Research status, hot spots, difficulties and future development direction of microbial geoengineering

Microbial geoengineering technology,as a new eco-friendly rock and soil improvement and reinforcement technology,has a wide application prospect.However,this technology still has many deficiencies and is difficult to achieve efficient curing,which has become the bottleneck of large-scale field application.This paper reviews the research status,hot spots,difficulties and future development direction microbial induced calcium carbonate precipitation(MICP)technology.The principle of solidification and the physical and mechanical properties of improved rock and soil are systematically summarized.The solidification efficiency is mainly affected by the reactant itself and the external environment.At present,the MICP technology has been preliminarily applied in the fields of soil solidification,crack repair,anti-seepage treatment,pollution repair and microbial cement.However,the technology is currently mainly limited to the laboratory level due to the difficulty of homogeneous mineralization,uneconomical reactants,short microbial activity period and large environmental interference,incidental toxicity of metabolites and poor field application.Future directions include improving the uniformity of mineralization by improving grouting methods,improving urease persistence by improving urease activity,and improving the adaptability of bacteria to the environment by optimizing bacterial species.Finally,the authors point out the economic advantages of combining soybean peptone,soybean meal and cottonseed as carbon source with phosphogypsum as calcium source to induce CaCO3.

Numerical simulation of dynamic response of operating metro tunnel induced by ground explosion

To evaluate the effects of possible ground explosion on a shallow-buried metro tunnel, this paper attempts to analyze the dynamic responses of the operating metro tunnel in soft soil, using a widely applied explicit dynamic nonlinear finite element software ANSYS/LS-DYNA. The blast induced wave propagation in the soil and the tunnel, and the von Mises effective stress and acceleration of the tunnel lining were presented, and the safety of the tunnel lining was evaluated based on the failure criterion. Besides, the parametric study of the soil was also carried out. The numerical results indicate that the upper part of the tunnel lining cross-section with directions ranging from 0° to 22.5° and horizontal distances 0 to 7 m away from the explosive center are the vulnerable areas, and the metro tunnel might be safe when tunnel depth is more than 7 m and TNT charge on the ground is no more than 500 kg, and the selection of soil parameters should be paid more attentions to conduct a more precise analysis.

Thickness regression for backfill grouting of shield tunnels based on GPR data and CatBoost&BO-TPE:A full-scale model test study

Ground penetrating radar(GPR)is a vital non-destructive testing(NDT)technology that can be employed for detecting the backfill grouting of shield tunnels.To achieve intelligent analysis of GPR data and overcome the subjectivity of traditional data processing methods,the CatBoost&BO-TPE model was constructed for regressing the grouting thickness based on GPR waveforms.A full-scale model test and corresponding numerical simulations were carried out to collect GPR data at 400 and 900 MHz,with known backfill grouting thickness.The model test helps address the limitation of not knowing the grout body condition in actual field detection.The data were then used to create machine learning datasets.The method of feature selection was proposed based on the analysis of feature importance and the electromagnetic(EM)propagation law in mediums.The research shows that:(1)the CatBoost&BO-TPE model exhibited outstanding performance in both experimental and numerical data,achieving R^(2)values of 0.9760,0.8971,0.8808,and 0.5437 for numerical data and test data at 400 and 900 MHz.It outperformed extreme gradient boosting(XGBoost)and random forest(RF)in terms of performance in the backfill grouting thickness regression;(2)compared with the full-waveform GPR data,the feature selection method proposed in this paper can promote the performance of the model.The selected features within the 5–30 ns of the A-scan can yield the best performance for the model;(3)compared to GPR data at 900 MHz,GPR data at 400 MHz exhibited better performance in the CatBoost&BO-TPE model.This indicates that the results of the machine learning model can provide feedback for the selection of GPR parameters;(4)the application results of the trained CatBoost&BO-TPE model in engineering are in line with the patterns observed through traditional processing methods,yet they demonstrate a more quantitative and objective nature compared to the traditional method.

Experimental study on performance of spring damping support structure system for large deformation tunnel in soft rock

According to the convergence confinement theory,it is an effective measure to control the large deformation of high ground stress in fractured soft rock tunnels by using yielding support.The yielding support can be classified as either radial or circumferential yielding support.Circumferential yielding support is achieved by transforming radial displacement into circumferential tangential closure without compromising the support capacity of the primary lining support structure.Based on this,and inspired by the design principle of dampers,a yielding support structure system with spring damping elements as its core was developed,based on the connection characteristics of steel arches in highway tunnel,which can provide increasing support resistance in the yielding deformation section.Then the mechanical properties of spring damping elements were obtained through indoor axial pressure and flexural tests.In addition,according to these results with numerical calculations,the yielding support structure system with embedded spring damping elements can reduce the internal force of the support structure by approximately 10%and increase the area of the plastic zone of the surrounding rock by 11.23%,which can fully utilize the self-bearing capacity of surrounding rock and verify the effectiveness of circumferential yielding support.Finally,the spring damping support structure system was designed with reference to the construction process of the tunnel excavated by drilling and blasting method,and the transformation of the spring damping element to spring damping support structure was achieved.Based on field test results,surrounding ground pressure for the yielding support optimization scheme was reduced by 40%and more evenly distributed,resulting in the successful application and a reduction in the construction cost of large deformation tunnels in soft rock.

