Abstract:To study the deformation characteristics of existing structures induced by rectangular pipe jacking crossing soft soil layers and further clarify the deformation laws caused by pipe jacking construction in soft soil layers, this article is based on a pipe jacking project at an entrance and exit in Nanjing. Firstly, on-site tests of rectangular pipe jacking construction were carried out to analyze the surface and structural deformation laws caused by rectangular pipe jacking crossing bridge foundations and pipelines. On this basis, considering the influence of geological losses on structural deformation, a dynamic numerical analysis model for rectangular top pipe jacking was constructed, and the influences of soil shrinkage rate, box culvert to top pipe spacing, and palm face pressure on the deformation of existing structures were analyzed. The results indicate that as the top pipe section advances step by step, the surface cross-section and pipeline exhibit deformation characteristics of large settlement in the middle and slight uplift on both sides. The deformation characteristics of the bridge foundation mainly manifest as deviation from the direction of the pipe section. Compared to the distance between the box culvert and the top pipe and the pressure on the palm surface, the change in the soil shrinkage rate has the greatest impact on the deformation of existing structures.

Abstract:Considering the influence of water level fluctuations and the dimensional structure of impermeable walls on the seepage characteristics of embankments, 28 scenarios were designed to compare and analyze the effects of the thickness of impermeable walls, the embedding depth of impermeable walls, and the permeability of the embankment based on the seepage flow, the height of the seepage line behind the membrane, and the hydraulic slope at the bottom and overflow point of impermeable walls under fluctuating water levels. The results indicate that, compared to changes in the thickness of impermea-ble walls, increasing the embedding depth of impermeable walls can more effectively control seepage flow of embankments, reduce the height of the seepage line behind the membrane, and decrease the hydraulic slope at overflow points. For embedding depths ranging from 0 m to 2 m, the hydraulic slope decreases initially with increasing depth, showing a trend of rapid decline followed by a slower decrease. Beyond 2 m, the hydraulic slope increases with depth, reaching its peak at 5 m before sharply declining when exceeding 5 m. Additionally, in suspended-type impermeable wall designs, when controlling the dam base seepage at 75%, the hydraulic slope at the overflow point remains below 0.25. A robust logarithmic-linear relationship exists between the embedding depth of the impermeable wall and the dam base permeability coefficient. The derived fitting equation can be applied for the preliminary design of impermeable wall embedding depth in similar construction projects or for evaluating seepage control in existing projects.

Abstract:This paper takes buried X80 pipeline as the research object, and discusses the influence law of incidence angle, corrosion parameters and insulation layer on seismic response of pipeline corrosion area. Under the excitation of P wave and SV wave, the stress in the center of the pipeline corrosion area reaches the maximum value of 556.7 and 559.7 MPa and increases by 26.1% and 28.0% when the incidence angles θ_v and θ_h are 60° and 45° and 30° and 45°, respectively, compared to that of 441.3 and 437.0 MPa under the vertical incidence. When the incidence angle was the maximum response angle, the influence ratio of corrosion depth, length and width on corrosion pipe stress under P wave and SV wave was 58.0% and 51.9%, 22.8% and 27.1%, and 19.2% and 21.0%, respectively. The increase of the thickness of the pipeline insulation layer can effectively reduce the maximum stress in the corrosion zone of the pipeline under earthquake. Therefore, in the seismic design and maintenance of pipelines, we should pay attention to the incidence angle of seismic waves and corrosion depth, and consider the seismic isolation effect of insulation layer.

Abstract:The experiment utilized a composite cementitious system comprising ordinary Portland cement and fast-hardening sulfoaluminate cement, with crushed limestone serving as the fine aggregate. A full machine-made sand grout was prepared using this system. Silica fume, fly ash, and stone powder were employed as mineral admixtures to investigate their impact on the flowability, compressive strength, and vertical expansion rate of the full machine-made sand grout. Additionally, SEM electron microscopy was used to analyze the microscopic mechanisms of the full machine-made sand grout. Research findings indicate that the concurrent use of mineral admixtures is advantageous in enhancing both the flowability and mechanical properties of the grout while also improving the transition zone between the grout and aggregate. The optimal dosage of mineral admixtures obtained through orthogonal experimentation is 5% silica fume, 6% fly ash, and 8% slag.

Abstract:To study the law of clay evaporation cracking, the evaporation cracking tests of plain soil samples; xanthan gum, guar gum and their 1∶1 mixed gum composite clay samples were carried out to explore the changes of water content and evaporation rate of different types of biological glue composite clay samples with time, and the characteristics of the fracture rate and fracture development morphology of the sample with the change of water content. The microstructure and mechanism of the composite clay samples were further analyzed by scanning electron microscopy. The results show that the evaporation process of soil sample experienced the loss of surface free water, internal free water and weak bound water, while the evaporation rate gradually decreased. During the process of evaporation, the formation of cracks reduces the water migration path, and the entry of air reduces the permeability coefficient of the sample, and the interaction between them makes the evaporation rate dynamic equilibrium. When the force between soil particles is balanced, the cracks no longer develop and the evaporation rate gradually decreases. The anti-cracking ability of the sample was enhanced and the crack development was wea-kened by the incorporation of biological glue.

