Showing papers in "Ksce Journal of Civil Engineering in 2021"

Improvement of the Shearing Behaviour of Loess Using Recycled Straw Fiber Reinforcement

Abstract: Reinforcing structural members and construction materials using recycled fibers has become popular in the past decades due to sustainable development concerns. The recycled fibers as soil reinforcement elements contribute to the increase in shear strength by distributing stresses exerted in the soil along the length of the recycled fibers. Loess, widely spread over the Chinese Loess Plateau, is featured with metastable structure, large porosity, and high water sensitivity. This study presents the results of applying the large-scale stress-controlled direct shear tests on the recycled straw fiber-reinforced loess. The formation mechanism of shearing behaviour enhancement of the loess by straw fiber inclusion is revealed. The associated strain-hardening behaviour can be manifested using the dilation angle or the difference in friction angle between the large-displacement friction angle and the peak friction angle. Further, the shear strength using the displacement-controlled direct shear tests presents good correspondence with that using the stress-controlled direct shear tests. The test results explore the potential of using the recycled straw fiber-reinforced loess to protect the fragile loess environment in the northwest of China.

Prediction of Catenary Action Capacity of RC Beam-Column Substructures under a Missing Column Scenario Using Evolutionary Algorithm

Abstract: Catenary action plays crucial role in resisting the applied vertical load at large deformations stage in reinforced concrete (RC) structures. This paper aims to predict the catenary action capacity of RC beam-column substructures by utilizing the distinctive properties of gene expression programming (GEP). The input parameters selected for the modelling are: double-beam span-to-depth ratio, relative axial restraints stiffness, relative rotational restraints stiffness, bottom and top longitudinal reinforcement ratios, and yield strength of longitudinal rebars. A comprehensive and reliable database was collated from internationally published research articles to develop and verify the model. The GEP-based model was assessed by comparing its performance with regression based model. Various statistical indicators and external validation criteria suggested in literature proved that the model is accurate and possess high prediction and generalization capacity. Sensitivity analysis was carried out to show the contributions of the input parameters, while parametric analysis was performed to show that the proposed model is not merely a combination of the input parameters but can accurately represent the given physical system. The proposed formulation from GEP is found to be simple, robust, and easy to utilize for pre-design purposes.

Triaxial Shear Behavior of Basalt Fiber-Reinforced Loess Based on Digital Image Technology

Abstract: Engineering construction in loess areas often requires improvement of loess. Basalt fiber-reinforced soil due to complexity of material composition often exhibits poorly predictable mechanical behavior. In this study, digital image technology-based unconsolidated-undrained (UU) triaxial shear tests were carried out on loess samples at three fiber lengths (L) and four fiber contents (η). Results prove the improvement of the shear strength of loess by basalt fiber inclusion, which varies in inverted u-shaped pattern with fiber length or fiber content, with the maximum at η = 0.6%, L = 12 mm. Digital Image Technology was employed to analyze the damage characteristics and strain field of the surface of the sample at different loading time. The volumetric strain of the reinforced sample decreases at higher fiber content or fiber length, from shear contraction to dilatancy. The unreinforced sample exhibits a typical brittle failure mode with visible shear band, while plastic failure for reinforced samples with an overall bulging failure mode. A statistical damage constitutive model of fiber-reinforced loess was established with limited parameters calibrated. The rationality of the model was verified by comparisons of measured and calculated stress-strain data.

A Comparative Study on Prediction of Monthly Streamflow Using Hybrid ANFIS-PSO Approaches

Abstract: Monthly prediction of streamflow is a fundamental and complex hydrological phenomenon. Accurate streamflow prediction helps in water resources planning, design, and management, particularly for hydropower production, irrigation, protection of dams and flood risk management. Hence, in this paper, a hybrid robust model integrating adaptive neuro-fuzzy inference system (ANFIS) with particle swarm optimization (PSO) algorithm was developed for monthly streamflow prediction of Barak River basin, India. Multiple factors like Precipitation (Pt), temperature (Tt), humidity (Ht), Infiltration loss (It), are considered as the inputs for determining the streamflow. For validating the model performance, 70% of data (1980–2007) were used for training them and 30% of data (2008–2019) were used for testing them. A comparison is made between results of developed hybrid model with simple artificial neural network (ANN) and ANFIS models for assessing accuracy and efficiency of model performances. Obtained results of proposed models were evaluated based on four assessment indices including by Root Mean Square Error (RMSE), Mean Absolute Error (MAE), determination coefficient (R2) and Nash-Sutcliffe Coefficient (ENS). Based on comparison of results, it was concluded that robust ANFIS-PSO model with RMSE = 5.887, MAE = 4.978, R2 = 0.9668, and ENS = 0.961 demonstrated best performance with more reliability and accuracy in comparison to ANFIS and ANN models. Findings of this research proved that hybrid ANFIS with an evolutionary optimization algorithm is a reliable modelling approach for monthly streamflow prediction.

