Active Ground Fissure Research Articles

Analytical Solution of the Mechanical Response of a Shield Tunnel Crossing an Active Ground Fissure Zone

Analytical Solution of the Mechanical Response of a Shield Tunnel Crossing an Active Ground Fissure Zone

Deformation and Failure Analysis of the Urban Cloud Rail Crossing an Active Ground Fissure in Xi’an, China

Deformation and Failure Analysis of the Urban Cloud Rail Crossing an Active Ground Fissure in Xi’an, China

Model test of prefabricated underground utility tunnel crossing active ground fissures

The establishment of an underground utility tunnel system has been projected for Xi'an, the transportation center in western China. However, this city are suffering the damage that ground fissures have inflicted on the subterranean engineering. The traditional cast-in-place underground utility tunnel could not well adapt to thr activity of ground fissures. The activity of ground fissures may result in numerous damages such as tunnel fractures and waterproof failure. To reduce such hazards, a large-scale physical model was set up to study the stress and deformation characteristics of the prefabricated underground utility tunnel crossing active ground fissures. The findings from the analysis of the soil pressure, distribution of soil cracks, and structure deformation show that waterproof rubber is more susceptible to failure due to a large interface tension displacement occured near the ground fissure.

Numerical Simulation Analysis of the Impact of Active Ground Fissures on Damage to Urban Overpasses

Urban overpasses, being long-span linear projects, are inevitably affected by ground fissure activities. This study focused on the three-span continuous overpass, and used the MIDAS GTS NX finite element simulation software to establish the model of an urban overpass crossing active ground fissures with different straddling ground fissure positions and hanging wall settlements. This study analyzed the deformation and stress characteristics of soil and bridges induced by ground fissures under different working conditions. The results demonstrate that the soil’s displacement response is mainly concentrated near the ground fissures, and the displacement changes decrease with increasing ground fissures. Ground fissure activities redistribute the stress inside the beam and pier, resulting in the tilting of the pier. When the fissure activity is small, the use of multi-span beams to straddle the ground fissures can effectively reduce the influence of ground fissure activities on bridge deformation. However, when the fissure activity is significant, the bridge may be damaged, and excessive deformation of the bridge and piers may not meet code requirements. In such cases, the multi-span beam structure type should be changed to adapt to the ground fissure activity. The research results provide significant reference value for urban traffic planning and overpass design.

Theoretical analysis of the overburden stratum load on metro tunnel induced by active ground fissure

Ground fissures are the most common urban geohazard in Xi’an, China. The activities of ground fissures often trigger stratum dislocation, which do harm to the built metro tunnels. Thus, tunnel structures must be designed to reasonably withstand the stratum load during ground fissure activity. In this study, a simplified solution was proposed to calculate the stratum load and the vertical stress of metro tunnel under the action of active ground fissure. The stress characteristics of metro tunnel subject to ground fissure dislocation were analyzed and its progression was divided into three stages, the initial elastic stage, the local void area stage, and the maximum void area stage. The vertical stress of the tunnel at each stage was calculated according to the corresponding mechanical characteristics. Compared with results from numerical simulations, the calculation method developed in this study, which accounts for the stratum holding effect and slip plane, is reliable and reasonable. Additionally, according to the variability of stress magnitude and the impacted range, the tunnel is roughly divided into four stress zones, namely, stability and influence zones in the footwall, and deformation and micro deformation zones in the hanging wall of the ground fissure. This theoretical analysis provides a reference for stratum load calculations and engineering design of metro tunnels crossing active ground fissures.

Deformation and failure analysis of metro shield tunnel induced by active ground fissure in Xi'an, China

Ground fissure is an important urban geohazard in Xi'an, China, which poses a security threat to Xi'an metro construction. In this paper, a 3D numerical model was performed to analyze the mechanical behavior of shield tunnel of Xi'an metro (line 8) crossing an active ground fissure. The results indicate that the lining structure near the ground fissure is in a tension–compression state. The deformations of tunnel and surrounding soil do not match owing to their different stiffness, and then the bottom of the tunnel in the hanging wall and the top of the tunnel in the footwall separate from the soil, resulting in the reduction of support from surrounding soil. The tunnel at the ground fissure is subjected to large shear force, and the structure presents segment dislocation and lining cracks around bolts when the ground fissure dislocation reaches 20 cm. The deformation and failure of shield tunnel orthogonally intersecting with ground fissure is in a shear failure mode. It is suggested that structural reinforcing measures such as special segments and bolts are needed within the influence area of the ground fissure.

