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Freeze–thaw cycle is one of the primary rock physical weathering agents which causes the deterioration and softening of rocks in cold regions. The frost-weathered rocks are prone to damage and destruction under loading. Determining the deterioration and stress–strain behavior of rocks following cyclic freezing and thawing is of crucial importance for evaluating the stability of rock excavation engineering in cold regions. A long-term artificial freeze–thaw cycles test on fresh sandstone samples was designed in this paper. The saturated condition was selected to accelerate the effect of freeze–thaw weathering. The mechanical behavior of the specimens undergoing different freeze–thaw cycles was further investigated through the uniaxial compression test. Experimental results indicate that the cycling of freezing and thawing causes a gradual decline in uniaxial compression strength followed by a rapid fall. An obvious beginning compaction stage can be observed in the stress–strain curve and the strain of the compaction stage increases during the freezing and thawing process. The deterioration of the sandstone was expressed by uniaxial compression strength, elastic modulus, and frost resistance coefficient in a piecewise decay model. A damage critical point can be distinguished in the model. Then, piecewise damage strain equations under the combination of freeze–thaw action and loading were derived by introducing the damage mechanics theory. The presented model was validated by the test results in this paper and a published article. It demonstrates that the simulated data agree well with the test results, indicating the effectiveness of the presented model in describing the stress–strain behavior of sandstone suffering long-term freeze–thaw weathering. [ABSTRACT FROM AUTHOR]

Freezing and thawing are typical weathering phenomena in periglacial and permafrost areas. The fresh rock mass discovered by engineering excavation in cold climates will inevitably experience daily and seasonal cycles of freezing and thawing, significantly altering its geotechnical quality. Thus, the study of the durability of the rock mass is of great importance to engineering in cold regions. In this paper, physical and mechanical tests were carried out on sandstone samples collected from the Qinghai-Tibet Plateau after different cycles of freezing and thawing. The nuclear magnetic resonance (NMR) test was also conducted to comprehend the variation of pore structure. It was found that the physical and mechanical properties, including morphology, weight, porosity, P-wave velocity, uniaxial compressive strength (UCS) and elastic modulus, induced by freeze-thaw cycles change greatly, demonstrating an accelerated deterioration trend of sandstone. On the basis of the test results, a generalized deterioration function was presented to describe the degradation of mechanical properties. The failure modes, which reflected the fabric weakening of specimens, under axial compression after different freeze-thaw cycles were further concluded and four typical failure modes were distinguished. Finally, the deterioration mechanism of sandstone under the action of alternated freezing and thawing was discussed from the view of pore structure evolution. • Tests address the impacts of long-term freeze-thaw cycles on sandstone's performance. • A novel deterioration function shows the degradation of mechanical properties. • NMR data and microscopic pore structure evolution reveal the damage mechanism. [ABSTRACT FROM AUTHOR]

Mechanical behavior of frozen rock-soil mixture was investigated through direct shear test based on remolded specimens. The peak shear strength of rock-soil mixture increases greatly when it is fully frozen. The shear process goes through four stages including compaction, elastic deformation, plastic yield, and failure. The specimen has slight compaction in vertical direction at the beginning of shear test; then it changes to dilatancy. The temperature and ice content have vital important effect on the shear behavior of frozen rock-soil mixture. Results indicated that the peak shear strength of rock-soil mixture increases with temperature decreasing when temperature ranges from −1°C to −16°C. But the curve has clear inflexion at −5°C. When temperature is higher than this degree, the peak shear strength increases sharply with temperature decreasing. Otherwise, the rise of the peak shear strength with the decrease of temperature becomes gentle. The shear strength of rock-soil mixture goes up first and then down with ice content increasing at −5°C for samples with initial water contents varying from 9% to 14%. The shear strength reaches its peak value at initial water content ranging between 10% and 12% by weight. [ABSTRACT FROM AUTHOR]

