Excavation Scheme Research Articles

Recent rainfall- and excavation-induced bedding rockslide occurring on 22 October 2018 along the Jian-En expressway, Hubei, China

On 22 October 2018, at 17:20 (UTC+8), a bedding rockslide occurred on the right bank of the Jian-En expressway in Jianshi County, Hubei Province, Central China. Fortunately, a systematic displacement monitoring network provided an early warning. Thus, no casualties were caused by the rockslide, although two transport vehicles and three houses were damaged. To deduce the triggering factors and failure mechanism of the bedding rockslide, the geological characteristics, hydrogeological characteristics, slope excavation scheme, and rainfall data statistics were systematically investigated based upon field investigations, UAV photography, geological drilling, and laboratory tests. It was found that the bedding characteristics, presence of well-developed joints, and properties of the weak interlayers were the internal factors inducing the rockslide. The free face in front of the slope, the weak interlayer with low shear strength, and the through-going joint that formed the back boundary of slope constituted the boundary of the rockslide. The combined effects of improper slope excavation and concentrated rainfall were external factors that directly triggered the rockslide. The well-developed joints provided an effective infiltration channel for rainwater, and continuous rainfall deteriorated the shear strength of the weak interlayer ultimately causing the rockslide.

Influence of excavation schemes on slope stability: A DEM study

Slope failure due to improper excavation is one of common engineering disasters in China. To explore the failure mechanism of soil slope induced by toe excavation, especially to investigate the influence of excavation unloading path and rate on slope stability, a numerical slope model was built via particle flow code PFC2D. The development of crack and strain during excavation were obtained and used to evaluate the deformation characteristics. Furthermore, excavation types representing different unloading paths and rates were compared in terms of crack number and strain level. Results indicate that crack number and strain level induced by horizontal column excavation are much greater than those of vertical column excavation and oblique excavation. The crack number and strain level increase with excavation unloading rate. Besides, the feasibility of taking the average strain of slope surface and the average value of maximum strain along monitoring lines to represent the global deformation characteristics were discussed. This study can provide a theoretical guidance for slope monitoring and preliminary optimal selection of excavation scheme in the design and construction of slope engineering.

Influence of Underpinning Pile Drilling Construction on the Bearing Behavior of Existing Loaded Foundation Piles: Case Study

The mechanism of drilling borehole and its influence on the bearing behavior of existing foundation piles are unclear, hindering the application of excavation techniques. This paper proposes a new excavation scheme for high‐rise buildings in downtown and develops theoretical formulas to calculate the skin friction and end resistance of existing foundation piles affected by adjacent borehole drilling for installing underpinning piles. These underpinning piles are installed and connected with the existing pile by the head cap before excavation. In a case study, the parameter analysis was then performed to understand the effect of underpinning construction on the bearing behavior of existing foundation piles in terms of skin friction and end resistance. The results show that borehole diameter, depth of drilling borehole, distance between the existing foundation pile and drilling borehole, and number of boreholes have a negligible influence on the end resistance of existing foundation piles. The effect of drilling parameters on the skin friction of existing foundation pile, as well as the influence extent, varies for different parameters. The depth of drilling borehole and the number of boreholes have significant influence and thus should be considered in real engineering design while the borehole diameter and the pile‐pile distance have a negligible effect. The proposed new excavation technique could be potentially adopted for real engineering design of underneath excavation projects for high‐rise buildings in downtown.

