Safe Excavation Research Articles

Stability analysis of underground water-sealed oil storage caverns in China：A case study

The stability of underground water-sealed oil storage caverns is of great importance for safe excavation and operation. To analyze the scope of the failure zone and underground cavern stability accurately, a new method was developed that integrates the rock tunneling quality index Q-system and stability graph method with 3D laser scanning and numerical simulation. The point cloud data were obtained by 3D laser scanning, and the cavern model was built by using DIMINE software, which directly shows the 3D shape of the cavern. The rock mass physical and mechanical parameters and the corresponding stability coefficients were obtained based on Q-system and stability graph method. The plastic zone distribution and deformation characteristics of surrounding rock were analyzed through numerical simulation. Then, the corresponding relationship between caving zone and plastic zone was determined by comparing the numerical simulation results with the 3D laser scanning contour. The new method provides a reliable way to analyze the stability of the underground water-sealed oil storage cavern and also will helpful to design or optimize the subsequent support.

Combined Application of Pipe Roof Pre-SUPPORT and Curtain Grouting Pre-Reinforcement in Closely Spaced Large Span Triple Tunnels

The platform of the Badaling Great Wall Underground Station consisted of large span triple tunnels. The triple tunnels passed through several major faults. Based on preliminary in situ monitoring, the interaction behavior among triple tunnels was significantly severe, and the original supports failed to meet the safety requirement. Therefore, pipe roof pre-support (PRPS) and curtain grouting pre-reinforcement (CGPR) were used as the pre-construction techniques. By numerical investigation, the pipe diameter, the arrangement angle of PRPS, and the grouting thickness of CGPR were optimized as 108 mm, 150°, and 3 m, respectively. According to numerical results, PRPS predominantly bore loose rock and reduced mean crown settlement (MCS), while CGPR primarily improved the mechanical properties of rock and decreased the pillar plastic ratio (PPR). PRPS and CGPR had complementary advantages in time, space, and mechanical properties. PRPS could timely form a strong arch structure far ahead of the tunnel face, CGPR could effectively restrict the development of plastic zone. They mutually and actively formed a strong permanent ring in front of the tunnel face. After the field application of PRPS and CGPR, the mean surrounding rock pressure reduced by 33.4%, the MCS reduced by 58.7%, and no support damage was observed. The excavation safety was guaranteed.

Application of Directional Long Borehole Technology in Working Face of Thick Coal Seam Along Top Driving

With the increasing of gas content in a coal mine in Shanxi Province, when the coal seam roadway is driving along the top, the extraction effect of ordinary borehole is not good under the complicated geological condition of high gas content and thick coal seam. The traditional “step type” gas control method of ordinary borehole has seriously affected the mine excavation replacement and safety production. In view of the existing problems of gas control in mine heading face, this paper introduces the technology of long directional borehole extraction. Through the field test, investigation, comparison and analysis, the tunneling speed of the tunnel is increased from the original 150m / month to 240m / month; compared with the safe excavation of the 400m roadway, the directional long borehole extraction process was 37 days faster than the traditional ordinary borehole extraction process; the gas concentration in the working face and return air flow was reduced by about 0.3% on average, which greatly reduced the ventilation pressure during the excavation and ensured the safe excavation of the working face. Finally, the extraction technology and parameters of the long directional borehole along the heading face of the thick coal seam are investigated.

Engineering Geology and Hydrogeology Aspects of Sedimentary Jurong Formation in Singapore: Implication on Safe Excavation of Underground Storage Caverns

The first commercial underground rock caverns for hydrocarbon storage in South East Asia, the Jurong Rock Caverns (JRC) Project, has recently been completed in Singapore. Extensive in situ permeability tests in boreholes and intact strength testing on rock cores were carried out to determine required design parameters in feasilibity study stage and during construction period. In-situ horizontal stresses of rock mass were measured in construction stage. After correlation between hydrogeological test results and geological characteristics of the tested interval, the geological and hydrogeological model is established. Geology face mapping were performed at every location after blasting of rock faces for the records of discontinuities parameters, Geological Strength Index (GSI), Tunnel Quality Index (Q) and Rock Mass Rating (RMR). The general correlation equation between Q and RMR in JRC is established. From the intact strength properties, equivalent rock mass parameters were successively determined after applying relevant GSI and D (Excavation Damage Factor) of rock masses. The main aim of this study is to document the new discoveries of the project including observation after broad analyses on the engineering properties for stability of the project.

