高圍壓下卸載速率對飽和黏土力學(xué)性質(zhì)的影響試驗及其微觀機理
發(fā)布時間：2018-11-11 00:37
【摘要】：本文采用高壓三軸試驗和微觀分析方法,對重塑飽和黏土和原狀飽和黏土進(jìn)行了固結(jié)不排水卸載試驗,研究了在高圍壓下,卸載速率、圍壓以及土樣性質(zhì)對飽和黏土的應(yīng)力應(yīng)變、孔隙水壓力等力學(xué)特性的影響。主要工作與獲得的認(rèn)識如下:(1)試驗獲得了不同卸載速率對土樣應(yīng)力應(yīng)變特性的影響特點。當(dāng)卸載速率為5k Pa/min和50k Pa/min時,重塑土樣應(yīng)力應(yīng)變曲線呈應(yīng)變軟化型,且卸載速率越小,峰值點所對應(yīng)的軸向應(yīng)變越大。當(dāng)卸載速率為10k Pa/min~50k Pa/min時,最大偏應(yīng)力值隨卸載速率的增大而增大,且卸載速率越大,應(yīng)力應(yīng)變曲線的起始坡度越陡;當(dāng)卸載速率減小到5k Pa/min時,應(yīng)力應(yīng)變曲線的變化趨勢有所改變,最大偏應(yīng)力不是減小反而增大,曲線起始坡度也變陡,即在5k Pa/min~10k Pa/min之間存在一個“轉(zhuǎn)換卸載速率”;原狀土樣與重塑土樣的應(yīng)力應(yīng)變曲線變化規(guī)律相似,但“轉(zhuǎn)換卸載速率”值有所不同,原狀土樣“轉(zhuǎn)換卸載速率”在20k Pa/min~40k Pa/min范圍內(nèi)。(2)試驗獲得了不同的卸載速率對土樣孔壓特性的影響特點。整體上原狀土樣的孔隙水壓力峰值比重塑土樣的峰值大,但是原狀土樣和重塑土樣在相同的卸載速率下孔隙水壓力隨偏應(yīng)力變化曲線的發(fā)展規(guī)律是不相同的。重塑土樣孔壓隨軸向應(yīng)變的發(fā)展存在一個“拐點”,即“拐點”前后孔壓隨軸向應(yīng)變的增長速率有所改變,在“拐點”前孔壓隨軸向應(yīng)變增長快,在“拐點”后增長速率變慢,且卸載速率越大,“拐點”所對應(yīng)的軸向應(yīng)變值越大�？讐�-軸向應(yīng)變變化曲線表明,卸載速率在20k Pa/min~50k Pa/min范圍內(nèi)存在一個“轉(zhuǎn)換卸載速率”,使得在這一卸載速率上下土樣的孔壓特性有所改變。(3)試驗獲得了不同固結(jié)圍壓對土樣應(yīng)力應(yīng)變特性的影響特點。同一卸載速率20k Pa/min,當(dāng)固結(jié)圍壓為2MPa、3MPa時,原狀土樣應(yīng)力應(yīng)變曲線為應(yīng)變硬化型,固結(jié)圍壓越大,偏應(yīng)力峰值越大。當(dāng)固結(jié)圍壓為6MPa時,應(yīng)力應(yīng)變曲線為應(yīng)變軟化型,偏應(yīng)力峰值變小;在同一固結(jié)圍壓下,當(dāng)偏應(yīng)力大小相等時,圍壓越小,土樣變形越大。(4)通過環(huán)境掃描電子顯微鏡對卸載試驗后土樣微觀分析。重塑土樣和原狀土樣經(jīng)過三軸卸載試驗后,土樣結(jié)構(gòu)變得松散,孔隙變多,發(fā)生剪切變形破壞的土樣在剪切面有明顯的定向性擦痕;剪切面上有數(shù)條拉張裂縫,且張裂縫大多處于較大的顆粒周圍,主裂縫旁邊衍生出許多細(xì)小的次級裂縫。(5)利用液氮吸附試驗研究卸載試驗前后土樣孔隙變化。發(fā)現(xiàn)隨著卸載速率的增加,平均孔直徑減小,對于原狀土樣,直徑由5.77nm減小到4.76nm,對于重塑土樣,直徑由8.38nm減小到6.73nm;且在相同圍壓下卸載速率增大,吸、脫附曲線類型有所變化,由L2類曲線變?yōu)長3類曲線,即孔隙的連通性由差變好。
[Abstract]:In this paper, high pressure triaxial test and microscopic analysis are used to study the undrained unloading test of remolded saturated clay and undisturbed saturated clay, and the unloading rate under high confining pressure is studied. The influence of confining pressure and soil sample properties on the mechanical properties of saturated clay such as stress strain pore water pressure and so on. The main results are as follows: (1) the influence of different unloading rates on the stress-strain characteristics of soil samples has been obtained. When the unloading rate is 5k Pa/min and 50k Pa/min, the stress-strain curve of the remolded soil shows strain softening type, and the smaller the unloading rate, the greater the axial strain corresponding to the peak point. When the unloading rate is 10 k Pa/min~50k Pa/min, the maximum deflection stress increases with the increase of unloading rate, and the higher the unloading rate, the steeper the initial slope of the stress-strain curve. When the unloading rate decreases to 5 k Pa/min, the variation trend of the stress-strain curve changes, the maximum deflection stress increases instead of decreasing, and the initial slope of the curve becomes steeper. That is, there is a "conversion unload rate" between 5k Pa/min~10k Pa/min; The stress-strain curves of undisturbed soil samples are similar to those of remolded soil