Design, Construction and Uncertainties of a Deep Excavation Adjacent to the High-Rise Building

In present infrastructure development, deeper basements are provided to satisfy parking scarcity. Safety and economy decide the system of shoring to go deeper below the ground level. This paper provides the design and construction of a deep excavation for an office building located at Bengaluru. Finite element model developed through PLAXIS 2D software is used for designing the shoring system in the present case study. The design and construction of two different deep excavation schemes are discussed in this paper, they are proposed based on the soil profile, constraint of space, presence of adjacent structures and service lines. Along the excavation line at some locations, existing buildings were located in very close proximity leading to lack of space for providing required slope for stabilising with driven nails, so in order to keep the excavation sides stable in those locations contiguous pile with soil/rock anchors was proposed. This deep excavation was of particular interest because of the uncertainties faced during construction which lead to failure of almost 20 m deep slope adjacent to existing high-rise building. The existing adjacent high-rise building was fully functional at the time of deep excavation. Potential large deformation of the adjacent high-rise building caused due to slope failure was one of the main concerns immediately after the failure. The immediate remedial measures taken to safeguard the footing of the existing high-rise building has also been included in this paper. The measure includes like immediate backfilling followed by grouted nail proposed along the failure surface.

Optimization Construction Scheme of Single-Sided Shallow Tunnel Enlarging

At present, the construction schemes of tunnel enlarging are analogized by creating a new tunnel through a traditional method. However, the traditional excavation method ignores the advantage of long-term support and stability of the original tunnel lining to the surrounding rock, and the construction efficiency is also reduced. The optimized construction plan was theoretically analyzed using the case of the Chongqing Yuzhou tunnel enlarging. The optimization construction schemes of single-sided shallow tunnel enlarging were extracted in accordance with the foundation of the study on the construction mechanics of a shallow tunnel, that is, the way of the rational arch axis enlarging in the crosswise direction and the jump-driving method in the lengthwise direction. The construction analysis was compared with the field monitoring measurement results and ANSYS simulation of the 3D finite element calculation of the entire tunnel enlarging process. By optimizing the construction scheme, the calculation value of the compressive stress of the original tunnel lining was increased by excavation face advancing. The original tunnel lining that had not been dismantled can play the role of the column and bear the surrounding rock pressure caused by the jet-hopping excavation. This lining could effectively improve the safety and stability for tunnel enlarging. The adopted rational arch axis excavation in the transverse direction could reasonably and significantly transfer the surrounding rock pressure. This process could reduce the tensile stress and increase the compressive stress of the initial support structure. Results of the numerical calculation and field monitoring data showed that the excavation scheme of the shallow tunnel is optimized after unilateral expansion. The optimization construction schemes can change the original rock stress path and play a role in the surrounding rock stability. The displacement of the tunnel vault can be reduced by 16%-20%, and the tunnel vault does not appear in the tension zone. The optimization of construction scheme can reduce the arch subsidence and tensile stress of the lining, ensure the safety of construction, and shorten the construction period. These obtained beneficial conclusions can be supplied to the next similar tunnel enlarging projects.

Characteristics of failure area and failure mechanism of a bedding rockslide in Libo County, Guizhou, China

Owing to the continuous rainfall, a bedding rockslide occurred at a construction site on the San-Li highway (Sandu County to Libo County) at 18:05 (UTC+8) on September 23, 2017, in Libo County, Guizhou Province, China. This bedding rockslide caused three deaths, six injuries, and an accumulation zone of approximately 1.8 × 105 m3 of medium weathered limestone that blocked the main line of the M ramp. To explore the triggering factors of this rockslide, the engineering geological condition, hydrogeological condition, slope excavation scheme, and statistics of rainfall data were investigated based on field investigations and geophysical drilling. The blasting failure of the upper unstable and dangerous rock masses after the bedding rockslide was analyzed. Three instability behaviors characteristics are distinguished: (1) the bedding characteristics of the rock formation and weak interlayer, (2) the steep slope (the largest dip angle being 46°), and (3) the appearance of the free face induced by the slope excavation. The results indicate that the above conditions are objective factors, and continuous rainfall triggers the bedding rockslide. The landslide follows the step-path failure mode.

