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 Bulletin of Engineering Geology and the EnvironmentJournal Prestige (SJR): 0.896 Citation Impact (citeScore): 2Number of Followers: 15      Hybrid journal (It can contain Open Access articles) ISSN (Print) 1435-9537 - ISSN (Online) 1435-9529 Published by Springer-Verlag  [2469 journals]
• Physico-mechanical and mineralogical investigations of red bed slopes
(Cluj-Napoca, Romania)

Abstract: The southern slope of the Cetățuia-Hoia Hill, located in the urban setting of Cluj-Napoca (Romania), consists of clayey deposits interbedded with sands and sandstones. The slope deposits belong to the Moigrad Formation and are representative of “red bed” continental deposits found across the world. Although documented as a landslide-prone area, the hillslope receives increased attention due to urban development and real estate pressure. The slope was affected by an old, deep-seated landslide; mudflows; and anthropogenic interventions. The stability of the old landslide is close to equilibrium (1.35) and its reactivation may be triggered by rainwater infiltration. The Moigrad Formation deposits are mostly active, expansive, and display medium to high plasticity. Their shearing resistance is described by effective friction angles of 6.7–33.7° and effective cohesive strengths of 7–122 kPa. With regard to mineralogy, the deposits are made up of quartz, feldspar, calcite, dolomite, and phyllosilicates (micas, chlorite, kaolinite, and minerals belonging to the smectite group), while their clay-sized fraction (< 2 µm) is made up of illite–smectite interstratifications, illite, chlorite, kaolinite, and quartz. The physical and mechanical properties of the deposits are closely related to the type and amount of clay-sized minerals, especially to the illite–smectite interstratifications and illite, which are the main components in the clay-sized fraction. Interactions between these components and water infiltrated within the hillslope are proposed as driving mechanisms for landslide reactivation and as active phenomena undermining the stability of the area.
PubDate: 2022-01-21

• Effect of unsteady flow dynamics on the impact of monodisperse and
bidisperse granular flow

Abstract: Protective barriers provide crucial resistance against the impact of granular flows. However, the adoption of characterized flow depth and velocity values in impact force estimation remains unclear and requires further investigation, especially with consideration of unsteady flow dynamics. Previous practices suggest that the bulk flow velocity with the assumption of uniform distribution should be used in impact force estimation, while we observe the lower part of the flow consistently exhibits lower velocities than the upper part, because granular shear behavior is enhanced within the boundary layer, which strongly affects the flow velocity. As a result, using a bulk velocity in debris impact force estimation may result in that a larger dynamic pressure coefficient must be used in hydrodynamic model. We made a quantitative assessment. For rapid granular flows, the use of a bulk velocity to calculate the dynamic force component could result in underestimation of approximately 10–30%. Therefore, based on the numerical results, it is suggested that the average velocity of the upper 50% of the flow body can be adopted in impact force estimation. If the front flow depth is used to calculate the dynamic impact force component, the results may be approximately 50% lower than the true value, which indicates that the dynamic force on a barrier is likely not controlled by the granular flow front and that a maximum flow depth may be more appropriate if a hydrodynamic model is adopted. In addition, it seems that the strategy we proposed can be used for both of monodisperse and bidisperse granular flow when boulder impact is excluded.
PubDate: 2022-01-20

• Experimental investigation on stress-induced failure in D-shaped hard rock
tunnel under water-bearing and true triaxial compression conditions