Calculation of the Vertical Strata Load of Utility Tunnel Crossing Ground Fissure Zone

A ground fissure is a geological disaster in which the vertical dislocation of strata causes surface rupture. Ground fissures can cause extreme harm to the surface and underground buildings. Ground fissure activity can result in different settlement on the two sides of the strata, which will generate additional stress (pressure) that differs from the stress of the general stratum on underground structures across the ground fissure zone. It is essential to assess the effective stress of strata in the design of underground engineering structures across a ground fissure zone. The Xi’an ground fissure through a utility tunnel was focus of the research, and a physical model and data for oblique crossing of the 45° ground fissure were analyzed. A model of the utility tunnel structure was established, including the surrounding soil load as an active ground fissure environment. This model was used to calculate the vertical formation pressure of the overlying soil on the utility tunnel. A method to calculate the overlying load on the utility tunnel caused by ground fissure activity was proposed and compared with the calculation based on the A. Marston principle. The results showed that the ground fissure load calculation method based on the strata-holding effect can effectively calculate the earth pressure of the surrounding soil layer of the utility tunnel in the cross-ground fissure section. The results of this work provide guidance and reference value for the design of a utility tunnel in an area with the potential for a ground fissure.

The study of road deformation induced by ground fissure in Xi’an, Central China

Tremendous losses and threaten traffic safety were caused by ground fissures as it covers over half of the area of Xi’an, in China. This study summarizes the formation of ground fissures and found that variations in the dip angles and cross angles influence road deformation and cracking. Based on survey data, numerical simulation using MSC.MARC finite element software was conducted to analyze the impact of ground fissures on roads. The results show that the cross angle has a negative correlation with the deformation range and a positive correlation with the tensile and compressive stresses, plastic strain and shear stress. The dip angle has a negative correlation with the maximum tensile stress and plastic strain and a positive correlation with the vertical displacement of pavement, but it has little effect on the maximum compressive stress. It is recommended to take some engineering measures for prevention and treatment when road projects cross a ground fissure, such as avoiding ground fissures, changing the road structure, and establishing a monitoring system. These conclusions can serve as a reference for structural design and preventative measures for roads passing through active ground fissure zones.

Experimental Study on Deformation Mechanism of a Utility Tunnel in a Ground Fissure Area

This paper discusses the deformation mechanism of a utility tunnel crossing active ground fissures in Xi’an as observed in a physical model test. The purpose of this work is to confirm the precise effects of ground fissures on utility tunnels. The physical simulation experiment is carried out to measure the earth pressure and the strain relationship of the structure and the structural displacement. The structure appears to have been destroyed by torsion. The structural deformation located in the tunnel’s footwall was more serious than that in the hanging wall. However, at the top of the utility tunnel structure, the earth pressure in the footwall was less than that in the hanging wall. The increased range of the hanging wall at 0.3–1.5 m (the prototype within the range of 22.5 m) and decreased range of the footwall at 0.3–0.8 m (the prototype within the range of 12 m) were basically consistent with changes in the contact pressure at the structure’s bottom. This was roughly consistent with the main deformation zone of ground fissures mentioned in the specification, with the hanging wall at 0–20 m and footwall at 0–12 mm. Displacement meter data shows that the structure tends to deform to the lower right as the utility tunnel is “twisted” clockwise. These observations mark a notable departure from the previously published failure mode of metro tunnels under active ground fissures.

Land Subsidence and Ground Fissures in Beijing Capital International Airport (BCIA): Evidence from Quasi-PS InSAR Analysis

Land subsidence is a global environmental geological hazard caused by natural or human activities. The high spatial resolution and continuous time coverage of interferometric synthetic aperture radar (InSAR) time series analysis techniques provide data and a basis for the development of methods for the investigation and evolution mechanism study of regional land subsidence. Beijing, the capital city of China, has suffered from land subsidence for decades since it was first recorded in the 1950s. It was reported that uneven ground subsidence and fractures have seriously affected the normal operation of the Beijing Capital International Airport (BCIA) in recent years before the overhaul of the middle runway in April 2017. In this study, InSAR time series analysis was successfully used to detect the uneven local subsidence and ground fissure activity that has been gradually increasing in BCIA since 2010. A multi-temporal InSAR (MT-InSAR) technique was performed on 63 TerraSAR-X/TanDem-X (TSX/TDX) images acquired between 2010 and 2017, then deformation rate maps and time series for the airport area were generated. Comparisons of deformation rate and displacement time series from InSAR and ground-leveling were carried out in order to evaluate the accuracy of the InSAR-derived measurements. After an integrated analysis of the distribution characteristics of land subsidence, previous research results, and geological data was carried out, we found and located an active ground fissure. Then main cause of the ground fissures was preliminarily discussed. Finally, it can be conducted that InSAR technology can be used to identify and monitor geological processes, such as land subsidence and ground fissure activities, and can provide a scientific approach to better explore and study the cause and formation mechanism of regional subsidence and ground fissures.

