Excavation Conditions Research Articles

Instability Modes and Stability Analysis of Perilous Rock Groups with Control Fissures Under the Conditions of Excavation and Rainfall

Influenced by external factors, perilous rock is prone to evolve into geo-hazard. Prevention and control design of geo-hazard is closely related to the correct quantitative analysis of the stability as well as in-depth study of the instability mode. As the main rock, limestone is widely exposed in the study area, which has resulted in perilous rock groups with control fissures at trailing edges. Monitoring data and investigation reveal that rainfall and roadway excavation are the main external inducing factors of perilous rock groups. Representative geo-mechanical models of the perilous rock groups were constructed based on the engineering geological investigation. Their mechanical behaviour affected by different inducing factors was analyzed, and the instability mode under the most dangerous condition was examined by the numerical simulation based on the discrete element theory. It is found that influenced by rainstorm and excavation, the overall instability mode of perilous rocks with specific geological structure can be divided into sliding and toppling tensile-shear failure. Furthermore, the overall stability of perilous rocks corresponding to these two modes was quantitatively analyzed using the limit equilibrium and fracture mechanics theories. The calculation results are considered to be reasonable and reliable due to the good agreement of the calculation theories with the failure mechanism of perilous rocks.

Deformation Characteristics of the Surrounding Rock of a Six‐Lane Multiarch Tunnel under Different Excavation Conditions

Highway tunnel plays an increasingly prominent role in the development of high‐grade highway traffic in mountainous countries or regions. Therefore, it is necessary to explore the deformation characteristics of the surrounding rock of a six‐lane multiarch tunnel under different excavation conditions. Using the three‐dimensional indoor model test and finite element analysis, this paper studies the dynamic mechanical behavior of a six‐lane construction, reveals the whole process of the surrounding rock deformation process of class II surrounding rock under different excavation conditions, and puts forward the best construction and excavation method. The results show that the maximum displacement rate of excavation scheme III is the largest, and the maximum displacement rate of excavation scheme I is basically the same as that of excavation scheme II. Therefore, in terms of controlling the displacement rate of the surrounding rock, the effect of excavation scheme I is basically the same as that of excavation scheme II, while that of excavation scheme III is poor. In terms of construction technology, scheme II is simpler than scheme I and can ensure the integrity of the secondary lining. Therefore, in class II surrounding rock of the supporting project, it is recommended to adopt scheme II for construction.

Behaviour of Square Footing Due to the Effect of Adjacent Excavation in Sand

In today scenario, urbanization and related infrastructure development in the form of an excavation adjacent to the existing structure are inevitable. In this case, the stability of an existing structure closer to the excavation is a serious concern. The main issue here is that, what is the safe distance at which new construction can take place from the existing structure? There are many research articles that states on the failure of an existing structure due to new construction adjacent to it in the form of excavations. Given the above, the paper presents the numerical results based on the finite element analyses that were performed for various parameters to examine the behaviour of existing square footing due to the effect of adjacent excavations in loose sand using PLAXIS3D software. In the finite element analysis, the behaviour of the footing and sheet pile walls were modelled using a linear elastic material and the elastoplastic behaviour of soil was modelled using a Mohr-Coulomb model under drained conditions. The literature available on this topic reveals that the excavation dimensions, shape of the footing, depth of the footing, location of the footing from the excavation, relative stiffness factor and relative density of sand are influencing the response of existing footing. Two different shapes of excavations such as a long length with narrow excavation under plane strain condition and short length of excavation under three-dimensional conditions were considered in this study. Numerical results indicate that the response of the square footing due to the effect of adjacent excavations are very much significant and mainly depends on the size of the excavation. The vertical and horizontal displacement, bending moment of the footing is increasing with an increase in depth of excavation. The footing located very closer to the excavation is significantly influenced as compared to the footing located far away from the excavation. The safe location of the square footing based on the settlement criteria is found to be 1.3 m from the excavation for shorter length excavation under three-dimensional conditions and 10 m for longer length of excavation under three-dimensional conditions.

Investigation of the excavation of stony soil slopes using the virtual element method

This study improved two parts of the virtual element method (VEM) to ensure that the stability of a stony soil slope, especially under excavation conditions, could be better studied. One of the improvements was the specific realization of the excavation algorithm, including the determination of how to identify polygonal elements that needed to be excavated, and the “deactivate and reactivate polygonal elements” used to calculate the excavation load during the slope excavation process. The second improvement was the calculation of the factor of safety (FOS) of a slope by combining shear strength reduction and the φ−ν inequality so that the stability of the stony soil slope could be better evaluated. The principal goal was to extend the latest developed virtual element method to the analysis and calculation of the excavation of a stony soil slope. Because the VEM was shape independent, it also allowed the number of nodes in an element to be chosen flexibly and fluidly, so the number of nodes could be changed easily during a simulated procedure. Two numerical examples of the one-step excavation of a homogeneous slope and the two-step excavation of a stony soil slope were solved with the improved VEM. The numerical results showed that the VEM could accurately simulate the excavation process of the slope.

