Three Dimensional Numerical Analysis of Ground Settlement Induced by Shield Tunneling

Taking the shield tunnel project of Guangzhou Metro Line 8 from Tongdewei Station to Shangbu Station as the research background, using the research method of finite element simulation and site monitoring, this paper analyses the influence rules of shield tunneling on ground subsidence under the condition of different hard rock height ratios. The research results show that in the process of crossing different hard rock height ratio composite stratum, as the hard rock height ratio decreases, the value of ground settlement decreases and settlement tank becomes shallow. The surface subsidence in different hard rock height ratio strata is obviously different, and the maximum difference is about 8.6 mm; The influence of the hard rock height ratio on the surface longitudinal settlement is mainly reflected in the position change of the beginning and the end of the settlement. With the increase of the hard rock height ratio, the shield construction reduces the amount of the surface longitudinal settlement and its influence range; Through the research, it is found that the hard rock height ratio in the 0-0.2 and 0.5-1 is the sensitive interval, and the settlement value in these two hard rock height ratio interval varies greatly. It is necessary to pay attention to the uneven settlement of the ground surface caused by shield construction in the sensitive hard rock height ratio interval. The research results of this paper can provide reference value for similar shield construction in upper soft and lower hard composite stratum.

Surface settlement in saturated loess stratum during shield construction: Numerical modeling and sensitivity analysis

Ground settlement during shield tunnel boring is a construction problem closely related to a variety of factors. To better control ground settlement, this paper proposes a ground settlement control method based on three collaborative methods: ground settlement prediction by FLAC3D numerical simulation, ground penetrating radar (GPR) backfilling grouting quality inspection and surface settlement monitoring. The results show that: the settlement pattern calculated by numerical simulation during excavation satisfies the peck settlement curve, and the maximum settlement does not exceed 6mm; the quality monitoring and dynamic feedback mechanism of backfill grouting can effectively guide the grouting construction and ensure compact grouting, and the results of monitoring the settlement of the tunnel surface show that the settlement of the surface and the settlement and tilt values of the building are within the permissible range.

This study utilizes ABAQUS finite element software to analyze embankment deformation during shield tunneling. Results reveal that shield tunneling effects are manageable. The left tunnel line successfully tunnels beneath the embankment, causing a maximum settlement of 8.7 mm, meeting regulations. The ground surface exhibits a “V” shaped lateral settlement trough, approximately five times the tunnel centerline width. Conversely, the right tunnel line induces a more extensive impact, with a 12.2 mm maximum settlement. Different lateral settlement patterns emerge in soil at varying depths. The left tunnel creates a “V” shape, with slightly increasing settlement above the tunnel axis as depth increases, accompanied by narrower troughs. The right tunnel line results in a pronounced “W” shape, especially at the grouting layer depth. Horizontal displacement forms an “S” shape, with maximum displacement at positions ±i from the tunnel axis. The right tunnel line induces greater maximum horizontal displacement than the left. In summary, this numerical analysis provides insights into embankment deformation during shield tunneling, aiding in assessing the impact and guiding safe tunneling beneath embankments.

In this study, a method for calculating the ground loss-induced ground settlement during quasi-rectangular shield (QRS) tunnelling was investigated. Based on stochastic medium theory, an equation for calculating QRS tunnelling-induced transverse ground settlement was derived. A tunnelling face convergence mode coefficient, α, was introduced to make the derived equation applicable to various tunnelling face convergence modes. A modified equation for calculating the longitudinal variation in the ground loss ratio (e) was proposed to calculate e for any arbitrary cross-section in the tunnelling direction. On this basis, the proposed equation was longitudinally expanded, and an equation for calculating the three-dimensional (3D) ground settlement was obtained. A simplified model for additional grouting pressure was established, and the influence of additional grouting pressure on surface deformation was analysed. In addition, the proposed method was used to calculate the QRS tunnelling-induced ground settlement, and the results were compared with actual measurements. It is found that the predicted ground settlement obtained using the proposed method matches the actual measurements relatively well and reflects the 3D variations in the ground settlement. As α increases, the maximum ground settlement increases and the width of the ground settlement trough decreases, whereas the positions of the inflection points of the settlement curve remain unchanged. The horizontal distance between the inflection points is approximately twice the width of the tunnel.

