Increase In Dry Density Research Articles

Laboratory study of the effects of using magnesium slag on the geotechnical properties of cement stabilized soil

In this paper, the effects of magnesium slag and cement were investigated on the chemical, mechanical and microstructure parameters of soil. An increase was recorded in pH with increasing the content of both magnesium slag and cement, which is indicating an improvement in soil conditions for better implementation of pozzolanic and hydration reactions. Also, adding both substances led to the granulation of soil particles. An increase in maximum dry density (MDD) and optimum moisture content (OMC) was recorded by adding both additives.The uniaxial compressive strength test was investigated in three curing periods of 7, 28 and 56 days, which showed an increase in this parameter for the simultaneous and separate addition of both substances to the soil. The optimum content of magnesium slag was by 20% in this test and cement had the maximum content of 6%, which resulted in 14.3 MPa strength. The TCLP test was also performed to investigate the environmental issues in the sample with the abovementioned optimum percentages. By studying the microstructure, an improvement in soil structure was observed in the form of filled voids between the particles as well as density and continuity created between the particles.

Gas breakthrough tests on saturated GMZ01 bentonite using RCP technique with consideration of dry density effect

In this study, gas breakthrough tests were conducted on GMZ01 bentonite specimens with dry densities 1.3, 1.5 and 1.7 Mg/m3 under rigid boundary conditions using the residual capillary pressure (RCP) technique. Prior to the gas breakthrough tests, water permeability tests were performed for determining intrinsic water permeability and establishing full water saturation for the follow-up gas breakthrough tests. The intrinsic water permeability measured ranges between 11 and 150 nDarcy (1.10×10-20 and 1.50×10-19 m2). As dry density increases, the residual capillary pressure differences of the initially water-saturated bentonite specimens recorded increase from 0.12 to 0.61 MPa. Meanwhile, the time to breakthrough was recorded to increase sharply as dry density increases. In addition, the maximum effective gas permeability decreases from 8.91×10-18 to 8.92×10-19 m2 as dry density increases from 1.3 to 1.7 Mg/m3. These results indicate that the capillary drainage in the bentonite specimen is highly related to the capillarity effects in the largest pores. The higher dry density, the smaller flow channels, resulting in more difficult for gas phase to dispel water from the interconnected flow pathways and a better sealing capacity with a higher residual capillary pressure.

Experimental study on tensile strength of unsaturated fine sands

This paper describes the development of a direct tension apparatus and its application to test the tensile strength of unsaturated fine sands. The apparatus consists of two halves of wedge-shaped specimen molds. A criterion is developed for designing the inclination angle of the inner sidewall of the specimen molds as a function of soil–wall interface frictional angle and soil dilatancy angle. Tensile strength of unsaturated fine sands is measured over a range of dry density and water content. Results show that tensile strength generally increases with the increase in dry density. For relatively dense sand, tensile strength follows a non-monotonic double-peak pattern with increasing water content. The first peak occurs in the pendular regime and is attributed to peak occurrence of interparticle stress contributed by pendular water bridges. The second peak occurs in the capillary regime and is attributed to the capillary component of interparticle stress arising from negative pore pressure.

Assessing Relations Between Electrical and Geotechnical Properties of Sand-Clay Mixtures Using Jonscher Fractal Power Law Model

The geotechnical properties of unconsolidated geo-materials such as soils are influenced by modifications of their micro-structure, texture, mineralogy, water content and imposed effective stress levels. Fundamental relations between the characteristic electrical parameters describing the electrical responses soils based on a fractal power law model with scaling properties, and parameters influencing their geotechnical behavior are investigated. Low frequency electrical conductivity laboratory measurements were performed on sand and clay mixtures subjected to varying effective stress levels with concurrent measurements of their geotechnical properties. The conductivity spectra of the mixtures were described using a Jonscher fractal power law model characterized with three characteristic parameters, the dc conductivity ( σdc), the characteristic frequency ( fc) and an exponent ( n). Changes in effective stress, water content, clay content, and other engineering properties of the mixture such as dry density, porosity, pore size and intergranular void ratio are discussed with respect to changes in the electrical parameters. The dc conductivity and characteristic frequency decrease with an increase in effective stress levels. The exponent, however, has the opposite behavior and increases with an increase in effective stress. As the water content increases, σdc and fc increase while n decreases for all mixtures. With increasing stress levels, the average pore size of the mixtures decreases which results in a decrease in σdc and fc but an increase in the values of the exponent. An increase in dry density of the mixtures leads to a decrease in σdc and fc whilst n increases. Both σdc and fc increase with increase in the intergranular void ratio of the mixture whilst the exponent values decrease with an increase in the intergranular void ratio. This study serves as a contribution to our quest in utilizing electrical geophysical methods, to assess and monitor non-invasively, the geotechnical properties of the subsurface in a less expensive and faster manner.

