Compared with straight tunnels, over-excavation occurs on the inner side of the curved section during shield construction of small radius curved tunnels, and the disturbance to the ground surface and ...mechanical properties of surrounding rock and segment are more severe. This paper establishes the numerical models of small radius curve tunnels and straight tunnels to study the characteristics of surface deformation caused by the shield excavation of small radius curved tunnels and the influence of shield construction parameters on ground settlement, surrounding rock deformation, and segment force. The maximum error between the numerical simulation results and the measured surface settlement curve is 7.3%, which is in good agreement. The results show that: (1) The maximum value of the surface settlement of the small radius curve tunnel appears inside the curve section, and with the decrease in the curve radius, the surface settlement increases, and the distance between the peak settlement point and the tunnel center is larger. (2) When the curve radius of the tunnel is smaller, the lateral displacement of the ground surface moves farther to the inner side, and the range of soil mass with lateral displacement in the inner side is also wider. (3) Increasing the heading face pressure and grouting pressure can reduce surface settlement, but the heading face pressure should not exceed 350 kPa, and the grouting pressure should not exceed 250 kPa. (4) When the curve radius is smaller, the deformation of surrounding rock and the segment stress is larger.
This article presents an investigation on effects of heat treatments in the range 400–700℃ on morphology, fractal dimension, pore size distribution, and air permeability of superfine glass fiber ...felts. During the heat treatments, the released residual stress, thermal decomposition, and thermal contraction make fibers bend to different degrees, corresponding with different fractal dimensions. The felt pores are formed by the random interlacing of fibers, varying with the different bending degree of fibers, which results in an influence on the air permeability of the felt. The results show that there was no visible change in the morphology of the heated felt at 400–550℃. However, the treatment at 600℃ could cause the breakage of some fibers, and above 650℃ the damage of felts. The fractal dimension of heated felt decreased at 400 and 450℃, but then increased above 500℃. The lowest fractal dimension was 1.8827 at 450℃, and the highest was 1.9666 at 600℃. Besides, the pores tend to distribute in a smaller size and a narrower scale under high temperatures, resulting in a decrease in the air permeability. However, the air permeability had the same variation trend with fractal dimension at 400 and 450℃, but opposite above 500℃. The relationship among them was verified by comparing the experimental and theoretical results. At 600℃, the mean pore size and the air permeability reduced by 16% and 31%, respectively.
This paper establishes a three-dimensional symmetrical shield model to investigate the influence of a double-line shield tunnel undercrossing an existing foundation pit and of changed grouting ...pressure on the deformation and mechanical characteristics of both the foundation pit and the tunnel itself, and it proposes a method of symmetrical segmented pressure, in which different grouting pressure is applied in different sections of the tunnel. The monitoring data are used to verify the reliability of the model, and the maximum relative error is 5.44%. The numerical results show that the maximum subsidence of the retaining pile and anchor are 3.76 mm and 10.33 mm, respectively, and the maximum tensile stress of the anchor is increased by 32.4%. The subsidence shape of the foundation pit raft is an arch with four corners warping upward and the maximum subsidence difference is 3.17 mm. Uneven subsidence of the tunnel occurs along the longitudinal direction, and large and small subsidences are located at the outside and underpart of the foundation pit, respectively, and the maximum and minimum values are 11.15 mm and 2.13 mm, respectively, and the maximum subsidence difference is 9.02 mm. The deformation and mechanical characteristics of both the foundation pit and the tunnel are significantly decreased by appropriately increasing the grouting pressure, and it is recommended that the grouting pressure should not exceed 300 kPa. The proposed method of segmented pressure can reduce the differential subsidence by 47.2% and the maximum tensile stress by 27.2%, so it can significantly reduce the uneven subsidence of the tunnel and improve the tunnel stress condition. The research results can provide a theoretical basis for the safe construction of shield tunnels under the existing foundation pit.