DNMA: A double normalization-based multiple aggregation method for multi-expert multi-criteria decision making

This paper develops a comprehensive algorithm for multi-expert multi-criteria decision making problems considering quantitative and qualitative criteria in forms of benefit, cost or target types. We focus on using probabilistic linguistic term sets to express the qualitative evaluations due to their excellence in expressing complex individual and collective linguistic assessments. Firstly, we develop a target-based linear normalization technique and a target-based vector normalization technique. A weight adjustment method is proposed to achieve the tradeoff between criteria after normalization. Given that the two target-based normalization techniques have different advantages, we then propose a ranking method, which consists three subordinate models, based on these two target-based normalization approaches and three aggregation techniques. Reliable results of a multi-expert multi-criteria decision making problem are determined by integrating the subordinate utility values and the ranks of alternatives. The proposed method is implemented to solve the green enterprise ranking problems and the excavation scheme selection problem for shallow buried tunnels, respectively. The advantages of the proposed method are emphasized through comparative analyses with other ranking methods.

Technological Indicators of Direct Dumping Zone as a Part of Combined Mining Method

Under the conditions of a combined mining system overburden is developed using a transport and non-transport technologies, specific costs for non-transport technology are lower than transport costs. The change in the non-transport bench height led to the redistribution of the volumes of transport and non-transport overburden. With an increase in the volume of non-transport overburden, the share of more expensive transport overburden is decreases, while the technical and economic indicators of the non-transport zone deteriorate due to an increase in re-excavation volumes. The change in the non-transport bench height affects the recasting ratio and the annual advance coal face line, which determine the cost of developing the overburden. This article presents the results of a study of the laws of change in the recasting ratio and the annual advance coal face line, depending on the non-transport bench height within a combined mining system of flat seam. The obtained patterns were established as a result of solving problems of substantiating typical excavation schemes of the direct dumping method and developing a mathematical model for identifying excavation schemes with the subsequent calculation of their technological indicators.

The Elastic–Plastic Damage Analysis of Underground Research Laboratory Excavation for Disposal of High Level Radioactive Waste

The deep geological disposal is an internationally recognized method for the disposal of high level radioactive waste. As an essential facility, the construction safety of underground research laboratory (URL) is very important. Taking the China’s first URL in Beishan, Gansu Province as engineering background, considering the influence of arranged joints in rock mass, an elastic–plastic damage numerical method for fractured rock mass is presented and the corresponding subprogram in Flac3D is developed. Based on the numerical calculation of underground research laboratory construction, the optimized excavation scheme of URL is obtained and the distribution rules of surrounding rock displacement field, stress field and plastic damage zone are studied. The research result can provide important guidance for the construction of Beishan URL.

Excavation Optimization and Stability Analysis for Large Underground Caverns Under High Geostress: A Case Study of the Chinese Laxiwa Project

In situ investigations and detailed laboratory tests indicated that the granite at the Laxiwa hydraulic station is a typical hard rock, with high compressive strength and elasto-brittle failure modes, such as spalling and slabbing, and that the underground caverns are prone to brittle failure. Thus, an intelligent optimization method for cavern excavation was developed to improve the underground engineering’s stability during its construction. This artificial intelligence method utilized the advantages of both the particle swarm optimization algorithm, which is capable of global optimization, and the support vector machine algorithm, which is capable of highly nonlinear mapping. The corresponding numerical analysis indicated that this optimization of excavation sequencing can considerably reduce both the total volume of the damage zone and the brittle failure of the surrounding rock. Furthermore, the measured deformations, the depth of the tested excavation damage zone, and the exposed in situ failures resulting from the applied excavation scheme were similar to the results predicted by the numerical simulation of the cavern excavation.

Numerical simulation of the behaviors of test square for prehistoric earthen sites during archaeological excavation

During the process of archaeological excavation in the regions of Southeast China, collapse of test square usually occurs due to poor site-specific conditions. In this paper, the fast Lagrangian analysis of continua in three dimensions (FLAC3D) is employed to reveal the behaviors of test square. Taking the archaeological works in Liangzhu prehistoric earthen sites as the research background, the paper first introduces the geological setting, excavation procedure and monitoring scheme of the studied test square. Then, the deformation of four sides of the test square is modeled using FLAC3D. By comparison, it shows that the numerical results are consistent with the results from field monitoring. The result suggests that the numerical simulation can be effectively applied to representing the actual behaviors of the test square, which is helpful for determination of excavation scheme and stability evaluation of the test square during archaeological excavation.