Detailed engineering geological studies and stability assessments were carried out on Xiari rock slope in southwestern China. Geomorphic analysis of digital elevation models, detailed structural field mapping and boreholes data indicate that the slope has a poor rock mass quality and complex deformation mechanism. The necessary rock mass parameters were determined by means of slope mass rating (SMR), geomechanic classification system ( Q) and geological strength index (GSI). Slope stability analyses were performed by means of kinematic, limit equilibrium and numerical modeling techniques. Analyses results indicate that slope stability is mainly controlled by the discontinuities. The combination of discontinuities and topography makes the slope susceptible for a large landslide. The major potential mode of slope failure is planar failure. Planar failure has a higher probability in comparison to wedge failure, while wedge failure contributes towards a more severe hazard, like the landslide in part A of the study area. Numerical analysis results indicate a catastrophic landslide in the future, with a volume estimated to be more than 2.5 × 10 m. [ABSTRACT FROM AUTHOR]

Earthquake-induced liquefaction is one of the major causes of catastrophic earth dam failure. In order to assess the liquefaction potential and analyze the seismic performance of an earth dam in Fujian, Southeastern China, the in situ shear wave velocity test was firstly carried out. Results indicate that the gravelly filling is a type of liquefiable soil at present seismic setting. Then the effective stress model was adopted to thoroughly simulate the response of the soil to a proposed earthquake. Numerical result generally coincides with that of the empirical judgment based on in situ test. Negative excess pore pressure developed in the upper part of the saturated gravelly filling and positive excess pore pressure developed in the lower part. The excess pore pressure ratio increases with depth until it reaches a maximum value of 0.45. The displacement of the saturated gravelly soil is relatively small and tolerable. Results show that the saturated gravelly filling cannot reach a fully liquefied state. The dam is overall stable under the proposed earthquake. [ABSTRACT FROM AUTHOR]

There has been a growing interest in polymer applied for soil reinforcement in recent years. However, there little attention has been paid to the effects of polymer on soil cracking behavior, and cracks significantly change soil strength and hydraulic properties and alter reinforcement effectiveness. This study investigated the desiccation cracking behavior of polyurethane (PU) and polyacrylamide (PAM) admixed clayey soils with different polymer concentrations by performing desiccation cracking tests. Scanning electron microscope (SEM) observation was also carried out to obtain the internal structure of these soils. The results show that PU and PAM addition both prolonged the initial evaporation stage, accelerated later evaporation processes, and the effects were related to polymer concentration. Final cracks morphology analyses show that PAM addition slightly reduced the cracking and crushing degree and kept the soil relatively intact, while PU addition slightly enhanced the cracking and crushing degree of soil. In addition, PU and PAM addition both increased the width and length of cracks. The scanning electron microscopy (SEM) analyses show that the effects of polymer on soil evaporation and cracking could be concluded as: (1) storing water in voids, (2) influencing water immigration channel, (3) providing space for soil shrinkage, and (4) enhancing the connection between aggregates, which did not fully come into play because of the existence of hydrogel form. These achievements provide a certain basis for the research of desiccation cracking behavior of polymer treated soil and make significant sense for the safe and effective running of related projects. [ABSTRACT FROM AUTHOR]

Air-hardening organic polymer (AHOP), a new soil stabilizer, can form a cross-link among soil particles with high strength and toughness. In this study, the effect of the polymer content and density on the mechanical behavior of stabilized silty sand was investigated. The results indicate that the unconfined compressive strength and tensile strength of stabilized silty sand keep a prominent linear relationship with AHOP content that increases with the increment in density; the increment in AHOP content also leads to a higher elastic modulus of stabilized silty sand. The cohesion was also significantly enhanced by the increase in AHOP content and density; the internal friction angle of loose specimens (ρ≤1.50 g/cm3) keeps increasing with AHOP content; however, for dense specimens (ρ≥1.55 g/cm3), 3% polymer content is a turning point, at which the internal friction angle changes nonmonotonically. AHOP film can connect loose silty sand particles and adhere to the surface of particles, leading to silty sand with good strength properties. Based on failure modes, the failure of polymer–particle interactions can be divided into four modes, including (1) tensile fracture at membrane, (2) tensile fracture at polymer–particle interface, (3) shear at membrane, and (4) shear at polymer–particle interface. [ABSTRACT FROM AUTHOR]

