Abstract:The grouting defects of rebar sleeve greatly affects the connection performance of the prefabricated shear wall. Therefore, it is necessary to study the detection and evaluation method of the grouting quality of the sleeve. The grouting defects of fabricated shear wall sleeves were identified by using the impact echo method, and the fabricated shear wall models with double rows of 18, 20 and 25 mm grouting sleeves were established respectively, and the impact echo finite element analysis was performed. The impact-echo test of fabricated shear wall specimens under mass was carried out, and the spectral characteristics and time-frequency characteristics of echo signals under different impact loads were studied. The results show that the echo signal spectrum presents different distribution characteristics under different impact loads. The frequency spectrum and time-frequency diagram of the grouting area and the non-grouting area under the impact of 5 mm steel balls are different, which can identify the grouting situation inside the sleeve near the impact point. The test results are consistent with the finite element analysis results.

Abstract:Combined with the design process of a support project in Handan city when dealing with the change of the depth of the foundation pit, in view of the different stress characteristics of the front and rear rows of the double row piles, the design idea of the long and short combined double row piles is proposed. Through the analysis and calculation of various working conditions by the straightening software, a more economical solution of the long and short combined double row piles is obtained on the premise of safety and reliability and the implementation of the current conditions of the foundation pit. The practice results show that the long and short combined double row pile support system can give full play to the different functions of the front and rear rows of piles, and can be used to solve the problem of insufficient embedded depth of existing support piles after the change of foundation pit depth, and can also be used in the normal foundation pit support design.

Abstract:In order to study the applicability of H-type prestressed concrete revetment piles in inland waterways, field tests were carried out to monitor the soil pressure at the pile-soil interface and the internal stress-strain of the piles in conjunction with the second phase of the waterway reconstruction project of the Hujia-Shen Line. The monitoring results show that:the displacement of the soil body on the backwater side is restrained by the old revetment and the upper load and the soil body is squeezed more compactly and the horizontal soil pressure is larger; while the waterfront side is the river and close to the river axis and the horizontal soil pressure is smaller and the final horizontal soil pressure coefficient is around 1.1~1.2; the internal stress of the pile body is larger than the effective precompressive stress of the concrete of this type of H-type revetment pile, and the compressive strain at each measurement point decreases after sinking the pile. Based on the test results, the calculation method of soil pressure of H-type revetment pile was optimized to make it closer to the measured value.

Abstract:In order to improve the anti-seepage performance of the cover, this paper aims to use super absorbent polymer (SAP) particles to improve the water storage capacity of the soil, and to mix them into the soil to build an SAP composite soil cover, but the law of water movement is still unclear. In this paper, a series of simple evaporation unit tests and soil column model tests were carried out to measure the changes of the pore water pressure and volume water content in SAP composite soil cover at different depths. The results showed that the saturated volume water content of SAP mixed soil formed by mixing 1% SAP particles into the soil increased by 29%, and the absolute value of the slope in the descending section of the soil water characteristic curve increased by 36%, but the air intake value hardly changed. In the process of water loss, the pore water pressure decreased rapidly, while the volume water content decreased slowly, and there was a strong hysteresis effect. The volume water content (water storage) of SAP composite soil cover decreased with the increase of depth. Under the extreme rainfall condition of once-in-a-century in Nanjing, the infiltration amount of SAP was only 12.7 ml, while that of homogeneous sandy soil cover is 2 510 ml, indicating that the anti-seepage performance is good.

Abstract:In the construction of islands and reefs in the South China Sea, calcareous sand is an easily obtained raw material, but it also has disadvantages of being porous and fragile. To ensure the safety and stability of the construction of islands and reefs, the MICP-solidified calcareous sand samples are designed to undergo immersion tests and dry-wet cycles in seawater and pure water respectively to explore the durability of MICP-solidified calcareous sand samples in different environments and treatment methods. The results show that:(1) the MICP-solidified calcareous sand has good erosion resistance, which effectively improves with the increase of reinforcement rounds. It deteriorates the fastest in seawater dry-wet cycles and the slowest when immersed in pure water; (2) both immersion tests and dry-wet cycles can adversely affect the durability of the samples, and the degradation of the dry-wet cycles is greater; (3) when controlling variables, the durability of the samples in seawater is worse than that in pure water.

