Crown Settlement Research Articles

Analysis of Monitoring and Measurement of Small Clear Spacing Tunnel in the Excavation by NATM

Due to its convenience, quickness, cheapness and so on, NATM is widely used in the tunnel excavation. In order to guarantee security when tunnel construction and study the stability of tunnel surrounding rock, Supervision and measurement is essential in the tunnel excavation, the result of which may influence tunnel excavation directly. Based on the analyses of measured data, the distribution characteristics and variation laws of the ground settlement, crown settlement and convergence around the tunnel, the displacement of the interior of surrounding rock are all studied. The study results are drawn to provide the basis for modifying and optimizing the design and construction scheme.

Mechanical Analysis of Construction Process for Shallow Weaking Surrounding Rock Multi-Arch Tunnel

Based on a practical engineering, considering the characteristics such as shallow,weaking surrounding rock, large span, double-arch of the tunnel, the stress and strain of surrounding rocks, support structure and mid-wall were analyzed by FEM for different excavating procedure. The simulation results were compared with in-situ monitoring results. The crown settlement and convergence displacement are divided two obvious increasing stages. Surrounding rock upper and under the mid-wall generate bigger plastic strain and should be strengthened. Temporary support of the pilot bears bigger load and should be reinforced. Bearing bigger horizontal direction tensile stress and uneven load, the bottom of mid-wall must have enough reinforcing steel bar or employ augment foundation. The analysis results provide a scientific basis and technical guidance for the construction optimization of the tunnel constructed by three-pilot excavation method.

Mechanical Analysis of Construction Process for Shallow Weaking Surrounding Rock Multi-Arch Tunnel

Based on a practical engineering, considering the characteristics such as shallow,weaking surrounding rock, large span, double-arch of the tunnel, the stress and strain of surrounding rocks, support structure and mid-wall were analyzed by FEM for different excavating procedure. The simulation results were compared with in-situ monitoring results. The crown settlement and convergence displacement are divided two obvious increasing stages. Surrounding rock upper and under the mid-wall generate bigger plastic strain and should be strengthened. Temporary support of the pilot bears bigger load and should be reinforced. Bearing bigger horizontal direction tensile stress and uneven load, the bottom of mid-wall must have enough reinforcing steel bar or employ augment foundation. The analysis results provide a scientific basis and technical guidance for the construction optimization of the tunnel constructed by three-pilot excavation method.

Monitoring Data Analysis of Dalian Subway Tunnel and Inversion of Rock Parameters

The finite element method combines with differential evolution algorithm to develop the displacement back analysis program. For the field excavation of Dalian subway tunnel, the ground subsidence, crown settlement and convergence displacement are monitoring measurement, then data fitting and regression analysis; Using the independent development program and monitoring data to back analysis so that we can address rock mechanics parameters are not accurate "bottleneck"; According to the inversion parameters, the forward analysis of the finite element numerical simulation, to form a comprehensive monitoring and information feedback system based on the field monitoring - displacement back analysis - being analyzed - field monitoring. The results show that the mechanical parameters of displacement back analysis program are very close to the project survey, while the monitoring and information feedback system has an important theoretical and practical value for safety of surrounding rock and stability of construction process.

<i>In Situ</i> Test and Mechanical Analysis of Multi-Arch Tunnel with Large Section in Soft and Weak Rock Mass

According to the characteristic of multi-arch highway tunnel,based on a practice engineering, the monitoring work was consisted of four sections:the displacement of surrounding rock; such as crown settlement, displacement of the ground, displacement of inner surrounding rock; that of stress and stain of support structure; that of force in middle-wall. In course of construction,monitoring data was analyzed in time.Structural timbering parameters were modified in response to abnormal monitoring data in order to guarantee safety.the testing results of the safety monitoring system are satisfactory, which serves as a symbol of our research work. Thus, our engineering practice has proved the applicability and feasibility of the safety monitoring and information construction methods.

Numerical modeling of tunnel excavation in weak sandstone using a time-dependent anisotropic degradation model

This paper presents a shear-induced anisotropic degradation model involving time-dependent behavior to simulate the deformational characteristics of weak sandstone. The stress–strain relationship of the proposed model was originated from the degradation of moduli K and G subjected to different loading conditions. An anisotropic factor β is introduced to indicate the tendency of shear-induced volumetric deformation. Furthermore, to incorporate time-dependent deformation behavior of sandstone, this anisotropic degradation model is further extended using a generalized Burger’s model. As a result, the proposed model is characterized by the following features: (1) being capable of describing shear-induced volumetric deformation, either compression or dilation, prior to the failure state; (2) being versatile in the time-dependent (creep) deformations; and (3) the anisotropic factor β serves as a convenient index regarding whether shear-induced volumetric deformation dilates or not. Afterward, the proposed model has been verified by comparing to experimental results. It is found that the proposed model is versatile in simulating short-term and long-term deformations of sandstone under different stress paths. Moreover, this model has been incorporated into finite element program and used to analyze a case of tunnel squeezing. Comparing with other existing models, it is found that the prediction of the proposed model is closer to reality and reveals a larger crown settlement, namely a squeezing condition, owing to larger extent of dilation zones. Overall, although the proposed model is a simple variable moduli model, it is capable of describing the key deformation behavior of weak sandstone reasonably-well, including time-dependent and shear-induced deformations.