The compressibility and rebound properties of sand reinforced with polymer and fibers were studied with respect to polymer content, dry density, and types and content of fibers using laboratory standard consolidation experiments. The following conclusions are drawn: (1) with the increase in polymer, the compressive coefficient of reinforced sand decreases gradually. Up to 4%, the compressive coefficient decreases slowly and the resilient rate keeps increasing; (2) with the increase in dry density, the compression coefficient decreases rapidly at first and then changes slowly. Up to 1.55 g/cm3, the compression coefficient changes slowly, while the resilient rate keeps increasing; (3) with the increase in fiber content, the compressive coefficient increases and the compressive characteristics of the sand after adding polypropylene fibers become stronger than those of the sand with addition of sisal fibers. The resilient rate of the reinforced sand keeps increasing and the sand reinforced with sisal fiber has a higher resilient rate; (4) the polymer forms a parallel connection model between sand particles, and the curing film can fill the pore between particles. A spatial stereo structure is formed within the sand mixed with fibers reducing the compression characteristics and increasing the resilience under larger vertical loads. [ABSTRACT FROM AUTHOR]

This study focuses on the shear-strength properties of polyurethane polymer–treated sand stored at different temperatures. The triaxial test was performed at unconsolidated and undrained conditions on the specimen after 2 days of curing at room temperature and 1 day of curing at various temperatures. The effects of polymer content and dry density on strength properties were also considered. Polymer reinforcement mechanism was analyzed using scanning electron microscope images. Results indicated that the stress-strain relationship exhibited increasing ductility as temperature increased; the shear strength, energy absorption, and cohesion tended to decrease initially and then increase, while the friction angle remained stable at approximately 30°. The strength properties were in proportion to an increment in polymer content, and the trend became more apparent in a warmer environment. The shear strength, energy absorption, and cohesion increased up to about 2.4 MPa, 65 kPa, and 400 kPa, respectively. A higher dry density resulted in significant improvement in strength properties, except for a slight reduction in ductility, no matter the temperature. The presence of a polymer matrix formed a honeycomb and special net structures among sand via coating, bridging, and filling effects; hence, the treated sand turned into a whole system exhibiting favorable strength properties. This reinforcement effectiveness depended on polymer content, dry density, ambient temperature, soil grain, and polymer characteristics. [ABSTRACT FROM AUTHOR]

A considerable number of engineering hazards are caused by loose internal structure of sands. Thus, many researchers have explored a variety of reinforcement methods. A new reinforcement technique was experimentally evaluated in this study. In particular, a hybrid method with a combination of fiber and polymer was studied. Three different types of fibers (sisal, polypropylene, and palm) in combination with varying concentrations of polymers were experimented to improve the internal structure and strength of sand samples reconstituted at different densities. Through a series of laboratory tests, the compressive and tensile strength variations of different combinations were obtained, and the interaction between fibers and polymer inside the sand was evaluated by scanning electron microscopy (SEM). The experimental results show that the tensile and compressive strength of the reinforced sand increases with the increase of the polymer concentration, sample density, and different fiber combinations. This provides some references for future practical engineering applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • GHG emissions from an industrial-scale AD plant were assessed. • The AD process before digestate treatment achieved carbon offset. • Electricity consumption caused the major GHG emissions. • Waste oil recovery and biogas reuse are pivotal for offsetting GHG emissions. • Net GHG emissions from digestate process varies with different final disposal ways. Anaerobic digestion (AD) has been widely applied for treating organic waste and is known as a carbon-offsetting process. However, most studies relied on laboratory-scale experiments or literature to calculate carbon emissions from AD process, and the impact of digestate processing was overlooked. This study assessed the carbon footprint for an industrial food waste co-digestion plant with operational data. The results indicated that carbon emission before digestate treatment is −88.5 ± 4.4 kg CO 2 -eq/t. The major source of carbon emission is electricity provision, followed by fuel combustion, unburned biogas, and fugitive gas emissions, while waste oil recovery and biogas utilization offset the carbon emissions. Considering digestate treatment and disposal options, the plant's net carbon emissions are as follows: −86.1 ± 6.2 kg CO 2 -eq/t (incineration) < -80.7 ± 6.5 kg CO 2 -eq/t (land application) < 6.7 ± 12.2 kg CO 2 -eq/t (landfilling). This work aims at providing a roadmap for making site-specific calculations of the carbon footprint for AD process. [ABSTRACT FROM AUTHOR]

