Poor Geological Conditions Research Articles

Preliminary design of a viaduct on new Highspeed line RS2 VRT Jižní Morava

AbstractThe newly proposed high‐speed rail in Czech Republic creates a set of new challenges for engineers in design overall. In this case, the most significant challenge was to design a viaduct over several obstacles due to the crossing of Special Area of Conservation (SAC), part of Natura 2000. This aims to limit impacts in short‐term, during construction and more importantly in the long term. Construction of the viaduct will mitigate an impact to the natural surrounding area, whilst allowing immigration of its natural habitats. Nevertheless, the viaduct design and operational speeds will reach 320 km/h with possible raising to 350 km/h limit, with minimal impact within the area.Initial length of the viaduct was over 1 300 m and the main requirement given by an infrastructure manager was to design a viaduct without railway expansion joints. Due to such a long distance, the viaduct had to be separated into several dilatation segments in order to avoid the use of rail expansion joint. The most susceptible parts of SAC were in proximity of the river Šatava and surrounding wetlands. This area created an obstacle, which had to be crossed by a long span avoiding the implementation of bridge piers. Poor geological conditions close to the watercourse had to be taken into consideration for design of pier foundation, therefore the span had to be shortened to a compromised length.The final design of the viaduct consists of 16 segments, of which 14 are continuous segments and 4 are single spans. Overall, there are 29 spans over the length of the viaduct. Construction method of incremental launching had been chosen to reduce the short‐term impact in the SAC.

Construction Technology and Application of TBM in Shengli Tunnel of Tianshan Mountain under poor geological conditions

When a tunnel boring machine (TBM) excavates in poor geological conditions like fracture zones, soft rock with high ground stress, hard rock with high ground stress, and water inrush ground, severe problems such as surrounding rock collapse, convergence, rock burst and water and mud outburst are usually encountered. These problems existed in the Tianshan Shengli Tunnel project in Xinjiang, China. Several methods and techniques were adopted to reduce construction risks and improve construction efficiency. The seismic wave reflection long-distance geological forecasting method was employed to forecast and predict these adverse geological conditions. The pre-reinforcement construction method was employed on the surrounding broken rocks in front of the tunnel face to lower the risks of tunnel collapse and machine jamming. A combined steel arch was applied to prevent tunnel arch collapse. An artificial cap method was applied to prevent the jamming caused by high-ground stress soft rock. Measures such as spraying water on the tunnel face and drilling stress holes were employed to prevent rock bursts caused by high-ground stress in hard rock. Implementing the advanced pipe shed method during water influx, sudden mud, and other working conditions reduced the risk of groundwater damage to equipment and lowered risks to personnel safety. The successful application of these techniques can provide a reference for TBM tunnel construction in similar ground conditions.

Longitudinal seismic analysis for underground structures passing through soft-hard strata based on periodic stratum deformation

Poor geological conditions, e.g., soft and hard strata, have a significant impact on the seismic response of underground structures. In this study, a series of longitudinal seismic analysis for underground structures passing through soft-hard strata were conducted based on the concept of periodic stratum deformation. Firstly, the analytical expressions of stratum deformation in soft-hard strata at the oblique incidence of plan P-, and S- wave were obtained via decomposing the stratum deformation into the reflected- and transmitted wave fields. Then, the wave propagation history in soft-hard strata in the time domain was transformed into strata deformation in a period via introducing concept of the periodic stratum deformation. Base on the proposed expressions, a self-developed Python program was implemented into finite element software ABAQUS to establish seismic analysis model and to calculate the longitudinal seismic response of underground structures. Finally, example analyses were conducted to study the influence of plane P- and S- wave, wave velocity ratio of soft and hard media, as well as incident wave angle on the seismic response of underground structures located in soft- hard strata. This study may provide a reference for seismic design of underground structures located in soft- hard strata.

