Initial Compaction Research Articles

Micro-scale investigations on the mechanical properties of expansive soil subjected to freeze-thaw cycles

Freeze-thaw (FT) cycle is one of the most important factors contributing to the deterioration of expansive soil properties in seasonal frozen regions. In this study, a multiscale approach was used to investigate the impact of FT cycles on the volume deformation, mechanical properties and microstructure of expansive soil with different initial compaction states. FT cycle, unconfined compression, scanning electron microscopy and mercury intrusion porosimetry tests were carried out. The test results indicated that the volume deformation of the frozen expansive soil showed a completely opposite trend and varied in magnitude with different initial compaction states. The failure strength and elastic modulus of the expansive soil sample decreased significantly with increasing number of FT cycles. Under the impact of FT cycles, the porosity of the expansive soil increased significantly and the proportion of macropores grew. The growth of macropores and the generation of microcracks in the expansive soil were the main causes of FT damage. Besides, the FT damage variable was defined by the failure strength and had a good linear relationship with the soil porosity. In addition, the strength of loose and dense soil samples decreased significantly after FT cycles. It is found that an optimal compaction state may exist at around 95% compaction and the water content can be controlled on the dry side of the optimum water content, where FT cycles have minimal effect on the soil strength and microstructure. The study can provide guidelines for selecting the appropriate initial compaction and water content for the expansive soil projects in seasonal frozen regions.

Plastic and damage energy dissipation characteristics and damage evolution of Beishan granite under triaxial cyclic loading

The damage and failure of rock under triaxial stress is an irreversible process of energy dissipation, which mainly includes plastic energy dissipation and damage energy dissipation. However, it is difficult and rare to separate plastic energy dissipation and damage energy dissipation and to conduct relevant research on this basis. In this work, a loading control method with a combination of load (0.5 kN/s) and circumferential deformation (0.01 mm/min) was used, and triaxial cyclic loading and unloading tests under five different confining pressures were performed on granite from the Beishan site area of China's high-level radioactive waste repository. The results indicate that the angle between the main fracture surface and the longitudinal axis increases with the increase of confining pressure. According to the characteristics of the stress–strain curve and energy dissipation, the test process can be divided into five stages: the initial compaction and elastic stage, the stable crack growth stage, the unstable crack growth stage, the postpeak unstable fracture stage and the residual stress stage. Importantly, a separate determination method of plastic energy dissipation and damage energy dissipation was proposed, and the evolution characteristics of plastic energy dissipation and damage energy dissipation were revealed. The ratio of plastic energy dissipation to input energy decreases slightly in the initial compaction and elastic stage, stabilizes at a low level in the stable and unstable crack growth stages, increases significantly in the postpeak unstable fracture stage and remains at a high level in the residual stress stage. Meanwhile, the ratio of damage energy dissipation to input energy increases slightly before the unstable crack growth stage, increases abruptly at the end of the unstable crack growth stage and the initial part of the postpeak unstable fracture stage, then declines rapidly, and finally remains at a low level. Furthermore, the qualitative and quantitative research results of damage evolution show that the plastic shear strain and damage variable established by damage energy dissipation can qualitatively and quantitatively describe the damage evolution of Beishan granite respectively. Finally, the verification results of Beishan granite and two other rock types show that the separation method for calculating plastic energy dissipation and damage energy dissipation proposed in this work has good adaptability, and the qualitative damage development analysis based on plastic shear strain can be verified and supplemented with the quantitative damage development analysis based on energy theory.

Mechanical properties and energy damage evolution mechanism of fiber-reinforced cemented sulfur tailings backfill under uniaxial compression.

