Uplift Displacement Research Articles

Seismic response of column supported tanks considering uplift effect and soil‐structure interaction

AbstractIn this paper, the seismic responses of column supported tanks under horizontal earthquake are obtained by finite element method. Two types of structures are discussed including the anchored tank with columns fixed on the ground and the resilient tank whose columns can uplift. The uplift effect is realized by the contact algorithm to allow the column move upwards in a vertical direction and the soil‐structure interaction (SSI) is considered by equivalent soil springs. Different soil types and hard ground condition are adopted to study SSI effect on natural frequencies of tanks and seismic responses of the anchored tank, as well as coupling effect (both uplift and SSI effects) on seismic responses of the resilient tank. The structural displacement and acceleration, the stress of tank walls and columns, the base shear and the overturning moment, the uplift displacement of columns are discussed. The results of tanks in different conditions are compared with each other, which show that SSI has a significant impact on seismic responses of column supported tanks. As the stiffness of soil decreases, the tank has larger displacement, smaller natural frequency, and stress level of structural members especially when it is sited on softer soil type. Compared to the anchored tank, due to the combination of both uplift effect and foundation deformation, the resilient tank has smaller displacement to prevent its overall collapse and lower responses such as the base shear and the overturning moment. The resilient tank has better seismic performances regardless of soil conditions.

Shaking table tests on the liquefaction-induced uplift displacement of circular tunnel structure

Underground structures are susceptible to float and move upward during earthquakes when located in a liquefiable soil deposit. There are examples of this phenomenon in past major earthquake events. In this study, the uplift of circular tunnels in a liquefiable sand layer was investigated with a series of shaking table tests. The research has focused on the buried depth of the tunnel, tunnel diameter, tunnel weight, liquefaction extent, uplift mechanism, and factor of safety against liquefaction-induced uplift. According to the test results, the shallow buried depth, larger diameter, and lower weight can intensify the tunnel uplift, so the displacement in post-liquefaction time continues at the same rate as during the shaking time. Due to the shear-induced dilation, pore water pressure generation around the tunnel was reduced compared with that of the free field. The excess pore water pressure dissipation in the soil overlying the uplifted tunnel was significant, which leads to suction in the soil deposit. Furthermore, the acceleration response of overlying soil with the uplifted tunnel was similar to that of the free field. However, the soil acceleration response around the tunnel without uplift was similar to the base motion.

Adaptability Evaluation of Rotary Jet Grouting Pile Composite Foundation for Shallow Buried Collapsible Loess Tunnel

The deformation control effect of loess tunnel composite foundation plays an important role in optimization design and reinforcement effect evaluation. Systematically evaluate the adaptability of the composite foundation of jet grouting pile in shallow collapsible loess tunnel. Taking the shallow buried section of Fujiyao Tunnel with a buried depth of 20 m as an example, using MIDAS finite element numerical simulation software, the foundation deformation control during construction and settlement control after construction are systematically studied, the differential deformation control is analyzed, and the reinforcement effect of the tunnel bottom is evaluated. The results show that the uplift displacement can be controlled by changing the pile length and increasing the replacement ratio. The combination of long and short piles can significantly reduce the uneven settlement and plastic zone of the foundation. The uneven settlement of 9 mm can be used as the evaluation index of the composite foundation reinforcement effect in a shallow buried section of the loess tunnel.

Effects of Foundation Excavation on Metro Tunnels at Different Locations and Performance of Corresponding Reinforcement Measures: A Case of Shenzhen Metro Line 11, China

Symmetrical excavation of a foundation pit inevitably causes stress redistribution and deformation in adjacent tunnels, even threatening the safety of their operation. Therefore, it is of practical significance to evaluate the deformation characteristics of adjacent tunnels and propose corresponding reinforcement measures after the excavation of a foundation pit. This study, based on the overlapping tunnel project of the section between Nanshan Station and Qianhaiwan Station of Shenzhen Metro Line 11, analyzes the influence of overlapping foundation pit excavation on adjacent tunnels by numerical simulation method. The deformation characteristics of adjacent tunnels at different locations caused by foundation pit excavation are studied, and the soil reinforcement measures applicable to tunnels at different locations are proposed, respectively. Some useful conclusions have been drawn as follows. The deformation characteristics of adjacent tunnels caused by foundation pit excavation can be divided into three areas: the settlement zone, the transition zone, and the uplift zone. Moreover, for different zones of the tunnel, corresponding soil reinforcement measures are taken, respectively. Soil reinforcement measure makes the soil more monolithic and thus make the stress and strain transfer more uniform, which is effective in reducing soil rebound displacement and tunnel uplift displacement.