The prevailing research on forecasting surface deformations within mining territories predominantly hinges on parameter-centric numerical models, which manifest constraints concerning applicability ...and parameter reliability. Although Multi-Temporal InSAR (MT-InSAR) technology furnishes an abundance of data, the underlying information within these data has yet to be fully unearthed. Consequently, this paper advocates a novel methodology for prognosticating mining area surface deformation by integrating ensemble learning with MT-InSAR technology. Initially predicated upon the MT-InSAR monitoring outcomes, the target variables for the ensemble learning dataset were procured by melding distance-based features with spatial autocorrelation theory. In the ensuing phase, spatial stratified sampling alongside mutual information methodologies were deployed to select the features of the dataset. Utilizing the MT-InSAR monitoring data from the Zixing coal mine in Hunan, China, the relationship between fault slippage and coal extraction in the study area was rigorously analyzed using Granger causality tests and Johansen cointegration assays, thereby acquiring the dataset requisite for training the Bagging model. Subsequently, leveraging the Bagging technique, ensemble models were constructed employing Decision Trees, Support Vector Regression, and Multi-layer Perceptron as foundational estimators. Furthermore, the Tree-structured Parzen Estimator (TPE) optimization algorithm was applied to the Bagging model, resulting in an optimal model for predicting fault slip in mining areas. In comparison with the baseline model, the performance increased by 25.88%, confirming the effectiveness of the data preprocessing method outlined in this study. This result also demonstrates the innovation and feasibility of combining ensemble learning with MT-InSAR technology for predicting mining area surface deformation. This investigation is the first to integrate TPE-optimized ensemble models with MT-InSAR technology, offering a new perspective for predicting surface deformation in mining territories and providing valuable insights for further uncovering the hidden information in MT-InSAR monitoring data.
Based on an actual excavation of a metro station in Tianjin, China, a fluid–solid coupling numerical model was developed to study the characteristics of groundwater flow and strata movement induced ...by dewatering and excavation considering the barrier effect of pre-existing adjacent underground structures. Two parameters were selected for the model: the distance between the excavation and the existing underground structure (D), and the buried depth of the adjacent structure (H). By comparing the distribution of groundwater drawdown and deformation modes of the retaining structure and the strata under different working conditions, the influence mechanism of adjacent structures on the movement of groundwater and strata was revealed. The results show that the pile foundations have different effects on the groundwater flow and excavation deformation. Generally, the maximum groundwater drawdown could be enlarged by considering the adjacent underground structure, while the retaining structure deflection would be reduced and the ground settlement could be either enlarged or reduced. Additionally, as D decreases and H increases, a much greater groundwater drawdown and a much smaller retaining structure deflection would appear, which together affect the ground behavior. On the one hand, greater groundwater drawdown would lead to greater ground settlement by soil consolidation, while on the other hand, a smaller retaining structure deflection would lead to smaller ground settlement. Thus, a complex development of ground settlement would appear, and a specific analysis should be performed to assess this in practice, based on a specific H and D.
The surface settlement formula of large slope tunnel is derived firstly. Then, the finite element model of shield tunnel is established by using ABAQUS software. Finally, the influences of tunnel ...slope, grouting pressure and shield tail clearance on ground surface settlement, and mechanical properties of surrounding rock and segments are studied by the field measurement and numerical simulation method. The results show that (1) For the slope is less than 4°, the slope increases by 1°, the settlement of ground surface increases by about 2.85 %, the shear stress of surrounding rock increases by about 4.5 kPa, and the tensile and circumferential stresses of segment increase by about 5 % and 3.1 %, respectively. (2) The proper grouting pressure is beneficial to the settlement of ground surface, and the mechanical properties of surrounding rock and segment. (3) For the shield tail clearance is less than 15 cm, the clearance increases by 1 cm, the settlement of ground surface increases by about 0.65 mm, the shear stress of surrounding rock increases by about 4.77 kPa, and the circumferential stress of segment reduces by about 0.02 MPa. Therefore, the grouting pressure with 200 kPa and the shield tail clearance with 10 cm are recommended.