This paper studies mechanical properties and energy damage evolution of fiber-reinforced cemented sulfur tailings (CSTB) backfill. The effects of fiber length and fiber content on the stress, toughness and failure properties of the CSTB were systematically revealed. In addition, the energy index evolution law was studied, and the energy damage evolution mechanism of CSTB was revealed. The results show that the deformation failure of fiber-reinforced CSTB mainly goes through four stages: initial crack compaction, linear elastic deformation, yield failure and post-peak failure. The peak stress and residual stress of the CSTB firstly increase and then decrease with the increase of fiber content and the addition of fiber can promote the change from brittle failure to ductile failure of the CSTB. Adding appropriate amount of fiber can improve the toughness of CSTB, and the influence degree of fiber length on the toughness index of CSTB is 6mm>12mm>3mm. The total strain energy increases linearly along the variation of fiber content, while the elastic strain energy and dissipated energy increase exponentially at the peak stress point. In the process of CSTB deformation and failure, "gentle-linear growth-slow growth-rapid decline" is for elastic strain energy, while "gentle-slow growth-rapid growth-linear growth" is for dissipation energy. The damage and failure of CSTB mainly experienced four stages: initial damage, slow growth of damage, accelerated damage and damage failure, and the damage evolution curve also showed the changing characteristics of "gentle-slow growth-rapid growth-linear growth". The CSTB without added fiber showed obvious "Y-type" and "linear-type" shear failure characteristics and the phenomenon of shear cracks penetrating the backfill appeared. No big shear crack occur when it is damaged, showing that the fiber addition restrain the crack growth and improve the overall crack resistance of the CSTB. Hydration products are obviously distributed on the surface of the fiber, which indicates that the fiber will be evenly dispersed in the CSTB and form a certain bonding force with the cement-tailings matrix, thus improving the overall mechanical properties of the CSTB.

Influence of initial compaction and confining pressure on the hydraulic conductivity of compacted iron ore tailings

The hydraulic conductivity of iron tailings is an important factor affecting the stability of tailings storage facilities. Stacking compacted filtered ore tailings is a promising alternative for safer tailings disposal. These tailings storage facilities’ internal drainage systems must be designed appropriately to avoid excessive seepage pressure, saturation, and slope failure. In this context, the factors that affect hydraulic conductivity must be adequately evaluated. Therefore, the hydraulic conductivity behavior of compacted iron ore tailings still needs to be investigated. In addition, the effect of high confining pressure on hydraulic conductivity needs to be evaluated. This study investigates the impact of the initial compaction and the confining pressure on hydraulic conductivity. For this, the flexible wall permeameter tests were carried out on filtered ore tailings compacted in three degrees of compaction: 77, 94, and 101% of optimum dry density as determined by the standard Proctor method. These specimens were saturated and then consolidated with different confining pressure. It is possible to affirm that the increased confining pressure decreases the hydraulic conductivity. The hydraulic conductivity decreases by less than one order of magnitude, regardless of the initial compaction. Moreover, the data suggest that hydraulic conductivity’s decay rate depends on initial compaction—the hydraulic conductivity of the loose specimen decays at a greater rate than that of the dense specimens. However, the reductions of the void ratio under the confining pressure of 1600 kPa and 2200 kPa were not enough to decrease the hydraulic conductivity. Thus, under high-stress confining, the hydraulic conductivity becomes practically constant.

Study on mechanical properties and acoustic emission characteristics of deep diorite under uniaxial compression