The Effects and Vertical Bearing Capacity of Two Jacked Model Piles in Sand

The effects and vertical bearing capacity of two jacked piles in sand are still not well understood, and the mechanism of the adjacent pile’s uplift caused by the jacking pile in a double pile system is especially unclear, but these facets are important to the stability of the jacked pile. In this paper, a series of tests is performed on jacked model piles in sand, where in the influences of the pile length and the driving pile’s speed on the effects and vertical bearing capacity of two jacked piles were studied. The results revealed that the effects and vertical bearing capacity of the two jacked piles were mainly in relation to pile length and influenced by the driving speed. The horizontal displacement of the top of the first jacking pile during the installation of the post-jacking pile was caused by the difference in the stress state of the first jacking pile between the side of the pile’s face and its back side, in which the uplift displacement of the first jacking pile was also involved. The radial stress of the pile increased nonlinearly with the depth under different pile lengths and gradually converged to the passive earth pressure. The ultimate capacity of the double pile is approximately twice that of a single pile, and the ratio of the ultimate capacity of a single pile to the final jacking pressure was approximately 1.04.

Model test and numerical simulation on the invert heave behaviour of high-speed railway tunnels with rainstorm

Extreme weather with torrential rainstorms has brought a new challenge to the operation of railway tunnels in karst areas. Especially for high-speed railway (HSR) tunnels, the uplift of the invert structure caused by the high external water pressure (EWP) seriously affects the normal operation of the HSR line. This paper presented a series of 3D printing model tests to investigate the occurrence mechanism and evolution law of invert heave disease after rainstorm and drainage blockage. Numerical simulations were used to study the mechanical response of the tunnel structure under different groundwater levels and drainage blockage degrees. The results show that the uplift displacement of the invert increases with the EWP. The maximum EWP occurs at the invert whether the drainage system is blocked or not, which is the main factor leading to such disease. Drainage blockages increase the severity of the disease. Especially with blockages exceeding 50%, the EWP on the invert and the corresponding uplift displacement increase significantly. Furthermore, groundwater levels and drainage blockages will both cause increased stresses in the tunnel bottom structure, leading to problems such as excessive uplift displacement and cracking. Some useful suggestions for tunnel construction and operation were obtained from the results.

Dynamic Response of Rectangular Tunnels Embedded at Various Depths in Spatially Variable Soils

This study investigated the seismic response of rectangular tunnels with various embedment depths considering the spatial variability of soil shear modulus. The spectral representation method was adopted to simulate the anisotropic random field of soil. The excess pore water pressure, the liquefied zone, the ground displacement and the uplift displacement of the tunnel were obtained through the random finite difference method to analyze the seismic response. It was observed that the soil excess pore water pressure ratio under the tunnel gradually decreased and the liquefaction degree reduced with depth increase. The peak value of the liquefied zone range increased with the increase in embedment depth. The mean response of stochastic analysis was smaller than the deterministic calculation results when the tunnel embedment depth was less than 10 m. The maximum tunnel floating displacement obtained from random analyses had the probability of 67.3%, exceeding the value calculated by deterministic analyses when H = 12 m.

Suction effects during uplift of steel pipes buried in compacted soil

This paper presents an experimental study on quantifying the effects of soil suction on the resistance offered by compacted unsaturated backfills to uplift of buried steel pipes and identifying the mechanisms that contribute to increased resistance compared to similar pipes buried in dry sand. This is achieved by means of 1-g physical model experiments, with the pipe buried in sandy loam–Kaolin soil beds of varying water content (suction), compacted to the same dry unit weight. The main experiments are supplemented by benchmarking experiments performed in dry sand of similar grain size distribution, as well as in compacted soil beds inundated with water to achieve conditions close to full saturation. The experiments are supported by a detailed characterisation study of compacted sandy loam–Kaolin mixtures and mini-CPT tests performed to evaluate the uniformity of the soil beds. Measurements of the reaction developing on the pipe as function of its uplift displacement are co-evaluated together with images of the failure mechanisms obtained using particle image velocimetry and continuous measurements of soil matrix suction. We conclude with a simplified method to predict the peak reaction to pipe uplift that allows considering the contribution of suction and the tensile–shear failure mechanism observed during the experiments.

