Vertical Earth Pressure Research Articles

Analytical solution of overlying pressure for shallowly buried underwater box tunnel: A case study of box jacking in Suzhou, China

Accurately predicting the overlying pressure is crucial for determining an appropriate cover depth of underwater box tunnels to avoid the uplifting failure. Based on the project of box jacking crossing the Beijing-Hangzhou Grand Canal in Suzhou, the characteristics of overlying pressure variation during tunneling are investigated. The monitoring results reveal that the fluctuation of overlying pressure is weakened during the rapid tunneling process. A modified analytical model for vertical earth pressure is conceived, in which the active and passive limit states for multi-layered soils are both considered. The probable range of overlying pressure obtained by the proposed model is suitable to cover the actual values. The anti-floating behavior of underwater box tunnels for two different working conditions is discussed by calculating the minimum cover depth. Using the calibrated analytical models, a parametric study is conducted to explore the influence of injection pressure, hardened slurry unit weight, soil internal friction angle, soil cohesion, and tunnel geometry. It is found that the injection pressure during the construction process is crucial for determining the necessary cover depth, and the change of box tunnel height makes it easier to trigger the variation of minimum cover depth.

Research on the method of identifying vertical earth pressure of hinged prefabricated culvert box culvert on the top slab

In China, several expressways have been designed as prefabricated box culverts with hinge connections, which have different structural features from the prefabricated culverts in other countries. The difference would contribute to the culvert–soil interaction of prefabricated box culverts, which could affect the earth pressure on the culvert. Based on the field test and numerical simulation method, a hinged prefabricated box culvert (HPBC) with a span of 4 m and a rise of 4 m was investigated, which was applied to the Xi-Yu expressway in China. The objective of this research was to investigate the vertical earth pressure on the top slab of the HPBC culvert at different backfill heights through the field tests. The FLAC3D software was employed to conduct further analysis of the effects of backfill height, backfill modulus, and foundation modulus on the vertical earth pressure on the top slab of HPBC. The differences between the HPBC and monolithic box culvert (MBC) were also examined. Furthermore, a revised method for calculating the vertical earth pressure on the top slab was put proposed and compared with the AASHTO method for calculating earth pressure on the top of culverts and the values taken from the Chinese culvert design code. The proposed method is capable of improving the accuracy of the earth pressure approach, making it more representative of actual conditions. Subsequently, the sensitivity analysis of backfill height, backfill modulus and foundation modulus to the vertical earth pressure concentration coefficient of the top slab was carried out by using the principle of orthogonal array analysis and the modified calculation method proposed in this paper. The findings of this study offer valuable insights into the determination of culvert top earth pressure of HPBC.

Method of Average Vertical Earth Pressure for HFCCTs Based on Differential Settlement

AbstractThis paper presents a modified and simplified calculation method, taking into account the differential settlement between the soil columns surrounding the cut-and-cover. High-filled cut-and-cover tunnels (HFCCT) are usually subjected to high earth pressures above the top of the CCT due to an ultra-high backfill. However, the estimation methods for earth pressure above the top of CCT are ambiguous. Through the theoretical analysis of the average vertical earth pressure (AEP) at the top of the CCT, it is found that an additional earth pressure above the top of the overburden pressure is induced, and the magnitude is related to the differential settlement between interior and exterior soil columns. Thus, through a combined theoretical derivation and numerical analysis, a modified formula is proposed. The results show that the vertical earth pressure increment above the top of CCT can be linearly correlated to the differential settlement. In addition, the correlation needs to be calibrated by considering several effects on sites, such as slope angle, groove-width ratios, cross-sectional shape, and the type of backfill. The change in influencing factors has no effect on the function type of the p−δ fitting curve, but it will affect the coefficient k.

Experimental analyses of high-filled cut-and-cover tunnel for reduction of the earth pressure

ABSTRACT The pressure distribution over buried structures like pipes and tunnels are considered a main factor in the economic design of such structures. This study shows the effect of using crumb rubber mixed with sand and geogrid layers to enhance the soil pressure distribution over that buried structure. That method is titled a high-filled cut-and-cover (HFCCT) construction method. Crumb rubber particles pieces mixed with sand as a lightweight fill material (LFM) in HFCCT are used to reduce the vertical earth pressure (VEP) on that buried tunnel. Geogrid reinforcement layer above the HFCCT system to strengthen the soil layers above the tunnels were implemental. A physical model is built to simulate such conditions by applying external loads to the treated soil layers above the tunnel. The strains are measured on the external body of the tunnel, while the soil pressure is assessed through pressure gauges around the tunnel. The results obtained from the crumb rubber models are compared with those obtained from the geogrid model. It was deduced that using crumb rubber and geogrid, reduces the earth pressure above the cut-and-cover tunnel (CCT). As compared to the use of geogrid, the utilization of rubber as a substitute for soil results in a 27% drop in pressure. The obtained results show that the use of geogrids in sandy soils leads to uniform stress, while using rubber sand could reduce the maximum stress of the soil above the tunnel.

