Abstract:To limit the settlement of double-layered soft ground formed by the dredging blow filled soft soil and the natural deposited soft soil, precast square pile and deep mixing column with expanded head are combined to improve the ground. A field test was carried out in Lianyungang port railway project. The ground settlement, differential settlement between pile and soil, layered soil settlement, deep horizontal displacement, pore water pressure and loading ratios between pile, soil and column were studied. The test results show that the column-soil stress ratio of composite foundation increases with the external loadings. The foundation deformation occurs in the filling stage, and the settlement in the preloading period continues and tends to be stable. Filling load transfers to the precast square pile and T-shape deep mixing column by 56.2% and 20.4% of the total loadings, respectively, the replacement ratio and soil condition is the main influential factor for the proportion of loadings.

Abstract:The suction stress profile is of obvious nonlinear characteristics under steady flow condition. This study supplemented the Prandtl assumption under the condition of considering the single vertical seepage and deduced the calculation model of bearing capacity for foundation of unsaturated soil under steady flow condition by means of rigid body balance method in the range of Prandtl sliding surface. It also discussed the influence of change of the groundwater and ratio flow on bearing capacity. The results show that the bearing capacity formula of unsaturated soil foundation under steady flow can take into account the influence of the nonlinear distribution of the soil suction stress; when suction stress increases firstly, and then decreases with the depth, the bearing capacity decreases first, and then increases as groundwater lever is lowered.

Abstract:Stress wave propagation and attenuation laws of underground openings reinforced by dense bolts at anchor top and long-dense bolts are studied by anti-explosion model tests under repeated top explosions. After each explosion, with the increase of scaled stance, peak pressure stresses on vault gradually decrease in the form of a power function, and the corresponding power functions to fit the curves are obtained, of which the indexes of fitting stress wave attenuation are smaller than those of undisturbed rock. Under the action of explosion stress waves, the rock near the anchorage zone is compacted firstly, and then damaged continuously. Under the same conditions of explosions, with the increase of scaled stance, the difference of pressure stresses with two underground openings is reduced gradually at the same scaled stance and peak pressure stress on vault of the underground opening reinforced by dense bolts at anchor top is greater than that of the underground opening reinforced by long-dense bolts firstly at the same scaled stance, and then smaller. Under the same conditions of explosions, the stress wave attenuation law and peak pressure stress of the nearest measuring points from two underground openings are similar.

Abstract:An anchor cable connecting plate and ball was developed mainly for overcoming deficiency of current foundation subjected to both compressive and pull-out stresses, as well as the difficulty of construction in problematic ground conditions. The basis primarily consists of the cement soil column, the upper plate, the lower ball and the beard anchor. The cement soil column, lower ball and the beard anchor formulate the ball cable foundation, which handles the uplift force. Combining theoretical analysis with numerical simulation, the anti-tensile mechanisms of the ball cable foundation were explored, and the interaction between the ball cable foundation and soil mass was investigated. Moreover, we also studied the deformation process of the soil mass surrounding the ball cable foundation. The results revealed the evolving law of the deformation of the soil mass surrounding the ball cable, and the relationship between the uplift force and the bury depth.

Abstract:Rock-socket pile foundations have been widely used in engineering practices. It is important to determine the ultimate side shear resistance of the piles socketed into rock for designers. In this study, the results of 145 compression load tests were collected to examine several issues related to the bearing capacity behavior of rock-socket piles. All these load test results were representative since they were carried out worldwide, on different rock types and rock-socket conditions, for a long time period. Using these available load test case history data, the socketed rock type of piles, diameter and embedment depth of socketed piles, uniaxial compressive strength of rock in nature, and the ultimate bearing side resistances were collected. The ratio of ultimate side shear resistance to unconfined compressive strength of the rock was denoted as the ultimate side shear resistance factor of the piles socketed into rocks. Effects of pile diameter, rocked depth, ratio of rock rocketed depth to diameter, and the unconfined compressive strength of the rock on ultimate side shear resistance and the influential factors were evaluated. Empirical relationships between the ultimate side shear resistance factor and the unconfined compressive strength are suggested, and based on the statistical results, the specific design recommendations for the ultimate side shear resistance factor are provided.

