基坑开挖对邻近地埋管线影响规律研究

近年来随着基坑开挖方面的发展, 基坑开挖引起邻近地埋管线变形、断裂的事故频发, 该研究课题日益受到重视。以有限元软件ABAQUS为基础, 利用数值模拟的方法研究基坑开挖对邻近地埋管线的影响规律。分析地埋管线在不同管径和不同材质下, 基坑开挖对地埋管线的位移影响, 归纳总结基坑开挖过程中不同管径和不同材质对管线位移影响规律。     

Probability of serviceability failure in a braced excavation in a spatially random field: Fuzzy finite element approach

A simplified framework is proposed for evaluating the probability of “serviceability failure” in a braced excavation in a spatially random field. Here, the “serviceability failure” is said to occur when the excavation-induced wall or ground movement exceeds specified limiting values. Knowledge of this probability can aid in engineering decision-making to prevent damage to adjacent infrastructures. The proposed framework consists of five elements: (1) finite element method (FEM) for analyzing wall and ground responses in a braced excavation, (2) fuzzy set modeling of parameter uncertainty, (3) spatial averaging technique for handling spatial variability, (4) vertex method for processing fuzzy input through FEM model, and (5) interpretation of fuzzy output. The proposed framework is demonstrated through a well-documented case history. The results show the proposed framework is simple and effective for assessing the probability of serviceability failure in a braced excavation in a spatially random field. To focus on the proposed fuzzy FEM approach, the scope of this paper is limited to one-dimensional modeling of spatial variability with an assumed exponential autocorrelation function.     

A simplified method for predicting ground settlement profiles induced by excavation in soft clay

A series of parametric studies was performed to examine the influence factors affecting the settlement influence zone induced by excavation in soft clay. It was found that the excavation depth, width, the soft clay bottom depth and the rock-like soil depth are all related to the settlement influence zone. The potential failure surface, as deduced from the failure mechanism, covering the above-mentioned parameters, is consistent with the settlement influence zone. Thus, a simple method based on the analysis results is proposed to predict the settlement influence zone. Ten case histories and statistical data for the settlements in the Shanghai area were used to verify the proposed method.     

http://www.sciencedirect.com/science/article/pii/S167498711200062X

This paper focuses on the formation mechanism of fractures induced by excavation of a gallery in soft sedimentary rocks in the Horonobe area of Japan.Detailed fracture mapping of the gallery indicates that the fractures consist of both pre-existing shear fractures and excavation damaged zone(EDZ) fractures. EDZ fractures correspond to weak planes associated with bedding planes or transgranular cracks.The EDZ fractures terminate against pre-existing shear fractures.Therefore,even for excavations in soft sedimentary rocks,formation of the EDZ fractures are controlled by pre-existing fractures and earlier weak planes.     

A simple estimation model for 3D braced excavation wall deflection

A series of two-dimensional (2D) and three-dimensional (3D) finite element analyses using the Hardening Soil (HS) model were carried out to investigate the influences of soil properties, wall stiffness, excavation length, excavation depth, clay thickness at the base of the excavation and wall embedment depth, on the maximum wall deflection induced by braced-excavation. The results show that the 3D maximum wall deflections are generally much smaller than those for 2D. Comparisons were also made with other commonly used semi-empirical charts. Based on the finite element results in this study, a simple wall deflection equation was developed for estimating the maximum wall deflection that takes the 3D effects into consideration through different ratios of excavation length over excavation width.     

Analysis of tetrahedral and pentahedral key blocks in underground excavations

This paper presents a study the non-pyramidal key blocks of the rock mass. After a review of the Key Blocks Method (KBM), the study focuses on the analysis of key blocks formed by three and four discontinuity planes in underground excavations. The concept of non-pyramidal key blocks is described and their generation from a geometric operation called dislocation, thus determining the pentahedral key blocks that may be formed. To do so, the software program ASTUR (Analysis of the Support of Tunnels in Rock) was used, which develops a ubiquitous approach and allows the analysis of both pyramidal and non-pyramidal tetrahedral and pentahedral blocks.     