Discussion on the Application of Grouting in Underground Engineering

With the development of China's economy, in some large cities, surface transportation alone can no longer meet people's needs today, and the development of underground engineering is increasingly catering to the needs of the public. During the excavation process of subway tunnels, it is inevitable that they may be threatened by groundwater, and grouting technology is one of the effective methods for preventing and controlling water in underground engineering. The mechanism of slurry flow and diffusion varies depending on the soil conditions. When underground projects such as subway tunnels pass through poor geological conditions, it is highly likely to cause significant surface subsidence, and even engineering disasters such as water inrush and collapse may occur. To ensure the safety of underground engineering construction in the geological strata, it is often necessary to carry out advanced grouting in the strata to achieve the purpose of reinforcement or water blocking. Advanced grouting reinforcement belongs to concealed engineering, and the existing advanced grouting construction mostly relies on experience and on-site grouting tests, making it difficult to achieve the expected grouting effect. Therefore, it is of great theoretical and engineering significance to conduct in-depth research on the diffusion mechanism of slurry in geological grouting reinforcement engineering, as well as the influence of factors such as slurry water cement ratio and geological characteristics on the diffusion form of slurry.

A Study on the Stability of Reinforced Tunnel Face Using Horizontal Pre-Grouting

As tunnel excavation under poor geological conditions is liable to cause ground collapses, reinforcement measures are necessary to reduce construction risks. The stability of a tunnel face that was reinforced using horizontal pre-grouting was investigated through numerical simulation and theoretical analysis in this study. An analytical model was developed using the limit equilibrium method and taking into account the impact of horizontal grouting reinforcement (HGR) on the tunnel face. Subsequently, a comprehensive numerical simulation was conducted to confirm the validity of the model. By performing a parametric analysis, it was found that the limit support pressure exhibited a linear relationship with the cohesion and friction angle. In addition, the limit support pressure is more sensitive to changes in the cohesion and friction angle than changes in the stiffness ratio and thickness of HGR. The HGR more effectively decreases the limit support pressure in conditions of low cohesion (or friction angle) compared with conditions of high cohesion (or friction angle).

Evaluation of excavation method on point load strength of rocks with poor geological conditions in a deep metal mine

In the field of deep mining engineering, it poses a challenge to promptly determine the mechanical properties of rocks under poor geological conditions through in-situ tests. However, the indirect determination of uniaxial compressive strength (UCS) of rocks can be achieved through the point load strength index (PLSI) test on irregular samples. In the present study, laboratory uniaxial compressive and field PLSI tests were carried out on irregular ore and rock blocks extracted through mechanical mining methods from a stope at a lead–zinc mine in Yunnan Province, China, with a depth of approximately 1000 m. The effects of mechanical excavation and drilling-blasting methods on the PLSI of rocks and ores are compared. It is found that there are significant differences in the point load strength indexes obtained by different excavation methods, and the Is(50) obtained after the mechanical excavation method approximates the actual value of ore and surrounding rocks. Two correction methods were utilized to obtain the point load strength indexes Is(50)-1 and Is(50)-2 of irregular rock samples. The correlation factors (k) linking Is(50) to UCS and Brazilian splitting strength are derived based on testing results. The findings indicate that using the conversion factor (k) recommended by ISRM to predict the UCS of rocks may significantly underestimate the actual strength of rocks in intricate mining environments. This study can serve as a benchmark for analogous deep mining projects.

Intelligent identification algorithm and key point detection of abnormal vibration of transmission tower based on machine learning

Abstract In some special geological areas, the inclination and displacement of transmission line towers are relatively common, which should be analyzed from various factors. Transmission towers are the support structure for overhead transmission lines and play a pivotal role in the safe operation of the power grid. Transmission lines are widely distributed. Transmission poles and towers are generally built in areas with poor geological conditions such as goaf, river bed and slope. Under severe weather conditions, the force on the tower may be affected to a certain extent, causing the tower to tilt, deform, or even collapse, and thus causing a wide range of power system failures, which have a great impact on people’s production and life. Based on this objective problem, this paper has mainly studied the intelligent recognition methods and key technologies based on machine learning. In the experimental study of support vector machine (SVM) model based on machine learning, the average training time of genetic algorithm support vector regression (GA-SVR) was the longest, reaching 1.462 s. The average training duration of double chain quantum genetic algorithm-least squares support vector regression (DCQGA-LSSVR) was the shortest, with 0.156 s. The average pose error of double chain quantum genetic algorithm-support vector regression (DCQGA-SVR) was the smallest, only 0.136, while the average attitude error of genetic algorithm-least squares support vector regression (GA-LSSVR) was the highest, reaching 0.45. Therefore, it is of the great significance to analyze abnormal vibration of the transmission towers based on machine learning method.