samples, but the values of "transfer and unloading rate" are different. The "conversion and unloading rate" of undisturbed soil samples is in the range of 20k Pa/min~40k Pa/min. (2) the effects of different unloading rates on pore pressure characteristics of soil samples are obtained. On the whole, the peak value of pore water pressure of undisturbed soil sample is larger than that of remolded soil sample, but the development law of pore water pressure with deviation stress curve is different at the same unloading rate between undisturbed soil sample and remolded soil sample. There is a "inflection point" between pore pressure and axial strain of remolded soil sample, that is, pore pressure changes with the growth rate of axial strain before and after "inflection point", and increases rapidly with axial strain at "inflection point" and slows down after "inflection point". The larger the unloading rate, the greater the axial strain value of the inflection point. The change curve of pore pressure and axial strain indicates that there is a "conversion unloading rate" in the range of 20k Pa/min~50k Pa/min. The pore pressure characteristics of soil samples at this unloading rate have been changed. (3) the effects of different consolidation confining pressures on the stress-strain characteristics of soil samples have been obtained. At the same unloading rate of 20k Pa/min, when the consolidation confining pressure is 2 MPA, the stress-strain curve of the undisturbed soil is of strain hardening type. The larger the confining pressure of consolidation is, the greater the peak value of deflection stress is. When the consolidation confining pressure is 6MPa, the stress-strain curve is strain-softening type, and the peak value of deflection stress becomes smaller. Under the same consolidation confining pressure, the smaller the confining pressure is, the larger the deformation of soil sample is. (4) the microcosmic analysis of soil sample after unloading test is carried out by environmental scanning electron microscope. After triaxial unloading test, the structure of the remolded soil sample and the undisturbed soil sample become loose, the pores become more and more, and the shear deformation failure of the soil sample has obvious directional scratches on the shear surface. There are several tensile cracks on the shear surface, and most of the tensile fractures are around the larger particles, and many small secondary cracks are derived from the main cracks. (5) the pore changes of soil samples before and after unloading test are studied by liquid nitrogen adsorption test. It is found that with the increase of unloading rate, the average pore diameter decreases from 5.77nm to 4.76 nm for undisturbed soil samples and from 8.38nm to 6.73 nm for remolded soil samples. Under the same confining pressure, the unloading rate increases, the type of absorption and desorption curves changes, from L2 type curve to L3 type curve, that is, the connectivity of pore becomes better from difference.
