Abstract:Snowflake shaped steel sheet pile is a new type of special-shaped pile with large specific surface areas and high bearing capacities while saving materials. In this paper, the optical frequency domain reflectance (OFDR) technology is used to carry out the uplift model test of snowflake steel sheet piles, and the strain at different positions of the pile body and the horizontal displacement of soil at di-fferent distances during the uplift process of the steel sheet piles are obtained. The test results show that OFDR can accurately monitor the deformation characteristics of the snowflake steel sheet pile during the process of uplift, and reveal the deformation laws of different parts of the pile body. The strain magnitude and fluctuation of the snowflake steel sheet pile are different at different positions of the pile body during the process of uplift, the strain of junction of the web is the smallest and the strain of the flange edge is the largest. The results show that the horizontal displacement of the soil around the snowflake steel sheet pile increases with the increase of the load during the uplift process, the horizontal displacement of the soil at 200 mm from the model pile is about 19.15% of the soil at 100 mm.

Abstract:The interfacial bonding performance between ultra-high performance concrete(UHPC) permanent template and ordinary concrete (NC) is the key to their synergistic effect. The effects of diffe-rent keyway types, concrete strength, and curing conditions on the interfacial bonding performance of UHPC-NC were studied. The results indicate that keyway can improve the bonding strength of UHPC-NC interface, with B-type keyway mechanical interlocking contributing the most. The strain of the central axis of the interface of the splitting tensile specimen is greater than that of the two sides, and the interface crack expands from the horizontal tensile strain to the compressive strain region. The existence of keyways in composite specimens causes cracks to extend from one end to the other inside the concrete, rather than developing inward from both ends. As the compressive strength of post poured concrete increases, the increase rate of the interfacial splitting tensile strength decreases. Steam curing specimens result in a larger initial shrinkage deformation and a larger stress concentration area than standard curing specimens. The interfacial splitting tensile strength of composite specimens can be calculated from the compressive strength of concrete cubes and the fitting parameter c. The optimal permanent template keyway parameters and maintenance conditions are proposed.

Abstract:In order to reveal the torsional action mechanism of PC composite box girder with corrugated steel webs, the section torque distribution and torsional deformation compatibility condition were analyzed according to the thin-walled structure theory. The USTMT model was used to calculate the whole torsional process of PC composite box girders with corrugated steel webs. Based on this model, the concrete compressive strength, the thickness and yield strength of corrugated steel webs, the initial force of prestressed tendons, and the strength ratio of the reinforcement were analyzed. The results show that it is reasonable to take the same torsional curvature of concrete slab and steel web as the deformation compatibility condition in PC composite box girders with corrugated steel webs. The cracking torque, yield torque and ultimate torque develop with the increase of the concrete cube compressive strength, but the torque carried by corrugated steel webs is almost unchanged. The thickness of corrugated steel webs has little effect on the torque carried by concrete slabs, but increases the torque carried by corrugated steel webs. The yield strength f_wy of corrugated steel webs has little effect on the cracking torque and the ultimate torque carried by concrete slabs, but it increases the yield torque and the ultimate torque carried by corrugated steel webs. The higher the concrete strength, the higher the strength grade of steel that can make the corrugated steel web yield. The ultimate torque increases with the increase of the ratio of the strength of the reinforcement, and there is a sensitive region to ξ. At the same time, it increases li-nearly with the increase of the initial prestress of the tendons, but the increase rate is small, especially for the torque carried by corrugated steel webs.

Abstract:Taking the foundation pit project of Shaoxing Metro Line 2 station as an example, by analyzing the on-site monitoring data of the horizontal displacement, support axial force, and surface settlement of the diaphragm wall, the relevant deformation laws of the foundation pit engineering enclosure structures in Shaoxing area are obtained, and the corresponding control measures are provided. The results show that the horizontal displacement of the wall basically follows an inward convex pattern, with the maximum lateral displacement ranging from 40 to 60 mm. The surface settlement of the foundation pit follows a groove shaped pattern, with the surface settlement mainly concentrated around 50 to 80mm. For the maximum lateral displacement of the diaphragm wall δ_hm within the range of (0.05%, 0.37%) H, the average value is 0.21%H. The maximum lateral displacement point burial depth of the underground continuous wall δ_hm mainly falls within the range of (0.69%, 0.94%) H. For the maximum surface settlement behind the wall δ_hm within the range of (0.01%, 0.5%) H, the average value is 0.26% H.

Abstract:In view of the seismic problem of the gas engineering headquarters in Xinjiang Province, the seismic isolation technology was adopted to strengthen the headquarters, and the methods of "pad the column joist" and "clamp the wall beam" were adopted for construction to ensure the safety of its superstructure. Based on the method of time history analysis of seismic isolation and reinforcement, the structure was analyzed by ETABS, an internationally accepted three-dimensional finite element software. On this basis, the damping effect is analyzed. The construction technology and the corresponding key technologies adopted in this project are also introduced. The results show that the isolation effectiveness is relatively remarkable and it can better meet the requirements of the current norms. Therefore, it is feasible to design and construct the base isolation reinforcement.