Physical Modeling and Numerical Simulation of the Seismic Responses of Metro Tunnel near Active Ground Fissures

Ground fissures pose serious hazards to underground, as well as aboveground, structures. In underground railways, which are near ground fissures, the potential for disasters is even higher since tunnels face threats from fissure activities. To determine the interaction between a tunnel and ground fissure in the event of an earthquake, field surveys and data analysis were applied to study the activity and damage caused by the fissure. Shaking table tests and a numerical simulation model were used to understand the dynamic response of the fissure site and tunnel. The fissure site had a clear hanging wall effect, where the acceleration amplification was larger in the hanging wall than that in the footwall both on the surface and at the middle of the fissure site. The zone of influence was also wider in the hanging wall. The acceleration magnification factor increased with the burial depth and peak acceleration of the input earthquake. The peak ground acceleration (PGA) decreased with the burial depth on both sides of the fissure. The greatest PGA coefficient was obtained at the surface of the site. The vertical soil pressure was influenced by the metro tunnel and fissure. The vertical soil pressure was larger in the hanging wall, especially in the zone near the fissure, but was less near the tunnel. The horizontal soil pressure above the tunnel was less than that near the fissure. The results of this study are essential for the safe design of underground railway systems.

Dynamic Characteristics of Metro Tunnel Closely Parallel to a Ground Fissure

Shaking table model test and numerical simulation model were conducted on scaled tunnel model to investigate the mechanism and effect of seismic loadings on metro tunnel which is closely parallel to an active ground fissure. Key technical details of the experimental test were set up; for example, similarity relations, boundary conditions, sensors layout, and modelling methods were presented. Synthetic wave, El Centro wave, and Kobe wave were adopted as the input earthquake waves. Results measured from shaking table model and numerical model were compared and analyzed. It is found that the fissure increased the dynamic response features as accelerations and strains of the tunnel, especially in the part close to the fissure. Average incremental percentage of acceleration amplifying coefficient was 8.33% from the wall close to fissure than the symmetrical one. The short distance to fissure led to serious circumferential dynamic strain, while the distance to fissure influenced the axial dynamic strain less. The numerical analysis results have a good correspondence with those of the shaking table model test. The waves at the top of tunnel have more scattering and emission effect. The fissure increases the dynamic response of the tunnel close to it.

Dynamic characteristics of a ground fissure site

The seismic response of an active ground fissure site was simulated by a shaking table test and a FLAC3D numerical simulation model. Coupled dynamic ground motions of earthquake and fissure activity were loaded on the model. The characteristics of the fissure site, that is, the movement of the hidden fissure, the uneven subsidence, the acceleration and the lateral and vertical soil pressures, were monitored and analyzed. The following observations were made from this study. The subsidence of the hanging wall was greater than that of the footwall. The stretch caused by the uneven subsidence led to the appearance of the hidden fissure and the gradual widening of the fissure. The peak acceleration in the hanging wall was larger than that of the footwall. The PGA increased with the height of the site. The magnification coefficient of the PGA had the largest value in the fissure, and the magnification coefficient of the PGA decreased with earthquake intensity. The increments of lateral and vertical soil pressure also increased with earthquake intensity. The vertical soil pressure at the location of the fissure was the largest. These dynamic characteristics are vital to the safety design of underground structures in a fissure site.

Deformation of Linfen-Yuncheng Basin (China) and its mechanisms revealed by Π-RATE InSAR technique

The Linfen-Yuncheng Basin (LYB) in China is a region possessing severe geo-hazards, including active tectonic fault movement, land subsidence and ground fissures among others. Interferometric Synthetic Aperture Radar (InSAR) technique is applied to map surface deformation associated with various geo-hazards in this basin. The poly-interferogram rate and time-series estimator algorithm (Π-RATE) is used over forty-nine scenes of SAR data to generate the deformation maps over the entire LYB. The precision of InSAR results is around 3 mm/yr. Some active faults and ground fissures are successfully detected. The spatiotemporal characteristics of tableland uplift, faults displacement and basin subsidence are quantitatively monitored with InSAR technique ranging from 2 mm/yr to 142 mm/yr. Finally, the mechanisms of surface deformation regarding large scale Zhongtiaoshan fault, middle scale basin land subsidence and small scale ground fissures are discussed in terms of interseismic movement, underground water level changes and hydrostratigraphic heterogeneity.

