Excavation compensation theory and supplementary technology system for large deformation disasters

Given the challenges in managing large deformation disasters in energy engineering,traffic tunnel engineering,and slope engineering,the excavation compensation theory has been proposed for large deformation disasters and the supplementary technology system is developed accordingly.This theory is based on the concept that“all destructive behaviors in tunnel engineering originate from excavation.”This paper summarizes the development of the excavation compensation theory in five aspects:the“theory,”“equipment,”“technology,”the design method with large deformation mechanics,and engineering applications.First,the calculation method for compensation force has been developed based on this theory,and a comprehensive large deformation disaster control theory system is formed.Second,a negative Poisson's ratio anchor cable with high preload,large deformation,and super energy absorption characteristics has been independently developed and applied to large deformation disaster control.An intelligent tunnel monitoring and early warning cloud platform system are established for remote monitoring and early warning system of Newton force in landslide geological hazards.Third,the double gradient advance grouting technology,the two-dimensional blasting technology,and the integrated Newton force monitoring--early warning--control technology are developed for different engineering environments.Finally,some applications of this theory in China's energy,traffic tunnels,landslide,and other field projects have been analyzed,which successfully demonstrates the capability of this theory in large deformation disaster control.

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 PFC2 D.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.

Large deformation and failure mechanism analyses of Tangba high slope with a high-intensity and complex excavation process

The Tangba high slope is mainly composed of coarse soils and supplies core wall materials for the construction of the Changheba dam. Since the filling intensity of the Changheba dam is high, the Tangba high slope suffers from a high-intensity excavation process, and reinforcement measures are usually not implemented immediately. Moreover, the distribution of useful materials is uneven and insufficient, and the mixing of different soil materials is necessary; thus, multiple simultaneous excavations and secondary excavation are inevitable. In the construction period from 2012 to 2016, large deformations occurred in this area, and one of the largest monitored horizontal deformations whose direction points to the opposite side of the valley even reached more than 8000 mm. According to field investigation, site monitoring and theoretical analysis, the large deformation in the Tangba high slope can be divided into two phases. In the first phase, the excavation construction breaks the original stress equilibrium state; in the second phase, the precipitation infiltration accelerates the deformation. Thus, the excavation construction and precipitation infiltration are the two major factors promoting the deformation, and the high-intensity and complex excavation process is the fundamental cause. Notably, rate of slope deformation significantly accelerated in rainy seasons due to precipitation infiltration; the rate also accelerated in early 2016 due to the high-intensity, complex excavation process. Comprehensively considering the above factors, timely and effective reinforcement measures are essential.

Finite element analysis of steep excavation slope failure by CFS theory

The distribution of Coulomb failure stress （CFS） change in the steep excavation slope is calculated by finite element method in this paper, and the failure mechanics under different conditions have been investigated. Comparing the CFSs before and after the slope excavation （stress loading and unloading processes）, the dangerous internal zone and the most likely failure external area are attained. Given the shear cracks on the top surface while tensile stress or cracks along the toe of the slope, we analyze the high cutting-angle steep slope in Kaixian county of the Three Gorges Reservoir region. We bring forward that the peak value of CFS after excavation can reach to the order of 0.1 MPa, which is greatly higher than that of before. Our preliminary results are useful for optimizing the reinforcement structure during the steep slope stabilization engineering.

Slope excavation quality assessment and excavated volume calculation in hydraulic projects based on laser scanning technology

