Excavation Deformation Research Articles

Observed Performance and FEM-Based Parametric Analysis of a Top-Down Deep Excavation in Soil-Rock Composite Stratum

This paper investigates the performance of a top-down deep excavation in soil-rock composite stratum. The behavior of the excavation bracing system, consisting of ground anchors and end-suspended piles, has not been well understood due to the lack of relevant research. Based on the observed data of a typical deep excavation case history for the May Fourth Square Station in Tsingtao, China, the characteristics of the horizontal and vertical pile displacements, ground surface settlements, building settlements, axial forces in ground anchors, earth pressure, and pore water pressure during excavation were analysed. Two-dimensional finite element simulations were carried out to further explore the deformation and internal force responses of end-suspended piles and to capture the effects of pile diameter, embedded depth, and rock-socketed depth on the horizontal displacement and bending moment distributions along the pile shaft. It was found that the pattern of the vertical pile displacements could be categorized into three types: rapid settlement, slow settlement, and rapid heave. The magnitudes of the ground and building responses can be well controlled within allowable limits by combining the top-down method with the adopted bracing system. Among the investigated parameters, pile diameter is dominant in affecting the horizontal pile displacement. The primary influence zone for pile bending moment varies, depending on the parameters. It is recommended that a combination of top-down method, ground anchors, and end-suspended piles be adopted for restraining excavation deformation and lowering construction costs of similar deep excavations in soil-rock composite stratum.

Displacement Monitoring during the Excavation and Support of Deep Foundation Pit in Complex Environment

Taking a super large deep foundation pit project as an example, the horizontal displacement of crown beam and driveway, surface settlement, axial force of anchor cable, and underground water level in the construction process of the foundation pit are dynamically monitored and analyzed. The excavation deformation rule of the deep foundation pit and the influence of excavation on surrounding buildings are analyzed. The results show that, with the excavation of the foundation pit, the crown beam and driveway of the foundation pit incline towards the direction of the pit and eventually tend to be stable. The variation of axial force of the prestressed anchor cable in the first layer of the foundation pit is basically consistent with the variation of horizontal displacement time history. The variation trend of the groundwater level at each side of the foundation pit is different but tends to be stable in a short time. In the whole monitoring period, the cumulative settlement value of each area of the foundation pit is within the controllable range, but the surface settlement of the north side of the foundation pit and a surrounding building has not reached stability, so it is suggested to extend the monitoring time of settlement in the relevant area.

The Comparison and Analysis between Numerical Simulation and Monitor Data of Deep Foundation Pit Excavation Deformation

Taking a large-scale deep foundation pit project in Guangzhou financial city as the research background, the construction process of the foundation pit is analyzed by the finite element software Midas GTS-NX. The simulated results are compared with the monitoring data, and the surface settlement deformation of the foundation pit and the horizontal displacement of supporting piles are compared and analyzed. Although the comparison results are different, the overall change trend is the same and the data are similar, and within the range of engineering deviation, the results show that the numerical simulation can provide reference for foundation pit deformation monitoring scheme design and construction scheme design.

In Situ Monitoring and Numerical Experiments on Vertical Deformation Profiles of Large-Scale Underground Caverns in Giant Hydropower Stations

Spatial response is a feature of rock deformation in regions surrounding large-scale underground caverns and includes significant vertical components due to the construction method of layered excavation. This vertical response is different to the longitudinal response of excavation deformation surrounding shallow tunnels. The study of longitudinal deformation profiles (LDPs), which describe the spatial response of longitudinal tunnel excavation and surrounding rock deformation, is a mature field. However, there has been no independent discussion of the relationship between vertical excavation and the spatial response of deformation in large-scale underground caverns nor the incremental characteristics of layered excavation. In this paper, we define the attenuation function λ x of unloading strength based on theoretical analyses and numerical simulations. We also propose the concept and form of the vertical deformation profile (VDP) curve for the first time and apply it to the Baihetan and Lianghekou Hydropower Stations. After fitting the complete VDP curve with a Levenberg-Marquardt algorithm, we verify its validity by comparing predicted data with in situ monitoring data. The curve can be used to quantitatively analyze the relationship between layered excavation and incremental deformation of surrounding rock, providing a basis for the rapid evaluation of staged deformation during the excavation of large underground caverns. This study has practical significance for the control of deformation in rock surrounding excavations and decision-making during the construction progress.

