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Advanced drilling was employed for the ongoing excavation of a tunnel on Wu-Kai Expressway in Chongqing, aiming to characterize the ground condition ahead of the tunnel face and avoid potential geohazards. Measurement While Drilling (MWD) system and the hydraulic rotary crawler drilling machine are used for the advanced drillhole in the weathered argillaceous limestone rock mass. However, the MWD data exhibits random variations in penetration rate and cannot be correlated with ground conditions. In addition, there is little MWD data on the weathered argillaceous limestone with time-series algorithm in relevant open literature. This paper presents further analysis of the MWD data, resolves the random variation issue in penetration rate, and re-interprets the MWD data along three advanced drillholes in this tunnel project. The re-calculated penetration rate with the time-series algorithm for each drillhole is a stepped function of the drillhole depth. The constant penetration rates for the different homogeneous zones can be further correlated with the weathering degrees of the rock and compared with those from other five ground sites with different ground conditions in China and London. The findings of the paper can enhance the general applicability of MWD data for accurate profiling of weathered argillaceous limestone rock mass for safe tunnelling. [ABSTRACT FROM AUTHOR]

• A simulation method for single shield TBM has been studied in ADINA. • The influence of rock parameters on the ground settlement has been analyzed. • The influence of TBM tunneling parameters on the ground settlement has been analyzed. • The deformation law on end-bearing piles in composite rock stratum has been analyzed. • The empirical parameters of TBM have been verified in the study area in this paper. Considering that the subway tunnelling projects in the Chongqing region are located in strata dominated by sandstone and mudstone, the main empirical construction parameters (excavation thrust = 5 880 ∼ 6 860 kN, average pea gravel content (APC) ≥ 85%, and grouting pressure (GP) = 0.3 MPa) were obtained by engineering surveys; these empirical parameters were similar to those optimized under interval tunnel construction conditions. Additionally, a simulation method was developed based on the construction characteristics of a single shield TBM by using the ADINA software to simulate the construction process of subway tunnels undercrossing the pile foundations (end-bearing piles) of an old surface building in the composite strata of the Chongqing Rail Transit Loop Line. A sensitivity analysis was performed on the calculation parameters first because the changes in the stratigraphic and TBM construction parameters greatly influenced the calculation results. Then, we used the modified calculation parameters to study the effects of tunnel construction on the settlements of the ground surface and pile foundations in the composite strata, and these effects were compared to the field monitoring results. The results showed good agreement between the numerical calculations and the monitoring findings. Thus, the methodology and empirical construction parameters adopted in this paper can provide a reference for the construction of other tunnel sections of this project in similar construction conditions. [ABSTRACT FROM AUTHOR]

• A new seepage experimental method is proposed for small interval tunnels. • The spatial distribution of seepage and stress fields is investigated. • Reduction effect of grouting circle on water pressure and earth pressure is analyzed. • Influence of high groundwater level on structural safety performance is revealed. The complicated interaction between seepage field and stress field of tunnels in water-rich region has an important impact on the stratum deformation stability, structural safety performance, groundwater resources and ecological environment protection, etc. Especially for large-span urban tunnel with small spacing, the seepage funnels of the two holes will partially overlap and affect each other, making the seepage field distribution much more complex, and the difficulties in prediction water drainage and safety performance of supporting structure increase sharply. In this paper, in order to investigate the seepage field distribution and its influence on the structural mechanical behavior of small interval tunnel in water-rich region, using the self-developed seepage model test equipment, tests under different hydrostatic head heights were carried out on the Kexuecheng Tunnel, which is a typical small interval tunnel under complex hydrogeological environment in Chongqing, China. According to the test results, with the increase of buried depth and water level, the water pressure at each monitoring point gradually increased. For small interval tunnel, the average water pressure on the inner side decreased by 10–15 % compared with the outer side. Benefiting from the grouting circle can effectively block the supply of pore water in the rock mass, the water pressure behind the lining can be significantly reduced by 32 %–42 %. But with the increase of the hydrostatic height, the proportion of water pressure that can be shared by the grouting circle decreased gradually, and further aggravated the asymmetric distribution of the water pressure on lining structure. Meanwhile, the water pressure evolution curve shown a W -shaped distribution in horizontal direction and a V -shaped descend funnel along the tunnel axis, the predicted seepage influence range may increase to over 60–70 m under high water pressure. Contrary to the asymmetric distribution of water pressure, the earth pressure at the inner side was about 10 % higher than that at the outer side. Influenced by the tunnel excavation unloading effect, the closer to the tunnel face, the smaller the surrounding rock pressure. The minimum safety factors of the lining structure under water level of 0, 30, 40 and 50 m were 4.28, 3.85, 3.41 and 2.98, the structural safety performance significantly decreased with the increase of the hydrostatic head height. [ABSTRACT FROM AUTHOR]