• The ongoing of polymer air-hardening process was investigated by NMR and UCS tests. • The polymer-filled pores were divided into micropores, mesopores and macropores based on the T 2 spectra. • The microstructure and mechanical properties of stabilized sand were affected by the curing time and polymer content. • The relationship between the strength and microstructure index was determined. The polymer has been widely used in soil stabilization, but the microstructure and the polymer film formation process are seldom investigated. This paper investigated the time-dependent changes in microstructure and strength of the polymer-stabilized sand during the air-drying process using nuclear magnetic resonance (NMR) and unconfined compressive strength tests. Different polymer contents (1%, 2%, 3% and 4%, by the weight of dry sand) and curing time (0, 24, 48, 72 and 96 h) have been considered to highlight the ongoing polymer air-hardening reaction. The results indicate that the polymer-occupied porosity decreased exponentially with the increase of curing time and increased by the rise in polymer content. The elastic modulus and compressive strength increased gradually with polymer content and curing time increment. The air-hardening process of polymer can be classified as the rapid air-hardening stage (first 48-hour curing) and slow air-hardening stage. The polymer-filled pores can be divided into micropores, mesopores, and macropores. Based on the corresponding relaxation time and amplitudes of the peak value and envelope area of the relaxation time curve in NMR, it can be found that the size of polymer-filled pores and the proportion of macropores decreases and the proportion of micropores increases during the air-drying process. During the air-drying process, the water in the polymer film evaporated; therefore, the shrinkage occurred in the polymer film, and the polymer-occupied space decreased. Additionally, the polymer film has higher strength and toughness under the action of air-hardening, which results in higher elastic modulus and compressive strength of polymer-stabilized sand. The present work may be helpful to understand the polymer stabilization mechanism and shed light on the new stabilization techniques of the problem soil. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mechanical properties of PU treated sand enhance with PU content and dry density at different temperatures. • Positive and negative temperatures both make positive effect on PU treatment. • PU coats sand grains and bonds them together. • PU bonding effect depends on PU content, dry density and temperature. In this study, the mechanical behavior of a polyurethane (PU) polymer-sand mixture was investigated by performing a series of uniaxial compression (UC) and direct tensile (DT) tests at different polyurethane polymer contents (PUC), dry densities (DD) and temperatures (TP). Results show that the axial stress–strain relationship depends on PUC, DD and TP, in particular, the failure mode gradually changes from fragile to ductile feature; the uniaxial compressive strength (UCS), secant modulus (E 50) and tensile strength (TS) all linearly increase with increasing PUC and DD at different TPs. Positive and negative temperatures (i.e., 35℃ and 50℃, −20℃ and − 10℃) both make positive effect on PU treatment since the UCS ratio, E 50 ratio and TS ratio all are higher than unity. Positive temperature significantly increases the strength and ductility, while negative temperature obviously affects the strength and modulus. Linear relationships of E 50 -UCS, UCS-TS are obtained, and these relationships depend on temperature. Scanning electron microscope (SEM) observation reveals that the presence of PU additive links adjacent grains together, improving the mechanical properties of the mixture. As this bonding effect is expected to be dependent on PUC, DD and TP, the strength, ductility and stiffness are different in different scenarios. [ABSTRACT FROM AUTHOR]