The research object is diorite in the Lingbei TBM section of the Hanjiang-To-Weihe River Qinling tunnel, with a buried depth of over 1 km. Using MTS-2000 microcomputer-controlled electro-hydraulic servo universal testing machine and DS5-16b acoustic emission (AE) monitoring system, uniaxial compression and acoustic emission monitoring tests were carried out on rock samples, to study the uniaxial compression mechanical properties and acoustic emission characteristics of the deep diorite. The results of the study indicate that: (1) During uniaxial compression, diorite undergoes four stages: initial compaction, elasticity, yield and failure, in which the curve of the initial compaction stage is significantly smoother. The uniaxial compressive strength is 41.95 MPã102.42 MPa, with an average of 74.07 Mpa; The axial peak strain ranges from 1 % to 1.4 %, and the failure mode belongs to brittle ductile splitting failure. (2) The cumulative ringing count and energy showed a very slow increase trend during the calm period; After entering a surge period (with the appearance of Kaiser points), both show a significant transition state; During the slow increase period, the overall growth rate of the two slowed down and remained almost silent. (3) On the basis of the analysis of RA-AF values during the deformation and rupture process of diorite, it can be seen that the damage type of diorite is tensile damage by the significant low RA value and high AF value characteristics, which coincides with the actual damage fracture characteristics of the rocks in the sample. (4) During the compaction stage, there are few acoustic emission location points, which correspond to low energy and are mainly distributed at the higher and lower ends of the sample; After entering the elasticity stage, the number of positioning points significantly increases and gradually expands towards the middle; Near Kaiser point, the number of location points and corresponding energy are both in a sharp increase state, and this trend is in good agreement with the changes in the ringing count-time and energy-time curves. (5) The damage time mainly starts at the end of the calm period, and the pattern of change in the damage curve coincides with the localization point and energy evolution. The results of the research can be used as a referential basis for the development of the excavation, protection and other construction plans for the Lingbei TBM section of the Hanjiang-To-Weihe River Qinling tunnel or similar surrounding rock tunnels, as well as for further conducting triaxial unloading tests on diorite.

Damage evolution of rock-encased-backfill structure under stepwise cyclic triaxial loading

Rock-encased-backfill (RB) structures are common in underground mining, for example in the cut-and-fill and stoping methods. To understand the effects of cyclic excavation and blasting activities on the damage of these RB structures, a series of triaxial stepwise-increasing-amplitude cyclic loading experiments was conducted with cylindrical RB specimens (rock on outside, backfill on inside) with different volume fractions of rock (VF = 0.48, 0.61, 0.73, and 0.84), confining pressures (0, 6, 9, and 12 MPa), and cyclic loading rates (200, 300, 400, and 500 N/s). The damage evolution and meso-crack formation during the cyclic tests were analyzed with results from stress-strain hysteresis loops, acoustic emission events, and post-failure X-ray 3D fracture morphology. The results showed significant differences between cyclic and monotonic loadings of RB specimens, particularly with regard to the generation of shear microcracks, the development of stress memory and strain hardening, and the contact forces and associated friction that develops along the rock-backfill interface. One important finding is that as a function of the number of cycles, the elastic strain increases linearly and the dissipated energy increases exponentially. Also, compared with monotonic loading, the cyclic strain hardening characteristics are more sensitive to rising confining pressures during the initial compaction stage. Another finding is that compared with monotonic loading, more shear microcracks are generated during every reloading stage, but these microcracks tend to be dispersed and lessen the likelihood of large shear fracture formation. The transition from elastic to plastic behavior varies depending on the parameters of each test (confinement, volume fraction, and cyclic rate), and an interesting finding was that the transformation to plastic behavior is significantly lower under the conditions of 0.73 rock volume fraction, 400 N/s cyclic loading rate, and 9 MPa confinement. All the findings have important practical implications on the ability of backfill to support underground excavations.

Research on global optimization mechanism of intelligent compaction parameters of soil subgrade based on difference method

The global optimization mechanism plays a crucial role in enhancing construction efficiency and ensuring construction quality of soil subgrade such as building foundation or roadbed, within the context of intelligent compaction technology. There are three parts in the global optimization mechanism, which are determining the optimal work parameters, judging the compaction quality, and the feedback adjustment method. To establish a global optimization mechanism for intelligent compaction of subgrade soil, this paper developed a numerical simulation model for subgrade intelligent compaction, defined the necessary numerical simulation conditions for the global optimization mechanism of intelligent compaction. In this way, it provides a source of data for the establishment of global optimization mechanisms. Furthermore, the optimal working parameters are determined by the method of multivariate nonlinear fitting and calculating its extreme value. Meanwhile, an intelligent compaction quality judgment mechanism is established. Additionally, a feedback adjustment method for intelligent compaction was developed using the difference method to form a comprehensive global optimization mechanism. Finally, the intelligent compaction's global optimization mechanism has been validated through field experiments. The results of this study demonstrate that the boundary between low speed and medium speed rolling is 1.7 m/s. The optimal number of rolling passes is four and the ideal rolling speed ranges from 1.2 to 1.3 m/s when initial compaction degree reaches between 80 % and 90 %. The compaction degree, CMV (Compaction Meter Value) and AICV (Acceleration Intelligent Compaction Value) all exhibit a decreasing trend of subgrade compaction quality with increasing rolling speed, and the rate of decrease gradually accelerates.

