本文選題：散體沙 + 休止角�。� 參考：《武漢大學(xué)》2014年博士論文

【摘要】：休止角是反映散體內(nèi)在力學(xué)關(guān)系的宏觀參數(shù),可作為評(píng)價(jià)散體流動(dòng)性好壞和邊坡穩(wěn)定性的量化指標(biāo)。在變化的水環(huán)境中,干濕交替變化和水動(dòng)力的作用將對(duì)散體沙的力學(xué)性質(zhì)和邊坡穩(wěn)定性產(chǎn)生影響,這些影響可以通過休止角的宏觀變化展現(xiàn)出來。變化水環(huán)境中散體沙休止角的研究對(duì)于散體介質(zhì)力學(xué)、泥沙運(yùn)動(dòng)力學(xué)以及河道中散體沙邊(岸)坡、堤壩、洲體失穩(wěn)等實(shí)際問題的研究具有重要的科學(xué)理論意義和工程實(shí)踐價(jià)值。 本文采用理論分析和靜、動(dòng)態(tài)試驗(yàn)結(jié)合的方法,考慮干濕變化和側(cè)向水流作用兩種變化水環(huán)境,建立了散體沙堆積體邊坡穩(wěn)定的力學(xué)模式,研究了散體沙的顆粒特性、含水狀態(tài)和水動(dòng)力條件對(duì)休止角的影響規(guī)律與機(jī)理。并根據(jù)實(shí)測(cè)數(shù)據(jù),分析了三峽蓄水后壩下游不飽和水流沖刷作用下散體沙洲灘休止角、坡角的變化及其對(duì)邊坡穩(wěn)定性的影響。主要結(jié)論和認(rèn)識(shí)如下： (1)在干燥狀態(tài)下,散體沙的內(nèi)摩擦力僅包含咬合力和分子吸附作用力,復(fù)合粗糙度較大的散體沙的內(nèi)摩擦力主要受咬合力影響,復(fù)合粗糙度較小的散體沙的內(nèi)摩擦力主要受分子吸附作用力影響。當(dāng)散體沙不飽和含水時(shí),顆粒接觸區(qū)的液橋形成彎月面,產(chǎn)生液橋力,引起阻礙顆粒相對(duì)運(yùn)動(dòng)的液橋吸附作用力。此時(shí),內(nèi)摩擦力中增加了液橋吸附作用力,其大小和對(duì)內(nèi)摩擦力的影響程度隨水膜厚度的增大而增大,隨散體沙的復(fù)合粗糙度增大而減小。當(dāng)散體沙飽和含水時(shí),液橋吸附作用力不存在,咬合力和分子吸附作用力因?yàn)樗さ臐櫥饔脺p到最小。散體沙的內(nèi)摩擦系數(shù)是水膜厚度和散體沙復(fù)合粗糙度的函數(shù)。 (2)當(dāng)散體沙邊坡不受外力作用時(shí),休止角接近但不等于散體沙的內(nèi)摩擦角。在干燥狀態(tài)下,散體沙的休止角主要受其顆粒特性影響,與復(fù)合粗糙度有關(guān)。當(dāng)散體沙含水率很小時(shí),休止角隨含水率增加緩慢,當(dāng)含水率超過一定值后,休止角隨含水率迅速增大至最大值并保持基本穩(wěn)定不變。休止角隨含水率變化的過程受顆粒特性影響,休止角增速變化的轉(zhuǎn)折點(diǎn)含水率的大小與散體沙的復(fù)合粗糙度成正比。散體沙休止角的最大值遠(yuǎn)大于其干燥狀態(tài)下的休止角,呈現(xiàn)類似粘性土的性質(zhì)。當(dāng)散體沙處于水下淹沒狀態(tài)時(shí),休止角減至極小值,休止角隨顆粒特性的變化規(guī)律與干燥狀態(tài)下一致。本文構(gòu)造了休止角的函數(shù)表達(dá)式,并結(jié)合試驗(yàn)實(shí)測(cè)數(shù)據(jù)進(jìn)行了初步驗(yàn)證,計(jì)算值與試驗(yàn)實(shí)測(cè)值接近,能夠表達(dá)休止角隨含水率變化的規(guī)律。 (3)基于考慮側(cè)向水流作用的散體沙邊坡力學(xué)平衡模式,提出相應(yīng)動(dòng)水休止角的基本表達(dá)式和邊坡泥沙起動(dòng)流速公式。在側(cè)向水流作用下,當(dāng)流速小于散體沙邊坡上泥沙的起動(dòng)流速,邊坡是穩(wěn)定的,動(dòng)水休止角等于靜水休止角；當(dāng)流速超過坡面泥沙起動(dòng)流速又不達(dá)到揚(yáng)動(dòng)流速時(shí),邊坡經(jīng)過坡角調(diào)整可以達(dá)到“靜”／“動(dòng)”平衡,此時(shí)動(dòng)水休止角隨流速增大而減小,隨散體沙粒徑的增大而增大；當(dāng)流速超過揚(yáng)動(dòng)流速時(shí),邊坡發(fā)生沖刷失穩(wěn)。 (4)當(dāng)水流飽和時(shí),動(dòng)水休止角僅與坡面泥沙組成和流速、水深等水流條件有關(guān)；當(dāng)水流過飽和或不飽和時(shí),坡體將發(fā)生沖淤變化,直接改變坡角大小和邊坡形態(tài),引起局部水流條件的變化,從而影響休止角的大小。三峽蓄水后壩下游不飽和水流的沿程沖刷,使得河床組成粗化,存在部分二元結(jié)構(gòu)岸灘散體沙砂層出露,岸灘抗沖性變差,休止角減��；枯水流量增大使得最小流速增大,散體沙休止角減小；同流量下枯水位降低和水流動(dòng)力軸線擺動(dòng)影響岸灘附近流速和水深的大小及橫向分布,進(jìn)而對(duì)散體沙休止角產(chǎn)生復(fù)雜影響；江心洲(灘)、邊灘的沖刷使得洲緣、岸坡變陡,坡角與休止角的差距縮小,易發(fā)生滑塌。
[Abstract]:The repose angle is a macroscopic parameter that reflects the mechanical relations in the bulk , and can be used as a quantitative index to evaluate the dispersion fluidity and the stability of the slope . In the changing water environment , the alternation of dry and wet alternation and the action of hydrodynamic force will have an influence on the mechanical properties and the stability of the slope .