Effect of Adding Mixture of (Concrete Waste and Asphalt Waste) on the Properties of Gypseous Soil

The Gypseous soil which is used is taken from Tikrit city in Salah Aldeen governorate and specially from Tikrit University from a depth (1.5-2) m. It's type is sandy gravely with a small percentage of silt and clay while the percentage of gypsum is (34-36) %. The tests on soil are standard proctor compaction, direct shear, collapsibility and California bearing ratio. The number of samples is (70). The effect of adding concrete waste (2, 4, 6 and 8%) and waste of Asphalt mixture (2, 4, 6 and 8) % on dry soil, as well as the effect of mixture of the optimum percentages of both additions on the properties of gypseous soil, is the aim of the study. Adding concrete waste at optimum percentage (6) % causes an increase in maximum dry density at (16)% and a decrease in optimum moisture content at (5) %. Whereas adding concrete mixture waste in its optimum percentage (2) % caused a decrease in maximum dry density values with an increase of optimum moisture content, and when adding a mixture of optimum percentage of waste, an increase happened in the M.D.D.(14)% with a decrease in O.M.C. at (4) %. Adding the optimum percentage (8) % for both, the value of cohesion increases (100) % when adding concrete waste with an increase in the angle of internal friction (14)% and a decrease in collapsibility in a percentage of (90)% , while adding waste of asphalt mixture shows an increase in cohesion value (112) % with a decrease in the angle of internal friction (2) % and a decrease in collapsibility in a percentage of (90) %, when adding mixture of optimum percentages the value of cohesion increase (108) % with an increase in angle of internal friction (14)% and a decrease in collapsibility in a percentage of (91) %. Values of California Bearing Ratio in dry and soaked condition increases (49) % when adding (8) % of concrete wastes which is the optimum percentage, while adding waste of asphalt mixture causes a decrease in the value of C.B.R. and the optimum percentage is (2) % , but adding optimum percentages mixture of them causes an increase in values of (52) % in dry condition and (53)% in soaked condition.

Effect of Pore-Water Salinity on the Electrical Resistivity of Partially Saturated Compacted Clay Liners

The aim of this paper is to investigate the effect of pore-water salinity on the electrical resistivity (ER) of different compacted clay liners (CCLs) in terms of its mineralogical composition. For this purpose, an experimental programme was conducted where ERs of different kaolin-dominant CCL specimens, reconstituted using water having different concentrations of NaCl (0 M, 0.5 M, and 1.0 M), were measured. The kaolin-dominant CCL specimens tested in this study include pure kaolin, three different kaolin-bentonite mixtures, and three different kaolin-sand mixtures. The experimental results show that the ERs of CCL specimens decrease as the salt concentrations in pore water, moisture content, and dry density increase. At constant density and moisture content, the test results also indicate that increasing the sand content in kaolin-dominant CCL specimens increases its ER regardless of the water salinity level. This behaviour could be attributed to the lower surface conduction of sand compared to kaolin. However, at constant density and moisture content, increasing the bentonite content in kaolin-dominant CCL specimens decreases its ER in the distilled water environment as surface conduction of bentonite is higher compared to that of kaolin. On the contrary, in saltwater environments, ER increases as the bentonite content increases. This behaviour could be explained in terms of the expected aggregated microstructure of bentonite in the saltwater environment that could reduce the number and area of interparticle contacts, and consequently, increase the ER of CCL specimens.