A novel meso-damage constitutive model of rock under true triaxial stress with three-dimensional cracking strength, threshold and closure effect

Deep underground engineering is in a true three-dimensional stress state, and the adjustment of the three-dimensional stress state caused by engineering excavation will induce the fracture or even instability of the surrounding rock. However, three-dimensional mechanical model research suitable for the stability analysis of deep surrounding rock is very scarce. Therefore, a series of tests under different true triaxial stresses on two rocks (rhyodacite and marble) were conducted, and the characteristic strength (crack stable propagation initiation stress, crack unstable propagation initiation stress and peak strength) and deformation characteristics were further analyzed. After that, using the Lemaitre strain equivalence hypothesis and rock statistical damage theory, a new statistical damage constitutive model at true triaxial stress states was proposed, which introduced the three-dimensional strength criterion Modified Wiebols Cook to characterize the three-dimensional strength of the rock microelement. Therefore, the intermediate principal stress can be reasonably considered. The damage threshold, initial compaction effect and residual strength of the rock microelement at different true triaxial stress conditions were also considered. Then the relationships between the proposed model parameters and σ2 and σ3 were analyzed. Furthermore, sensitivity analysis of the influence of parameters m and F0 in proposed model on the shape of rock stress–strain curve and peak strength was also investigated. The comparison between the results predicted by proposed model and the experimental data shows that the new model established in this study can well simulate the prepeak and postpeak deformation characteristics of rock and the intermediate principal stress effect under true triaxial stress conditions.

Effect of interlayer mixed zone and effective stress on permeability anisotropy of NGH turbidite reservoir

Resulting from the bedding structure of turbidite reservoir, permeability anisotropy is an essential parameter for natural gas hydrate (NGH) exploitation. Fundamentally, the evolution of permeability anisotropy under increasing effective stress are investigated in this study. Taking the turbidite sediments in northern Cascadia as an example, a series of experimental tests and co-simulations of discrete element method (DEM) and computational fluid dynamics method (CFD) are conducted. For layered turbidite sediments, an interlayer mixed zone will be formed in the interface between fine-grained layer and coarse-grained layer after loading. Fine particles will migrate to the coarse layer, blocking the horizontal preponderance flow paths and further reduce the permeability anisotropy. Moreover, the development of interlayer mixed zone mainly occurs in initial compaction stage and slows down in higher stress level, for which the permeability anisotropy shows a staged reduction with increasing effective stress. Considering the effect of interlayer mixed zone, a predictive model of permeability anisotropy is proposed and verified by the experimental results, which has higher accuracy than traditional “layered cake” model. The finding of this research also confirms the mixing effect in deep sediments, which may affect the geological history records in target sedimentary sequence.

Combined effects of solution environment and freeze-thaw cycling on the crack propagation characteristics in sandstone during loading

