Geomechanical effects of stress shadow created by large-scale destress blasting

This study aims to determine if large-scale choked panel destress blasting can provide sufficient beneficial stress reduction in highly-stressed remnant ore pillar that is planned for production. The orebody is divided into 20 stopes over 2 levels, and 2 panels are choke-blasted in the hanging wall to shield the ore pillar by creating a stress shadow around it. A linear-elastic model of the mining system is constructed with finite difference code FLAC3 D. The effect of destress blasting in the panels is simulated by applying a fragmentation factor(α) to the rock mass stiffness and a stress reduction factor(β) to the current state of stress in the region occupied by the destress panels. As an extreme case, the destress panel is also modeled as a void to obtain the maximum possible beneficial effects of destressing and stress shadow.Four stopes are mined in the stress shadow of the panels in 6 lifts and then backfilled. The effect of destress blasting on the remnant ore pillar is quantified based on stress change and brittle shear ratio(BSR) in the stress shadow zone compared to the base case without destress blasting. To establish realistic rock fragmentation and stress reduction factors, model results are compared to measured stress changes reported for case studies at Fraser and Brunswick mines. A 1.5 MPa immediate stress decrease was observed 20 m away from the panel at Fraser Mine, and a 4 MPa immediate stress decrease was observed 25 m away at Brunswick Mine. Comparable results are obtained from the current model with a rock fragmentation factor α of 0.2 and a stress reduction factor α of 0.8. It is shown that a destress blasting with these parameters reduces the major principal stress in the nearest stopes by 10-25 MPa.This yields an immediate reduction of BSR, which is deemed sufficient to reduce volume of ore at risk in the pillar.     

Comprehensive Urban Renewal of Old Urban Districts in Shenyang

IntroductionShenyang is the capital of LiaoningProvince,a hub of communications inNortheast China and an important na-tional industrial base.Surrounded by agroup of cities such as Anshan,Liaoyang,Benxi,Fushun and Tieling,Shenyang isthe largest city in the Northeast.It hasnow under its jurisdiction 9 districts and2 counties with an area of 8,515 squarekilometres and a population of 5.41     

Discrimination on the Concept of Historic City in China

In 1982,the State Council announced a list of historic cities in China,aiming to set up a conservation measure to conserve the cultural heritages from the perspective of a city.The historic city is a concept in relation to urban administrative governance.Its conservation scope and specific contents should be defined in conservation planning.Since the conservation planning of historic city is a part of the city master planning,its planning area should be the same as that in the master planning,with focus on the central urban area.The conservation planning of a historic city should define its objects in view of the interconnection between city history and culture and thus specify its conservation scope and contents accordingly.     

The Development of Theories in Planning

Regional structure is defined as the spatial integration of the natural,ecological,econom-ic and social structure of a region.It can be divided into a number of sub-systems.Since na-tional planning is usually carried out on the basis of regions,it is therefore important for us tostudy on the structural characteristics,regions;its mechanisms of changes;its degree ofopenness;its stages and rationality of development.Through the study of the relationship incorresponding changes of different structures and their basic characters within different re-gions,we could then have a scientific basis for modifying the pattern of national planning inmacro level,determining the scale and direction of economic development in regional plan-ning,and identifying the industrial structure and urban systems which are in line with themechanism of economic development.     

News in Brief

Editor’s Note: Referring to the whole process from having a desire, choosing a tool, and completing the behavior of mobility, urban mobility, as a new complex concept to demonstrate the ability of a city to meet the demands of itself and all its citizens for mobility, is deeply in? uenced by its subject of the city and its citizens, its object of the     

非洲城市供水面临的挑战

Infrastructure and basic services have a crucial role to play in alleviating urban poverty, especially in A frica. Alack of or inadequate access to water, sanitation and energy denies individual rights to dignity and health. It also has major repercussions on education, gender equality, nutrition and income-earning capacity. With 72 percentor 187 million people- of its urban population living in slums, infrastructure and basic services are a major challenge for Africa. As part of its strategy to reduce urban poverty, UN-Habitat launched its Water for African Cities programme in 1999. This article gives a brief account of the programme.     