Study on Propagation Characteristics of Seismic Wave in Rock Tunnel Excavation Blasting

Based on the excavation of rock tunnel in Da’anshan coal mine, the paper carried out the vibration monitoring on blasting excavation is carried out in the rock tunnel. Through analyzing the time and frequency of the monitored blasting seismic wave by HHT transformation, the energy distributions of blasting vibration characteristics and seismic wave are obtained, which provides a strong basis for the establishment of rock absorption measures and safe excavation in rock tunnels.

A new empirical approach to estimate temperature effects on strut loads in braced excavation

In deep excavation designs, strut loads play a key role to ensure excavation safety. During the construction, temperature fluctuation inevitably leads to a variation in strut loads. Therefore, how to quantitatively estimate the effects of temperature on strut loads is a matter of concern. In this study, the incremental changes in wall deflection due to temperature fluctuation were assumed to be piecewise linear. Based on the beam-on-elastic-foundation (BEF) model, an empirical approach accounting for the variation in temperature-induced strut loads at all levels was established. This model was further calibrated against a reported case study for a more precise predictive performance.

Search and graphical display of hazardous blocks in underground roadway roofs

The study of search and graphical display of hazardous blocks on roadway roofs is of great importance to the safe excavation and long-term utility of roadways. In this paper, the GeneralBlock program was used to carry out preliminary analyses of blocks, which were developed based on the General block method. Following this, the removability and stability of the buried and fixed blocks under engineering disturbances were analysed according to the minimum fixed area of the blocks. In addition, accurate positioning and three-dimensional graphical displays of hazardous blocks were carried out through the coupling of GeneralBlock and 3DMine. Finally, a technology for searching and displaying hazardous blocks on roadway roofs in underground mines was developed, and it was subsequently applied to the production roadway in #92 ore body and the development roadway in Zinc polymetallic ore body of the Tongkeng mine, Guangxi, China. One hundred and twenty hazardous blocks were found on the test site during the production process of #92 ore body. These blocks were mainly located in the segments of 0–3 m and 12–20 m on the Y-axis; a total of 31 hazardous blocks were found in the development roadways of the levels 255 and 305 in Zinc polymetallic ore body, and the volume of the largest hazardous block located in the B5 roadway was 1.44 m3.

Damage Prevention for underground utilities using machine guidance

Abstract More than half of the world's population resides in urban areas, which has resulted in increased demand for utility services. Properly designed and well-managed utility infrastructure systems play an important role in the sustainability of cities. The complexity of underground utilities is highly problematic, as it has many types of service lines comprised of different materials. Damage to underground utilities during excavation is a serious problem that can result in casualties, injuries, project delays, disruptions in costly services, and large repair costs. Missing depth information, inaccurate available utility position data, and lack of visual guidance for utility locations have been identified as the major reasons for utility strikes during excavation operations. These accidents can be prevented if the machine operator is aware of the utility location with reference to the equipment position. In this paper, a novel approach is presented to model underground utilities for a machine guidance system to provide visual guidance to the operator. This approach is useful for avoiding catastrophic utility strike accidents and promoting safe excavation operations. Two case studies were conducted for reviewing the proposed methodology and its application in the machine guidance system. The underground utility data was collected by using GPR in combination with a highly accurate RTK GPS system. An uncertainty buffer zone is proposed that enclosed the true location of the utility as an extra safety measure to avoid a utility strike during excavation. The objective of this research is to devise a simple and easy process to model the underground utilities for a machine guidance system to promote safe excavation.

Practical Considerations in Establishing the Statistical Reliability of Geomechanical Data

In an underground mining operation, the design of safe excavations can be influenced by the quality and quantity of collected geomechanical data. Data collection is the first step in mine design, and a sufficient level of confidence in the input data should be reached depending on the project stage and the design requirements (e.g. temporary and non-entry vs. permanent and entry excavations). This paper compares two statistical analysis methods for quantifying the level of confidence in the intact rock properties obtained through a series of laboratory tests. The laboratory testing database of an underground hard rock mine was used to highlight the variations in the two methods. The impact of the two methods, from an engineering perspective, was illustrated with an example using the Kirsch analytical solution. This investigation demonstrated that the selection of the appropriate analysis method should be guided by the project requirements.

