Abstract:Many experimental studies on the thermal consolidation of saturated normal-consolidated soil show that the volume change of the soil has a thermal compression behavior when the temperature increases， which is contrary to the principle of thermal expansion and contraction. To solve this problem， a numerical simulation of the thermal consolidation test of saturated normally consolidated soil was conducted by the thermal-hydro-mechanical （THM） fully coupled finite element program in this paper. Because the thermal conductivity and permeability of clay are relatively small， in the heating process， a temperature difference will occur inside the sample， which will cause excess pore water pressure， and finally the soil will show thermal contraction with the dissipation of the excess pore water pressure. When the permeability coefficient of the soil is increased， the excess pore water pressure is not generated inside the soil， and the soil exhibits thermal expansion. Therefore， the thermal contraction phenomenon of saturated normally consolidated soil caused by the increase of temperature is not the basic mechanical property of the soil， but a boundary value problem.

Abstract:In this paper， an unsaturated triaxial test was conducted on Masado using axis-translation technique （ATT） with ceramic disk/microporous membrane filter （MM filter）. The stress-strain relation and drainage properties in the shear stage was obtained under the constant suction condition. Then， the finite element method （FEM） was utilized to simulate the triaxial test as a boundary value problem. The drained/vented triaxial tests results show that the degree of saturation and the drainage discharge of the specimen with the ATT of the MM filter is different from that of the ceramic disk. The calculated global stress-strain relation basically has a similar tendency as the triaxial test. The suction and the saturation are non-uniformly distributed within the specimen. The ATT with the MM filter is able to control the suction better during the shear stage than that with the ceramic disk. Thus， the unsaturated triaxial test with the ATT would be considered as a boundary value problem instead of an element test.

Abstract:Post-liquefied sand flow involves a phase transition process from fluid to solid. To overcome the limitation of normal triaxial loading mode for loose sand， a two-staged loading method， stress- and strain-controlled loading， was applied to obtain the initial liquefaction state and investigate the mechanical behavior in the post-liquefaction process. Based on test results， a fluid-solid transition parameter was proposed to combine solid and fluid constitutive models. Finally， the stress-strain relation of post-liquefied sand was established to simulate the fluid-solid transition process at different relative densities.

Abstract:Granular bentonite materials have a multi-scale pore structure （i.e.， inter-pellet pores， inter-aggregate pores， and intra-aggregate pores）， which makes it difficult for the traditional two-porosity constitutive model to accurately describe the mechanical behavior. In this paper， a constitutive model considering triple-porosity structures was proposed based on the BExM model for unsaturated expansive soils. The elastic-plastic deformation behaviors and the coupling effects of multi-scale pore structures were described by two yield-surface equations and two coupling functions， respectively. A comparison of the measured and predicted results shows that the proposed model could well describe the swelling pressure property， the swelling deformation behavior， and the pore evolution characteristic of unsaturated granular bentonite materials.

Abstract:A series of high-pressure consolidation tests on two kinds of calcareous sand were conducted at a termination pressure of 8 MPa to study the particle breaking evolution of the calcareous sand with different particle morphologies and different particle groups. The test results show that the mineral components of the two calcareous sand samples （S₁ and S₂） are basically the same， but the different depositional environments have caused significant differences in particle shape. The compressibility and the breakage rate of the calcareous sand （sample S₂，） which is dominated by flaky particles are both significantly higher than that of the calcareous sand （sample S₁）， which is dominated by massive particles， and for these two samples， the relative particle breakage rate Br increases with the increase of particle size. For the two different calcareous sand， there is a good power function increasing relationship between the relative rate of crushing B_r and the amount of compression deformation， indicating that the degree of particle breakage is closely related to the amount of compression deformation.