Seismic responses of rectangular tunnels in liquefiable soil considering spatial variability of soil properties

The objective of this paper was to investigate the dynamic response of a tunnel-soil system in the soil with spatial variability of shear modulus with various coefficients of variation and scales of fluctuation. The soil shear modulus was highlighted and modeled as an isotropic random field using the spectral representation method, then mapped into the finite difference model. The dynamic stochastic responses of the excess pore water pressure ratio, the liquefied zone, the ground displacement, and the uplift displacement of the tunnel were discussed. It was observed that the effect of coefficient of variation was pronounced in which an increase of the coefficient of variation brought out a reduction in the corresponding dynamic stochastic responses. However, the scale of fluctuation was found to be insignificant in the tunnel soil system.

Experimental study on uplift mechanism of pipeline buried in sand using high-resolution fiber optic strain sensing nerves

Reliable assessment of uplift capacity of buried pipelines against upheaval buckling requires a valid failure mechanism and a reliable real-time monitoring technique. This paper presents a sensing solution for evaluating uplift capacity of pipelines buried in sand using fiber optic strain sensing (FOSS) nerves. Upward pipe-soil interaction (PSI) was investigated through a series of scaled tests, in which the FOSS and image analysis techniques were used to capture the failure patterns. The published prediction models were evaluated and modified according to observations in the present study as well as a database of 41 pipe loading tests assembled from the literature. Axial strain measurements of FOSS nerves horizontally installed above the pipeline were correlated with the failure behavior of the overlying soil. The test results indicate that the previous analytical models could be further improved regarding their estimations in the failure geometry and mobilization distance at the peak uplift resistance. For typical slip plane failure forms, inclined shear bands star from the pipe shoulder, instead of the springline, and have not yet reached the ground surface at the peak resistance. The vertical inclination of curved shear bands decreases with increasing uplift displacements at the post-peak periods. At large displacements, the upward movement is confined to the deeper ground, and the slip plane failure progressively changes to the flow-around. The feasibility of FOSS in pipe uplift resistance prediction was validated through the comparison with image analyses. In addition, the shear band locations can be identified using fiber optic strain measurements. Finally, the advantages and limits of the FOSS system are discussed in terms of different levels in upward PSI assessment, including failure identification, location, and quantification.

The influence of the underpassing frozen connecting passage on the deformation of the existing tunnel

Based on the engineering background of the contact channel between Shangyang and Gushan of Fuzhou Metro Line 2 undercrossing the existing tunnel line, the freezing temperature field of the contact channel, the displacement field of the existing tunnel line and the contact channel with different net distances and horizontal angles are analyzed by ANSYS finite element software and field measurement method. The obtained results indicate that during the freezing period, the temperature drops at different measuring holes are almost the same. The temperature near the bottom freezing tube drops faster than that far from the tube. It is found that the bilateral freezing technique improves the formation of the freezing wall in the intersection area. In this case, the intersection time of the cross-section is 7 days faster than that of the adjacent ordinary section. The change curve of the displacement of the surface uplift in different freezing periods with the distance from the center of the channel is “M” shaped. The maximum uplift displacement at 12 m from channel center is 25 mm. The vertical displacement of the measuring point located above the central axis of the connecting channel is large. The farther the point from the central axis, the smaller the corresponding vertical displacement. When the horizontal angle between the existing tunnel and the connecting channel is less than 60°, the existing vertical displacement of the tunnel changes rapidly with the horizontal angle, reaching 0.17 mm/°. Meanwhile, when the net distance is less than 6.1 m, the change rate of the vertical displacement of the tunnel is up to 2.4 mm/m.