Experimental Study on Vibration Velocity of Piled Raft Supported Embankment and Foundation for Ballastless High Speed Railway

In recent years, the high development of high-speed railway lines cross through areas with poor geological conditions, such as soft soil, offshore and low-lying marsh areas, resulting geotechnical problems, such as large settlements and reduction of bearing capacity. As a new soil reinforcement method in high speed railway lines, the piled raft structure has been used to improve soil conditions and control excess settlement. In order to study the dynamic behavior of piled raft supported ballastless track system in soft soil, an experimental study on vibration velocities of piled raft supported embankment and foundations is presented in soft soil with different underground water levels. Vibration velocities at specified positions of the piled raft supported embankment and foundations are obtained and discussed. The vibration velocity curves on various testing locations of piled raft foundations are clearly visible and have sharp impulse and relaxation pattern, corresponding to loading from train wheels, bogies, and passages. Vibration velocity distribution in the horizontal direction at three train speeds clearly follows an exponential curves. Most of the power spectrums of vibration velocity at various locations are mainly concentrated at harmonic frequencies. The change in water level has slight impaction on the peak spectrum of vibration velocity at harmonic frequencies. The vibration power induced by train loads are transmitted, absorbed, and weakened to a certain extent through embankment and piled raft structure. The dynamic response character of embankments are affected by their self-vibration characteristics and the dynamic bearing capacity of the piled raft structure.

Methods and Systems for Modeling Porous Medium of Nanomaterials with Poor Geological Structure Based on ct Detection Technology

China is a country with frequent geological disasters. The geological disasters in different regions are different, such as earthquakes, landslides, collapses, karst collapses, and ground subsidence. With the development of science and technology and the improvement of engineering technology, the combination of image technology and digital technology is constantly developing. People can improve the accuracy of prediction by studying the characteristics of rock formation under different geological conditions while collecting geological data and sorting various information. And reliability, can more accurately identify poor geological conditions, can increase construction safety and reduce economic losses. Based on the comprehensive CT geological survey data, this paper uses nanomaterials to construct software DEM to model the porous medium of the Yanziyan dangerous rock mass in Jinfo Mountain, Nanchuan District, Chongqing and to estimate the area and volume of the collapse potential area of the high-steep dangerous rock mass parameter.

Real-time hard-rock tunnel prediction model for rock mass classification using CatBoost integrated with Sequential Model-Based Optimization

In-time perception of changing geological conditions is crucial for safe and efficient TBM tunneling. Precisely detecting or predicting the rock mass qualities ahead of the tunnel face can forewarn the geological disasters (e.g., burst or squeezing behaviors of surrounding rock mass). A novel hybridization model based on CatBooost and Sequential Model-Based Optimization (SMBO) is proposed in this study. Firstly, a database incorporating 4464 samples acquired from the Songhua River Water Diversion Project is established using the capping method. Owing to SMBO’s different surrogate types (GP, RF, and GBRT) and performance validation, the comparisons of SMBO-CatBoost’s three types and other six hybridized models (SMBO-XGBoost, SMBO-AdaBoost, SMBO-RF, SMBO-SVM, SMBO-KNN, and SMBO-LR) are successively carried out. As a result, in terms of the optimization speed, performance, and sensitivity to poor geological conditions, SMBO(RF)-CatBoost is the most suitable model for rock mass class prediction; furthermore, it achieves the best performance ACC¯ = 0.9207 and F1¯ = 0.9178 among the seven hybridized models. Next, the scientific feature selection methods (i.e., filter, embedded) are used to reduce the model’s complexity (i.e., feature dimensions) step by step to increase the model’s on-site practicality. The determined ten influential features still can keep the model’s ACC¯ and F1¯ greater than 0.85, and only respectively declines 5.4% and 5.6% in contrast to the original performance. Subsequently, in order to explore the importance of the first-hand features and the second-hand features (i.e., composite features), a new method for more accurately calculating the rock mass boreability indices (regarded as the second-hand features) is proposed based on the big data at a relatively high sampling frequency of 1 Hz, this newly-proposed method could make these indices more of significance under the complex geological conditions. With the SHAP technique, the modified torque penetration index (TPI’) is more valuable than other second-hand and some first-hand features.