Abstract: To investigate the influence of water on stress-induced failure in D-shaped hard rock tunnels, a series of true triaxial tests were performed on naturally saturated red sandstone cube samples containing a D-shaped hole. A self-developed real-time monitoring device was used to observe and record hole failure in real time, and the process and characteristics of stress-induced failure in D-shaped holes were summarized. The influence of water on failure form, energy storage properties, surrounding rock stability, and axial stress on the stability of the surrounding rock was discussed, and the mechanism of water on stress-induced failure was revealed. The results show that the stress-induced failure in a water-bearing D-shaped tunnel can be divided into buckling deformation, tension cracking, macrocrack propagation and coalescence, and slab flaking. The dominant failure mode of the stress-induced changes from tension around the tunnel to shear of the surrounding rock in depth. A quiet period exists between two adjacent significant AE counts, and the length of the quiet period increases as the two horizontal principal stresses increase. Under the influence of water, the capacity of the surrounding rock to store elastic strain energy decreases, and the dissipated energy required for deformation and failure increases; the form of stress-induced failure changes from spalling accompanied by occasional rockburst to spalling. The increase in lateral stress can enhance the stability of the surrounding rock, and the influence of axial stress on the stability of the surrounding rock is related to the magnitude of lateral stress.
PubDate: 2022-01-18

• Description of different cracking processes affecting dispersive saline
soil slopes subjected to the effects of frost and consequences for the
stability of low slopes

Abstract: To deal with soil salinisation and improve ecosystems in western Jilin Province, the local government initiated water diversion projects to wash the salinised lands. The slopes of many water channels were found to be damaged. This has motivated the study of failure mechanism of saline soil slopes to provide a theoretical basis for the treatment of slopes. In this study, it was found that the soil in the study area had properties of soda saline soil, seasonally frozen soil, dispersive soil, and fissured soil. Form field investigations, it was found that owing to geological and environmental factors, cracks develop on soil slopes and are mainly freeze-heave cracks, scouring cracks, suffosion cracks, and unloading cracks. First, periodic freeze–thaw cycles led to the development of frost-heave cracks on the slope and induced the formation of fissured soil. Next, under precipitation, soil slope experienced erosion damage, forming scouring cracks in the direction perpendicular to channel. In addition, because the study area is consisted of soda saline soil, which contains soluble carbonate salts with a relatively high content of Na+, suffosion occurred due to water seepage, forming suffosion cracks. Moreover, along with the completion of channel construction and injection of water, the toe of slope was prone to collapse owing to the long-term soak, this triggered the unloading of the slope toe and the development of unloading cracks in the direction parallel to the strike of channel. Eventually, the slope experienced tensile failure and creep-cracking failure under the effect of multi-environmental fields.
PubDate: 2022-01-17

• Analytical and numerical simulations to investigate effective parameters
on pre-tensioned rockbolt behavior in rock slopes

Abstract: Pre-tensioning of rockbolts is permitted to ensure better confinement between bedding rock slopes. The resulting shear adherence between layers is then increased, and a resistance against the rock block’s movement is developed. This paper develops a simple analytical approach to better understand the performance of pre-tensioned grouted rockbolts in bedding rock slopes. The force method approach and the deformation compatibility principles are used to model the contribution of developed axial and shear bolt forces at the intersection between the bolt and the joint plane to evaluate the behavior of the rockbolt in the elastic state. The effects of the pre-tension, the joint roughness, bolt inclination with respect to the joint plane, and rock strength are investigated, and the influence of the bolt contribution to preventing rock layer sliding is discussed. Furthermore, a 3D numerical approach is used to study the bolt performance in a plastic state. The results show that when the bolt is completely perpendicular to the discontinuity, the lower bolt contribution is generated. The pre-tensioning and joint roughness caused an improvement in resistance at the joint due to the utilization of the bolt axial capacity. Besides, the pre-tensioned rockbolt will be more useful for high-strength rock slopes.
PubDate: 2022-01-17

• Experimental investigation of nano-ZnO effect on mechanical properties of
cemented clayey sand

