蠕變對凍土塑性屈服應(yīng)力的影響研究
發(fā)布時間：2018-10-08 15:31
【摘要】：對于融土,在荷載持續(xù)作用下,會發(fā)生水和空氣的擠出以及土顆粒相應(yīng)的移動,此過程即為融土的固結(jié)過程。融土的固結(jié)過程常常伴隨著土體內(nèi)部結(jié)構(gòu)的改變,并將融土歷史上所承受的最大固結(jié)壓力稱為前期固結(jié)壓力,其實質(zhì)是土體內(nèi)部結(jié)構(gòu)的宏觀反應(yīng)。與融土類似,凍土內(nèi)部也存在各種不同形式的結(jié)構(gòu),那么也應(yīng)當(dāng)存在類似前期固結(jié)壓力的指標(biāo),學(xué)者們稱為“似前期固結(jié)壓力”或“準(zhǔn)前期固結(jié)壓力”,在凍土中其實質(zhì)為塑性屈服應(yīng)力。不同于融土的是,在荷載作用下,由于凍土的滲透系數(shù)遠(yuǎn)遠(yuǎn)小于融土,并不存在像融土那樣的固結(jié)過程,但在荷載持續(xù)作用下凍土?xí)l(fā)生蠕變,導(dǎo)致凍土內(nèi)部的結(jié)構(gòu)或發(fā)生強(qiáng)化或發(fā)生弱化,可以料想在荷載持續(xù)作用下(蠕變),表征凍土結(jié)構(gòu)性的力學(xué)指標(biāo)——塑性屈服應(yīng)力應(yīng)當(dāng)發(fā)生相應(yīng)的變化。為了探究凍土蠕變對塑性屈服應(yīng)力的影響規(guī)律,本文先介紹了幾種典型的凍土蠕變理論,并指出它們各自的適用性,在此基礎(chǔ)上介紹由融土發(fā)展而來的等速線模型。為了驗證該模型在描述凍土蠕變時的適用性,本文做了不同溫度條件下經(jīng)過不同蠕變時間后的K0加載試驗,通過理論計算和試驗的對比發(fā)現(xiàn)該模型能很好的描述凍土的蠕變行為,并且具有參數(shù)較少、各參數(shù)都有明確的幾何及物理意義,還能將凍土的蠕變過程和塑性屈服應(yīng)力聯(lián)系起來的優(yōu)點。最終得出塑性屈服應(yīng)力是初始塑性屈服應(yīng)力、壓縮系數(shù)和回彈系數(shù)的函數(shù),且其對數(shù)與蠕變應(yīng)變(時間)呈線性關(guān)系的結(jié)論。凍土與融土在力學(xué)性質(zhì)和行為方面存在諸多差異,其中最明顯的一個差異就是凍土對溫度的敏感性,由于等速線模型由融土發(fā)展而來,故沒有考慮到溫度的影響,從試驗中可以看到該模型最主要的三個參數(shù)回彈系數(shù)、壓縮系數(shù)和蠕變速率參數(shù)均與溫度相關(guān),所以為了利用該模型更加準(zhǔn)確和合理地描述凍土的蠕變過程,就需要對該模型參數(shù)修正成溫度相關(guān)函數(shù)。結(jié)果發(fā)現(xiàn)修正后的模型能很好的預(yù)測凍土蠕變趨勢,在知道凍土溫度條件時直接可以確定模型參數(shù),使該模型在描述凍土蠕變時更加簡潔方便和準(zhǔn)確。最后回歸實際工程,模擬了塊碎石護(hù)坡U形路基在15年間的蠕變沉降情況,結(jié)果發(fā)現(xiàn)U形路基上部土層蠕變量較大,在第13年左右后進(jìn)入第三蠕變階段,路基下部土層蠕變較小在該計算時間段內(nèi)并沒有進(jìn)入第三蠕變階段,與此同時,路基上部土層還出現(xiàn)了較大的水平位移,這是由于U形外圍護(hù)坡不穩(wěn)固所致。針對這些問題本文提出了在路基施工時分層填筑每層之間鋪設(shè)土工隔柵或土工織物的辦法使這些土工合成材料對路堤兩側(cè)的位移形成拖拽作用,從而使整個路堤更加穩(wěn)固。
[Abstract]:For the thawing soil, the extrusion of water and air and the corresponding movement of soil particles will occur under the continuous load, which is the consolidation process of the thawing soil. The consolidation process of the thawed soil is often accompanied by the change of the internal structure of the soil, and the largest consolidation pressure in the history of the thawing soil is called the pre-consolidation pressure, which is essentially the macroscopic response of the internal structure of the soil. Similar to the thawing soil, there are also various forms of structures in the frozen soil, so there should also be indicators similar to the pre-consolidation pressure, which scholars call "quasi-prophase consolidation pressure" or "quasi-pre-consolidation pressure". In frozen soil, its essence is plastic yield stress. Different from thawing soil, the percolation coefficient of frozen soil is much smaller than that of thawing soil under load, so there is no consolidation process like thawing soil, but the frozen soil will creep under the continuous load. As a result of strengthening or weakening of the structure of frozen soil, it can be expected that the plastic yield stress, the mechanical index of the structure of frozen soil, should be changed correspondingly under the continuous load (creep). In order to investigate the influence of frozen soil creep on plastic yield stress, several typical creep theories of frozen soil are introduced in this paper, and their respective applicability is pointed out. On this basis, the isokinetic model developed from thawed soil is introduced. In order to verify the applicability of the model in describing the creep of frozen soil, a K _ 0 loading test under different temperature and different creep time has been done in this paper. Through the comparison of theoretical calculation and experiment, it is found that the model can well describe the creep behavior of frozen soil, and has fewer parameters, and each parameter has definite geometric and physical significance. It is also an advantage that the creep process of frozen soil can be connected with plastic yield stress. Finally, it is concluded that plastic yield stress is a function of initial plastic yield stress, compression coefficient and springback coefficient, and its logarithm is linearly related to creep strain (time). There are many differences in mechanical properties and behaviors between frozen soil and thawed soil. One of the most obvious differences is the sensitivity of frozen soil to temperature. Because the isokinetic model is developed from thawed soil, the influence of temperature is not taken into account. It can be seen from the test that the three main parameters of the model are the springback coefficient, the compression coefficient and the creep rate parameter, which are all related to temperature, so in order to describe the creep process of frozen soil more accurately and reasonably by using this model, It is necessary to modify the parameters of the model into a temperature correlation function. The results show that the modified model can predict the creep tendency of frozen soil very well, and the parameters of the model can be determined directly when we know the temperature condition of frozen soil, which makes the model more concise, convenient and accurate in describing the creep of frozen soil. At last, the creep settlement of U-shaped roadbed is simulated in the past 15 years. The results show that the creep of the upper soil layer of U-shaped subgrade is large, and the third creep stage is entered after 13 years. At the same time, the upper soil layer of the roadbed also appeared a large horizontal displacement, which was caused by the unstable U-shaped peripheral slope protection. In view of these problems, this paper puts forward a method of laying geotextile or geotextile between each layer in subgrade construction to make the geotechnical composite material drag and drag the displacement of both sides of the embankment, thus making the whole embankment more stable.
