proposed based on the microscale analysis so as to capture the effects of water content on the strength.

Exploring implication of variation in biochar production on geotechnical properties of soil

Biochar produced from the pyrolysis of plant-based feedstock has been advocated as an alternative soil amendment for landfill cover. Previous literature indicated that the pyrolysis temperature influences the intra-pore distribution and surface functional groups (especially hydroxyl groups), resulting in “love-hate relationship” of the biochar-amended soil (BAS) with water. From the purview of geotechnical engineering, the effects of pyrolysis temperature on geotechnical properties are rarely investigated. In total, three biochar rates (0, 5, and 10%) were considered for a set of geotechnical experiments in sand clay mixture soil with biochar produced at 350°C and 550°C. Test results show that biochar addition in soil, in general regardless of pyrolysis temperature, increased the optimum moisture content (OMC), plasticity index, and soil water retention characteristics (SWRC) and decreased the maximum dry density (MDD), shear strength parameters (cohesion, friction), and erosion rates. Whilst comparing the pyrolysis temperature effects on two biochar-amended soils, only marginal effects (in terms of magnitude) on SWRC were observed. The most significant decrease of MDD (or increase of OMC) for 5% (w/w) and 10% (w/w) biochar additions occurred at pyrolysis temperatures of 550 °C and 350°C, respectively. In addition, biochar produced at lower pyrolysis temperature (350 °C) was more effective in reducing cracks and enhancing shrinkage area ratio. Ten percent of biochar addition with pyrolysis temperature of 350 °C was the optimum combination in resisting soil erosion. The study provides evidence that the geotechnical properties of biochar-amended soils for landfill cover soil applications could be tailor made by controlling the pyrolysis temperature. Graphical abstract

A comprehensive experimental study on the monotonic behavior of clay-sand mixtures

The main object of this research is the investigation of the behavior of clay-sand mixtures in undrained condition. For this purpose, the behavior of clay mixed with the different percentage of sand (i.e., 0%, 20%, 40%, and 60%) was studied by carrying out undrained triaxial tests on normally consolidated and overconsolidated specimens under different effective stresses. The results showed that sand inclusion up to 20–40% (depend on sand size) does not affect considerably the shear strength of the clay, but when the amount of sand is more than 40%, the shear strength raises 74 to 260%. Maximum pore water pressure at low confining pressures remains unchanged by changing sand content from 0 to 60%. At high confining stress, this parameter for specimens consists of 40% sand is higher than the corresponding values of the other ones. For overconsolidated specimens, irrespective of some exceptions, dependent on sand size, the values of shear strength improve 43 to 73% when sand content varies from 0 to 60%. In addition, deformation modulus of both normally consolidated and overconsolidated mixtures increases 9 to 136% by an increase in sand content from 0 to 40%, and, then, the values diminish rapidly by changing sand content from 40 to 60%.

Effect of Adding Sand on Clayey Soil Shear Strength

The effect of adding sand on clayey soil shear strength is investigated in this study. Five different percentage of clay-sand mixtures are used; 100% clay with 0% sand termed 100C, 60% clay with 40% sand termed 60C-40S, 30% clay with 70% sand termed 30C-70S, 15% clay with 85% sand termed 15C-85S, and as well as 100% sand termed 100S. The used clay was obtained from Baghdad city in Iraq and classified as CH soil, while the used sand was taken from Al-Khider area from Iraq and classified as SW soil. The initial dry unit weight for all mixtures is 16 kN/m3. The results show that the variations of the soil shear strength properties with soil components content changes almost as polynomial function. The results show that the soil cohesion (C) decrease as the sand percentage increases, while the angle of internal friction (ϕ) increases as the sand percentage increases. The cohesion (C) decreases with 68%, 99%, 97% and 100% as the sand percentage increases with 40%, 70%, 85% and 100% respectively from pure clay soil 100C. While, the angle of internal friction (ϕ) increases with 148%, 410%, 471% and 676% as the sand percentage increases with 40%, 70%, 85% and 100% respectively from pure clay soil 100C. Finally, a predicted (fitting) equations are achieved for the variation of the clayey soil shear strength properties with sand content with good agreement.

