Showing papers in "Ksce Journal of Civil Engineering in 2017"

Artificial neural network for modeling nitrate pollution of groundwater in marginal area of Zayandeh-rood River, Isfahan, Iran

Abstract: Excessive use of chemical fertilizers, especially nitrogen fertilizers to increase crop and improper purification, and delivery of municipal and industrial wastewater are proposed as factors that increase the amount of nitrate in groundwater in this area. Thus, investigation of nitrate contamination as one of the most important environmental problems in groundwater is necessary. In the present study, modeling and estimation of nitrate pollution in groundwater of marginal area of Zayandeh-rood River, Isfahan, Iran, was investigated using water quality and artificial neural networks. 100 wells (77 agriculture well, 13 drinking well and 10 gardens well) in the marginal area of Zayandeh-rood River, Isfahan, Iran were selected. MATLAB software and three-layer Perceptron network were used. The back-propagation learning rule and sigmoid activation function were applied for the training process. After frequent experiments, a network with one hidden layer and 19 neurons make the least error in the process of network training, testing and validation. ANN models can be applied for the investigation of water quality parameters.

Data-driven support vector machine with optimization techniques for structural health monitoring and damage detection

Abstract: Rapid detecting damages/defeats in the large-scale civil engineering structures, assessing their conditions and timely decision making are crucial to ensure their health and ultimately enhance the level of public safety. Advanced sensor network techniques recently allow collecting large amounts of data for structural health monitoring and damage detection, while how to effectively interpret these complex sensor data to technical information posts many challenges. This paper presents three optimization-algorithm based support vector machines for damage detection. The optimization algorithms, including grid-search, partial swarm optimization and genetic algorithm, are used to optimize the penalty parameters and Gaussian kernel function parameters. Two types of feature extraction methods in terms of time-series data are selected to capture effective damage characteristics. A benchmark experimental data with the 17 different scenarios in the literature were used for verifying the proposed data-driven methods. Numerical results revealed that all three optimized machine learning methods exhibited significantly improvement in sensitivity, accuracy and effectiveness over conventional methods. The genetic algorithm based SVM had a better prediction than other methods. Two different feature methods used in this study also demonstrated the appropriate features are crucial to improve the sensitivity in detecting damage and assessing structural health conditions. The findings of this study are expected to help engineers to process big data and effectively detect the damage/defects, and thus enable them to make timely decision for supporting civil infrastructure management practices.

Landfill site selection using GIS and AHP: a case study: Behbahan, Iran

Abstract: Finding a suitable site to dispose solid waste is a difficult task for municipality because it is necessary to consider the different factors and criteria in the landfill siting process. In this study, in order to consider all parameters, a combination of Geographic Information System (GIS) and the Analytic Hierarchy Process (AHP) was used for landfill site selection. For the purpose of making decisions in landfill site selection a hierarchy structural was formed and different parameters have been identified, including distance to groundwater, distance to surface water, sensitive ecosystems, land cover, distance to urban and rural areas, land uses, distance to roads, slope, soil type and distance to waste generation places. At first, the rating method was used to evaluate each criterion individually. Then, the relative importance of criteria to each other was determined by an analytic hierarchy process (AHP). Simple Additive Weighting (SAW) method was applied to evaluate the land suitability. The results showed that 38% of the study area have high suitability for land filling. Finally, five sites were a candidate for field investigation with more details.

Firefly algorithm for discrete optimization problems: A survey

Abstract: Firefly algorithm is a nature-inspired metaheuristic algorithm inspired by the flashing behavior of fireflies. It is originally proposed for continuous problems. However, due to its effectiveness and success in solving continuous problems, different studies are conducted in modifying the algorithm to suit discrete problems. Many engineering as well as optimization problems from other disciplines involve discrete variables. Recent reviews on the application and modifications of firefly algorithm mainly focus on continuous problems. This paper is devoted to the detailed review of the modifications done on firefly algorithm in order to solve optimization problems with discrete variables. Hence, advances on the application of firefly algorithm for optimization problems with binary, integer as well as mixed variables will be discussed. Possible future works will also be highlighted.