Experimental Investigations on Rheological Properties of Mudstone in Kilometer-Deep Mine

The soft rock roadway in deep high-stress environment has the problems of strong rheology and large deformation. Based on the analysis of the stress distribution of the surrounding rock of the roadway in a kilometer-deep mine, rheological tests under different stress paths are carried out for mudstone in a kilometer-deep mine. The rheological deformation curve, damage characteristics, and change rule of the main mechanical parameters of mudstone under different stress conditions are studied. The results show the following: (1) the peak strength of the triaxial compression of mudstone is closely related to confining pressure, and, with increasing confining pressure, the confining pressure effect decreases gradually; (2) the strain increases slowly under uniaxial loading, and, with increasing axial pressure, the velocity of rheological deformation increases nonlinearly, and the amount of mudstone deformation increases with time; (3) under the condition of unloading confining pressure with constant axial pressure, with decreasing confining pressure, the instantaneous axial and radial strains of mudstone specimen increase nonlinearly, the rheological strain and velocity of mudstone increase gradually, and the lateral rheological strain is close to the axial rheological strain; and, (4) in the unloading confining pressure with axial compression triaxial test, with increasing deviating stress, the axial and radial instantaneous strain increments of mudstone decrease gradually, the lateral strain and rheological velocity of mudstone increase gradually, and the lateral strain is approximately 2.05 times the axial strain. These conclusions reveal the rheological characteristics of the mudstone under different surrounding rock conditions and provide a theoretical basis for the excavation deformation and support control of roadways.

Analysis and Research on excavation deformation of deep foundation pit support engineering of metro station

With the rapid economic and social development, the construction of urban underground rail transit is in full swing, and even many second and third tier cities are starting to build, In order to control the environmental impact of the excavation team and control the deformation, this paper takes a deep foundation pit project of a station in Wuhan Metro as the research object, combining with theoretical analysis, field monitoring and Midas GTS Nx numerical software simulation and other methods are used to discuss the ground settlement around the foundation pit, the impact on the adjacent bridge pile foundation, and the deformation control analysis.

Grouting Reinforcement Technology of Weak Fractured Rock Mass in Subway Open-cut Station

In the process of subway open-cut station construction, excavation deformation seriously threatens the safety of municipal pipelines and buildings. To ensure the effectiveness of grouting reinforcement, drilling exploration and pressure water test were conducted on the basis of the grouting reinforcement project of the excavation of an open-pit station in Qingdao metro, the permeability coefficient and crack characteristics were studied, and the equivalent crack width was calculated on the basis of cubic law. To determine the injectability index of grout and realize the optimal selection of grouting materials, the statistical distribution law of the equivalent crack width was analyzed on the basis of the Pareto distribution, and an effective method of grout selection was proposed. The PQT curve in the grouting process was analyzed by flow dimension theory to realize the dynamic adjustment of the grouting process. Finally, the grouting reinforcement effect was evaluated on the basis of the core sample and borehole TV. Results show that if the permeability coefficient is subject to Pareto distribution with parameters tmin and k, then the distribution curve of the permeability coefficient in the logarithmic coordinate is a straight line; the equivalent crack width obtained on the basis of the cubic law is also subject to the Pareto distribution with parameters bmin and 3k. Therefore, the equivalent crack width distribution curve can be obtained to provide a basis for the grout selection.

Performance of buildings around a long irregular excavation by top-down technique in downtown Nanjing

A 1257 m-long irregular deep excavation was located in the city center of Nanjing, China. The full-width and half-width top-down construction method was adopted. The deformation characteristics of the settlement of adjacent buildings based on field data is discussed, and the interrelationships between building settlement and excavation process, structural system and geological conditions are also considered. The analysis results show that building settlement is related to the excavation deformation, construction sequence, structure forms, foundation types and the distance to the foundation pit. Corner effect has played an important role in building settlement and will affect the settlement pattern eventually. The settlement surface of building outside the pit corner is three-dimensional, while the building located in the middle of the long side of the pit has a two-dimensional settlement surface.

Numerical Analysis of Deformation of Deep Foundation Excavation in Soft Clay Considering Influences of Time-effect

The traditional foundation pit design generally only considers the transient deformation. However, the excavation deformation characteristics of deep foundation pits in soft soil layers not only consider the small strain characteristics during the excavation, but also consider the time effect. Taking a foundation pit in Wenzhou as the engineering background, based on the HSS model and the SSC model, PLAXIS finite element software was used to simulate the excavation process of the deep foundation pit. The deformation characteristics of retaining structures and deep excavation are compared and analyzed. Calculations prove that: The deformation rules of the foundation pit with the time effect is basically the same as those without the time effect. During the excavation of the foundation pit, the horizontal displacement of the diaphragm wall, the ground settlement and the foundation upheaval calculated based on the SSC model are larger than those calculated based on the HSS model. The calculation results based on the SSC model show that after the completion of the excavation, the deformations of the foundation pit continue to increase with time, showing a rheological effect. The conclusion can provide theoretical guidance for the construction of foundation pit excavation in Wenzhou area to ensure the safe implementation of the construction process.