Influence of Tunnel Excavation on the Stability of a Bedded Rock Slope: A Case Study on the Mountainous Area in Southern Anhui, China

Abstract: Tunnel excavation has a substantial effect on the stability of rock slopes. The influence of tunnel excavation on the deformation and mechanical characteristics of a bedded slope is investigated by analysing the cumulative displacement, stress, and strain of the slope using the finite-element method (FEM) and field monitoring method. The deformation characteristics of the surrounding rock of the tunnel and slope with a supporting structure were analysed using the FEM under the conditions of support or without support. The results show that the deformation characteristics of the slope are controlled by its discontinuities. The deformation of the slope is mainly concentrated in the area above the second discontinuity; in particular, the deformation above the first discontinuity is the largest. In addition, the deformation and mechanical characteristics of the support structure are analysed. The supporting structure has influence on the deformation of the slope, which reduces the cumulative displacement, stress and strain. The shear strains of the second and third discontinuities are greatly influenced by the supporting structure. The mechanical properties of the tunnel support structure are controlled by the first discontinuity, and a stress concentration occurs near the first discontinuity. Moreover, based on the combination of the numerical and field test results, the deformation of the rock slope is closely related to the distance from the slope surface. Tunnel excavation mainly has a significant impact on the deformation of surface slope within a certain range, especially the slope deformation within the range of 4 m, which is the largest.

Mechanical Properties and Microstructure of PVA Fiber Reinforced Cemented Soil

Abstract: In this work, the experimental study of unconfined compressive strength tests, direct tensile strength tests and three point bending tests were carried out to evaluate the effect of PVA fiber reinforcement on the mechanical behaviour of cemented silty soil. In general, the addition of polyvinyl alcohol (PVA) fiber lead to an increase in compressive strength, and it was observed more significant improvement in tensile strength and flexural strength, moreover, the inclusion of fibers effectively altered the brittle failure pattern of unreinforced cemented soil and improve the toughness and ductility. In addition, the microstructural of interaction between fibers and cemented soil was investigated. The proposal of regression model was utilized for predicting compressive strength, tensile strength and flexural strength.

Study on Properties of Expansive Soil Improved by Steel Slag Powder and Cement under Freeze-Thaw Cycles

Abstract: Expansive soil is considered to be an unfavorable soil due to its swelling-shrinking behavior. In order to improve the properties of expansive soil, the addition of steel slag powder (SSP) has been used to improve expansive soil that has been mixed with the cement. In this study, a series of cylindrical improved expansive soil specimens were prepared, which were improved either by the addition of cement, cement SSP, or cement SSP sodium hydroxide (NaOH). All of the specimens were prepared with an optimum water content and then subjected to a maximum of 12 closed-system freeze-thaw (F–T) cycles. The specimens were subjected to different curing times and temperatures (−5°C,−10°C and −15°C) during the tests. After each freeze-thaw (F–T) cycle, the volume of each specimen was measured and an unconfined compression strength (UCS) test was performed. The results have shown that as the temperature of the F–T cycle decreased, the volume expansion rate increased with the increase of the length of the F–T cycle. As the curing time increased, the effect of the F–T cycles on the volume change rate of the specimens reduced and the UCS increased. The first F–T cycle had the greatest influence on the volume of the specimen as well as the UCS of the improved expansive soil. After the improved expansive soils had undergone more than eight F–T cycles, the volume change rate of the specimen tended to stabilize. The maximum F–T volume change rate of the improved soil was 1.93%. When the curing age was 60d and 90d, the strength of the specimen with cement SSP sodium hydroxide was 377.3 kPa and 294.7 kPa higher than the specimen with cement only (ES specimen), and its strength degradation rate was 18.737% and 9.97% lower than the ES specimen. The results have shown that the addition of SSP and cement improved the expansive soil; moreover, NaOH inhibited the degradation of the soil during an F–T cycle.

Experimental Study on Mechanical Properties of Cement-Stabilized Soil Blended with Crushed Stone Waste

Abstract: Waste generated by the processing of natural stone poses environmental and economic problems. One promising use for stone waste is soil stabilization. In this paper, a number of tests including unconfined compressive strength (UCS) and California bearing ratio (CBR) of crushed stone were performed to study the effect of curing time, soaked and unsoaked conditions and freeze-thaw cycles on the geotechnical characteristics of cement-stabilized specimens. The results indicate that crushed stone waste can be combined with cement as a stabilizer to improve soil properties. Also the optimum moisture content (OMC) and maximum dry density (MDD) are dependent on the cement content and almost independent of the crushed stone waste content. The CBR increased significantly as the crushed stone waste and cement contents increased under both soaked and unsoaked conditions, but these had little effect on the UCS at curing times of less than 14 days. Cement-stabilized specimens with 10% crushed stone waste showed a significant increase in UCS. The CBR and UCS of unsoaked specimens were higher than for soaked specimens at different crushed stone waste and cement contents. The CBR and UCS values increased with an increase in curing time. However, the curing time had a more obvious effect on UCS than on CBR.