Optimum tuned mass damper design in frequency domain for structures

Abstract: The design of tuned mass dampers for reduction of seismic vibrations in multiple degree of freedom structures is also a complex problem and the optimization of design parameters of tuned mass damper are needed for the best reduction of structural responses. In the optimization process, frequency or time domain solutions can be iteratively used. In this paper, a frequency based optimization technique is presented to find design variables such as mass, period and damping ratio of tuned mass damper on the top of a structure. A music inspired metaheuristic algorithm called harmony search is employed to reach the optimum solution. The optimum results were obtained for two 10-story and one 40-story structures. According to comparisons with time domain based method, frequency domain based methods is effective to reduce maximum values and to obtain a steady stead response for critical excitations.

Exposure to Fear: Changes in Travel Behavior During MERS Outbreak in Seoul

Abstract: Disaster management teams could learn much from the Middle East Respiratory Syndrome (MERS) outbreak in South Korea in 2015. The virus outbreak provoked public fear, which resulted in a mass reduction in transit use in the Seoul Metropolitan Area (SMA). Its effect differed among socioeconomic groups and geographical areas. A typical way to analyze this is to associate individual reactions to the disaster with socioeconomic characteristics. However, a more structured approach, which considers behavioral characteristics resulting from the societal position of an individual, would identify the basic reason for such associations. The study hypothesized that the degree of fixity that individuals have in their daily life may elucidate these associations. When fear is prevalent, people having the flexibility to change their lifestyle will make more changes in daily activities and travels. The study examined the influence of public fear of a pandemic disease on travel behavior and the effect of life fixity on individual response to the fear. To this end, smart card data of transit use and changes in travel behavior during the MERS period were examined. The study found that fear was powerful and influenced travel behavior differently depending on life fixity levels and regional characteristics.

Unascertained measure model of water and mud inrush risk evaluation in karst tunnels and its engineering application

Abstract: Water and mud inrush is one of the typical geological disasters during tunnel construction in karst areas. In order to effectively control the water and mud inrush risk and guarantee the safety of tunnel construction, an unascertained measure model of water and mud inrush risk evaluation is established based on unascertained measure theory. First, according to geological factors and engineering factors in tunnel zone, unfavorable geology, formation lithology, ground water level, topography and geomorphology, attitude of rocks, contact zones between soluble rock and non-soluble rock, crack in rock stratum, surrounding rock grade, construction technology level, and management level are selected as risk evaluation indexes of water and mud inrush, which constitutes the index system of water and mud inrush risk evaluation. Through collecting and collating information of typical water and mud inrush examples of karst tunnels, the uncertainty measure function of each evaluation index is obtained based on the measured data. Meanwhile, the index weight of each factor is ascertained by entropy-information theory, and the risk grade of water and mud inrush is judged by credible degree recognition criteria. In engineering application, the water and mud inrush risk of Qiyueshan tunnel is evaluated based on the established unascertained measure model. The results show that: (1) The evaluation results agree well with practical construction situation. (2) The unascertained measure model is scientific and reasonable, which can achieve the risk level evaluation of water and mud inrush systematically. (3) The unascertained measure model provides an effective method for water and mud inrush risk evaluation of karst tunnels, which can be applied to practical engineering.

Response Surface Methodology for Optimization of Stabilizer Dosage Rates of Marginal Sand Stabilized with Sludge Ash and Fiber Based on UCS Performances

Abstract: Optimization of the stabilization materials in terms of their dosage rates specifically used for stabilization applications have become a great interest by the experimenters due to the concerns of strength performance, time and economy for the construction projects. Using a relatively recent optimization technique, Response Surface Methodology (RSM), this paper is mainly focused on investigation of the optimum amounts of stabilizers (Sewage Sludge Ash (SSA) and Polypropylene Fiber (PF)) and Curing Time (CT) that yield to maximum unconfined compressive strength (UCS) for stabilization of a marginal sand (poorly-graded sand). For this purpose, an experimental study has been carried out conducting UCS tests, where the stabilizer proportions are 0-30% for SSA and 0-1% for PF, by total dry weight of sand+SSA. Also, the curing times considered prior to testing are 0, 7 and 14 days. All UCS tests have been performed following the experimental program by central composite design that used the ranges of stabilizer proportions and curing times. On the basis of experimental data, a full quadratic model with natural log transformation and backward analysis has been built through RSM considering the factors of SSA, PF, CT, and the response of UCS. The results indicate that the mathematical model built in this study is statistically significant (p ≤ 0.05) through the analysis of variance (ANOVA), thus it is applicable for optimization process. The findings from the optimization effort demonstrate that the most potential values for SSA, PF and CT are 19.95%, 0.57% and 12.15-day, respectively. The proposed values could be beneficial for the experimenters in practice specifically for preliminary evaluations prior testings of stabilizations.