Slope excavation is one of the most crucial steps in the construction of a hydraulic project. Excavation project quality assessment and excavated volume calculation are critical in construction management. The positioning of excavation projects using traditional instruments is inefficient and may cause error. To improve the efficiency and precision of calculation and assessment, three-dimensional laser scanning technology was used for slope excavation quality assessment. An efficient data acquisition, processing, and management workflow was presented in this study. Based on the quality control indices, including the average gradient, slope toe elevation, and overbreak and underbreak,cross-sectional quality assessment and holistic quality assessment methods were proposed to assess the slope excavation quality with laserscanned data. An algorithm was also presented to calculate the excavated volume with laser-scanned data. A field application and a laboratory experiment were carried out to verify the feasibility of these methods for excavation quality assessment and excavated volume calculation. The results show that the quality assessment indices can be obtained rapidly and accurately with design parameters and scanned data, and the results of holistic quality assessment are consistent with those of cross-sectional quality assessment. In addition, the time consumption in excavation quality assessment with the laser scanning technology can be reduced by 70%e90%, as compared with the traditional method. The excavated volume calculated with the scanned data only slightly differs from measured data, demonstrating the applicability of the excavated volume calculation method presented in this study.

Discussion on blasting vibration monitoring for rock damage control in rock slope excavation

Drill and blast is a commonly used method for rock slope excavation in hydropower engineering.During blasting excavation of rock slopes,far-field vibration monitoring on the first upper berm for statutory compliance is usually performed to control the blast-induced rock damage to the final slope face.In this study,for the rock slope excavation in the Jinping-I hydropower station,the field vibration monitoring and acoustic testing are presented to investigate the vibration characteristics on the first upper berm and the damage depth in the current bench.The relationship between the PPV on the first upper berm and the PPV damage threshold on the damage zone boundary is also studied through three-dimensional FEM simulations.The results show that on the first upper berm,the maximum vibration velocity component occurs in the vertical direction.While on the blasting damage zone boundary,the horizontal radial vibration velocity is the maximum component.For the Jinping-I slope with a bench height of 30 m,the radial PPV on the inner side of the first upper berm is 2.06%of the PPV threshold on the damage zone boundary.This ratio is increased as the bench height decreases.Therefore,the bench height of the rock slope is an important factor that cannot be ignored in determining the allowable vibration velocity for rock damage control.

Human-induced landslide on a high cut slope: a case of repeated failures due to multi-excavation

The paper attempts to represent a case of repeated failures on a high cut slope due to multi-excavation. The characteristics of each failure induced by excavation are analyzed through geological investigation, and then a geological model at different failure stages is proposed. The geological analysis shows that the excavation-induced repeated failures are related to the exposure of the weak bedding plane and the toe unloading of the cut slope, Numerical modeling is conducted based on a sequential method, taking into account the main failure stages of cut slope. The simulation results fairly coincide with the practical phenomena observed in field. It is shown that the decrease in normal stress of displaced mass on cut slope will induce the increase in shear stress in bedding planes and that at the toe of the cut slope. The released stress leads to repeated gravitational instabilities of cut slope due to the decrease in normal stress and the increase in shear stress along the bedding planes of mudstone.

REINORCING THEORY AND TECHNIQUE OF SLOPE EXCAVATION

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IBIS-FM radar as a tool for monitoring hill slopes during excavations in hydropower projects:A case study from Bhutan Himalayas

Excavation is common in the construction of hydropower projects.Monitoring for both stable and unstable slopes is a pressing requirement during progressive excavations with or without cut-slope support measures.The present study is about an excavation carried out in a proposed concrete gravity dam site on the right bank slope of the Punatsangchhu River in western Bhutan.During the excavation,the right bank abutment witnessed multiple events of slope failures of various magnitudes.One major landslide occurred on 23 July 2013 in the toe of the right abutment,where foliation/multiple sheared/fractured zones/seams in quartz-feldspathic biotite gneiss dip towards the valley.During further excavations/piling works,a subsequent landslide on the downstream,within the body of the July 2013 landslide,occurred on 12 August 2016.As a result,a real-time monitoring of the slope became necessary to facilitate further excavations for achieving the dam foundation.Thus,the advanced slope monitoring instrument like Image By Interferometric Survey e Frequency Modulated(IBIS-FM)radar was deployed for monitoring the right bank slope during the excavation for the construction of~129 m high dam.The displacement of the hill slope is assessed based on this system by monitoring point locations as well as areas by assigning different threshold values for providing timely alerts.This real-time monitoring was effective in identifying the reactivation of August 2016 landslide that occurred on 22 January 2019.Thus,this study showcases the efficiency of IBIS-FM radar in monitoring slope instability with sub-millimeter accuracy on a near real-time basis.

