Abstract:The unloading creep properties of soft soil under the excess pore water pressure are important for analysis of the deformation and stability of underground excavation in water-rich soft soil region. In this paper, the silty soft soil in Shenzhen was investigated via conducting unloading K₀ consolidation undrained triaxial test and unloading creep test under different initial static pore water pressures. Results show that a higher initial excess pore water pressure and a smaller consolidation confining pressure will cause more abrupt unloading failure of the soft soil. The stress-strain curve of the unloading strength of soft soil is in the form of hyperbola. The results of hyperbolic function fitting show that the unloading strength decreases linearly with increase of initial excess pore water pressure. The unloading creep deformation is found to be sensitive to the initial excess pore water pressure. The failure deviatoric stress in unloading creep test is about 90% of the deviatoric stress in unloading strength test. The unloading failure and creep failure are more likely to occur under stress path with UU0.5 compared with UU0.0. Therefore, the confining unloading rate and the excess pore water pressure should be cautiously controlled in engineering practice.

Abstract:Solidification is a major treatment method for the dredged sludge from rivers and lakes. In order to investigate the wetting/drying stability of the solidified materials, a series of tests measuring the shear strengths of solidified dredged sludge during drying/wetting process were performed. Besides, the variation pattens of the shear strength were revealed and the influential factors are analyzed quantitatively. The test results show that the shear strength of solidified dredged sludge changes gradually with the increasing number of drying/wetting cycles, and finally tends to be stable. The shear strength of solidified dredged sludge with a cement content of 100 kg/m³ decreases after drying/wetting, while the shear strengths of solidified dredged sludge with cement contents of 150 and 200 kg/m³ increase after drying/wetting, which indicates that the influence of drying/wetting on the mechanical behaviors of sludge relates to the cement content. A higher drying temperature promotes the hydration reaction of cement during the drying/wetting process. Therefore, it resulted in the increase of hydration products and the increase in shear strength. However, the development of crack inside the material during drying/wetting leads to the decrease of its shear strength. The overall influence of drying/wetting on the shear strength of solidified sludge depends on the compromises of the two factors.

Abstract:The freezing and thawing, shrinkage and expansion, and damage of tailings sand can cause great harm to the project of tailing dam in cold regions. In order to explore the deformation characteristics of tailing dam and reveal its deformation mechanism under freeze-thawing, down-scale tailings dam model tests were carried out on a self-designed device under different freezing temperatures (-5, -25, -45℃). The soil pressure, displacement and pore water pressure at each key position of tailing dam during the freeze-thaw cycle were measured by the dynamic data acquisition instrument. The test results show that:the internal stress of the dam increases with decrease of freezing temperature; the stress growth rate in the early stage of freeze-thaw cycleat each key position is higher than that at the other stages. The pore water pressure in the dam decreases with decrease of freezing temperature. The variation range, periodicity and regularity of pore pressure increases with the position depth of the dam. Besides, it is revealed that the freezing temperature has obvious position effect. The closer to the tailings dam edge, the greater the deformation magnifude of dam body and the higher of the deformation rate.

Abstract:It is of great importance to investigate the characteristics of end-bearing capacity and to determine the resistance factor for rock-socketed piles. In this study, based on the results of 165 compression load tests several key issues with regard to the end-bearing capacity behavior of rock-socket piles were examined. These load tests were conducted on different rocks with different rock-socketed pile conditions throughout the world. The influential factors include the type and the uniaxial natural compressive strength of rocks, the diameter and the embedment depth of socketed piles, and the ultimate end-bearing resistances. In this study, the ratio of ultimate end-bearing capacity to the unconfined compressive strength of the rock was defined as the end-bearing resistance factor of rock-socketed pile. Effects of the key factors on the ultimate end-bearing capacity and the end-bearing resistance factor were comprehensively investigated. An empirical equation between the unconfined compressive strength.

Abstract:According to the engineering properties of sandy soil foundation in desert area and the shortcomings of the existing transmission tower foundation, a foundation of plate and ball connected by an anchor cable is developed. By combining the similar model uplift tests and numerical simulations, the displacement of the foundation under different uplift loads is analyzed. Besides, the influence and its rule of buried depth ratio, spherical diameter and column diameter on the ultimate uplift bearing capacity coefficient of the foundation and the radius of main rupture surface of soil surface are studied. The results show that the numerical simulation results are in good agreement with the experimental results. The load-displacement curve presents a three-stage form, which corresponds to the three stages of soil deformation evolution. The ratio of buried depth is of the greatest influence on the ultimate uplift resistance of foundation, and there is a positive correlation between them. The ultimate uplift bearing capacity coefficient increases first and then decreases with increase of burial depth ratio. It is negatively correlated with the sphere diameter and positively correlated with the cement-soil column diameter. The radius of the main rupture surface of soil is negatively correlated with the buried depth ratio, spherical diameter and column diameter.