Consolidation characteristics of a thermally cured sand–bentonite mixture

Consolidation behavior of clays and sand–clay mixtures is an important topic in environmental geotechnics, thermal geostructures and disposal of hazardous wastes. The purpose of this paper is investigation of the changes in consolidation behavior of a sand–bentonite mixture due to the pre-curing at elevated temperatures. For this reason, 1:1 mixture of sand–bentonite was used to prepare samples 100 mm in diameter and 200 mm in height. The specimens were cured at 40, 60 and 80 °C for 1, 3 and 5 days under a constant confining pressure in a modified thermal triaxial cell. Then, consolidation behavior of the prepared samples which have been named as cured samples was investigated. The results show that the cured samples shifted from a reconstituted state to a quasi-structured one. A distinct yield stress was observed in compression curves of cured samples which was not apparent for reconstituted ones. The preconsolidation pressure of cured samples increased with increase in curing temperature and curing time. Also, the coefficient of consolidation and permeability increased as temperature increased, while both values decreased with an increase in curing time. Moreover, a number of specimens were tested under cyclic thermal paths which clearly proved change in behavior of cured samples to a structured one compared to the samples without thermal curing.

A comparative study on the undrained shear strength results of fall cone and vane shear tests in sand–clay mixtures

This paper presents an intensive series of laboratory testing results from vane shear and fall cone tests that were conducted on various clay–sand mixtures to understand the link between these methods which are often used for determining the undrained shear strength (su). Three different gradations (2.0–1.0 mm, 1.0–0.6 mm, and 0.6–0.3 mm) of rounded and angular sands were mixed with low-plasticity clay at ratios of 0%, 10%, 20%, 30%, 40%, and 50%. The results of the tests demonstrated that the su values obtained from the vane shear tests were found to be always higher than those obtained from the fall cone tests. It was shown that the sand content used in the mixtures changed the su parameters of the specimens significantly. The results indicated that the su values were significantly influenced by grading characteristics of the sands (d10, d20, d30, d50, d60, cu, cc). The values of su were lower for the samples that had a larger size of sand grains. Finally, shape characteristics of the sand grains were found to be effective on the results. The samples with angular sand grains have higher su values than the samples with rounded sand grains, for all gradations employed in the present study.

Effects of Geofoam Particles on Geotechnical Properties of Clay-dune Sand

Nowadays, new materials are widely used for improving the bearing capacity of the soils and geosynthetics include the type of these materials which are utilized in this regard. In addition, the geofoam panel type of geosyntethic materials is useful and an alternative for backfill in retaining wall or pavement layers. The present research mainly aimed to investigate sthe effects of geofoam particles (0.2, 0.5, & 1%) on improving the bearing capacity of the clay-sand mixture. To this end, dune sandy soil (passed from sieve No.30 and residue on sieve No.50) was provided from Shore of the Lake Urmia and mixed with kaoline industrial clay at 15, 30, and 50 percentages. Then, compaction, uniaxial in three loading speed (0.5, 1, & 1.5 mm/min), direct shear (in vertical stresses 1, 2, & 3 kg/cm2), and falling head permeability tests were performed to evaluate the influence of geofoam particles on geotechnical properties of the mixed soil. The results showed that maximum dry density and elastic modulus increased by a 0.5% increase in the geofoam in the soil mixture. Meanwhile, the shear strength of the specimens increased as well. Finally, permeability and the drainage condition improved by adding geofoam to the specimens.

Water retention characteristics of biopolymer hydrogel containing sandy soils

Microbial biopolymers are introduced as a new soil binder which regarded to be environmentally-friendly materials in terms of low carbon emission and low impact on the soil ecosystem. In geotechnical engineering and agriculture, various gel-type materials have been used to improve the water absorbability of sandy soils, and control surface erosion. In this study, the soil-water characteristics of xanthan gum biopolymer-treated sand-clay mixtures are evaluated through a laboratory program using a soil-water characterization apparatus. Sand-clay mixtures are treated with different xanthan gum concentrations as 0% (untreated), 0.1%, 0.25%, 0.5%, 0.75% and 1.0%, to the mass of soil, respectively. Consequently, the xanthan gum-soil water characteristic curve results show the enhanced water holding capacity of soils with higher xanthan gum contents. The presence of xanthan gum hydrogels in the soil increases the initial and residual water contents. Biopolymers retain moisture loss from the soil, which makes the slope of the soil-water reduction curve to be more gradual.