Damage threat to sensitive structures of a thermal power plant from hard rock blasting operations in track hopper area: A case study

The article deals with the development of controlled blast design patterns and methodologies for excavation of hard rock for foundation work of a track hopper in a running thermal power plant in close proximity of many sensitive structures. Test blasts were conducted with different blast geometries and charge loading patterns at selected locations. The results of the test blasts were analysed to evolve safe controlled blast design patterns and methodologies for completing the total excavation work. The threshold value of vibration for the safety of various structures/foundations present has been taken as 25 mm/s based on the dominant frequency content as well as guidelines from the regulatory authority. The dominant frequency content of the ground vibration waves was in the range of 10–40 Hz. Controlled blast design parameters, namely maximum explosive per delay, size of the blasts and blast geometry were formulated based on established ground vibration predictor equation and nearness of structures concerned from the blasting point. Two blasting zones were classified for safe excavation work. For the first zone within 20 m from the structures, controlled blasting using 32-mm diameter blast holes with small blast geometry was suggested, whereas for the second zone beyond 20 m, controlled blasting with 100-mm diameter holes with lesser hole depth and limited number of holes was suggested. The whole excavation work in the track hopper area was completed safely without causing any damage to the nearby sensitive structures of the running thermal power plant.

Improvement of Gas Drainage Efficiency of Low-Permeability Coal Seams Using Ultra-High Pressure Hydraulic Cutting Technique

With the increase in the coal mining depth, the dynamic disasters of deep coal seam under the combined effects of high crustrals stress and high gas pressure seriously restrict the safety production of the coal mines. Moreover, it is very difficult to lower the gas content of the low-permeability coal seams. Even though numerous boreholes have been drilled inside the coal seam and gas drainage have been performed for a long period. High-pressure water jet cutting technology can effectively increase the exposure area of coal seams, improve the gas flow state in coal seams, so that the coal can be evenly and fully discharged in a certain range, and then the goal of rapid discharge and permeability enhancement can be achieved. After cutting the coal seam between 1m and 2m interval, a uniform pressure relief space is formed inside the boreholes to increase the permeability of the coal seam and improve the gas drainage efficiency The field test results shows that the equivalent diameter of boreholes with cutting is about 5 times that of boreholes without cutting. The gas drainage radius of boreholes with cutting is 2.8 times that of boreholes without cutting, which significantiy shortens the gas drainage time of the coal lane strip, and then attributes to relizing the rapid and safe excavation of coal seam roadway. This technique can provide reference significance for the modification of low-permeabilety coal seans in the similar condition area.

Excavation Safety Modeling Approach Using BIM and VPL

Soil excavation is a fundamental step of building and infrastructure development. Despite strong enforcement of construction best practices and regulations, accidents in construction industry are comparatively higher than other industries. Likewise, significant increase in injuries and fatalities are recently reported on geotechnical activities such as excavation pits and trenches. Academic researchers and industry professionals have currently devoted vital attention to acquire construction safety in preconstruction phase of the project. They have developed various algorithms to enhance safety in preconstruction phase such as automated generation of scaffolding and its potential risk analysis, checking BIM model for fall risks, and limited access zone allocation in wall masonry. However, safety in geotechnical works at preconstruction phase is yet unexplored. This paper proposed automatic safety rule compliance approach for excavation works leveraging algorithmic modeling tools and BIM technologies. The focused approach comprises of the following three modules: information extraction and logic design (IELD), information conversion and process integration (ICPI), and automodeling and safety plan generation (ASPG). Specifically, the scope of the paper is limited to major risks such as cave‐ins, fall, safety egress, and prohibited zones risks. A set of rules‐based algorithms was developed in commercially available software using visual programming language (VPL) that automatically generates geometric conditions in BIM and visualizes the potential risks and safety resources installation along with their quantity take‐off and optimized locations. A case study has been presented to validate the proof of concept; automated modeling tool for excavation safety planning generated the required results successfully. It is anticipated that the proposed approach has potential to help the designers through automated modeling and assist decision makers in developing productive and practical safety plans compared to the conventional 2D plans for excavation works at the preconstruction phase. Moreover, it is realized that the same approach can be extended to other rule‐dependent subjects in construction.

Design and Application of a Monitoring System for a Deep Railway Foundation Pit Project

With the development of urban underground space in China, foundation pits have followed a trend toward larger area and greater depth. To ensure the safe excavation of foundation pits, it is necessary to monitor their deformation and the internal force of supporting structures and then use assessments of pit and building stability to guide construction. This paper introduces the design and development of a safety monitoring and warning system for deep foundation pits and adjacent buildings. The monitoring information management system uses Visual Studio 2013 as its development platform and adopts the SQL and C# programming languages to realize its powerful data management and visualization functions. By combined consideration of the monitoring information and the layout of the measuring points, monitoring data on the deformation of the deep foundation pit, ground subsidence and deformation of adjacent buildings are analyzed comprehensively. The results show that: first, the horizontal deformation of the side wall of the rock foundation pit achieves its peak value when 50% of the excavation has been completed and tends to change steadily after the completion of anchor construction. Second, the ground surface around the Fengjing area exhibits upward vertical deformation closest to the side wall of the foundation pit, and then downward deformation at greater distances from it. The ground surface relatively far from the side wall exhibits settlement. Third, the internal force of a plate-ribbed anchor retaining wall in the Fengjing area becomes greater at greater depths. Finally, the excavation of a rock foundation pit has relatively little influence on the inclination of adjacent buildings.