Abstract:In order to analyze the impact of rock plasticity on crack closure during production, an elastic-plastic crack closure model was established using the Drucker Prager yield criterion based on the Herz contact model. The effects of different in-situ stresses and rock plasticity parameters on the crack closure behavior were analyzed. The results indicate that the elastic modulus, hardening parameters, and cohesion are key factors affecting the plastic crack closure. The greater the cohesion, the greater the initial yield stress. The larger the ratio of hardening parameters to the elastic modulus is the greater the subsequent yield stress, and the weaker the plastic effect of crack closure. In addition, the in-situ stress also has a significant impact on crack closure. The higher the normal stress in the normal direction of the crack surface, the higher the plastic effect coefficient of crack closure.

Abstract:In order to study the influences of the dip angle and moisture content of weak interlayer on the mechanical properties and failure characteristics of composite rock mass containing weak interlayer, the composite rock mass samples containing 5 kinds of weak intercalations with five different dip angles and three kinds of moisture content are made and the indoor uniaxial tests are carried out through indoor sample preparation. The results show that with the increase of the dip angle, the peak strength and deformation modulus of the weak intercalation decrease and the peak strain increases; In the experiment, regardless of the inclination angle of the weak interlayer, both sides of the weak interlayer are the first to fail. When the inclination angle θ of the weak interlayer is 15°, 20°, and 25°, the weak interlayer not only develops bilateral failures, but also develops through oblique cracks starting from the top surface on the left side and ending at the bottom surface on the right side. The corresponding failure mode has also been inferred through theoretical research. When the inclination angle of the weak interlayer remains unchanged, as the water content of the weak interlayer increases, the peak strength and deformation modulus of the weak interlayer first increase and then decrease, and the strain at the peak strength point first decreases and then increases, and the bearing capacity of the samples with 8% moisture content is the strongest, and at this time, the peak strength and deformation modulus of the weak interlayer are the highest.

Abstract:In view of the engineering disasters caused by the deterioration of rock mechanical properties, the sandstone was taken as the research object, and the graded cyclic loading tests were carried out under different crack dip angles. The effects of crack dip angles on the mechanical properties and crack growth characteristics of sandstone were analyzed. The development of microcracks was analyzed based on the characteristics of the acoustic emission spectrum, and finally, the ordered degree of the deformation and failure was quantitatively described using the correlation dimension. The results indicate that as the crack inclination angle increases, the peak load of the specimen gradually decreases, but there is no obvious pattern of pre-crack propagation. The occurrence of frequency domain signals is consistent, indicating that the initiation, development, and propagation of microcracks within rocks are synchronized to form large-scale cracks. The orderliness of rock deformation and failure can be quantitatively described by the correlation dimension, which indicates that the larger the correlation dimension, the more complex the rock failure. The magnitude of the change in the correlation dimension can characterize the severity of the development of internal cracks in the rock.

Abstract:Triaxial consolidated drained shear tests were carried out to study the influence of particle strength on the strength and deformation characteristics of the coarse grained soil by preparing cement spherical particles with different strengths and artificial coarse grained soil with a certain grade. The test results show that the particle strength has an obvious influence on the strength and deformation characteristics of the coarse grained soil. The increase of the particle strength causes the increase of the shear strength and the decrease of the volume deformation. Under low confining pressures, the coarse grained soil with high particle strength shows strain softening, while the coarse grained soil with low particle strength shows strain har-dening, and the volume deformation for all the coarse grained soil is dilatation. Under high confining pressures, the coarse grained soil with various particle strengths shows strain har-dening and the volumetric deformation shows shear shrinkage. The relationship between the linear strength index c, φ and Duncan E-B model parameter K,K_b and the particle strength of the simulated material can be expressed by a straight line, while the relationship between the nonlinear index φ₀,φ and the particle strength can be expressed by a quadratic curve approximately. The peak friction angle φ_f also has a linear relationship with the particle strength of the simulated material. When the particle strength increases by 1 MPa, the peak friction angle φ_f increases by 0.066 5°.

Abstract:In order to investigate mechanical performance of corrugated steel composite bridge decks, three groups with 9 specimens were designed and tested based on the push-out tests, and the failure pa-ttern, ultimate load and slip were analyzed. Then the finite element models were established and the deflection, interface slippage, corrugated steel plate stress and its distribution, shear connector stress and its distribution were analyzed under the concentrated load of the middle-span of the corrugated steel compo-site bridge deck. The results show that the failure of perfobond (PBL) shear connectors are divided into three stages: elastic stage, plastic stage and failure stage. The specimens are failed by concrete shear fai-lure and showed good ductility when failure occurred. The transversal reinforcement and bonding friction have an important effect on the bearing capacity and slippage of shear connectors. The ultimate bearing capacity of the 5 m span steel-concrete composite bridge deck is 630 kN. The bridge deck undergoes four stages under load: elastic stage, crack development stage, yield stage and failure stage. PBL shear connectors can effectively combine the two structures together, and the yield areas of corrugated steel plates and shear connectors are concentrated in the mid span, with the valley region being the most obvious.