Glass fiber reinforced plastics geogrid has a wide application in the field of soil reinforcement because of its high strength, good toughness, and resistance to environmental stress, creep ...resistance and strong stability. In order to get high-powered glass fiber reinforced plastics geogrid and its mechanical characteristics, the properties and physical mechanical index of geogrid have been got through the study of its raw material, production process and important quality index. The analysis and study have been made to the geogrid＇s mechanical properties with loading speed, three-axial compression, temperature tensile test and FLAC3D numerical simulation, thus obtain the mechanical parameters of its displacement time curve, breaking strength and elongation at break. Some conclusions can be drawn as follows： （a） Using glass fiber materials, knurling and coated projection process, the f~acture strength and corrosion resistance of geogrid are greatly improved and the interlocking bite capability of soil is enhanced. （b） The fracture strength of geogrid is related to temperature and loading rate. When the surrounding rock pressure is fixed, the strength and anti-deformation ability of reinforced soil are significantly enhanced with increasing reinforced layers. （c） The pullout test shows the positive correlation between geogrid displacement and action time. （d） As a new reinforced material, the glass fiber reinforced plastics geogrid is not mature enough in theoretical research and practical experience, so it has become an urgent problem both in theoretical study and practical innovation.
The glass fiber felt owned opening pore structure and chemical stability, which was widely used in various of cabins of vessels, aircraft, vehicles, etc. The surface characteristics of fiber affected ...the drainage performance of felt, thus affecting the temperature and humidity environment in the cabin. In this paper, the physical properties of heat-treated and hydrophobic modified glass fiber felt were studied and compared. After heat treatment, the surface sizing agents were removed and the felt surface became smoother. The water contact angle (WCA) of all heated felt was 0°. The residual water of 1.5 cm and 0.5 cm felt decreased by 27% and 15%, respectively, while that of 2.5 cm felt increased 324%. The excellent drainage performance could be obtained by reducing the heated felt thickness. However, the tensile strength of felt decreased by 35%–45%. In addition, the fiber diameter, the thickness, and average pore size of heated felt all decreased. After hydrophobic modification, abundant nano particles adhered to the felt surface, making the surface of felt rough. The WCAs of 2.5 cm, 1.5 cm and 0.5 cm hydrophobic modified felt were 152°, 141°, 144°, respectively. The residual water decreased by more than 60%, indicating that the drainage performance of felt could be significantly improved. The tensile strength of felt was increased by 30%–40%. The fiber diameter increased, but the thickness and the average pore size of felt decreased. Compared with the heat treatment, the hydrophobic modification could obtain excellent drainage performance and increased the felt tensile strength, which was suitable for more occasions.
Bridge deformation monitoring usually adopts contact sensors, and the implementation process is often limited by the environment and observation conditions, resulting in unsatisfactory monitoring ...accuracy and effect. Ground-Based Synthetic Aperture Radar (GBSAR) combined with corner reflectors was used to perform static load-loaded deformation destruction experiments on solid model bridges in a non-contact manner. The semi parametric spline filtering and its optimization method were used to obtain the monitoring results of the GBSAR radar’s line of sight deformation, and the relative position of the corner reflector and the millimeter level deformation signals under different loading conditions were successfully extracted. The deformation transformation model from the radar line of sight direction to the vertical vibration direction was deduced. The transformation results of deformation monitoring and the measurement data such as the dial indicator were compared and analyzed. The occurrence and development process of bridge deformation and failure were successfully monitored, and the deformation characteristics of the bridge from continuous loading to eccentric loading until bridge failure were obtained. The experimental results show that GBSAR combined with corner reflector can be used for deformation feature acquisition, damage identification and health monitoring of bridges and other structures, and can provide a useful reference for design, construction and safety evaluation.
Superfine glass fibers have high-temperature resistance, but they are rarely used and investigated at high temperature. In this article, the morphology, diameter and mesoporous are investigated by ...treating the superfine glass fiber felt during 400-650 °C. The result shows that the surface of heated fiber is smoother than original one; the diameter increases at 400 °C, then decreases with the increasing temperature, finally decreases by 14% at 600 °C; the mean mesoporous size increases with the increasing temperature, except at 500 °C, it increases 5.13 times at 600 °C. During heat treatment, the sizing agents gradually melt, decompose, and finally accumulate in very tinier areas on the surface of fiber; however, inside the fiber, the residual stress is released, the carbonate decomposes and melts. The released residual stress contributes to the increase of diameter, while thermal decomposition and thermal contraction cause the diameter to decrease and the mesoporous size to increase. The fiber stays in a metastable state, and has weight gain phenomenon when heated during 400-550 °C, while in a stable state at 600 °C, finally are destroyed at 650 °C.
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