Deformation characteristics and safety assessment of a high-speed railway induced by undercutting metro tunnel excavation

Stratum deformation (settlement) is a challenging issue in tunnel engineering, especially when construction of metro tunnels has to undercut high-speed railway. For this purpose, we used the FLAC3D software to analyze the stratum settlement characteristics of high-speed railway at different crossing angles intersected by metro tunnel, in terms of ground settlement trough, stratum slip line and irregularity of ballastless tracks. According to the evolution of the stratum settlement at different angle regions, an optimized angle is proposed for the actual project design. In order to reduce the influence of stratum settlement on the safety of high-speed railway, an approach of safety assessment is proposed for the shield engineering undercutting high-speed railway, as per Chinese specifications using numerical results and on-site conditions. A case study is conducted for the shield tunnel section crossing the Wuhan – Guangzhou High-speed Railway between the Guangzhou North Railway Station and the Huacheng Road Station, which represents the first metro tunnel project passing below a high-speed railway in China. A series of measures is taken to ensure the safe excavation of the shield tunnel and the operation of the high-speed railway. The results can provide a technical support for performing a safety evaluation between high-speed railways and metro tunnels.

Application of Pre-extraction Drilling in Anti-burst of Low Permeability Coal Seam

In order to eliminate the outburst danger of coal seam with low gas permeability and consider the economic cost of anti-burst measures, the gas pre-extraction coal seam gas prevention technology in the coal roadway excavation process is studied to relieve the coal seam pressure and gas content. The pressure is reduced, and the gas content of the coal body is reduced to 8m3/t within the allowable excavation range. The maximum gas cuttings Smax of the gas is reduced to less than 6kg/m after the anti-burst effect test, which effectively eliminates the prominent danger of the coal seam. During the implementation of the regional anti-burst measures, it can assist the gas release from the gas release, reduce the gas content of the coal seam, release the gas potential of the coal body, and strictly implement the regional defense according to the requirements of the two “four-in-one” anti-burst measures. The comprehensive anti-burst measures supplemented by the sudden measures and the local anti-burst measures eliminate the prominent danger of the coal seam and ensure the safe excavation of the coal roadway.

GPR Study of a Thrust-Fault in an Active Limestone Quarry (SW Slovenia)

After conducting a successful GPR pilot study in a tectonically complex area of the Karst Thrust Edge, a follow-up study was carried out. In the pilot study, the geometry and spatial extent of the Socerb thrust-fault, which separates limestone above from flysch below, were investigated using a 50 MHz antenna in the Črnotiče quarry. After one part of the quarry was deepened and widened, new flysch outcrops were exposed and GPR profiling was made possible in areas where the thrust contact could not be reached before. By comparing the first GPR results with the locations of new flysch outcrops, we found it reached the surface almost exactly where we had predicted. In order to gain new information about the location of the thrust contact, nine new profiles were recorded. In this newly deepened area, the thrust contact runs close to the surface, therefore a 250 MHz antenna was used in addition to the 50 MHz antenna in order to ensure an adequate level of resolution. This combination of antennas provided the depth penetration of 34 m as well as resolution high enough to obtain accurate information from the shallowest parts. GPR profiles were used to create a 3D model of the thrust-fault plane, providing information about the spatial position and lateral undulations of the thrust contact. The results provided new data about the geometry of the Socerb thrust-fault and correlated well with existing borehole data. The results also showed the importance of using appropriate antenna frequencies as other features capable of becoming hazardous during excavation (air-filled and sediment-filled karst caves) could otherwise be misinterpreted or overlooked. The follow-up research not only provides new data important for understanding the tectonic setting of the area, but also information needed for calculating exploitable material quantities and for planning safe excavation processes.

Analysis and Solution for Fallout Repair and Tunneling in Sandy Soil Conditions for a Wine Cave in Southern California

The design and construction of wine caves can be difficult due to low ground cover, weak rock or soil, presence of sand and complicated by the elaborate curves and labyrinth-style floor plans. This paper will focus on southern California’s first wine cave in the Temecula wine region that was constructed by mining techniques. An excavation procedure was needed to reinstate tunneling excavation at the Oak Mountain Winery in Temecula, CA USA after a fallout with an estimated 6.1 meter diameter and 6.71 meters overburden. Sandy soils with low cohesive properties and low saturation have created difficult tunneling and safety conditions. The proposed excavation sequence was divided into four stages using spilling if needed until less sandy or stronger material was encountered The following analyses were performed to provide supporting calculations and information to provide safe tunnel excavation conditions as required by mining regulatory oversight. Analyses using cellular concrete for fallout conditions were also modeled. Results, recommendations and conclusions are presented.