【學(xué)位授予單位】：蘭州大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TU445
本文編號：2257293
[Abstract]:For the thawing soil, the extrusion of water and air and the corresponding movement of soil particles will occur under the continuous load, which is the consolidation process of the thawing soil. The consolidation process of the thawed soil is often accompanied by the change of the internal structure of the soil, and the largest consolidation pressure in the history of the thawing soil is called the pre-consolidation pressure, which is essentially the macroscopic response of the internal structure of the soil. Similar to the thawing soil, there are also various forms of structures in the frozen soil, so there should also be indicators similar to the pre-consolidation pressure, which scholars call "quasi-prophase consolidation pressure" or "quasi-pre-consolidation pressure". In frozen soil, its essence is plastic yield stress. Different from thawing soil, the percolation coefficient of frozen soil is much smaller than that of thawing soil under load, so there is no consolidation process like thawing soil, but the frozen soil will creep under the continuous load. As a result of strengthening or weakening of the structure of frozen soil, it can be expected that the plastic yield stress, the mechanical index of the structure of frozen soil, should be changed correspondingly under the continuous load (creep). In order to investigate the influence of frozen soil creep on plastic yield stress, several typical creep theories of frozen soil are introduced in this paper, and their respective applicability is pointed out. On this basis, the isokinetic model developed from thawed soil is introduced. In order to verify the applicability of the model in describing the creep of frozen soil, a K _ 0 loading test under different temperature and different creep time has been done in this paper. Through the comparison of theoretical calculation and experiment, it is found that the model can well describe the creep behavior of frozen soil, and has fewer parameters, and each parameter has definite geometric and physical significance. It is also an advantage that the creep process of frozen soil can be connected with plastic yield stress. Finally, it is concluded that plastic yield stress is a function of initial plastic yield stress, compression coefficient and springback coefficient, and its logarithm is linearly related to creep strain (time). There are many differences in mechanical properties and behaviors between frozen soil and thawed soil. One of the most obvious differences is the sensitivity of frozen soil to temperature. Because the isokinetic model is developed from thawed soil, the influence of temperature is not taken into account. It can be seen from the test that the three main parameters of the model are the springback coefficient, the compression coefficient and the creep rate parameter, which are all related to temperature, so in order to describe the creep process of frozen soil more accurately and reasonably by using this model, It is necessary to modify the parameters of the model into a temperature correlation function. The results show that the modified model can predict the creep tendency of frozen soil very well, and the parameters of the model can be determined directly when we know the temperature condition of frozen soil, which makes the model more concise, convenient and accurate in describing the creep of frozen soil. At last, the creep settlement of U-shaped roadbed is simulated in the past 15 years. The results show that the creep of the upper soil layer of U-shaped subgrade is large, and the third creep stage is entered after 13 years. At the same time, the upper soil layer of the roadbed also appeared a large horizontal displacement, which was caused by the unstable U-shaped peripheral slope protection. In view of these problems, this paper puts forward a method of laying geotextile or geotextile between each layer in subgrade construction to make the geotechnical composite material drag and drag the displacement of both sides of the embankment, thus making the whole embankment more stable.
【學(xué)位授予單位】：蘭州大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TU445
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