Effects of Deformation of Wave-Dissipating Works on Wave Forces Acting on Caisson Breakwaters

The evaluation of wave forces acting on caisson breakwaters with deformed wave-dissipating works is important from the view point of caisson sliding. Wave pressures and wave forces acting on caisson breakwaters were measured to investigate the effect of the deformation of the wave-dissipating works on wave pressures and wave forces. Several cross sections of wave-dissipating works defined based on the previous study. When the crown of wave-dissipating work settles near the still water level, the impulsive wave pressure occurs and leads to increase in wave force. This wave force increases with progress of wave-dissipating works deformation indicated with a settlement of crown and decrease in the width of wave-dissipating works.

A new rheological model and its application in mountain tunnelling

The time-dependent features of soft rock, named rheology generally, should be taken into account in the long-term design and maintenance of mountain tunnels. Based on the classic Burger-MC rheological model, a Burger-deterioration rheological model is proposed in this paper and is implemented in the numerical codes FLAC 3D. A deterioration threshold and two deterioration ratios are introduced in this model to consider the time-dependent strength deterioration aspect of the rock mass. The proposed model is applied to an engineering instance (Ureshino Tunnel Line I, Nagasaki, Japan) to account for the delayed deformations that occurred after its completion since November 1992. The delayed crown settlement and invert upheaval computed from simulations are featured by an exponential characteristic and a stair-typed characteristic, respectively, which agree well with the in-site monitoring data qualitatively. In addition, the realistic rheological parameters involved in the proposed model can be back-analyzed from the in-site monitoring data.

Synthetical analysis on monitoring of Wushaoling railway tunnel

Wushaoling railway tunnel, the longest single-track railway tunnel in China, is the key project of Lanzhou-xinjiang railway line. It goes through four regional faults (F4-F7). The geological and geostress conditions are quite complicated. According to the characteristics of soft rock tunnel with large deformation on complicated stress condition, comprehensive monitoring is executed in construction of Wushaoling tunnel. Based on the measured results of the crown settlement, the horizontal convergence, the axial force of rock bolt, the surrounding rock pressure, the stress in steel set, the stress in shotctete and the stress and pressure in the secondary lining, the relation between surrounding rock pressure and displacement, the distribution rule of displacement, the coefficient of lateral pressure, the shared ratio of secondary lining pressure, the construction time of secondary lining etc, are analysed in this paper. The above information is feedback to the construction in time. The structure stability is analysed and the corresponding measures are adopted. It can also provide the numerical coefficients for data simulation and theoretical analysis. It is proved that the effect is reliable, the surrounding rock is stable and the structure is in good condition, providing a reliable technical guarantee for the perforation of the section. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

3D FEM analysis of horizontal jet grouting prelining in a tunnel under asymmetric loads

The entrance portion of Songjiaping Railway Tunnel, located in Shaanxi Province, China, was subject to asymmetric load due to the presence of a sharp slope on the left. By the routine bench excavationsupport method, up to 12 cm of crown settlement of initial support and 4cm wide crack on the slope were encountered. To reduce the deformations, the horizontal jet grouting technique was used to presupport the soft ground. To estimate the strengthening effect of the technique, a 3D elasto-plastic finite element model is used in this paper to simulate the mechanical behavior of the horizontal jet-grouted prelining The results of the simulation and those from field measurements shows that the jet-grouted arch shed can be used to confine the ground deformation. (A) This paper was presented at Safety in the underground space - Proceedings of the ITA-AITES 2006 World Tunnel Congress and the 32nd ITA General Assembly, Seoul, Korea, 22-27 April 2006. For the covering abstract see ITRD E129148. Reprinted with permission from Elsevier.