Analysis and Comparison of Slope-cutting Widening Schemes in Highway Reconstruction and Expansion Project Based on MIDAS Software

In this paper,the geological condition of the right-side slope of the K114+694–K115+162 section of Yong-tai-wen Expressway is investigated and analyzed with the results showing that the strength of rock mass is the main contributor to the stability of the slope.Then,two widening schemes are proposed,which are the steep slope with strong support and the gentle slope with general support schemes.The static/slope module of MIDAS GTS finite element analysis software and the strength reduction method were used to compare the two schemes.The results show that the steep slope with a strong support scheme has obvious advantages in land requisition,environmental protection,and safety and is more suitable for reconstructing and expanding the highway slope.

New risk assessment methodology for coal mine excavated slopes

This paper presents a new risk assessment methodology for coal mine excavated slopes. This new empirical-statistical slope stability assessment methodology(SSAM) is intended for use by geotechnical engineers at both the design review and operational stages of a mine's life to categorise the risk of an excavated coal mine slope. A likelihood of failure is determined using a new slope stability classification system for excavated coal mine slopes developed using a database of 119 intact and failed case studies sourced from open cut coal mines in Australia. Consequence of failure is based on slope height and stand-off distance at the toe of the excavated slope. Results are presented in a new risk matrix, with slope risk being divided into low, medium and high categories. The SSAM is put forward as a new risk assessment methodology to assess the potential for, and consequence of, excavated coal mine slope failure.Unlike existing classification systems, assumptions about the likely failure mode or mechanism are not required. Instead, the SSAM applies an approach which compares the conditions present within the excavated slope face, with the known past performance of slopes with similar geotechnical and geometrical conditions, to estimate the slope's propensity for failure. The SSAM is novel in that it considers the depositional history of strata in an excavated slope and how this sequence affects slope stability. It is further novel in that it does not require explicit measurements of intact rock, rock mass and/or defect strength to rapidly calculate a slope's likelihood of failure and overall risk. Ratings can be determined entirely from visual observations of the excavated slope face. The new SSAM is designed to be used in conjunction with existing slope stability assessment tools.

Experimental study on instability mechanism and critical intensity of rainfall of high-steep rock slopes under unsaturated conditions

Two critical factors,namely intense precipitation and intricate excavation,can trigger rock mass disasters in mining operations.In this study,an indoor rainfall system was developed to precisely regulate the flow and intensity of precipitation.A large-scale model experiment was conducted on a self-designed physical simulation experiment platform to investigate the failure and instability of high-steep rock slopes under unsaturated conditions.The real-time reproduction of the progressive failure process in high-steep rock slopes enabled the determination of the critical rainfall intensity and revealed the mechanism underlying slope instability.Experiment results indicated that rainfall may be the primary factor contributing to rock mass instability,while continuous pillar mining exacerbates the extent of rock mass failure.The critical failure stage of high-steep rock slopes occurs at a rainfall intensity of 40 mm/h,whereas a rainfall exceeding 50 mm can induce critical instability and precipitation reaching up to 60 mm will result in slope failure.The improved region growing segmentation method(IRGSM)was subsequently employed for image recognition of rock mass deformation in underground mines.Herein an error comparison with the simple linear iterative cluster(SLIC)superpixel method and the original region growing segmentation method(ORGSM)showed that the average identification error in the X and Y directions by the method was reduced significantly(1.82%and 1.80%in IRGSM;4.70%and 6.26%in SLIC;9.45%and 12.40%in ORGSM).Ultimately,the relationship between rainfall intensity and failure probability was analyzed using the Monte Carlo method.Moreover,the stability assessment criteria of rock slope under unsaturated condition were quantitatively and accurately evaluated.