Seismic stability assessment of the portal of a hydraulic tunnel under obliquely incident P waves

Tunnel portals are one of the most vulnerable sections that suffer the risk of instability during earthquakes because they are generally located in poor geological conditions. What makes this case studied in this work even more special are the oblique incident seismic waves and the large amounts of water in the hydraulic tunnel, both of which are believed to cause more complex mechanical behaviors and larger seismic response of hydraulic tunnels. In this paper, a full three-dimensional finite element model that takes the oblique incident seismic waves and hydrodynamic pressure into account is established to evaluate the stability of the tunnel portal under different incident angles of seismic waves. The numerical results indicate that: (1) the stress and displacement responses induced by oblique incident P waves are much larger than that by horizontal and vertical incident P waves; (2) the closer to the tunnel portal, the larger seismic response of the tunnel; (3) tunnel portal is where damage occurs first and suffers severe damage; (4) both oblique incident seismic waves and hydrodynamic pressure are likely to cause larger damage zone and more severe damage.

Deformation and failure analysis of surrounding rock mass in deep buried tunnels subjected to excavation

With the rapid development of underground engineering, the construction of hydraulic tunnel is faced with complex geological conditions. Rock burst and deformation have become the bottleneck of engineering construction. The study of deformation and failure mechanisms of surrounding rock mass during the excavation of deep buried tunnel has become important for the field of underground engineering. The traffic tunnel of Shuangjiangkou hydropower station is studied to identify the failure mechanism of surrounding rock mass of deep buried tunnel. We introduced microseismic monitoring technology to delineate potential risk areas and reveal the space-time evolution of microfractures. The failure type of the surrounding rock is determined by source parameters. The relationship between surrounding rock deformation and excavation dynamic response is analyzed based on the geological and microseismic data. The results show that the 3D microseismic visualization model can realize the advanced detection of the internal damage of surrounding rock. The source parameters reveal that tensile failure is the main form of failure in the tunnel surrounding rock. Strong unloading and poor geological conditions are the main factors affecting the stability of surrounding rock mass. The study combines microseismic monitoring with field investigation, and then comprehensively evaluates the stability of the tunnel surrounding rock providing a reference for similar underground engineering.

Displacement process analysis of deep tunnels with grouted rockbolts considering bolt installation time and bolt length

This study investigates the interaction process between grouted bolts and tunnel surrounding rock, and establishes an analytical model for deep tunnels reinforced with active grouted rockbolts of the convergence-confinement type. The rock mass is assumed to be elastic-perfectly plastic, obeying the Hoek–Brown criterion. The longitudinal displacement profile is introduced to represent the space effect of the tunnel face, based on which the fictitious pressure along the tunnel axis is determined. Because of delayed installation and limited length of the rockbolts, a rock mass may behave elastically or plastically at bolt installation with the rockbolts anchored in different zones. Six different evolution paths possibly encountered on the basis of the relative magnitude between the anchorage and plastic zones are proposed. The tunnel displacement, plastic radii, and stresses are determined. The analytical results are validated by comparing with those obtained from numerical simulations and an existing model. A parametric analysis shows that doubling bolt length from 2 to 4 m in a 14-m-diameter tunnel reduces the tunnel wall displacement up to 20%. Installing rockbolts close to the tunnel face (less than 1 m) can reduce tunnel wall displacement up to 51%. Doubling the pretension load can reduce tunnel wall displacement up to about 20%. Increasing the support density can reduce the tunnel wall displacement by up to about 50%. The analysis shows that the proposed model outperforms Fahimifar’s model, which deals with infinite rockbolts, in solving tunnel responses under grouted rockbolts, particularly in the case of large cross-sectional tunnels excavated in poor geological conditions.