Self-healing capacity of fiber reinforced cementitious composites. State of the art and perspectives

Abstract: Design of building structures and infrastructures is mainly based on four concepts: safety, serviceability, durability and sustainability. The latter is becoming increasingly relevant in the field of civil engineering. Reinforced concrete structures are subjected to damages that produce cracks which, if not repaired, can lead to a rapid deterioration and would result into increasing maintenance costs to guarantee the anticipated level of performance. Therefore, self-healing concrete can be very useful in any type of structures, as it allows to control and repairing cracks as soon as they are likely to occur. The effectiveness of self-healing can be improved with the use of fibers due to their capacity to control crack width and enhance multiple crack formation. In that way, researchers should use advanced cement based materials (FRCC, HPFRCC, etc.) and techniques (autogenous and engineering healing) to satisfy all demands in which sustainability and durability are key factors. Compared to the large number of investigations on selfhealing of plain concrete, self-healing studies on Fiber Reinforced Cementitious Composites (FRCC) are still limited. Therefore, the main objective of this paper is to provide a deep literature review on this subject in order to clarify what is known (What now?) and finally to identify those gaps which still require further studies (What next?) such as: healing capacity under sustained stress, repeatability healing/cracking cycles as well as healing capacity for cracks and damages occurring at later concrete ages.

Free vibration of functionally Euler-Bernoulli and Timoshenko graded porous beams using the transfer matrix method

Abstract: In this paper, an analytical method is developed to study the dynamic behavior of functionally imperfect Euler-Bernoulli and Timoshenko graded beams with differing boundary conditions, namely, hinged-hinged, clamped-clamped, clamped-hinged, and clamped-free. A transfer matrix method is used to obtain the natural frequency equations. The modified rule of mixture is used to describe the material properties of the functionally graded beams having porosities. The porosities are assumed to be evenly distributed over the beam cross-section. In this study, the effects of boundary conditions, material volume fraction index, slenderness ratio, beam theory, and porosity on natural frequency are determined. The present results are validated with results available in the literature.

Filler effect of pozzolanic materials on the strength and microstructure development of mortar

Abstract: The utilization of pozzolans in cementitious system (concrete and mortar) minimizes both cost and energy. It also enhances mechanical strength and durability of the system. The total contribution of pozzolans can be categorized into two: (i) physical or filler effect which is attributed by the fineness of the particles and (ii) chemical or pozzolanic effect which is attributed by the pozzolanic reaction. It is difficult to quantify the strength development of cementitious system caused by the filler and pozzolanic effect separately. Therefore, the individual contribution of pozzolans in cementitious system because of its physical and chemical effects need to be profoundly understood by the scientific community. This paper reviews available literatures to understand the effect of non-reactive fillers that attributed as the microfiller effect of pozzolans in cementitious systems. The previous studies utilized chemically inactive materials that attributed only the microfiller activity of pozzolans for a partial replacement of cement. It was reported that filler effect is equal or sometimes more significant than pozzolanic effect in concrete. A larger range of replacement percentages (like 5%, 10%, 15% or 10%, 20%, 30% etc.) was used in the previous studies. However, probabilities of the optimum compressive strength because of the filler effect may lie in between two larger range of replacement percentages. Therefore, an experimental work is also carried out using natural ground sand of size 7.6-μm at a lower range of cement replacement percentages (like 2.5%, 5%, 7.5% etc.) in mortar. Compressive strength of mortar at different ages and microstructure analysis of mortar at 28 days were performed in this study. Test results showed that the filler effect is more pronounced at a lower replacement percentages of cement (0-10%) while using smaller non-reactive fillers. The maximum strength due to filler effect of ground sand is acheieved at 7.5% replacement of cement. Scanning Electron Microscope (SEM) images also confirmed the effect of fillers on the microstructure development of mortar.