Abstract:Based on the collected series of experimental data and many well-known rotational hardening expressions, a rotational hardening expression for different stress paths is proposed, mainly including 2 parameters which can be determined in a direct way through analysis. The proposed rotational hardening expression has been implemented to the MCC model and adopted to represent the stress-strain behavior of clays under different loading paths. The simulations are compared with the experimental results. The comparisons show that the simulated results with this proposed method have good agreement with the experimental results, verifying the rationality of the proposed rotational hardening expression.

Abstract:The soil around the pipe pile and pile core soil are regarded as viscoelastic medium, and the stress-strain relationship for them are described by fractional derivative Kelvin viscoelastic constitutive model. The torsional vibrations are solved by Fourier transformation and separation variable method by considering the circumferential displacement of the soil only. Considering the forces acting on the pipe piles, the torsional vibration in the fractional derivative Kelvin viscoelastic soil is established. The torsional complex stiffness at pipe pile head is obtained by solving the torsional vibration of the pipe pile. The results show that the model soil parameters α₁ and T_b1 have certain influence on the torsional vibration while the influence of the pile core soil model parameters α₂ and T_b2 is related to frequency. The curves of real and imaginary parts of torsional complex stiffness with frequency fluctuate more greatly when the shear modulus ratio μ is larger and μ<1, and the influence of shear modulus ratio μ on the torsional vibration of pipe pile is very small when μ>1. Wall thickness, length diameter ratio of pipe pile, as well as the shear modulus of pipe pile and soil have great influence on the torsional vibration of pipe pile.

Abstract:To examine the frictional characteristics of wheat straw in saline soil, which is influenced by water content, dry density and embedment length of wheat straw, the pulling-out test is carried out. The unconfined compressive test and triaxial test of four kinds of samples, including saline soil, wheat straw-saline soil, lime-saline soil and wheat straw-lime-saline soil, were conducted. The results showed that the friction strength decreases with the increase of water content, and increases when the dry density and embedment length increase. It has been certified that the influences from the dry density, water content and the embedment length on friction strength decrease successively. In comparison with saline soil and lime-saline soil, unconfined compressive strength, triaxial shear strength and deformation resistance of the soil are significantly improved due to the added wheat straw. The frictional characteristics of wheat straw in saline soil have been revealed and the reinforcing effect is considerable, providing an effective method for soil stabilization.

Abstract:The Kriging method is widely used for the spatial interpolation. However, the conventional Kriging method which only considers a singer factor generally leads to a considerable inaccuracy. In this paper, a cooperative kriging method based on particle swarm optimization is proposed to estimate the soil thickness distribution. Estimation is divided into two steps. Firstly, the particle swarm optimization is used to fit the semi-variance function. Secondly, the cooperative Kriging method which uses the altitude as an auxiliary variable is employed for estimation. In addition, a root mean square error is obtained to evaluate the estimation uncertainty of soil thickness. The proposed method is applied to estimate the soil thickness of a slope in Wansheng, Chongqing. It shows that compared with the conventional method, the cooperative Kriging approach improves the estimation accuracy by reducing the standard deviation by 39.32%, indicating that the proposed method is advantageous in improving the accuracy of spatial interpolation.

Abstract:The direct shear apparatus amended from the RMT-150B system is adopted to conduct the direct shear test on the coarse sand with the water contents of 0%, 8%,16% and 24%, respectively. The contact surfaces with four kinds of concrete basements with different roughness and strengths under different normal stresses are considered. The results have proved that the ultimate shearing strength under high stress increases with the normal stress. The shearing rigidity decreases with the shear displacement development while the initial shearing rigidity decreases when the normal stress increases. The shear displacement keeps increasing as the roughness of the contact surface grows up to a normal stress of 2 MPa. The initial shearing rigidity of the dry sand with the water content of 0% is greater than that of the wet sand under the same normal stress. Regression analysis based on the experimental data shows that the displacement for the contact surface between the coarse sand and concrete under the high-stress direct shear conditions can be described via the hyperbolic model. In addition, the ultimate and initial shearing strength of the contact surface can be estimated through the regression parameters. It has been shown that the ultimate shearing strength is the most significantly influenced by the normal stress followed by the roughness of the contact surface, and the influence of the water content is slightly greater than the strength of the concrete interface. The relative crushing ration of particles is subjected to the significant influence from the normal stress, followed by the water content and basement hardness and the influence from the contact surface roughness is minimum. In addition, the relative crushing ratio of particles increases as the normal stress develops and decreases while the concrete roughness and basement hardness become smaller. The peak of the existing crush increased with the water content.