Advanced Stability Analysis of the Tunnels in Jointed Rock Mass Based on TSP and DEM

Abstract: The discrete element method (DEM) can analyze the large deformation and large displacement of rock mass effectively, and it is widely used in underground engineering, slope engineering and other fields. However, due to the low accuracy of rock mass structural surface information acquisition, the application of discrete element method in the analysis of jointed rock mass stability is still deviated. In this paper, combined with the advantages of the tunnel seismic prediction (TSP) in obtaining discontinuous geological interface information and the discrete element method in the calculation and analysis of jointed rock mass stability, this paper proposes an advanced analysis method for jointed rock mass stability based on TSP and DEM. Compared to the traditional methods, the analysis results of the jointed rock mass stability are more reliable. Firstly, relying on the advanced detection system — Tunnel Seismic Prediction 203Plus, the unstructured rock mass structure information of the tunnel is obtained, and the spatial attitude of the discontinuous geological interface is further determined. Secondly, based on the Fish programming language, the non-continuous geological interface information can be expressed in the discrete unit software — 3D Distinct Element Code (3DEC). In this way, the excavation calculation model of the tunnels in jointed rock mass can be constructed. Finally, based on the DEM, the excavation of the tunnels in jointed rock mass can be simulated, analyze the stability of surrounding rock during the tunnel excavation process, and realize the stability analysis of surrounding rock stability of jointed rock mass. Based on the Huangjiazhuang Tunnel Project, this paper uses the above method to carry out on-site application. The results show that the location of the dangerous block is predicted to be consistent with the actual exposure of the tunnel surrounding rock based on TSP and DEM, which verify the accuracy and feasibility of this method, and the research results have practical guiding significance for the safe construction of the tunnels in jointed rock mass.

Mechanical Properties and Damage Characteristics of Coal-Rock Combination with Different Dip Angles

Abstract: The effect of the dip angle of an interlayer coal seam on rock mass mechanical behavior and damage characteristics is seldom discussed. To address the lack of the existing research, a numerical simulation was conducted using the Particle Flow Code (PFC2D), and its damage to mechanical behavior, acoustic emission (AE)characteristics, and damage characteristics were analyzed. The outcomes exhibit the peak strength and elastic modulus of coal-rock combinations are between that of rock and coal. As the coal inclination angle rises, the elastic modulus and peak strength gradually decrease. AE model experiences the initial growth period, stable growth period, and rapid decline period. The value of AE hits and the generation of the AE signal is affected by the size of the inclination angle. The degree of damage to the coal-rock combination gradually rises as the angle rises. The damage process of the coal and rock composite sample encompasses an initial damage phase, damage stable evolution phase, accelerated damage phase, and a failure phase. The damage values of the stable evolution stage for varying dip angle models are also different. As the inclination angle increases, the damage value gradually increases, while the strain at the same damage value gradually decreases.

Assessment of Steel Slag and Steel Fiber to Control Electromagnetic Shielding in High-Strength Concrete

Abstract: This study investigates the influence of steel slag (SS) and steel fibers on the electrical resistivity and electromagnetic (EM) shielding effectiveness of high-strength concrete (HSC). It was found that the electrical resistivity of mixtures were mainly influenced by free water. Thus, the EM shielding effectiveness was evaluated without the effect of free water. HSC with 20% replacement ratio of SS exhibited slightly improved EM shielding, lower electrical resistivity, and reduced strength (compressive and flexural) compared to HSC without SS. However, HSC with steel fibers exhibited significantly improved EM shielding, lower electrical resistivity, and higher strength and toughness compared to HSC without steel fibers. An increase in the steel fiber content in the HSC significantly decreased the electrical resistivity and increased the shielding effectiveness, strength, and toughness. Regardless of the fiber content in the fiber volume fraction of mixture, the shielding effectiveness is similar for cases with and without SS whose electrical resistivity values differ only slightly. This proves that the EM shielding effectiveness was mainly affected by the electrical resistivity and these properties are significantly correlated when the electrical resistivity values differ noticeably. HSC reinforced with rebar with 50 mm spacing exhibited a 23.5–75.6% increase in the shielding effectiveness in the 600–1,000 MHz frequency region compared to pristine HSC.

