Indoor Model Research Articles

Experimental Study and Theoretical Analysis of the Effect of Surcharge/Unloading at Both Sides of the Ground Surface on an Existing Shield Tunnel at Different Burial Depths

This paper investigates the impact of surcharge/unloading at both sides of the ground surface on an existing underground shield tunnel at varying burial depths. A large-scale indoor model experiment was conducted to study the vertical convergence deformation, tunnel settlement, and additional surrounding pressure of the tunnel at different burial depths when surcharge/unloading occurred at both sides of the ground surface. The effect of tunnel burial depth, surcharge mass, and uneven surcharge at both sides of the ground surface on the additional surrounding pressure of the existing underground shield tunnel was further investigated by theoretical calculation. The results indicate that under the same conditions, greater tunnel burial depth leads to reduced vertical convergence deformation, tunnel settlement, and additional surrounding pressure. Unloading can partially reduce the vertical convergence deformation and tunnel settlement, but it does not completely counteract the effect of the preceding surcharge. In cases of a symmetrical surcharge at both sides of the ground surface above the tunnel, the additional surrounding pressure of the tunnel is symmetrically distributed, with higher pressures at the arch top and arch bottom of the tunnel and lower pressures at the arch waist. This suggests that the arch top and arch bottom of the tunnel are vulnerable points under surcharge and require special attention. The surcharge above the tunnel has the most pronounced effect on the tunnel, followed by the surcharge at both sides of the ground surface, and, finally, the smallest effect from the bias load.

ArrangementNet: Learning Scene Arrangements for Vectorized Indoor Scene Modeling

We present a novel vectorized indoor modeling approach that converts point clouds into building information models (BIM) with concise and semantically segmented polygonal meshes. Existing methods detect planar shapes and connect them to complete the scene. Some focus on floor plan reconstruction as a simplified problem to better analyze connectivity between planes of floors and walls. However, the connectivity analysis is still challenging and ill-posed with incomplete point clouds as input. We propose ArrangementNet to estimate scene arrangements from an incomplete point cloud, which we can easily convert into a BIM model. ArrangementNet is a novel graph neural network that consumes noisy over-partitioned initial arrangements extracted through non-learning techniques and outputs high-quality scene arrangement. The core of ArrangementNet is an extended graph convolution that leverages co-linear and co-face relationships in the arrangement and improves the quality of prediction in complex scenes. We apply ArrangementNet to improve floor plan and ceiling arrangements and enrich them with semantic objects as scene arrangements for scene generation. Our approach faithfully models challenging scenes obtained from laser scans or multiview stereo and shows significant improvement in BIM model reconstruction compared to the state-of-the-art. Our code is available at https://github.com/zssjh/ArrangementNet.

Experimental Investigation on Deformation Characteristics of Strutted U-Shape Sheet Pile Flexible Retaining Structures in Excavations Using 3D Printing

U-shape steel sheet piles are widely used in deep and large excavation engineering due to their excellent soil-retaining and water-stopping performances. To achieve deformation control in excavations, an experimental investigation on the deformation characteristics of a strutted U-shape sheet pile flexible retaining structure was conducted. Single-layer and double-layer strutted retaining structure excavation indoor model tests in sand, where U-shape sheet piles were formed by 3D printing, were successfully accomplished. Deformation was monitored in real time during the test. The results show that the lateral displacement mode of the retaining structure transformed with the change in excavation from the “cantilever” to the “bulge” and finally developed into an intricate “recurve bow”. The average maximum lateral displacement was 0.756% of the excavation depth. With a maximum settlement of 0.375% of the excavation depth on average, the distribution of ground settlement behind walls changed from “exponential” to “triangular” before ultimately transforming into “trough” or “trapezoid” mode. The maximum settlement to maximum lateral displacement ratio (smax/δmax) on average was 0.54; the maximum settlement deformation rate was always less than the maximum lateral displacement deformation rate.

Automated methods for indoor point cloud preprocessing: Coordinate frame reorientation and building exterior removal

Raw indoor datasets acquired from laser scanning may be tilted and contain outliers, which negatively influence the accuracy of subsequent tasks. Therefore, an automatic framework with three steps is provided to preprocess indoor point cloud. First, a hybrid segmentation method is proposed to extract planar primitives from noisy points. Then, a nonlinear optimization is designed to discover the dominant orientations of the building with topological constraints. Finally, the outdoor points are removed through a novel graph-cut formulation. The experiments on six various buildings indicates that our methods successfully reorient the point cloud and preserve the indoor points. In comparison with other methods, we achieve superior performance on visual inspection and evaluation metrics. Besides, our work only relies on the geometric position and is not limited by Manhattan-World assumption. We present a reliable solution for indoor point cloud preprocessing that have potential for indoor modelling, floorplan generation, and objects detection.