Effect of freeze-thaw cycles on triaxial strength properties of fiber-reinforced clayey soil

Abstract: Understanding effect of freezing phenomenon in a fiber-reinforced soil structure is essential to foundation technology, road construction and earthwork application in cold region. This research aims to present the results of experimental investigation relative to the unconsolidated-undrained triaxial compression behavior of fine-grained soil as a function of freeze-thaw cycles and fiber volume fractions. All measurements were carried out for 3 selected glass and basalt fiber fractions (0%, 0.5%, and 1%) and 5 selected freeze-thaw cycles (0, 2, 5, 10, and 15). It has been observed that for the studied soil, strength of unreinforced soil reduced with increasing number of the freeze-thaw cycles while fiber-reinforced soil shows greater effect and the strength reduction amount reduces from 40% to 18%. Moreover, the reduction trend for cohesion of the fiber-reinforced soil decreased, this was seen more prevalent on 1% glass fiber-reinforced soil. The resilient modulus of all specimens reduced with increasing number of the freezethaw cycles. The experimental results demonstrated that different fiber fractions and their mixtures could be employed as supplement additive to improve the freeze-thaw performance of cohesive soils for road construction and earthworks.

Analysis of cost-increasing risk factors in modular construction in Korea using FMEA

Abstract: The modular system is a very efficient construction method with various strengths and advantages that is expected to replace Reinforced Concrete (RC) or steel (S) structures. It is appreciated as a faster, more efficient, cheaper, and eco-friendly method capable of solving labor problems in the construction industry. However, the modular system has in fact failed to meet expectations in the Korean construction market, mainly due to higher construction costs as compared to RC structures. This study, therefore, sought to derive the construction cost-increasing factors for each phase of a modular project in Korea then analyzed what improvements should be made to secure economic feasibility. For the purpose of this study, the Failure Mode and Effects Analysis (FMEA) method was employed to find critical factors responsible for causing cost increases throughout the modular construction life-cycle from the perspective of the modular construction company. A total of 35 types are evaluated, which increased to 49 factors when overlapping is allowed over the phases. The result of the FMEA shows that there is a higher risk of a construction cost increase at the beginning of the design phase, highlighting the importance of initial planning and direction setting. It also demonstrates that workforce-related problems take up about half of the risk factors, indicating that the Korean modular construction industry needs well trained and experienced specialists. The results further imply that many of the serious risks of cost increases come from factors relating to market size and the maturity of modular construction, which the modular construction companies can’t control on their own. More publicity detailing the advantages and superiority of the system, its technical improvement and innovation in terms of quality and performance, could change customer interest in the system. These efforts should run parallel with the effort to lower costs.

Prediction of suspended sediment load using ANN GA conjunction model with Markov chain approach at flood conditions

Abstract: Development of cities, destruction of forests and pastures, population growth and other factors have increased suspended sediment load in rivers of developing countries. Measurement of suspended sediment load is a challenging issue for engineers at flood conditions. The case study of this research is Idenak hydrometric station on the Marun River in the south west of Iran. The used data consists of 42 years (1968 to 2009) flood discharge. A perceptron artificial neural network is trained and validated by observed data. For training of Artificial Neural Network (ANN), momentum and Levenberg-Marquardt training methods are applied. For decreasing of Normalized Mean Square Error (NMSE) and increasing of correlation coefficient (R), parameters of ANN are optimized by Genetic Algorithm (GA) method. GA method optimizes the number of nodes of hidden layers of ANN that is trained by Levenberg-Marquardt training method while it optimizes the number of nodes and momentum of ANN that is trained by momentum training method. GA method can reduce NMSE to 80% while GA method doesn’t increase R significantly. In order to predict flood condition, the Markov chain method is applied. The results show that suspended sediment load may be increased almost from 400000 ton/day to 800000 ton/day at future.