Locally Resonant Periodic Wave Barriers for Vibration Isolation in Subway Engineering

Abstract: Subway transportation is being promoted worldwide to effectively solve urban congestion However, the vibration induced by subway traffic has caused a major adverse impact on building safety, precision instrument operation and human health Wave barriers have been proven effective in mitigating ground vibration, whereas they have some limitations in achieving ideal attenuation zone and high efficiency to cover the low-frequency vibration in underground railway system Based on locally resonant phononic crystals theory, this paper designs three-component locally resonant periodic wave barriers (LRPWBs), and investigates the effects of geometrical and material parameters on the bandgap features in detail The band structures are calculated using improved plane wave expansion (IPWE), the transmission spectra and vibration modes are obtained by finite element method (FEM) The results indicate LRPWBs are able to give lower and wider bandgap to cover the main frequency of subway environment, which is proved by time and frequency domain analysis For the bandgap mechanism, the local resonance features of LRPWBs result in the energy conversion between kinetic energy and elastic strain energy, thus the elastic wave energy is localized in resonance unit and then the locally resonant bandgap is created In addition, the bandgap can be adjusted by carefully selecting proper geometrical and material parameters to actualize low-frequency broadband attenuation Further studies about multi-oscillator system indicate that the appropriate combination of multiple LRPWBs are conductive to diverse and broad bandgaps The investigations can provide inspiration for periodic wave barriers design in multi-frequency vibration attenuation field

Agent-Based Simulation for Pedestrian Evacuation Behaviour Using the Affordance Concept

Abstract: Simulation modelling is a necessary tool to analyse pedestrian movement behaviour in order to predict the social and collective behaviour in different situations. Psychological aspects of human behaviour in interacting with the environment is the critical point in the pedestrian simulation context. The affordance theory originated from psychology and humanities is a key concept to address this issue and model the relationship between an agent and his/her environment. This study aims to introduce a prototype of an agent-based model using the affordance concept to simulate the decision-making process during an evacuation. The proposed approach was tested to model the behaviour of evacuees in a platform of a subway station through both normal and emergencies. The results of the test including the evacuation time and flows toward different scenarios, showed that the model can work properly. The proposed approach can yield a useful tool for designers to mention pedestrian movement behaviour in their building designs.

Mechanical Property and Microstructure of Fly Ash-Based Geopolymer Activated by Sodium Silicate

Abstract: Sodium silicate is one of the common alkali activators of geopolymers. The modulus, concentration and dosage of sodium silicate have significant effects on the activation of fly ash, the strength and microstructure of geopolymer. In this paper, unconfined compressive strength test, X-ray diffraction analysis (XRD), Fourier transform infrared light (FTIR), 29Si nuclear magnetic resonance (29Si NMR), scanning electron microscope and energy disperse spectroscopy (SEMEDS), and physisorption experiment (BET) were carried out to study the effects of the sodium silicate modulus and dosage on the mechanical property and microstructure of fly ash-based geopolymer. The results indicated that the main product of the geopolymer activated by sodium silicate was hydrated sodium aluminosilicate (N-A-S-H). When modulus value decreased and meanwhile dosage of sodium silicate increased, the reorganization and polymerization of gel products were accelerated so that the integrity and continuity of the microstructure of geopolymer were improved, and then the strength increased. When the modulus of sodium silicate was 3.28, the maximum value of the strength was at the dosage of 10%. According to this study, it was investigated that modulus value and dosage of sodium silicate had obvious influence on the alkali- activated reaction of fly ash, which can provide an engineering reference for the special soil solidification with geopolymers.

Optimization of Construction Material Cost through Logistics Planning Model of Dragonfly Algorithm — Particle Swarm Optimization

Abstract: Managing a construction project is challenging because of cost, time, safety, and quality considerations. In the most projects, the cost of construction is one of the most critical aspect because material cost alone accounts for significant ratio of the total project. Therefore, the cost of construction materials should be controlled. In this study, we proposed the use of material requirements planning (MRP) to control the cost of construction materials. After determining the demand for the materials required for construction, we estimated both the quantity of materials required and time taken to deliver the materials to the construction site. Although economic order quantity models have been applied to analyze construction material costs, they do not accurately reflect concerns related to material cost. Therefore, we used the material supply chain model (construction logistics planning) to analyze material costs. To optimize MRP according to the current progress of a project, a novel approach combining the dragonfly algorithm (DA) and particle swarm optimization algorithm (PSO) was proposed. To verify the advanced searchability of the DA–PSO algorithm, the algorithm was compared with the gray wolf and the genetic algorithms.

Deep Learning-Based Real-Time Crack Segmentation for Pavement Images

Abstract: Crack is the early form of most pavement defects and has a great negative effect on road service life. Timely detection and maintenance of cracks may minimize the loss caused by it. In this paper, we propose a lightweight crack segmentation model based on a bilateral segmentation network, which achieves a good balance between inference speed and segmentation performance. The model contains two parts: context path and spatial path. The network used in context path is inspired by Xception, which is used to rapidly down-sample the feature map. Spatial path employs three convolutional layers to encode sufficient spatial information. The F1_score and IoU achieved by our model on the Crack500 dataset are 0.8270 and 0.7379, respectively. The proposed model gains superior performance in FPS compared to other four models. In addition, the model is able to process images at 1,024 × 512 pixels in real-time (31.3 FPS). Through the comparison of training time, our model can save 54.04% of the time.