Monitoring of tunnel behaviour through cataclastic rocks

Field instrumentation was used in the construction of two twin tunnels for the new Egnatia Motorway in Greece. This paper describes the displacement monitoring results taken during tunnelling through heavily fragmented limestone varying from a block size >10 cm down to sandy gravel and sandy silt or gouge. The primary lining displacements monitored by surveying methods appear to be directly related to the detailed geological subdivisions of the limestone observed at the tunnel face. Maximum values of settlement were recorded during tunnelling through the gouge and reached 80 mm, while horizontal movements up to 40 mm were recorded associated with outward deflection of the support frames. The development of settlement with time shows that settlement of the tunnel crown and sides increased sharply while the face of the tunnel was within a tunnel diameter of the station point under consideration and reached equilibrium when the excavation face was at least 3 to 4 tunnel diameters beyond it. Surface settlements above the axis of the tunnel were first observed when the face of the tunnel was directly beneath the station. At the entrance portals of the tunnels the limestone overlies a thin sedimentary clay formation and gypsum. Horizontal movements along the interface between the limestone and the underlying clay sequence as well as within a clay/gypsum layer at the portals were observed using a standard inclinometer.

Characterizing the deformation behavior of Tertiary sandstones

Abstract Tertiary sandstones possess deformational behavior different from hard rocks, especially the relatively larger amount of volumetric dilation during shearing. Such excess dilation contributes to the increase of crown settlement during tunnel excavation and accounts for several cases of tunnel squeezing within Tertiary sandstones. Therefore, the deformation behavior of Tertiary sandstones sampled from more than 13 formations was studied. To distinguish the volumetric deformation induced by hydrostatic stress or by shear stress as well as to decompose the elastic and the plastic components of strains, special experimental techniques, including pure shear tests and cycles of loading–unloading were applied. The experimental results reveal that the deformation of Tertiary sandstone exhibits the following characteristics: (1) significant amount of shear dilation, especially elastic shear dilation; (2) non-linear elastic and plastic deformation; (3) plastic deformation occurs prior to the failure state. Furthermore, features of plastic deformation were inferred from experimental results and, as a result, the geometry of plastic potential surface and the hardening rule were accordingly determined. A constitutive model, involving nonlinear elastic/plastic deformation and volumetric deformation induced by shear stress, is proposed. This proposed model simulates the deformational behavior for the shear-dilation-typed rocks reasonably well. Furthermore, tests on the versatility of the proposed model, including varying hydrostatic stress and stress paths, indicate that the proposed model is capable of predicting deformational behavior for various conditions.

Getechnical monitoring by digital precise photogrammetry

Monitoring is a key element of observation design and construction method in civil engineering structures. In the case of tunnel measurement, convergence measure and electro-optical distance measuring instruments are usually used for inner displacement survey and crown settlement survey, respectively. As for slope measurement, a borehole displacement meter or an electro-optical distance measuring instrument has thus far been used for displacement survey. These methods, however, are weighed down by many disadvantages. Therefore, a new method must be developed. In this paper, a new geotechnical monitoring system by digital precis e photogrammetry is proposed as a monitoring method for observational design and construction method in civil engineering structures. Then the model experiment of the geotechnical monitoring system by digital precise photogrammetry developed by author was carried out in the laboratory. Based on measurement result obtained, it can be concluded that there is substantial potential for the exploitation of digital precise photogrammetry technique in civil engineering measurement. This study also demonstrated that the proposed methodology is routinely capable of achieving object displacement accuracy well in survey in civil and geotechnical engineering applications.

Deformational characteristics of weak sandstone and impact to tunnel deformation

In northern Taiwan, a tunnel under construction along a segment where weak sandstone, the Mushan sandstone, was encountered and an excess crown settlement (14–30 cm) has been reported. This paper studies the deformational characteristics of Mushan sandstone and its impact on tunnel deformation. To distinguish the volumetric and the shear deformation of the sandstone, experiments with controlled stress paths, including hydrostatic compression, pure shearing and conventional triaxial compression, were conducted. The measured deformations were then decomposed into elastic and plastic components further exploring the stress–strain behavior of weak sandstone. The results indicate that, similar to other soil-like geo-materials, this sandstone has plastic strain before the stress path reaches the failure envelope and significant shear dilation is induced, especially when approaching the failure envelope. Meanwhile, the distinct features of deformation have also been highlighted by comparing the experimental results to the prediction, derived from existing constitutive models that were originally developed for other geo-materials. These features include significant plastic volumetric strain at low levels of confining stress, suppression of plastic volumetric strain at higher levels of confining stress, and the fact that the actual amount of shear compression is less than that predicted by the model. Numerical analysis indicates that the weak rock leads to the greatest inward displacement, which results from the shear dilation prior to failure state.

Subsidence above Shallow Tunnels in Soft Ground

The paper investigates the influence of the depth of burial and crown settlement on the surface subsidence above shallow tunnels driven in soft ground. Model tests were conducted on tunnels in sand and in clay, and these are compared with one another and with observations of settlements above some real tunnels. There is good agreement between the model behavior and the field records. The error, or normal probability curve, may be used as an approximation for the trough of surface subsidence, and the standard deviation is an appropriate measure of the width. Empirical relationships exist between the depth of burial, the trough width and the crown and surface settlements for tunnels in sands and in clays.