Abstract: To date, various nanomaterials have been used in the literature for soil improvement. However, the application of Nano-ZnO (NZ) to the ultrasonic pulse velocity (UPV) in cement-cured clayey sand soils and the relationship between UPV and unconfined compressive strength (UCS) have not been addressed. A series of UCS and UPV tests were performed to investigate the effects of NZ on the mechanical properties of cemented clayey sand. In addition, the microstructural properties of cemented clayey sand with NZ additive were investigated using a high-resolution field-emission scanning electron microscopy (FESEM). The response surface method (RSM), an experimental technique to reduce the number of tests and the cost of research, was used to design the experiments and evaluate and optimize the results. The results showed that using NZ as an additive enhances the mechanical properties of cemented clayey sand. The correlation with an acceptable determination coefficient between UPV and UCS was suggested at different ages. The correlation with a high determination coefficient between elastic modulus and UCS was also presented. The examination of FESEM images showed that the micro-cracks are reduced in the samples containing NZ. Also, in the samples containing NZ, the calcium hydroxide (CH) size decreased and its orientation is also moderated.
PubDate: 2022-01-15

• Influences of water on the microstructure and mechanical behavior of the
Xigeda formation

Abstract: As a typical hard soil and soft/weak rock, the Xigeda formation is a set of Cenozoic lacustrine semi-rock discontinuously distributed in south-western China. Engineering practice shows that water exerts a significant influence on the mechanical properties of the Xigeda formation. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and triaxial compression tests were conducted by means of in situ sampling of the Xigeda formation in Zhaizi village along the Jiasha River. The mineral composition and microstructure were determined, the deformation and failure mechanisms were investigated, and influences of the water content on both deformation and strength indices were discussed. The results show that (a) the Xigeda formation has a characteristic weakly cemented structure, which differs from that of soil and rock, and this cemented structure is easily damaged under saturated conditions; (b) with increasing water content, both average modulus and shear strength of the Xigeda formation decrease significantly, and influence of water content on peak strength is much greater than that on residual strength; and (c) in the range of tested conditions (w = 17.79 ~ 30.83%, σ3 = 200 ~ 800 kPa), both the peak and residual strengths meet the Mohr–Coulomb criterion. The results can provide an experimental basis and mechanism informing engineering practice in the Xigeda formation.
PubDate: 2022-01-13

• System safety assessment with efficient probabilistic stability analysis
of engineered slopes along a new rail line

Abstract: A proper stability assessment of engineered cutting and embankment slopes is crucial to safe train operation and the performance management of rail infrastructure. Through the presentation of a case study, this paper develops a methodology for the safety evaluation of large-scale slope systems incorporating efficient probabilistic stability analysis of engineered slopes for a long rail line under construction. A long geotechnical slope is equally segmented into multiple consecutive sections according to the representative value of the local failure lengths of three-dimensional slopes, and each section is assessed for its probability of failure ( $${P}_{f}$$ ). Soft computing by multivariate adaptive regression splines (MARS) is incorporated into the reliability analysis of a batch of slope segments. The construction of a MARS model requires a subset of data samples obtained from a limit equilibrium slope stability program; the validated MARS model is then used to generate the probability of failure of the rest of slope sections. The $${P}_{f}$$ values for 2691 sections in total, determined by either direct probabilistic stability analysis or the MARS-derived predictive model, is subsequently introduced into a reliability-based performance evaluation of the long railway geotechnical slope system. The k-out-of-n system model is adopted to characterize the relationship between the entire system and its components concerning safety. The effect of remediation on the reliability of geotechnical system is finally explored by examining the variation characteristics of $${P}_{f}$$ with a tolerable number of failure segments in the system. The proposed methodology can be readily extended to assess large-scale geotechnical systems for an operational rail line.
PubDate: 2022-01-12

• Influence of wing crack propagation on the failure process and strength of
fractured specimens