Experimental Study on Endurance Performance of Lime and Cement-Treated Cohesive Soil

Abstract: An earthwork design requires to consider the influence of severe climatic conditions on enduring performance of soils treated with chemical additives. This study was focused on investigating the mechanical behavior of a lime and cement-treated cohesive soil under the effects of repeated cycles of wetting and drying. The soil samples were prepared by adding different concentrations of cement (2, 6, 10, 12, 16, 20%) and quicklime (2, 4, 6, 8, 10%). Due to low-plastic nature of the host soil, the effectiveness of cement to reduce the plasticity of soil was relatively higher compared to lime-treatment. Likewise, an increase in optimum moisture and decrease in maximum dry unit weight was observed for both the additives and these effects were significant for lime treated soil compared to cement. Moreover, an increase in strength from 0.57 MPa to 12.9 MPa at 20% cement and from 0.57 MPa to 2.03 MPa at 2% lime was observed in unconfined compressive strengths (UCS) tests on soil samples. To investigate the durability characteristics of the treated soil, the samples were subjected to 12 cycles of wetting and drying with each cycle consisting of 5 hours of immersion in potable water and subsequent drying in oven for 43 hours. The compressive strength, volume change and weight loss of soil samples were determined at the 1st, 3rd, 6th, 9th and 12th cycle. It is observed that the durability behaviour of treated soil is multipart due to parallel processes of positive aging (hydration process associated with binding agents) and negative aging (induced weathering). For a sustainable mechanical performance of the treated soil, an optimum dose of 6% lime or 16% cement is recommended and some correlations are proposed to quantify the effects of repeated wetting and drying.

Consolidation of Unsaturated Drainage Well Foundation with Smear Effect under Time-Dependent Loading

Abstract: In real practice, the construction of drainage wells is always accompanied by smear effect, whereas it is scarcely discussed in the field of unsaturated soils. In this case, on the basis of the widely-accepted consolidation theory for unsaturated stratum by Fredlund, this paper studies the equal strain consolidation characteristics of unsaturated foundation with drain wells affected by smear effect under time-varying loading (exponential loading as a case). Firstly, with the consideration of corresponding boundary conditions, the governing equations under the equal strain hypothesis are obtained. Afterwards, decoupling process, constant variation method and Fourier series expansion theory are utilized to get the analytical solutions, which are then verified to be credible by means of the finite difference method. Finally, the consolidation patterns of the drainage well foundation modeling in unsaturated soils are studied against hydraulic coefficients, modeling sizes and loading parameter. It reveals that the smear effect can significantly restrain the consolidation process of the foundation by drain wells, while different parameters will lead to various results.

Impact of Safety Worker Behavior and Safety Climate as Mediator and Safety Training as Moderator on Safety Performance in Construction Firms in Nepal

Abstract: The study targeted to find the pragmatic relation on mediating role of Safety Climate (SCL) and Safety Worker Behavior (SWB), and moderating role of Safety Training (ST) for better Safety Performance (SP). The target area of the study is on construction firms in developing countries like Nepal. A structured questionnaire tool was applied to conduct the survey. Out of 350 response targets, only 293 respondent’s data were analyzed using statistic SPSS 23 and were empirically tested using AMOS 23. The analysis explored complementary partial mediation of the mediating variable SCL and SWB between Safety Culture (SCU) and Safety Performance (SP). Besides, the study also showed how ST moderated the relation between SWB & SP and justified the insignificant moderation role of ST on relation between SCL& SP This research shed the light on the mediating impact of SCL and SWB adding the moderation relation of ST on the effective safety performance in the construction firms. Besides, this industrial approach research will widen and improve the literature of SP in construction firms in developing nations in modernizing the policy. Consequently, this study would widen the knowledge of policymakers prompting effective safety performance in the construction project.

Wall Displacement and Ground-Surface Settlement Caused by Pit-in-Pit Foundation Pit in Soft Clays

Abstract: The number of pit-in-pit foundation pit is increasing quickly because of the continuous utilization of underground spaces in urban areas. Based on the co-construction project of Shanghai Museum of Natural History foundation pit and Shanghai Metro Line 13 foundation pit in Shanghai, China, the deformation characteristics of pit-in-pit foundation pit are researched by field observation and centrifugal model tests. The lateral wall displacement of inner foundation pit includes global deformation caused by the outer foundation pit excavation and deflection caused by the excavation of itself. The effect of inner foundation pit excavation on the lateral wall displacement of outer foundation pit and ground-surface settlement is smaller. The two factors affecting the deformation characteristics of pit-in-pit foundation pit, the distance between inner and outer foundation pits (D) and the excavation width of inner foundation pit (Win), are analyzed by centrifugal model tests. The result shows that the maximum lateral wall displacements of inner and outer foundation pits decrease nearly linearly with the increase of D, but increase with the increase of Win.

