Increase In Degree Of Compaction Research Articles

Mechanical properties and field test of lime-soda residue stabilized soil for subgrade

To broaden the sources of subgrade filler and the utilization of Soda Residue (SR), SR was employed to modify clay by adding a small amount of lime for further stabilization, forming a Lime-Soda-Residue-Stabilized Soil (LSRSS). A set of intensive research paths was established, from testing of laboratory mechanical property, mechanism disclosure, and field verification to operational effect. Through Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), and Resilient Modulus (MR) experiments, it was concluded that with the increase in SR content, the UCS, CBR, and MR values of LSRSS showed an increasing trend then followed by a decrease, reaching their peak values, respectively of 0.62 MPa, 65.0%, 78.83 MPa, all at 30% SR content. An optimal proportion was determined for LSRSS as 6% lime, 30% SR, and 70% clay. The UCS, CBR, and MR values of optimal proportion all increased with the increase of compaction degree, but increased first and then decreased with the increase of water content. Their maximum values did not correspond to the OWC of 23% but to 27%, called the compaction water content, which was suitable for application in the actual LSRSS subgrade. Field test results showed that the UCS, CBR, and MR values were 0.85 MPa, 86.5%, and 135.7 MPa, which all were higher than the laboratory values, and the long-term road performance was outstanding. The analysis demonstrates that the better strength and road performance of LSRSS are mainly determined by the superior gradation and the reaction of three materials. The laboratory and field test results collectively provide data evidence for excellent performance and lay a solid foundation for the wider application of the LSRSS subgrade.

Mechanical Properties and Dry–Wet Stability of Soda Residue Soil

To effectively utilize the effectively the solid waste-soda residue (SR) and fly ash (FA), a mixture of 70% SR, 20% FA, and 10% clay was formed to produce soda residue soil (SRS). By adding cement and/or lime, four different SRS proportions were prepared. The compaction properties, mechanical properties, and dry–wet stability. Furthermore, the mechanical mechanisms of SRS were explored, and the improvement effect and efficiency of cement and/or lime on the mechanical performance of SRS were analyzed. The results show that the SRS is lightweight and easy to compact and shape, which is conducive to construction. Compared to cement, lime has a greater impat on the compaction properties of SRS. The mechanical properties of SRS are enhanced after adding cement and/or lime; the unconfined compressive strength (UCS), California Bearing Ratio (CBR), and resilient modulus all increase significantly. The UCS, CBR, and resilient modulus of SRS with different proportions all increase with the increase of compaction degree; the CBR and resilient modulus can meet the requirements of the subgrade, and the UCS can meet the requirements of the base and sub-base. The contribution rate of cement per unit amount is better than that of lime to the mechanical performance of SRS. As dry–wet cycles increase, the dry–wet stability of SRS with different proportions first increases and then decreases, which is affected by hydration and dry–wet deterioration together, with a critical cycle number for the strength transition. The excellent mechanical performance of SRS benefits from the gradation and chemical action. The particles of SR, FA, and clay can complement each other and perform an interlocking action. Therefore, SRS has a good gradation and forms a dense and stable structure. Also, the chemical reactions between materials are very important. The cement and/or lime have a hydration and gelling effect, FA and clay participate in pozzolanic reactions, and SR and FA have certain alkali-activated effects.

Experimental Study and Numerical Simulation of the Wetting Settlement of Remolded Loess

By conducting collapsibility test, the changing rule of collapsibility coefficient of remolded loess is obtained. According to the numerical simulation method of equivalent humidity field with temperature field, the collapsibility coefficient is converted into temperature change, so the calculation of wetting settlement is realized. The results show that the collapsibility coefficient of loess decreases significantly with the increase of compaction degree and initial water content. It increases first and then decreases with the increase of overlying pressure at lower compaction degree, while increases gradually with the increase of overlying pressure at higher compaction degree. The numerical simulation based on the theory of equivalent humidity field with temperature field can accurately simulate the wetting settlement test results of remolded loess.