Seepage–Deformation Coupling Analysis of a Core Wall Rockfill Dam Subject to Rapid Fluctuations in the Reservoir Water Level

Core wall rockfill dams are susceptible to cracking at the dam’s crest, as well as collapse and settlement of the rockfill during storage and operation periods, particularly due to rapid fluctuations in the water level in pumped storage power stations. Most studies on the impact of fluctuations in the reservoir’s water level on dam deformation have considered fluctuations of less than 5 m/d, while pumped storage power stations experience much larger fluctuations. Additionally, the seepage and stress fields within the dam’s rock and soil interact and influence each other. Few studies have used the coupling theory of seepage and stress to analyze seepage and deformation in core wall rockfill dams. To address these issues, a finite element model using seepage–stress coupling theory was utilized to investigate the variations in the phreatic line, earth pressure, and deformation of a core wall rockfill dam due to rapid fluctuations in the reservoir’s water level. Additionally, the results of the finite element simulation were compared with and analyzed alongside safety monitoring data. The results indicated that, upon a sudden decrease in the reservoir’s water level, there was a lag in the decline of the phreatic line in Rockfill I, which created a large hydraulic gradient, resulting in a reverse seepage field on the dam’s slope surface and generating a drag force directed upstream. Consequently, a significant concentration of stress occurred on one-third of the upstream slope surface of the dam and the seepage curtain, and the increase in horizontal displacement was substantially greater than the increase in settlement from one-third of the rockfill’s height to the dam’s foundation. The deformation was more sensitive to the lowest water level of the reservoir rather than to the fastest rate of decline. Sudden rises in the reservoir’s water level result in decreased horizontal displacements and settlement of the dam. Amid rapid fluctuations of the reservoir’s water level, changes in the vertical earth pressure were more pronounced at the bottom of the core wall than in its midsection. Compared with the core wall, variations in the vertical earth pressure in the upstream and downstream filter layers were minor at similar elevations. A peak horizontal displacement of 6.5 mm was noted at one-third the height of Rockfill I, with the greatest increase in settlement of 3.5 mm at the dam’s crest. To ensure a project’s safety, it is crucial to control the elevation of the lowest point during a sudden drop in the reservoir’s level and to carefully monitor for cracks or voids within approximately one-third of the dam’s height in Rockfill I and at the dam crest. This study’s results provide a scientific basis for assessing core wall rockfill dams’ health and securing long-term safety at pumped storage power facilities.

Long-term stress characteristics of a box culvert with a load reduction system using geogrids and EPS under high fill

Laying geogrids and compressible materials, such as expandable polystyrene (EPS), on the tops of culverts under high fill can improve the stability of the fill and reduce the earth pressure on the tops of culverts. The creep of geogrids and compressible materials under high fill affects the stress state of culvert–soil systems. However, the long-term behaviour of culverts with geogrids and EPS is not clear. This paper investigates the long-term behaviour of culvert–soil interactions under high fill, specifically focusing on the creep effects of geogrids and EPS boards. A novel mechanical model for determining the long-term stress characteristics of culverts is proposed based on limit equilibrium theory. A comparison with finite difference simulation results was conducted to validate the proposed model. The findings reveal that the vertical earth pressure on the culvert top gradually transfers to the culvert side, exhibiting a nonlinear decrease over time. Moreover, the horizontal earth pressure on the culvert sidewall exhibits nonlinear growth with time, decreasing incrementally with depth. The maximum horizontal earth pressure on the culvert sidewall increases by 12.5% postconstruction, emphasizing the importance of accounting for the creep effects of geogrids and EPS boards in engineering design to prevent structural issues.

