Abstract:Biogeotechnology mainly utilizes microorganisms that widely existed in natural environment, and the metabolic functions of these microorganisms will induce serials of bio-chemical reactions with other materials in the environment. The physical mechanical and engineering properties of geo-material would remediate after the biochemical process, and thus achieving the aims of environmental purification, soil remediation and foundation treatment, etc. As a new branch of geotechnical engineering, biogeotechnology has gradually become a popular trend, many researchers have carried out a lot of related researches in recent years. This paper summarizes the representative microorganisms, the biochemical reaction processes and the function mechanisms of the microorganisms involved in the field of bio-geotechnical engineering. Then, the related researches and its applications from the aspects of bio-soil improvement technology, bio-sealing technology and metal contaminated soil remediation technology are summarized and discussed. Through the collection and summary works on this topic, it is expected to promote more comprehensive and in-depth basic researches and contribute to more practical promotion and application of the bio-technology in geotechnical engineering.

Abstract:Microbial-induced calcite precipitation (MICP) has the prominent advantage of significant improving the shear strength of soil, while MICP sand also has the obvious shortcoming of brittle failure. A certain amount of fiber was added into MICP sand in order to improve the brittleness, and based on consolidated drained triaxial compression tests, the shear strength characteristics of fiber-reinforced bio-cemented sand was studied. And then, the effects of fiber content, fiber length and initial relative compactness of samples on the shear characteristics of fiber-reinforced bio-cemented sand were discussed. Finally, the corresponding mechanisms of strength enhancement and ductility improvement were also investigated through scanning electron microscope. The results show that during the process of MICP, calcium carbonate crystals deposited on the fiber surface effectively improve the roughness of fibers surface, while the mixture of calcium carbonate and sand provides anchorage to the fibers, enhancing the shear strength of MICP sand and improving the strain softening characteristic, and it is concluded that fiber has the potential to improve brittleness of MICP sand.

Abstract:Free-fall penetrometers (FFPs) are used to measure undrained shear strength of cohesive soils. FFPs are featured with quick operation and good economical efficiency, with significant potential in offshore in-situ investigations. However, the data interpretation of FFP tests is impaired by uncertainty in the dynamic penetration mechanism of FFPs. Reduced-scale model tests were conducted in kaolin clay with different strength profiles, whilst a simplified analytical model was modified to predict the undrained strength through the penetration velocity profile. The analytical model was validated by comparison with the testing data. Based on parametric study, the "FFP mass-impact velocity" contours are proposed for quick design of the in-situ tests given the rough range of undrained strength from local experiences.

Abstract:How to control the post-construction settlement of deep soft soil foundation in high-speed railway is a worldwide problem. Therefore, analysis of settlement monitoring data of 100 km subgrade during the operation period of 3 years based on the Shanghai-Nanjing inter-city high-speed railway is performed in this paper, and the post-construction settlement is divided into four grades which can be used to evaluate the settlement control effect. Combined with the sedimentation estimation, it is further divided into four states:stability, basic stability, critical overrun and overrun. Aiming at addressing the problems existing in the routine analysis method of post-construction settlement control of foundation treatment measures, the concept of "equivalent soft soil thickness" is proposed, which can quantitatively analyze the effect of post-construction settlement control of foundation treatment measures. Results obtained from the comprehensive analysis show that the post-construction settlement of the high-speed railway subgrade is positively related to the thickness of the weak soil. There exists a "critical" equivalent soft soil thickness in the different treatment measures, and the thickness of the equivalent settlement of the foundation in the pile-soil is 1.7 times of that of pile-raft composite foundation, and it is 2.2 times of pile-net composite foundation. Pile-plate structure treatment foundation is equivalent to weak soil thickness, and its corresponding post-construction settlement is only 59% of pile-raft composite foundation. In addition, the raft composite foundation is 76% of the pile-net composite foundation.