Deformation and Stability Analysis of Embankment over Stone Column-Strengthened Soft Ground

Abstract: Compacted granular columns are commonly used to support embankments over soft soils. Using a reinforcement layer under the embankment causes the total stress to be further transferred to the column rather than soft soil, thus reducing total deformations of the subsoil. In this paper two dimensional (2D) numerical analysis was used to study the influence of stone columns and basal geosynthetic on deformations and stability of an embankment over soft deposit by means of Plaxis 2D finite element code. Unit cell to plane strain conversion approach was applied to transform columns into equivalent walls thus allowing to simulate a full embankment over a group of columns. Comprehensive parametric analysis was then performed to investigate the role of different critical parameters on embankment behavior. Results showed that the use of stone columns yielded the total deformations of the subsoil to significantly reduce, while its influence was less remarkable as a high stiffness geogrid was placed under the embankment. It was also found that the stone column length was the most influential parameter on the embankment total deformations, so that increasing columns length from 0.25Hs to 0.75Hs reduced the vertical and horizontal deformations by about two and five times, respectively. In addition, the use of a high stiffness basal geogrid caused the stability of the embankment to remarkably improve as the value of safety factor at the end of construction increased from 1.25 to about 1.9.

Building Information Model and Optimization Algorithms for Supporting Campus Facility Maintenance Management: A Case Study of Maintaining Water Dispensers

Abstract: Effective management for the maintenance of water dispensers dispersed throughout an academic campus is essential for ensuring the quality of drinking water. Conventionally, water dispenser maintenance is conducted approximately bimonthly or when a passive fault notice is obtained. This maintenance frequency usually results in ineffective allocation of maintenance staff and poor maintenance quality. This study proposes a new model for campus facility maintenance management that enables maintenance staff to maintain water dispensers at the optimal time and select the shortest maintenance path. The proposed model was developed using the maintenance information of the Construction Operations Building Information Exchange obtained from building information models of multiple buildings, water dispenser operation data from a water dispenser monitoring module, and an optimization algorithm developed by integrating Dijkstra’s algorithm, simulated annealing, and a genetic algorithm to identify the shortest maintenance path. The proposed model was tested on a campus in Northern Taiwan. The application results revealed that maintenance strategies could be systematically established to determine the optimal time to dispatch maintenance staff based on the lowest unit cost criterion; this approach was also used to identify the shortest maintenance path through multiple buildings.

Transverse Flexural Behaviour of Steel-Engineering Cementitious Composites (ECC) Composite Deck under Negative and Positive Bending Forces

Abstract: Orthotropic steel bridge deck system usually consists of an orthotropic steel deck and an asphalt overlay. Fatigue cracks of the orthotropic steel deck and premature damage of the asphalt overlay are frequently reported for such system. Engineering cementitious composites (ECC) was therefore proposed to replace the asphalt overlay to address the aforementioned issues. The current study presents an investigation on the transversal flexural behaviour of the ECC under bending forces. Influence of the bending force direction, cover thickness, the number of longitudinal reinforcement steel bars on the flexural performance was revealed. Responses with regard to the load-deflection curve, failure mode, the ultimate capacity, the cracking behaviour, the interfacial slip between ECC and steel deck and the nominal cracking stresses were analysed. The results showed that the load-deflection response under both negative and positive bending forces exhibits elastic stage, crack-developing stage and yield stage. Compared with the reinforcement ratio, cover thickness plays a more significant role on the flexural performances. When the cover thickness decreases from 35 mm to 25 mm, the peak load increases by 21%–25%. ECC maintains its feature of being ductile, with high tensile and compressive strain capacity in the composite slab. From the design point of view, reducing the cover thickness and increasing the reinforcement ratio can improve the ultimate load and cracking stress, and reduce the internal slip, strain and crack width of the composite slab. It is expected that the current study can provide basic knowledge to the design and application of the steel-ECC composite deck system.