Effects of Freeze–Thaw Cycles on Volume Change Behavior and Mechanical Properties of Expansive Clay with Different Degrees of Compaction

Freeze–thaw (F-T) cycles are one of the main deterioration factors for the performance of expansive clay in seasonally frozen soil regions. This study designed a unidirectional environmental boundary loading device for F-T cycle tests. Laboratory tests were conducted to quantitatively evaluate the effects of the F-T cycle on volume change behavior and mechanical properties of expansive clay with different degrees of compaction below the canal in Xinjiang. The SEM image processing was performed with the Image-Pro Plus image processing software to get pore parameters. The results showed that during the F-T cycle, the volume change of the sample gradually changes from contraction to expansion as the degree of compaction increases. As the degree of compaction increases, the hardening characteristics of the expansive clay are weakened, and the F-T cycle promotes the softening of the stress–strain relationship. The first F-T cycle resulted in a significant decrease of failure strength, and the failure strength of different compaction degrees decreased by 56.07%–67.54% after seven cycles. The failure strain and resilient modulus of the samples are attenuated to varying degrees after F-T cycles. The correlation rate between the porosity and the attenuation rate of the failure strength is 0.719–0.882, the corresponding weight reaches 0.419–0.445, and there is an excellent linear relationship between them. The research offers some important insights into the construction and maintenance of expansive clay engineering such as the Xinjiang Canal.

Laboratory fatigue performance of the cement-stabilised loess fabricated using different compaction methods

Herein, the fatigue performance of cement-stabilised loess (CSL) designed using two compaction methods were investigated. The reliability of the vertical vibration testing method (VVTM) was verified by comparing the physical properties of the laboratory samples prepared using the VVTM and the proctor compaction test (PCT) and the mechanical properties of the core samples obtained using these methods and from the construction site. Further, the CSL samples fabricated using the two compaction methods were subjected to indirect tensile fatigue tests to establish a fatigue equation. Finally, the influence of the compaction method, compaction degree and cement content on the fatigue performance of CSL was analysed based on the fatigue equation of CSL. Results showed that the correlation between the mechanical strength of the CSL sample prepared using VVTM and the core sample obtained from the construction site is more than 90%. The fatigue equation based on the Weibull distribution can effectively evaluate the fatigue life of CSL. Furthermore, the fatigue performance of VVTM sample is better than PCT sample. The equivalent fatigue life of VVTM sample with 4% cement dosage can be increased by at least 33% compared with PCT sample under the same condition. With the increase of compaction degree or cement content, the fatigue performance is gradually enhanced.

Reinforcing effect of recycled polypropylene fibers on a clayey lateritic soil in different compaction degrees

The present research investigates the reinforcing effect of recycled polypropylene (R-PP) fibers on a compacted clayey lateritic soil in different compaction degrees. R-PP fibers of 12 mm length were mixed with the soil in the contents of 0.1 and 0.25% of soil dry weight. Unconfined compression strength tests (UCS), direct shear tests and indirect tensile strength (ITS) tests were conducted. Fibers addition showed no significate alterations in the optimum compaction parameters. The study evidenced increases in UCS, changing the soil behavior from a brittle failure to a ductile failure, while fiber contribution was most effective for 0.25% R-PP fibers content and 95% compaction degree. The use of fibers improved the shear stress-strain behavior of the composites and soils compacted at different degrees of compaction showed similar shear behavior, which is coherent to the soil water retention curves (SWRC) results. Significant increases in the tensile behavior of soil-mixtures for both fiber contents used were observed, and fibers increase was more significate than increase in soil degree of compaction. The stretching of the fibers and fibers orientation at the sheared interface in direct shear tests and the fiber “bridge” effect in ITS tests could be observed.

Effect of Thickness and Compaction Degree of Overburden Soil on Radon Reduction for Uranium Tailings Reservoir

The thickness and compaction degree of the overburden soil on the beach of the uranium tailings reservoir has an important influence on the radon reduction rate. A theoretical model of radon exhalation is established and an experimental device is designed. The main results are as follows. (1) The radon reduction rate increases with the increase of thickness. When the soil compaction degree is 85.5%, 90.2%, and 94.8%, the radon reduction efficiency increases significantly when the thickness increases from 5 cm to 10 cm, and when the soil thickness is over 10 cm, the increase of radon reduction efficiency tends to be stable. When the compaction degree is 80.9%, the radon reduction rate always increases obviously with the increase of the thickness of the overburden soil, but the increase rate shows a downward trend. (2) The radon reduction rate increases gradually with the increase of compaction degree, and the increasing trend becomes less obvious when the compaction degree is more than 85.5%. Besides, the effect of the change of soil compaction on radon reduction rate decreases with the increase of soil thickness. The calculation formulas about the effect of thickness and compaction degree on radon reduction rate can guide the design and construction of radiation protection of uranium tailings reservoir.