Mechanical Behavior of Geogrid Flexible Reinforced Soil Wall Subjected to Dynamic Load

The geogrid flexible reinforced soil wall is widely used in engineering practice. However, a more comprehensive understanding of the dynamic behavior of reinforced soil wall is still required for a more reasonable application. In order to explore the mechanical behavior of a geogrid flexible reinforced soil wall, the model test was carried out to investigate the dynamic deformation of geogrid reinforced soil wall subjected to a repeated load. The numerical simulation was also conducted for comparison and extension with regards to the earth pressure and the reinforcement strain. The change rules for the deformation of the wall face, the vertical earth pressure and the reinforcement strain subjected to dynamic load with four frequencies (4, 6, 8 and 10 Hz) and four amplitudes (30–60, 40–80, 50–100 and 60–120 kPa) were obtained. The factors that affect the mechanical behavior of geogrid flexible reinforced soil wall were analyzed. The results show that the dynamic deformation characteristics of reinforced soil wall are affected by the number of vibrations, the amplitude of dynamic load and the frequency of vibration. The maximum lateral displacement of the reinforced soil wall occurs on the third to the fifth layer. With an increase in dynamic load amplitude, the development of dynamic deformation gradually increases, and after a cumulative vibration of 200 × 104 times, the cumulative lateral deformation ratio and the cumulative vertical deformation ratio of the wall face is less than 1%. The vertical earth pressure of geogrid flexible reinforced soil wall increases partially along the length of the reinforcement, and the vertical earth pressure of the third layer is basically unchanged when subjected to a dynamic load. With an increase in vibration number, the change in the reinforcement strain of the third layer is more complex, and the change rules of the reinforcement strain of each layer are different. The reinforcement strain is small, with a maximum value of 0.1%.

Laboratory experimental study of the forming and failure mechanisms of soil arching during EPBS tunnelling in sand

The effect of soil arching often leads to delayed ground collapse disasters when the tunnelling instability of earth pressure balance shields (EPBS) in sand. To reveal the formation and evolution of soil arching in sand, a laboratory-scale EPBS tunnelling model test was conducted. This EPBS tunnelling system simulated the entire process of shield tunnelling, which includes stable tunnelling, tunnel face instability, and ground collapse. The application of multi-field monitoring and three-dimensional scanning has revealed the influence of soil arching on sand layer collapse. The results indicate that: (1) Controlling the actual sand discharge rate to approach the theoretical rate can achieve stability of the tunnel face during the excavation process; (2) Maintaining higher soil pressure on the cutterhead can alleviate the loosening of the sand layer ahead; (3) The loosening zone in the vertical direction of the excavation section is significantly larger than that in the horizontal direction; (4) After the loose zone develops to the surface, each failure of the soil arching will cause significant surface subsidence, which can serve as a precursor to sudden ground collapse. The study provides a reference for the safe construction of tunnel engineering in sand.

Numerical Simulation of Polymeric Strap Material Reinforced Walls Under Seismic Excitation

This paper presents a comparison between the two-dimensional finite element and experimental results of shaking table tests on six one-third-scale polymeric strap or polymeric geostrip reinforced walls performed under seismic excitation at given peak ground accelerations [Formula: see text]. The effects of initial tangent stiffness or the stiffness of polymeric strap material [Formula: see text] and the slope angle of the cohesionless backfill material [Formula: see text] on the maximum relative displacement, [Formula: see text], of the reinforced earth wall, the values of the horizontal incremental dynamic earth pressure [Formula: see text] with distributions, acceleration responses, horizontal dynamic active earth pressure coefficient [Formula: see text] and maximum dynamic tensile forces [Formula: see text] were assessed in this study. Moreover, the vertical dynamic active earth pressure coefficients [Formula: see text] and the angles of the resulting dynamic active force with horizontal [Formula: see text] were predicted from the numerical analysis. Closely matched responses between the experimental and numerical studies were attained. Data obtained from experimental and numerical studies illustrated that increasing the slope angle of the cohesionless backfill material resulted in an increase in the values of horizontal displacement in the walls, and in dynamic earth pressure and root mean square acceleration [Formula: see text]. Increasing the stiffness of the reinforcement material caused a decrease in horizontal reinforced earth wall displacement and increases in dynamic earth pressure. In addition, the conventional pseudostatic limit equilibrium methods overestimated [Formula: see text] values, whereas they underestimated [Formula: see text] values, and the recommended [Formula: see text] values by current design codes were not found to be compatible with the numerical and experimental results.