Abstract:In view of three types of foundation pit in the Huanghe River basin with different geo-mechanical characteristics, this paper aims to explore the yield behaviour and application conditions of five prescribed constitutive models. Combing geo-mechanical parameter characteristics in typical area of thick alluvium, the constitutive model matching structural deformation of foundation pit excavation in respective area, by employing secondary development platform of finite difference method simulation software as well as field test data. Results show that:geo-mechanical characteristics varies significantly along the Huanghe River alluvium. Generally, the eastern stratum shows well grain size gradation, while the deep western stratum is mainly consist of unconsolidated clay and fine sand. The deformation behaviour of retaining pile for foundation pit in Jinan can be precisely simulated by Jene model, and meanwhile, the law of foundation pit surface deformation development can be described by Duncan Chang model. M-C model fits the active earth pressure with high accuracy in Zhengzhou, the time-dependent change law of axial force simulated by modified Cambridge model is in good accordance with the field test data.

Abstract:The direct shear tests of clayey soil-concrete interface with six series of shear rates were carried out by using the self-developed large-scale constant normal stiffness pile-soil interface shear apparatus. The effect of shear rate on shear strength of clayey soil-concrete interface was explored in this paper. The test results indicate that excess pore water pressure increases with the increased shear rate. The excess pore water pressure is influenced by both normal stress and shear rate, which is closely related to shear peak strength and shear failure strain of clayey soil-concrete interface. The shear stress-shear strain curves are basically identical at the beginning and then deviate in a certain range, which deviate the more obviously and present significant strain-softening appearing, with higher normal stress and faster shear rate. The decreased magnitude on shear strength of clayey soil-concrete interface increases, and the friction coefficient decreases to 0.1 and the effective adhesive force varies from 0.81 kPa to 5.93 kPa as the shear rate increases from 0.4 mm/min to 5.0 mm/min.

Abstract:The penetration resistance of jacked pile was calculated by using the specific penetration resistance of single bridge cone penetration test. According to the comparison between estimated bearing capacity from Technical Code for Building Pile Foundation (JGJ 94-2008) and measured value, the calculation method of estimating the penetration resistance of jacked pile was put forward, which took comprehensive correction coefficient α and β of pile tip resistance and skin friction of pile into consideration. Besides, the calculation formula of base resistance and side resistance were also defined. Several suggestions for determination of comprehensive correction coefficient were given for different soil layers. The proposed approach was compiled in the Visual Basic visualization program, and the corresponding results were displayed in the form of graphics. Through the simulation of specific engineering and test results of pile driving pressure, the results further showed that it was feasible to use the comprehensive correction coefficient to calculate the pile resistance. The obtained results could provide guidances for the design and construction of jacked pile under similar condition in engineering practice.

Abstract:Based on the analysis of ground settlement caused by shield tunneling excavation of a certain section of 4th Line of Wuhan Metro considering tempo-spatial effect of ground settlement, the ground settlement has been divided into five stages as follows:no effect stage, earlier stage, passing stage, tail void stage, passed stage. The distance of each stage between the excavation face and the monitoring section have been suggested. In addition, the ratios of ground settlement in different stages to total settlement have been calculated. The main influence factors of ground settlement in different stages are investigated by introducing time parameter into Mindlin solution. Results show that the friction force and ground loss have more influence on ground settlement before the cutter of the shield machine through monitoring section, and the ground loss has great effect on ground settlement after the cutter through monitoring section. The additional thrust and friction force tend to cause ground-uplifting at the Earlier-stage. Besides, the additional thrust, friction force and grouting pressure may lead to ground resilience during the passed-stage. More importantly, a formula of calculating the real-time ground settlement has been proposed to offer a technical support in engineering construction. The calculated results are in good agreement with the corresponding measured values, indicating that the formula is able to accurately predict the ground settlement in real time.

Abstract:The creep deformations developed in steel significantly affect the deformation and bearing capacity of steel structures in fire. However, such creep effect was not considered in fire-resistance calculation method of steel columns in current specification of Code for Fire Safety of Steel Structures in Buildings (GB 51249-2017). Load bearing capacity of steel columns at elevated temperature after considering creep effect was analyzed by ANSYS soft package. A comparative study is performed in this paper to compare the finite element results with measured data obtained from fire test,and it is found that the numerical results and measurements show good agreement when considering the creep effect. Subsequently, the validated model was used for parametric studies. It is shown that the initial imperfection (i.e., residual stress, geometric imperfection, and load eccentricity), bend direction, load ratio, slenderness ratio and heating rate have a significant influence on the load bearing capacity of steel columns when considering high temperature creep. In contrast, the load bearing capacity of steel columns is less sensitive to the section shape and yield strength of steel. A simple design method is proposed to calculate the load bearing capacity of steel columns at elevated temperature.