文登地下厂房开挖方案围岩稳定性分析

文登地下厂房开挖方案围岩稳定性分析

Analysis on Ground Surface Settlement of Newly Built Tunnel under Existing Expressway

Relying on the Beihuan tunnel project, the numerical calculation of the excavation of the newly built tunnel down-traversing the existing expressway is carried out. The ground settlement deformation law of the expressway under different excavation schemes is analyzed, and the applicability of Peck formula in the calculation of the influence scope of ground settlement is discussed. The results show that: the numerical calculation of surface settlement range corresponds to Peck formula predicted result well.

Numerical Investigation of the Optimal Construction Sequence of an Actual Super Shallow Large-Span Tunnel

The construction process of super shallow large-span tunnel is quite complicated comparing with the construction technique of regular tunnels; therefore, it is deserved to investigate the optimal construction sequence which determines the schedule and safety management of the tunnel excavation. To address this issue, the optimal excavation procedure of the super shallow large-span tunnel is investigated using numerical analysis in this study, based on a practical tunnel project. First, the analytical finite element model of an actual tunnel structure is established to implement the numerical simulation of different tunnel excavation. Second, some numerical results are analyzed for the selection of the optimal construction excavation, such as the variation rules of the surface settlement, crown displacement and side wall deformation etc. The analytical results show that the ground surface heaves with the tunnel excavated and the crown displacement improves gradually. Finally, the optimal excavation scheme is determined by comparing the deformation of the tunnel structure and the law of surface subsidence.

In situ observation of spalling process of intact rock mass at large cavern excavation

This paper presents the results of in situ observation of rock spalling process of a large underground powerhouse, with 34m in span and 88.7m in height, during excavation layer by layer over two years. A method for in situ observation of rock spalling process has been established in pre-installed boreholes by using digital borehole camera. Observation results clearly show the whole process of rock fracturing and the associated spalling failure. Not only could the development of rock fracturing and spalling affected by the step-by-step excavations along the cavern's axis be captured, but also could the effect of the subsequent excavation layer by layer on the previous rock fracturing and spalling area be observed. The failure mechanism of rock mass surrounding the large cavern, which involves complex excavation sequences, could be better understood through the observation results. The difference of rock spalling behavior between large cavern and small tunnel is discussed. Influence of geostress, geological structures, rock mechanical properties, and layered excavation process on rock spalling process has been analyzed. The results in this study is instructive for rethinking the engineering design including the excavation and support at similar large underground caverns, as well as for the dynamic adjustment of excavation schemes and support optimization during the construction of a large cavern subjected to high geostress.

Discrete element modeling of progressive failure in a wide coal roadway from water-rich roofs

Progressive failure of roadway roofs is a common failure mechanism in underground coal mines, especially when water-rich roofs are in close proximity to the roadway. In this case study at a Chinese coal mine, the UDEC-Voronoi method was used to investigate the process of progressive roof failure in a wide coal roadway from water-rich roofs. In the numerical scheme, the studied domain was partitioned into polygonal blocks bonded through contacts with pre-defined dimensions. The parameters of polygons and contacts in the Voronoi program were calibrated to rock mass properties obtained through laboratory tests. Based upon laboratory tests and previous research findings, a time-dependent strength degradation process from water absorption was assumed and implemented in the numerical modeling. Next, the progressive failure of a roadway from water-rich roofs was analyzed in detail. The numerical results agreed well with field measurements and observations. This method was demonstrated to reproduce the real phenomenon of roof failure in all of its complexity. The numerical results revealed that the progressive failure mechanism was characterized by an initial fracturing of the roof due to strength degradation, which was followed by significant dilation as fractures grew. The large span of the roadway further contributed to the roof failure process. The results also clearly showed that shear cracks were predominant in the roof and played a major role in the behavior of the roadway roof. Additionally, support and excavation schemes that affect roof stability were observed.