Experimental investigation of the effect of using expanded polystyrene geofoam and geogrid in different forms on vertical earth pressure on high-filled cut-and-cover roadway tunnel

Experimental investigation of the effect of using expanded polystyrene geofoam and geogrid in different forms on vertical earth pressure on high-filled cut-and-cover roadway tunnel

Automatic monitoring and structural stress analysis during ultra-large onshore caisson sinking construction

During the sinking process of ultra-large onshore caisson, the structural stress of caisson will change significantly due to the changes of earth pressure, end resistance, water level in caisson and attitude of caisson. Based on the south anchoring onshore caisson project of Nanjing Longtan Yangtze River Bridge, the structural stress analyses were carried out based on the automated caisson monitoring data. The results show that the automated monitoring system can acquire the key data of caisson in real time and efficiently, and the monitoring results reflect the structural stress and displacement characteristics in different construction stages. The vertical earth pressure at the bottom four corners of the caisson is significantly greater than the other positions, indicating that there is an obvious stress concentration phenomenon at the four corners. The stress at the bottom of the horizontal earth pressure monitoring is smaller than that at the middle and bottom of caisson, which verifies the existence of stress disturbance area around the cutting. Steel shell concrete at the bottom of partition wall is the weakest position of caisson structure, and the structural safety risk is higher from the first casting to the second sinking. If the risk of tensile cracking occurs in the process of casting, each diagonal can be carried out several times to make full use of the structure's own resistance to reduce the development of tensile stress. The conclusion can be used for reference in the design and construction of similar projects.

Multi-Parameter Fiber Bragg Grating (FBG)-based Sensor Fabricated using 3D Printing Technology for Precise Measurement of Vertical Earth and Pore Pressure

Multi-Parameter Fiber Bragg Grating (FBG)-based Sensor Fabricated using 3D Printing Technology for Precise Measurement of Vertical Earth and Pore Pressure

Vertical Earth Pressure for a High-Filled Cut-and-Cover Tunnel: Site Measurements and DEM Simulations

Vertical Earth Pressure for a High-Filled Cut-and-Cover Tunnel: Site Measurements and DEM Simulations

Experimental Study and Numerical Simulation of the Effect of Rigid Pile Composite Foundations on Slab Culverts

For culverts installed in soft soil, the rigid composite pile foundation is used for soil treatment, and the stresses around the culverts are complicated. Centrifuge experiments and numerical simulations are conducted to investigate the vertical earth pressures and soil settlement over a slab culvert under high backfill in soft soil, and the foundations are treated with rigid composite piles. The influences of lateral pile length and pile spacing on the earth pressures at the top of the culvert are analysed, and they have significant effects on the vertical earth pressure coefficients. It also indicates a strong correlation between the backfill height and the vertical earth pressure coefficients. For a high-backfill culvert, there is a uniform settlement surface where the settlement of the interior and exterior soil prisms is at the same level. According to the experiments, the height of the uniform settlement surface and the vertical earth pressures decrease with increasing the lateral pile length and pile spacing. Numerical simulations were conducted using finite element software Midas GTS to evaluate the performance of the experiments. Further, recommendations for selecting an appropriate pile composite foundation for slab culvert in soft soil are provided.

Seismic response of utility tunnel in horizontal nonhomogeneous site based on improved discrete element method

During the construction of the utility tunnel, it is inevitable to cross a horizontal nonhomogeneous site, which adversely affects the seismic resistance of the utility tunnel. This study investigates the dynamic response and damage mechanism of both the utility tunnel and surrounding soil under seismic action through shaking table tests and improved discrete element numerical methods. Firstly, a scaled model of the utility tunnel was constructed and subjected to shaking table tests. Then, an energy-based differential quadrature method (DQM) and Newmark-β method were derived and applied to the discrete element to construct the tunnel numerical model. The vertical displacement, increment in earth pressure, relative slippage between the tunnel and soil, as well as strain within the tunnel were analyzed in detail, and the response mechanism of the tunnel and the surrounding soil was revealed by using the improved discrete element method. It was observed that the sidewall earth pressure increment follows an approximately parabolic distribution; higher flexibility ratios generally result in larger deformations of structures; a significant impact on tunnel deformation during large earthquakes is caused by relative slippage between soil and tunnels. The intrinsic relationship between the vertical displacement, earth pressure, relative slippage and strain was investigated to provide a basis for the seismic rescue and seismic design of tunnels.

Experimental study on the mechanical behavior of buried steel pipeline subjected to the local subsidence

Localized subsidence of soil layer is a typical geological disaster for buried long-distance oil and gas pipelines, which seriously threatens the safe operation of oil and gas pipelines. Therefore, a series of large-scale model tests are performed to investigate the mechanical response of the buried pipe induced by surrounding soil when the localized soil layer sinks. Results indicate that the subsidence height has a relatively greater impact on pipe strain and soil pressure than the subsidence range. Moreover, the distribution of the pipeline strain presents obvious regional characteristics and is divided into subsidence regions, non-subsidence affected regions, and non-subsidence unaffected regions. With the increasing moisture content of the backfill, the strain of the pipeline and the earth pressure around the pipe was reduced. In addition, the modified Marston earth pressure formula is proposed to estimate the vertical earth pressure on the top of the pipeline. The vertical earth pressure calculated using the proposed method fits well with the test results.