Abstract:Based on the research background of Suzhou Metro foundation pit engineering, combined with the actual engineering data and numerical simulation results, the relationship between the embedment ratio, stability and deformation of foundation pit was analyzed. Through numerical simulation, the position of the sliding surface and its relation with the embedment ratio and the depth of the foundation pit were clarified. The formula for determining the position of the sliding surface was derived, and the sliding radius of the circular sliding method was improved in the analysis of basal heave stability. The results show that the formula for determining the position of sliding surface can accurately predict the position of the sliding surface when Suzhou foundation pit fails by basal heave. On this basis, the embedment ratio determined by the improved calculation method of basal heave stability is in good agreement with the calculation results of the existing foundation bearing capacity method, which is 41% lower than the embedment ratio obtained by the traditional circular sliding method. The embedment ratio design of the subway foundation pit supporting structure is optimized.

Abstract:For the strength issue of solidified sludges, cement is used as the solidification matrix material for the composite agent, and the material comparison strength tests are conducted to optimize the admixture of the composite agent. The strength tests are carried out on solidified sludges under different cement and bentonite additions to study the strength characteristics of solidified sludges. The results show that bentonite can be used as the preferred admixture, and its special ion exchange and agglomeration effect make bentonite composite cement have a better solidification effect on municipal sludges compared to clay and shale. The unconfined compressive strength of the solidified sewage soil generally increases with the increase of the cement and bentonite added. The experiment shows that the combination of cement and bentonite can effectively solidify municipal sludges and improve the strength characteristics. The strength prediction model for solidified soil based on the experimental data can accurately predict the unconfined compressive strength of solidified soil.

Abstract:In order to adapt to the characteristics of rapid and frequent changes of the Yellow River Delta wetland, improve the strength of data interpretation, and provide necessary references for the scientific planning, management and protection of the Yellow River Delta, the temporal and spatial changes of wetland were studied from the perspective of intensive observation and the driving factors were quantitatively analyzed based on the Landsat image intensive observation of the Yellow River Delta wetland in 15 periods from 1986 to 2021, The results show that: (1) the Yellow River Delta wetland has the characteristics of fluctuation and stage change, the natural wetland reduces 1 579.07 km², the loss rate of mudflat and meadow shrubs is more than 60%, while the area of artificial wetland increases by 1 210.67 km²; (2) the expansion of farmland, construction land and constructed wetland is significantly correlated with the shrinkage of natural wetland, with the correlation coefficients of -0.682, -0.963 and -0.976, respectively. After 2009, the impact of reclamation weakens due to the return of farmland to wetlands; (3) the correlation coefficient between sediment transport and natural wetland area is 0.614, which plays a dominant role in hydrological factors, the sedimentation effect of estuary is stronger than that of ocean erosion effects before 1993 and then reversed. (4) Elevated temperatures and drought events have exacerbated wetland losses.

Abstract:As the main auxiliary equipment of power plants, the air preheater inevitably generates expansion and displacement during operation, which poses potential hazards to the safe operation of the unit. Therefore, under the premise of obtaining the temperature field using the difference method, the finite element analysis was conducted on the preheater during the start-up process to obtain the stress and displacement fields of the rotor and shell of the preheater. The results show that the expansion displacement of the outer ring of the rotor is different and the maximum expansion displacement occurs at the rotor position at the circumferential flue gas outlet. The maximum deformation of the top vertex of the rotor at this position is about 36.65 mm and that of the lower vertex of the rotor is approximately 26.86 mm. By analyzing the radial seal rubbing, it is determined that the cold end radial seal at the outlet position of the circumferential flue gas side near the central cylinder may collide. During shutdown maintenance or operation, the appropriately adjustion of the operating position of the fan plate can avoid rubbing and reduce radial air leakage.

Abstract:GH3536 nickel-based superalloy was fabricated by selective laser melting technology (SLM) and heat treated at 900 ℃ for different holding times (0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h). Optical microscopy, X-ray diffraction, electron backscatter diffraction, nanoindentation and Vickers hardness were used to analyze the microstructure and mechanical properties of the deposition and different heat treatment states. The results show that there are fine dendrites in the deposited microstructure, some of them disappear after heat treatment, while some of them change into recrystallized grains. Grains of horizontal plane (Z plane) in the deposited state mainly grow along the (111) plane and (001) plane. After heat treatment, the grains mainly grow along the (101) plane. The hardness of the deposited sample is 303 HV_0.5, and Young's modulus is 218 GPa. After heat treatment, Young's modulus is basically unchanged, but the hardness significantly decreases to about 273 HV_0.5.