The shield tunneling method is widely used in urban subway construction. However, as the layer stress state changes during shield tunnel construction, layer displacement and surface deformation occur accordingly. This study tries to investigate the settlement and deformation of the masonry structure in shield cutting the composite foundation of group piles in a shield tunnel project at Zhengzhou Metro Line 5. To understand the distribution characteristics and changing rules of building settlement during the process of shield cutting group piles composite foundation passing through the masonry structure, a thorough analysis of the ground surface settlement and building settlement, including on‐site measured, was conducted. The results show that piles go down through a composite foundation during shield cutting. The cumulative maximum settlement and maximum differential settlement of the masonry structure were concentrated at the intersection of the tunnel axis and the building. The longitudinal distribution of the cumulative settlement of the south and north wall of the masonry structure changes continuously with the change of the position of the shield excavation surface. That behavior may cause the building to be tilted and deformed and cause the structure to undergo rigid rotation and twisting deformation. Based on the composite pile foundation project of the Shield Tunnel Cutting Group in a specific section of Zhengzhou Metro Line 5, this paper analyzes the surface settlement and foundation settlement data of the building caused by the construction of the shield. It obtains the changes of the surface settlement and the settlement of the foundation of the building. No other changes have been made to the existing cracks in the external walls of the building. At the same time, because of the low angle between the longitudinal axis of the masonry structure and the tunnel axis (22°) and the positive effect of the ring beam and column of the structure in the building, it is clear that the construction of this project has little effect on the upper building, thus showing improved control.

Ground settlements above a tunnel as a result of tunnel construction can be predicted with the help of input variables that have direct physical significance. Several empirical and artificial intelligence methods for estimating ground settlements have been established by researchers. However, these methods have some limitations because the large number of influential factors involved makes tunnel–ground interaction complicated. In this work, a random forest (RF) was developed and employed to predict ground settlements above tunnels. To achieve this goal, tunnel geometry, geological properties, and construction parameters were investigated as input variables to utilize in the RF modeling, resulting in the maximum surface settlement value (Smax) and trough width (i) as the ground surface settlement index. To demonstrate the applicability of the RF model, two data sets associated with different features, which were obtained from a detailed investigation of different tunnel projects published in literature, were utilized for model development and were applied to check the performance capacity of the developed model. A fivefold cross-validation procedure was then applied to identify the optimal parameter values during modeling, and an external testing set was employed to validate the prediction performance of the model. Two performance measures, R2 and RMS error, were employed. The relative importance of different parameters in the prediction of ground settlements was also investigated. Findings demonstrate that the RF method provides promising results and offers an alternative means in predicting ground settlements induced by tunneling.

This study investigates the behavior of shield tunneling based on a complete case record of an excavation in sandy cobble ground. Both numerical and analytical analyses were conducted to estimate the surface displacement along the tunnel axis and the surface-zone affected by the shield tunneling. This paper presents the performance of the Peck method in forecasting the transversal surface settlement trough caused by the shield tunneling in a sandy cobble layer. In particular, this study has made a comparison with the vertical surface displacement monitored during the advancing excavation to the settlements estimated by using the Peck method and by conducting a three-dimensional finite element analysis. The effective measures to provide the necessary face support pressure and to reduce the formation of sinkholes and ground settlements in sandy cobble ground were also investigated and discussed.

As to shield tunneling, that soil is reinforced into the void is one of the most important reasons which cause the ground settlement, and always most important factor in the tunnel construction and the relative research. The numerical simulation studies presented in this paper focus on the different grouting pressure causing different ground settlement, plastic area and stress growth behavior. Based on the simulation results and the engineering ground settlement limit, propose reasonable synchronous slurry injection pressure and the relative method of controlling ground settlement. Propose reasonable suggestion for the determination of grouting pressure during shield construction.

<p>In recent years, China's construction demand for shield tunnel in soft soil continues to increase, and the control of ground settlement in tunnel boring process affects the safety of the tunnel itself and its superstructure directly. Paying close attention to controlling the strata loss and the ground settlement by multiple means is important to ensure construction safety. In this paper, the intelligent real-time monitoring system with dual-frequency ground penetrating radar (GPR) is used to detect the quality of back-fill grouting of shield tunnel, while monitoring points are arranged on the ground surface to acquire the settlement values in real time. The collaborative analysis of ground and underground monitoring results reveals the relationship between grouting and settlement values, and realizes the dynamic guidance on grouting operation, which helps to achieve the purpose of controlling ground settlement better. Last but not least, this paper proposes an outlook on a multiple-data fusion system based on cloud computing platform to adapt to more complex and multiple data in the future, so as to achieve the higher accuracy, efficiency and intelligence of monitoring data analysis.</p>

Surface subsidence characteristics of fully overlapping tunnels constructed using tunnel boring machine in a clay stratum

The excavation of adjacent pits following the initial foundation pit excavation can significantly influence ground settlement. Using a foundation pit excavation project in Changzhou as a prototype, this study employed the numerical simulation method in conjunction with the HSS model to analyze the settlement deformation characteristics of the original excavation and compare them with the recorded monitoring values. In this study, the analysis focused on the ground settlement between two pits by varying the spacing between them at different excavation depths. The findings revealed that the ground settlement does not exhibit a significant increase when the new pit is excavated at a shallow depth. However, it rapidly increases when the excavation depth of the new pit surpasses that of the existing pit. Furthermore, an increase in the distance between the two pits causes the maximum settlement position to shift towards the edge of the new pit. The maximum ground settlement is found to have a linear relationship with both the maximum horizontal displacement of the two pits and the spacing between them.

