Excavation Conditions Research Articles

Expansion of Terzaghi Arching Formula to Consider an Arbitrarily Inclined Sliding Surface and Examination of its Effect

This study expanded Terzaghi arching formula, which assumed a vertical surface as a sliding surface, to consider an arbitrarily inclined surface as a sliding surface and examined the effect of a sliding surface. This study firstly developed a formula to expand the existing Terzaghi arching formula to consider an inclined surface as well as a vertical surface as a sliding surface under the downward movement of a trap door. Using the expanded formula, the effect of excavation, ground, and surcharge conditions on a vertical stress was examined and the results were compared with them from Terzaghi arching formula. The comparison indicated that the induced vertical stress was highly affected by the angle of an inclined sliding surface and the degree of influence depended on the excavation, ground, and surcharge conditions. It is expected that the results from this study would provide a better understanding of various arching phenomenon in the future.

Experimental and analytical studies of the parameters influencing the action of TBM disc tools in tunnelling

The use of tunnel boring machines (TBMs) is increasingly popular in tunnelling. One of the most important aspects in the use of these machines is to assess with certain accuracy the effectiveness of the action of the discs on the cutter-head in the different rock types to be excavated. A specific machine, called an intermediate linear cutting machine (ILCM), has been developed at the Politecnico di Torino in order to study, on a reduced scale in detail in the laboratory, the interaction between the discs of the TBM and the rock: this machine allows a series of grooves to be cut on a rock sample of 0.5 × 0.3 × 0.2 m, through the rolling of a 6.5-in. disc, and evaluation, during testing, of the parameters associated with the action of the cutting tool. The parameters measured during the tests were compared with the results obtained employing two analytical methods widely used for predicting the performance of TBMs: the Colorado School of Mines (CSM) model and the Norwegian University of Science and Technology (NTNU) model. The latter showed a greater ability to reproduce tests conducted using the ILCM. However, as with the CSM model, it does not allow the optimal excavation condition (the ratio, which minimizes the specific energy of excavation, between the groove spacing and the penetration of the disc), necessary for the correct design of the TBM cutter-head, to be identified. An example, based on a real case of a tunnel in Northern Italy, allowed a demonstration of how the NTNU model provides results in line with the measurements taken during the excavation and represents, therefore, a model that is able to reliably simulate both laboratory tests and the action of a TBM on site. The NTNU model, together with the results of the tests with ILCM targeted on the identification of the optimal conditions of excavation, may allow the correct dimensioning of the TBM cutter-head to be attained in order to effectively implement the excavation.

Independent analyses of cutting and friction forces applied on a single polycrystalline diamond compact cutter

This paper presents an analysis of the excavation forces involved in the cutting action and in the friction of a cutter/rock contact. A vertical lathe-type device provided data on the forces applied on a single cutter under dry excavation conditions. A cutting device was used to perform cutting experiments with unworn and worn cutters. A tribometer was used to perform friction tests on the cutters wear flat previously realized with the vertical lathe. The experiments display results conform to the literature as the non-dependence of the cutting coefficient to the rock properties. Then, this study focuses on the cutting forces and explains that these forces include a component of rock shearing and impact friction. The impact friction is induced by the interaction between ejected rock particles and the cutting active area. The evidence of this impact friction is then brought by the formation of an eroded zone on the cutting active area.

Evolution of Design and Construction Approaches in the Field of Tunnelling: The Results of Applying ADECO-RS When Constructing Large Underground Works in Urban Areas

In the last 25 years in Italy, over 1000km of tunnels have been constructed in urban and extra-urban areas. Despite being constructed in very complex and difficult grounds; generally these were completed (from the design stage to the construction and actual opening of activity) with industrial methods, and within the technical times and costs foreseen by the design laid out by the tenders. This extraordinary result has been made possible since the public administrations have adopted modern design and construction approaches in their contract specifications, based on strictly scientific criteria and which leave nothing to the typical vagueness of those design and construction systems from the twentieth century, which remedied cavity instability solely by means of partitioning the excavation face. Today we know that full-face advancement is all the more necessary the more difficult the excavation conditions are. Memory serves to illustrate the criteria that helped define modern design and construction concepts and an example of their application for constructing a great twin tunnel (258 m2 + 258 m2 in section) in the urban area of Rome.