Feasibility of Growing Chlorella sorokiniana on Cooking Cocoon Wastewater for Biomass Production and Nutrient Removal.

The feasibility of microalgae cultivation using cooking cocoon wastewater (CCW) collected from a silk production factory was investigated in this work. Results showed that Chlorella sorokiniana grew well on the CCW whether it was autoclaved or not. After 7-day cultivation, the biomass increased by 1.57, 2.78, 3.33, and 3.14 times, and by 3.65, 4.03, 3.27, and 2.82 times when this alga was cultivated in the raw CCW (R-CCW) and autoclaved CCW (A-CCW) at the initial dry cell densities of 0.01, 0.04, 0.08, and 0.16g/L, respectively. The algal photosynthetic growth was not affected when this alga grew on the R-CCW at an initial dry cell density of ≥ 0.04g/L, while it was significantly inhibited when the initial dry cell density was 0.01g/L. Additionally, this alga could remove nutrients rapidly from the CCW, and the removal efficiency increased with the increase of initial dry cell density. Thus, it was concluded that the CCW could be used as a good-quality medium for the algal growth, which is worthy of further study and promotion.

Influence of Granite Cutting Waste Addition on the Geotechnical Parameters of Cohesive Soil

The current study analyzes the effect of granite cutting waste addition on the properties of cohesive soil. Representative samples of cohesive soils were collected from the Mansehra and Balakot areas of Hazara, Pakistan and their major geotechnical properties determined following the standard ASTM procedures. The determined properties include the Atterberg limits, i.e. Liquid Limit (LL), Plastic Limit (PL), Plasticity Index (PI), and Maximum dry density, Optimum moisture contents, Un-confined compressive strength, Activity and Expansion. Both the soils are classified as active soils possessing high expansion capacity and low strength due to the presence of Ca-montmorillonites. Following an increment of 5%, up to 25% streaks of cutting waste from Susalgali and Baffa granites were added to the Mansehra soil and Balakot soil respectively. A thorough analysis of the test results reveals a continuous decrease in the Atterberg limits, optimum moisture contents and expansion capacity, and increase in the maximum dry density and overall strength of both the soils with increasing amounts of the added granite cutting waste streaks. The reduction in Atterberg limits, optimum moisture contents and expansion capacity reflects the low activity and lower absorption capacity of the added granite. Besides, the concomitant increase in strength and maximum dry density of the treated soils suggests suitability of granite waste addition as a potential means for enhancing bearing capacity and reducing settlement issues in civil engineering

Small-strain shear stiffness of compacted bentonites for engineered barrier system

The shear modulus (G) of two different bentonites was measured by means of a resonant column apparatus. The samples were compacted at different dry densities and degrees of saturation and tested with different confinement pressures and strains levels for studying the influence of these parameters on the shear modulus. The results show similar tendencies in both bentonites: the shear modulus increases as the dry density increases and exhibits maximum shear modulus when degree of saturation is around 80%. An empirical equation, taking into account the microstructure of the clays, is used to evaluate the shear modulus at small strains as a function of dry density and degree of saturation. Although the values of the shear modulus measured are similar in both bentonites for a given stress and degree of saturation, there is difference in the elastic strain limit of the soil. Bentonite clay is going to be part of the Engineered Barrier System (EBS) in deep geological disposal facilities for the long-term confinement of spent nuclear fuel. In order to fully understand their long-term performance, their behaviour in shearing conditions should be assessed.

Effect of Bentonite Addition on Geotechnical Properties of Oil-Contaminated Sandy Soil

Oil and its derivatives not only change the chemical and biological properties of the soils, but also affect their geotechnical properties. Effects of oil contamination on a sandy soil which mixed with bentonite was assessed in terms of compaction, shear strength, and consolidation behavior. The experiments were carried out by polluting dry sandy soil with 2.5, 5, 7.5, 10% w/w crude oil at different bentonite contents (0, 5, 10, 15, 20% w/w). Results of compaction tests indicated that at a fixed bentonite content, with increasing crude oil content, the maximum dry density increases, while the optimum water content decreases. Similarly, at a fixed contaminant content, increasing the bentonite content in the soil leads to increase in soil maximum dry density and the optimum moisture content. Moreover, direct shear tests revealed that at a specific bentonite content, higher contamination concentration causes lower internal friction angle. The effect of oil content on the coefficient of consolidation (Cv) and void ratio of soils with 0, 5, 10, 15, and 20 percent bentonite contents was studied. The results of consolidation tests indicated that at a fixed bentonite content Cv has an overall increasing pattern which is in its maximum amount at 5% oil content.