Numerical analysis of the tunnel uplift behavior subjected to seismic loading

Seismic loading has always been a major concern for any engineering structures, and thereby, underground facilities (e.g., tunnels) are not exceptional. It is due to the seismically induced uplift and instability of tunnels caused by the large deformation of liquefiable soils. Therefore, the tunnel uplift behaviors subjected to seismic loading are always taken into account in any designing stages of tunnels. This study's main goal was to evaluate how a tunnel buried in liquefiable and non-liquefiable soils would behave when subjected to seismic stress. Seismic and liquefaction potential assessments of the soils surrounding the tunnel were carried out using the finite-element method. In this study, PM4sand, an advanced constitutive model was adopted in all finite-element models. In addition, the uplift displacement and excess pore pressure of liquefiable soils were studied, under a typical earthquake. Investigations were also conducted into how the thickness of the non-liquefiable soil affected seismic loading, tunnel uplift displacement, and the buildup of excess pore water pressure. As a result, during the earthquake, liquefaction was triggered in most parts of the sand layer but not in the clay layer. In addition, the tunnel uplift displacement was triggered due to the relative motion and interaction at both sides of the tunnel. In addition, this study found that the thickness of the non-liquefiable soil layer (sand layer) had a significant impact on the build-up of excess pore water pressure and, consequently, the tunnel uplift displacement. The uplift displacement and excess pore water pressure build-up were higher the thinner the non-liquefiable layer was.

Prediction of Ultimate Antifloating Force of Bored Piles in Urban Road Crossing Overpass

As an effective antifloating measurement in underpass engineering, uplift piles have been widely employed in the antifloating design of underground structures, such as basements, underground roads, and underground shopping malls. For the purpose of studying the antifloating behavior of bored piles and predicting the uplift bearing capacity in underpass engineering, the on-site pull-out tests of bored piles are carried out in laboratory. Besides, the MMF growth curve model, the ordinary hyperbolic model, and the exponential model are employed to fit and predict the ultimate bearing capacity of the measured uplift load and uplift displacement data of three test piles, respectively. The research results indicate that three test piles meet the stability requirements of antibuoyant bearing capacity, and the pull-up load-displacement curves of test piles are gentle and steep. Meanwhile, the fitting accuracy of the pull-displacement curve is high; specifically, the correlation coefficient is above 0.98619, and the average value is 0.99134, thereby verifying that the fitting effect of MMF growth curve model is better than those of the hyperbolic model and the exponential model. Therefore, the MMF growth curve model proposed in this paper not only describes the fitting of the uplift load-uplift displacement curve of uplift piles accurately but also predicts the ultimate bearing capacity of test piles. The research results provide an important reference for the antifloating behavior of bored piles in underpass engineering.

Influence of Open-Pit Coal Mining on Ground Surface Deformation of Permafrost in the Muli Region in the Qinghai-Tibet Plateau, China

The Qinghai-Tibet Plateau (QTP) is the largest mid-to low latitude and high-altitude permafrost. Open-pit coal mining and other activities have caused serious damage to the alpine ecological environment and have accelerated the degradation of permafrost on the QTP. In this study, the influence of open-pit coal mining on the time series ground surface deformation of the permafrost in the Muli region of the QTP was analyzed from 19 January 2018 to 22 December 2020 based on Landsat, Gaofen, and Sentinel remote sensing data. The primary methods include human-computer interactive visual interpretation and the small baseline subsets interferometric synthetic aperture radar (SBAS-InSAR) method. The results showed that the spatial distribution of displacement velocity exhibits a considerably different pattern in the Muli region. Alpine meadow is the main land use/land cover (LULC) in the Muli region, and the surface displacement was mainly subsidence. The surface subsidence trend in alpine marsh meadows was obvious, with a subsidence displacement velocity of 10–30 mm/a. Under the influence of changes in temperature, the permafrost surface displacement was characteristics of regular thaw subsidence and freeze uplift. Surface deformation of the mining area is relatively severe, with maximum uplift displacement velocity of 74.31 mm/a and maximum subsidence displacement velocity of 167.51 mm/a. Open-pit coal mining had resulted in the destruction of 48.73 km2 of natural landscape in the Muli region. Mining development in the Muli region had increased the soil moisture of the alpine marsh meadow around the mining area, resulting in considerable cumulative displacement near the mining area and the acceleration of permafrost degradation.