Analysis and estimation of gripper TBM performances in highly fractured and faulted rocks

This paper focuses on performance analysis of Tunnel Boring Machine (in particular gripper TBMs) in highly jointed rock masses and fault zones. In order to investigate possible relationships between these difficult excavation conditions and TBM performance, the data of several tunnel projects have been collected in a specific database (TBM-performance database). Despite the difficulties in gaining complete TBM data sets and detailed geological information, this database compiles data from the field, laboratory tests and literature. Preliminary analyses have been carried out in order to find possible correlations between TBM performance parameters (penetration and advance rates) and rock mass characteristics, such as rock strength and fracturing degree, generally used in common TBM performance prediction models. Although some trends could be identified, the scattered results confirm the difficulties in predicting the machine performance in complex geological environments starting from characterising indexes proper to good rocks. Then, a classification system for highly fractured rock masses and fault zones has been developed, based on representative parameters, providing a more complete geomechanical description of disturbed zones. Four “fault zone” classes have been identified. For each class a reduction rate of the selected TBM-performance parameters (i.e. cutterhead rotation speed, penetration rate and daily advance rate) has been evaluated with respect to the tunnelling performances recorded in good ground conditions. The results of these analyses allow effectively quantifying the effects of degrading rock masses on the TBM performances.

H-pile로 보강된 Sheet pile 흙막이 벽체의 적용을 위한 수치해석

This paper is results of numerical study for application of sheet pile retaining wall reinforced with H-pile as sheet piles are needed in field for a cutoff wall and are limited to use because of driveability in the ground condition of having a larger strength than a weathered rock. Extensive 101 cases of numerical approach were conducted to investigate the behavior of sheet pile retaining wall reinforced with H-pile, changing installing members of two types of sheet pile and three types of H-pile, the embedded depth of sheet pile and H-pile, the horizontal space between H-piles and excavation conditions. As the results of numerical analysis, combined use of the sheet pile SP-IIIA with H-Pile H250 and the sheet pile SP-IV with H-Pile H350 among precast products was found to be efficient since two members tended to reach allowable stresses simultaneously or have similar stress concentration ratios. Increased stiffness in reinforced sheet pile showed reduction of lateral displacement of wall. Embedded depth of sheet pile did not affect stability of wall significantly so that driving the penetrable depth of sheet pile should be enough to maintain stability of wall and satisfy purposes of cutoff and stiffness increase of wall.

Study of reducing ground resistance for transmission tower on rocky mountain tops with constrained area

An effective device to reduce the earth resistance of grounding systems for power transmission towers on rocky mountain tops with high soil resistivity and constrained area is proposed in this paper. In these scenarios, conventional methods such as using horizontal electrodes to reduce ground resistance require more space and fine‐grained soil for backfill. These methods are not applicable to scenarios where the ground consists of rock or crushed stone. To tackle such limitations, we propose an effective approach with less space and soil requirements. Based on the steady electric current field theory and the electrostatic field, the proposed approach designs a central grounding system by a special steel reinforcement cage. The layout of the cage is strictly based on theoretical calculations. The resistance of the central grounding system can be obtained by calculation and measurement. Results show that this scheme can reduce ground resistance effectively in comparison with the traditional method of imbedding horizontal radial electrodes in high‐resistivity soil on mountain tops where space is limited and excavation conditions are poor. The proposed method has also been validated in practical applications. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Mitigation of rock burst events by blasting techniques during deep-tunnel excavation