Abstract:Based on the local deformation theory, the anchorage mechanism of anchor-grout interface failure type is analyzed and studied. The grouting body and surrounding rock mass regarded as a whole with zero relative displacement. The stress distribution of the shear stress and axial load on anchor-grout interface is obtained by determining its main influential coefficient (r and k_s). Via the comparison between the numerical simulations by Flac 3D and the experimental results, the rationality of this method was verified. A virtual coefficient T is used to describe the interface properties of the bolt and the grouting body and its influence is analyzed. The results show that the anchoring effect can be enhanced by increasing the length of the anchor in a certain range. However, excessive increase of the bolt length has marginal effect on shear stress and axial load. With increase of the anchor radius, the shear stress peak of the anchor surface is non-linearly reduced and range of action is increased. To avoid stress concentration, the anchor rod with small radius should be avoided. The virtual coefficient T can reveal the difference degree of anchor grouting interface. With the increase of T, the shear stress on the anchor grouting interface increases, while the homogeneous degree of the stress and the action length of the axial load reduce. By taking appropriate T value the anchoring effect is best. The effect of T value on the anchoring mechanism of bolt is significant.

Abstract:Taking a foundation pit near the urban rail transit structure in southern Jiangsu as an example, the soil parameters were obtained by inverse analysis and three-dimensional finite element method simulations. On this basis, the influence of different excavation distances, excavation qeometries, number of foundation pits and construction procedure on the deformation of adjacent subway elevated structure is studied. The results show that, when the horizontal distance between foundation pit and structure is less than 2H (H represents the depth of the foundation pit), the lateral deformation of the structure is larger than that of vertical. The horizontal displacement and settlement of elevated bridge pier reach the maximum when horizontal distance is 1H. Besides, the additional deformation of subway viaduct piers increases rapidly with width of foundation pit. It decreases significantly when the width of foundation pit is larger than 8H. The depth of excavation of the foundation pit has the greatest influence on viaduct pier within 4H range of the central line of the foundation pit, especially when the excavation depth is more than 10 m. It is found that the structural deformation caused by multiple foundation pit construction shows obvious nonlinear superposition effect, while the construction procedure of multiple foundation pit has a slight influence on the total deformation of the structure.

Abstract:High-rise building may experience severe damage under far field strong earthquake. A common measure to reduce the seismic damage is using dampers which can mitigate the response of the structure. Current seismic design code has already been implemented with a general damper design method. However, whether the actual seismic response of the building deviates from the design, and whether the performance of different dampers under the same seismic precaution is different, are still unknown. In this study, firstly, a 20-story steel frame structure based on current seismic design code is established as the Benchmark model, and three different types of typical dampers, including friction damper, vicious damper and buckling-restrained brace are designed under the same control target. Numerical models of the three types of dampers are established according to the fitting of damper experiment curves. Based on the site types, ten ground motions have been selected for incremental dynamic analysis, and the control effect of the structural collapse resistance of the three types of typical dampers were compared. In the meantime, displacement-based structural seismic performance level is taken as the evaluation indicator to compare the control effect of three types of typical dampers, respectively. The results show that for the high-rise building-damper system designed according to the Chinese code, the viscous damper performs the best, followed by friction damper and buckling-restrained brace.

Abstract:HRB600E bar is a new type of high-strength reinforcing bar. For improving the seismic performance of rectangular columns and popularizing the HRB600E bar, the reversed cyclic loading test for different coaxial compression ratio, reinforcement strength and longitudinal reinforcement ratio is firstly carried out for the six high strength reinforced concrete columns with HRB600E bars. Then, the hysteric curve, skeleton curve and longitudinal reinforcement strain curve of specimen under low cyclic reversed loading were obtained. Finally, the failure characteristics, hysteresis characteristics, skeleton curves and stiffness degradation of high strength reinforced concrete columns are analyzed. The results showed that the failure characteristics of the high strength reinforced concrete columns with HRB600E are similar to the common reinforced concrete columns. Reducing the axial compression ratio or increasing the reinforcement strength can improve the hysteresis characteristics of high strength reinforced concrete columns with HRB600E bars. Besides, the seismic performance of the specimen can be improved by reducing stiffness degradation. The mechanical behavior of the high strength reinforced concrete columns is better when used with high strength concrete.