Analytical solution for the response of lined trapezoidal canals under soil frost action

Lined canals are important water suppliers and provide water for irrigation and other activities; however, they accumulate serious frost damage in cold regions. The frost heaving of frozen soil and its normal and tangential interactions with the canal lining are complex, which make it difficult to simplify analytical models; thus, research on analytical solutions for the response of canal lining under soil frost heaving are limited. First, trapezoidal canal frost heave characteristics were analyzed, and a new analytical solution based on the elastic foundation beam model considering tangential contact conditions at the lining–frozen soil interface was proposed. This solution is used to calculate the normal and tangential frost heave forces on the lining. Then, the proposed analytical solution and the traditional solution using an Euler beam on a Winkler foundation were compared with two case histories including field measurements and numerical simulations. The new solution agreed with the case histories and predicted the frost heave and stress of the lining, while the traditional solution neglecting tangential contact predicted only the normal lining frost heave, which was overestimated. Finally, the effects of the tangential and normal foundation coefficients, groundwater depth, canal size and uplift displacement at slope toes on canal frost heaving were investigated by parametric analysis. The proposed analytical solution can help engineers design canals using structural deformation and strength indexes and is applicable to frost heave response analyses of concrete face dams, slab foundations, culverts, and retaining walls.

Full-field shingle uplift measurements using StereoDIC: Comparison of single and double sealant three-tab shingle responses when subjected to hurricane velocity winds

For the first time, the vision-based measurement method Stereo Digital Image Correlation (StereoDIC) is applied successfully to quantitatively assess the response of asphalt shingles installed in a model roofing system and subjected to hurricane velocity winds. By mounting a low profile asphalt-shingled plywood roof facsimile without building firmly to a rigid steel frame and supplying sustained winds of 67.1 m/s perpendicular to the leading edge region, StereoDIC measurements were obtained at 1 Hz to measure the full-field uplift displacements for shingles sealed using either single or double sealant strips. By varying the sealant activation process (time and temperature), the effect of installation in winter and summer seasons is also quantified throughout the wind loading process. Results indicate that with lower temperature sealant activation, both single and double sealant shingles sustained catastrophic failure within a short time when the wind speed reached 67.1 m/s, with the double sealant system lasting for about 500 s; visual inspection of the separation surfaces for the low temperature activation showed large specular reflecting regions, indicating either no bonding or minimal adherence. For a higher sealant activation temperature, (a) both single and double sealant shingles remained intact for more than 2 h in 67.1 m/s wind speeds, with no sealant separation observed and (b) displacements for the shingle with double sealant strips were significantly lower than for the single sealant system, confirming the efficacy of a double sealant strip system. As a general observation, StereoDIC measurements clearly show that shingle uplift displacement is not constant across the width of a shingle tab, with the edges of the shingle (tab cutout regions) having significantly larger uplift displacements that may serve as sealant separation initiation sites.

Uplift Performance of Plate Anchors in Cement-Stabilised Aeolian Sand

Comparative pullout tests were carried out on model plate anchors in uncemented aeolian sand (UAS) and cement-stabilised aeolian sand (CAS) with different embedment ratios of the embedment depth (H) to the width (D) of the plate to examine the effectiveness of the insertion of cement in aeolian sand to enhance the uplift performance of plate anchors. Experimental results demonstrated that significant increases in failure resistance and uplift stiffness can be achieved, irrespective of embedment ratios of H/D, when a relatively small amount of cement (an optimal cement content of 6% by weight of dry aeolian sand determined by direct shear test in this study) was added to the aeolian sand backfill. However, distinct load–displacement responses were observed in all the tests on the model plate anchors embedded in CAS and UAS backfills: two-phase of pre-peak and post-peak behaviour in CAS and three-phase of initial linear, nonlinear transition to peak uplift resistance, and post-peak behaviour in UAS; failure of the former started at tiny displacements and that of the latter appeared at large displacements. Therefore, the significant increases in uplift failure resistance and pre-peak uplift stiffness were limited to relatively low uplift displacements because of the brittle nature of the improved CAS backfills shear strength characteristics.