Analysis of Influence Factors of Anti-Slide Pile with Prestressed Anchor Cable Based on Bearing and Deformation Characteristics of Pile Body

In order to deeply study the mechanism of prestressed anchor anti-slide pile, an indoor model experimental device was developed, and a finite difference and particle flow numerical analysis model of slope anchor cable anti-slide pile was established based on the reinforcement project of prestressed anchor cable anti-slide pile in a mountain road slope. Based on the analysis of the force and displacement characteristics of the anti-slide pile, the influence of the prestress of the anchor cable, the inclination angle of the anchor cable, the width and column spacing of the anti-slide pile and the inclination angle of the landslide, the height and nature of the filling soil on the force and deformation characteristics of the pile are discussed, and some design parameters are optimized. Results show that the larger the prestress of the anchor cable, the smaller the displacement of the pile body, but the excessive stress is not conducive to the safety of the pile body. The optimal tension should be 50–70% of the designed tension of the anchor cable. With the increase in the inclination angle of the anchor cable, the displacement of the pile decreases first and then increases, and there is an optimal inclination angle of the anchor cable. In the double row piles, with the increase in pile spacing, the front row piles gradually change from supporting the soil between the double row piles to supporting the sliding body with the back row piles, and the double row piles are plum-shaped. When the pile spacing is 2.5 times the pile diameter, the force of the front and rear piles is the most reasonable. In the process of soil arching evolution, the influence of cohesion on the soil arching effect is greater than that of the internal friction angle.

Progressive Model-Driven Approach for 3D Modeling of Indoor Spaces

This paper focuses on the 3D modeling of the interior spaces of buildings. Three-dimensional point clouds from laser scanners can be considered the most widely used data for 3D indoor modeling. Therefore, the walls, ceiling and floor are extracted as the main structural fabric and reconstructed. In this paper, a method is presented to tackle the problems related to the data including obstruction, clutter and noise. This method reconstructs indoor space in a model-driven approach using watertight predefined models. Employing the two-step implementation of this process, the algorithm is able to model non-rectangular spaces with an even number of sides. Afterwards, an “improvement” process increases the level of details by modeling the intrusion and protrusion of the model. The 3D model is formed by extrusion from 2D to 3D. The proposed model-driven algorithm is evaluated with four benchmark real-world datasets. The efficacy of the proposed method is proved by the range of [77%, 95%], [85%, 97%] and [1.7 cm, 2.4 cm] values of completeness, correctness and geometric accuracy, respectively.

Experimental Investigation of the Bearing Performance and Failure Characteristics of Double-Row Pile-Slab Structures in Steep Mountainous Areas

Considering the pile-slab subgrade project of the Hangzhou-Huang Shan Passenger Dedicated Line as the basis, this paper conducts a 1:10 large-scale indoor model test for the horizontal bearing capacity of the pile-slab structure in steep mountainous areas to study the distribution of the pile-slab structure stress, soil pressure and structural deformation and analyze the failure mode of the structure and slope. The research shows that when the subgrade with a double-row pile-slab structure is subjected to horizontal loading in the steep slope section, the steel bars of the pile body above the sliding surface are compressed, and the steel bars of the pile body below the sliding surface are under tension. With the increase in the horizontal load, the stress of the pile body steel bar remains basically unchanged or shows a steady increase and finally sharply increases. The deformation of the bearing plate is dominated by the horizontal displacement, and the horizontal displacement reaches 7.25 mm when the plate is broken. In addition, warping deformation of the inner high and outer low occurs. When the horizontal load reaches 157 kN, shallow damage and local collapse of the slope occur, and transverse and diagonal cracks occur at the top of the pile and near the sliding surface of the pile. During the test, the pile-slab structure always deforms more than the slope, and the overall stability of the structure is good. The test is suitable for sections where the remaining sliding force is less than 770 kN/m (equivalent to a slope length of 79.123 m).