The failure of ancient rock ruins is affected by freeze-thaw cycles is an important phenomenon in cold region. The degree of freeze-thaw damage be significantly influenced and show an obvious difference during the complex solution environments. However, few studies have been conducted to investigate the combined effects of complex solution environments and freeze-thaw (F-T) cycles to the crack propagation mechanism of loading freeze-thawed sandstones. To study the coupling effects of complex solution environments and freeze-thaw on argillaceous sandstone in ancient ruins, the physical and mechanical properties were investigated through weighing tests, ultrasonic tests, and uniaxial compression tests. The complete failure process of each sample was concurrently monitored using a combination of AE and MS techniques. The crack propagation mechanism at different scales was systematacially investigated through a comparative analysis of microseismic (MS) and acoustic emission (AE) signal characteristics. Additionally, the orthogonal test was designed to effectively analyse the sensitivity of the primary influencing factors to freeze-thawed damage. The findings indicate that:(1) NaCl concentration influences the frost heave force and salt crystallization pressure. While pH levels impact the integrity of the rock structure, leading to significant changes in volume expansion and frost heave force. These aspects are regarded as the main causes of sandstone softening. (2) Compared to the NaCl concentration, varying pH have a more pronounced effect on the freeze-thawed damage. (3) The micro-cracks propagation during loading process is classified into three stages: initial compaction, incubation, and rapid propagation. The macro-cracks propagation is divided into two stages: uniform propagation and rapid propagation. With the increase of NaCl concentration and acidity of solution, the relative duration of incubation in micro-cracks propagation decreased, while the relative duration of uniform propagation in macro-cracks increased. When NaCl concentration and acidity surpass a specific threshold, both the micro-cracks and macro-cracks rapidly propagate from the beginning of the loading process.

Wooden beam damage evaluation under bending loading based on the integration of acoustic emission and principal component analysis

This paper proposes a comprehensive evaluation index based on the combination of acoustic emission (AE) technology and principal component analysis (PCA) to address the issue of low accuracy of any single AE parameter in identifying damage to wooden beams caused by accumulative damage. Four-point bending tests were conducted on wooden beams to monitor the process of performance degradation and evaluate damage progress. The results indicate that the proposed comprehensive evaluation index can divide the damage evolution process of wooden beams into four stages: initial compaction, elastic deformation, crack propagation, and instability fracture. These stages are consistent with the mechanical properties of wooden beams. The time of crack initiation can also be determined according to the comprehensive evaluation index value. The proposed wooden beam damage detection method based on the AE technique provides a reference for further research on the damage evolution mechanism of wooden structures and in situ monitoring methods.

Mechanical response of stress damaged cemented tailings backfill based on pore structure and acoustic emission characteristics

The mechanical response of cemented tailings backfill (CTB) is essential for its achievement of underground mine ground pressure management and productivity improvement. However, long-term, continuous, high-intensity mining causes CTB subject to mining stress disturbance, which inevitably affects its mechanical properties and stability when serving as a load-bearing structure. Therefore, the stress-damaged CTBs (SDCTB) were prepared to take 20%, 40%, 60%, and 80% uniaxial compressive strength (UCS) as the stress-disturbed levels (SDL) in this study. The effects of SDLs and curing ages (3, 7, 14, and 28d) on the mechanical properties and damage characteristics of STCTB were also investigated. The results showed that as SDL enhanced, the UCS and elastic modulus of the backfill (except SDCTB with 60%–80% SDL) increased and then decreased, and 20% SDL was the turning point. Meanwhile, the external load disturbance significantly affected the initial compaction stage of the stress–strain curve of the backfill. Proper SDL reduced the porosity of SDCTB and induced the transformation of macropores to mesopores and micropore. In addition, the AE signals of CTB and SDCTB with 20% SDL showed an active-calm-active stage during compression. The AE signals of SDCTB with 40%–80% SDL remained active stage. The higher SDL aggravated the crack sprouting and expansion rate of the backfill. Also, the correlation dimension (D) of AE ringing counts and amplitudes fully reflected the rupture characteristics of the backfill. The failure mode of SDCTB changed from mixed tensile-shear to tensile failure as the curing age increased. Comprehensive macro-mesoscopic experimental outcomes, the effect of compaction enhancement and cracking damage of the backfill under the external load were proposed, and the two were competing. The results of this study provide a theoretical basis for the stability assessment of the backfill under mining stress disturbance.