Experimental study on unconfined compressive strength of expansive soil improved by lignin and cement

Aiming at the question of improvement expansive soil in Nanyang area, the composite improvement method of lignin and cement was adopted. Based on the unconfined compressive strength test, the variation law of unconfined compressive strength of improved expansive soil with different lignin content, different compaction degree and different curing age was studied. The test results show that the composite of lignin and cement can effectively improve the unconfined compressive strength of expansive soil. The unconfined compressive strength of L-C (lignin and cement) improved expansive soil reaches the maximum when the cement content is fixed at 4% and the lignin content is 1%. The unconfined compressive strength of L-C improved soil increases with the increase of compaction degree and curing age, and the strength growth mainly concentrated in the first 7 days of curing age. From the point of improvement mechanism, the hydration and gelation reaction of cement occur in expansive soil, and gel material with higher strength is formed to enhance the strength of expansive soil. The appropriate amount of lignin can fill the pores between soil particles and make the connection between soil particles more closely, so as to improve the strength of expansive soil.

Experimental Research on Steel slag Stabilized Soil and its Application in Subgrade Engineering

An experimental program was carried out to explore the feasibility of steel slag replacing lime used in the pavement of highway subgrade. The compaction test, the bearing ratio test, the unconfined compressive strength test, the splitting tensile strength test and the water stability test were carried out for different mixture ratio. And field test was also carried out to verify the application of steel slag. The test results showed that the immersion bearing ratio of steel slag stabilized soil increased with the increase of compaction degree and content of steel slag. The CBR value of Steel slag stabilized soil with 8–15% slag content was basically equivalent to that of 4% lime soil. The failure strain of 8% or 15% steel slag soil is larger than that of lime soil or cement soil. The strength of lime soil, cement soil and steel slag stabilized increased monotonously with the increase of curing age, but the growth rate of lime soil was significantly higher than that of steel slag stabilized soil. The 7d unconfined compressive strength of 8% steel slag stabilized soil reached 0.41 MPa, which met the requirements of highway subgrade materials. The initial moisture content had a great influence on the steel slag stabilized soil, and it was necessary to strictly control the moisture content for subgrade constructing. The content of steel slag in the steel slag stabilized soil was measured by EDTA method which is effective. The deflection value of 8% steel slag stabilized soil was 130.8 (10−2 mm), which can meet the requirements of the design specification [232.9(10−2 mm)].

Influence of Degree of Compaction on Unsaturated Hydraulic Properties of a Compacted Completely Decomposed Granite

It is crucial to understand hydraulic properties, i.e., soil-water characteristic curve (SWCC) and unsaturated permeability function (UPF), of completely decomposed granite (CDG) for relevant engineering projects in southeastern China. Previous studies mainly focused on SWCCs of CDG, whereas UPFs of CDG have not yet been well understood. In this study, the effects of the degree of compaction (DOC) on SWCCs and UPFs of CDG were investigated based on experiments where suction range was from 0 to 500 kPa. The microstructure of soil specimens was then analyzed by mercury intrusion porosimetry (MIP). Furthermore, the UPFs of CDG under different values of DOC were calculated using four prediction models and compared with experimental data. Results showed that the pore volume of specimens at higher DOC was smaller than that at lower DOC, and there were more macropores observed in specimens at lower DOC. Meanwhile, it was found that increasing compaction effort produced negligible influence on the volume of micropores. When the suction was less than 100 kPa, the permeability was reduced with the increase in DOC, due to the decrease of macropore volume. However, the influence of DOC on SWCCs and UPFs became marginal when the suction exceeded 100 kPa. The Fredlund and Xing model provided the best prediction of UPF among the four models when suction was smaller than air entry value (AEV). It is suggested that these models could be improved to capture UPFs at higher suctions than AEV by considering suction-induced volume contraction.

Experimental Study on Dynamic Resilient Modulus of Lime‐Treated Expansive Soil

Dynamic resilient modulus is the design index of highway subgrade design code in China, which is significantly affected by the traffic loads and environmental changes. In this study, dynamic triaxial tests were conducted to investigate the influence of moisture content, compaction degree, cyclic deviator stress, and confining pressure on lime‐treated expansive soil. The suitability of UT‐Austin model to lime‐treated expansive soils was verified. The results indicate that the dynamic resilient modulus of lime‐treated expansive soils increases nonlinearly with the increase of compaction degree, while decreases nonlinearly with the increase of dynamic stress level. The dynamic resilient modulus decreases linearly with the increase of moisture content and increases linearly with the increase of confining pressure. Moreover, the moisture content has a more significant effect on the dynamic resilient modulus of lime‐treated expansive soil. Therefore, it is necessary to ensure the stability of soil humidity state and its excellent mechanical properties under long‐term cyclic loading for the course of subgrade filling and service. Finally, the calculated results of the UT‐Austin model for dynamic resilient modulus show a good agreement with the test results.

