Earth Pressure Research Articles

Assessment of plasticity of muddy soil for earth pressure balance shield tunneling

This research delves into managing the plasticity of muddy soil in earth pressure balance (EPB) shield tunneling, crucial for ensuring tunnel stability and efficient sediment management in urban construction. The study utilizes a combination of a small-scale model experiment and a computer-aided engineering (CAE) analysis through the moving particle simulation (MPS) method to investigate how the plasticity of muddy soil, adjusted by mixing excavated soil with a bentonite solution, impacts the earth pressure within a tunneling chamber. The experimental setup meticulously simulates the tunneling process, measuring the variations in earth pressure that occur in response to the different states of plasticity induced by the agitation of the muddy soil. The findings reveal that earth pressure is a reliable indicator of the soil’s plasticity, significantly correlating with the slump value and vane shear strength, thus affecting tunnel stability and the operation of machinery. The CAE analysis, underpinned by MPS, accurately mirrors the experimental outcomes, endorsing its use for assessing and visualizing the plasticity and fluidity of muddy soil in tunneling scenarios. The results of this study demonstrate that MPS-CAE analysis is an effective tool for improving sediment management strategies and optimizing EPB shield tunneling operations, highlighting the critical role of soil plasticity in ensuring tunnel face stability and project success. This research reveals that earth pressure measured by the agitation blade can serve as a reliable indicator of the plasticity of muddy soil in the chamber. This enables real-time and on-site evaluation of soil conditions during EPB shield tunneling.

Influence of sand layer thickness on the collapse mechanism of tunnels in soil-sand-rock composite strata

Collapse is a severe event during metro tunnel construction, particularly in soil-sand-rock composite strata. Variations in the thickness of sand layers, owing to their high compressibility, flowability, and thixotropic properties, significantly impact the mechanical response and deformation of strata, which also directly determine the stability of tunnel excavation processes. Regarding the complexity of the engineering response of the soil-sand-rock composite strata, a series of model tests were conducted to reveal the collapse mechanism of the metro tunnel in the soil-sand-rock composite strata subjected to varying sand layer thickness in this paper. Meanwhile, the influence of sand thickness on the evolution of collapse form, the response of strata stress, and the variation of the displacement and strain fields were systematically discussed by the monitoring data from the miniature earth pressure cells and a two-dimensional full-field deformation measurement system. Moreover, the collapse evolution process was recorded by the industrial camera. The test results indicated that the horizontal displacement of the tunnel shoulders was more affected by the increase in sand layer thickness than the horizontal displacement of the haunches before the tunnel collapse. The high compressibility of the sand layer resisted the transmission of surcharge load to the rock layer. Once the overlying rock layer above the tunnel vault lost its bearing capacity, the thixotropy and flowability properties of the sand layer caused the collapse face to expand funnel-shaped to both sides. The collapse width of the sand-soil interface was proportional to the sand layer thickness. The greater the sand layer thickness, the weaker the ability to provide stable support for the foot of the temporary stratigraphic arch, further reducing the stability of the temporary stratigraphic arch and leading to a faster collapse rate of the composite strata. In general, the results of this research offer valuable guidance for preventing and controlling tunnel collapse in soil-sand-rock composite strata.

The Performance of a Circular Excavation Supported by a Prefabricated Recyclable Structure in a Full-Scale Test

Excavations for underground structures, such as working shafts, underground grain silos, and parking garages, are characterized by uniformity, consistent dimensions, large quantities, and strict timelines. Prefabricated recyclable supporting structures (PRSS) are gaining attention over traditional retaining structures due to their standardized design, efficient construction, and reusability, which suit such excavations better. To validate their performance, full-scale tests are conducted to analyze the deformation and stress characteristics of PRSS. The results show that the average maximum lateral displacement of supporting pile is 0.07% of the excavation depth (He), roughly half that of steel plate. Differences in ground surface settlement behind steel plates and the supporting piles are not as significant as those in their lateral displacements. While the displacement of the supporting piles is insufficient to induce soil movement into the active limit state on the non-excavation side, the circular excavation’s arching effect reduces the earth pressure on this side of the supporting piles below the active earth pressure limit. Furthermore, the earth pressure acting on the steel plates is lower than that acting on the supporting piles, suggesting the presence of a soil arching effect between two adjacent piles. These findings offer valuable insights for guiding the construction of PRSS.