Abstract:Through the modal analysis and test of the 1:10 down-scale model test of 60 m circular spoke cable-trusses, the influences of three parameters including the cable prestress, rise to span ratio, as well as the diameter ratio of inner and outer ring on the natural vibration characteristics of the structure were investigated. The results obtained from test and theoretical formulation of the first four order modal were compared and analyzed. It can be seen that:The first and the second order vibration modes of the structure are antisymmetric upper and lower vibrations, the third order is the inner ring torsional vibration, and the fourth order is the relative torsional vibration of the inner ring. The frequency error is less than 10%, and the experimental mode of vibration is in good agreement with the theoretical mode. The frequencies of the first four modes are all larger than 10 Hz, indicating that the spoke cable truss structure is of low frequency dynamic response, and the natural frequency is small and the distribution is dense. When prestress level of the structure is higher, the modal frequency will increase, and the stiffness will also increase. With the increase of sagittal height, the structural frequency will decrease, and the structure is more prone to lateral instability. With the increase of the inner and outer ring diameter ratio, the torsion stiffness of structure will decrease and torsion instability will also occur.

Abstract:In order to investigate the relationship between the unstressed state amount and the prefabricated configuration of the plane beam element, a mathematical relationship between parameters of the prefabricated configuration and the unstressed state amount of the plane beam element was established by analyzing the geometrical configuration of the plane beam element considering the displacement of the joint. Taking a cantilever beam as an example, two types of alignment were used as inputs to verify the proposed mathematical relationship. The results show that the unstressed configuration is uniquely associated with the unstressed state amount of the element. The unstressed state amounts of different elements correspond to different prefabricated configurations. Although the prefabricated configurations of the two alignments are different, they have minimal influence on the joint elevation control when assembling the main beam segments. In engineering practice, the prefabricated configuration of the beam segment can be different as long as the joint elevation satisfies the elevation requirement of the target alignment.

Abstract:Upright tube's six degrees-of-freedom are constrained by horizontal tube and diagonal brace at the coupler connection joint, the strength of such constrains is the key factor of the stable bearing capacity of the scaffold. To determine the efficiency of the constraints, single factor sensitivity analysis and eigenvalue buckling analysis methods are applied to measure each constraints' contribution on stable bearing capacity. The efficiency analysis results of their contributions indicated the constraint mechanism of horizontal tubes and bracing tubes. Reasonable effectiveness of six constrains is tentatively researched according to the published experimental data of couplers, and then a multi-parameter simulation method of semi-rigid node is proposed. The premise condition of the multi-parameter simulation method is validated by the comparison between the experimental loads and the the inner forces' calculating results of the couplers, in which effective length method and linear elastic second-order analysis method are adopted. Accompanying with the research of multi-parameter simulation method, some common deficiencies or limitations of ordinary methods which are based on single parameter assumption are listed and analyzed.

Abstract:The reliable connection of pultrusion forming GFRP pipe joints is a prerequisite to ensure the normal operation of the components. In order to explore its tensile connection performance, two kinds of connection modes of bonding connection and bolt connection in GFRP pipe and steel pipe connector are adopted in this study to carry out the tensile test. The distribution characteristics, force mechanism, failure process and the influence of bonding length on load-bearing capacity of glue layer shear stress along the length direction were studied in the adhesive bonding test. The results show that the shear stress of the glue layer is large at both ends and small in the middle along the length direction at the initial stage of loading. As the load increased, the stress gradually shifted towards the loading end of the glue layer. The increase of bonding length can significantly improve the load-bearing capacity of the connecting parts, but when the length reaches 1.6 times of the pipe diameter, the increase of the bonding length is not sensitive to the increase of the load-bearing capacity any more. Therefore, the 1.6 times the pipe diameter can be regarded as the effective bond length of the GFRP pipe. Additionally, the influence of e/d(edge distance/bolt diameter) and bolt row number on the connection load-bearing capacity and failure mode were studied in the bolt connection experiment. The results show that when e/d is equal to 7, the load-bearing capacity reaches the maximum value and the main failure mode is extrusion failure. According to the relationship between the bolt row number and the load-bearing capacity, the corresponding reduction coefficient can be readily deduced for calculating the load-bearing capacity.