Abstract:In order to study the dynamic response of the ballast bed in the section of the ballast track foundation bed, a set of model test equipment was made to simulate the process of the railway foundation bed slurry. The subgrade model was filled with silty clay and ballast gravel, and three SmartRock sensors were embedded in different positions of the ballast layer to monitor the vibration acceleration and movement attitude changes of ballast in real time. The test results show that the vibration of ballast particles in the ballast becomes more intense after the mud invades the ballast bed, and the deepening of the mud invades the ballast bed will increase the vibration level of ballast particles. In the clean road bed, there will be a strong restraint between the ballast particles, and the ballast particles are not easy to rotate. Regardless of the track bed condition, the degree of ballast particles rotating around the transverse and longitudinal is greater than that around the vertical. When the mud intrudes into the ballast bed, the ballast particles will produce a large rotation around the transverse and longitudinal directions, and the rotation angle around the vertical has no obvious change.

Abstract:To study the formation mechanism of frost heave and tilt disease on railway bridge abutments in permafrost regions and analyze its deformation law, a finite element model of the bridge abutment subgrade is established to analyze the temperature field characteristics of the subgrade behind the bridge abutment and the frost heave and tilt law of the bridge abutment. Based on the theory of unsaturated soil seepage and heat conduction, the water and heat differential equations of frozen soil are established, and the deformation field is calculated using ice content to achieve the coupling of water and heat fields. By Using COMSOL software, a three-dimensional bridge abutment subgrade water thermal coupling model is developed and verified through indoor freeze-thaw tests. Finally, taking a railway bridge abutment in a permafrost area as an example, this study analyzes the upper limit of permafrost and the inclination of bridge abutment frost heave in the next 30 years for the roadbed behind the abutment. The results indicate that in the next 30 years, the upper limit of permafrost on the roadbed after the bridge abutment will continue to decrease, But the continuous input of cold air in the cross section of the bridge abutment has affected the depth of the upper limit of permafrost at various positions along the roadbed. At a distance of 4 m from the bridge abutment, the upper limit of permafrost on the sunny slope of the roadbed will decrease by 0.99 m in the next 30 years and that at the center of the roadbed will decrease by 0.92 m. At a distance of 16 m from the bridge abutment, the upper limit of permafrost on the sunny slope foot of the roadbed will decrease by 1.6 m in the next 30 years and that at the center of the roadbed will decrease by 1.81 m. In the next 30 years, the roadbed behind the bridge abutment will continue to experience a differential horizontal frost heave, with a cumulative horizontal displacement of 155.6 mm at the top and 23.6 mm at the bottom, resulting in an overall tilt of the bridge abutment.

Abstract:In order to study the influence of bridge deck railing on the vortex-induced vibration performance of main beams, a domestic scenic pedestrian suspension bridge with wide-span ratio of 0.028 4 was taken as the engineering background, and the vortex-induced vibration response characteristics of main beams with and without railings were analyzed and calculated by CFD numerical simulation me-thod. The effects of the railing form and different air permeability on the vortex-induced vibration charac-teristics of the main beam are analyzed and summarized. On this basis, the influence mechanism of vortex stripping on the vortex-induced vibration performance of the main beam is revealed from the evolution form of vortex stripping and the distribution of wind pressure coefficient. The results show that the maximum vortex-induced vibration amplitude of the main beam with railings is 2.2 times that of the main beam without railings. Increasing the railing radia will increase the vortex-induced vibration amplitude of the main beam, but increasing the air permeability of the railing can effectively reduce the vortex-induced vibration amplitude of the main beam. Compared with those without railings, the vortices formed on the upper surface of the main beam with railings are larger in scale and more in number, and the curves of the average wind pressure coefficient and the fluctuating wind pressure coefficient both fluctuate greatly, which explains the reason for the increase of the vortex-induced vibration amplitude of the main beam after the railings are set up to a certain extent.