Review of Analytical and Empirical Estimations for Incident Blast Pressure

Abstract: Recently, the blast load has become more recognized in the structural engineering field because the blast load can result in not only disproportionate structural failure but also tremendous casualties of lives and injuries. As an effort to overcome this problem, blast resistant analyses and designs have been developed, and the methodology would be incorporated into the conventional construction design. Analysis of structures exposed to blast load is the first step for the design, and it requires good understanding of blast phenomena and the following dynamic response of structures. This paper provides an up-to-date comprehensive review of the incident blast wave and its parameters for air and ground blasts. Considering the Unified Facilities Criteria (UFC 3-340-02) as a benchmark, a quantitative comparison between the empirical results presented by researchers and the result given in UFC charts is conducted for a span of scaled distances. We discuss the appropriate use of empirical or analytical equations for precise prediction of blast pressures, and recommend equations that match well the results presented in UFC.

Effect of sodium hydroxide and sodium silicate solutions on strengths of alkali activated high calcium fly ash containing Portland cement

Abstract: In this paper, the mechanical performance of fly ash and Portland cement geopolymer activated with sodium hydroxide and sodium silicate solutions was studied. The Geopolymer Mortars (GM) were made from high calcium Fly Ash (FA) and ordinary Portland Cement (PC) with FA:PC weight ratios of 100:0, 95:5, 90:10, 85:15, and 80:20. The GMs were activated with three combinations of sodium Hydroxide Solution (SH) and sodium Silicate Solution (SS) viz., SH, SH+SS (SH:SS=2) and SS. For all mixes, 10 molar SH, alkali activator liquid/solid binder ratio of 0.60 and curing at ambient temperature of 25oC were used. The result indicated that the compressive and shear bond strengths of GM depended on the alkali activators used and the amount of PC. The use of SH and SHSS resulted in the formation of additional Calcium Silicate Hydrate (CSH) which coexisted with sodium aluminosilicate hydrate (NASH) gel. Whereas, the use of SS resulted in NASH gel with only a small amount of CSH. The increasing of PC content enhanced the compressive and shear bond strengths of GMs due to the formation of additional CSH. The 15% PC mixed with SHSS gave the optimum compressive and shear bond strengths.

Effect of nanosilica on the compressive strength development and water absorption properties of cement paste and concrete containing Fly Ash

Abstract: Fly Ash (FA) as a Supplementary Cementitious Material (SCM) increases the sustainability of concrete by decreasing CO2 emissions from cement production. The present study investigated the effect of nanosilica (nS) on the properties of cement paste and concrete, especially those containing FA. Fifteen cement paste and concrete mixtures with 15% to 25% of the cement content replaced with FA and four replacement ratios of nS (1.5%, 3%, 5%, 7.5%) were examined. The compressive strength development was measured and water absorption properties were tested by immersion and capillary absorption to investigate their early-age and long-term properties. The results demonstrate that the addition of nS accelerated the reactivity of early-age FA-based concrete and increased the strength development of cement paste and concrete over those without nS. The use of optimal ratios of up to 5% nS with 15% FA significantly improved the ITZ in FA concrete and noticeably decreased water absorption and the sorptivity coefficient of the concrete specimens.

Adsorption of phenol onto Banana Peels Activated Carbon

Abstract: The present paper reports adsorption of phenol onto Banana Peels Activated Carbon (BPAC). The effect of adsorbent dose (m), initial pH (pH 0), contact time (t), initial phenol concentration (C o ) and temperature (T) on the adsorption of phenol has been studied using batch experiments. The study revealed that about 83% phenol gets removed at an initial concentration of 50 mg/l, whereas the removal is 60% at an initial concentration of 500 mg/l. The phenol uptake of 6.98 and 48.58 mg per gram of BPAC at respective concentrations was found at an optimum dose of 6 g/l at 303 K. The optimum pH and contact time were found to be 6 and 60 minutes respectively. The pseudo second order kinetic model found best representing the kinetic study. Toth and Redlich-Peterson models were found best suited for describing the adsorption equilibrium data. From thermodynamic study it is confirmed that, phenol adsorption decreases with increase in temperature and is spontaneous and exothermic in nature.