Abstract:A 3D meso-scale simulation model was developed to study the failure behavior of reinforced concrete (RC) beams, in which the concrete heterogeneities and the nonlinear concrete-steel interaction were taken into account. The developed meso-scale simulation method was then validated by comparing the simulation results with the available tests for RC cantilever beams. In addition, the effects of stirrups ratio, shear-span ratio and loading mode on the size effect in shear strength of RC beams with a maximum depth of 2 000 mm were explored. The simulation results indicate that:1) The shear strength of beams without web reinforcement presents obvious size effect, and the influence coefficient of section height proposed by Chinese Code for design of concrete structures cannot fully reflect the size effect of RC beams; 2) The web reinforcements can inhibit size effect on the shear strength of RC beams, and the size effect on shear strength of beams gradually weakens with the increase of stirrups ratio; 3) As the shear-span ratio increases, the shear capacity of the beam decreases, and the size effect becomes to be weakened; 4) Compared with monotonic loading, cyclic loading leads to the low-cyclic fatigue failure of RC beams, and thus it makes the size effect in shear strength more prominent.

Abstract:Reasonable seismic design input energy spectrum is important basis for promoting the engineering application of energy method. Based on 259 seismic records on 3 site conditions, the input energy spectrum of elastic single degree of freedom (SDOF) systems were studied. Using the normalization method, the elastic input energy spectrum are characterized as the product of the maximum of input energy spectrum (E_Imax) and the normalized input energy spectrum. According to correlation analysis, influence factors and estimation method of the maximum of input energy spectrum are given; based on characteristics of the normalized input energy spectrum on different site conditions, the simplified normalized input energy spectrum is established by multiple fitting, and the calculation method of design input energy spectrum of elastic SDOF systems with the damping ratio of 0.05 is proposed and verified.

Abstract:To study the pulse effect on the seismic response of steel coal-conveyer gallery in thermal power plant, dynamic analysis of a typical coal-conveyer gallery structure was carried out in this paper. Firstly, the energy-based pulse-like ground motion identification method was adopted to select nine ground motions with different pulse periods. Secondly, the corresponding ground motions without pluses were obtained by using standard mathematical pulse model to remove the pulses from the selected pulse-like ground motions, and then, a comparative analysis was conducted considering the ground motions with and without pulses. Results show that pulse-like ground motions can significantly affect the structural responses, especially when the pulse period is close to the fundamental period of the structure. The pulse effect on the responses of coal-conveyer gallery is most obvious when the three-direction input is used, and the maximum value of amplification factor is 2.1. Under the pulse-like ground motions, the displacements of column top is 1.36 times of the elastoplastic displacement limit, which will cause serious damage beyond expectations. The mid-span deflection of steel truss is 2.97 times of the serviceability limit, which may adversely affect the serviceability of the structure and the safety of the attached equipment. Therefore, in seismic design, to avoid misleading estimates of the responses of structure, it is suggested that the pulse effect and the multi-dimensional input should be considered cautiously for the coal-conveyer gallery in the neat fault region.

Abstract:Sulfate ions in seawater penetration into concrete would lead to damage of concrete in marine environment. In this paper, the air entraining concrete with 0-65% of GGBS content was exposed to marine tidal zone, atmosphere zone and submerged zone for 1~2 a. The water-soluble and acid-soluble sulfate ions profile were tested, and the corrosion products of cement paste in marine environment was analyzed. The experimental results shown that the order of the migration sulfate ion content and transmission depth of concrete exposed to different corrosion zones was in order of:tidal zone>submerged zone> atmosphere zone. The relationship between reactive sulfate ion and total sulfate ion in concrete could be expressed as a linear function. The reacted sulfate ion content accounted for more than 90% of total sulfate ions, and the amount reaction sulfate ion increased with the corrosion time. The amount of corrosion products including ettringite and gypsum were generated in pastes exposed to tidal zone and submerged zone. The corrosion product of concrete exposed to the atmosphere zone was only ettringite. For C40 concrete prepared with P.I.52.5 cement, cement replacement by 65% GGBS helps to improve the capacity of concrete to sulfate ion attack in marine environment.