Centrifuge modeling of soil slopes overlying bedrock under excavation conditions

A number of landslides occur in the soil slopes overlying bedrock due to excavation. However, the excavation-induced deformation and failure behavior and the coupling influential mechanism of the bedrock and excavation have not been clearly elucidated, although they are essential for the stability analysis of slopes overlying bedrock under excavation conditions. In this paper, a series of centrifuge model tests was conducted on the slopes overlying bedrock under excavation conditions with different bedrock shapes. The slopes overlying different bedrocks experienced a significant progressive failure process under excavation conditions, and the slip surface gradually developed from the excavation area at the slope toe to the slope top. The failure mechanism of the slope that overlies the bedrock under the excavation condition can be illustrated by the significant coupling of the deformation localization and failure. There was a shear zone, where the shear strain was concentrated with a substantial increase rate. The displacement direction of the soil in the shear zone was consistent and invariable for a slope overlying the bedrock after the shear zone appeared. Excavation led to a significant influence area inside the slope overlying the bedrock, which was significantly affected by the shape of the bedrock: steeper bedrock corresponded to a wider significant influence area, and flatter bedrock corresponded to a narrower one.

Wave Field Characteristics of Small Faults around the Loose Circle of Rock Surrounding a Coal Roadway

The geological conditions of coal roadway excavation are complicated. Seismic advanced detection is strongly influenced by the loose circle of fractured rock surrounding the competent coal seam. However, the three-dimensional wave field characteristics of small fault advanced detection in the condition of the loose circle of coal roadway have not examined. In this paper, numerical modeling and field tests were conducted to address this knowledge gap. The results indicate that when a seismic source near the tunnel face is excited, the body waves and a Love channel wave propagate in the tunneling direction toward the small fault, then produces reflected body waves whose amplitude is relatively weak, and a reflected Love channel wave whose amplitude is relatively strong. When reflected body waves and the reflected Love channel wave enter the loose circle of surrounding rock, the former's signal is unrecognizable in seismic record; but the latter converts to a Love wave whose amplitude is strong in the loose circle of coal seam. The Love wave which has a large interval from other wave trains in the time domain is easily recognizable in seismic record, which makes it suitable for advanced detection of small fault. The signal-to-noise ratio of seismic record of X component is higher than those of Y component and Z component.

TUNNEL SUPPORT BY ROCK QUALITY INDEX (Q) SYSTEM FOR ULTRABASIC ROCK: A CASE STUDY IN TELUPID, SABAH, MALAYSIA

The study area is underlain by the ultrabasic rock of partly Sabah Ophiolite Complex of Cretaceous ages. The objectives of this study are to determine the Q-value and to estimate the permanent support measures for 20m span, 10m high and eastern direction of the proposed tunnel in the study area. Engineering geological mapping (lithological and surface mapping and discontinuity survey), laboratory study (petrographical study) and testing (Uniaxial Compressive Strength testing) and data analysis (stereographic plots, Q system parameters evaluation and support estimation) was used in this study. The results show that the rock mass is classified as lherzolite, strong, excellent quality, more than four joint sets, slightly altered discontinuity wall, dry excavation and favourable stress condition. The equivalence dimension (De) are 15.4 for the permanent roof. The Q-value for permanent roof and wall of the proposed tunnel are 1.4 (Class D or poor and type 5) and 3.5 (Class D or poor and type 3), respectively. The permanent and temporary supports for the roof and wall are systematic bolting, 700J energy absorption of fiber reinforce sprayed concrete, 9-12 and 5- 6 cm thick fiber reinforce shotcrete, respectively.

Effect of excavation stress condition on hydraulic fracture behaviour

The fracture behaviour of single- and multi-stage hydraulic fracturing (HF) under varying excavation stress conditions was studied using a flow-coupled discrete element method (DEM). Conventional HF theories and analytical solutions for excavation stress redistribution are used to verify the numerical model. The numerical simulation results indicated that for the single-stage HF, both the in situ stresses and injection location have major influences on the HF propagation path, caused by the redistributions of the local maximum and minimum principal stresses under excavation conditions. Fractures generally propagate perpendicular to the local minimum principal stress (σmin) and also propagate preferentially towards the area with lower σmin. Hydraulic fractures propagation is dominated by tensile failure, and the generation of fracture branches is disfavored because of the high local compressive stress field induced by the HF process itself. As for multi-stage HF, different excavation stress conditions may cause different fracture development performances because of alterations of the preferred fracture orientation, blunting of propagating fractures, or creating a more complex fracture geometry in the affected zone. Therefore, when using high-pressure HF for preconditioning the rock mass to assist mechanical excavation in hard rock mining, performance can be enhanced by understanding the impact of stress changes and careful selection of appropriate HF methods depending on the in situ stress.