Abstract:A thermo-mechanical coupling numerical model is established for the metro segments under different boundary conditions， and the deformation and internal force of the lining segments at different loads and high temperatures are analyzed by adopting the sequential coupled thermo-stress analysis method. The model was verified by fire test data. Loading bear proportion is a key factor affecting deformation characteristics of segments at elevated temperatures. When the load increases， the mid-span displacement of segments develops more quickly during the heating stage， while the ultimate compressive stress of the concrete at the lower edge decreases. For different boundary conditions of support， the lining segments also have different mechanical behaviors affected by elevated temperatures. When the horizontal displacements at both ends of the lining segments are constrained， due to the non-negligible deformation of the lining segments during the heating process， the bearing reaction force first increases， then decreases， and finally continues to increase until the end of heating.

Abstract:A new type of prefabricated composite wall was developed， whose inner and outer steel mesh reinforced concrete plates were connected with the reinforced truss grid， and a foamed cement block was embedded in the middle of the inner plate and outer plate to be used as thermal insulation material， which could be used either as a load-bearing member or as an enclosure member， having the advantages of convenient production， low cost， and convenient installation. In this paper， monotonic horizontal loading tests and low cycle repeated loading tests were conducted on three kinds of prefabricated composite walls， including interior walls， exterior walls， and exterior walls with opening， respectively. The failure modes of the walls at two kinds of loads were the same： concrete crushing and partial steel truss and steel wire mesh yielding under tension. The results of monotonic horizontal loading tests show that the prefabricated walls have a good bearing capacity， and the peak loads of the interior wall， the exterior wall， and the exterior wall with opening are 206.16， 314.15， and 201.99 kN， respectively. Moreover， the prefabricated wall with opening can effectively increase the ductility and reduce the ultimate bearing capacity. The results of low cycle repeated loading tests indicate that the skeleton curve of the wall was similar to the load-displacement curve of the wall at monotonic horizontal load， and prefabricated composite walls have a good ductility and energy dissipation capacity. The deformability and energy dissipation capacity of the exterior wall are obviously better than those of the external wall and interior wall. Generally， prefabricated composite walls have a good bearing capacity and ductility， which can be used in low-rise or multi-storey prefabricated buildings. Finally， the bearing capacity of prefabricated thin-walled composite walls at monotonic horizontal load were analyzed using finite element analysis software ABAQUS. A comparison between the numerical and experimental results suggest that the finite element model can simulate the failure modes and stress state of the wall accurately， which can verify the effectiveness of the finite element model.

Abstract:The solution foundation of mesoscopic carbonation is summarized and improved. According to the path dependent feature of transport and reaction， the solution of huge-size matrix in traditional methods is avoided， and a diffusion path dependence mapping （DPDM） method is proposed. Based on the Dijkstra shortest path calculation algorithm， the paths from environmental boundary to any nodes in cement mortar are calculated with the modification of the influence of the interfacial transition zone. With the agent model of cement mortar， the complex coupling process of the hydration reaction， the carbonation reaction， and the change of material properties（concentration of Ca（OH）₂）can be solved. Finally， the solution results of the agent model are mapped on the mesoscopic model with the same length of diffusion path， and the temporal-spatial distribution of critical substance concentration can be accurately and efficiently predicted. The comparison and verification with material test indicate that the simulation results of diffusion path dependence mapping method can accurately simulate the carbonation depth in concrete. Compared with the traditional solution based on partial difference equation， the proposed method can precisely reflect the mesoscopic distribution of critical components， where the solution efficiency can be improved by more than 20 times， and the storage requirement can be reduced to less than 2%.

Abstract:In this paper， MIKE21 is used to establish a two-dimensional hydrodynamic and mass transport model based on the triple nested non-structured grid and the measured data are used to verify the tide level， the current speed， and the current direction. In combination with the satellite remote sensing image data， the evolution of Qilihai Lagoon from 1950 to 2018 is simulated. The water flushing time scale is used to investigate the changing characteristics of water exchange capacity under different conditions and the results show that under natural conditions， the runoff change is more significant on water exchange capacity compared with water level changes. The opening of the tidal sluice is a key factor affecting the water exchange capacity of the lagoon. The reclamation project reduces the tide prism， but the slight reduction has a little impact on the water exchange capacity. The construction change of tidal inlet is the main factor affecting the water exchange capacity. The change of tidal inlet from bending to straight and its widening enhance the water exchange capacity of the lagoon.