Abstract:With the rapid development of modern industry, heavy metal ion waste water, printing and dyeing wastewater discharged from the production process are increasing. Thus searching for more efficient water treatment materials has become an urgent issue in environmental protection. Magnetic chitosan microspheres are emerging water treatment absorbents, which draw lots of attention for their excellent absorption effects on various pollutants and the characteristics of being recovered and reused. More functional properties were introduced by modification. The preparation and relevant studies of magnetic chitosan microspheres, the modification methods, mechanism and application of chitosan and Fe₃O₄ are reviewed in this paper. Furthermore, their future development tendency are predicted.

Abstract:Metal ions and organic pollutants can coexist in the environment in a variety of ways and therefore, generate combined pollution. Because of the interaction between metal ions and organic pollutants, their physicochemical property, transformation, and eco-toxicity would change, which gives rise to great challenge for the water treatment process and ecological toxicity assessment of these pollutants. This paper reviews the sources of combined pollution, the interaction between metal ions and organic pollutants, the influences of coexistence on the removal efficiency of both metal ions and organic pollutants, and the studies on ecological toxicity of combined pollution, which aims to provide a theoretical reference for the prevention and treatment of combined pollution.

Abstract:A novel inorganic-organic modified composite coagulant polyaluminum chloride-titanium cationic polyacrylamide(PTA-CPAM) was prepared by chemical reaction with aluminum chloride(PAC), titanium tetrachloride(TiCl₄) and cationic polyacrylamide(CPAM). The infrared spectroscopy, scanning electron microscopy with energy dispersive spectrometer(SEM-EDS) and differential thermal analysis(TG-DTA) were applied to analysis the structural characteristics, composition and thermal stability of the polymer. The coagulation properties of PTA-CPAM was investigated, and the results showed that the better water purification effect of coagulant could be obtained when the mass ratio of CPAM and Al was 2:5, the optimum dosage was 9 mg/L and the pH value was 9.0. Moreover, PTA-CPAM had better turbidity removal ability for water samples with different initial turbidity, and the PTA-CPAM had stronger adsorptive neutralization and adsorption bridging ability due to the synergistic effect, which led to excellent turbidity removal performance.

Abstract:The development of urban lighting and the widespread use of LED have led to increasingly bright outdoor light conditions, common colored light in residential areas and increasingly impacts on residents' indoor recreational activities before curfew. From the perspective of residents' subjective feelings, the subjective evaluation experiment results in the interference threshold of urban colored light on residents' watching TV activities under the condition of normal indoor lighting, which includes the "lightness threshold" characterizing residents' visual perception and the "brightness threshold" characterizing of light source reality. This paper analysed that the seasonal difference, gender difference and hue difference of urban lighting color interfered with residents' indoor activities. And the applicability of threshold conclusion was also discussed.

Abstract:Based on the survey data of 11 large public libraries and university libraries, the multivariate linear regression equation is established to investigate the relationship between the objective lighting parameters and subjective evaluation, which aims to establish the prediction model of subjective evaluation of visual satisfaction associated with lighting parameters. The model shows that when using the electronic reading media in open reading space of the library, the readers' visual satisfaction would be improved with the increase of average value of horizontal illumination and vertical illumination, the decrease of the average degree of slope illumination, the increase of the uniformity of oblique illumination and vertical illumination. The results indicate that the uniformity of oblique illumination has a greater impact on visual satisfaction.