The buried depths of the auxiliary tunnels of the Jin-ping II Hydropower Station in China are between 1500m and 2300m, and some violent rock bursts were encountered during the excavation process. The measures of rock burst prevention adopted at this station are summarized in this paper, and the mechanisms of these measures are studied and discussed. Combined with the monitoring of the in-situ stress state and the burst proneness of surrounding rocks, the spatial distribution of the rock bursts along the deep tunnel axes and the statistics of rock bursts around the blasting working face are studied. It lays the foundation for generating the strategies for rock burst prevention. The results indicate that the development of rock bursts depends primarily on the level of in-situ stress and on the brittleness of rocks. Disturbances from excavation particularly under blasting excavation conditions have an important influence on the intensity and the scale of rock bursts. Therefore, two primary guidelines for controlled blasting are followed to control rock bursts. One is to decrease stress of the surrounding rocks; the other is to control the disturbance from the excavation. First, the stress-relief blasting method is adopted to reduce the stiffness of the surrounding rocks and reduce the concentration of stress in the blast area. Two different stress-relief blasting design schemes are applied and the extent of the damage and stress relieving effects are compared. Second, the effects of the blasting excavation disturbance in high-stressed rocks are examined. The results indicate that reducing the excavation footage can be used to control the blasting excavation disturbance in deep tunnels. The energy release rate (ERR) for different excavation footages is simulated to verify this conclusion. After the proper excavation footage and perimeter blasting parameters are adopted, the method is applicable to the control of blasting excavation and the reduction of rock burst intensity in engineering practices.

The Coupling Dynamic Analysis and Field Test of TBM Main System under Multipoint Impact Excitation

Damage by excessive vibration is serious engineering problem in TBM boring process. Dynamic characteristic analysis is essential for TBM antivibration design. According to TBM horizontal support structure, a dynamic coupling nonlinear model is established, with consideration of time-varying impact load and multicomponent complex relationship from cutter to gripper shoe. A set of field vibration tests is set up to accurately collect data under extreme work conditions; then, field data is collected from Liaoning northwest engineering. Field data is applied to validate simulation model to make sure time-varying damping stiffness, support cylinder stiffness, and the TBM machine stiffness distribution are reasonable. Simulation indicates the weakest part of TBM in axial and torsional DOF is the cylinder hinge and the connection shaft between motor and pinion, and the horizontal and vertical weak parts are bull gear. It also shows that, in normal excavation conditions, the acceleration amplitude of the cutterhead in three directions ranges from 1.5 g to 2 g. These results provide theoretical basis for the antivibration design and structural optimization of TBM.

Study on Effect of Frame Structures Crossed by Shallow-Buried and Mining Tunnelling

During the shallow-buried tunnel excavation, the formation will be affected and the nearby buildings will be caused fracture. By using three dimensional software MIDAS/GTS, the interactions among structures-soil-tunnel system is considered in this paper, and the working condition of shallow-buried underground excavation is simulated in the independent foundation of frame structures. It is indicated that building will tilt to the side of tunnel as the horizontal distance L between building and tunnels is increasing, after reaching certain distance, the influence to the building tends to little, at the same time, the maximum first principal stress P1 and maximum deformation rate E1 show a trend of decrease. When the kind of soil is worse, the settlement and non-uniform settlement of buildings increase, meanwhile P1 and E1 increase. With the increasing story of the framework, the settlement of building is nearly not affected, and P1 and E1 decrease slightly.

Determination of Main Influence Angle of Ground Settlement Caused by Xi'an Metro Tunnel Construction

Peck method and Stochastic medium method (SMM) are widely used in the field of ground movement included by urban soft ground tunnelling in China. The determination for the key parameter for SMM is also a problem because of the relative little experience from the engineering application in China. Through discussing the theoretical relationship between Peck method and SMM, Peck method can be regarded as a simplification of SMM where is used in relatively deeper excavation condition, and the method of determination for the key parameter for SMM is suggested. The suggested method are proven and verified by some practical engineering projects. Finally, they can significantly improve the adaptability of SMM in engineering application.

