Bedding Layer Research Articles

Optimising creep constitutive modelling of layered soft rocks using particle swarm method

ABSTRACT Investigation of constitutive models is crucial for understanding the creep behaviour of soft rock and mitigating large deformation disasters. However, the presence of bedding layers in rock masses complicates the determination of creep parameters, increasing testing costs. Therefore, this study aims to conduct parameter optimisation analysis using the particle swarm method to refine creep parameters for soft rock with varying dip angles and analyse their effects. The framework and methodology of the model are presented, where the classical Burgers model was chosen as the constitutive model and the creep parameters to be optimised were determined. The dataset records the creep behaviours of soft rock with different dip angles prepared through laboratory experiments on 3D printing specimens. The proposed model is applied to this dataset to determine optimal creep parameters. Results indicate that transient and steady-state creep parameters increase proportionally with the dip angle, while the viscosity coefficient decreases. The optimised model demonstrates improved descriptive capabilities, contributing to understanding the creep properties of challenging geological formations and guiding on-site reinforcement measures.

Hydraulic Fracture Propagation in Layered Heterogeneous Rocks with Spatially Non-Gaussian Random Hydromechanical Features

AbstractThis study proposes a stochastic method to analyse the propagation of hydraulic fractures affected by layered heterogeneity in rocks in a toughness-dominated regime. The study utilises the phase-field method in the context of two-dimensional finite element analysis to model the hydraulic fracture (HF) propagation in rock materials in laboratory scale. Field data on hydrogeologic properties of some rocks reveal that material heterogeneity may appear in the form of leptokurtic marginal distributions. Generalised sub-Gaussian (GSG) model is capable of capturing physical characteristics of such rocks, and it is employed to stochastically model rocks with layered lithologic heterogeneity by generating a large number of auto- and cross-correlated random fields for hydro-geomechanical properties. To investigate the sensitivity of the cracking response to the inherent characteristics of material heterogeneity, various GSG distribution forms are considered in Monte Carlo (MC) analyses. The HF’s deviation from the theoretically predicted direction, which is perpendicular to the direction of the minimum in situ stress, is correlated with the distribution of hydro-geomechanical properties, showing a Gaussian-type distribution. This study concludes that the differential stress and the bedding orientation are the main factors affecting the HF deviation and the required breakdown pressure for initiating the HF propagation from a borehole. In the application of directional hydraulic fracturing (DHF), the effect of bedding layers becomes dominant when the bedding orientation is aligned with the direction of perforations in the boreholes.

Stability Of Concrete Armor Unit (Tetrapod) On Rear Side Of The Rubble Mound Structures With Rectangular Super Structure

The coastal structures allow the wave overtopping within a certain quantity. However the extreme wave overtopping could cause the damage of coastal structures. The most of the previous researches for the stability of armor unit were performed about the armor units placed on sea side of coastal structures. A rubble-mound structure is normally composed of a bedding layer and a core of quarry-run stone covered by one or more layers of larger stone and an exterior layer or layers of large quarry stone or concrete armor units. Coastal Engineering Manual (USACE, 2006) suggested the design figures without super structures and showed the ratio of the armor weight for each location of rubble mound structures and it could be known that the same weight ratio was needed to the sea side and harbor side slope of rubble mound structures. In this design figure, the filter rule is applied to the design figures of CEM, that is, the weight ratio for under layer is W/10 for the main armor weight ratio (W) to prevent smaller rocks in the under layer from being pulled through an over layer by wave action

Engineering and Technical Research on Combined Application of Stormwater Regulation Pond and PP Modular Cistern in Wet Trapped Loess Area