Abstract:Impact of acid rain on foamed light soil with river sludge (FMLSS)was studied by percolation method. Physical and mechanical indexes of specimens, pH value and Ca²⁺ concentration of leachate, as well as the change of mineral composition of FMLSS after acid rain infiltration were measured during test, to investigate the influence of acid rain on properties of FMLSS. Experimental results show that acid rain results in the hydrolysis of minerals and dissolution in the form of Ca²⁺ ions leading to neutralization of FMLSS. It is found that the stronger the acidity of simulated acid rain, the higher the degree of neutralization. At the same time, new minerals are generated in the process of neutralization, which changes the relative content of minerals in the mixed soil and leads to the changes of physical and mechanical properties. Compared with those in the normal water condition, moisture content and density increase, while the peak strength decreases. In addition, the failure mode evolves to the brittle type after acid rain. Based on the results, it can be safely arrived at that the stronger the rain acidity, the greater the degree of physical and mechanical changes.

Abstract:The previously developed industry has contaminated part of groundwater and soils in Wenzhou with high concentration of Cu²⁺ in waste water, such as tannery, electroplating and etc. To study the characteristics of typical Wenzhou soft clay with Cu²⁺, the soil samples are remodeled to test the electrical resistivity with different concentrations of Cu²⁺ and reasonable amount of cement for consolidation. Electrical resistivity tests were carried out via the self-designed one-dimensional consolidation compression apparatus. The resistivity variation can be directly observed during the compression process. The testing results indicate that:while the concentration of Cu²⁺ and water in soil is high, electrical resistivity measurement should not be applied to assess the compression process of the soil. However, this measurement is a good indication for characteristics changes in soil after adding cement. Therefore the electrical resistivity might be taken as an effective means to estimate the degree of contamination of soil in practical engineering.

Abstract:Based on the three-point bending beam fracture tests on the crumb rubber concrete with different specimen geometries and rubber volumes, the experimental curve of the whole fracture crack process was obtained, and the fracture energy and K-R resistance curve were studied. Through the digital image correlation method, the whole field displacement and strain distribution perpendicular to the direction of crack propagation were determined,from which the crack propagation and evolution process of fracture and damage can thus be examined. The results indicate that the fracture energy displays an increasing tendency with specimen geometry and rubber volume. The K-R resistance curve reveals the size effect by change of specimen geometries and shows no indicative relationship with 0%~14% rubber volume which was designed in this study.

Abstract:In order to analyze the reliability of circular hollow concrete filled steel tube short column under axial compression, the experimental results as well as the data sets from literatures were collected. The model errors were taken into consideration via Normal, Lognormal, Weibull, Gamma distribution assumptions. Reliability analysis was carried out based on Technical Code of Concrete Filled Steel Tube Structure and the modified formula presented by the authors. Monte Carlo sampling was also performed and the calculated reliabilities satisfy the target reliability index. The reliability index of the code formula is greater than that of the modified formula within 5%. As the concrete strength and loading ratio increase, the reliability index increases. The reliability index decreases with the reduced steel ratio. The hollow ratio and steel strength have marginal influence on the reliability index. Parameter analysis was also carried out in considering the influence of model error distribution types, which indicated that mode error and live load type have less significant influence on partial factor of resistance, than the safety levels and the loading ratio. The partial factor of resistance under different loading ratios should be 1.21, 1.32 and 1.41, respectively.