Analysis of the effect of the loading path on the failure behaviour of slopes

The effect of the loading path on the failure behaviour of slopes was investigated based on the centrifuge model test observations under the application of two typical loading paths: self-weight loading by increasing the centrifugal acceleration and excavation at a constant centrifugal acceleration. Compared with the self-weight loading condition, the slope was more likely to fail under excavation condition, with a significantly deeper slip surface. The quantification results showed that the sequences of slip surface formation associated with the two types of loading path proceeded in opposite directions. A reasonable stability analysis method of slopes should consider the progressive failure and the effect of loading path.

Evaluation of wall deflections and ground surface settlements in deep excavations

A study to illustrate the ground surface and wall movements due to excavation is undertaken based on two-dimensional nonlinear finite element (FE) modeling and analysis. The FE model and nonlinear solution strategy are built in the open-source software platform, OpenSees, of the Pacific Earthquake Engineering Research Center. A drained analysis was carried out using Drucker–Prager multisurface kinematic plasticity model for sand. The proposed model is verified using a case history in an urban excavation. The ground surface settlement and wall deflection for the various conditions of excavation are calculated. The results indicate that the extent of the settlement zone depends on excavation depth and is predicted as 2.5–3 times excavation depth, and the upper limit of the maximum ground surface settlement is equal to the maximum lateral wall deflection.

At the root of the early penguin neck: a study of the only two cervicodorsal spines recovered from the Eocene of Antarctica

The spinal column of early Antarctic penguins is poorly known, mainly due to the scarcity of articulated vertebrae in the fossil record. One of the most interesting segments of this part of the skeleton is the transitional series located at the root of the neck. Here, two such cervicodorsal series, comprising reinterpreted known material and a new specimen from the Eocene of Seymour Island (Antarctic Peninsula), were investigated and contrasted with those of modern penguins and some fossil bones. The new specimen is smaller than the counterpart elements in recent king penguins, whereas the second series belonged to a large-bodied penguin from the genus Palaeeudyptes . It had been assigned by earlier researchers to P. gunnari (a species of “giant” penguins) and a Bayesian analysis—a Bayes factor approach based on size of an associated tarsometatarsus—strongly supported such an assignment. Morphological and functional studies revealed that mobility within the aforementioned segment probably did not differ substantially between extant and studied fossil penguins. There were, however, intriguing morphological differences between the smaller fossil specimen and the comparative material related to the condition of the lateral excavation in the first cervicodorsal vertebra and the extremely small size of the intervertebral foramen located just prior to the first “true” thoracic vertebra. The former feature could have resulted from discrepancy in severity of external pneumatization. Both fossils provided valuable insights into the morphology and functioning of the axial skeleton in early penguins. Keywords: Antarctic Peninsula; La Meseta Formation; Palaeogene; early Sphenisciformes; cervicodorsal vertebrae. (Published: 20 November 2014) Citation: Polar Research 2014, 33 , 23861, http://dx.doi.org/10.3402/polar.v33.23861

Response Analysis of Block-Bearing Structure due to Tunnel Excavation in Clay Ground