Long-term strength and deformation size effect of gangue cemented backfill in acid mine water

The mine water environment can seriously affect the long-term strength and deformation of the backfill body, thereby affecting the stability of the goaf. In this study, the gangue cemented backfill (GCB) of different sizes were placed in different environments (air, water, single H2SO4 solution, and H2SO4 solution coupled with load), the deformation and ultrasonic pulse velocity (UPV) of specimens were recorded with age. The compressive strength, acoustic emission (AE), and resistivity of GCB during the uniaxial compression at 360 days were monitored. In addition, the microscopic morphology of GCB was observed by scanning electron microscopy (SEM), and the damage model of GCB in the process of uniaxial compression was established. The research showed that: the deformation of GCB was fast in the first 90 days and gradually slowed down. The bigger the size was, the greater the instantaneous creep of the GCB was, and the faster the increase rate of the initial deformation was. The UPV of eroded GCB experienced three stages of growth-stability-decrease. The UPV of the smaller GCB increased rapidly in the early stage and decreased rapidly in the later stage. At 360 days, the order of compressive strength of GCB in different media is: water > air > single H2SO4 solution > H2SO4 solution coupled with load, and the compressive strength decreases with the increase of specimen size. In the process of uniaxial compression, the larger the size of the GCB, the larger the number of AE rings detected. The smaller the size of GCB, the stronger the AE characteristics appeared in the initial compaction stage. During the loading process, the resistivity curve of GCB changed approximately in a “U” shape. The smaller the size of GCB, the slower the increasing rate of resistivity in the post-peak failure stage. The abrupt change in the AE ring and the stable resistivity stage could be used to predict the failure of the GCB. The research could provide a reference for the design of the erosion resistance of GCB.

Effects of initial compaction condition and temperature on swelling characteristics of compacted bentonite

Given that isolated high-level radioactive waste repository cannot be modified during operation, understanding the influence of the buffer's initial conditions is critical. This study investigates the influence of the initial dry density and water content on the swelling pressure and consolidation characteristics of Korean bentonite, which is a buffer candidate in the engineered barriers of the repository. In order to consider the high temperature repository condition, samples of various dry densities and water contents were tested at different temperature. Prediction models were developed using the test data and the models were used to analyze the effects of initial conditions. The research findings indicate that the influence of dry density, water content, and temperature on swelling pressure is not absolute and can show different tendencies depending on the case. In terms of consolidation behavior, the compression index and pre-consolidation pressure differ with dry density and temperature, while recompression is unaffected. The study's results align with prior research on compacted expansive clays, with the double structure of clay serving as a suitable explanation for the swelling phenomenon's dependence on the initial compaction condition.

Mechanical and seepage characteristics of polyvinyl alcohol fiber concrete under stress-seepage coupling

This study presents an experimental investigation of the coupled stress and seepage water pressure loading test conducted on polyvinyl alcohol (PVA) fiber concrete, which had undergone salt attack freeze-thaw (F-T) cycles. This study delves into the influence of the number of salt attack F-T cycles, as well as the magnitude of seepage water pressure, on the triaxial compression seepage mechanical properties and permeability evolution of the specimens. Additionally, the nuclear magnetic resonance (NMR), scanning electron microscope (SEM) and X-ray diffraction (XRD) test results were analyzed, revealing that sodium sulfate solution penetrates the interior of PVA fiber concrete and reacts with cement stone to form ettringite and gypsum, which initially fills and compacts the pore structure. The increased production of such compounds causes pore structure to expand, with the maximum number of mesopores and macropores increasing by 115.5%. Macroscopically, it was observed that the mass and peak strength of the specimens increased at the beginning of the cycle, and the initial permeability decreased. However, the opposite phenomenon occurred after 15 cycles. When seepage water pressure was increased from 1 MPa to 3 MPa, the crack initiation stress, crack damage stress, and peak stress of the specimens decreased by 13.1%, 16.9%, and 15.6% on average, respectively, and the initial permeability increased by 69.3% on average. The deformation process of PVA fiber concrete under stress-seepage coupling loading was divided into five stages, including the initial compaction stage, elastic deformation stage, crack initiation and stable propagation stage, crack unstable propagation stage, and post-peak deformation stage. Correspondingly, the permeability exhibited a rapid decline, followed by a relatively stable phase, a slow rise, a rapid rise, and a continuous increase. Besides, the relationship between permeability and volume strain in compression and expansion stages was clarified.