Deformation Monitoring and Result Analysis on the High Excavated Slopes of TGP's Permanent Shiplock

To ensure the stability of the high rock slopes of the permanent shiplock of the Three Gorges Project is the key to the successful construction and normal operation of the shiplock. In the course of the slope excavation, effective deformation monitoring, well understanding of the deformation characteristics, and reasonable analyzing and predicting of the deformation trend of the high slopes are important aspects of work for the slope excavation and dynamic design of the shiplock. The optimized design, successful implementation of deformation monitoring and accurate monitoring results are the important guarantee for carrying out the project. The monitoring design of the permanent shiplock was conducted in accordance with the general principles of "laying stress on the key points, considering parts as well as the whole, planning uniformly and conducting in stages". The deformation monitoring system of the permanent shiplocks is composed of survey network for horizontal and vertical displacements, monitoring points, inverted plumb lines, tension wires, extensimeters, etc.

Crucial problems on security assessment of a building site adjacent to an excavated high slope

The subject of this work is the assessment on the stability of an excavated high slope in order to insure the security of the building site adjacent to the slope, which is frequently encountered in town construction in mountainous areas due to terrain limit. On the base of some typical engineering cases in Chongqing, several crucial problems on security assessment of building site adjacent to an excavated high slope, including the natural geological conditions and man-destroyed degree, engineering environment, potential failure pattern of the high slope, calculation parameters and analysis methods, are roundly discussed. It is demonstrated that the conclusion of security assessment can be determined according to the aspects above-mentioned, and the security assessment is one of the fundamental data to insure the safety of the related construction, site and buildings.

Slope deformation partitioning and monitoring points optimization based on cluster analysis

The scientific and fair positioning of monitoring locations for surface displacement on slopes is a prerequisite for early warning and forecasting.However,there is no specific provision on how to effectively determine the number and location of monitoring points according to the actual deformation characteristics of the slope.There are still some defects in the layout of monitoring points.To this end,based on displacement data series and spatial location information of surface displacement monitoring points,by combining displacement series correlation and spatial distance influence factors,a spatial deformation correlation calculation model of slope based on clustering analysis was proposed to calculate the correlation between different monitoring points,based on which the deformation area of the slope was divided.The redundant monitoring points in each partition were eliminated based on the partition's outcome,and the overall optimal arrangement of slope monitoring points was then achieved.This method scientifically addresses the issues of slope deformation zoning and data gathering overlap.It not only eliminates human subjectivity from slope deformation zoning but also increases the efficiency and accuracy of slope monitoring.In order to verify the effectiveness of the method,a sand-mudstone interbedded CounterTilt excavation slope in the Chongqing city of China was used as the research object.Twenty-four monitoring points deployed on this slope were monitored for surface displacement for 13 months.The spatial location of the monitoring points was discussed.The results show that the proposed method of slope deformation zoning and the optimized placement of monitoring points are feasible.

Comprehensive Analysis Method of Slope Stability Based on the Limit Equilibrium and Finite Element Methods and Its Application

To study the safety and stability of large slopes, taking the right side slope of the Yuxi’an tunnel of the Yuchu Expressway Bridge in Yunnan Province as an example, limit equilibrium and finite element analysis were applied to engineering examples to calculate the stability coefficient of the slope before and after excavation in the natural state. After comparative analysis, it was concluded that the former had a clear mechanical model and concept, which could quickly provide stability results;the latter could accurately determine the sliding surface of the slope and simulate the stress state changes of the rock and soil mass. The stability coefficients calculated by the two methods were within the stable range, but their values were different. On this basis, combined with the calculation principles, advantages and disadvantages of the two methods, a comprehensive analysis method of slope stability based on the limit equilibrium and finite element methods was proposed, and the rationality of the stability coefficient calculated by this method was judged for a slope case.