Abstract: The wing cracks are usually the first crack that appears in the loading process in studies about fractured rocks, and a certain correlation exists between the wing crack propagation process and the peak strength of fractured specimens. To further explore the correlation between wing crack propagation and the peak strength of specimens, specimens containing the main flaw and prefabricated wing cracks were chosen as the test object, and compression tests and numerical simulations were carried in this study. To some extent, it can be regarded as a step-by-step simulation and reproduction of the propagation process of wing cracks. The loading and monitoring processes and the analysis of results reveal that specimens with the prefabricated wing cracks show more plasticity in the loading process than the other specimens without the prefabricated wing cracks. However, the length of prefabricated wing cracks does not affect the peak strength of the specimen. The wing crack has a critical length of the stable propagation for each specimen with a single flaw under uniaxial compression, which determines the peak strength of specimen. When the length of wing cracks extends to this critical value, the specimen reaches its peak strength. On this basis, the peak strength of the fractured specimen can be solved using this critical value. This paper provides a reference for the theoretical analysis of the peak strength of fractured specimens.
PubDate: 2022-01-12

• Three-dimensional method for slope stability with the curvilinear route of
the main sliding

Abstract: The route of the main sliding is considered to be a linear line in the existing three-dimensional limit equilibrium methods for slope stability analysis. However, there is a curvilinear route for the main sliding caused by the translational movement and the rotation of the sliding body in slope failures. In this study, a three-dimensional limit equilibrium method was proposed for slope stability with the curvilinear route of the main sliding. The basic physical quantities for slope stability analysis in the orthogonal curvilinear coordinate system were obtained by the mapping between the orthogonal curvilinear coordinate system and the Cartesian coordinate system. The four equilibrium equations (a force equilibrium equation and three moment equilibrium equations) were established by the equilibrium conditions of the entire sliding body. The three-dimensional factor of safety for the slope with the curvilinear route of the main sliding was deduced by an analytical or a numerical method. Some examples proved that the present method can calculate the factor of safety and evaluate the stability of the slope. The results of examples showed that the factor of safety of the curvilinear route was significantly smaller than that of the linear route. The three-dimensional limit equilibrium method for slope stability analysis was further developed in this study, which provided a theoretical basis for the scientific and reasonable evaluation of slope stability.
PubDate: 2022-01-12

• Short- and long-term transports of heavy metals through earthen liners:
physical and numerical modeling

Abstract: The effectiveness of earthen liners in preventing the migration of heavy metals (HM) from the landfill requires the study of the transport parameters of HM and the determination of the optimum thickness of the earthen liners that can effectively retain the HM within their permissible concentrations during the lifetime of a landfill. The aim of this study is to investigate the transport behavior of four HM (cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn)) through an earthen liner via physical and numerical modeling. Subsequently, the optimum thickness of earthen liners required to prevent the breakthrough of HM for different assumed landfill life expectancies was assessed from the long-term migration profiles of HM. In general, the extent of HM migration in two types of compacted residual soil liners, which were clayey sand and silty sand, followed the sequence of Zn < Cd < Cu < Pb. It is observed that the extent of HM migration was greater in the compacted silty sand sample attributed to its higher porosity and lower HM adsorption capacities. The numerical simulations results further revealed that the optimum thickness required for compacted clayey and silty sand liners to retain the four studied HM within their regulatory threshold values for a period of 100 years were 1 m and 1.9 m, respectively. Considering the higher mobility and more stringent allowable concentration of Cd, Cd can serve as a key indicator of early HM contamination caused by leachate migration from Malaysian municipal solid waste landfills.
PubDate: 2022-01-12

• Investigation on intrusion of bentonite–sand mixtures in fractures with
consideration of sand content and seepage effects