Joints mechanical characteristics of prefabricated subway station considering bending stiffness difference

In prefabricated subway stations, the presence of joints leads to an uneven circumferential distribution of structural stiffness. However, there has been limited research focusing on the variability in bending stiffness of joints so far. Therefore, this paper proposes a theoretical framework to study deformation characteristics considering the differences in bending stiffness. This study aim to analyze the deformation characteristics of prefabricated structures, with a specific focus on the impact of variations in bending stiffness on the overall structural behavior. The research scope includes the calculation methods for the bending stiffness of joints, predicting maximum settlement of the top plate, and analyzing the influence of key parameters such as joint positions, geometric shapes, and dimensions, overburden density γ, lateral earth pressure coefficient λ, overburden thickness hf, and concrete density ρ on the joint bending stiffness. Results validate the reliability of the proposed method for calculating joint bending stiffness and demonstrate the key factors contributing to differences in bending stiffness.

Shaking table test for near-valley underground station: Influence of diaphragm walls

Diaphragm walls are commonly employed as a permanent support for the building of metro stations near urban valley, and in conjunction with the interior sidewalls of the station structure to withstand the pressure from surrounding soils. Despite their prevalent use, the effect of underground diaphragm walls on the seismic response of stations is not yet fully understood. In this paper, a series of 1-g shaking table tests is designed to investigate the seismic response of a near-valley station with underground diaphragm walls within the elastic range. Modeling the stratum-structure-diaphragm walls system is accomplished by employing granular concrete reinforced with galvanized steel wires and synthetic model soils, and a station without diaphragm walls is included, serving as a benchmark for comparative analysis to understand the influence of diaphragm walls on the seismic behavior of the station. The experiment was designed for three depth-to-width ratios (DWRs), i.e. 1/3, 1/4, and 1/8, of arc-shaped valley topography, as well as the seismic excitations for the test include actual seismic records with the amplitude of 0.2 g, 0.4 g, and 0.8 g, respectively. Results show that the underground diaphragm walls enhance the lateral stiffness of the near-valley station compared to structures without diaphragm walls, and thus significantly reducing the racking deformation of structure during earthquakes. The presence of diaphragm wall would decrease the amplification of dynamic earth pressure caused by valley effect at the structural sidewalls, and significantly reduce the lateral vibration and shear effect of the station near a valley with a larger DWR. Notably, bending moment response at the connection between the diaphragm walls and structural sidewalls are dramatically amplified under strong seismic loading, and such adverse effects gradually increase with the DWR of the valley.

Experimental response of a fusible PVC pipe with service connections to axial pullout

This paper investigates the axial pullout response of a fusible polyvinyl chloride (FPVC) main pipe with two service connections. A large-scale pullout experiment in dense sand was conducted to investigate the behaviour of service lines to axial pullout of the main pipe and the impact of service connections on the main pipe’s axial pullout resistance, axial force distribution, and moment distribution. The study assesses the response of both crosslinked polyethylene (PEX) and copper service lines as well as the role of goosenecks. Distributed fibre optic sensors (DFOS) have provided insight into the strain distributions along the main pipe and service lines. The experimental results have shown that service connections significantly increase the axial pullout resistance of the main pipe when compared to a previous test on an identical pipe without service connections. The movement of the service connections was found to reduce the earth pressure in a region behind the service connection. Hinging of the service saddles was observed to result in single curvature bending of the service lines. DFOS data along the main pipe has been used to approximate the individual load-displacement responses of the PEX and copper service connections.

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.

On-bottom stability of a radial fin integrated surface-laid pipe-section against vertical penetration

This study focuses on the on-bottom stability of surface-laid submarine pipelines during vertical penetration under thermal-induced buckling. Submarine pipelines are susceptible to buckling due to their high slenderness ratio, and the resistance to such displacement relies on pipeline stiffness and soil resistance. To investigate this, laboratory model tests were conducted using a scaled-down pipe section placed on a clay bed. The clay bed was prepared with remoulded Kaolin clay, ensuring uniform moisture content, and the model pipe was scaled down from a typical industry prototype. These tests were conducted in 2D plane strain conditions within a tank, equipped with observation windows to monitor pipe movement and soil behaviour. A significant improvement in the pipe section's penetration resistance and on-bottom stability was observed after incorporating fin in the pipe. The addition of fins altered the earth pressure distribution beneath the vertically loaded pipe, leading to a larger failure mechanism in the adjacent soil. Furthermore, the soil-surface-heaving progressed towards the tank wall with increasing angular distance between the radial fins. Thus, the research demonstrated the effectiveness of radial fins in enhancing the stability and resistance of submarine pipelines against vertical penetration, shedding light on potential improvements in submarine pipeline design and deployment.