Weibull model for wind speed data analysis of different locations in India

Abstract: Wind speed data should be fitted by a suitable statistical model like Weibull to determine expected number of hours per year in the critical wind speed range for a slender structure, which is required to determine the expected number of stress cycles in the projected working life of the structure. Apart from this, for the assessment of wind energy potential wind speed data should be fitted by an appropriate probability distribution. In the present scope of study, wind data of various locations of India have been fitted by Weibull model. Wind speed data are initially sampled in knot by Indian Meteorological Department and later converted into integer km/h before supplying them to the end user. Due to this conversion, wind speed data cannot be properly fitted by Weibull distribution and in this regard, the choice of appropriate class width becomes very much important. Without the choice of appropriate class width, estimated Weibull parameters become biased which would yield incorrect estimation of expected number of hours in critical wind speed ranges as well as wind energy potential. After taking appropriate class width of 4 km/h, it has been found that Weibull model is an adequate model to describe wind speed distributions of India. Weibull model has also been compared with other models such as Gamma and inverse Weibull distributions to establish its suitability than the others. In this study, the values of Weibull shape parameters vary from 1.3 to 2.3, whereas the values of scale parameters vary from 1.4 m/s to 6.5 m/s. The validity of Weibull model is also verified with a target confidence interval of 90%. The uncertainties involved in the estimation of available wind energy potential as well as the expected number of hours per year in critical wind speed ranges have also been considered due to random variation of wind climate in each year.

Numerical simulation analysis of damage mode of concrete gravity dam under close-in explosion

Abstract: The study of damage mode of a concrete gravity dam under close-in explosive impact is a critical issue to assess the dam’s antiknock security. In this paper, a fluid-structure coupled finite element numerical method with combination of Lagrangian and Eulerian algorithm is applied, taking into consideration the damage development process of the Huangdeng concrete gravity dam. The damage mode of a square reinforced concrete slab under close-in blast loads has been simulated and discussed as a comparison with real experiment to verify the feasibility of the numerical simulation. The influence of the presence of spillway tunnel on damage mode of the concrete gravity dam has been investigated. Different damage modes of the concrete gravity dam are compared and studied for different standoff distances and different detonation depths. The damage process of the dam with time course is researched. The influence of different mediums, where the explosion occurs, on the failure mode of the dam is also researched. The analysis results show that attention should be paid to the concrete gravity dam subjected to close-in upstream shallow underwater blasts. It also should be focused on that the presence of spillway tunnel can affect the damage result of the dam.

Application of model tree and Evolutionary Polynomial Regression for evaluation of sediment transport in pipes

Abstract: Prediction of critical velocity for sediment deposition is a significant component in design of sewer pipes. Because of the abrupt changes in velocity and shear stress distributions, traditional equations based on regression analysis can fail in evaluating sediment transport efficiently. Therefore, different artificial intelligence approaches have been applied to investigate sediment transport in sewer pipes. This study proposes two different approaches to predict the critical velocity for sediment deposition in sewer networks: Model Tree (MT) and the Evolutionary Polynomial Regression (EPR), a hybrid data-driven technique that combines genetic algorithms with numerical regression. The hydraulic radius, average size of sediments, volumetric concentration, total friction factor, and non-dimensional sediment size were considered as input parameters to characterize sediment transport in clean sewer pipes. The present study implements data collected from different works in literature. The proposed modeling approaches are compared to some benchmark formulas from literature, and discussed from the accuracy and knowledge discovery points of view, highlighting the advantage of both proposed techniques. Results indicated that both techniques have similar accuracy in predictions, but EPR allows to physical validation of returned formulas, allowing identifying the most influent inputs on the phenomenon at stake.

Back-fill Grout Experimental Test for Discharged Soils Reuse of the Large-diameter Size Slurry Shield Tunnel

Abstract: The construction of a slurry shield tunnel produces large amount of excavated soil. Direct discharge of the excavated soil by transportation not only increases the overall construction cost but also raises environmental concerns of pollution. In this study, we explore in-situ recycle of excavated soil in the Nanjing Yangtze River tunnel project as the back-fill grout. A series of laboratory were carried out to determine the synchronous grout parameters, including compression strength and shear strength, initial setting time, fluidity, consistency, and bleeding rate. The mixture ratio of the back-fill grout is also discussed to optimize the grout performance. It is found that: (1) the excavated soil produced from the construction of slurry shield tunnel in this project can be reused as the material of back-fill grout in the sand stratum; (2) Proper selection of binder/sand ratio and fly ash/cement ratio improves the performance of the synchronous grout. The test results demonstrated that the discharged soil can be recycled in-situ as the grouting material in the sand stratum.