SWCCs of Silt in Yudong Zone and its Prediction Under Different Drying–Wetting Cycle Conditions

Soil–water characteristic curves (SWCCs) play a key role in unsaturated soil mechanics. A series of SWCC tests on Yudong silt with different compaction degrees and drying–wetting cycles were conducted using a GCTS pressure plate apparatus. The test results showed that the SWCCs exhibited hysteresis during the drying–wetting cycles and were affected by the compaction degree. The hysteresis area decreased with increasing drying–wetting cycles. The hysteresis area was obviously affected by the first cycle. The second and third cycles had less obvious effects compared with the first one, but their effects could still be seen. The SWCC’s parameters of Van Genuchten model were obtained by using a Lsqacurve fit function. On basis of the relationships among the fitting parameters, compaction degree, and drying–wetting cycles, a practical and novel approach was proposed to predict SWCCs for Yudong silt under different compaction degrees and drying–wetting cycles. The microstructure changes associated with variations in dry density or compaction degree have been photographed by the scanning electron microscopy (SEM). The SEM results show that the increase in dry density or compaction degree would change the macropore and surface roughness of aggregates, which will produce greater interaction among aggregates, and thus increases the air-entry value.

Effect of Basalt Fiber on the Strength Properties of Polymer Reinforced Sand

This paper displays an experimental study of the effect of basalt fiber on the strength properties of polymer reinforced sand. Laboratory trials of unconfined compression test (UCS), direct shear test, and tensile test were conducted on the specimens treated with polymer and basalt fiber, and several factors including polymer content, fiber content and dry density of sand that will influence the strength behaviors are investigated in detail. Based on test results and scanning electron microscope (SEM) images, the reinforcement mechanism was analyzed. The results showed that the polymer content, basalt fiber content and dry density of sand had greatly improved the strength behaviors of reinforced specimens. The increase in polymer and fiber content had an active effect on strength characteristics, while the angle of internal decreased slightly. The strength properties were enhanced with the increase in dry density, and the effect of dry density on tensile strength is affected by fiber content. The presence of randomly distributed fibers has formed a spatial fiber-sand net in sand, and the additive of polymer solution formed membrane to enwrap sand particles and connect sand and fibers, thereby formed a stable structure in sand. These structures have increased the bonding and interlocking forces between sand and fibers, and decreased the void ratio of reinforced specimens.

Influence of thermal loading on index and physicochemical properties of Barmer bentonite

Abstract The concept of the deep geological repository (DGR) has been widely accepted for the safe disposal of high-level nuclear waste (HLW). Compacted bentonite/bentonite-sand mixture is considered as buffer material in the deep geological repository due to its favorable physicochemical and hydro-mechanical properties. The bentonite buffer is expected to be exposed to high temperature for a long duration because the heat released from the waste canister and due to the geo-thermal gradient inside the deep geological repository. The temperature from the waste canister can go initially as high as 200 °C and probably reduce to ambient temperature upon the decay of the waste material. This long duration temperature variation induces a thermal loading on the bentonite buffer, affecting its index, physicochemical and hydro-mechanical properties. Hence there is a need to critically examine the effect of the induced thermal loading on the long-term performance of the buffer as this study will be quite useful for the preliminary understanding before fixing its design values for the use as a part of engineered barrier system (EBS) in DGR. In the present study, two bentonites (Barmer 1 (B1) and Barmer 2 (B2)) from Barmer district of Rajasthan, India, was subjected to four temperature levels, i.e., 60 °C, 110 °C, 150 °C and 200 °C for a time duration of 3, 7, 15, 21, 28 days. Changes in the physicochemical properties of both bentonites were observed and reported. The decrease in the Atterberg's limit, swelling, specific gravity, optimum moisture content, pH and exchangeable monovalent cation and increase in maximum dry density was recorded with an increase in temperature as well as with the duration of heating.