Abstract:The interface performance between steel plate and concrete is the key to strengthened concrete structure. Firstly, a total of 27 specimens for steel plate bonded concrete under hydrothermal environment were carried out in this study. The accelerated hydrothermal aging was conducted in 5 days, 10 days and 15 days, respectively. Then, the double-shear test was performed to obtain the ultimate load, strain distribution and relationship of load-displacement during the shear failure process on steel plate-concrete interface. After long term temperature and humidity coupling, the durability of the steel plate-concrete interface was studied. Considering the analysis of bond failure mode, loading process and the relative displacement evolution on bonding interface, the expression of shear stress and slip was proposed, which was related to temperature and humidity. Finally, the bond-slip constitutive model was established in consideration of the temperature and humidity. The numerical simulation results were in good agreement with the experimental results.

Abstract:The influences of water-to-binder ratio, binder type and exposure time on the surface chloride concentration C_s,ts of concrete exposed to marine tidal and splash zones were investigated systematically in this study based on 304 sets of field test data selected from different sites around the world. Then, the correction factors of four binder types can be determined using the two-phase multiple nonlinear regression technique, including the ordinary Portland cement, fly ash, slag and silica fume. Finally, an improved model for C_s,ts was developed. The applicability of the improved model for C_s,ts was validated in comparison with existing models and field test data. Analysis results show that the surface chloride concentration increases linearly with water-binder-ratio, while the influence of binder type on C_s,ts cannot be ignored. Moreover, C_s,ts increases over exposure time exponentially, which appears a fast increase in the first 5 years and then becomes constant.

Abstract:The design parameters of cementitious materials mixture ratio of nano ultra-high strength and high-flow concrete were proposed by orthogonal test, and the influence of nano-SiO₂ on the strength and workability of traditional ultra-high strength cement-based material doped silica fume and fly ash was studied. Same water-binder ratio, the concrete mix proportion test was carried out. Afterwards, the effect and mechanism of nano-SiO₂ on the compressive strength of concrete were explored. The results indicated that the optimum ratio of cementitious material in ultra-high strength and high-flow concrete is:nano-SiO₂:silica fume:fly ash:cement=1:8:20:71. In the range of 600~1 000 kg/m³, its fluidity has increased with increase of cementitious material, the compressive strength first increases and then decreases, with the maximum compressive strength of cementitious material of 800 kg/m³. It is concluded that the ternary multiscale stacking system formed by nano-SiO₂, silica fume and fly ash can optimize the compaction effect of powder materials in concrete micro-aggregates. Additionally, the secondary reaction of hydration reaction of nano-SiO₂ also improves the micro-structure of hardened cement stone and optimizes its morphology distribution, further increased its strength.

Abstract:In order to improve the permeable performance of pavement,polymer pervious concrete has been widely used in the construction of sponge city. Polymer experiment, special fine sand and epoxy resin were used to prepare materials required in tests. The influence of particle size and polymer content on the compressive strength and permeable coefficient of permeable concrete were discussed by controlling variable method. At the same time, the simulation experiment of blockage is carried out. Based on the image analysis, the pore of the permeable concrete is analyzed. Finally, the mechanism of its performance change is analyzed by observing the microscopic structure of the concrete. The experimental results show that with the increase of the amount of epoxy resin admixture, the compressive strength of epoxy resin permeable concrete increases and the permeable coefficient decreases. The compressive strength of epoxy resin permeable concrete will increase initially and then decrease with the increase of the dosage of the large particle size aggregate. The aggregate blending ratios with particle sizes of 0.15~0.3 and 0.3~0.6 were 1:1, with a compressive strength of 41.7 MPa and a permeation coefficient of 1.7 mm/s,as the best performance. After the product blocks four cycles, the permeability attenuation coefficient is less than 20%, and the anti-blockage performance is satisfactory and promising.

Abstract:The effect of humic acid (HA) on the stability of nano-TiO₂ was analyzed, and the effects of coagulant dosage, pH and calcium(Ⅱ) concentration on the removal efficiency of HA-TiO₂ composite pollutants by the coagulation-ultrafiltration process were investigated. The results showed that the electrostatic adsorption and coordination reaction occurred between nano-TiO₂ and HA in the aqueous solution, which caused the decrease of effective particle size of nano-TiO₂, the enhancement of electrostatic repulsion, more uniform dispersion of colloid, the increase of system stability and easy migration. These posed a threat to the safety of drinking water. The optimum parameter for HA-TiO₂ composite pollutants removal was that the coagulant concentration is 0.46 mmol/L, and the initial pH value is between 7 and 8,the higher membrane flux and lighter membrane fouling was achieved under this condition. The calcium ion in the solution will lead to the increase of membrane fouling.