A Mitigation Technique to Reduce Ground Settlements Induced by Tunnelling Using Diaphragm Walls

Ground movements due to the excavation of shallow tunnels may cause damage or loss of functionality to nearby buildings: embedded diaphragm walls pre-installed between the tunnel and the building can be effective in reducing these movements thus preventing damage on existing structures. Plane strain finite element analyses are first presented in the paper in which a continuous diaphragm made by adjacent panels was modelled to evaluate the effects of different geometrical and mechanical parameters. For a limited set of these parameters, 3D FE analyses were also performed maintaining a plane strain excavation scheme to evaluate the effectiveness of an infinite diaphragm made by closely spaced piles. A 3D study is finally presented in which the horizontal diaphragm length needed to attain the same efficiency provided by an infinite diaphragm is evaluated. Completion of tunnel construction was assumed in both 2D and 3D studies.

Comparative Analysis of Excavation Schemes for a Tunnel Constructed through Loose Deposits

AbstractBecause of weak surrounding rock, tunnels constructed in loose deposits are prone to collapse, and secondary linings commonly suffer excessive deformation. Therefore, it is important to select an appropriate excavation scheme, which will affect both tunnel construction safety and subsequent tunnel operations. This paper takes the Tingziba tunnel, a highway tunnel shallowly buried in loose deposits of diluvial and proluvial origin, as an example. During construction, this tunnel experienced many instances of vault collapse and advanced support destruction. Isotropically consolidated drained (CD) compression tests were carried out on reconstituted specimens to obtain the mechanical parameters of the loose deposits. Three-dimensional modeling was performed to simulate stress and deformation distributions in the tunnel after excavation by three different schemes, i.e., up and down bench tunneling, three-bench tunneling, and single-side heading tunneling. The comparative analysis results showed that si...

Comprehensive evaluation of high-steep slope stability and optimal high-steep slope design by 3D physical modeling

Abstract High-steep slope stability and its optimal excavation design in Shuichang open pit iron mine were analyzed based on a large 3D physical simulation technique. An optimal excavation scheme with a relatively steeper slope angle was successfully implemented at the northwest wall between Nos. 4 and 5 exploration lines of Shuichang Iron Mine, taking into account the 3D scale effect. The physico-mechanical properties of rock materials were obtained by laboratory tests conducted on sample cores from exploration drilling directly from the iron mine. A porous rock-like composite material was formed for the model, and the mechanical parameters of the material were assessed experimentally; specifically, the effect of water on the sample was quantitatively determined. We adopted an experimental setup using stiff modular applied static loading to carry out a visual excavation of the slope at a random depth. The setup was equipped with acoustic emission (AE) sensors, and the experiments were monitored by crack optical acquirement, ground penetrating radar, and close-field photogrammetry to investigate the mechanisms of rock-mass destabilization in the high-steep slope. For the complex study area, the model results indicated a clear correlation between the model’s destabilization resulting from slope excavation and the collected monitoring information. During the model simulation, the overall angle of the slope increased by 1–6 degrees in different sections. Dramatically, the modeled excavation scheme saved over 80 million tons of rock from extraction, generating enormous economic and ecological benefits.

Construction and stability of an extra-large section chamber in solid backfill mining

In solid backfill mining without gangue removal, the gangue is separated directly underground and backfilled into goaf. This necessitates the underground construction of an extra-large section chamber for separation equipments. For the construction of an extra-large section chamber in the Tangshan mine, we proposed an active support through a combination of bolting, anchor cables, lining, and a reinforced chamber floor by inverted arch pouring. ABAQUS software was used to analyze the surrounding rock deformation and the plastic zone development of the chamber under different excavation schemes. The best excavation scheme was determined, and the effectiveness of the combined supports was verified. In practice, the engineering installation showed good overall control of the movement of the surrounding rock, with roof-to-floor and side-to-side convergences of 154.6 and 77.5mm, respectively, which meets the requirements for underground coal gangue separation.