Abstract:Low frequency cyclic loading tests were conducted on two steel fastener connection and three grouting sleeve connections of precast reinforced concrete columns. The failure patterns, hysteretic curves, skeleton curves, displacement ductility, reinforcement strain, stiffness degradation and energy dissipation capacity were analyzed. The influences of connecting type, axial compression ratio on the seismic behavior were also investigated. The results show that the seismic performance of Z-1 is better than that of Z-2. The three grouting sleeve connections can effectively transfer the load, and no slip faulting occurred in combination with surface. The hysteresis curve and energy dissipation of the Z-1 as well as the grouting sleeve connection of precast reinforced concrete columns are comparable. However, the latter is more shape-shifting. For the precast concrete columns with high axial compression ratio, the skeleton curve goes down steeper, less shape-shifting yet more power-wasting. The bearing capacity of the precast column which uses larger diameter longitudinal reinforcement grouting sleeve connection is slightly lower. In addition, as the skeleton curve goes down steeper, the stiffness decays faster and the precast column is subjected to less deformation.

Abstract:In order to study the beam end anchorage bar with effect of stirrups on the structural behavior of beams, static loading tests were carried out for three root anchorage depths of 20D, 25D, 30D, respectively from the anchorage end without a stirrup anchorage beam. ANSYS finite element simulations for anchorage depths of 20D, 25D, 30D of the anchorage beam were also conducted to investigate the flexural mechanical properties, the drawing span load deflection curves, the bar with load stress changes. It is found that the reaction has no additional effect on the beam stirrups. The cyclic loading tests and FE simulations show the addition of stirrups at the end of the anchorage can alleviate the concentration and improve the general ductility, anchorage beam cracking load, ultimate load stress of anchorage end, and reduce the reinforcement strain, as well as the residual deformation.

Abstract:Considering large errors of damage identification during actual monitoring process, a two-stage detection method based on the improved particle swarm optimization(PSO)algorithm was proposed. The algorithm is then used to detect the structural damage locations preliminarily,and to validate the locating results and determine the damage extents precisely. The comparisons between the simulation and experiments show that the first phase of damage identification reduced the number of suspected damage locations, making the search domain of the second stage based on the improved particle swarm optimization algorithm significantly reduced. The presented two-stage recognition method can identify the damage locations and detect the damage extent precisely for multi-damage and small damage,with considerable capacity in anti-noise.

Abstract:The accuracy of traditional shear strength models for corroded reinforced concrete (RC)beam are far from satisfactory, since these models generally belong to the empirical methods which are lack of theoretical basis and do not take into account the various influential factors comprehensively. Hence, a shear strength model of corroded RC beam which takes into account the influences of corrosion on key factors including the critical diagonal crack angle, the effective shear cross-sectional area, the reinforcement ratio and the stirrup ratio was established based on the modified compression field theory (MCFT). The accuracy of the proposed model was validated by comparing with 85 sets of experimental data and several existing models. Analysis results show that the proposed model is of good accuracy and small discreteness.

Abstract:The detections of reinforcement and target are affected by shallow buried reinforcement in concrete member with ground penetrating radar(GPR)testing defects. It is of great importance to study the cause and elimination of the interference. Based on the theoretical calculation, the numerical experimentations were designed, and the reinforcement detection was simulated by embedding reinforcement of different depths in the sand tank. Moreover, the signal was processed by various migration methods. The results show that the interference is relevant with the length of shallow reinforcement within GPR detection area. By comparing with diffraction stack, Kirchoff and F-K migration methods, Tau-p domain migration can deal with the reinforcement detection signal better. The position of reinforcement is more accurately identified. The 3D image of GPR become flat and clean through Tau-p domain migration. Finally,the GPR data in a practical project was well analyzed by Tau-p migration.

Abstract:Laboratory experiments were carried out to investigate the behavior of Q460 high strength angle members under axial compression via the static testing method. The various supporting conditions, including the spherical hinge, single knife-edge and double knife-edge bearing, are applied to study their effects on bearing capacity of members. The results show that the supporting conditions can represent the behavior of specimens. Specimens with small slenderness ratio of 30 to 45, of which the ultimate bearing capacity are determined by strength of steel instead of slenderness ratio, are subjected to a local buckling failure. While specimens with large slenderness ratios of 60 to 80 are mainly subjected to global bending instability. Comprehensive comparisons indicate that the test results are in good agreement with the calculations from the American regulation ASCE10-97, and are significantly greater than those from the Chinese regulation of DL/T 5154-2002.