An analysis of the ground deformation caused by shield tunnel construction combining an elastic half-space model and stochastic medium theory

Abstract: The ground movement induced by the construction of shield tunnels affects the safety of nearby underground pipes and aboveground structures. Therefore, the reliable prediction of ground movement is important. In this paper, a model describing the interaction between soil and an EPB shield used in tunnels is presented, based on the classical elastic theory of Mindlin. In this model, the changing location of the working shield is considered. The equations describing the ground deformation around the tunnel caused by the additional force on the shield working surface and the frictional force between the outer surface of the shield and the surrounding soil are derived. The ground deformation caused by ground loss due to shield tunnel construction is derived using stochastic medium theory. Finally, this model is applied to two running tunnels, and the sensitivity of the ground deformation to the calculation parameters is discussed.

Estimation of dissolved oxygen by using neural networks and neuro fuzzy computing techniques

Abstract: Dissolved oxygen, one of the most important water quality parameters, is a crucial parameter for the aquatic ecosystems. In this study, some advanced chemometric techniques included in a multi-layer perceptron, radial basis neural network, and two different adaptive neuro-fuzzy inference system methods are developed to model dissolved oxygen concentration. Moreover the estimations of these models are compared with the multiple linear regression. In this context, monthly mean quantities of the temperature, pH, electrical conductivity, discharge and dissolved oxygen data recorded at Broad River near Carlisle, SC in USA are used. The accuracy of the models is compared with one other by using determination coefficient, mean absolute error, root mean square error and mean absolute relative error statistics. Results indicate that radial basis neural network method performs better than the other methods in modelling monthly mean dissolved oxygen concentration. The temperature, pH, electrical conductivity, and discharge are found to be effective on dissolved oxygen concentration.

Deformation rule and mechanical characteristics of temporary support in soil tunnel constructed by sequential excavation method

Abstract: The temporary support of tunnel constructed through sequential excavation method is considered one key point because of its large deformation and complex force. The in-situ deformation of temporary support was monitored in two soil tunnels. Results show that the temporary support presents “convergence–expansion–stability” regularity in the horizontal direction and “settlement–uplift–stability” regularity in the vertical direction. Finite element numerical simulation method was used to obtain the displacement and stress of the temporary support based on the stratum geological parameters at tunnel site. Compared with the field test results, the numerical simulation values have differences, but the deformation rules are consistent. The temporary support bear not only axial force, but also the frequently variable bending moments and shear force. Combined the results of field test and numerical simulation, we proposed that the longitudinal connection reinforcement between each steel frame and steel fabric should be set in the temporary support. Alternatively, steel fiber-reinforced shotcrete could be used in the temporary support when necessary.

The investigation of rock indentation simulation based on discrete element method

Abstract: Rock indentation is widely encountered in rock engineering, such as oil & gas drilling process. The rock indentation represents the fundamental process for mechanical rock breaking. Therefore, it is necessary to research the failure mechanism during the rock indentation process. For this purpose, the Uniaxial Compressive Strength (UCS) and Brazilian Tensile Strength (BTS) tests are performed to calibrate the relations between micro-properties and macro-properties of the rock specimens. The rock indentation process and crack propagation with the effects of lateral pressure, hydraulic pressure, ledge, wedge angle and joint are researched by PFC2D in this paper. The results show that: with the indenter penetrating into rock, the sub-vertical crack is formed from the damaged zone and it will extend to bottom edge of the rock at last; the initiation and propagation of the sub-vertical crack is mostly driven by the tensile contact force. The development of sub-vertical crack and damaged zone are restrained with increasing lateral pressure, the lateral pressure increases led to an increase in the critical penetration depth and the size of the damaged zone decreases and its shape flattens with the lateral pressure increasing. On the contrary, the development of sub-vertical crack and damaged zone are promoted with increasing hydraulic pressure. With the wedge angle increases the size of crushed zone underneath the indenter increases, it promotes the formation of sub-vertical crack; larger wedge angle causes a larger indentation force. The existence of a ledge leads to crack initiation and propagation towards the free surface and the presence of the joint also promotes crack initiation and propagation towards the joint; when the crack propagates to the joint, the crack will no longer propagate towards the intact rock mass but along the joint.