Beijing''''s Old and Dilapidated Housing Renewal(Phase 1)

"Beijing-an incomparable masterpiece of urban planning. "Now, during the last decade of the millennium, Beijing, like a silk-worm in spring, is undergoing a profoundmetamorphosis-through the renewal of the old and dilapidatedhousing at its core. In such a famous city, so important to worldhistory and culture, this grand undertaking of renewal is boundto find its place in the annals of urban construction. Our research team has taken part the Old and Dilapidated Housing Renewal (Wei Jiu Fang Gai Zao) program since its very be-ginning. We have done the planning for the Deshengmen Wai,Guan Yuan, and Chaoyangmen Nei renewal districts. Each ofthese parcels is about 40 hectares, located along the Second Ring Road surrounding historic Beijing. Presently, our team is alsobeginning the planning for Nanchizi Street at the very centre ofthe city. The members of the research team include Tao Tao, a lectur-er at Tsinghua's School of Architecture; Daniel Abramson, a vis-iting scholar from the Massachusetts Institute of Technology inthe United States; graduate students Wu Zheng, Wu Li, TanYing, and Liu Yang: a group of thesis-level undergraduates eachyear; and myself, the author. A group from MIT collaborated withus in the planning of Deshengmen Wai during a summer studioin 1992. Summer studios in 1993 will also bring researchers fromthe University of British Columbia in Canada and the Uni-versityof Trondheim Norway to collaborate in the planning of NanchiziStreet. The following article is the first of a series describing thedifferent phases of our work and its outcomes. It is offered in thespirit of inviting further cooperation from abroad, and in the hopethat we may hear responses from many quarters.     

Some Empirical Examples of Central Place Model in China

At the beginning of 1980s,the Central Place Theory was introduced into China from the West.The authors ofthis article are the initiators of applying this model to China's urban and regional planning as well as to the allocationof commercial activities.Since the commodity economy has been developing in China for thousands of years,most ofthe areas in eastern plains and inland basins of China show the spatial structure of typical central places scene.Duringsome six years,the authors participated in a lot of rural,urban and regional planning projects in which the spatialphenomena and relevant internal mechanism proved this model and its deformation.This paper gives only a few ex-amples of the application of central place theory in China:1.the distribution of rural markets,the empirical study isbased mainly on the situation in Shengfang town and its vicinal area;2.the spatial combination of urban systems,problems about city allocation in North China are emphasized;3.commercial centers in city and the network,a cru-cial study on commercial centers in city and the network,a crucial study on commercial distribution of themetropolis.Beijing is done by using central place model.     

基于可靠度的组合桥梁设计及维护策略(英文)

Currently,the design practice of highway bridges around the world are moving towards limit states design,a reliability-based design procedure.Canadian Highway Bridge Design Code(CHBDC)is the first design code entirely developed based on limit states design philosophy,including foundations and FRP components.However,reliability of a structure decreases in service due to environmental attacks and material deterioration such as fatigue,corrosion and many other reasons.Therefore,the structure should be inspected periodically,and the reliability of the structure should be evaluated according to its age and field data.If its reliability is reduced to a certain level,a repair should be scheduled as well as some preventive maintenance measures should be implemented to prevent further deterioration.Recently,many research works have been conducted to investigate reliability-deterioration mechanisms for each type of infrastructure and its components,optimize the inspection and maintenance strategy,predict remaining service life,estimate its life cycle cost.This paper is focused on the study of reliability-deterioration mechanisms of slab on steel girder bridges due to fatigue and corrosion of steel girders as well as corrosion of reinforcement in the deck slab.Examples will also be given to illustrate the proposed life cycle management strategy for composite slab on steel girder bridges.