Studies on ground settlement and pre-arching stress of pre-cutting tunnelling method

According to Rabcewicz (1964, 1965), tunnels should be driven full face whenever possible. The pre-cutting method is a popular tunnelling method based on this idea. This method allows safe excavation even in poor ground conditions by creating continuous pre-arching around tunnel periphery in advance. Because of high costs and safety risk in field test, the previous studies on pre-cutting method are limited and qualitative, which mainly focused on its machine, construction procedure and applicable conditions. To further develop this method, systematic and quantitative studies on ground settlement and pre-arching stress caused by it are needed. In this study, a 1:10 geo-mechanical physical model test was performed to understand the mechanism of pre-cutting method by simulating its construction process. The ground settlement, earth pressure and pre-arching stress during tunnelling were investigated. Afterwards, three-dimensional numerical simulations were performed to simulate the process of physical model test so as to compare with experimental results. The effects of different pre-cutting parameters such as length, thickness, lap length and sequence of cutting slots, which can’t be sufficiently covered by the model test, were studied by numerical method. Comparative studies between pre-cutting and New Austrian Tunnelling Method (NATM) under the same geological conditions were also carried out. In general, the comparative analysis shows that the physical model test has achieved satisfactory results and the pre-cutting method has a great advantage in controlling ground deformation compared with NATM.

Physical experiment and numerical modelling of tunnel excavation in slanted upper-soft and lower-hard strata

During the excavation of tunnels, the heading face often encounters alternating soft and hard strata. Many accidents have been reported to be closely related to the change in strata. To investigate the effect of alternating soft and hard strata on the stability of rock surrounding tunnels, physical experiments and numerical simulations were performed to simulate tunnel excavation in slanted upper-soft and lower-hard strata. The evolution laws and distribution features of stress, displacement and failure were analysed. During the process of stress redistribution, the radial stress of the surrounding rock has a step-type decrease trend with step excavation, but the evolution laws of tangential stress are closely related to lithology and the distance from the free face. The failure process of the surrounding rock under un-supported conditions began with a shearing crack in the roof that then extended further and coalesced at the interface between the hard and soft rock. Both the physical and numerical results revealed that the final failure model shows obvious asymmetrical deformation; the soft rock area experiences block dropping and roof falling, while the hard rock only shows shrinkage deformation. Therefore, excavation and support design need to pay attention to the asymmetrical deformation failure in complex rock strata, especially the large deformation of soft strata. Based on the numerical analysis results, the influence of composition of strata lithology on the failure mode were further discussed. These results can provide helpful references for the safe excavation and scientific support design of tunnels across alternating soft and hard strata.

Rock Mass Characterization using Rock Mass Rating and Encountered Geological Problems in TRT’s Component of Tehri Pumped Storage Plant, Uttarakhand, India

As an integral part of Tehri Hydro Power Complex (HPC) located in the state of Uttarakhand in Northern India; an underground 4x250 MW Tehri Pump Storage Plant (PSP) parallel and close to the existing 1000 MW Tehri Hydro Power Plant (HPP). Tehri PSP is located on the left bank of Bhagirathi River in the district of Tehri about 1.5 km downstream of its confluence with River Bhilangana. The major project components are machine hall, upstream surge shafts, Butterfly valve chamber (BVC), Penstock assembly chambers (PAC), downstream Surge Shafts, a pair of Tail Race Tunnels (TRTs) and outlet structures are in construction stage. During underground excavation, one of the important aspects for a speedy and safe excavation is to characterize rock mass for its stand up time. Case history of Himalayan tunnel reveals that Barton’s & Bieniawski’s classification system provide better assessment of the rock mass behavior. In TRTs of Tehri PSP, Rock Mass Rating (RMR) classifications were implemented during excavation and based on their ratings, rock mass was supported. Construction stage geotechnical assessments were made, and suitable remedies were adopted for all the components of the project after geological traverses, detailed geological mapping, drift logs and logging of cores was done. This paper deals with rock mass characterization of underground structures specially in TRT’s using RMR classification and encountered geological problems during excavation.HYDRO Nepal JournalJournal of Water, Energy and Environment Issue: 23Year: 2018