Characteristics and modification mechanism of recycled waste silty clay slurry as the shield slag conditioner

The construction process of earth pressure balance shield (EPBS) generates a large amount of shield slag. In China, the conventional methods for treating shield slag involve crude landfill and stockpiling, resulting in increased cost and significant environmental issues. To expand the recycling of shield slag, this study proposes to use waste silty clay to completely replace bentonite as a conditioner in coarse-grained strata. Firstly, the physical properties of silty clay slurries are investigated with four additives. There are six modified silty clay slurries with good improved performance. Then, analyzing the rheological properties of six modified silty clay slurries, and verifying the feasibility of replacing bentonite slurry with modified silty clay slurry. Next, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Zeta potential were used to analyse the micromechanisms, molecular structures and molecular forces of 14 % bentonite slurry, silty clay slurry with a soil-water ratio of 1:1, sodium carbonate 3 % and sodium silicate 0.1 % in a silty clay slurry with a soil-water ratio of 1:1. Finally, the slump test was carried out to verify the improvement effect of the modified silty clay slurry on the shield slag. The results show that sodium carbonate modified silty clay slurry has a higher interlayer water content and greater ion exchange capacity. When the soil-water ratio is 1:1 and the concentration of sodium carbonate is 3 %, the apparent viscosity and shear force of the modified silty clay slurries are between those of bentonite slurries with a concentration of 10 % and 14 %. Additionally, the modified silty clay slurry showed a stable microstructure and good residue amendment effect, making it suitable as a soil conditioner during EPBS construction in coarse-grained strata. This study offers a viable approach for recycling EPBS slurry.

Evaluating densification effect of ideal compaction grouting in unsaturated soils by volumetric water content

Compaction grouting is primarily applied based on empiricism, and it is challenging to quantify its densification effect. To address this issue, five sets of laboratory model tests on ideal compaction grouting were conducted, with varying pressures from 400 kPa to 800 kPa, to quantitatively evaluate the densification effect in unsaturated soils. The response of surrounding soil during compaction grouting was monitored. The changes in dry density and void ratio induced by compaction grouting were obtained by monitoring volumetric water content to determine compaction efficiency. In addition, a model was developed and validated to predict the effective compaction range. The results show that soil dry density increased rapidly during compaction grouting before being stabilized at a consistent level. As expected, it is positively correlated with grouting pressures (GPs) and negatively correlated with the distance from the injection point. At higher GPs, the difference in densification effect around the injection point after compaction grouting was significant. Interestingly, variations in ultimate dry density and peak earth pressures perpendicular to the injection direction exhibited axisymmetric behavior around the injection point when comparing the dry density and earth pressure results. Furthermore, soil densification resulted in a decrease in suction. However, no significant effect of GP on suction at different soil positions was observed. Moreover, compaction efficiency decreased with increasing distance from the injection point, showing a strong linear relationship. In addition, the model results for the effective compaction range were basically consistent with the extrapolated values from the experimental results.

Intelligent optimization prediction of screw conveyor speed for earth pressure balance shield machine based on complete ensemble empirical mode decomposition of adaptive noise and deep learning