There is much uncertainty to estimate the ground settlement associated with shield tunnelling due to the complicatedly interacted conditions between tunnelling methods and soil characteristics. Accordingly, if the shape of the ground settlement could be quantitatively predicted, it would be very effective for the assessment of its influence on the existing structures. It is presented that the shape of the ground settlement trough can be expressed as the product of the normal distribution function and the error function by introducing the mathematical model. The field observations were also carried out at the four sites of the shield tunnel construction in the Metropolitan areas. Besides, the model test was done, in which the settlements of sand layers were measured by the X-ray techniques. The following conclusions are obtained. The lateral and longitudinal profiles of the ground settlement trough are well fitted with the normal distribution curve and the error function curve, respectively. The parameter which represents the width of settlement is roughly proportional to depth of tunnel and its proportional constant depends upon soil characteristics. In clay the ratio of lost ground is positively correlated with OFS (Simple Overload Factor) defined by construction conditions and soil characteristics. Consequently the maximum settlement can be calculated by using these relationships.

Settlement is an important criterion in the design of the foundations. It is classifying into immediate (or elastic) settlement and consolidated settlement (primary and secondary). The factors that affect the shallow foundation settlement are the applied loads, soil stiffness, and geometric shape of foundation. Calculations of settlement depend on the parameters of soil which can be obtained from field and laboratory tests. Field and laboratory tests were conducted for twenty three sites in three different regions in Iraq (Mosul, Baghdad, and Basrah). In this research, field and laboratory tests results adopted for two sites from each region depended on the maximum and minimum bearing capacity values. Settlement for each site was calculated using numerical (mathematical) calculations and PLAXIS software under different added loads. The results of settlements beneath the foundation were competing for the sites with maximum value of bearing capacity in Mosul; Baghdad and Basrah. Also, the comparison conducted for sites of minimum bearing capacity value and the results showed different settlement values of each site. The change of settlement values under different loads was linearly in the six sites using numerical (mathematical) calculations. While, the settlement values obtained from PLAXIS software for sites with maximum bearing capacity value showed that Mosul site had the highest value due to the type of soil layers and the difference models of soil used in the software. Basrah site had a settlement value higher than Baghdad site due to the soil layers of sand type only. PLAXIS results for sites with minimum bearing capacity showed that for Basrah site the soil went to failure. While, the settlement values for Mosul and Baghdad sites were close to each other due to have nearly same soil layers. Therefore, high rise buildings could not be used in some sites. Also, soil in some locations and under some added loads needed to be improved before the implementation of any constructions.

Due to its inherent advantages, shield tunnelling has become the primary construction method for urban tunnels, such as high-speed railway and metro tunnels. However, there are numerous technical challenges to shield tunnelling in complex geological conditions. Under the disturbance induced by shield tunnelling, sandy pebble soil is highly susceptible to ground loss and disturbance, which may subsequently lead to the risk of surface collapse. In this paper, large-diameter slurry shield tunnelling in sandy pebble soil is the engineering background. A combination of field monitoring and numerical simulation is employed to analyze tunnelling parameters, surface settlement, and deep soil horizontal displacement. The patterns of ground disturbance induced by shield tunnelling in sandy pebble soil are explored. The findings reveal that slurry pressure, shield thrust, and cutterhead torque exhibit a strong correlation during shield tunnelling. In silty clay sections, surface settlement values fluctuate significantly, while in sandy pebble soil, the settlement remains relatively stable. The longitudinal horizontal displacement of deep soil is significantly greater than the transverse horizontal displacement. In order to improve the surface settlement troughs obtained by numerical simulation, a cross-anisotropic constitutive model is used to account for the anisotropy of the soil. A sensitivity analysis of the cross-anisotropy parameter α was performed, revealing that as α increases, the maximum vertical displacement of the ground surface gradually decreases, but the rate of decrease slows down and tends to level off. Conversely, as the cross-anisotropy parameter α decreases, the width of the settlement trough narrows, improving the settlement trough profile.