Analytical solutions of limit support pressure and vertical earth pressure on cutting face for tunnels

This paper focuses on theoretical analytical models to calculate the limit support pressure and vertical earth pressure on the cutting face for tunnels. The failure zone is divided into two parts: a sliding failure zone and an upper loosen zone, and the limit support pressure calculation equation is derived. To verify the rationality of the theoretical model, it was compared with the existing theory, numerical simulation, and centrifugal test, and then the parameter analysis was carried out. The results show that the results of this paper agree well with the existing theory, numerical simulation, and centrifugal test. The inclination angle of the proposed mechanism is determined based on the results of the existing centrifuge test, and the recommended inclination angle is between 52° + φ/2 and 54° + φ/2. The method is proven to be safe and accurate. It can provide a theoretical basis for similar projects.

Case Study: Extension of MSW landfill with reinforced earth berm

This paper reports a case study of an extension design of an existing municipal solid waste (MSW) earth berm in Guangzhou, China. The berm has limited space for extension and was constructed during a rainy season. Due to the space constraint, the extended berm was designed with a steep slope 1.1 horizontal to 1.0 vertical (1.1H:1.0 V). Due to the rainy season, the new extended earth berm was built with a mix of gravel and sandy clay (i.e. Vgravel/Vclay = 50:50). To make the new berm design satisfies the stability requirement, it has been reinforced with geotextile layers within the berm and piles at the toe of the berm. A 2D finite-element analysis has been conducted to demonstrate the rationality of the design. The performance of the new berm was monitored using field sensors, which include the vertical and lateral displacements of the berm, vertical earth pressure of the berm, and tensile strain of the geotextile layers during and after the berm construction. Numerical and field tests results show that the failure surface appears along the interface between the old berm and the horizonal displacements are mainly observed in the new berm. The results of this study proven that a steep slope berm with geotextiles reinforcement can resistant the load from extended MSW landfill, which can provide a guidance for the design and construction of the extension of MSW landfill.

Analysis of face stability at the launch stage of shield or TBM tunnelling using a concrete box in complex urban environments

An emerging construction method using a concrete box can effectively reduce the risks such as face collapse and extrusion at the launch stage of shield or tunnel boring machine (TBM) tunnelling. It occupies a small construction plant and can be applied to complex urban environments, especially in mountainous cities. However, the failure mechanisms of the tunnel face at the launch stage of the novel method are still not properly understood. Based on the upper-bound theorem of the limit analysis (LA), two multi-block failure models are proposed in this work for tunnelling launch in semi-infinite body and in areas with slope overburden. The limit equilibrium (LE) method is used to obtain the vertical earth pressure of upper finite soil mass considering the soil arching effect. The comparisons of the support pressure, failure zone and dip angle of the slip surface obtained from the proposed models with the results of numerical simulations and previous studies indicate that the proposed approach provides realistic and satisfactory predictions. The effects of soil cohesion, internal friction angle, slope dip angle, reduction coefficient and the ratio of tunnel diameter to overburden width are further assessed. The proposed models were applied to two practical engineering cases to determine reinforcement measures using grouting and pipe-roof methods required during the tunnelling launch, and were demonstrated to be able to provide useful guidance for the practical operations.

A 3D torus-slice model for limit equilibrium analysis of shield tunnel face under soil arching effect

This paper proposes a torus-slice model to estimate the tunnel face critical support pressure, (σcrit) from the shield machine under the influence of soil arching. The failure envelope of the tunnel face is created by a cluster of discrete points using a spatial discretization technique. The vertical earth pressure loaded on the failure soil mass in front of the face is determined by an arching mechanism based on the rotation trajectory of the major principal stress. The tunnel face support pressure distribution is derived from the stress interaction using a stepwise method between the horizontal slices divided from the torus. The comparisons between the centrifuge tests and analytical solutions demonstrate the accuracy of the proposed model. The pressure distribution is further validated by the results of a FLAC3D model and analytical solutions. The failure envelope is compared to the geometry of the shear band from the numerical model, indicating the rationality of the proposed method. With an improved geometry considered, the proposed torus-slice model demonstrates the advantages over the classical silo-wedge model. Finally, the effects of material and geometrical parameters on a required tunnel face pressure are discussed. The results show that the soil internal friction angle φ’, cohesion c’, the soil-shield interface friction angle δ, and the geometric shape factor Tm all have significant effects on the tunnel face stability.