Numerical Study on Deposition Behavior of Micron-Sized Suspended Solids in Broken Rock Mass within a Goaf Based on Coupled CFD-DEM Method

After coal mine wastewater is artificially injected into a groundwater reservoir transformed from a goaf, micron-sized suspended matter in the wastewater is purified by the broken rock mass in the goaf. Existing studies can only analyze the macroscopic changes in the content of suspended solids during the purification process, and it is difficult to explain the microscopic deposition mechanism of the suspended solids in broken rock. This paper studied the microscopic deposition behavior of micron-sized suspended solids inside the broken rock mass via numerical simulation using a coupled CFD-DEM method. In addition, indoor model tests were carried out to verify the accuracy and reliability of the model in comparison. The study results show that suspended solids’ deposition behavior varies significantly under broken rock masses’ different pore sizes (0.47 mm, 1.14 mm, 3.00 mm, and 5.33 mm). Within the goaf, the adsorption of suspended solids by the broken rock mass plays a dominant role. At the same time, suspended particles are mostly collected in the inlet area, and the difference in the number of deposited particles can reach 74% when comparing the first 50 mm range as well as the 50–100 mm range. The number of deposited particles at a flow rate of 0.02 m/s is 14% more than that at a flow rate of 0.06 m/s. This work offers new ideas for studying the purification mechanism of coal mine wastewater within a goaf.

Experimental and numerical analysis of chloride ion transportation in concrete under bending load with reverse seepage

The paper investigates a new technique, named as Reverse-seepage and Saturation based Active Anti-corrosion Technology (RS-AAT), for preventing chloride ion invasion within the marine concrete under the loading effect. By the indoor model experiments, the effect of RS-AAT on chloride ion invasion within the marine concrete under 10%, 20%, and 30% ultimate bending loads are explored and the results indicate that RS-AAT can effectively reduce 24.36% and 27.29% in chloride ion concentration in the compression and tension regions, respectively. Otherwise, the use of RS-AAT can effectively decrease the surface chloride ion concentration. Furthermore, the chloride ions convection-diffusion model with loading effect is established based on the mesoscopic structure theory of concrete pores and the K-C model, of which variability is verified by comparing with the experimental results.

Predictive modeling of plant uptake of Pb and Cd: Implications of aerial deposition and the origin of parameterisation data

We developed ordinary least squares regression models to predict uptake of cadmium and lead, two metals that are of public health significance because of their toxicity, in the edible tissues of lettuce. Models were parameterised using data on soil metal concentration, pH, and organic carbon. To assess the impact of physical contamination in form of aerial deposition and soil-splash on the metal concentration in lettuce, separate linear regression models were parameterised for indoor- and outdoor-grown lettuce, assuming the physical contamination to be negligible for indoor conditions. Both Cd models showed high model fit and strong predictive performance, when tested on an independent dataset, suggesting uptake via roots to be dominant. For Pb, the indoor model performed better than the outdoor model, indicating that physical contamination, contributes significantly to metal concentration in lettuce leaves. Our results highlight the importance of the parameterisation data when developing uptake models for predictions and risk assessment. Regression models for predicting Pb concentration in lettuce based on indoor data should not be used for predicting lettuce concentrations cultivated in outdoor conditions unless the contribution of physical contamination is explicitly accounted for.

Lateral damage mechanism of the double-track tunnel in the mountainous layered soft rock and NPR anchor cable control

Due to complex geological formations, lateral damage often occurs during excavation in mountainous layered soft rock double-track tunnels. This paper discusses the stresses and the damage characteristics of the surrounding rock under overload in a mountainous layered soft rock double-track tunnel through indoor model experiments to provide a basis for the effective control of lateral damage. The experiments show that the conventional support method cannot effectively control the lateral damage due to interlayer sliding. Therefore, the negative Poisson’s ratio (NPR) anchor/cable control method is proposed. And the scientificity and feasibility of the NPR anchor/cable control technology are proved by the field application and monitoring data of the Minxian Tunnel and Changning Tunnel. It is further demonstrated that high preload is the most effective way to control the lateral damage in layered soft rock tunnels.

Study on model test of the new O-cell load test method with two loading directions

Aiming at the possible problems of the new O-cell load test method with two loading directions in engineering practice, the operability and feasibility of this new method is studied by using indoor model tests and finite element numerical simulations. According to the similar principle, three groups of the traditional static load test, the O-cell load test and the updated O-cell load test under the same working conditions are designed and poured to obtain the pile ultimate compressive bearing capacity for comparison. Strain gauges and optical fibers are also used to detect the strain of the outer surface of the pile and the soil layer around the pile. The research results show that based on the bearing capacity results of the traditional static load test, the results of the physical model under the updated O-cell load test are compared with the results under the O-cell load test. The deviation is reduced by 3.54%-7.34%. At the same time, based on the physical test, the finite element analysis shows that the longer the pile length, the greater the deviation reduction. When the pile length is twice the physical model test, the contrast deviation reduction value is 9.15 %-15.71%. The strain results in the physical test also reflect the mechanism of pile-soil interaction well, and there is also a deficiency that the position of the equilibrium point needs to be determined.