Abstract:In view of the salinization problem caused by water scarcity and high evaporation in western China, a new water-soluble water-retaining agent is selected for the ecological improvement of saline soils, aiming to enhance their water retention capacity. This paper carries out indoor water retention tests and selects the appropriate concentration of new water-soluble water-retaining agent to be applied in field tests according to the water retention test results. Meanwhile, the soil moisture, temperature and conductivity changes are monitored and analyzed to investigate the effect of the new water-soluble water-retention agent on the water retention capacity of saline soils. The result shows show that:(1) the new type of water-soluble water retaining solution reacts with soil particles to form a milky elastic mucosa, which makes part of the water to be stored between the membrane structure and soil particles, and the existence of the membrane structure also changes the time of water movement upward and delays the evaporation effect; (2) when the concentration of water retaining solution is 0.5%, the water retention capacity of the soil is significantly improved, and, the soil water retention capacity is gradually enhanced with the concentration of water retaining solution; (3) The use of new water-soluble water retaining solution can improve the temperature and humidity of soil in salinized areas to a certain extent, reduce the salt separation on the surface of soil layer. The results can provide some references for improving soil water conservation in saline soil area under strong evaporation.

Abstract:In order to study the stability analysis on slanting type tied-arch bridges with steel box arch ribs (five arch ribs), relying on the project of diverting the Huaihe River from the Yangtze River, the through slanting type arch bridge-Chuangxin Avenue Bridge, the suspender cable force detection was carried out on the slanting type arch bridge after completed bridge, a finite element model of the tied-arch bridge on slanting type tied-arch bridges with steel box arch ribs considering the geometric and material nonlinearity was established. The former evaluated the overall tensioning control effect of the bridge suspenders and the latter verified the reliability of the tit over-arch model, then the stability of the tilt-over-arch bridge was studied. The results show that:(1) the maximum error between the measured and designed values is 3.91%, and the overall tensioning control effect of the tilt-over-arch bridge is good. The maximum error between the measured and simulated values is 0.63%, which verifies the reliability of the model; (2) the stability coefficient of the arch bridge structure during the whole construction process meets the engineering requirements, and the slanting type arch bridge with steel box improves the stability by 72%; (3) the elastic stability depends on the difficulty of the out-of-plane instability of arch rib, and the initial geometric defects have a great influence on the stable bearing capacity of the slanting type tied-arch bridge. In addition, the cooperative work of the slanting arch ribs and the wind bracing can significantly improve the stable bearing capacity of the structure; and (4) the design suggestions for this type of tied-arch bridge are given, which can provide a reference for the construction and design of similar projects.

Abstract:Based on a long-span highway tunnel project, the velocity and spectral characteristics of the surrounding rock in the front and rear of the tunnel face were compared and analyzed by monitoring the response during the lower step of the tunnel blasting. The numerical simulation method was used to study the attenuation law of blasting vibration velocity in the front and rear of the surrounding rocks with different surrounding rock levels. The results showed that the velocity of surrounding rock ahead of the tunnel face was V_Z>V_X>V_Y, while the velocity of surrounding rock behind the palm face was V_X>V_Y>V_Z. The difference of the front and rear vibration characteristics of the tunnel face was due to the spacing distance between the explosion source and the measuring points, the difference of the propagation medium and the boundary conditions. Owing to the vibration reduction effect of the air isolation layer in the excavated tunnel behind the tunnel face, the diffraction and refraction of the blasting seismic wave occurred in the rear propagation process, and thus the resultant vibration velocity of the surrounding rock in the rear was significantly smaller than that in the front and decayed more rapidly. The vibration dominant frequency of the rear surrounding rock was significantly lower than that of the front of the tunnel face, and the rear spectrum bandwidth was narrower than that of the front. The prediction formula of vibration velocity of surrounding rock in the front and rear of the tunnel face with different surrounding rock levels was obtained by curve-fitting. The prediction formula of blasting vibration velocity of the surrounding rock was proposed by considering reduction coefficient of the air isolation layer. According to the relationship between the front and rear positions of the tunnel face and the existing pipelines, the safety charges of the front and rear were calculated by using the prediction formula of the blasting velocity of the front and the rear surrounding rock, respectively. The precise blasting vibration control of the whole process before and after the tunnel crossing the pipeline was realized and the construction efficiency was greatly improved.

Abstract:In order to study the deformation law and its influencing factors when the shield tunnel underpasses the high railway foundation, a three-dimensional numerical model is established based on the actual project in Xi'an city, and the variation laws of the displacement of the high railway foundation and the displacement of the track bed when the shield tunnel underpasses the existing high railway foundation are analyzed. At the same time, orthogonal experiments are used to study the influences of tunnel excavation distance, tunnel underpass angle and other factors on the high railway foundation. The results show that the maximum vertical displacements of roadbed and roadbed after shield tunnel construction are 9.18 mm and 7.43 mm, respectively. The maximum lateral displacements of subgrade soil in different directions are 0.24 mm and -0.29 mm, respectively. The maximum displacements of the track bed in different directions are 0.17 mm and -0.13 mm, respectively. In addition, the vertical clear distance has the greatest effect on the vertical deformations of the existing high railway foundation and the high railway foundation bed. The underpass angle has the greatest influence on the transverse deformation of the existing high railway foundation bed.