Abstract: During the long-term operation of a repository, bentonite–sand mixture could invade into fractures in the surrounding rock with infiltration of groundwater, resulting in loss of bentonite from the barrier with possible leakage of nuclides and consequently endangers the safety of the repository. In this work, an apparatus was designed with an artificial joint (fracture) being made between two parallel stacked transparent acrylic plates with a stainless-steel gasket inserted. Intrusion tests were conducted on the mixture specimens with different sand contents into artificial fractures with two sizes. A flow with constant velocity was applied to simulate seepage in the surrounding rock formations. Images were regularly captured with a camera, and parameters including the intrusion distance and widths of the non-accessory and accessory mineral rings were determined using a commercial software. Simultaneously, fluid was collected at the outlet and the erosion rate bentonite was determined by a turbidimeter. Finally, based on the force equilibrium, an intrusion model for describing bentonite–sand mixture intrusion into fractures with consideration of sand content and seepage effects was established and verified. Results show that the intrusion distance, two-region widths, and erosion mass decrease significantly with increasing sand content. After intrusion, the dry density of the bentonite specimen nearby the extrusion port decreases with increasing sand content and fracture size. Meanwhile, results of XRD tests indicate that the ratio of accessory minerals in the accessory mineral ring was higher than that in the pure Gaomiaozi bentonite specimen. Verifications confirmed that the intrusion model proposed in this work can well simulate the data measured.
PubDate: 2022-01-12

• Effect of pH on the mechanical performances of cement/slag-stabilized
marine sediments: Experimental and analytical constitutive modelling

Abstract: While stabilized marine sediment (SMS) is widely used in construction projects, its mechanical response may be influenced by its environment, such as contact with liquids of different pH value, the extent of which is not well understood. In this context, a marine sediment stabilized with Ordinary Portland Cement (OPC) and Ground-Granulated Blast Furnace Slag (GGBS) is studied in this paper. Unconfined compressive strength (UCS) tests, mass loss analyses and micro-structure evaluations were conducted on SMS specimens having different curing durations (7, 28, 56 and 98 days) and in contact with liquids with different pH values (1, 7 and 10) for 100 days in a tank leaching setup. The results indicate that 1) replacement of OPC by GGBS in the ratio of 1:1 is most efficient in improving the UCS of the SMS considered herein; 2) UCS values determined after leaching at pH=7 and 10 are greater than those without leaching, whereas UCS values after leaching at pH=1 are lower than those without leaching, and 3) a reduced mass loss and a more compact structure occurs with greater leachate pH. Based on the experimental observations, a novel elastoplastic constitutive model with analytical stress–strain solutions is presented to describe the mechanical behaviour of SMS. The influences of two factors (leachate pH and curing durations) on the model parameters are analysed using the binary quadratic nonlinear regression method. The analytical model is shown to be capable of predicting the mechanical performance in various pH environments, representative of a variety of SMS applications.
PubDate: 2022-01-11

• Physical model test on deformation and failure mechanism of deposit

Abstract: Rainfalls with heavy intensity and long duration are the main factors that trigger landslide. A large-scale test of physical model of landslide induced by gradient rainfall is conducted to investigate the mechanism of landslide caused by rainfalls with an indoor large-scale physical model test system. By monitoring the variation of pore water pressure, soil pressure, slope surface displacement, and groundwater level, the deformation and failure mechanism of deposit landslide under gradient rainfall are studied. The results show that the pore water pressure and soil pressure increase with the increase of the duration of rainfall, and the greater the rainfall intensity is, the greater the peak values of pore water pressure and soil pressure are. The intensity and duration of rainfall are the main influencing factors of landslide deformation. The decrease of effective stress and the rise of groundwater level are the root causes of landslide deformation. During a rainfall, excessive pore water pressure appears in the slope, which can be used as an early warning indicator of landslide deformation and failure. The deformation of slope body is nonlinear and shows a stepped pattern under gradient rainfall. During a rainfall, the toe of the slope is usually damaged first. Tension cracks appear in the rear edge and the middle part of the slope successively, showing the characteristics of traction failure.
PubDate: 2022-01-11

• Geochemical, mineralogical, and microstructural characteristics of fault
rocks and their impact on TBM jamming: a case study