Abstract This paper analyzes the engineering characteristics of loess and the factors affecting wet subsidence, briefly outlines the application effect of PP modular cisterns, and combines the two to design a PP modular cistern based on rainwater harvesting. Combined with the analysis of the pre-engineering conditions of the storage tank, propose the treatment method for wet subsidence loess foundations. Design the structure of the storage tank by determining the volume of the tank by comparing the difference between the inlet and outlet flow during the storage time integral. Simulate the modeling of storm floods and the process of emptying stormwater regulating ponds. Evaluate the geologic conditions for the construction of the regulating pond project. Compare the original investigation report with the results of this paper’s test of the engineering foundation’s wet subsidence coefficient. Set different thicknesses of bedding layers and calculate the settlement of the center of the pool under different humidity levels of the loess layer. Simulate the 2.3-hour rainstorm process, analyze the storage volume of the storage pond during the period, and calculate the cumulative storage volume of the storage pond. This project’s foundation loess wet subsidence coefficient is medium, and the actual additional pressure is much smaller than the starting pressure of wet subsidence. It is appropriate to use the soil bedding program (1.6m plain soil bedding layer and then rammed 0.4m thick 2:8 gray soil, with PP module seepage control). Combined with the local hydrological conditions, it is known that the peak present time of the peak outflow from the regulating pond T P =85min, and the volume of the regulating pond is 22543.47 m 3.

DETERMINATION OF THE COMPRESSION MODULUS WITH A DYNAMIC CIRCULAR PLATE

<p><span class="fontstyle0">Geotechnical soil tests in order to achieve the best possible performance of new buildings or rehabilitation of existing buildings occupy one of the leading places in construction. Due to the lack of investigative work, a large number of buildings are exposed to danger. In order not to have bad effects on buildings in the future, it is necessary to minimize ground subsidence. Testing of the compressibility modulus / determination of the compressibility modulus is performed during the construction of roads, railways, buildings, parking lots and embankments, on the foundation soil, replacement layers, bedding and embankment layers and buffer. The purpose of the test is to ensure that, due to insufficiently compacted layers during installation, they do not settle after some time, as well as cracking of the floor in the building, deterioration of part of the building, deterioration of the pavement structure of roads and parking lots (potholes), etc. A circular plate is the name for an instrument used to test the compressibility module of a building's foundation. A dynamic test with a falling weight plate enables simpler and faster testing and immediate results.</span></p>

DETERMINATION OF THE COMPRESSION MODULUS WITH A DYNAMIC CIRCULAR PLATE

<p><span class="fontstyle0">Geotechnical soil tests in order to achieve the best possible performance of new buildings or rehabilitation of existing buildings occupy one of the leading places in construction. Due to the lack of investigative work, a large number of buildings are exposed to danger. In order not to have bad effects on buildings in the future, it is necessary to minimize ground subsidence. Testing of the compressibility modulus / determination of the compressibility modulus is performed during the construction of roads, railways, buildings, parking lots and embankments, on the foundation soil, replacement layers, bedding and embankment layers and buffer. The purpose of the test is to ensure that, due to insufficiently compacted layers during installation, they do not settle after some time, as well as cracking of the floor in the building, deterioration of part of the building, deterioration of the pavement structure of roads and parking lots (potholes), etc. A circular plate is the name for an instrument used to test the compressibility module of a building's foundation. A dynamic test with a falling weight plate enables simpler and faster testing and immediate results.</span></p>

Chuaria and Tawuia fossils from ∼1.0 Ga rocks in North China: Implications for a polyphyletic origin of Chuaria and a potential biological link between these two widespread Proterozoic taxa