Unascertained Measure-Set Pair Analysis Model of Collapse Risk Evaluation in Mountain Tunnels and Its Engineering Application

Abstract: Collapse is a major geological disaster that occurs during mountain tunnel construction. However, the accuracy of collapse risk assessment is generally restricted by evaluation factors or methods. This paper proposes a novel integrated collapse risk evaluation method for mountain tunnels based on case-based reasoning, rough set theory, and unascertained measure-set pair analysis (UM-SPA) theory. First, the risk surroundings and risk factors involved in tunnel collapse are summarized by the analytic hierarchy process, and a preliminary risk evaluation index system is established. Then, an attribute reduction algorithm based on the conditional information entropy of a rough set is proposed and applied to cases with similar attribute characteristics as those of the tunnel to be evaluated, to remove the relatively insignificant or redundant indices and improve the reliability of risk assessment. Finally, taking the relationship between tunnel collapse and its evaluation indices as an unascertained system, Set Pair Analysis (SPA) theory is introduced to optimize the credible degree recognition criteria of unascertained measure theory (UMT). Combined with the modified entropy weight method, a UM-SPA model for tunnel collapse risk evaluation is established to calculate the level of collapse risk quantitatively and predict the development trend of risk dynamically. Taking Xiucun Tunnel passing through fault F18 as an example, collapse risk is evaluated and compared with the evaluation results of traditional UMT and field status. The results demonstrate the feasibility and efficiency of the proposed approach and provide a new idea for collapse risk prediction while constructing mountain tunnels.

Blast-Resistance and Damage Evaluation of Concrete Gravity Dam Exposed to Underwater Explosion: Considering the Initial Stress Field

Abstract: There is an increasing concern on the vulnerability of concrete gravity dams under blast loads. To a better evaluation of the blast-resistance, the effect of the initial stress field is taken into consideration herein. Firstly, a fluid-solid coupling numerical model is established to investigate the blast-resistance of concrete gravity dams. The numerical results indicate that the initial stress field has non-neglectable effect on the shock wave propagation, blast vibration, and failure mode of concrete gravity dams. The damage of dam base may be overestimated without the consideration of initial stress field. Moreover, a parametric study are carried out for further investigations of the dynamic responses and damage properties under various explosion scenarios (explosive charge, detonation depth, and standoff distance). With the consideration of the initial stress field, it can be concluded that the dam head nearest the explosive source is the weakest part, and the safety of the dam base is another important consideration, which may lead to severe dam-break floods. At last, a new method is proposed and recommended to evaluate the blast resistance of the whole concrete gravity dam, where the blast-induced vibration and penetration depth of cracks are suggested for the dam crest and dam base, respectively.

An Integrated Evaluation Method for the Grouting Effect in Karst Areas

Abstract: Our proposed integrated evaluation method for the grouting effect in karst areas is based on the cloud model (CM), the analytic hierarchical process (AHP), and a fuzzy comprehensive evaluation system. Our method fully considers the fuzziness and randomness of the evaluation indices, and bridges the gap between qualitative information and a quantitative evaluation value. The evaluation index system for the grouting effect is established by integrating metrics related to the construction technology, apparent parameters, and observational data from inspection holes and geophysical exploration techniques. First, the weight of each index is calculated using the AHP, which has been modified by the CM. Then, we calculate the cloud model membership degree for each index. Finally, we determine the comprehensive evaluation level by examining the similarity measures between the various cloud models. In this case study, we use our integrated method to evaluate the initial results of the grouting treatment project in the China Resources Cement (Pingnan) Limestone Mine. Our results are validated by subsequent monitoring results for this project. This study provides valuable insight into the treatment of water inflow in karst areas.

A BIM-Based Visual Warning Management System for Structural Health Monitoring Integrated with LSTM Network

Abstract: Structural health monitoring is an important task in the construction and maintenance stage. Because sensors are widely distributed in large and complex building space, it is difficult to visualize and locate hazard sources. In this paper, a visual warning framework of structural health monitoring is proposed based on the building information modeling (BIM) platform. The monitoring data bound with the sensors is stored in the database, and the monitoring data is mined to obtain the warning information by the deep learning algorithm long short-term memory (LSTM); The BIM elements are associated with sensors to make the monitoring area correspond to the BIM model so that the sensor and monitoring area can be visible on the BIM platform. Through the development of an integrated plug-in, the user interface and the database are connected by back-end controls to realize the three-dimensional display of the monitoring space on the BIM platform, corresponding with the visualization of the monitoring data and the automatic warning based on LSTM. This study also integrates the Internet of things technology to automatically control the indicator lights based on real-time sensor data and prediction data. The system framework integrates the application of BIM, deep learning algorithm and Internet of things in structural health monitoring, it realizes the spatial visualization of monitoring area corresponding with monitoring data information, quickly locates and issues early warning of dangerous components. It provides a basis for remote structural health monitoring and safety management.