【學(xué)位授予單位】：中國礦業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TU411
本文編號：2324020
[Abstract]:In this paper, high pressure triaxial test and microscopic analysis are used to study the undrained unloading test of remolded saturated clay and undisturbed saturated clay, and the unloading rate under high confining pressure is studied. The influence of confining pressure and soil sample properties on the mechanical properties of saturated clay such as stress strain pore water pressure and so on. The main results are as follows: (1) the influence of different unloading rates on the stress-strain characteristics of soil samples has been obtained. When the unloading rate is 5k Pa/min and 50k Pa/min, the stress-strain curve of the remolded soil shows strain softening type, and the smaller the unloading rate, the greater the axial strain corresponding to the peak point. When the unloading rate is 10 k Pa/min~50k Pa/min, the maximum deflection stress increases with the increase of unloading rate, and the higher the unloading rate, the steeper the initial slope of the stress-strain curve. When the unloading rate decreases to 5 k Pa/min, the variation trend of the stress-strain curve changes, the maximum deflection stress increases instead of decreasing, and the initial slope of the curve becomes steeper. That is, there is a "conversion unload rate" between 5k Pa/min~10k Pa/min; The stress-strain curves of undisturbed soil samples are similar to those of remolded soil samples, but the values of "transfer and unloading rate" are different. The "conversion and unloading rate" of undisturbed soil samples is in the range of 20k Pa/min~40k Pa/min. (2) the effects of different unloading rates on pore pressure characteristics of soil samples are obtained. On the whole, the peak value of pore water pressure of undisturbed soil sample is larger than that of remolded soil sample, but the development law of pore water pressure with deviation stress curve is different at the same unloading rate between undisturbed soil sample and remolded soil sample. There is a "inflection point" between pore pressure and axial strain of remolded soil sample, that is, pore pressure changes with the growth rate of axial strain before and after "inflection point", and increases rapidly with axial strain at "inflection point" and slows down after "inflection point". The larger the unloading rate, the greater the axial strain value of the inflection point. The change curve of pore pressure and axial strain indicates that there is a "conversion unloading rate" in the range of 20k Pa/min~50k Pa/min. The pore pressure characteristics of soil samples at this unloading rate have been changed. (3) the effects of different consolidation confining pressures on the stress-strain characteristics of soil samples have been obtained. At the same unloading rate of 20k Pa/min, when the consolidation confining pressure is 2 MPA, the stress-strain curve of the undisturbed soil is of strain hardening type. The larger the confining pressure of consolidation is, the greater the peak value of deflection stress is. When the consolidation confining pressure is 6MPa, the stress-strain curve is strain-softening type, and the peak value of deflection stress becomes smaller. Under the same consolidation confining pressure, the smaller the confining pressure is, the larger the deformation of soil sample is. (4) the microcosmic analysis of soil sample after unloading test is carried out by environmental scanning electron microscope. After triaxial unloading test, the structure of the remolded soil sample and the undisturbed soil sample become loose, the pores become more and more, and the shear deformation failure of the soil sample has obvious directional scratches on the shear surface. There are several tensile cracks on the shear surface, and most of the tensile fractures are around the larger particles, and many small secondary cracks are derived from the main cracks. (5) the pore changes of soil samples before and after unloading test are studied by liquid nitrogen adsorption test. It is found that with the increase of unloading rate, the average pore diameter decreases from 5.77nm to 4.76 nm for undisturbed soil samples and from 8.38nm to 6.73 nm for remolded soil samples. Under the same confining pressure, the unloading rate increases, the type of absorption and desorption curves changes, from L2 type curve to L3 type curve, that is, the connectivity of pore becomes better from difference.
【學(xué)位授予單位】：中國礦業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TU411
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