The Proterozoic witnessed the emergence and rise of early eukaryotes and Proterozoic carbonaceous compression macrofossils provide a valuable window for our understanding of this ecological expansion. Among them, the discoidal Chuaria and tomaculate Tawuia, which often co-occur in the same bedding layer, are perhaps the most common fossil forms in Proterozoic successions with extremely long temporal and broad geographical distributions. However, their phylogenetic interpretations and the relationship between them have been debated for decades, due to their simple morphologies lacking phylogenetically diagnostic features. In this study, we used an integrated application of reflected and transmitted light microscopy, scanning electron microscopy, biometric analysis, and Raman spectroscopy to characterize well-preserved carbonaceous compression macrofossils of Chuaria and Tawuia from the Tonian Liulaobei Formation in Huainan region, northern Anhui province, North China. The fossils are abundantly preserved in a ca. 1–2 cm thick homogeneous mudstone layer and can be considered to be closer to an ecological community than fossils from multiple different layers or localities. The comprehensive analysis shows that even Chuaria vesicles from the same layer may have a polyphyletic origin and three groups of Chuaria vesicles have been identified. Among them, small Chuaria vesicles with minimum diameter < 1.2 mm can be either related to the sphaeromorphic acritarch Leiosphaeridia or interpreted as multicellular aggregates. In contrast, large Chuaria vesicles with minimum diameter ≥ 1.2 mm are more comparable to the type material of Chuaria circularis from the Chuar Group and more closely related, either phylogenetically or ontogenetically, to Tawuia vesicles. This study takes a step on the path to solving the mystery of the most common and widely distributed Proterozoic macrofossil assemblage (i.e., Chuaria-Tawuia assemblage), and urges thorough and systematic evaluations to be taken on the possibility that Chuaria vesicles from the same Chuaria-Tawuia assemblages or sole Chuaria assemblages in other localities might also be polyphyletic.

Influences of shale microstructure on mechanical properties and bedding fractures distribution

The difference in microstructure leads to the diversity of shale mechanical properties and bedding fractures distribution patterns. In this paper, the microstructure and mechanical properties of Longmaxi marine shale and Qingshankou continental shale were studied by X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM) with mineral analysis system, and nanoindentation. Additionally, the typical bedding layers area was properly stratified using Focused Ion Beam (FIB), and the effects of microstructure and mechanical properties on the distribution patterns of bedding fractures were analyzed. The results show that the Longmaxi marine shale sample contains more clay mineral grains, while the Qingshankou continental shale sample contains more hard brittle mineral grains such as feldspar. For Longmaxi marine shale sample, hard brittle minerals with grain sizes larger than 20 μm is 18.24% and those with grain sizes smaller than 20 μm is 16.22%. For Qingshankou continental shale sample, hard brittle minerals with grain sizes larger than 20 μm is 40.7% and those with grain sizes smaller than 20 μm is 11.82%. In comparison to the Qingshankou continental shale sample, the Longmaxi marine shale sample has a lower modulus, hardness, and heterogeneity. Laminated shales are formed by alternating coarse-grained and fine-grained layers during deposition. The average single-layer thickness of Longmaxi marine shale sample is greater than Qingshankou continental shale sample. The two types of shale have similar bedding fractures distribution patterns and fractures tend to occur in the transition zone from coarse-grained to fine-grained deposition. The orientation of the fracture is usually parallel to the bedding plane and detour occurs in the presence of hard brittle grains. The fracture distribution density of the Longmaxi marine shale sample is lower than that of the Qingshankou continental shale sample due to the strong heterogeneity of the Qingshankou continental shale. The current research provides guidelines for the effective development of shale reservoirs in various sedimentary environments.

Study on the control effect of local basement replacement on the stability of dump.

This study focuses on effectively controlling landslides at the boundary of a soft rock open-pit dump while ensuring safe increases in the dump's capacity and optimal utilization of external dump sites. To achieve this, the adoption of a local filling method for the dump base is proposed. By leveraging the concepts of limit equilibrium theory and equivalent shear strength parameters, the mathematical expression of the slope stability coefficient in the Morgenstern-Price method is derived and improved. This improved method is then applied to a real engineering example to determine the optimal basement replacement rate required to maintain slope stability. The findings reveal that the local filling of the base is well-suited for slopes susceptible to potential landslides associated with cutting layers, bedding layers, and swelling. For practical ease, it is advisable to choose the lowest step in the dump's slope for construction convenience. As the local replacement rate of the base increases, the slope's stability coefficient gradually improves, with the K-Fs ratio showing a prominent role in this process. Additionally, numerical simulation methods are employed to elucidate the mechanism of the dump's landslide following local basement replacement, thereby providing comprehensive evidence of the engineering applicability of this method. The research results demonstrate a promising practical application prospect for effectively controlling the stability of soft base dump slopes.