Abstract:Relying on Xishanying tunnel of Sanqing expressway, the influence of fault morphology on the deformation of surrounding rock and the stability of supporting structure of the tunnel are explored by using the methods of numerical simulation and field monitoring, and the best reinforcement scheme is put forward. The results show that the maximum value of vault settlement increases in a "logarithmic" curve with the increase of fault thickness. With the increase of fault dip angle, it is distributed in a "parabola" curve, and reaches the maximum when the fault dip angle reaches 90°; and the most unfavorable fault shape is dip angle + thickness (83° +70 m); Then, the numerical model of optimization reinforcement comparison is established, and it is obtained that the pipe shed grouting reinforcement can effectively control the deformation of surrounding rock and inhibit the development of plastic zone. Combined with the measured data, it is found that the difference between the simulated value and the measured value is small, which verifies the correctness of the numerical simulation results.

Abstract:Aiming at the main safety problems of shield tunnel construction of Guangzhou Metro Line 18, which are presented by the surface subsidence and segment floating, the deep learning network-deep belief network is used to construct the prediction model for the construction safety based on the big data between construction parameters and safety problems obtained from field monitoring. The influence of six main parameters on construction safety is studied. The results show that the deep belief network can obtain more accurate prediction values of surface settlement and segment floating based on the big data of field monitoring. Moreover, the surface settlement decreases with the increase of the soil bin pressure, grouting volume and grouting pressure, and increases with the increase of the jack thrust, cutter torque and tunneling speed. The floating capacity of the segment increases with the increase of the soil bin pressure and grouting pressure, and decreases with the increase of the jack thrust and grouting volume. The torque of the cutter head and the tunneling speed have little effect on the floating of the segment.

Abstract:A reinforced earth retaining wall of a fill slope subgrade in Qinling-Bashan Mountains collapsed six years after its completion, resulting in the destruction of the road fence at the top of the slope and the damage of the houses at the foot of the slope. The failure characteristics of the reinforced earth retaining wall were found out through field investigations, and the inducing factors and formation process of the failure of the reinforced earth retaining wall were comprehensively analyzed combined with numerical simulations. The results show that the main failure characteristics of the reinforced earth retaining wall are the face slab collapses in a large area, and the reinforced filler behind the slab still maintains a good overall stability. The collapse of the reinforced earth retaining wall panel is mainly due to the fact that the fill slope blocks the original drainage channel, and the "anti-slide pile + retaining plate + reinforced earth retaining wall panel" in the retaining structure forms a relatively impermeable boundary, while the water infiltrated from continuous rainfall and domestic water cannot be drainaged in time, resulting in the rise of the groundwater level and of hydrostatic pressure. The failure process of the reinforced earth retaining wall is as follows:increasement of hydrostatic pressure, failure of bottom panel tie bar connection, increasement of upper and middle panel stress and overall failure of panel.

Abstract:Taking the diversity inclusion indicators of physical examination in a city in North China as the research object, the evaluation index of diversity inclusion in a city was calculated by the method of entropy, the weight of index was determined by krill swarm algorithm-projection pursuit model, which was compared with the diversity inclusion development level of 10 neighboring cities in North China to judge the impact degree of related indexes on the urban inclusive development level. For different levels of development of the city in accordance with local conditions, different development requirements were put forward.

Abstract:The space of T-shaped comprehensive pipe corridor is narrow and long and the branches are connected, which increases the difficulty of fire smoke control and aggravates the risk of fire accidents. The influences of different ventilation modes on smoke emission are simulated by using PyroSim software model, and the influences of the air inlet, outlet position and outlet wind speed on the smoke spread in the cabin are explored when there is a fire at the intersection of T-shaped integrated pipe corridor cable cabin. The results show that the one-in-two-out ventilation mode with central air intake, left and right air outlet and a critical ventilation velocity of 1.75 m/s is the most favorable mode for fire smoke control, and the direction of air inlet is suitable to be used as an emergency evacuation channel, which can provide references for the design of T-shaped comprehensive pipe corridor.

Abstract:The system error model is established by taking the single degree of freedom wire counterweight system as the research object. In order to evaluate the influences of various types of geometric errors and inertial forces on the compensation accuracy, the deviation of the lifting point and suspension point is taken as the error evaluation index, and the error evaluation index corresponding to the synchronization error is selected for error matching, which can analyze the influences of various types of errors. It is found that the length of the hanging wire is positively correlated with the compensation accuracy, and there are differences in the influence of various types of geometric errors on the evaluation index. The error caused by inertia force can be equated by solving the suspension chain line problem, and it is found that the inertia force causes the deflection of the lifting point direction as the biggest influencing factor. The calculation example shows that the system has higher requirements on the length of the hanging wire when the angular acceleration is too large.