Abstract: Faults can represent adverse geological conditions that frequently cause the jamming of tunnel boring machines (TBMs). In this study, we present a case study of TBM jamming at mileage 106 + 402.8 in the TBM 2 bid section of the Central Yellow River Diversion in China. Firstly, we identify possible jamming hazards. In addition, a fault between dolomitic limestone and granite was revealed by the geological investigation. Secondly, by comprehensively analyzing the geochemical, mineralogical, and microstructural characteristics of the host and fault rocks, we identify the compressional torsional fault FT2 and the nearby fault rocks. Finally, we explore how the geological characteristics of the fault rocks affect the likelihood of TBM jamming. Our results indicate that geochemical effects and long-term tectonic stresses caused major changes in the structure and composition of the migmatitic granite host rock; the fault rocks exhibit mylonitization and cataclastic breccia fabrics. Hydrothermal fluid alteration transformed the biotite and plagioclase into chlorite. In addition to the precipitation of carbon-rich fluids, which resulted in the formation of graphite, the weaknesses of these fault rocks were compounded by the presence of clay minerals and their obvious cataclastic structures. The comprehensive effect of the geological characteristics of fault rock, geological structure, ground stress, and TBM excavation unloading leads to collapse and large deformation of the weak rock in the fault zone as the main geological reason for the TBM jamming; the corresponding engineering treatment measures and recommendations are proposed. This case aims to provide reference and learning for avoiding the re-occurrence of similar jamming accidents.
PubDate: 2022-01-10

• Experimental and numerical study of the mechanism of block–flexure
toppling failure in rock slopes

Abstract: Block-flexure is the commonest mode of toppling failure and can be frequently encountered in anti-inclined rock slopes. In this work, the failure mechanism of block–flexure toppling (BFT) was investigated using centrifugal and numerical models. The numerical model was configured using the Universal Distinct Element Code (UDEC) and calibrated with the results of the centrifuge test. All the simulation results, including the measured displacements, failure load, and failure surface, are generally in line with that of experimental results. Further, the results of simulations show that, well before the appearance of instability in the jointed rock slope, slipping failure and opening fractures had occurred in the interlayer. Moreover, all the acting points of normal forces in steep joints are located between the bottoms and the midpoints of the columns under consideration, in the process of toppling failure. Finally, sensitivity of joint parameters, including the connectivity rate of discontinuous cross-joints, the thickness of the rock column joint, joint friction angle, and joint cohesion, were performed to investigate the effects of the tensile strength of intact rock. The results indicate that joint cohesion and thickness of the rock column greatly influence the failure load (represents safety factor of the slope). The connectivity rates of the discontinuous cross-joints and joint friction angle were found to have significant effects on the shape and location of the basal failure plane. This research would provide a deep understanding on the failure mechanism of BFT for relevant scholars.
PubDate: 2022-01-10

• The effect of mineralogy on the microwave assisted cutting of igneous
rocks

Abstract: Hard rocks can be excavated difficultly by some mechanical miners such as roadheaders. Tunnel boring machines (TBMs) can excavate hard rocks, but the cost is high due to low advance rate and high tool wear. The difficulties in hard rock excavation can be overcome by exposing hard rocks to microwave energy while cutting. This study investigates influence of mineralogy on the microwave assisted cutting of igneous rocks. The normal and cutting forces were measured during the cutting tests, and the specific energy values were calculated. The optimum specific energy (SEopt.) values reduce quite steadily with the increasing microwave power. The SEopt. of some tested crystalline rocks first increases at the low power (3 kW) and then decreases at the high power (6 kW). The losses in the SEopt. range from 22.5 to 38.7% at the power of 6 kW. The equations were also developed for the estimation of the SEopt. loss. Concluding remark is that the same rock types may be affected differently by microwave energy because of the different mineral types and percentages, and thus they behave diversely under cutting tests. The derived equations will be useful for the prediction of the SEopt. loss due to the microwave treatment.
PubDate: 2022-01-10

