| A rampart is a length or bank of wall that functions as a structure of military fortification and defense,of which rammed-earth ramparts,constructed of raw earth as the predominant material and by earth-ramming with manual labor as the technique,constitute an important type in ancient China.The most typical extant sites of historical rammed-earth ramparts include the Great Wall and large ancient city-walls distributed in the dry areas of Northwest China.These sites are representative samples of earthen heritage which convey rich historical,cultural and political messages,hence highly valuable for cultural heritage conservation research and practice.Studies on earthen heritage site conservation has been mainly focusing on the anti-weathering,anchoring and grouting.However,historical ramparts are characterized by their geographically-wide-distribution,geometrically-large-scale as well as structural and diagnostic complexity.They have always been threatened and damaged by structural instability occasioned primarily by factors including wind and salt corrosion,capillary water freezing and thawing,biological deterioration as well as earthquakes.Identification of such occasioning factors necessitates the employment of multi-disciplinary know-how such as that of cultural heritage conservation,material science,geotechnical engineering,earthquake engineering,etc.,for which systematic theoretical research findings are hitherto still on the horizon.This dissertation thus engages with relatively large-scale rammed-earth rampart sites situated in dry areas targeting a theatrical and methodological study on their structural types,deteriorations,damaging modes,theoretical modeling for stability assessment,diagnosis and prognosis.Starting from analyses of under-stress stability-failure of the rammed-earth structure and being advertent to environmental and deteriorative characteristics involved,methods including in-situ inspection,experimental research,theoretical and numerical analyses were employed in the work,which included:(1)A mechanical identification and summarization of the types and features of deteriorations rampart sites suffer from,for which in-situ survey combined with literature research was carried out.These sites were,based on their materials,building techniques and deteriorations,categorized first into 6 structural types and further into 13 sub-types.(2)A gradation criterion for structural cracking was proposed predicated on the influence by evolution of said cracking on site structural stability with advertence to mechanical and environmental changes.(3)9 structural damaging modes of rampart sites were proposed predicated on ultimate balance and block stability theories with advertence to structural types,encountered deteriorations and environmental factors.The characteristics of damaging in each mode was examined,targeting each phase of the deteriorating and mechanical changing process,to ascertain the damaging mechanism and limit state pertaining to each mode.Major factors occasioning damaging were also analyzed.(4)Aided by inputs from soil mechanics,elastic-plastic theory,structural dynamics,etc.,theoretical calculation models and formulas were devised for all 9 damaging modes.The employment of these models,with considerations of deterioration occasioning factors,revealed assessment criteria of structural damage pertaining to each mode.(5)Traditional manual techniques were adopted to manufacture rammed-earth wall test-pieces,in terms of both a real-life-size sample and smaller-scale blocks.Dynamic performance testing on the former and compression modulus testing on the latter,combined with finite element dynamic analysis,developed the testing method for rammed-earth wall equivalent elastic modulus.This could provide a new direction of study and parameter-identifying approach for the prognosis of rammed-earth rampart,in terms of deformation,damaging and deteriorations. |
PDF Full Text Request