The role of salt weathering in the origin of the Qattara Depression, Western Desert, Egypt

Field studies and petrographic examinations of core samples and of the bedrock of the floor of the Qattara Depression, Egypt, indicate that salt weathering predominates in its western part in marked contrast to its eastern part. The eastern part of the depression is covered with more than 120-cm-thick, moist sands with sporadic occurrence of halite and gypsum due to the low salinity of the groundwater table. At the western part of the depression, the strongly saline, sodium chloride nature of the groundwater table favors crystallization of halite (and sometimes gypsum) at or near the surface of the outcropping bedrock of the Moghra clastics and/or Dabaa shale. Crystallization of halite and/or gypsum generates increased pressure that leads to mechanical disintegration of the bedrock into fine-grained debris. Features related to disintegration include blistering of the rock surface, splitting, spalling and/or granular disintegration.Alternation of dry and wet cycles favor halite crystallization, mechanical disintegration of the outcropping bedrock and dissolution of the halite cement, which exposes fine-grained debris to wind deflation. Removal of the debris from the floor of the depression leads to the accumulation of lunettes and other dunes in the downwind direction.Therefore, salt weathering provides fine-grained debris that are easily removed by deflation, which accounts for the topographically lower level of the western part of the depression (134 m below sea level (b.s.l.)). In contrast, the presence of moist sediments at the eastern part of the depression inhibits deflation and encourages sedimentation by adhesion of wind-blown sand to the damp surface of the sabkha at an elevation of 45 m below sea level.The disintegration of the bedrock of the Qattara Depression by salt weathering has been in effect since the onset of aridity in northern Egypt in Quaternary time. Whereas the initial excavation of the depression started in Late Miocene or Pliocene time by fluvial erosion, karstic process, mass-wasting and wind deflation.     

Simple procedure for quantification of the gravitational stress field in fractured hard rock massifs

In this paper, a quantitative procedure for evaluating the gravitational stress field in a hard rock massif is presented, using only a geological hammer and compass. Using the orientation of the fracture planes and their statistical distribution, a method for calculating of the tendency of the fractures to reactivate under gravitational load is proposed, based on Coulomb failure criterion. The method is applicable for assessing the most stable layout of the underground excavations and for evaluating the geometry of the stress field at a point during the initial stage of rock failure.     

River basin approach and integrated water management: Governance pitfalls for the Dutch Space-Water-Adjustment Management Principle

This article describes the turn to new integrative water management strategies in the Netherlands. It illustrates that some of the new and the general objectives and principles are not easily applied in practice. First, the article focuses on the development of integrative management of water and spatial development. A main policy line, the ‘Room for the River’ directive, was originally an ad hoc reaction to unexpected floods, but accompanied by other policy reforms it grew into an application of the river basin approach with an emphasis on its spatial consequences. The resulting Space-Water-Adjustment Management Principle (SWAMP) emphasizes the mutual adjustments in policy that must be made in both water policy and spatial development. Officially, water is proclaimed as an ordering element, yet actual spatial developments still follow lines of economic and social priorities as executed by institutional powers. Three case studies are presented to illustrate the emergence of new principles and governance issues linked to these management approaches. In practice, the paper concludes, spatial planning and land use decisions show a centralization tendency that is not in line with the proclaimed prevalence of local identity, resilience and open decentralized and deliberative governance in the SWAMP-based integrated river basin management.     

西南某电站河床坝基开挖卸荷条件下变形破坏的数值分析

西南某电站河床坝基开挖过程中,在河床底部出现大量表征岩体卸荷的变形破坏现象。开挖卸荷深度与卸荷强度成为大坝建设及其长期稳定性的关键问题。采用三维有限差分程序FLAC3D,分析开挖卸荷条件下坝基岩体变形破坏特征。结合现场卸荷裂隙现象调查资料,综合确定出所研究的河床坝基开挖卸荷影响深度及强度。为坝基综合治理提供必要的参考信息,也为今后此类中等地应力边坡开挖卸荷分析储备可以借鉴的资料。