• Experimental investigation of unconsolidated undrained shear behaviour of
peat

Abstract: This study conducted a series of standard classifications to determine the physical properties of peat, followed by 28 unconsolidated undrained triaxial tests to investigate undrained peat shear behaviour. Results show that the undrained deviatoric shear resistance of peat grows continuously with increasing shear strain, but ends up with no obvious peak strength even at very large strain (i.e. 25%). The shear stiffness of peat specimens degrades substantially with increasing shear strain. To make the stiffness of peat specimens comparable, the secant shear modulus G is then normalized with the shear modulus $${G}_{0.1\%}$$ at relatively small strain of 0.1%. Furthermore, results from 16 previous unconsolidated undrained tests and 66 consolidated undrained tests available in literature were taken into account together with 28 lab test data obtained in this study, aiming to reveal the general behaviour of peat shear stiffness degradation. For all the test data, the shear strain $$\gamma$$ is normalized with a reference strain $${\gamma }_{\mathrm{ref},0.1\%}$$ , at which the stiffness $$G$$ / $${G}_{0.1\%}$$ = 0.5. A hyperbolic function is then adopted to fit the relationship between the normalised stiffness versus the normalised shear strain. Over 78% of the data falls within a ± 30% margin within 5% shear strain, while the predicted stiffness out of the margin is usually underestimated.
PubDate: 2022-01-08

• Fracture analysis of central-flawed rock-like specimens under the
influence of coplanar or non-coplanar edge flaws

Abstract: To better understand the influence of edge flaws on the fracture behaviors of central-flawed specimens, a series of uniaxial compression tests were carried out on the central-flawed rock-like specimens with two edge flaws using a servo-controlled testing apparatus. Two edge flaws were divided into coplanar and non-coplanar distribution (F-L1 and F-L2). The acoustic emission, digital image correlation and high precision video were applied simultaneously to monitor the internal AE signals, surface strain, and crack propagation of rock-like materials, respectively. The results show that the degradation effect of non-coplanar edge flaws on the peak strength, elastic modulus, and crack initiation angle are more significant than that of coplanar edge flaws. When the inclination angle of the central flaw increases from 15° to 60°, the peak strength, elastic modulus, and crack initiation angle decrease. In contrast, the complete initiation angle, total energy density, and accumulated acoustic emission energy first decrease and then increase. The acoustic emission counts and acoustic emission accumulated energy occur a sudden increase when the rock-like specimen deforms into the next stage. Moreover, central flaw controls the initiation of new cracks, whereas edge flaws influence the propagation trajectories of new cracks. Furthermore, the coalescence between the central and edge flaws in the F-L2 specimen is easier to happen than that in the F-L1 specimen.
PubDate: 2022-01-08

• An extreme gradient boosting technique to estimate TBM penetration rate
and prediction platform

Abstract: An accurate prediction of the penetration rate (PR) of a tunnel boring machine (TBM) is essential for the schedule and cost estimation of tunnel excavation. To better meet the needs of modern information construction, more computer technologies are being used to integrate the analysis and management of construction data. Herein, an online prediction platform based on a data mining algorithm using ensemble learning (extreme gradient boosting (XGBoost)) is developed for TBM performance prediction. The platform establishes the model and displays the prediction results, while storing a considerable amount of machine data, and providing services for TBMs of multiple projects simultaneously. In establishing the prediction model, users can change the algorithm parameters according to the engineering situation. The prediction capabilities of the platform are demonstrated by 200 field samples obtained from the Songhua River water conveyance project in Jilin. The mean absolute percentage error, coefficient of determination, root mean squared error, variance account for (VAF), and a20-index of the PR are 6.07%, 0.8651, 3.5862, 87.06%, and 0.925, respectively. The results show that the prediction model has a reliable prediction accuracy, which is higher than that of the gradient boosting decision tree, and these results can be displayed on the online platform. It provides effective help for TBM intelligent tunneling.
PubDate: 2022-01-07

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