Influences of spring thaw on working performance of airport soil field surface in cold region

By considering the temperature-rising effect during spring-thawing period, the frozen soil samples with water content of 15%, 17%, 19% and 21% and compaction degrees of 90%, 95% and 98% are prepared to investigate the variation characteristics of thermal conductivity and shear strength in the soil field surface of airport lifting zone in cold region by pre-embedded temperature sensor, steady plate method and fast direct shear method. Laboratory experiments on the frozen soil samples are conducted to achieve internal temperature changes, thermal conductivity variations and fast direct shear strengths. The characteristics of thermal conductivity and mechanical properties of the frozen soil samples are obtained and the influences of the spring-thawing effect on the working performance of airport soil field were summarized. The results show that, there are significant internal temperature variations in the frozen soil samples during the process of temperature rise. The existence of frozen core makes its melting process present four stages, including rapid heating period, moderate melting variation period, accelerated melting variation period and melted period. By analyzing the thermal conductivity variation curves of twelve sets of frozen soil samples, it is found that the thermal conductivity of frozen soil samples decreases as a whole, but still fluctuates, during the temperature rising process, which is also consistent with the internal temperature field. By analyzing the results of fast direct shear tests on sixty sets of the frozen soil samples at ambient temperatures of -5, -1, 3, 7 and 11 ℃, it is proved that the shearing strength increases with the increase of compaction degree and decreases with the decrease of water content significantly during the temperature rising process.

Experimental Study on Shear Strength Parameters of Natural Sulfate Saline Soil

The factors affecting the shear strength of sulfated saline soil are complex, and the variation law is difficult to explore. In order to determine the variation of shear strength of sulfate-based roadbed saline soil under different water content, compaction and confining pressure, the internal friction angle and cohesion, which are two important parameters of shear strength, were analyzed. The test results show that the stress-strain curve of sulfate-based saline soil is strain-softening type distribution, and the smaller the confining pressure, the more obvious the softening type; the shear strength increases with the increase in confining pressure and compaction. The cohesive force first increases and then decreases with the increase in water content, and the maximum cohesive force occurs near the optimal water content; the cohesive force increases slowly with the increase in compaction degree; the cohesive force increases most obviously when the water content is 10.8%. The internal friction angle decreases with the increase in water content, and the peak area is not obvious; the internal friction angle increases as the degree of compaction increases

Test Research of Seepage Monitoring Based on Distributed Optical Fiber

In this paper, a theoretical model of temperature and velocity of a fiber is derived. A test model simulating seepage indoor is designed. The optical fiber heating temperatures under different compaction degree and seepage velocities are measured through applying AC voltage on the optical fiber. The analyzing results show that the optical fiber heating temperature and seepage velocity are related in quadratic function. The quantitative relations of optical fiber temperature and seepage velocity under different soil types and compaction degree are fitted. Analysis on how the compaction degree influences the relation of optical fiber temperature and seepage velocity shows that with the increase of compaction degree, optical fiber heating temperature will gradually decline. The influence of soil type on fiber heating temperature is very complex. In practice, according to the characteristics of the soil, determining quantitative relationship and implementing quantitative monitoring of the seepage velocity are needed.

Toward a better understanding of the effects of cement treatment on microstructural and hydraulic properties of compacted soils

This study deals with the problem of the experimental characterization of cement-treated compacted soils in terms of microstructural and hydraulic properties. Some tests are conducted on two different types of soil: silty sand and clay as fine soils and gravelous sand and alterite as granular soil. Some samples are mixed with 5% of cement and compacted at different levels (i.e., 85%, 95%, 100% and 105% of the maximum dry density, respectively, as achieved using the standard compaction method). The results of the mercury intrusion porosimetry (MIP) tests performed on these cement-treated soils reveal significant changes as regards macropores due to the combined effects of treatment and compaction. Consequently, a decrease in the permeability is clearly observed for all the tested soils when the degree of compaction increases. This decrease is significantly greater in fine soils, which are more sensitive to compaction effects than granular soils.

Carbon black and fumed alumina exhibiting high interface-derived mechanical energy dissipation

High interface-derived dissipation has been discovered by instrumented indentation in carbon black and fumed alumina. Both materials comprise nanoparticle aggregates that interlock mechanically upon compaction without a binder. The high dissipation is attributed to the high deformability and the abundance of interfaces. Compared to carbon black, similarly 600-kPa compacted 100-mN maximum-load tested fumed alumina gives lower dissipation (2.1 vs. 4.1 μJ, both values being higher than the highest previously reported value for any material, 0.175 μJ for dental enamel), lower maximum displacement (72 vs. 134 μm), higher fraction of displacement that is permanent (0.74 vs. 0.59), higher modulus (41 vs. 7 MPa), higher fractional dissipation (0.80 vs. 0.70), and lower solid content (12 vs. 18 vol.%). These differences are attributed to the greater compressibility of carbon black. The relative movement of the particles of carbon black or the graphite layers of exfoliated graphite becomes less reversible as the degree of compaction increases. Microwave-exfoliated graphite (5.25-MPa compacted, 37 vol.% solid) gives lower dissipation (1.0 μJ) and higher modulus than carbon black or fumed alumina. Furnace-exfoliated graphite (5.25-MPa compacted, 43 vol.% solid) gives even less dissipation than microwave-exfoliated graphite, due to its greater compressibility and consequent greater deformation reversibility.