Pipe-Soil Interaction and Sensitivity Study of Large-Diameter Buried Steel Pipes

Abstract: Large-diameter buried steel pipes (BSPs) have been widely utilized in water diversion and hydropower fields. This paper presents a comprehensive numerical investigation on the interaction between the large-diameter pipe and soil under three typical working conditions, to capture the structural mechanical behaviors of pipe deformation, soil displacement, and soil pressure. Furthermore, a parametric analysis of pipe diameter is conducted, along with the sensitivity study of soil parameters based on the orthogonal test method. The results show that the water weight increases the pipe deformation significantly by 14%, while the high internal water pressure decreases the deformation greatly with the maximum effect of 39%. The pattern of soil pressure at the top of the pipe changes from parabola to double-hump as the pipe diameter varies from 0.5 m to 5.0 m. The pipe deformation and soil pressure keep increasing with the pipe diameter, but the safety margin for prism load decreases gradually. Pipe deformation and soil pressure are very sensitive to the elastic modulus and Poisson’s ratio of backfill. Friction coefficients of soil-soil (trench sidewall) and pipe-soil have great influences on the soil pressure, while the bedding material and backfill cohesion have small effects on it.

DPIM-Based InSAR Phase Unwrapping Model and a 3D Mining-Induced Surface Deformation Extracting Method: A Case of Huainan Mining Area

Abstract: The mining subsidence in mining area could cause large-gradient deformation in a short period of time. When the deformation gradient exceeds the threshold value of the Differential Interferometry Synthetic Aperture Radar (D-InSAR) technology monitoring gradient, D-InSAR technology is likely to cause the failure of InSAR phase unwrapping algorithm. At this time, the InSAR technology is unable to monitor the 3D surface deformation. Aiming at these problems, an dynamic probability integral method (DPIM)-based InSAR phase unwrapping model and a method of extracting 3D surface deformation were proposed. The phase unwrapping model firstly used the empirical parameters of the probability integral of the mining face to predict the line of sight (LOS) direction deformation phase of the mining subsidence surface. Secondly, the phase of differential interferogram was unwrapped with the assist of the predicted LOS deformation phase under the constraint of DPIM, and the true LOS deformation phase was obtained, then the true LOS deformation phase transformed into LOS deformation. Finally, according to the geometric projection relationship between the LOS deformation and 3D deformation of mining subsidence surface, the probability integral prior model was brought into the equation of the geometric projection relationship. On the basis of relevant boundary conditions, the 3D surface deformation was extracted from the LOS direction deformation field of mining subsidence. The feasibility of the method was verified by the simulation experiment results. The differential interferogram of the subsidence basin was obtained by the differential interference processing of image data of Sentinel-1A on Nov. 16, 2017 and Dec. 10, 2017 of 1613 working face of Guqiao South Mine. By using the DPIM-based phase unwrapping model, the phase of differential interferogram was unwrapped and the 3D surface deformation during this period as well as the deformation extraction method were developed. The results showed that the maximum fitting error value of subsidence was 79 mm, about 8.33% of the maximum value of subsidence, and the fitting error of mean square of subsidence was ±33.5 mm. The results showed that the DPIM-based phase unwrapping model and the method of extracting 3D surface deformation proposed in this paper have certain engineering application values.

D-InSAR Monitoring Method of Mining Subsidence Based on Boltzmann and Its Application in Building Mining Damage Assessment

Abstract: Monitoring and predicting mining area subsidence caused by coal mining help effectively control geological disasters. Information regarding small surface deformations can be obtained using a differential interferometric synthetic aperture radar (D-InSAR), which exhibits high monitoring accuracy and can cover large areas; thus, D-InSAR are being applied for mining area settlement monitoring. However, mining areas are prone to large gradient deformations in short durations; obtaining information regarding such deformations is outside the scope of D-InSAR monitoring. To adapt to the characteristics of D-InSAR monitoring, this study selected a Boltzmann function model with a slow boundary convergence rate to address the problem of probabilistic integration methods exhibiting a high boundary convergence rate. The three-dimensional surface deformation of the mining area can be accurately obtained. According to the projection relationship between D-InSAR line of sight (LOS) directional deformation, subsidence, and horizontal movement, a D-InSAR monitoring equation for mining subsidence assisted by Boltzmann is derived. This equation is combined with the shuffled frog leaping algorithm (SFLA) to obtain the parameters to be estimated from the equation. The D-InSAR LOS deformation information of the 13121 working face in the Huainan mining area was obtained from July 14 to October 30, 2019. The proposed method was then used to obtain the predicted parameters of the working face under insufficient mining. The predicted parameters of mining subsidence were calculated to obtain the predicted parameters when it was fully mined. Then, the revised parameters were used to predict the subsidence and horizontal movement of the mining area and compared with the actual leveling observations. The results show that the mean square error of predicted subsidence is 97.1 mm, which is about 3.09% of the maximum subsidence value; the mean square error of predicted horizontal movement is 46.1 mm, which is about 4.1% of the maximum horizontal movement value. The predicted results of the aforementioned method were used to analyze the damage to the buildings above the working face and determine the damage level of the buildings to provide a reference for the demolition and maintenance of the Zhaimiao village.