Abstract:The novel cationic flocculant of CMCTS-g-CPAM was synthesized by polymerizing carboxymethyl chitosan (CMCTS), acrylamide (AM) and methacryloyloxyethyl trimethyl ammonium chloride (DMC) under ultraviolet (UV) radiation. The response surface method was adopted to obtain the optimum preparation conditions:illumination time 2 h, initiator mass fraction 0.04%, pH=8. FT-IR and ¹H-NMR of the graft copolymer indicated that AM, DMC and CMCTS have been successfully aggregated. Additionally, it can be verified by sludge dewatering test that it has good sludge dewatering performance:SRF decreased from 9.10×10¹³ m/kg to 1.96×10¹³ m/kg, and FCMC decreased from 90.15% to 79.28%,at the flocculant dosage and pH of 30 mg/L and 10, respectively. Sludge dewatering effect and economic benefits of CMCTS-g-CPAM are significantly precede to commercially available CPAM. Simultaneously, the research provides a reference for the flocculation treatment in the field of sludge dewatering and the application of chitosan modification in sludge dewatering.

Abstract:Due to the nonlinearity of residual chlorine in the pipe network, a PSO-SVM and BP neural network combined model was developed to prediction of residual chlorine.This model through particle swarm optimization algorithm (PSO) to optimization the characteristics parameter of the SVM, and use the BP neural network model to residual error correction. The prediction precision of combined model was ananysed by comparing the single prediction model of BP and SVM. The results show that compared with the single prediction of BP and SVM, the mean square error of the combined model decreased by 62.30% and 75.29% respectively, but the average relative error decreased by 55.03% and 54.27% respectively. In a conclusion, the combined model had strong nonlinear fitting capability, high prediction accuracy, and strong operation stability. This model plays an important role in controlling the residual chlorine dosing and setting the secondary chlorination point for water supply enterprise.

Abstract:Green roof has been recognized as a complement of urban green and an ecological solution to mitigate urban heat island (UHI) effects. The benefits of green roof in microclimate at the building scale have been identified by previous studies, but some quantitative data of the wider influence on neighborhood microclimate are still needed. Therefore, a field measurement was conducted in Chongqing to investigate the green-roof effects on outdoor microclimate. From the derived data, it has been verified that the thermal benefits of green roof begin from the high temperature noon to the next sunrise, and the humidification effect was more prominent at night, the most significant cooling effect of plants was at the surface. Meanwhile, the leaf area index of plants was inversely correlated with the amount of reflected radiation. The Sedum Makinoi had the best combined effect of three plants, the maximum cooling temperature was 11.7℃ during the day and the temperature was 4.64℃ and 3.97℃ respectively at 300 mm and 700 mm, the maximum humidification effect appeared at 19:00 at sunset and humidified 33.1%.

Abstract:With the improvement of the thermal insulation performance of building envelop, the influence of internal factors represented by occupant behavior have become the most important uncertain factors that impact cooling loads and energy consumption. With field test, it was found that the practical occupancy rate in the office buildings was only 40%~60% of that the cooling design condition and the power intensity of office equipment was also lower than 20 W/m². Oversized chillers were also related with over-estimated occupancy rate and equipment power intensity. With reconsideration of these coefficients, the "representative cooling load" was proposed to replace the separated occupant and equipment cooling loads, and modified the cooling results of the case buildings. Comparing with the maximum measured cooling load during testing period, assurance rate of modified cooling load were more than 90%.

Abstract:Tests of capillary radiant cooling system in Chongqing were carried out and thermal parameter were analyzed in conditions of three different capillary laying modes (ceiling, wall and floor) with 18℃ supply water temperature. It concluded that when capillaries were laid on the ceiling, wall and floor respectively, the average temperature of working area was 26.27, 27.22 and 26.57℃ respectively and the radiation surface temperature was 20.96, 21.14 and 22.76℃ in turn. By calculation, the PMV of three conditions was -0.27, 0.32 and -0.2 PPD results were 7.06%, 7.47% and 6.34% respectively. It illustrated that all three laying ways at this experimental conditions could meet the air temperature requirements (no more than 28℃) and PMV, PPD attain thermal environment category I.