Abstract:This paper, taking three watersheds in Zhejiang Province as the study objects, uses two models, i.e., the monthly water balance model with two parameters (XM model) and four parameters (ABCD model) to analyze the interval characteristics of hydrological simulation uncertainty in combination with the multiple objective functions of the GLUE method. It studies and analyzes the parameter transferability of different hydrological models under ENSO (El Nin?o Southern Oscillation) and different basin geographical conditions. The results show that the simulation effect of parameter transferability from El Nin?o period to La Nin?a period is better than that from La Nin?a period to El Nin?o period, the pass rate of the model with fewer parameters (XM model) is better than that of the model with more parameter (ABCD model). In addition, the effect of parameter transferability between adjacent watersheds is significantly better than that of remote watersheds, and the ABCD model has a better ability for spatial scale parameter transferability.

Abstract:To explore the mechanism of the speed perception of the driver， a driving simulation experiment was designed to collect the perceived speed and actual driving speed of the driver，which analyzes the influencing factors such as the geometric alignment of the underground expressway and the side wall change frequency on the speed perception sensitivity of the driver. The prediction model of the speed perception bias sensitivity threshold of the driver was constructed based on the constant speed theory and the machine learning method. The results show that at the 0.05 significant level， there are substantial differences in the speed perception sensitivity threshold of the driver at different speeds ， linear combinations， and sidewall change frequency groups. The Lasso variable filters the characteristic variables according to the short-term， mid-long-term， and long-term time windows. The determination coefficient R² of the constructed multivariate nonlinear model is 0.645， the determination coefficient R² of the multilayer perceptron model is 0.727， and the determination coefficient R² of the support vector regression model is 0.853.

Abstract:To improve the competitiveness of public transport， and aimed at eliminating the parking and waiting time in the intersection of buses， an active TSP （transit signal priority） method for short distance intersections is proposed， which takes the bus arrival prediction error into consideration， and fairly shares green losses or gains according to the criterion of the minimum signal deviations. Simulation experiments are designed and conducted to verify the effectiveness and applicability of the method. The results of the effectiveness experiments show that the proposed method decreases the parking and waiting time of buses by 90.8%， and outperforms the other three control methods with a 3.01% drop in per capita delays. The results of applicability experiments show that the proposed method is applicable for signalized intersections with a degree of saturation of no more than 0.8.

Abstract:The prediction of track geometric irregularity is the basis for the railway department to realize the transformation from periodic repair to state repair， which is the key to formulating the maintenance strategy. However， in the existing prediction models， the calculation is complex， and the impact of tamping， grinding and other composite operations on track irregularity is rarely considered. In order to improve the operation efficiency and prediction accuracy， considering the differences of different operation sections， taking the geometric irregularity deterioration function of ballasted track and the recovery function under tamping and grinding operation as the research object， the unique deterioration matrix of each section is formed by using numerical fitting and other methods， and the geometric irregularity prediction model of ballasted track under tamping and grinding combined operation is established. The results show that the established model is effective and the results meet the needs of field prediction.

Abstract:The active learning reliability method in combination with Kriging and Monte Carlo simulation （AK-MCS） is applied to the reliability analysis of the fatigue life of the cantilever internal pressured pipeline under the given working condition （i.e.， 28 MPa internal pressure， 5.06 mm longitudinal displacement cyclic load at free end） by considering the randomness of the design sizes， working load， and material properties. First， the Manson coffin fatigue life model of the pipeline is established by linear regression analysis， according to the results of three-point bending test. Then， the fatigue life failure probability/reliability curve of the hydraulic pipeline is obtained by using AK-MCS， which provides the life prediction value based on the probability for the engineering application of the pressured pipeline. Finally， the fatigue life frequency histogram is obtained by the curve. It is found that the bending fatigue life of the pipeline is generally normal distributed. Moreover， by solving the small probability event problem， it is shown that compared with MCS， AK-MCS reduces the time of the FEM （finite element method） analysis and ensures the accuracy of reliability analysis.