Cultivar-dependent differences in tuber growth cause increased soil resistance in potato fields.

Since soil compaction of potato fields delays shoot emergence and decreases total yield, the causes and effects of this compaction need to be better understood. In a controlled environment trial with young (before tuber initiation) plants, roots of cv. Inca Bella (a phureja group cultivar) were more sensitive to increased soil resistance (3.0 MPa) than cv. Maris Piper (a tuberosum group cultivar). Such variation was hypothesized to cause yield differences in two field trials, in which compaction treatments were applied after tuber planting. Trial 1 increased initial soil resistance from 0.15 MPa to 0.3 MPa. By the end of the growing season, soil resistance increased three-fold in the upper 20cm of the soil, but resistance in Maris Piper plots was up to twice that of Inca Bella plots. Maris Piper yield was 60% higher than Inca Bella and independent of soil compaction treatment, whilst compacted soil reduced Inca Bella yield by 30%. Trial 2 increased initial soil resistance from 0.2 MPa to 1.0 MPa. Soil resistance in the compacted treatments increased to similar, cultivar-dependent resistances as trial 1. Maris Piper yield was 12% higher than Inca Bella, but cultivar variation in yield response to compacted soil did not occur. Soil water content, root growth and tuber growth were measured to determine whether these factors could explain cultivar differences in soil resistance. Soil water content was similar between cultivars, thus did not cause soil resistance to vary between cultivars. Root density was insufficient to cause observed increases soil resistance. Finally, differences in soil resistance between cultivars became significant during tuber initiation, and became more pronounced until harvest. Increased tuber biomass volume (yield) of Maris Piper increased estimated mean soil density (and thus soil resistance) more than Inca Bella. This increase seems to depend on initial compaction, as soil resistance did not significantly increase in uncompacted soil. While increased soil resistance caused cultivar-dependent restriction of root density of young plants that was consistent with cultivar variation in yield, tuber growth likely caused cultivar-dependent increases in soil resistance in field trials, which may have further limited Inca Bella yield.

Effect of Additive Addition on RAP (Reclaimed Asphalt Pavement) as an Aggregate Substitution Against the Upper Surface Layer of The Road

As development in the field of infrastructure increases, it will require more materials of natural origin. The availability of materials from nature will be reduced and more limited. Meanwhile, the construction of infrastructure continues to run every year for the improvement and comfort of the community. With this, the importation of goods will also increase, especially for bulk asphalt materials, and it is possible that later the stone that becomes one of the main materials for hot asphalt mixture will also bring in from abroad. If waste from peeled asphalt (RAP) can be reused, it will automatically reduce the use of materials from nature and reduce import activities of goods which results in reduced state expenditure. The thesis task will discuss the reuse of peeled asphalt (milling) on the highway, starting from the benefits of RAP, the advantages of RAP, testing RAP materials and new materials, and how to produce RAP asphalt at the Asphalt Mixing Plant. The composition of the RAP used is 60% with SW1 rejunevile material of 3.8%, the addition of new aggregates of 40%, and the addition of new asphalt of 3.3%. The results of the compaction experiment in the field (trial compaction) which will be used for work reference are initial compaction (tandem roller 2 passing), intermediate compaction (tire roller 16 passing), and final compaction (tandem roller 1 passing), and the resulting density of hot mix beds of 98.36%.