The excavation stratum of the earth pressure balance (EPB) shield machine is complex and changeable. For ensuring the excavated interface stabilization, the rotational speed of screw conveyor must be precisely controlled to maintain the balance of earth pressure in sealed cabin and to avoid accidents such as ground collapse or upliftment. A data-driven intelligent optimal model is presented by the paper, which organically integrates the complete ensemble empirical mode decomposition of adaptive noise (CEEMDAN), sparrow search algorithm (SSA) and long short-term memory (LSTM) network to achieve accurate prediction of screw conveyor rotation speed. Firstly, Pearson correlation analysis method is used to analyze the historical data of shield tunneling, and the tunneling parameters strongly related to the change of screw conveyor rotation speed are obtained as model input. Secondly, the CEEMDAN is used to decompose the obtained parameter data set into several modal components, and then the denoised data is reorganized to capture the changing characteristics of the original data and reduce the complexity of the data. Then, the parameters such as the learning rate of the LSTM network are optimized by using the strong global search ability of SSA to enhance the prediction precision further in the model. Finally, based on decomposed and reorganized data, SSA-LSTM is used to establish a rotation speed intelligent prediction model realize precise controlling of screw conveyor rotation speed. The simulation experiment is carried out by using the construction data of a section of Beijing Metro Line 10, and the results of three evaluation indexes of the model are given: Mean Absolute Error (MAE) is 0.02878, Mean Absolute Percentage Error (MAPE) is 0.00882 and R2 is 0.99909, which shows that the model has good prediction performance. The control effect of the method on the earth pressure balance of the sealed cabin is tested, and the maximum error value is 0.25%, which verifies the engineering applicability of the method.

Soil structure interaction studies on earth retaining wall

Abstract The paper offers a brand-new analytical technique for figuring out retaining wall natural frequencies, which are essential for seismic design. Using translational and torsion springs to account for soil-backfill interaction and foundation flexibility, the approach applies the theory of beams on elastic foundations. There are three closed-form techniques offered for figuring out the natural frequencies of flexural and stiff modes. The analytical model takes into account several kinds of retaining walls and the interactions between soil and structure that go along with them, such as active, passive, and dynamic earth pressures. To make the analysis simpler, certain assumptions are made about the behaviour of the structure and the state of the soil. The suggested technique provides a trustworthy means of assessing retaining wall behaviour during seismic events, which is crucial for guaranteeing structural stability and averting failure.

Active and Passive Lateral Earth Pressure with Anisotropic Seepage Effect

Active and Passive Lateral Earth Pressure with Anisotropic Seepage Effect

Active Earth Pressure on the Rigid Support Structures of Excavations Parallel to Tunnel Construction

Active Earth Pressure on the Rigid Support Structures of Excavations Parallel to Tunnel Construction

Active Earth Pressure Calculation of Equilateral Convex Corners in Excavation Engineering

Active Earth Pressure Calculation of Equilateral Convex Corners in Excavation Engineering

Experimental Investigation on a Water Diversion Shield Segment Using a Newly Developed Model Test Chamber

Jinan City in China is known for its abundant spring water, and the protection of underground spring water transport channels is a key issue that needs to be paid attention to in Jinan subway construction. In areas where underground spring water transport channels are easily disturbed, when the shield tunnel passes through a composite formation with a permeable layer in the middle and an impermeable layer in the upper and lower parts, the underground spring water transportation channel is blocked, the spring veins are damaged, and the underground spring water is blocked in the upstream, resulting in an increase in the water pressure difference on both sides of the tunnel. In this paper, based on the working principle of a new type of pipe segment with a diversion function, a diversion function pipe model test box is designed and fabricated. Using this model box, the working state of the diversion function pipe segments is simulated. An earth pressure box and pore water pressure gauges are embedded in the model box to measure the earth pressure and pore pressure around the pipe under seepage unsymmetrical pressure. Strain gauges are attached in a circular shape on the inner side of the pipe to measure and calculate the strain and stress of the pipe. Through model tests, the effective repair of the diversion pipe on blocking groundwater flow and the relief effect of the unsymmetrical pressure of the pipe are verified.

Mechanism of slag discharge failures in earth pressure balance shield screw conveyor: A theoretical model-based investigation

The screw conveyor gushing may cause a sudden drop in pressure in the earth chamber, leading to excessive settlement of the surface and nearby buildings or structures, and even catastrophic accidents such as tunnel collapse. This paper presents a comprehensive investigation into slagging failures associated with earth pressure balance shield screw conveyors, categorizing them into rheological failure and permeability failure. Further, a permeability failure theoretical model and a Bingham fluid-based rheological failure model are developed. The above models can describe the conditions and mechanism of screw conveyor spurt taking into account shield parameters, formation characteristics, chamber pressure, and conditioned soil properties. In addition, a sensitivity analysis is conducted on the critical permeability coefficient and critical shear strength of the discharged soil, with a focus on a specific case project. The results underscore the significant impact of the screw conveyor pitch, water head at the entrance, and chamber pressure on the critical permeability coefficient and shear strength. Building on these findings, this paper proposes an anti-surge control index and strategy for shield screw conveyors, taking into account the ratio of shield covering soil thickness to shield diameter. It is recommended that when the shield soil covering layer thickness exceeds twice the shield diameter, real-time modification of the soil parameters, based on the shield tunneling depth, especially the shear strength, is essential for anti-surge control. This study provides engineers with valuable insights into conditioned soil and implements effective surge management strategies for screw conveyors.