公路改扩建高边坡既有锚杆受力特性离心试验

为研究改扩建边坡二次开挖下既有锚杆的受力特性及边坡稳定性,基于自主研发的模型试验锚杆角度支护装置,采用离心试验研究了锚固角度分别为10°、20°、30°、45°、60°及锚杆横向密度分别为1根/(18 cm)、1根/(12 cm)下顺层岩质高边坡开挖全过程中坡顶水平位移、锚杆轴力及坡内土压力变化规律。结果表明:相同锚固角度下,随着边坡开挖卸荷,坡顶累计水平位移非线性增加,且开挖坡顶增幅较开挖坡中大;锚杆轴力呈单峰分布,在开挖坡顶及坡脚时轴力增幅较大,轴力峰值靠近软弱面且随开挖卸荷先减小后增大,开挖后轴力峰值仍为开挖前的61%以上;随锚固角度的增加,坡顶水平位移先减小后增大,坡内土压力先增大后减小,即存在最佳锚固角度;建议边坡开挖宜采用分级开挖,并在开挖坡顶及坡脚时适当降低速率,综合考虑边坡坡度、岩层及软弱面倾角等因素,合理设计锚固角度。研究成果有助于工程技术人员在改扩建边坡二次开挖工程中选择合适的支护措施。

基于FLAC/Slope模拟分析输电线路塔位边坡的开挖稳定性

塔位边坡的稳定性是输电线路基础设计考虑的一项重要内容。基于强度折减理论采用FLAC/Slope软件建立了输电线路典型塔位边坡的有限元分析模型,数值模拟了塔位边坡分步开挖施工过程,对各施工阶段的稳定性进行了评价分析,特别考虑了边坡稳定系数随边坡开挖步的变化规律。结果表明塔位边坡的坡脚或坡体分层处存在较大应力集中,且施工开挖步是影响边坡稳定系数变化的重要因素。

基于有限元模拟的边坡稳定性分析

为了对某边坡进行稳定性分析,探究边坡失稳过程中体应变变化规律。该研究选取湖北省恩施土家族苗族自治州某新建水厂的挖方边坡为研究对象,建立FLAC3D计算模型,根据强度折减法以及fish语言,计算该挖方边坡的安全系数,研究计算过程中边坡体应变的变化曲线。计算结果表明,该挖方边坡在开挖后处于不稳定状态,安全系数为0.879,滑动面均贯穿整个边坡,且边坡失稳过程中其体应变呈现先缩小后迅速增大的规律。该研究最后基于理正深基坑7.0及Geo-Studio软件对该挖方边坡进行边坡支护设计,同时边坡失稳过程中的体应变变化规律对于监测边坡失稳具有重大意义。

邻近运营隧道的大型基坑放坡开挖影响与实测兮析

[目的]基坑及隧道因建设过程的差异存在复杂的耦合作用,在基坑施工过程中会不可避免地对既有运营隧道产生扰动,引起隧道的位移,严重时将影响隧道运营安全。因此,有必要研究合理的基坑开挖方法和开挖步序,以减少基坑开挖过程中对既有邻近隧道的影响。[方法]依托某下沉式广场基坑,采用有限元数值模拟的方法针对邻近既有隧道的基坑的4种开挖工况进行研究,分析了不同开挖方法、开挖步序下的隧道内力分布规律、位移变化趋势及地层变形特征,比较了不同工况对施工期间隧道变形的影响,并结合基坑开挖期间的现场实际监测数据加以验证分析。[结果及结论]与拉槽放坡开挖相比,普通放坡开挖引起的隧道竖向变形较小;与整层开挖相比,接续开挖引起的隧道竖向变形较小;不同工序的隧道竖向变形最终结果较接近;与接续开挖相比,整层开挖引起的隧道水平变形比较大,这主要是由开挖步序多、基坑的时空效应明显所导致。根据现场实际监测数据,施工期间隧道竖向变形、水平变形,以及轨道竖向相对变形呈现先增大、后减小的趋势。