Abstract:In this paper, application potential of phase change heat storage coupled with night ventilation technology in transition and hot seasons were investigated using EnergyPlus, based on a typical office building in Xi'an. Two factors, daily cumulative cooling amplitude (ΔT) and percentage of cooling potential (J), were introduced to evaluate its cooling effect. The characteristics of outdoor dry-bulb temperature were examined when the technology realized its best cooling potential. The performance of the technology on improving the indoor thermal environment was also analyzed based on the standard ASHRAE 55 Adaptive Comfort Model. The results indicate that the technology can obtain excellent application effect when the maximum of outdoor dry-bulb temperature exceeds the upper limit of the phase change range 3℃ and its minimum is less than the lower limit of the phase change range 3℃ and its average is in the phase change range. The application effect of this technology in transition season is superior to that in hot season. Compared with night natural ventilation technology, the cooling amplitude in transition season and hot season by using the technology are increased by 14% and 5.6%, respectively, and the number of hours meets ASHRAE 55 standard 80% acceptability limit in transition and hot seasons are increased by 8% and 1%, respectively.

Abstract:The Local Climate Zone (LCZ) scheme aims to provide an objective and standardized classification protocol for urban temperature studies in any city. The field temperature data (Jul.-Sept., 2016) from 12 LCZ sites located in urban and rural areas of Nanjing, China, was used to evaluate the LCZ scheme. For the 12 LCZ sites, the features of heat island and the differences of daily max/min temperature and heating/cooling rate were analyzed. The UHI intensity increases rapidly after sunset, reaching at maximum about three to five hours later, and then declines gradually, which is the result of the variation of the heating/cooling rates of a LCZ site. It was observed that the higher level of urbanization the stronger heat island effect for the LCZ sites. The heat island magnitudes may even be negative during the midday period. It was shown that the water area (LCZ G) produces cooling effect during the daytime as expected while shows warming effects during the night time. The daily maximum temperature difference between urban and rural occurs in the minimum rather than in the maximum. Distinct differences in air temperature among the LCZ sites reflect the thermal effects of local surrounding properties.

Abstract:At present, most of the dynamic prediction methods of ice storage air conditioning cooling load showed poor precision and slow convergence speed, due to bad correlation between model input variables and output results, high information redundancy. This paper proposes an improved PSO-BP neural network optimization algorithm to predict the cooling load of large public buildings. For the input variables and the output results, the degree of grey correlation analysis is used to eliminate the chance of the logarithm of the samples input variables, and the key factors affecting the cold load of the ice storage air conditioning system are determined as input variables to predict the dynamic cooling load of the ice storage air conditioning system. The results show that the key factors of the cooling load of ice storage air conditioning system include the outdoor air temperature at T h, the outdoor air temperature at T-1 h, the outdoor air humidity at T h, the solar radiation intensity at T h, the solar radiation intensity at T-1 h, and the air-conditioning cooling load at T-1 h. Therefore, these key factors act as the input variables of the prediction model which show higher accuracy and faster convergence speed than the traditional PSO-BP network model of full-variable prediction method.

Abstract:Nowadays, green roof is considered as a good strategy to improve the indoor hydrothermal environment. In order to investigate the influence of a light extensive green (LEG) roof on indoor temperature, humidity and human thermal comfort in summer in Chongqing, comparative experiments on two kinds of roofs, namely LEG and the common one, were carried out at two similar six-floor naturally ventilated residential buildings. The results showed that the room with LEG roof was characterized with a lower indoor temperature compared with the room with ordinary roof in summer. During the study period of July, monthly average indoor temperature of the tested room with LEG roof was 5.8℃ lower than outside and 4.9℃ lower than that of the room with ordinary roof at 14:00. On 24th July, the hottest sunny day in the study period, there was an obvious difference on indoor and outdoor temperatures of the room with LEG roof, which could reach as high as 7.6℃ at noon, while the indoor thermal environment had no significant temperature stratification. The humidity inside the room with LEG roof was relatively higher compared to that of the room with an ordinary roof. Assessed results from both PMV-PPD model and thermal sensation vote (TSV) indicate that LEG roof can significantly improve indoor thermal comfort. Higher level of indoor thermal comfort and lower indoor thermal dissatisfaction can be realized by the application of a LEG roof.