The Bearing Characteristics of Sand Anchors under Vibrating Load

In particular environments, such as the Gobi Desert, the problems encountered in a project are complex, resulting in reduced stability of the anchoring system and multiple forms of failure. This paper takes the factors influencing the stability of sand anchors under vibration loads as the research background. Theoretical analysis and indoor model tests were used to study the load-bearing performance of sand anchors under vibration loads; in addition, a comparative analysis of this performance along with failure forms of sand anchor systems, various sand soil moisture contents, and vibration parameters was performed. The results of the study showed that as the water content becomes higher, the cohesive force of the sand decreases and produces a higher displacement in the water content, with most of the anchor solids becoming prone to fatigue failure. When the water content and vibration frequency remain stable and the vibration amplitude increases, the anchor rod is disturbed after the ultimate pullout bearing capacity forms a decreasing trend, with a decline rate of approximately 40%. By keeping the water content and vibration amplitude stable and changing the vibration frequency, the ultimate pullout capacity of the anchor does not change significantly, and the frequency reaches a certain level when it attains a compacting effect on the surrounding soil and thus has less influence on the anchor. The anchor pullout resistance bearing is most sensitive to the change in sand moisture content, more sensitive to the vibration amplitude, and less sensitive to the vibration frequency, but its correlation is not significant.

Parametric analysis and multi-objective optimization of the coupling beam pile structure foundation

To optimize the structure of a new coupling beam pile foundation, a finite element model that is verified by an indoor model test was established and compared with a pile group foundation to improve the uneven settlement phenomenon. The effects of different structural parameters on settlement and coupled beam axial forces were analysed. The corresponding mathematical model is created using the response surface method, and the NSGAII genetic algorithm is utilized to carry out multi-objective optimization while taking cost into account. The best structural parameters are then determined through the analysis of various weighting factors. The findings show that using the response surface method instead of finite element modelling can significantly shorten the optimization time while maintaining a high accuracy; that the cost weight factor should not be regarded too seriously; and that a value of 0.5 is recommended. When the optimum parameters were chosen, the coupling beam's axial force increased by 2.8%, the project cost of the structure was cut by 57.99%, and the settlement was lowered by 34.87%. The study offers a new concept for structural optimization and foundation treatment.

Model tests and numerical modeling of the failure behavior of composite strata caused by tunneling under pipeline leakage conditions

Pipeline leakage is a frequent phenomenon in subway construction and has contributed to numerous underground collapses. In this study, the failure behavior of composite strata (i.e., an upper soft soil layer and a lower hard rock layer) caused by tunnel excavation under seepage conditions was investigated via indoor model tests and finite difference methods. It was found that the thickness of the hard overburden above a tunnel considerably influenced the stability of the tunnel. When the overburden thickness was less than half of the tunnel span (D), an increase in the seepage zone could induce the formation of sinkholes after tunnel excavation. When the overburden thickness was greater than 1D, a stable collapse arch was formed after tunnel excavation. Thus, strata between a tunnel overburden and a leakage zone should be reinforced to improve excavation stability.

Reliability Evaluation and Prediction of Deep Buried Tunnel Based on Similarity Theory and Model Test

Deep buried tunnel has a complex stress environment and large stress level. At present, it is difficult to dynamic monitoring for such tunnels. In order to make the safety evaluation and prediction of tunnel closer to the engineering practice, this paper deduces the tunnel reliability evaluation algorithm. The time-varying reliability of deep tunnel excavation process is analyzed and predicted. Based on the similarity theory, the actual deep tunnel excavation is simulated by indoor model test, the stress and deformation are monitored. The results show that after the tunnel excavation, the reliability of the structure does not decrease gradually, but increases slowly first and then decreases sharply. With the increase of the buried depth of the tunnel, the structural reliability decreases gradually. When the buried depth reaches a certain depth, the structural reliability will decrease rapidly. The influence of different parameters on the structural reliability has different sensitivity. The sensitivity of friction angle is the highest, and the sensitivity of gravity is the lowest. The sensitivity has little effect with the change of tunnel excavation time and tunnel buried depth. The accuracy of this method is verified by the comparative analysis of model box tests.