본 연구는 점토지반에서 터널의 굴착조건(터널깊이 및 터널직경)과 시공조건(지반손실량), 지반조건(연약점토, 단단한 점토)을 변화시키면서 터널상부에 위치한 구조물의 거동변화를 조사 및 분석한 것이다. 분석에 사용된 구조물은 4층 블록식구조물로서 변형 등에 의한 균열발생과 균열폭의 차이로 인해 구조물의 손상정도를 쉽게 파악할 수 있는 특징이 있다. 다양한 터널 굴착조건 및 시공조건, 지반조건에 대해서 발생할 수 있는 터널상부 블록구조물의 거동상태를 파악하기 위해 수치해석적 매개변수 해석을 수행하였으며, 수치해석은 구조물의 실제크랙 발생을 묘사할 수 있도록 개별요소법(DEM)에 근거하여 수행하였다. 다양한 매개변수 해석으로부터 얻어진 구조물의 거동상태에 대한 결과는 터널 굴착조건 및 시공조건, 점토 지반조건과 상호 연관하여 함께 반영될 수 있도록 도표화 하였으며, 이를 이용하여 향후 점토지반에서 다양한 터널굴착 및 시공조건, 지반조건으로 인해 유발되는 터널 상부구조물의 손상정도를 보다 용이하게 파악할 수 있을 것으로 기대된다. This study investigates the response of structures to tunnelling-induced ground movements in clay ground, varying tunnel excavation condition (tunnel depth and diameter), tunnel construction condition (ground loss), and tunnel ground condition (soft clay and stiff clay). Four-story block-bearing structures have been used because the structures can easily be characterized of the extent of damages with crack size and distribution. Numerical parametric studies have been used to investigate of the response of structures to varying tunnelling conditions. Numerical analysis has been conducted using Discrete Element Method (DEM) to have real cracks when the shear and tensile stress exceed the maximum shear and tensile strength. The results of structure responses from various parametric studies have been integrated to consider tunnel excavation condition, tunnel construction condition, and tunnel ground condition and provide a relationship chart among them. Using the chart, the response of structures to tunnelling can easily be evaluated in practice in clay ground.

다중회귀분석을 이용한 대규모 비탈면의 위험도 평가

In this study, the correlation of evaluation items and safety rating for 104 of large-scale slopes along the general national road was analyzed. And, we proposed the regression model to predict the safety rating using the multiple regressions analysis. As the result, it is shown that the evaluation items of slope angle, rainfall and groundwater have a low correlation with safety rating. Also, the regression model suggested by multiple regression analysis shows high predictive value, and it would be possible to apply if the evaluation items of excavation condition and groundwater (rainfall) are not clear.

Research of an Slope under Rainfall and Deep Excavation Condition with UDEC

The landslides often due to the rainfall and the excavation inside. Although both of them could influenced the stability of the slope, in the different combination of the condition of rainfall and excavation. The results would make a big difference from condition. The analysis results of Finite Element Method have a large difference with the actual situation, especially in the large deformation and landslide. Therefore, we use the Distinct Element Method to simulate and analysis the collapse of Zengziya in Chongqing. We collect different parameters to simulate the changed conditions of the combination of rainfall, half excavation and whole excavation. Then we will get the data of displacement of the rock and the stress redistribution of the slope. By the analysis of the those data, and the comparison from the field situation, we will draw a conclusion that the main factors of the landslides is the rainfall, and the excavation sometimes can simulate the landslides. At last, our research results can make some help of the practical engineering.

Research on the Mechanical Behavior Effect of around Composite Foundation under Soil Lateral Displacement

This paper takes Nanhu project of Tangshan City under the soil condition of foundation pit excavation as an example. A model is established to research on the mechanical behavior effect of around composite foundation of CFG under soil lateral displacement by using ANSYS finite element software. The model analyzes the distribution law of horizontal displacement, stress of pile, soil between piles of CFG composite foundation under soil lateral displacement. Put forward a calculation formula of pile displacement by considering excavation depth, excavation distance.