Dynamic characteristics research of a ground fissure site at Xi’an, China

This paper studies the seismic response of an active ground fissure site subjected to earthquake by the shaking table model test. The settlement was induced by the earthquake in the ground fissure site. The settlement increased with the earthquake peak acceleration. The differential settlement has a third-order polynomial relationship with the earthquake intensity. The process of the settlement has three periods, including the rapid deformation stage, the stable deformation stage, and the accelerated development stage. The greatest settlement is in the hanging wall close to the fissure. The secondary fissures and new cracks developed and appeared during the earthquake. The high frequency component of the wave was reduced from the bottom to the top of the site and the low frequency component was amplified. The Fourier amplitude gradual increases correspond to the earthquake acceleration. The results discovery the relationship of subsidence, widen of fissure and the earthquake. It is contribute to the metro design of the fissure area.

Experimental study of a segmented metro tunnel in a ground fissure area

This paper studies the seismic response of a segmented metro tunnel with flexible joints passing through active ground fissures in Xi’an by shaking table model test. A coupling dynamic ground motion was generated in the test model. The tunnel acceleration, earth pressure and tunnel structure strain were monitored and compared. It was observed that each part of the tunnel has an independent movement with flexible joints. The tunnel located in the hanging wall has 3.17 times peak acceleration than that in the foot wall. Higher magnitudes of earth pressures were recorded close to the areas of the ground fissures. The earth pressure in the hanging wall was greater than that in the foot wall. The coupling loads increase the earth pressure. The strain in the middle of the tunnel arch was the largest. The strain at the bottom of the floor was the secondary. The one on the top of the arch was the smallest. The strain increased less in each section because the tunnel is divided into four parts by flexible joints, and no sharp strain increase close to the ground fissure was observed. The results indicate that the flexible joints can decrease the stress concentration. The tunnel with flexible joints can adjust to large deformations in the ground fissure areas.

Model Test of the Impact of Active Ground Fissures on Metro Tunnel

A model test was performed to investigate the impact of active ground fissure on metro tunnel. The test results show that under the action of active ground fissure, the metro tunnel behaviors as a cantilever elastic foundation beam, and the top is in tension and its bottom is in compression. The tensile parts are located in the foot-wall with the range 0.75～2.33D（D is tunnel diameter） distance from active ground fissure and the compressive parts are mainly located in the foot-wall with the range 3D distance from the fissure. When the settlement of hanging wall of ground fissure reaches 1cm（25cm in prototype）, the tunnel bottom appear cavity in the hanging wall and cracks in the foot-wall. With the settlement development of the hanging wall of active ground fissure the vertical soil pressure on the top of tunnel greatly increases and reduces at the bottom of tunnel in the hanging wall.

Model Test on Soil Stress and Displacement Changes Induced by Active Ground Fissure

With a large-scale physical model test of active ground fissure, the rules of the soil stress and displacement changes induced by active ground fissure are studied. The results show that, the active ground fissure causes soil stress and displacement field changes within a certain area, namely, soil stress reduce in the hanging wall, but increase in the foot wall. The farther from ground fissure the area is, the smaller the reduction and increase of soil stress caused by ground fissure movement. There are generally 4 soil stress distribution zones induced by active ground fissure, which are, original stress zone of the foot wall, stress increase zone, stress reduction zone and original stress zone of the hanging wall and among which, stress reduction zone is 1.0 to 1.5 times that of stress increase zone. The active ground fissure leads to abrupt displacement phenomena, taking the step shape at its both sides, and as the strata goes from deep to shallow, soil deformation area in section increases obviously. The influence area in the hanging wall is bigger than that in the foot wall.

Active ground fissures in Xi'an, China

Once the ancient capital of China (Chang'an) and currently known worldwide as the home of the Terracotta Army, Xi'an is an important, modern, industrial centre of northwest China with steel, textile, chemical and machinery factories and a population of over 2.5 million. It lies on the River Weihe, approximately 1100 km southwest of Beijing in the Province of Shaanxi, of which it is the capital (Fig. 1). The surrounding valley is intensively farmed and is one of the main growing areas of northwest China. Climatically the area is part of humid and sub-humid, warm, temperate, north China. Several major crustal faults occur in the Xi'an area and form a fault-bounded, depositional basin of Early Tertiary age on the southwest part of the Huabei plate. The latest fill comprises up to 700 m of fluvial, lacustrine and loessic deposits of Late Tertiary to Recent age. There are three distinct river terraces on the broad flood plain of the River Weihe and additional terraces on the foot slopes of the Qinling Dabie Mountains which form the southern margin of the valley. On the hills surrounding the valley, to the north and south, there are fine grained, clayey, loess deposits of Late Pleistocene age lying on Middle Pleistocene loess. The main loess deposits are found to the north on the loess plain whose southern margin forms the northern boundary of the valley. The area is tectonically active and extension of the Xi'an region has resulted in the formation of a number of active