Theoretical Approach to Predicting the Diffusion Radius of Fracture Grouting in Soil–Rock Mixtures

Previously conducted studies have established that the soil–rock mixture in the Chongqing area has the characteristics of loose structure, poor stability, strong permeability, and so on. When building a tunnel in a soil–rock mixture stratum, it is necessary to reinforce the surface rock mass and surrounding rock by grouting to improve the safety of tunnel excavation. To study the diffusion mechanism of cement slurry (Bingham fluid) in soil–rock mixtures, based on the Bingham fluid flow equation and slurry diffusion model, the Bingham fluid fracture diffusion formula was derived, and field grouting tests and indoor model tests were carried out with soil–rock mixtures in the Chongqing area as the research object. The fracture grouting diffusion formula was verified and analyzed using the test data. The research results show that the theoretical calculation results of various working conditions are close to the actual test results (the error of indoor model test results is less than 3%, and the error of field test results is less than 5%). A Bingham fluid fracture diffusion formula has been developed that applies to various working conditions of fracture grouting of soil–rock mixtures and has a good prediction effect on the value of the fracture diffusion radius.

Frost jacking characteristics of prefabricated cone cylindrical tower foundation in cold regions

The foundations of high-voltage transmission lines in permafrost areas are often affected by frost heaving of the soil, which leads to engineering accidents, such as falling towers or poles. The tower foundation type that has been analyzed thus far cannot meet the construction requirements well. Based on research on the prefabricated cone cylindrical (PCC) tower foundation model, indoor model tests were conducted to study the frost jacking characteristics of the tower foundation under different temperatures. The temperature field distribution characteristics and the pattern of the frost jacking displacement were determined, and the anti-frost jacking mechanism of the PCC tower foundations was analyzed. The research indicates that the following. (1) The PCC tower foundation, which combines the structural characteristics of a tapered column foundation and prefabricated foundation with the technical advantages of frost resistance and easy construction. (2) The freezing rate decreases exponentially with time, and the frost jacking displacement increases in an “S” shape. (3) The mechanical conditions for the displacement of the foundation was proposed based on the mechanical analysis. (4) To promote economy and safety, a foundation engineering design criterion has been proposed for burying the upper surface of the foundation below the freezing depth line, which can prevent engineering accidents.

Numerical Simulation of Frost Heave Deformation of Concrete-Lined Canal Considering Thermal-Hydro-Mechanical Coupling Effect

This work presents a comprehensive coupled thermal-hydro-mechanical model to explore the frost heave mechanism of the concrete-lined canal under a freeze–thaw environment. Unlike previous models that regard concrete as a homogeneous material, this model considers concrete a porous medium and considers the effect of the concrete pore structure, as well as the water content, ice content, and ice-water phase transition, on the mechanical deformation of the canal. Firstly, based on the theories of unsaturated soil mechanics, thermodynamics, and poroelasticity, the thermal-hydro-mechanical coupling equations of the soil under the freeze–thaw condition are established. Then, based on the theories of thermodynamics, poroelasticity, and permeability mechanics of porous media, the thermal-hydro-mechanical coupling equations of the concrete under the freeze–thaw condition are established. Finally, the freeze–thaw simulation of a canal is carried out and compared with the referred indoor model test, in which the evolution behavior of temperature, frost depth, and frost heave deformation of the canal are studied. The results show that the freezing process of the soil foundation is a unidirectional process that develops from the surface to the bottom, and the thawing process of the soil foundation is a bidirectional process that thaws from the surface and bottom to the center. The frost heave deformation of the soil foundation at the 1/2~1/3 slope height area is the largest, which may easily lead to frost heave damage to the concrete lining in this area. The frost heave deformation of the canal obtained by the numerical simulation is consistent with the experimental results, which illustrates the validity of the established model for predicting the frost heave deformation of concrete-lined canals.

Quantifying urban heat exposure at fine scale - modeling outdoor and indoor temperatures using citizen science and VHR remote sensing

Global warming and advancing urbanization lead to an increased heat exposure for city dwellers. Especially during summertime heatwaves, extreme daytime as well as high nighttime temperatures expose vulnerable people to potentially deadly heat risk. This applies specifically to indoor air temperatures, since people spend a lot of their time indoors. Against this background, this study relates outdoor and indoor air temperature measurements to area-wide geospatial data regarding summertime urban heat in the city of Augsburg, Germany. Air temperature data is collected from formalized as well as citizen science measurements, while remote sensing data with very-high spatial resolution (VHR) is utilized for assessment of their drivers and influencing factors. A land use regression approach is developed for city-wide modeling of outdoor and indoor air temperatures at the level of individual residential buildings. Daytime outdoor temperatures could be largely explained by vegetation parameters and imperviousness, whereas nighttime temperatures were more related to the building stock and radiation properties. For indoor temperatures, building density as well as building height and volume are additionally relevant. Outdoor air temperatures could be modeled with higher accuracies (mean absolute error (MAE) < 0.5 °C) compared to indoor temperatures (MAE < 1.5 °C), whereas outdoor and indoor modeling results are consistent with well-known patterns across different local climate zones (LCZ).