Experimental investigation on the reinforcement of a high-pressure jet grouting pile for an ultra-shallow tunnel in a strongly weathered stratum

In this paper, the performance of a high-pressure grouting material and consolidation body, the key parameters of tunnel surrounding rock reinforcement, and the field reinforcement effect are compared and studied. The results show that 1) the compressive strength, elastic modulus, and seepage resistance of the consolidation body are related to the water–cement ratio. The permeability of the consolidation body increases with increasing water–cement ratio under the constant head; under the condition of a certain water–cement ratio, the strength increases with an increase in cement content. To meet the construction requirements and the slurry stability, a small water–cement ratio is appropriate. 2) Slurry pressure, rotary spray speed, and lifting speed on the single pile static load bearing capacity have a significant impact. Under the same static load conditions, the greater the slurry pressure, the lower the cumulative settlement value of the single pile, the cumulative settlement value increases less, and the amount of change in rebound is the same; with the increase in the rotational speed of the rotary spray, the lower the cumulative settlement value of the single pile, and the rate of change of the cumulative settlement value of the single pile decreases; and with the increase in the lifting speed, the cumulative settlement value of the single pile increases and the rate of change of the cumulative settlement value decreases. 3) The pile body cement soil is more uniform, has high strength, and is brittle, and the stratum where the slurry part is located is a loose powder clay layer and sandy layer. 4) After high-pressure jet grouting pile reinforcement, the top surrounding rock is more stable after the excavation of an ultra-shallow buried tunnel, the fissures between the surrounding rocks are filled with cement soil consolidation, and the integrity is improved. Certain piles also play a certain role in stopping water; high-pressure jet grouting pile reinforcement to improve the integrity of the surrounding rock played a role in consolidating the weak soil layer above the tunnel vault, creating conditions for the safe excavation of the shallow buried section of the tunnel

Quasi-static test study of tunnel with resistance-limiting shock absorption layer in high-intensity seismic

The Sichuan-Tibet Railway is faced with risks of active faults, unfavorable geological conditions, high in-situ stress levels, and a high potential for Traditional tunnel seismic measures that can no longer guarantee the safety of tunnel structures in high-intensity earthquake areas. The new shock absorption capacity layer with resistance-limiting is proposed in this paper and the resistance-limiting shock absorption principle. To study the safety of the new anti-shock lining structure, a large-scale quasi-static model test was carried out based on the improved static-dynamic coupling shear force. The test analyzes the response rules of strain, structural internal force, and lining failure form of tunnel lining, taking into consideration three influencing factors including layer layout position, layout density, and tunnel buried depth. The results showed that: 1) Under the action of low-cycle reciprocating shear strain, the failure mode of the shallow buried tunnel is mainly the tensile failure of the arch waist and the failure of the arch waist and the side wall, and the failure mode of the deeply buried tunnel is mainly the compression failure of the arch waist; 2) Compared with the case of no shock absorption layer, the lining tensile stress on the inner side of the arch waist position is significantly reduced. Under the high shear strain (0.20%), the increased tensile stress trend was slowed down on the inner side walls; 3) The main working area of the resistance-limiting layer can effectively improve the lining stress distribution underground vibration and protects the tensile damage on the arch waist to the side wall. The width and depth of the crack are weakened and the seismic bearing capacity of the width and depth of the crack is weakened and the seismic bearing capacity of the lining structure is greatly strengthened; 4) The lining cracks without the resistance limiting layer develop violently, and the crack at the arch waist runs The lining structure failure mode of the resistance limiting layer arranged at the arch waist is similar to The lining structure failure mode of the resistance limiting layer

Frost protection mechanism based on rubber airbag interlayered composite lining system for cold-region tunnels

Abstract To solve the problem of freezing damage in cold-region tunnels, this study proposed a rubber airbag interlayered composite lining system, and tested its performance of buffering, pressure adjustment, waterproofing, and heat preservation by simulating a low-temperature environment in an artificial freezing chamber. The experiment results show that the frost-heaving force exerted on the lining can always be lower than 1.69 kPa by constantly adjusting the airbag pressure, and the maximum frost-heaving force can reach 28.25 kPa without the airbag. In addition, the airbag also has good waterproof performance. Finally, the airbag can significantly improve the temperature field of the surrounding rock and reduce the freezing depth (6.75 cm < 17.25 cm). The insulation effect of the airbag is positively correlated with its thickness and negatively correlated with the thermal conductivity of the filling gas. The insulation effect of CO2 is better than that of air. The rubber airbag interlayered composite lining system provides a new scheme for freezing damage control in cold-region tunnels

Using Energy-Absorbing Dampers to Solve the Problem of Large Deformation in Soft-Rock Tunnels: A Case Study