Development of a 3D modeling algorithm for tunnel deformation monitoring based on terrestrial laser scanning

Deformation monitoring is vital for tunnel engineering.Traditional monitoring techniques measure only a few data points,which is insufficient to understand the deformation of the entire tunnel.Terrestrial Laser Scanning(TLS)is a newly developed technique that can collect thousands of data points in a few minutes,with promising applications to tunnel deformation monitoring.The raw point cloud collected from TLS cannot display tunnel deformation;therefore,a new 3D modeling algorithm was developed for this purpose.The 3D modeling algorithm includes modules for preprocessing the point cloud,extracting the tunnel axis,performing coordinate transformations,performing noise reduction and generating the 3D model.Measurement results from TLS were compared to the results of total station and numerical simulation,confirming the reliability of TLS for tunnel deformation monitoring.Finally,a case study of the Shanghai West Changjiang Road tunnel is introduced,where TLS was applied to measure shield tunnel deformation over multiple sections.Settlement,segment dislocation and cross section convergence were measured and visualized using the proposed 3D modeling algorithm.

Performance of overlapped shield tunneling through an integrated physical model tests,numerical simulations and real-time field monitoring

In this work,deformations and internal forces of an existing tunnel subjected to a closely overlapped shield tunneling are monitored and analyzed using a series of physical model experiments and numerical simulations.Effects of different excavation sequences and speeds are explicitly considered in the analysis.The results of the physical model experiments show that the bottom-up tunneling procedure is better than the top-down tunneling procedure.The incurred deformations and internal forces of the existing tunnel increase with the excavation speed and the range of influence areas also increase accordingly.For construction process control,real-time monitoring of the power tunnel is used.The monitoring processes feature full automation,adjustable frequency,real-time monitor and dynamic feedback,which are used to guide the construction to achieve micro-disturbance control.In accordance with the situation of crossing construction,a numerical study on the performance of power tunnel is carried out.Construction control measures are given for the undercrossing construction,which helps to accomplish the desired result and meet protection requirements of the existing tunnel structure.Finally,monitoring data and numerical results are compared,and the displacement and joint fracture change models in the power tunnel subject to the overlapped shield tunnel construction are analyzed.

Smart technology applications for the optimal management of underground facilities

This study centers on the use of smart technology to improve the lifecycle management of underground facilities.It presents a comprehensive digital solution that addresses the challenges of underground facilities,particularly those related to the extensive use of underground space,as well as the requirements for safety,sustainability,and quality of services.The proposed solution emerged from discussions with experts,companies,and cities involved in the design,construction,and management of underground facilities.In this paper,we first discuss the major challenges of underground facilities,then,we present the development of a smart solution to address these challenges.This study demonstrates a promising perspective for the use of smart technology in the optimal management of underground facilities,and paves the way for its implementation.

A measurable evaluation method of visual comfort in underground space by intelligent sorting and classification algorithms

Based on human perception and machine learning methods,this study proposes a measurable method for evaluating visual comfort in underground spaces.First,a comfort evaluation index based on the characteristics of human visual perception is proposed,and color features and segmentation extraction methods for intelligent methods are given.Then,using probability statistics and machine learning methods,a multi-class intelligent sorting and classification algorithm for ranking visual comfort levels is constructed and a comparison is made of the suitability of different intelligent methods for evaluating visual comfort.The random forest algorithm is then selected as the most effective measurable intelligent evaluation algorithm for underground spaces.Finally,the proposed method is compared to intelligent methods employed by previous research,and a case study,the Wujiaochang underground space in Shanghai,China,is applied as the background.Results show that the proposed method can effectively improve the quantification and refinement of human perception and evaluation of comfort in underground spaces;this method will also be useful in computer-aided generative design in the future.

Modal analysis of subway tunnel in soft soil during operation

Modal parameters are of great significance in civil engineering because they can characterize the properties of structures and be used for vibration control and structural health monitoring.Subway tunnels are long linear truss structures combined with the mutual cou-pling of the surrounding soil.Therefore,the operational modal analysis of a mutual coupling tunnel is complicate,as is the modal iden-tification of shield tunnels in a time–frequency domain,and these are hot civil engineering topics.Using the shield tunnel of Shanghai metro line No.12 project as a case study,we carried out the vibration response monitoring of a subway tunnel during operation and presented methods to identify structural modal parameters.The modal parameters of lower vibration modes were estimated using response measurements.Modal frequencies and shapes were identified with high precision and accuracy using the orthogonal polynomial clustering algorithm under hammer excitation conditions and the autoregressive-moving-average model under ambient excitation con-ditions.The dynamic behavior of a mutual coupling tunnel presented obvious low frequency characteristics,and the first 9th order mode frequencies were less than 100 Hz.The diagonal values of the modal assurance criteria were all greater than 0.85.The modal parameters can be used for the health monitoring of operational subway tunnels.