Improvement Effect of Water-Based Organic Polymer on the Strength Properties of Fiber Glass Reinforced Sand.

The mechanical properties of sandy soil can be effectively improved by the incorporation of water-based polymer and glass fibers. In order to study the reinforcement effects of a type of water-based organic polymer and fiber glass on sand, three strength tests (unconfined compression test, direct shear test and tensile test) and scanning electron microscopy were carried out. A series of polymer content, fiber content and dry density were selected for the tests. The results revealed that the composite reinforcement of water-based organic polymer and fiber glass can improve the strength. With an increase in polymer content and fiber content, the unconfined compression strength, the cohesion, and the tensile strength increase. The internal friction angles maintain a relatively stable state. All three strength properties increase with an increase in dry density. The results can be considered as the reference for sand reinforced engineering.

Failure modes and mechanisms of pavements in saline foundations

Saline soil causes problems for the construction of airfield pavements and results in some pavement failure modes that are different from or more serious than failure modes in non-saline soil. Through an investigation of several typical airports in China, the failure modes of airfield pavements were determined in this study as mainly blow-ups, faulting, slab cracking and black spots. These failures are mainly attributed to the subgrade course, cement-stabilising aggregate base course (CSABC) and concrete surface course subjected to different levels of sulfate and chloride attack. Salt-heaving experiments were conducted for the subgrade and base courses, while salt corrosion experiments were performed for the surface course. The results indicate that the salt-heaving pressure of soils not only increases with an increase in dry density of the soil and the content of sodium sulfate, but also varies with water content and reaches a maximum value at the optimum soil moisture. The compressive strength of the CSABC was found to increase first and then decrease as the contents of sulfate and chloride salt reached threshold contents of 0·3% and 0·2%, respectively. In addition, the impacts of sulfates on the flexural strength, dynamic modulus of elasticity and mass loss of concrete were found to be proportional to sulfate content.

Laboratory investigation of the relationship between electrical resistivity and geotechnical properties of phosphate tailings

Electrical conductivity of soil can be considered as a proxy of soil physical properties. Due to its non-destructive nature, electrical resistivity method is serving as an attractive tool in geotechnical engineering practice. In this study, the electrical resistivity of phosphate tailings was measured by laboratory tests using two-phase electrode method. The effects of moisture content, dry density, temperature and other factors on the electric resistivity of phosphate tailings were examined in detail. The electrical resistivity of phosphate tailings was found to decrease with increase in water content, dry density and temperature. A triaxial apparatus was modified to study the relationship between electric resistivity and shear strength characteristics of phosphate tailings. Triaxial shear tests were conducted on the phosphate tailings specimens to determine the stress-strain response, variation in the shear strength parameters (c and φ) and the corresponding changes in electric resistivity. The initial electric resistivity of phosphate tailings specimens correlated negatively with shear strength, cohesion and internal friction angle. During the course of triaxial shear tests, electric resistivity of phosphate tailings decreased continuously with the increase in strain. However the rate of decrease became larger with yielding of the specimen. Consolidation tests were conducted by a modified oedometer to correlate electrical resistivity with consolidation pressure, compression coefficient and compression modulus. The electrical resistivity was found to decrease at a decreasing rate with consolidating pressure. Further, it increased with compression coefficient, but decreased with the increase of compression modulus of soil specimen. The work done in this study can be beneficial for robust estimation of in-situ properties, as well as for the evaluation of shear strength characteristics of phosphate tailings by means of electrical resistivity measurement.