Empirical Method and Finite Element Analysis of Deep Foundation Pit Excavation in Ningbo Soft Soil

How to analyze and judge the excavation deformation of deep foundation pits in cities has become an urgent problem to be solved. Through the analysis of the excavation monitoring data of a deep foundation pit of a station on Ningbo Metro Line 3, the characteristics of horizontal displacement and surface settlement of the ground-connected wall during the foundation pit excavation in Ningbo soft soil area are obtained. And to compare and analyze the monitoring data by the empirical statistics method and the finite element method. Analysis shows that both can predict the deformation trend of foundation pit. However, due to the regional nature of the deep foundation pit engineering, the prediction accuracy of the empirical curve is poor. Compared with the empirical statistical method, the finite element method has better prediction accuracy, but the finite element method is more complicated. The advantages of the two methods can be applied in the project. In the study of deformation prediction of deep foundation pits, a more in-depth study of the combination of the two methods can be carried out.

Analysis of Mechanical Characteristics of Foundation Pit Excavation of Super High-rise Building in Strong Weathered Sandstone Area

The foundation pit excavation of the natural foundation of the super high-rise building in the strong weathered sandstone area of Lanzhou is the first foundation excavation project of Gansu Province. Excavation method and soil condition affect the excavation of foundation pits to different extents. In order to obtain the excavation method of foundation pit excavation in the area, based on the local soil conditions, he ABAQUS finite element software was used to establish the 3D numerical simulation of foundation pit excavation, and the stress and deformation curves during foundation excavation were drawn. The simulation results were compared with the specifications to obtain a feasible scheme for foundation pit excavation. Then a typical soil layer was selected for excavation, and the effects of elastic modulus and cohesion on the deformation of the foundation pit during excavation were studied, the model damage cloud diagram during the foundation pit excavation process is obtained. By comparing the deformation of a certain path in the model and drawing the curve, the influence of elastic modulus and cohesion force on the excavation deformation of the foundation pit is obtained. At the same time, this article can also provide reference for similar projects in the future.

Study on the Relation between Mineral Compositions of Rock and Construction Characteristics of Tunnel in Cold Regions: A Case

Mineral composition of rock has a very important influence on the physical and mechanical properties of tunnel surrounding rock. Take Dangjianshan tunnel in cold regions for example, the rock specimens in different parts of tunnel were taken to carry out the detection test of mineral composition. By the detail qualitative and quantitative analysis, the relationship between mineral composition and surrounding rock engineering properties was explored. First of all, the composition and content of minerals contained in in the rock specimens were detected by X ray fluorescence spectrometer and X ray powder diffraction. The detection results show that rock of tunnel contains high hardness minerals such as quartz and feldspar which were proven by initial engineering geological investigation report, in addition, it also contains several kinds of low hardness minerals including inclined chlorite and illite which may exhibit large deformation characteristic of soft rock after the tunnel excavation in case of meeting water and weathering conditions. The total content of inclined chlorite and illite accounted for a considerable component in main tunnel, inclined shaft and parallel pilot respectively and the influence on surrounding rock engineering properties cannot be ignored. Therefore, mineral composition detection must be paid attention to after tunnel excavation. Secondly, the effects of mineral composition on surrounding rock were analyzed in aspects of rock strength, weathering resistance, water softening property and excavation deformation through comparing the rock samples in different parts of tunnel. The comparative results showed that when the mineral contents is high with high hardness and poor hydrophilicity, tunnel surrounding rock plays a better performance of physical and mechanical properties, vice versa. Finally, according to the specific geological and construction parameters of the tunnel, the correlation analysis was studied about the vault settlement after tunnel excavation and the hydrophilicity mineral content in main cave. The logarithmic relationship between them was found and the correlation coefficient was 0.98. It can provide a useful reference for the settlement prediction of Dangjinshan tunnel construction.

A study into the behaviour of the formation level of an excavation under different unloading patterns in soft deposits

The construction of basements in urban areas is often associated with the possible damage to existing structures and services. The varying construction processes inevitably lead to different stress unloading patterns and therefore the dissipation of these excess pore-water pressures may lead to non-standard deformation profiles. The three main types of basement construction processes are layered excavation (LE), basin excavation (BE) and island excavation (IE). The effect of the various unloading patterns has been investigated by a three dimensional (3D) effective stress analysis method using the developed computer program 3DBCPE4.0. An excavation of length 50 m, width 50 m and depth 9 m in a certain homogenous and isotropic saturated soft soil was modelled. This included a diaphragm wall of 800-mm thickness embedded 18 m deep into the soft soil. The different excavation deformation profiles under different excavation patterns were related to the different unloading process, the exposure time of excavation face and the dissipation of negative excess pore-water pressures. The most favourable process for controlling the horizontal deformation of a retaining wall or the heave deformation of the formation level is suggested. The ground water potentials within the formation level are also presented.