A Study on the Load-Bearing Characteristics and Load Transfer Mechanism of Bag Grouting Pile in Soft Soil Areas

In soft soil areas, to compare the load-bearing characteristics of bag grouting piles and cement mixing piles and study the load-bearing mechanism of bag grouting piles, field tests are conducted in this study, including the comparative compressive test of bag grouting piles and cement mixing piles, and the analysis of pile axial force, pile side friction resistance, and pile end resistance. Moreover, a numerical simulation is developed using ABAQUS 2020 (finite element analysis software) for three-dimensional modeling. The numerical simulation results are compared with the field test results to verify the reliability of the numerical simulation. Furthermore, the influences of five factors are studied; namely, pile length, pile diameter, pile spacing, the thickness of the bedding layer, and grouting pressure are studied for their effects on the compressive bearing characteristics of the bag grouting pile. The results show the following: (1) For composite foundations, bag grouting piles are more effective than cement mixing piles in soft soil areas, and the former provide an 8.8% increase in the bearing characteristics. (2) With an increase in the load, the bag grouting pile experiences greater compression in the middle of the pile body, and the pile side friction resistance is increased; therefore, the pile side friction resistance can be fully developed, and the bag grouting piles have the ability to transfer the load from the top of the pile to the soil at the bottom of the pile. (3) When the external load is maximized, the sharing ratio of pile side friction resistance reaches 96.3%, which shows the excellent frictional performance of bag grouting piles. (4) Among the five factors mentioned above, the most important one is the pile diameter, followed by the pile length and pile spacing, the thickness of the bedding layer, and finally the grouting pressure. The optimal combination in this paper is a pile length of 18 m, pile diameter of 0.4 m, pile spacing of 1.0 m, bedding thickness of 0.3 m, and grouting pressure of 0.6 MPa. Therefore, changing the pile diameter can be given priority during the construction design. The findings in this paper can provide valuable insights and practical experience for the design of similar engineering projects.

Study of the inhibitory effect of a soft cushion on the propagation of pressure pulsation in pumped storage power stations

AbstractHigh‐frequency pressure pulsations are hydraulic phenomena that are frequently observed in pumped storage power stations. These pulsations can propagate through the steel pipes, concrete lining, and the surrounding rock system, which in turn may have detrimental effects on the environment, such as noise pollution, and relocation of the local residents. This paper proposes a vibration‐damping concept that involves wrapping a local soft cushion layer outside the buried steel pipe; this layer could partially eliminate the pressure fluctuations in the headrace tunnel, thereby reducing the ground vibrations caused by the pressure pulsations. In this study, the finite element method was used to model the propagation of vibrations in the surrounding rock and fluid‐filled pipes, including static simulation of the structure, and dynamic simulation of the surrounding rock. The simulation results suggest that adding an appropriate local soft bedding layer can effectively reduce the ground vibrations by more than 60% and the possible surface noise within the standard vertical vibration norms. The inhibitory effect of the soft cushion on the propagation of vibrations is determined by the wrapping angle, thickness, and material of the bedding layer. This effect increases with increasing wrapping angle and thickness of the bedding layer, and decreases with increasing elastic modulus of the material. After the addition of the bedding layer between the steel pipe and concrete lining, the pressure in the inner pipe is primarily borne by the steel lining rather than the coupling of the steel lining, concrete lining, and the surrounding rock. Hence, the thickness of the part of the steel liner in contact with the soft bedding layer should be increased. In addition, the thickness variations in the steel pipe joints should be smooth to avoid stress concentration.