The effect of the partial cement substitution with fly ash on Delayed Ettringite Formation in heat-cured mortars

Abstract: Delayed Ettringite Formation (DEF) is seen as a form of internal sulfate attack of cementitious materials, caused by early age heating to a temperature higher than 70°C. In this paper, the effect of fly ash on delayed ettringite formation of heat-cured cement-based mortars was investigated. To fulfil the aim of this study, a portion of cement was replaced by class F-fly ash, with three different dosages (10, 20 and 30%). The mortars were heat-cured at early-age, and the tests of expansion, mechanical strength, dynamic elastic modulus, mercury porosity and thermogravimetric analysis were carried on these mortars along a period of 650 days. Additionally, Scanning Electron Microscopy (SEM) observations were realized. The results obtained highlighted the mitigation effects of fly ash on DEF: A replacement of the cement used with 20% to 30% of fly ash was efficient to eliminate the long-term swelling due to DEF. This positive impact was explained by the combined effects of the high Al2O3 content of fly ash and the portlandite consumption induced by the pozzolanic reactions.

Flexural behaviour of reinforced concrete beams made with fine recycled concrete aggregates

Abstract: Even though in several countries there are regulations allowing, even at a small scale, the use of recycled aggregates in concrete production, practice shows that the cases in which this solution is implemented are still rare. However, in most of these countries the use of the fine Fraction of the Recycled Aggregates (FRA) from general Construction and Demolition Waste (CDW) is restricted or even banned. More recent studies have shown that the use of FRA is feasible and that the resulting mechanical performance is perfectly acceptable. This paper presents the flexural tests performed on reinforced concrete beams made with replacement of natural by recycled fine aggregates, comparing the results obtained in terms of ultimate load and deformation, ductility, bearing capacity and cracking with those from a reference beam, made with conventional concrete.

Surface settlement prediction for EPB shield tunneling in sandy ground

Abstract: Ground volume loss induced by shield tunnel construction is the major factor leading to ground settlement and deformation. The general equations predicting surface settlement based on ground volume loss involve a settlement trough width coefficient (parameter i) which in previous models was set as a constant in both the transverse and longitudinal directions. In this work, the equations predicting surface settlement during the construction were modified by introducing the parameter j – the width coefficient in the longitudinal direction, assumed to be different from that in the transverse direction. A model shield machine was adopted to carry a laboratory test under 1 g to investigate surface settlement induced by earth-pressure-balance shield tunnel construction in unsaturated sandy soil. The surface settlement during the excavating observed in the test was compared with that predicted by general equations from previous studies and the modified. The results showed that surface settlement above shield machine obtained by the modified equation proposed here fits the test data better than those obtained by the general equations because of the introduced longitudinal width coefficient.

The influence of amount and aspect ratio of fibers on shear behaviour of steel fiber reinforced concrete

Abstract: In this study, two grades of concrete namely C30 and C50 were investigated for the direct shear behavior of plain and steel fiber reinforced concrete. Shear tests were performed on concrete beams, 100 × 100 × 300 mm, reinforced with two different aspect ratios (l/d) of steel hooked-end fibers 65 and 80 and three percentages of fibers 0.5, 1.0 and 1.5 % by volume of concrete. The water/cement ratios (w/c) used were 0.5 and 0.43. The main objective of this study was to study the shear behavior of plain and fiber reinforced concrete at different aspect ratios and at different volume fractions of steel fibers. Test results for C30 and C50 concretes showed that, as the volume fraction of fibers increased from 0 to 1.5%, the shear strength increased about 2.15 and 2.46 times that of plain concrete, respectively. Also, test results showed that the aspect ratio of steel fibers has no clear effect on the shear strength. Relationships between shear strength and volume of fibers were determined, and a relationship obtained in terms of fiber factor and compressive strength to estimate the shear strength of fiber reinforced concrete. The obtained equations give good correlation with the experimental results.