Mechanism analysis and partition characteristics of a recent highway landslide in Southwest China based on a 3D multi-point deformation monitoring system

An increasing number of landslides are occurring during the construction of highways in mountainous areas all over the world. A recent highway landslide located in the mountainous region of Southwest China is taken as a representative example to carry out the initiation mechanism and deformation characteristics analysis, and study the intelligent partitioning method in this paper. The geological conditions of the landslide are obtained through detailed geological surveys and investigation. A three-dimensional (3D) monitoring network with a total of 72 multi-points, including 53 surface displacement monitoring points and 19 deep displacement monitoring holes, is established to examine the spatial deformation characteristics of the landslide for nearly 25 months. The monitoring results of the surface displacement show that the dynamic deformation of the landslide can be divided into three stages, namely initial deformation stage, accelerated deformation stage, and stabilization stage. Based on the strata distribution obtained by the borehole investigation and the results of deep displacement monitoring, the depth of the slip surface can be reliably determined. The smart contract method in blockchain technology combined with the multi-point monitoring dataset is novelty applied to realize the intelligent automatic partition of the highway landslide without any human involvement. This method can provide the basis for further independent analysis of different landslide zones. According to the investigation and analysis, the initiation mechanism for the highway landslides is attributed to both internal poor geological conditions and external intense precipitation and engineering excavation.

New Technologies and Challenges in the Construction of the Immersed Tube Tunnel of the Hong Kong-Zhuhai-Macao Link

The immersed tube tunnel of the Hong Kong-Zhuhai-Macao Link spans a total length of approximately 6.7 km and is currently the longest concrete immersed highway tunnel in the world. The maximum depth of the tunnel is 45 m, which enables the smooth navigation of 300,000 tons of fully loaded tankers through the waterway above. Accordingly, the construction of the immersed tube tunnel of the Hong Kong Zhuhai-Macao Link is regarded as one of the most challenging tunnel projects in the world due to the poor geological conditions, the remarkable length of the tunnel section, the harsh construction conditions at sea, and the complicated stresses on the structures in the transition sections between the artificial islands and the immersed tunnel segments. In this context, several innovations were implemented in the design, production and installation of the immersed tube segments, providing valuable engineering experience and a unique example of engineering technology for the construction of undersea tunnels worldwide.

Numerical Simulation of Mining‐Induced Damage in Adjacent Tunnels Based on FLAC3D

The Bayueshan (BYS) tunnels are adjacent tunnels which comprise key engineering structures important for Yurong highway from Chongqing to Sichuan, China. The tunnels were established crossing over the old goafs of a coal mine. The tunnels have been damaged three times between 2014 and 2016. To evaluate the reasons for the damage, fast Lagrangian analysis of continua in three dimensions (FLAC3D) was used to simulate the underground coal‐mine excavation yearly from 2012 to 2015. The simulation results show that the subsidence of the ground surface increased annually. The maximum subsidence of the left tunnel was 505 mm and that of the right tunnel was 512 mm. The excavation led to increase in the tunnels’ stress concentration. The simulations further show that uneven horizontal displacement and subsidence were the major factors in inducing tunnel construction defects. Poor geological conditions, water, and vehicle dynamic loads were also important factors that induced damage. Several engineering suggestions for ways to maintain the tunnels are given in this paper, and the research provides a reference for safety evaluation for tunnels crossing over an old goaf.