• A new test specimen for simulating rock pipe jacking has been designed. • The frictional law under seven complex contact condition has been analyzed. • A three-dimensional simulation method for pipe jacking has been studied in ADINA. • The causes of the sudden drastic increase in jacking force have been verified in the study area. In ultra-long-distance rock micro-shield pipe jacking, the pipe wall friction resistance is a key factor that determines the magnitude of the jacking force and the layout of the intermediate jacking stations (IJSs), whereas the pipe-rock contact condition is the critical factor controlling the pipe string wall friction resistance. This paper aims to reveal the variation law of the friction resistance between the outer wall of a large-section of concrete pipe string and the surrounding rock during construction via ultra-long-distance rock micro-shield pipe jacking. To that end, the shear friction behaviour and mechanical mechanism was investigated between sandstone and concrete pipe string walls under seven different complex contact conditions (primarily considering various combinations of the three substances, namely, extra-pipe in situ debris, bentonite slurry and sand-laden waste mud at the pipe-rock contact surface) through direct rock shear tests based on the actual pipe-rock contact condition at the Guanjingkou Water Conservancy Project in Chongqing. The average friction coefficient (AFC) of the residual phase of the contact surface under 7 contact conditions was obtained by friction testing. Combined with the contact situation between the surrounding rock and pipe strings at the stage of a rapidly increasing jacking force, a three-dimensional finite element model was established, and the displacement control method was used to simulate the jacking. The comparison with the field monitoring results shows that the numerical model can accurately predict the jacking force and verify the reliability of the AFC parameters in the numerical calculation. Therefore, the combination of indoor testing and the finite element method can be applied to study the jacking force for other ultra-long rock micro-shield pipe jacking applications. [ABSTRACT FROM AUTHOR]

• A simulation method for single shield TBM in ADINA has been upgraded. • The influence of TBM tunnelling parameters on the ground settlement has been analyzed. • The empirical parameters of TBM have been verified in the study area in this paper. The ground surfaces induced by the subway tunnel excavation has been an issue of great concern in the engineering field. When building subway tunnels in rugged mountainous cities, settlement problems are inevitable for shallow buried sections. Therefore, this paper analyzes the influence of some major tunnelling parameters on the surface settlement during excavation by creating a fine 3D FE model for the shallow-buried section of the Chongqing Metro Circle Line. Due to the lack of construction experience in the project area, the thrust force, backfilling pressure, backfill gravels and backfilling density of the right tunnel were suggested changeless as 6500 kN, 0.3 MPa and 85% separately based on similar engineering case. Simulations show that the settlement can meet the construction control requirements (<20 mm), then the construction parameters of the left tunnel were studied in detail under the condition of right tunnel excavated. The numerical computation results reveal that a tunnelling thrust of about 5000 kN and an average backfill gravels density of 89% of left tunnel corresponded to the minimum cumulative surface settlement. Finally, both the numerical prediction and field data show that the shape of surface settlement curves in the study area still follows the Gaussian distribution, which can provide a reference for other metro construction projects in this region. [ABSTRACT FROM AUTHOR]