Abstract:A 2.5-dimensional boundary element method（BEM） diffraction sound field model was established， by taking a rail transit fully-enclosed sound barrier as the research object and considering the incoherence of the simplified linear sound source. The accuracy of the model was verified by field noise tests along an urban line， and the prediction results were compared with those of the coherent source diffraction sound field. Finally， at the positions of the high-rise buildings along the line， the noise reduction effects of the fully-enclosed sound barrier on the passing noise of near or far rail vehicles were predicted. The results show that the incoherent line sources are more in accordance with the characteristics of urban rail transit noise sources. The prediction results of their diffraction sound field are more consistent with the measured results. For wheel-rail noise （315 to 1 000 Hz）， the fully-enclosed barrier has a considerable reduction effect at the area of the high-rise buildings， with the maximum 1/3 octave band insertion loss of 30.0 dB. For low-frequency noise （50 to 250 Hz）， the fully-enclosed barrier enhances the sound pressure levels at the area of the high-rise buildings， leading to negative values of the insertion losses. For the receivers near high-rise buildings， the top-arched transparent panels of the fully enclosed sound barrier have a more significant additional noise reduction effect on the passing noise of far rail vehicles， and the additional insertion losses at most receivers are higher than 5.0 dB.

Abstract:Taking the fully welded dimples plate air preheater as the object， the Workbench Fluent software is used to numerically simulate the influence of the characteristic structure parameters of the dimpled plate on the heat transfer and flow resistance performance by orthogonal experiment. Based on the parameter sensitivity analysis， the effect of single factor on the heat transfer flow resistance performance is obtained： longitudinal spacing of dimpled > long axis > horizontal spacing > depth. Moreover， the fact is obtained that under the synergistic effect of multiple factors， the structural parameters horizontal and longitudinal distance have a greater impact on performance than the depth-diameter ratio of the dimpled based on the analysis of the response surface method. Furthermore， three sets of better structural combinations within a given range are obtained based on the genetic algorithm， with the smallest friction factor， and the largest Nusselt number and comprehensive heat transfer factor as the optimization objectives.

Abstract:In combination with the advantages of the direct current resistivity （DCR） and radio-magnetotelluric （RMT） methods， a joint inversion of two-dimensional DCR and RMT data was performed in this paper. A balancing operator was proposed to adjust the weightings of the two types of data in the joint inversion. To obtain a reliable inverted resistivity model， a fuzzy C-means （FCM） clustering was added to the regularization objective function based on classical minimum structure constraint. In the inversion， a strategy of increasing the weight of the FCM part with the inversion iteration based on root-mean-square error calculation was applied. The single inversion and joint inversion of the DCR and RMT data were compared， and the advantage of joint inversion was summarized. The synthetic tests show that the recovered resistivity model with joint inversion is closer to the true subsurface structure than that with single inversion. Moreover， the FCM clustering constraint improves the accuracy of the inverted model.

Abstract:Starting from the uncertainty of risk factors， the risk preference is introduced. Based on the random cooperative game theory and the Shapley value method， the random Shapley value of PPP （public-private partnership） urban renewal project is calculated， in order to construct the optimal risk sharing decision model involving the government， the professional operating company， and the investment company in the PPP urban renewal project. In addition， the optimal risk sharing proportions of the three parties are obtained. Moreover， taking the PPP project of a town in Shanghai as a case example， the risk sharing proportions of the government， the professional operating company， and the investment firm are calculated. The result of the case analysis shows that the tripartite game project risk allocation model can well reduce the risk of the total urban renewal PPP project and increase the overall profit， which is conducive to improve the efficiency of urban renewal PPP project cooperation.