Effects of Fine Content on Undrained Shear Response of Sand–Clay Mixture

The aim of this paper is to investigate the influence of fines content on the undrained shear behavior of sand–clay mixtures with fines contents at 0%, 5%, 10%, 12.5%, 15%, 17.5%, 20%, 22.5 and 25%. The shear strength of the mixture has been evaluated in terms of skeleton void ratio and transitional fines content. Materials used are poorly graded sand from the eastern coast of Famagusta, and swelling clay from Nicosia, North Cyprus. Direct shear (DS) tests were used to evaluate the shear strength parameters of sand–clay mixtures at constant strain rate of 1 mm/min under normal stresses of 27.78, 55.56 and 83.33 kPa. The DS test results indicated a unique relation between the transitional fines content and the angle of internal friction, in which the internal friction angle increased with increasing fines until reached maximum value of 45.68° at the transitional fines content (10%). Therefore, additional fines content increased the shear strength up to the transitional fines content after which decrement occurred for all normal stresses.

Evaluating effective stress conditions in soils using non-invasive electrical measurements – Laboratory studies

Changes in the effective stress conditions in soils affect their strength with implications on the stability of near-surface earth materials. The ability to, therefore, characterize and monitor the gradual loss of soil strength due to a decrease in effective stress is essential to ensuring the safety and integrity of engineered structures and help in mitigating geohazards. A faster and cheaper alternative to quickly and non-invasively characterize and monitor changes in subsurface conditions is the utilization of geophysical techniques such as the electrical resistivity method. It can provide a means to effectively monitor and detect potentially unstable conditions (lower effective stress zones) in the earth subsurface.In this study, the effect of varying effective stress levels on the frequency-dependent resistivity measurements of sand-clay mixtures is evaluated. The effect of varying compressibility characteristics such as void ratio and coefficient of compressibility on the electrical parameters are also assessed. A bilinear relationship was found between the electrical parameters (resistivity and capacitance) and the compressibility parameters. The electrical parameters also revealed transitional effective stress or void ratio below which the soil material can barely sustain any mechanical loading. This transitional effective stress was found to be close to the liquid limit of the sample and represents the situation when the soil material begins to lose its strength and potentially become unstable. Being able to predict this transitional effective stress with electrical measurements may be cardinal and useful in our quest to use non-invasive methods in the assessment and monitoring of potential instability conditions in the earth subsurface.

Improved Packing Model for Functionally Graded Sand-Fines Mixtures—Incorporation of Fines Cohesive Packing Behavior

Binary soil mixture, containing large silica particles (sand) mixed with variable content of very fine silt or clay, is an example of a functionally graded material that is important for several science and engineering applications. Predicting the porosity (or void ratio), which is a fundamental quantity that affects other physical properties, of such material as function of fines (clay or silt) fraction can be significant for sediment research and material design optimization. Existing analytical models for porosity prediction work well for binary mixed soils containing multi-sized non-cohesive particles with no clay, while such models frequently underestimate the porosity of sand-clay mixtures. This study aims to present an analytical model that accurately predicts the porosity of mixed granular materials or soils containing sand and very fine silt or clay (cohesive particles). It is demonstrated that accounting for the cohesive nature of very fine particles, which exists due to the effect of inter-particle forces, is a major missing aspect in existing packing models for mixed soils. Consequently, a previously developed linear packing model is modified so that it accounts for fines cohesive packing in sand-fines mixtures. The model prediction is validated using various experimental published data sets for the porosity of sand-fines mixtures. Improvement in the prediction of permeability and maximum packing dry density when incorporating cohesive packing behavior is discussed. The current model also provides important insights on the conditions under which, the lowest permeability and maximum packing state are expected.

The influence of clay content on submarine slope failure: insights from laboratory experiments and numerical models

Abstract Submarine slope failures pose risks to coastlines because they can damage infrastructure and generate tsunamis. Passive margin slope failures represent the largest mass failures on Earth, yet we know little about their dynamics. While numerous studies characterize the lithology, structure, seismic attributes and geometry of failure deposits, we lack direct observations of failure evolution. Thus, we lack insight into the relationships between initial conditions, slope failure initiation and evolution, and final deposits. To investigate submarine slope failure dynamics in relation to initial conditions and to observe failure processes we performed physical experiments in a benchtop flume and produced numerical models. Submarine slope failures were induced under controlled pore pressure within sand–clay mixtures (0–5 wt% clay). Increased clay content corresponded to increased cohesion and pore pressure required for failure. Subsurface fractures and tensile cracks were only generated in experiments containing clay. Falling head tests showed a log-linear relation between hydraulic conductivity and clay content, which we used in our numerical models. Models of our experiments effectively simulate overpressure (pressure in excess of hydrostatic) and failure potential for (non)cohesive sediment mixtures. Overall our work shows the importance of clay in reducing permeability and increasing cohesion to create different failure modes due to overpressure.