Based on the measured data , the effects of particle characteristics , water - bearing state and hydrodynamic conditions on the angle of repose are studied .

( 1 ) In the dry state , the internal friction force of the bulk sand only contains the biting force and the molecular adsorption force , and the internal friction force of the bulk sand with larger composite roughness is mainly influenced by the molecular adsorption force . When the bulk sand is saturated with water , the influence degree of the particle contact area is increased with the increase of the thickness of the water film , and the influence degree of the size and the internal friction force of the liquid bridge is increased with the increase of the thickness of the water film .

( 2 ) The repose angle is close to but not equal to the internal friction angle of the bulk sand when the bulk sand slope is not acted by the external force . In the dry state , the repose angle of the bulk sand is mainly influenced by the particle characteristics . When the water content of the bulk sand is more than a certain value , the repose angle decreases with the water content rapidly to the maximum value and keeps the basic stable .

( 3 ) Based on the mechanical balance model of bulk sand slope considering lateral water flow , the basic expression of corresponding moving water stop angle and the formula of slope sediment start flow velocity are proposed . Under the action of lateral water flow , when the flow velocity is smaller than the starting flow rate of sediment at the bulk sand slope , the slope is stable , the moving water repose angle is equal to the rest angle of the static water ;
When the flow velocity exceeds the start - up flow velocity of the slope surface and does not reach the raising flow velocity , the slope angle adjustment can reach the " static " / " dynamic " balance , and the angle of repose of the moving water decreases with the increase of the flow rate , and increases with the increase of the particle diameter of the bulk sand ;
When the flow velocity exceeds the flow velocity , the slope is eroded and unstable .

( 4 ) when the water flow is saturated , the angle of repose of the moving water is only related to the sediment composition and the flow rate of the slope surface , the water depth and the like ;
When the water flow is too saturated or unsaturated , the slope body will change , directly change the slope angle and the slope form , cause local water flow conditions to change , thereby affecting the size of repose angle .
the flow rate of the low water flow is increased so that the minimum flow velocity is increased , and the repose angle of the bulk sand is reduced ;
The flow velocity and the water depth in the vicinity of the beach are affected by the decrease of the low water level and the fluctuation of the water flow power axis at the same flow rate .
The erosion of the beach and the beach makes the continental margin , the bank slope becomes steep , the gap between the slope angle and the repose angle is reduced , and the collapse is easy to occur .
【學(xué)位授予單位】：武漢大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：O347.7;TV223

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