Experimental Study on Deformation and Acoustic Emission Characteristics of Arch Roadway under Different Unloading Rates

The essence of roadway excavation is a process of unloading at the periphery, and the influence of unloading paths on surrounding rock damage is directly related to the selection of support design and construction technology. The real stress state of surrounding rock is often affected by different excavation conditions in the actual construction process. Therefore, a testing system of excavation and unloading model was developed to simulate the unloading process of the arch roadway under different excavation conditions. Small hollow cylindrical specimens used in this experiment were made of cement mortar. The load at the inner cavity of specimens was removed under the constant action of external pressure and axial force to simulate the real excavation unloading process. The deformation, the failure modes, and the acoustic emission evolution characteristics at the inner of specimens were obtained under unloading conditions using the strain and acoustic emission monitoring systems. The experimental results indicate that deformation laws of surrounding rock were similar under different unloading rates and initial geostresses, but failure modes and acoustic emission characteristics were quite different. Compared with that of slow unloading, the damage of surrounding rock under rapid unloading mainly accumulated after unloading, and it is easier to induce rockburst after unloading. As initial geostress increased, the occurring time of the main fracture may be delayed relatively, and the phenomenon that the distribution range of peak frequency expanded and the amplitude rose gradually can be regarded as the precursor information of the main fracture occurring. This study can be used to provide experimental support for the failure and supporting design of surrounding rock in deep underground engineering.

Failure Behaviour of Sandstone with a Preexisting Joint under Stepped Excavation

Much geotechnical construction needs to be carried out under the condition of stepped excavation. However, there is still a lack of research on crack coalescence and failure modes of jointed rock mass under stepped excavation conditions. In order to simulate the stepped excavation test of the real project, the polylactic acid (PLA) material is selected as the filler for the excavation area. The stepped excavation tests are performed on sandstone specimens containing a preexisting joint under different normal load conditions. The dynamic stepped excavation of simulating excavate rock engineering is realised. The constant normal loads during the excavation process are determined to be 80 kN and 100 kN. The influence of the joint inclination on the failure characteristics of the excavation process is analysed. Four typical failure modes are summarised: (a) Mode I: crack coalescence of tensile failure; (b) Mode II: crack coalescence of mixed failure; (c) Mode III: without crack coalescence of mixed failure; (d) Mode IV: without crack coalescence of shear failure. Furthermore, the failure characteristics of the area above the excavation hole and the preexisting joint are analysed. The results show that there are three failure modes: (a) Type I: spalling failure; (b) Type II: shear slip failure; (c) Type III: shear slip and spalling mixed failure.

Case Study and Numerical Simulation of Excavation beneath Existing Buildings

Excavation beneath existing buildings may cause the superstructure to tilt and crack, which seriously affects the normal use of the superstructure. Due to the new working conditions of excavation beneath existing buildings, related case reports are rare and limited. In the case of No. 3 section basement construction project of Ganshuixiang, we monitored the excavation construction by burying test instruments at the designated location. Afterwards, Plaxis 3D finite element software was used to establish an underpinning pile‐cap‐excavation model, which can analyze the influence of different pile cutting sequences on the bearing behavior of new basement structural pillars. By comparing the in situ measurement data with the finite element model, it can be concluded that when the excavation depth rises, the axial force of the underpinning pile gradually increases, and the pile skin friction is slowly exerted from top to bottom. Different cutting sequences will influence the bearing behavior of the structural pillar. Moreover, the pile cutting process also significantly impacts its bearing behavior and the settlement behavior of the superstructure. Compared with the clockwise pile cutting sequence, the symmetrical pile cutting is more advantageous. In the whole process of the storey adding and reconstruction, the superstructure settlement is related to the working condition of digging and adding layers. In the stage from soil excavation to the concrete curing period of the structural pillar, it increases slowly with time and tends to be stable in the concrete curing period. However, in the pile cutting stage, the superstructure settlement increases sharply, and after pile cutting, it becomes stable.