Sustainable Improvement of Marine Clay Using Recycled Blended Tiles

The usage of recycled material for improving problematic soil as a construction and pavement material has been a sustainable interest. Recycled blended tiles (RBT), a waste from ceramic tiles factories containing high amount of sodium and magnesium, was used as a soil stabilizer for marine clay improvement in this study. This research investigated the effects of sizes and percentages of RBT on the physical and strength properties, which included particle size distribution, Atterberg limits, compaction, and unconfined compressive strength (UCS) of marine clay. Microstructural characterization, including the scanning electron microscopic, energy dispersive X-ray spectroscopy, and X-ray diffraction was conducted on both untreated and treated marine clay-RBT samples to examine the mechanism of strength development. The addition of RBT reduced the water holding capacity, which then caused the reduction in soil plasticity (from 18 to 11%) and optimum water content (from 20 to 16%) along with the increase in peak dry density (from 1.66 to 1.74 Mg/m3). The UCS of marine clay increased from 50 to almost 220 kPa. The optimum RBT contents, providing the highest UCS, were at 20 and 30% for 0.063 mm RBT and 0.15 mm RBT, respectively. The UCS improvement of treated marine clay is attributed to the formation of cementation compounds, mainly aluminum magnesium silicate hydrate (A–M–S–H). The outcome of this research will allow the use of RBT as a low-carbon soil stabilizer across civil engineering applications.

Gas transport in compacted bentonite after 18 years under barrier conditions

The FEBEX in situ test was a full-scale experiment performed at the Grimsel Test Site (Switzerland) under natural conditions to reproduce the Engineered Barrier System of an underground repository for nuclear waste. After 18 years of operation under natural hydration from the granitic host rock and heating from a heater simulating the waste canister, the experiment was dismantled. The gas permeability of bentonite samples taken during dismantling at different positions around the heater was determined in a custom-built equipment.The gas permeability of the samples decreased with their water content and dry density. The samples closest to the heater had lower water content and higher dry density, whereas the samples closest to the granite had the highest water content and lowest dry density. Thus, the gas permeability of the samples was related to their position in the barrier, tending to be lower towards the granite, where the degree of saturation was higher, and hence, the void ratio accessible for gas flow, lower. The void ratio accessible for gas flow expresses the ratio between gas accessible volume and particle volume and is computed as e(1−Sr). Because of the high water saturation of most of the barrier after the long operation period, the accessible void ratio was below 0.15 in all the samples tested. The gas permeability of these samples was related to their accessible void ratio in the same way as expected for the FEBEX reference bentonite, decreasing with it according to a power law. In this respect no changes on the gas transport properties of the bentonite took place during operation.The increase of confining pressure during testing resulted for most samples in an irreversible increase in dry density and consequently a decrease of the gas permeability. Beyond a confining stress of 4 MPa no gas flow took place through any of the wetter samples. In contrast, flow took place through the drier samples even for confining pressures as high as 9 MPa.

Some properties of sustainable concrete containing two environmental wastes

This investigation includes the use of 15% of glass wastes as a partial substitution to cement in combination with plastic wastes as volumetric replacement to natural coarse aggregate to produce sustainable concrete. Different volumetric replacements of plastic waste to natural coarse aggregate (25%, 50%, 75%, and 100%) were used in concrete containing 15% glass powder as a replacement by weight of cement. Generally, the results show that the inclusion of 15% glass powder improves the compressive strength, splitting tensile strength and flexural strength by about 13.3%, 36.3%, and 34.7%respectively at 60 day age in comparison with reference concrete without wastes, also the results show a decrease in water absorption and an increase in dry density. The inclusion of plastic waste aggregate in the presence of 15% glass powder leads to a decrease in the compressive strength, flexural strength, splitting tensile strength, dry density, ultrasonic pulse velocity, and thermal conductivity. The percentage reductions are 59.8%, 46.3%, 43.6%, 20.5%, 28.6%, and 54.4% respectively for concrete specimens that including 100% plastic waste coarse aggregate in comparison with concrete specimens without plastic waste aggregate.

Analysis of Swelling Characteristics of Expansive Soil

Swelling and expansion are important characteristics of soil. The expansive soil can cause many problems in the foundation due to settlement in the form of shear. Therefore behavior of the expansive soil should be investigated properly before structural design. In this study the effects of swelling and expansive characteristics of soil are analyzed by experimental work. Moisture content and dry density are found to check the effect of their variation on the swelling of soil. Swell potential test and swell pressure test are carried out according to ASTM standards. From the obtained result it is observed that with the increase in the initial moisture content, swelling potential decreases and the increase in dry density causes decrease in swelling potential.