Investigation of shear behavior of notched bedding rock containing welded interface between hard and soft layers; an acoustic emission-based approach

The present work investigates the impacts of layer number, ratios of layer, brittleness of layer, layer angle, and length of notch on the shear failure of bedding rock with a welded interface, using experimental punch test and numerical modeling. The study also analyzed the acoustic emission (AE) events throughout the entire process, from initial shear stress applied to the notched bedding layer to final rock bridge failure. Rectangular samples with varying numbers of soft and hard layers were prepared. The ratio of soft gypsum thickness to total sample thickness in the one soft layered model, one hard layered model, two-layered model, three-layered model with soft interlayer, and four-layered model was 1, 0, 0.5, 0.33, and 0.5, respectively. Each model consisted of two vertical non-persistent edge notches in one direction, with notch lengths of 20, 40, and 60 mm. All layers had a horizontal configuration in the experimental test (layer angle 90°), while angle of bedding layers varied from 0° to 90° with increments of 15°. The considered models were investigated using punch shear tests. The results indicate that a tensile crack was initiated at the tip of the notch, propagating parallel to the shear loading axis until coalescence with the model boundary. Both peak shear strength and shear stiffness decreased as layer angles increased in models consisting of two and four layers. The mechanical properties of the three-layered model improved with increasing layer angles due to the increased presence of the hard gypsum layer in the shear failure surface. Increasing the number of layers resulted in an increased number of major AE hits, while increasing the notch length led to a drop in the number of observed AE hits. Moreover, the number of major AE hits was higher in hard ductile gypsum than in soft brittle gypsum. The failure mechanism was consistent between numerical simulation and experimental testing.

Assessing the key factors affecting the substructure of ballast-less railway track under moving load using a double-beam model and random forest method

In this paper, an approach is presented for analyzing the substructure of a slab track. The approach involves deriving a semi-analytical solution of the double-beam model, which incorporates a visco-elastic connection between two concrete beams and a spring-damping foundation. The model is then subjected to a concentrated moving load with a constant velocity. To more effectively assess the impact of various parameters, a random forest algorithm is utilized. The parameters considered include the spring-dashpot properties of the connection layer and the bedding layer, the thickness of the upper and lower beams, and the velocity of the moving load. The results of the random forest regression show that the stiffness of the intermediate and foundation layers have the greatest influence on the vertical deflection of the upper beam. However, the effect of stiffness of intermediate layer on the deflection and bending moment of the lower beam is found to be marginal. Moreover, for high-speed trains, the velocity of the concentrated moving load substantially changes the extreme responses attributed to the vertical deflection and bending moment. In this context, the damping properties of the interconnection layer and the subgrade course have a greater impact on the responses of the upper and lower beams.

Field implementation of enzyme-induced carbonate precipitation technology for reinforcing a bedding layer beneath an underground cable duct

A suitable bearing capacity of foundation is critical for the safety of civil structures. Sometimes foundation reinforcement is necessary and an effective and environmentally friendly method would be the preferred choice. In this study, the potential application of enzyme-induced carbonate precipitation (EICP) was investigated for reinforcing a 0.6 m bedding layer on top of clay to improve the bearing capacity of the foundation underneath an underground cable duct. Laboratory experiments were conducted to determine the optimal operational parameters for the extraction of crude urease liquid and optimal grain size range of sea sands to be used to construct the bedding layer. Field tests were planned based on orthogonal experimental design to study the factors that would significantly affect the bio-cementation effect on site. The dynamic deformation modulus, calcium carbonate content and long-term ground stress variations were used to evaluate the bio-cementation effect and the long-term performance of the EICP-treated bedding layer. The laboratory test results showed that the optimal duration for the extraction of crude urease liquid is 1 h and the optimal usage of soybean husk powder in urease extraction solution is 100 g/L. The calcium carbonate production rate decreases significantly when the concentration of cementation solution exceeds 0.5 mol/L. The results of site trial showed that the number of EICP treatments has the most significant impact on the effectiveness of EICP treatment and the highest dynamic deformation modulus ( E vd ) of EICP-treated bedding layer reached 50.55 MPa. The area with better bio-cementation effect was found to take higher ground stress which validates that the EICP treatment could improve the bearing capacity of foundation by reinforcing the bedding layer. The field trial described and the analysis introduced in this paper can provide a practical basis for applying EICP technology to the reinforcement of bedding layer in poor ground conditions.

