With an increase in tunnel construction and retention, traditional waterproofing and drainage systems have been unable to meet the needs of tunnels in heavy rainfall areas, and disasters such as tunnel lining cracking, leakage, and even collapse, occur frequently. In order to ensure the safe operation and maintenance of tunnels, this paper analyses the characteristics of the traditional waterproofing and drainage system, and puts forward a new drainage structure through numerical simulation and indoor testing. This structure removes the circular drainage blind pipe and adds a convex shell drainage plate between the waterproof board and the secondary lining. The research shows that the new drainage system greatly decreases the water pressure in the easily blocked area of the drainage structure. With the special surface discharge model, the external water pressure of the lining far away from the blocked area can quickly fall back to the normal level. In addition, the drainage capacity of different waterproof and drainage boards is different. With an increase in support pressure, the drainage capacity decreases; the geotextile decreases the most, followed by the capillary drainage board and then the convex shell drainage board. At the same time, after the muddy water drainage test of the three materials, it is found that the convex shell type drainage plate has the best anti-sludge performance. The research in this paper provides a beneficial attempt for the design of waterproofing and drainage structure of a water-rich karst tunnel, and provides a guarantee for the safe operation and maintenance of the tunnel.

In this study, we used a complex network analysis to examine the accessibility features of changing road networks in historic urban areas. We aimed to discover the pattern of evolution after studying the accessibility of the road network in the Changsha historic urban area over four periods of time. The results were as follows: the layout of the urban road network shows repetitive cluster–parent–subsidiary development, which provides evidence of adaptive adjustment in urban road development; vulnerability has been kept low in the changing urban road network, while the spatial framework of the Changsha historic center is fixed; the evolving urban road network generally shows a deteriorating level of stability, which is largely affected by the shape of the network; the degree centrality (1877, 1.87%; 1917, 1.32%; 1987, 1.85%; 2021, 1.51%) of the urban road network shows a decreasing trend, meaning that the network is generally becoming more balanced in its evolution; and the accessibility of land plots currently used to preserve cultural relics and historic sites remains at a medium to low level, and improvements are needed for some plots. In analyzing the changing accessibility of urban roads in the historic center of Changsha city, two major problems for road renewal were identified: (1) unbalanced development of the urban space due to capital-based projects and (2) providing an appropriate increase in plot accessibility while putting equal emphasis on the protection of the spatial framework in the historic urban area. We conclude that a dynamic review of urban road network accessibility and its targeted optimization are of great significance for the protection and development of Changsha’s historic urban area.

The Haoji railway in China is the longest heavy haul railway in the world, including 235 tunnels located along the 1837 km railway. With the increasing axle load of the new line and the basal deterioration of the existing heavy haul railway in China, studying the fatigue performance of the newly designed tunnel structure is essential. To study the coupling effect of the surrounding rock pressure and 30 t axle load train, in this study, we combined three-dimensional numerical simulation and three-point bending fatigue tests to investigate the fatigue performance of the basal structures. The results of numerical simulation indicate that the center of the inverted arch secondary lining is the position vulnerable to fatigue in the lower tunnel structures; the surrounding rock pressure performance exerts a stronger influence on the stress state of the vulnerable position than the dynamic train loads. The S–N formula obtained from the experiment showed that the fatigue life of tunnel bottom structures decreases with increasing surrounding rock pressure and dynamic load. In typical grade V surrounding rock and 30 t axle loads, fatigue failure will not occur in the newly designed tunnel bottom structures within 100 years if bedrock defects are lacking and pressure of surrounding rock is not excessive.

At present, most dust reduction methods do not consider the difference of dust particle diameter distribution along the tunnel and the applicability of droplet group under different parameters. In order to improve the dust reduction efficiency of each section, the particle size analyzer was used to analyze the dust samples of each section along the tunnel, and the migration law of dust of each particle diameter during the construction of Tunnel Boring Machine (TBM) was studied. The dust falling efficiency of droplets with different particle diameter under different sets of parameters was determined by the experimental platform built by ourselves. Research indicates: along the axis of tunnel, the farther away from the face of the tunnel, the higher the peak volume frequency of dust, and the distribution range of dust gradually narrowed to the direction of small particle diameter. The settling distance of dust with different particle diameter is quite different, and the content of small particle diameter dust shows an upward trend as a whole. The reduction efficiency of dust first increases and then decreases with the particle diameter, and there is particle diameter of the optimum dust reduction efficiency under the action of the same droplet group. The calculation formula of the air and water flow of the air-water nozzle and the particle diameter of the optimum dust reduction efficiency are put forward. This research can provide basis and guidance for multistage dust reduction and nozzle parameter setting in different sections of the tunnel.

Tridimensional cross tunnels usually manifest the vulnerable components of a high-speed railway caused by the sophistication of the structural pattern and the continuous shock from the train. The frequent defect of tunnel lining at the intersection would affect the safe operation of the two rails. As a result, attention has been paid to fatigue damage caused by the long-term dynamic load from a running train, in order to ensure the safety and serviceability of the cross tunnel lining. However, an influence zoning method with respect to tunnel crossing for the direct estimation of whether the lining structure is damaged due to the train load, and to what extent, is unavailable. In this paper, a systematic study that consists of numerical simulation and fatigue damage experiment is conducted to develop an approximate method to enable practicing engineers to evaluate reasonable design parameters. The initial static stress, which corresponds to the static tensile stress of secondary lining under the stratum load, and the maximum dynamic stress, which refers to the maximum dynamic tensile stress under the train load, are estimated according to the numerical simulation. A simplified damage evolution model and its parameters are identified on the basis of a systematic fatigue damage experiment. Finally, the influence zoning method is conducted on the basis of two criteria, namely (1) that initial stress level should not exceed 0.6, and (2) that load cycles should not exceed N = 2 × 10⁶ times. Thus, the practicing parameters during the cross tunnel design, such as surrounding rock mass, cross angle, rock pillar thickness between two tunnels, and train speed can be utilized conveniently by using the proposed calculation charts, according to the identification of initial stress level and the magnitude of dynamic stresses caused by the train load.

The construction site of the foundation pit support project in the urban area is narrow. Micropile has the advantages of flexible pile position layout, strong site adaptability, and fast construction speed, which can effectively control the horizontal displacement of the foundation pit and ensure the safety of surrounding buildings. However, the lateral bearing capacity of micropile is weak. In order to study the lateral force characteristics and failure characteristics of micropile, laboratory tests on the flexural and tensile strength of reinforced concrete micropiles with different diameters and with or without external steel pipes were performed. The authors studied the lateral force characteristics and failure characteristics of various types of micropiles. Based on numerical simulation software ABAQUS, the measured yield strength of the specimen was used as the loading force. And taking the occurrence and development of concrete damage into consideration, the loading process was simulated. The result shows the following: (1) the micropile specimens with external steel pipe had better flexural performance than the bare micropiles and the mechanical characteristics of the specimens changed from brittleness to plasticity; (2) the degree of concrete damage is greatly reduced after the external steel pipe is attached, and the bearing capacity of the micropile specimen of the same diameter is increased by 70% after the external steel pipe is added; and (3) the specimens were mainly damaged due to tensile damage. The calculation formula for the lateral bearing capacity of the concrete‐filled steel tube micropile considering the damage is proposed through fitting analysis. The calculation formula, the finite element calculation value, and the calculation formula proposed by other scholars are compared with the authors′ test and the test data of other scholars. The meta‐calculation results, experimental results, and formula calculation results proposed by the authors have high accuracy.