Earth Pressure Reduction and Transmission Between Rows of Portal Anti-Slide Piles

Earth Pressure Reduction and Transmission Between Rows of Portal Anti-Slide Piles

Geological adaptive intelligent control of earth pressure balance shield machine based on deep reinforcement learning

Scientific and precise control of tunnelling parameters is of utmost importance during the construction of shield machines. Given the complexity of the working environment, manual operation is highly prone to causing safety accidents. Therefore, achieving intelligent control of the shield machine is crucial. Based on this, this paper proposes a geological adaptive intelligent control method of earth pressure balance shield machine using the Deep Deterministic Policy Gradient (DDPG) algorithm as the framework, with Actor-Critic as the basis. Firstly, DDPG agent is constructed to replace the screw conveyor control system as the main body of strategy implementation. Secondly, an environmental model is established by utilizing the mechanism model between the sealed cabin pressure and the screw conveyor speed. The real-time sealed cabin pressure, target pressure, and pressure error serve as the state space, while the screw conveyor speed is used as the action space. A combined reward function is set based on safety and accuracy. Finally, the Actor network interacts with the environment under the supervision of the reward function and Critic network. Successful training is achieved when the cumulative reward value is maximized, resulting in the output of optimal control strategy. In this paper, the method dynamically regulates the screw conveyor speed by interacting with the geological environment, to realize the precise control of the sealed cabin pressure and ensure the dynamic balance between sealed cabin pressure and excavation face pressure. The test results show that this method has a good control effect on the sealed cabin pressure under various geological conditions, and can complete 72 kinds of soil transition tasks. It has strong soil adaptability and can respond well to the dynamic changes of soil conditions. This approach enhances the intelligence of the shield machine, mitigating inaccuracies attributed to human operation, which provides a guarantee of safe shield machine operation, whilst exhibiting valuable engineering applications.

Experimental study on granule trajectory tracking for the EPB shield tunneling in sandy cobble stratum

An investigation into the movement characteristics of granules during Earth Pressure Balance (EPB) shield tunneling contributes significantly to understanding the interaction between the shield machine and the soil. This understanding also enables researchers to gain deeper insights into the cutting and guiding effects of the shield cutterhead on the soil, thus providing a scientific basis for optimizing shield tunneling parameters and cutterhead designs. To achieve this, indoor model shield tunneling experiments were conducted using independently developed shield tunneling equipment and spatial positioning devices developed by our research group. The research investigated the spatial movement trajectories, radial diffusion, and axial movement characteristics of granules at the face subjected to the action of a spoke-type cutterhead. Furthermore, the study proposes the use of average diffusion degree and movement rates of granules as metrics for evaluating the cutting and steering performance of the cutterhead. The influence of cutterhead rotational speed and advance rate on the movement characteristics of granules was further explored based on these two indicators. The study’s findings reveal the following: (1) Granules at the face predominantly exhibit a spiral movement trajectory when the EPB shield tunneling machine operates in a dynamic equilibrium state. (2) The cutting and steering performance of the cutterhead’s various areas is enhanced progressively from the center to the outer edge, as evidenced by a gradual decrease in the average diffusion degree of granules and an increase in the average axial movement rate (AMR). (3) The AMR and average diffusion degree of granules are influenced by both the rotational speed of the cutterhead and the advance rate of the shield machine. Optimal matching of the rotational speed and advance rate maximizes the average AMR of granules, minimizes the average diffusion degree, reduces the torque on the cutterhead to its lowest point, and consequently, optimizes the efficiency of shield tunneling. This research presents a novel perspective and methodology for understanding the movement characteristics of granules during shield tunneling operations. The outcomes of this study provide valuable insights for the structural design of shield machine cutterheads and the optimization of tunneling parameters.