Before and after: A visual glimpse into the coking behaviour of coal macerals

Coal petrography as a tool for predicting coke quality has been employed for many decades. This paper first provides a brief review of some of the founding research in this area and secondly proposes and demonstrates a technique for direct optical comparison of a semicoke to its exact piece of precursory coal to observe the pyrolysis behaviour of individual macerals. The technique involves imaging a polished block sample of coal (with the polished face of interest having orientation perpendicular to the bedding layers), pyrolysing the sample in a furnace up to 525°C under conditions attempting to mimic those in a coke oven, embedding the resulting semicoke in resin and lightly re-polishing and re-imaging the surface of interest. Comparison of the optical images of the sample pre- and post-pyrolysis enables a 2-dimensional visual assessment of the coking behaviour of the inherent macerals. This method was applied to two Permian coals: a Mozambican coal with random reflectance of 1.21% and an Australian coal with random reflectance of 1.28%. The main observations were (i) anisotropic swelling, with swelling much greater in the direction perpendicular to the bedding layers compared to that parallel, (ii) noticeably different pore structure arising from the vitrinite macerals collotelinite and collodetrinite, and (iii) visual evidence of semifusinite reactivity. It is intended that application of this technique will enhance the fundamental understanding of maceral specific coking behaviour and thus assist coke-makers with their blend formulations.

Effect of mattress bedding layer structure on pressure relief performance and subjective lying comfort

Mattresses' pressure relief performance and comfort largely affect sleep quality. Mattress filling materials have been proven to affect the interface pressure distribution and comfort, but the effect of mattress structure is unclear. In this paper, the interface pressure distribution and subjective comfort of 10 subjects were assessed in the different bedding layer structures of mattresses, after mattress support performance was tested. The results show that the mattresses with bedding material hardness gradually increasing from the top layer to the bottom layer (BMH-ITTB) structure have a softer surface layer, a better support core layer, and higher fitness. This enables the mattress to achieve a better decompression effect. The low-pressure area (PAI≤0.67kPa) increased, while the high-pressure area (PAI≥2.67kPa and PAI≥4.00kPa), maximum pressure (P95), average pressure (P50), and pressure index (PI) decreased. This also enables the mattress to achieve higher subjective comfort scores.

Plants, people and fire: Phytolith and FTIR analyses of the post-Howiesons Poort occupations at Border Cave (KwaZulu-Natal, South Africa)

Border Cave is a well-known South African Middle and Early Later Stone Age site located in KwaZulu-Natal. The site has exceptional plant preservation, unparalleled in the African Middle Stone Age archaeological record. This study focuses on the phytolith and FTIR analysis of two Members (2 BS and 2 WA) of the under-documented post-Howiesons Poort occupations dating to ∼60 ka. These members contain complex successions of vertically overlapping, interdigitating light brown sediments, plant bedding and combustion features of various sizes. The complexity and distinctiveness of these deposits provide an excellent opportunity for the study of plant exploitation strategies and their associated human behaviour. Our taphonomic assessment inferred, through the variability of phytolith properties and minerals composing archaeological layers, that specific occupations suffered more physical weathering than others, for example in the form of trampling. The preservation of fragile and highly soluble phytoliths (eudicot leaf phytoliths) and the high frequencies of articulated phytoliths indicates that some bedding deposits experienced little disturbance after their deposition. Not all bedding layers dating to ⁓60 ka show, from a phytolith perspective, the same plant composition, which could be explained in terms of changes in human preference for the use of plants over time to construct bedding or because distinct types of living floors are represented. Finally, the systematic application of phytoliths and FTIR to the complex archaeological sequence of Border Cave confirm these analyses can be used in the future to identify bedding deposits not visible to the naked eye, and behavioural patterns obscured by diagenetic or biased processes during sampling.