Properties of Crushed Red-Bed Soft Rock Mixtures Used in Subgrade

Slaking red-bed soft rocks are widely distributed in the south of Anhui Province, China, and several highways will go through this area. It is important to evaluate their physical and mechanical characteristics for the purpose of using this kind of soft rocks as materials for road construction. In this paper, the compacting tests, the resilient modulus tests, the California bearing ratio (CBR) tests, and permeability tests have been carried out on crushed red-bed soft rock mixtures. The test results showed that, for a given degree of compaction, the resilient modulus decreases linearly with the increase of moisture content. For a given moisture content, the resilient modulus and CBR values increase linearly with the increase of compaction degree, while the soaking swelling, water absorption capacity, and permeability coefficient decrease linearly. In other words, the strength and water stability are enhanced with the increase of the degree of compaction. The results demonstrate that the crushed red-bed soft rock mixtures can be directly used as materials for the highway construction by taking corresponding measures.

Viscoelastic Behavior of Silica Particle Compacts under Dynamic Compression

Theviscoelastic behavior of model sandy soils in the form of silica particle compacts under dynamic compression (0.2-10.0 Hz) is reported. The solid content ranges from 24 to 28% by volume, as controlled by compaction. Both viscous and elastic characters are largely governed by the solid part of the compact. The elastic character stems from the stiffness of the silica, while the viscous character stems from the interparticle movement. The elastic character of the solid part (the storage modulus and solid content) is essentially independent of the degree of compaction, indicating validity of the rule of mixtures. The viscous character of the solid part (the loss tangent and solid content) decreases with increasing degree of compaction, indicating decreasing ease of interparticle movement as the degree of compaction increases. The loss modulus and solid content is essentially independent of the degree of compaction. All quantities decrease with increasing frequency. A low degree of compaction is recommended for fast decay of the vibration amplitude; no particular degree of compaction is recommended for mechanical energy dissipation. DOI: 10.1061/(ASCE)MT.1943-5533.0000831. © 2014 American Society of Civil Engineers. Author keywords: Soil compression; Viscoelasticity; Dynamic properties; Mechanical properties; Compression tests; Vibration damping; Silica; Particles.

Experimental Study on Unconfined Compression Strength of Compacted Granite Residual Soils

Granite residual soils are often used as compacted soils in engineering structures such as pavement, embankments and backfills in Xiamen. Many geotechnical problems such as bearing capacity, lateral earth pressures and slope stability require an assessment of the shear strength of soil. Since the geotechnical properties of residual soils are impaired in contact with water, a series of unconfined compression tests are carried out on granite residual soils. Results of tests include effects of degree of compaction, moisture content, degree of saturation and cyclic wetting and drying on unconfined compression strength respectively. The increase in degree of compaction and compacting effort increases unconfined compression strength and the former greatly affects the strength. Moisture content of soils is higher than the optimum one of 2.5% for high strength and it is lower than optimum one of 2.5% for good plasticity in Xiamen areas. The degree of saturation of high unconfined compression strength normally ranges from 64% to 76%. In addition, cyclic wetting and drying causes loss of unconfined compression strength and the maximum loss commonly occurs at the first cycle and then is slowed down by the following cycles till the strength remains approximately constant.

Study on Engineering Characteristics of Highly Weathered Weak Rock

When highly weathered weak rock used to fill embankment, compaction character and wetting deformation character are major evaluation indexes. Based on California Bearing Ratio (CBR) test for highly weathered weak rock under different compaction degree, it was shown that the value of CBR increased as the increase of compaction degree. By means of dry-wet double curve parallel tests and wetting deformation experiments of different compaction degree of highly weathered weak rock under complex stress, the results indicated that when the degree of compaction is 90%, under rather high deviatoric stress, wetting can not only generate high additional axial deformation, but also cause fairly high additional volumetric strain and partial strain. And wetting cause shear intensity of soil reducing. So increasing the compactions of subgrade filling is the important way to reduce wetting deformation and to enhance slope stability of subgrade.