Research on Influence of Pile-arch Conversion Structure on Existing Tunnel

Based on the actual project of Chongqing North Station project, this paper uses the software Flac3D to construct the excavation conditions of the foundation pit near the tunnel. A pile-arch conversion structure was applied above the tunnel. By examining the stress and axial force of the tunnel and calculating its safety factor, the advantages of the arch structure over the flat beam were explained, providing guidance and reference for similar projects in the future.

Antropoloji, Arkeoloji ve Sanat Tarihi Profesyonellerinde İskelet Sistemi Problemleri

Anatolia has been settled by numerous civilizations and many excavations uncover the traces of these civilizations. Excavation is a hard labor and some part of this hard work are performed by anthropologists, archaeologists and art historians. This can affect the skeletal systems of the workers after a long period of labor in excavations. In order to see wheteher physical activity has an effect, a survey was designed. The aim of the study is to reveal the most common skeletal system problems and their reasons in these professionals. A 20-questions-survey was applied to 303 academicians and museum staff who actively attend archaeological and paleontological excavations. The Google Forms application was used to apply the survey and its automatic statistic program yields the descriptive statistics for the research. The results reveal that working in excavation conditions cause effective skeletal system problems, especially in vertebral bones. 208 of 303 participants declare vertebra related problems, whereas 71 of them were diagnosed with herniated disc. These problems are seen in the later ages in the field work and therefore can be related with excavation conditions. Working in relatively short excavation periods and with a low budget, anthropologists, archaeologists and art historians have to overwork in little time. This is the major cause of working in unsuitable body postures. Nevertheless, a new strategy of the Ministry of Culture and Tourism plans to extend the excavations for the whole year with more professional workers to provide a chance to reduce skeletal system problems in anthropologists, archaeologists, art historians.

Usage of Human Labour in the History of Serbian Archaeology: Three Examples

Although archaeology is not the only research discipline where fieldwork is one of the tools in the process of acquiring knowledge, rare are the disciplines that harness and organize physical labour of non-professionals in the ways done by archaeologists during excavations. Throughout the history of archaeology the usage of physical labour has implied a firm hierarchical order in accordance to which archaeologists have bought or exploited human work during excavations. The physical effort to uncover the layers of earth covering archaeological sites is a tacitly implied part of the archaeological practice. The dichotomy and the relationship between an archaeologist/director of excavations/decision-maker, who considers, analyses and interprets the archaeological record, and the workers who undertake the more physically demanding tasks, has remained largely unchanged, conditioned by the traditional and commonsensical attitude towards archaeological practice. It is paradoxical that the research discipline, publicly mainly recognized through excavations, rarely investigates the conditions under which the human labour is organized and exploited during field campaigns. The paper treats some characteristic examples dating into the end of the 19th and the first half of the 20th century, starting with the excavations at Viminacium, the works at Stobi between the two world wars, and finally the forced labour during the World War II harnessed during the works at Kalemegdan. By discussing the ways and conditions under which human labour was used during these archaeological excavations, the paper raises the issue of the intention of archaeology and who is it aimed for. The cited examples point to the conclusion that the conditions of an archaeological excavation reflect the society, and the way in which the human labour was organized here speaks of the ways of valorising work. The examples of Viminacium and Stobi indicate that the idea of cultural heritage as a common good was shared by a small number of representatives of middle and higher social statuses, while physical labourers possessed no right over it. The excavations at Kalemegdan quite explicitly speak of the many ways in which the Third Reich exploited forced labour.

Dynamic Optimization Classification Model for Submarine Tunnel Surrounding Rocks and Its Application in Engineering

Hou, F.-J.; Xie, X.-K.; Shi, S.-S.; Song, S.-G.; Bu, L.; Li, L-P., and Zhou, Z.-Q., 2019. Dynamic optimization classification model for submarine tunnel surrounding rocks and its application in engineering. In: Gong, D.; Zhu, H., and Liu, R. (eds.), Selected Topics in Coastal Research: Engineering, Industry, Economy, and Sustainable Development. Journal of Coastal Research, Special Issue No. 94, pp. 311–315. Coconut Creek (Florida), ISSN 0749-0208.In order to make the classification of tunnel surrounding rocks more reasonable and accurate, a multi-index matter-element extension evaluation model was proposed for the advanced optimization classification of submarine tunnel surrounding rocks based on the extension evaluation method. Firstly, the rock mass integrity index Kv, Young's modulus E, the longitudinal wave velocity Vp, Poisson's ratio l, and groundwater W were selected as the evaluation indices. Secondly, the TSP detection technology was employed to collect quantitative indices. The main influencing factors, which were non-dimensional, were used to set up the matter-elements in order to make the evaluation indices comparable. Lastly, the matter-element extension evaluation model was applied to a submarine tunnel construction project in China and the evaluation results were compared against the excavation conditions on site.