Influences of Inclined Pre-Existing Flaw on Shale Failure Modes in Uniaxial Compression Tests

Numerous studies have focused on the mechanical properties of shale specimens to support hydraulic fracturing in shale gas engineering. However, the failure modes of shale specimens containing a pre-existing flaw are still not clear. A series of uniaxial compression tests were conducted on shale specimens containing a pre-existing flaw coupled with acoustic emission (AE) technology and a high-speed camera. A slow enough and variable loading speed scheme (0–50 kN: 0.1 kN/s, 50–100 kN: 0.05 kN/s; 100-failure: 0.02 kN/s) is adopted to allow microcracks to fully develop. The damage mechanism in the mesoscale from moment tensor inversion of the AE signals and the cracking behaviors on the macroscale were associated. Both the pre-existing flaw and the bedding layers had significant influences on the mechanical characteristics, progressive cracking, and failure modes of the shale specimens. The peak stress increases fluctuated as the bedding layer angle α increases, and the maximum and minimum values take place at α=90° and α=0°, respectively. In addition, the pre-existing flaw, the bedding layers, and the compression stress field jointly control the failure modes of the shale specimens. It was found that the α=0° specimen failed due to tension splitting, the α=30° specimen failed due to tension splitting and shear across the matrix, the α=60 specimen failed due to shear across the shale matrix and shear along the bedding layers, and the α=90° specimen failed due to tension along the bedding layers and shear across the shale matrix. The study can provide some references to the construction of complex crack networks in shale gas engineering.

Characteristics of mixed-mode Ⅰ-Ⅱ fracture of bedding mud shale based on discrete element method

Mud shale is an abundant unconventional source of oil and gas, with considerable potential for extensive exploration and development. Hydraulic fracturing is a core technology for the harvesting of mud shale resources. Mud shale usually contains developed bedding structures. A mixed-mode Ⅰ-Ⅱ failure occurs when hydraulic fractures meet the bedding layers. Understanding the characteristics of the mixed-mode Ⅰ-Ⅱ fracture of mud shale is of high practical significance. A numerical model for a semi-circular bend (SCB) specimen is built using a flat-joint model (FJM). The macroscopic mechanical parameters of the numerical model are calibrated, including the uniaxial compressive strength, elastic modulus, and Poisson's ratio. The microscopic parameters of the model are constantly adjusted using the trial-and-error method to realize an effective fit between the model and rock parameters. The results show variation characteristics of the stress field, displacement field, and fracture toughness are revealed on a microscopic scale during fracture initiation and propagation. The fracture propagation law under different bedding strengths and initial fracture angles is discussed, and the pattern of fracture interactions under different bedding angles and initial fracture angles is obtained. The results showed that the influence of the fracture toughness as the bedding angle decreased. The fracture arrest and the degree of fracture deflection upon reaching the bedding are more considerably influenced by the strength of the weak plane. The higher the bedding strength of the weak plane, the more likely the fractures were deflected in the bedding. However, fracture penetration of the bedding layer is more greatly influenced by the bedding angle.

Detection of cracks in cemented loess of ancient buildings using remote sensing

The bases of ancient Chinese buildings are prone to deformation, cracks, and other hidden problems due to their age and other reasons. Rainfall and water seepage produce great harm to the cracks of soil plinths. Based on a ground-penetrating radar method, detecting cracks and water erosion defects is important for protecting ancient buildings. This study examines the reflection characteristics of ground-penetrating radar (GPR) waves at different lithological interfaces. Physical experiments and their numerical and physical laws were used to study the reflection characteristics of GPR incidents from brick to air, unsaturated soil, water, and metal interfaces. The model was applied to detect defects of the Xi’an Bell Tower and the main research results are as follows. The echo amplitude of GPR was positively correlated with the relative permittivity of the bedding layer, and its basic law conforms to the positive logarithmic curve. The hyperbolic opening of water erosion imaging of the base-compacted soil is larger, the attenuation effect increases and the signal reflection is obvious. These results provide the theoretical basis and technical support for the actual detection of water erosion deterioration of loess in similar projects, and this provides theoretical and technical references for rapid identification and management of defects in ancient buildings.