Comparison and Selection of Construction Schemes for Cast-in-Situ girders of a Continuous Rigid-Frame Bridge

The continuous rigid frame bridge is one of the main bridge types used to span rivers in mountainous areas due to its high rigidity. However, due to the poor geological conditions in mountainous areas, the probability of instability and other safety accidents increases. Therefore, strict construction scheme design must be carried out. According to the cast-in-place section of the side span of a continuous rigid frame bridge in a mountainous area, this paper puts forward three construction schemes that may be applicable. The finite element software is used to establish the model, and the girder stress and bridge alignment with different construction schemes are analyzed. Combined with the grading index evaluation method, the optimal construction scheme is finally obtained.

Deformation mechanism and collapse treatment of the rock surrounding a shallow tunnel based on on-site monitoring

When tunnels are constructed at shallow depths in areas with poor geological conditions, such as portal sections, valleys and hillsides in regions with granitic bedrock, considerable excavation-induced deformation of the surrounding rock may occur, potentially resulting in tunnel collapses. The main reason for these problems is the lack of understanding of the deformation mechanism and evolution of the soft granitic rock surrounding the tunnel and the adoption of inappropriate construction technology and methods. This article analyzes the deformation mechanism of the rock surrounding a shallow tunnel based on in situ monitoring data as a case study and suggests that certain measures should be taken to effectively control the deformation of the surrounding rock and to minimize the potential for tunnel collapse. The results show that the deformation of the granitic soil surrounding the tunnel can be divided into three stages: the rapid deformation stage, the slow deformation stage and the stabilization stage. Appropriate construction methods should be carefully selected to ensure safety during tunnel excavation in the first stage. To avoid secondary disasters caused by tunnel collapses, three treatment measures may be implemented as part of safety management: enhancing the monitoring of the surrounding rock deformation, adjusting the construction methods and optimizing the support systems. In particular, accurate monitoring data and timely information feedback play a vital role in tunnel construction. Therefore, engineers with considerable engineering experience and professional knowledge are needed to analyze the monitoring data and make accurate predictions of tunnel deformation to ensure that reasonable measures are taken in the process of shallow tunnel excavation.

A Case Study on the Construction Optimization Decision Scheme of Urban Subway Tunnel Based on the TOPSIS Method

Because of the harsh environment around city subways and the typically poor geological conditions, it is often difficult to ensure the stability of a tunnel, which makes it prone to collapses and other accidents. The influence of multiple factors on tunnel stability was analyzed under the same geological conditions and environmental factors by using a three-dimensional numerical simulation. Taking into account the objective environment and manual operation and other factors, construction sequence, support closure time, and reinforcement area and parameters were chosen as the main factors affecting the tunnel stability. Finally, based on ground deformation, tunnel convergence deformation, and surrounding soil stress as evaluation indicators, a fuzzy analytic hierarchy process (FAHP)-gray correlation degree-technique for order performance by similarity to ideal solution (TOPSIS) model was established. It was found that the higher the relative closeness of the construction parameter combination, the greater the tunnel stability. The best combination of construction parameters was applied to the Tiantongyuan Station project of Beijing Metro Line 17. All geological conditions being equal, reasonable selection of construction parameters can ensure optimal tunnel construction stability, reduce construction risks, and support sustainable tunnel development. In addition, the FAHP-gray correlation degree-TOPSIS method achieved multi-index evaluation of tunnel stability, which provides practical guidance for the construction of similar projects.

Early demonstration and research on the key technical issues of large-basin hydropower development under the concept of harmony

Abstract As a typical representative of hydropower development in China, the Dadu River is characterized by abundant water resources, poor geological conditions, many resettlements and limited environmental capacity. Therefore, the technical problems faced by Dadu River hydropower development are numerous and complex. We analysed these technical problems, such as the hydropower-development mode, normal water level, dam-site selection, damming technology, migration resettlement and environmental protection. The concept and characteristics of harmonious hydropower development are identified. The harmonious hydropower-development concept has been applied to all aspects of the Dadu River hydropower-development feasibility study to solve the key technical problems of hydropower development on the Dadu River and to promote the development of China’s hydropower.