Deformation Characteristics of Deep Excavation for an Interchange Station Based on the Model of Hardening Soil

The interchange station of Foshan Metro Line 1 and Line 3 was regarded as the research object, and a three-dimensional finite element model was conducted by the software of Midas GTS to simulate the excavation of the metro station based on the constitutive model of hardening soil. The FEM results show that the diaphragm wall presents two deformation forms those are the kicking at the bottom of the wall and rigid translation into the pit. Comparing the numerical calculation and monitoring results of horizontal displacement of representative monitoring points of diaphragm wall under different excavation conditions, it is proved that the numerical results which based on the model of hardening soil is practicable in Pearl River Delta.

Finite Element Analysis of Geotechnical Excavation Based on COMSOL Multiphysics

As the current geotechnical excavation process is affected by many factors, excavation will easily lead to abnormal conditions in the geotechnical excavation process. Based on this, this study used COMSOL Multiphysics finite element analysis to analyze the various factors affecting the geotechnical excavation process and set the various parameters of the project. This study studied the geotechnical excavation works in the presence of buildings and the absence of buildings. At the same time, the data were statistically analyzed and the changes of various parameters in the process of geotechnical excavation were studied on the basis of finite element simulation analysis. The research shows that COMSOL Multiphysics finite element analysis can effectively imitate the geotechnical excavation conditions and draw effective laws, which will be helpful for the effective development of follow-up projects and provide theoretical reference for subsequent related research.

Dynamics Model of Backhoe Devices Considering Excavation Load for Hydraulic Excavators

This paper presents a new dynamic model of backhoe devices considering excavation load so as to study the dynamic characteristics when the backhoe device is excavating. The dynamic model for the backhoe device was derived in matrix form by using Lagrange equation. The program of fourth-order Runge-Kutta method was coded in MatLab software so as to solve the dynamic model. Then taking composite excavation conditions as examples, The proposed dynamic model was used to calculate the counterforce of the kinematic pairs at all hinge points and solved the rotational movement laws (such as angular displacement, angular velocity, etc.) of the main components of backhoe devices around their rotary axes. In order to verify the correctness of the dynamic model, experiments of composite excavation conditions were done by using an XG822FL excavator, and the results of the experiment demonstrated that the proposed dynamic model is correct and effective to calculate the counterforce of kinematic pairs and solve the rotary movement laws of main components during the course of excavation, which can be used to predict the counterforce of kinematic pairs during the design process of backhoe device.

Energy Evolution of Coal at Different Depths Under Unloading Conditions

To explore the differences in deformation failure and energy evolution and simulate the real excavation conditions of coal masses at different depths during the coal-mining process, an unloading failure experiment was conducted. The experiment included coal samples at different depths from the no. 15 coal seam of the Ji group in the Pingmei coal-mining area. The sample depths were 300, 600, 700, 850, and 1050 m. The in situ stress environment, physical rock properties, and excavation disturbance influence were considered in the analysis. The results show that as the depth increases, the peak strength and residual strength of coal samples increase nonlinearly and that the deformation capacity simultaneously increases. The elastic strain energy stored before the unloading of coal, the total energy input, the accumulated elastic energy, and the dissipated energy generated during failure all increase with increasing depth, and the ratios of these results for the 1050–300 m samples were 10.79, 3.75, 3.78, and 4.67, respectively. A prepeak stage energy evolution model was established for coal samples from different depths, and the energy transformation trends of the deformation and failure of coal were explored from the perspective of the energy evolution rate. The energy dissipation efficiency (ued) was defined to represent the energy dissipation generated per unit of energy input. When the energy input is mainly transformed to dissipation energy, the failure of coal occurs (ued > 0.5), and the energy is predominantly associated with crack growth at this point, so the coal is quickly destroyed. This conversion occurs earlier as the depth increases. The AE energy release trend exhibited a good correspondence with the increases in the energy dissipation, dissipation rate, and dissipation efficiency with depth during coal unloading failure, which indicates a more intense failure of the coal body at deeper depths.

The Finite Element Analysis of the Boom of 20-ton Backhoe Hydraulic Excavator Based on ANSYS

Taking the boom of 20-ton backhoe hydraulic excavator as the research object, this paper analyzed the strength of the boom by ANSYS software, simulated the load condition of the boom under the bucket excavation condition, and obtained the stress distribution cloud diagram of the boom. The analysis results show that the stress of the boom of the excavator is mainly concentrated on the hinge of the boom and the stick cylinder, which is the weakest link.