Three Dimensional Modeling and Visual Analysis on Slope Multiple Information of Hurongxi Highway, China

The construction of Hurongxi highway is the one of the most difficult highway in the world. Slopes of Hurongxi highway are studied in this paper. Comprehensive three-dimensional (3D) modeling and visual analysis technique based on rock stratum model and skirt weathering model are put forward. The comprehensive model consists of slope multi-information, such as 3D accurate terrain, excavation, engineering measures, monitoring facilities, underground water, bridges and tunnels. An information analysis system of slopes along the highway is established combining database platform. It provides an effective visualization support platform for the analysis of the geological conditions of slope during the construction, decision making of excavation and protection and deformation warning, meanwhile, it also contributes a lot to some other similar slope engineering.

Case Study of Innovative Top-Down Construction Method with Channel-Type Excavation

AbstractAlthough the conventional top-down construction method is widely used in deep excavation, it has the drawback of low efficiency attributable to the long hauling distance and the possibility of the occurrence of excessive excavation deformation and construction risk. This paper introduces a case of deep metro station excavation at West Shanghai Railway Station. The top-down construction method must be used because the excavation is located under a running high-speed railway, and an innovative excavation scheme is proposed to improve construction efficiency and to control excavation deformation. In this method, an operation channel for earth hauling is first excavated in the middle of the excavation. With the available operation channel, the soil on both sides of the channel is excavated simultaneously in a segment pattern, and the required strut systems are subsequently constructed. Both the excavated soil and the construction materials are transported through the channel. This channel-type constru...

Simulation Analysis on Deep Foundation Pit Construction Near the History Style Construction

Based on the impact of deep foundation pit excavation to the adjacent history style construction, FLAC3D was adopted to establish the excavation and supporting calculation model of a pit in Tianjin. The excavation deformation was analyzed, and the contact slip effect of the supporting structure and soil was considered. The results of study are as follows. (1) The pit has been dig to the third layer, and the values calculated are consistent with the monitored ones by comparing simulation values and measured results on B1 section. (2) Digging to the bottom of the pit, we can predict the biggest horizontal displacement of soil is 34.6 mm, and the value is 11.2mm in the history style construction. Therefore, the results of the study can play a guiding role in the engineering construction safety.

Model Test Research on Excavation Technology of a Tunnel in Altered Granite Zone

Phenomenon of surrounding rock deformation and collapse, groundwater lowering, ground collapse and cracking appeared in a tunnel project. It is necessary to guaranty construction safety and ensure the reliability of supporting structures. This paper, using large-scale model, considers the surrounding rock deformations and stress adjustments caused by cavern excavation and tunnel support in the alteration zone. It suggests engineering protective measures by summarizing the major determinant of excavation deformation.

Deformation Prediction of Deep Excavation Using Support Vector Machine

Support Vector Machine (SVM) is a new pattern recognition method developed in recent years on the foundation of statistical learning theory. It wins popularity due to many attractive features and emphatically performance in the fields of nonlinear and high dimensional pattern recognition. Due to the complexity of the deep excavation, deformation prediction problem has not been a good solution. In the paper the support vector machine model was proposed to predict the deep excavation deformation. On the basis of deep excavation displacement data measured with real time series, the model of deep excavation displacement with time was built by SVM. Typical deformation data of deep excavation is used as learning and test samples. Comparison analysis is made between calculated values generated by SVM method and observed values. The result shows this method is feasible and effective.

Mechanism and Calculation Research on Excavation Deformation of High Layered Dip Rocky Slope

Based on rock Mechanical theory under unloading, according to the analysis of rock mechanics state of pre and post excavation of the layered dip rocky slope, it was found that excavation unloading cause deterioration of rock constitutive relation and structure plane’s mechanical parameters, deformation mechanism of high layered dip rocky slope was analyses when rock is at unloading condition in this study. Its deformation consists of the two parts which are rock mass unloading rock mass springback displacement and bedding-slip displacement along the rock mass discontinuity, and deduced the calculating formula of slope displacement. Research results with great guide significance and practical engineering value to similar engineering construction afterward.

Mechanism and Calculation Research on Excavation Deformation of High Layered Dip Rocky Slope

Based on rock Mechanical theory under unloading, according to the analysis of rock mechanics state of pre and post excavation of the layered dip rocky slope, it was found that excavation unloading cause deterioration of rock constitutive relation and structure plane’s mechanical parameters, deformation mechanism of high layered dip rocky slope was analyses when rock is at unloading condition in this study. Its deformation consists of the two parts which are rock mass unloading rock mass springback displacement and bedding-slip displacement along the rock mass discontinuity, and deduced the calculating formula of slope displacement. Research results with great guide significance and practical engineering value to similar engineering construction afterward.