Abstract:To study the mechanical characteristics of the inverted arch structure of highway loess tunnel, taking the Fengshuiling highway loess tunnel as the engineering background, two tunnel sections with different embedded depths were selected. By embedding pressure boxes, concrete strain gauges, rebar gauges, surface strain gauges and other sensors, the evolution laws of surrounding rock pressure, shotcrete stress, steel frame stress, contact pressure between primary support and secondary lining, se-condary lining concrete stress, and reinforcement stress of the highway loess tunnel invert were studied, and the mechanical characteristics of the loess tunnel invert structure were analyzed. The experimental results show that the stress characteristics of the inverted arch structure of the loess tunnel are significantly different under different embedded depths. The pressure of the inverted arch surrounding rock in the section with a larger embedded depth is obviously greater than that in the section with a smaller embedded depth. Under different embedded depths, the stress characteristics of the inverted arch structure of the loess tunnel with the same cross section form and the same surrounding rock condition are diffe-rent, but the position of the arch foot is prone to the tensile stress. The tunnel invert structure with a large embedded depth is easy to show the states of upper compression and lower tension. The bearing capacity of the foundation of the loess tunnel invert has a significant effect on the mechanical characte-ristics of the invert.

Abstract:For the shallow tunnel of Qizishan with small net distance bias, the typical locations of the tunnel were selected to establish a fine three-dimensional model, and the tunnel construction process under different construction sequences was simulated. The effects of three different construction sequences of bias side first, bias side second and simultaneous construction on the formation deformation and structural stress were studied, which provided a basis for the determination of construction sequence. The results show that the first construction on the bias side causes the largest stratum displacement, followed by the simultaneous construction, and the last is the backward construction on the bias side. The maximum variation of the vertical and horizontal displacement of the stratum caused by the construction sequence is 15.50% and 62.50% respectively, and the maximum variation of the internal force of the supporting structure is 22.63%. Considering that the formation displacement and structural force variation caused by the change of construction sequence are within the allowable range, the on-site construction of Qizishan tunnel adopts the scheme of simultaneous tunneling of left and right lines, and the cons-truction process and monitoring data verify its rationality.

Abstract:Taking a tunnel project under construction in Suzhou as the research background, this paper proposes a shield attitude prediction model and correction method based on the machine learning technology. Firstly, the spatial features of shield posture data were mined through a convolutional neural network. Then, the temporal features of data were mined through a bidirectional long short-term memory neural network. Afterwards, the important temporal feature information was mined through the attention mechanism. On the basis of the prediction results, the Apriori algorithm is introduced to extract the association rules of shield data, and the shield attitude correction method is proposed. Experiments show that the proposed prediction model in this paper has good generalizability. Compared to the three selec-ted baseline models, it achieves the smallest root mean square error and mean absolute error values, indicating higher prediction accuracy. Based on the attitude theory control model, a multi-loop attitude control model is constructed to obtain parameter suggestions for attitude adjustment, which provides a theoretical reference for intelligent attitude control.

Abstract:This study elucidated the spatial variability of heterogeneous soil texture in the soil water zone combining the classical statistics, geostatistics and Voxler method for a real-world field in the Yanlou Township of the middle of Lankao County, Kaifeng City, Henan Province. The results showed that the spatial variability of different soil particles in the soil water zone in the study area was significantly different, and the variability intensity was sand>clay>silt, and the spatial variability intensity of soil texture increased with depth of soil water zone increasing. The spatial correlation degree of sand, silt and clay in soil water zone was different, and the spatial correlation strength was clay>sand>silt. In the soil water zone, the optimal distribution model of sand in the shallow layer is Gaussian model, and the optimal distribution model in the middle and deep layer is spherical model. The optimal models of particle spatial distribution in shallow and middle layers are Gaussian models. The optimal distribution model of clay particles is the spherical model in the shallow layer and deep layer, Gaussian model in the middle layer.

Abstract:A location planning scheme for electric taxi charging stations based on GPS trajectory data is proposed to address the problem of continuous growth in the number of electric vehicles and insufficient charging facilities to meet user needs. Firstly, the potential charging needs of users are analyzed using the taxi GPS data and demand distribution is extracted. Secondly, a DBSCAN clustering method based on the grid density partitioning is proposed, which reduces the DB index from 0.34 to 0.30 compared to traditional algorithms. The demand is clustered and divided into demand intensive areas, and pre-selected station locations are set. Finally, a set coverage model is developed to achieve site optimization. Using this scheme to simulate Daxing District,Beijing and taxi trajectory data, a reasonable site selection result is obtained, and the results can provide reference for the planning of electric taxi charging stations.

Abstract:A dense pedestrian detection algorithm based on the improved YOLOv7 is proposed to address the issues of small target scale and occlusion in dense pedestrian detection scenarios. Firstly, the MobileNet attention module is introduced into the feature extraction network to reduce the model computation and enhance feature extraction capabilities. Secondly, the addition of the BepC3 module in the feature fusion network enhances the ability of pedestrian multi-scale feature fusion. Finally, WD-Loss is used as the localization loss function to improve the localization accuracy of the model detection. Trai-ning and validation were conducted on the Wider-Person crowded pedestrian detection dataset, and the experimental results showed that the improved algorithm model AP50 achieved an accuracy of 0.784, leading the original YOLOv7 algorithm by 0.031.