The commonly used strength design concept of tunnel support structures is inadequate to address the large deformation of soft rock. This study designed a series of energy-absorbing dampers (EDs) with low stiffness and high deformation capacity based on the energy principle. The ED was directly installed on the steel arch, which used its compression deformation to release the surrounding rock pressure and absorb the surrounding rock deformation to ensure the stability of the initial support structure. A compression test analyzed the ED&rsquo;s mechanical properties, optimizing the structural parameters. The preliminary test results showed that the arc energy-absorbing damper&rsquo;s (AED-I) peak strength (15.33 Mpa) was lower than the standard compressive strength of C25 shotcrete, with a safety factor of 1.63. The AED-I&rsquo;s maximum compression ratio was 73.20%. To further improve the AED-I&rsquo;s reliability and ability to absorb the deformation of surrounding rock, the bending radius of the AED-I&rsquo;s energy-absorbing steel plate was reduced from 1800 mm to 1300 mm. After optimization, the AED-IO&rsquo;s peak strength was reduced to 10.5 Mpa, and the safety factor increased to 2.38. The maximum compression ratio of the AED-IO also increased to 75.79%. The AED-IO has been applied to treat the large deformation of soft rock in the Zhongshao Tunnel on the Yuchu Expressway. Compared with a traditional support method, the maximum surrounding rock pressure was only 0.13 Mpa in the section where the AED-IO was applied. The maximum steel arch stress was 122.26 Mpa, far less than its uniaxial compressive strength. The application of the AED-IO ensures the stability of the initial support structure. Meanwhile, using an AED-IO saves CNY 24,323.85 per meter and reduces waste emissions by 20 tons

Accurate estimation of concrete consumption in tunnel lining using terrestrial laser scanning

Abstract Accurate estimation of concrete (including shotcrete) consumption plays a crucial role in tunnel construction. A novel method has been introduced to accurately estimate concrete consumption with terrestrial laser scanning (TLS). The estimation needs to capture TLS data of tunnel surfaces at different stages of construction. Unrolling point clouds, a novel two-stage algorithm consisting of noise removal and hole filling has been used to generate resampled points. Furthermore, resampled points from two scans (before and after lining construction) ultimately generate an innovative computation model composed of multiple hexahedral elements, which is used for calculating volumes. The proposed technique was applied to the Tiantaishan highway tunnel and Da Fang Shan high-speed railway tunnel. The calculation relative error of the rebound rate is 0.19%, and the average relative error in predicting the demand for secondary lining concrete is 0.15%. Compared with 3D Delaunay with curve fitting, the proposed technique offers a more straightforward operation and higher accuracy. Considering factors such as tunnel geometry, support design, and concrete properties, a computational model will provide valuable insights into optimizing resource allocation and reducing material waste during construction

Using Energy-Absorbing Dampers to Solve the Problem of Large Deformation in Soft-Rock Tunnels: A Case Study

The commonly used strength design concept of tunnel support structures is inadequate to address the large deformation of soft rock. This study designed a series of energy-absorbing dampers (EDs) with low stiffness and high deformation capacity based on the energy principle. The ED was directly installed on the steel arch, which used its compression deformation to release the surrounding rock pressure and absorb the surrounding rock deformation to ensure the stability of the initial support structure. A compression test analyzed the ED’s mechanical properties, optimizing the structural parameters. The preliminary test results showed that the arc energy-absorbing damper’s (AED-I) peak strength (15.33 Mpa) was lower than the standard compressive strength of C25 shotcrete, with a safety factor of 1.63. The AED-I’s maximum compression ratio was 73.20%. To further improve the AED-I’s reliability and ability to absorb the deformation of surrounding rock, the bending radius of the AED-I’s energy-absorbing steel plate was reduced from 1800 mm to 1300 mm. After optimization, the AED-IO’s peak strength was reduced to 10.5 Mpa, and the safety factor increased to 2.38. The maximum compression ratio of the AED-IO also increased to 75.79%. The AED-IO has been applied to treat the large deformation of soft rock in the Zhongshao Tunnel on the Yuchu Expressway. Compared with a traditional support method, the maximum surrounding rock pressure was only 0.13 Mpa in the section where the AED-IO was applied. The maximum steel arch stress was 122.26 Mpa, far less than its uniaxial compressive strength. The application of the AED-IO ensures the stability of the initial support structure. Meanwhile, using an AED-IO saves CNY 24,323.85 per meter and reduces waste emissions by 20 tons

Automatic Extraction of Tunnel Lining Cross-Sections from Terrestrial Laser Scanning Point Clouds

Tunnel lining (bare-lining) cross-sections play an important role in analyzing deformations of tunnel linings. The goal of this paper is to develop an automatic method for extracting bare-lining cross-sections from terrestrial laser scanning (TLS) point clouds. First, the combination of a 2D projection strategy and angle criterion is used for tunnel boundary point detection, from which we estimate the two boundary lines in the X-Y plane. The initial direction of the cross-sectional plane is defined to be orthogonal to one of the two boundary lines. In order to compute the final cross-sectional plane, the direction is adjusted twice with the total least squares method and Rodrigues' rotation formula, respectively. The projection of nearby points is made onto the adjusted plane to generate tunnel cross-sections. Finally, we present a filtering algorithm (similar to the idea of the morphological erosion) to remove the non-lining points in the cross-section. The proposed method was implemented on railway tunnel data collected in Sichuan, China. Compared with an existing method of cross-sectional extraction, the proposed method can offer high accuracy and more reliable cross-sectional modeling. We also evaluated Type I and Type II errors of the proposed filter, at the same time, which gave suggestions on the parameter selection of the filter