모래지반에서 터널 굴착조건들을 반영한 상부 블록구조물의 거동변화 분석

본 연구는 모래지반에서 터널의 굴착조건(터널깊이 및 터널직경)과 시공조건(지반손실량), 지반조건(조밀한 모래, 느슨한 모래)을 변화시키면서 터널상부에 위치한 구조물의 거동변화를 조사 및 분석한 것이다. 분석에 사용된 구조물은 4층 블록식구조물로서 변형 등에 의한 균열발생과 균열폭의 차이로 인해 구조물의 손상정도를 쉽게 파악할 수 있는 특징이 있다. 다양한 터널 굴착조건 및 시공조건, 지반조건에 대해서 발생할 수 있는 터널상부 블록구조물의 거동상태를 파악하기 위해 수치해석적 매개변수 해석을 수행하였으며, 수치해석은 구조물의 실제크랙 발생을 묘사할 수 있도록 개별요소법(DEM)에 근거하여 수행하였다. 다양한 매개변수 해석으로부터 얻어진 구조물의 거동상태에 대한 결과는 터널 굴착조건 및 시공조건, 지반조건과 상호연관하여 함께 반영될 수 있도록 도표화 하였으며, 이를 이용하여 향후 모래지반에서 다양한 터널굴착 및 시공조건, 지반조건으로 인해 유발되는 터널 상부구조물의 손상정도를 보다 용이하게 파악할 수 있을 것으로 기대된다. This study investigates the response of structures to tunnelling-induced ground movements in sand ground, varying tunnel excavation condition (tunnel depth and diameter), tunnel construction condition (ground loss), ground condition (loose sand and dense sand). Four-story block-bearing structures have been used because the structueres can easily be characterized of the extent of dmages with crack size and distribution. Numerical parametric studies have been used to investigae of the response of structures to varying tunnelling conditions. Numerical analysis has been conducted using Discrete Element Method (DEM) to have real cracks when the shear and tensile stress exceed the maximum shear and tensile strength. The results of structure responses from various parametric studies have been integrated to consider tunnel excavation condition, tunnel construction condition, and ground condition and provided as a relationship chart. Using the chart, the response of structures to tunnelling can easily be evaluated in practice in sand ground.

지반굴착에 따른 흙막이벽 우각부 모서리 구간의 침하특성에 대한 실험 연구

본 논문은 다양한 굴착조건으로 모형실험을 실시하여 흙막이 벽체 우각부 구간의 거동에 대해 분석하였다. 실험대상 지반은 느슨한 상태의 모래지반으로 구성되었다. 실험의 시공조건은 우각부 길이, 근입깊이, 버팀대의 시공 유 무 등으로 구분하고 굴착은 총 4단계로 굴착하였다. 각각의 시공 및 굴착조건에 대해 모형토조 내 설치된 계측기를 이용하여 벽체변위 및 지표침하를 중점적으로 분석함으로써 우각부 모서리의 거동특성을 규명하였다. 실험결과 우각부의 길이가 길어질수록 벽체변위와 지표침하가 증가되어 직선구간에 비해 우각부구간이 구조적으로 불안한 구간으로 분석되었다. 근입깊이가 길어질수록 우각부 모서리구간의 지표침하가 약 40% 억제되는 것으로 나타나 설계 시 예상치보다 근입깊이를 증가시켜 적용하는 것이 안정성 확보에 유리하였다. 버팀대 추가 설치하여 우각부 모서리구간의 거동을 분석한 결과 최대지표침하는 약 40%, 최대수평변위는 약 30%의 감소효과가 있어 설계 시 우각부 모서리 구간에 근입깊이의 증가와 함께 버팀대를 추가 설치하는 방안이 안정성 확보에 효과적이었다. The experiment of model soil structures has been executed for the soil retaining wall in various conditions of excavation, in this study, to analyze the behavior of the corner of opening. The ground for experiment has been constituted with the sandy soil of relatively loose density, the construction condition has been divided into the opening length of corner, embedded depth, existence of strut, etc., and the excavation has been carried out for 4 stages in total. The behavior characteristics at the corner of opening area has been verified by concentrate analysis of the displacement of wall and the subsidence of ground surface, for each construction and excavation condition, using the measuring instrument mounted inside the model soil structure. In the result of experiment, it has been analyzed that the opening area of corner is unstable structurally compared to the linear area, as it shows that the wall displacement and subsidence of ground surface have been increased when the opening length of corner gets longer. The longer the embedded depth, ground surface settlement of coner was decreased 40%. To apply deeper embedded depth than designed estimate was an advantage in the safety. As a result of the analysis of coner behavior with added struts, maximum surface settlement and maximum horizontal displacement was evaluated 40% and 30%, respectively. Hence increased embedded depth with the added struts in coner edge was effective in the safety.