Modeling uplift failure of pipes buried in sand using material point method

Uplift of underground pipelines is frequently encountered in urban tunneling and landslide-prone areas, seriously affecting their structural integrity and serviceability. However, the uplift resistance of pipelines and the failure modes of surrounding soils under permanent ground deformation have not been fully understood. In numerical simulations, the element distortion phenomenon significantly restricts the application of mesh-based numerical methods in addressing such issues. In this paper, the material point method (MPM) is used to investigate the upward movement of pipes buried in dense sand and the mobilization of uplift resistance. Two typical constitutive models are used, and their model parameters are estimated using state index, whose values are dependent on relative density and confining pressure. The post-peak softening characteristics of soil have also been considered and a series of numerical simulations are conducted. The results from physical model tests in the literature are used to verify the numerical model. It is found that the experimental and numerical results agree well with each other in terms of force–displacement relationships and soil deformation patterns. The effects of burial depths on the uplift failure mechanism of pipes are investigated in detail. The numerical results show that for shallow burial conditions, the inclination of shear bands is approximately identical to the maximum dilation angle of sand at the peak resistance and then decreases when the pipe undergoes larger uplift displacement, leading to a reduction of uplift resistance. For deeply buried pipes, the inclination of shear bands does not change in the post-peak phase, but a failure pattern with a series of progressive shear zones gradually forms, which is analogous to the bearing failure modes of foundations. At large uplift displacements, significant flow-around phenomena are observed for various burial depths of the pipe. Finally, the distribution profiles of earth pressure acting on the pipe surface are explored. It is found that the normal pressure concentration area mainly rangesfrom 0°–45° from the pipe crown. In comparison, the tangential contact pressure primarily concentrates on the pipe shoulder within 15°–45° from the crown. Finally, the peak uplift forces and corresponding failure modes within the maximum embedment ratio of 50 are investigated to provide practical guidance for the design of underground pipelines.

Water pressure evolution and structural failure characteristics of tunnel lining under hydrodynamic pressure

With the frequent occurrence of heavy rainfall, the lining cracking, leakage, and buckling collapse accidents of water-rich mountain tunnels are becoming increasingly prominent. A large amount of surface water rushing into the tunnel in a short time and exceeding the drainage capacity of the tunnel is an important reason for the occurrence of water pressure diseases. To ascertain the failure characteristics of the lining structure under the condition of surface rainfall recharge and tunnel drainage, we designed a seepage model test system. The evolution law of water pressure behind lining, vertical displacement of invert and failure characteristics of structure under water pressure were studied. On this basis, the influence of the optimized drainage tunnel structure on the water pressure of the lining was further studied. The results show that the water pressure of the lining invert cannot be effectively reduced through the drainage system when the conventional drainage scheme is adopted, and the invert deforms and gradually cracks and fails under the action of hydrodynamic pressure. The cracking sequence of the lining structure is the invert center, the sidewall foot, the vault, and the sidewall. The type of cracks is mainly longitudinal, supplemented by circumferential and oblique. When the optimized drainage scheme is adopted, the water pressure at the bottom of the invert and the uplift displacement of the structure are significantly reduced, ensuring the safety of the lining structure.

Impact of earthquake direction and liquid sloshing on column supported tank

The finite element method is adopted to obtain the seismic responses of column supported tank including the anchored one and the resilient one by ANSYS. The dynamic behaviors are discussed under earthquakes from different directions, named 0° and 45°. And then the liquid sloshing is illustrated to observe its impact on both tanks. The liquid is modeled by two different methods with fluid element and solid element to make the structure with and without the liquid sloshing effect. The uplift in the resilient tank is built by contact algorithm to achieve the vertical movement of the column system in positive direction. The parameters studied are the displacement of the structure and the liquid, the stress distribution along the height of the wall, the stress level of walls and columns, the base shear and the overturning moment, the uplift displacement. The results show that 0° earthquake amplifies the seismic responses of both tanks in most cases, which should be paid attention to in engineering. The liquid sloshing effect is generally unfavorable to the anchored tank but helpful to anti-seismic performances of the resilient tank. However, the resilient tank has better dynamic properties and will not suffer plastic failure in the main structure even under extremely rare earthquake except for replaceable dampers.