Evaluation of Compaction Characteristics of Asphalt Mixture under Different Compaction Effects

To investigate the effects of different compaction methods on the water damage resistance, the air void and high-temperature stability of AC-13 asphalt mixture, Marshall compaction, roller wheel compaction, and gyratory compaction specimens were compacted with the same air void as the standard for comparative analysis. Then asphalt cement (AC)-13 (dense-graded), stone matrix asphalt (SMA)-13 (gap-graded), and porous asphalt concrete (PAC)-13 (open-graded) mixtures were compacted by gyratory compaction, and the gradation, compaction cycles, and initial compaction temperature, which affect the gyratory compaction characteristics of asphalt mixtures, were studied. The results show that the comprehensive compaction quality of the gyratory compaction specimen was the best considering the air void uniformity, uniaxial penetration strength (UPS), and residual Marshall stability of the three compaction methods. The slope of compaction degree and gyratory compaction times of gyratory compaction specimens can clearly reflect the ratio of compaction degree at different compaction phases. In this research, a new reasonable evaluation method for the laboratory compaction of an asphalt mixture is proposed, and the feasibility of using the corresponding fitting curves at different initial compaction temperatures to quickly determine the required gyratory compaction cycles to achieve the desired compaction degree is verified, which provides a reference for the evaluation of compaction methods and compaction characteristics of asphalt mixture specimens.

Hydrogeological Properties of Till Amended with Green Liquor Dregs (GLD): Recycling of an Industrial Residue for Reclamation of Acid Generating Mine Sites

The oxidation of sulfide minerals in mine wastes is a possible threat to the environment as it might have potential to generate acid rock drainage (ARD). A common method to reduce ARD is to apply a dry cover on the mine waste deposit. Considering the massive amounts of mine waste produced in Sweden (104-million-ton in year 2018) there is a great need for suitable dry cover materials. Using non-hazardous industrial residues in the dry cover would be beneficial for both the mining industry and the providing industry as stricter waste management legislation incentivizes them to develop their waste management strategies. The objective of this study was to investigate if an addition of Green Liquor Dregs (GLD), a residue from pulp production, can decrease the hydraulic conductivity and increase the water retention capacity (WRC) of three different tills, with the purpose of improving the performance of a dry cover material on a mine waste deposit. Another objective was to investigate how the hydraulic conductivity and WRC are affected by the contents of fines and clays in the tills. The study concludes that the water retention capacity of the tills improves with GLD addition, however, the hydraulic conductivity did not decrease enough to reach the in Sweden required < 10−8 m/s. Even though, GLD could still successfully be used in the reclamation of mine sites as the high WRC can be seen as the most important factor in deterring acid rock drainage by keeping the sealing layer close to saturation. This study further indicates that there are other factors than the particle size distribution of the materials that controls the hydraulic conductivity of the mixtures, such as initial water content, dry density, and compaction effort.

A new hydro-mechanical coupling constitutive model for brittle rocks considering initial compaction, hardening and softening behaviors under complex stress states

After the excavation of underground engineering, the failure and instability of surrounding rock under hydro-mechanical coupling conditions is a common type of engineering disaster. However, the hydro-mechanical coupling mechanical characteristics of rock have not been fully revealed, and suitable models for the stability analysis of surrounding rock under hydro-mechanical coupling conditions are very scarce. Therefore, a series of triaxial compression and cyclic loading and unloading hydro-mechanical coupling tests were carried out to study the mechanical characteristics, deformation and mechanical parameters of rock under different confining pressures and pore pressures. Then, based on Biot’s effective stress principle, a hydro-mechanical coupling damage constitutive model within the framework of irreversible thermodynamics was proposed to describe the initial compaction effect, pre-peak hardening and post-peak softening behaviors. The functional relationships between the proposed model key parameters (η and ζ) and the effective stress were established to characterize the pre- and post-peak nonlinear behaviors of rock. A compaction function Ck for the evolution of the undamaged Young’s modulus in initial compaction stage was introduced to characterize the pre-peak compaction effect. A user-defined material subroutine (UMAT) was compiled in ABAQUS to numerically implemented the proposed model. The numerical simulation results are highly consistent with the test results, the proposed model can also predict the hydro-mechanical coupling characteristics of rock under untested stress levels. In addition, the yield function of the proposed model considers the influence of intermediate principal stress, which is also suitable for the simulation of hydro-mechanical coupling characteristics under true triaxial stress states.Graphical abstract