發(fā)布時(shí)間：2018-04-05 09:10

  本文選題：主應(yīng)力方向旋轉(zhuǎn)　切入點(diǎn)：非共軸本構(gòu)模型　出處：《大連理工大學(xué)》2013年博士論文

【摘要】：在許多實(shí)際巖土工程問(wèn)題中,例如基坑開(kāi)挖、淺基礎(chǔ)地基承載力與變形特性、地震或波浪荷載對(duì)海床的作用等,主應(yīng)力方向的旋轉(zhuǎn)所引起的初始主應(yīng)力狀態(tài)的改變是不容忽視的。在主應(yīng)力方向的旋轉(zhuǎn)過(guò)程中,主應(yīng)力方向與塑性主應(yīng)變?cè)隽糠较虻男D(zhuǎn)變化趨勢(shì)不是一致的,即存在著非共軸現(xiàn)象。對(duì)于非共軸現(xiàn)象的描述及分析是當(dāng)前土力學(xué)研究中的熱點(diǎn)問(wèn)題之一。采用合理的本構(gòu)模型對(duì)非共軸現(xiàn)象及其影響進(jìn)行研究,通過(guò)離心機(jī)試驗(yàn)結(jié)果對(duì)非共軸模型的數(shù)值計(jì)算結(jié)果的合理性進(jìn)行驗(yàn)證,能夠完善傳統(tǒng)的巖土材料彈塑性本構(gòu)模型,也能夠?yàn)橹卮蠊こ探Y(jié)構(gòu)和地基設(shè)計(jì)提供依據(jù),具有重要的理論價(jià)值和實(shí)際工程意義。 本文圍繞著非共軸現(xiàn)象及其對(duì)應(yīng)力-應(yīng)變關(guān)系的影響進(jìn)行了系統(tǒng)的研究,通過(guò)砂土單剪試驗(yàn)的數(shù)值模擬研究了非共軸現(xiàn)象及其影響因素,針對(duì)淺基礎(chǔ)地基承載力與變形特性進(jìn)行數(shù)值計(jì)算分析和離心機(jī)模型試驗(yàn)研究,通過(guò)離心機(jī)試驗(yàn)結(jié)果對(duì)非共軸模型計(jì)算結(jié)果的合理性進(jìn)行了驗(yàn)證。主要研究?jī)?nèi)容和結(jié)論如下： 1.將角點(diǎn)結(jié)構(gòu)非共軸理論應(yīng)用到傳統(tǒng)彈塑性共軸本構(gòu)模型中,建立了一種非共軸本構(gòu)模型。對(duì)砂土單剪試驗(yàn)進(jìn)行有限元數(shù)值模擬,研究了非共軸現(xiàn)象及其對(duì)應(yīng)力-應(yīng)變關(guān)系的影響。研究結(jié)果表明：非共軸模型得到的主應(yīng)力方向和塑性主應(yīng)變?cè)隽糠较蛟诩羟凶冃蔚某跗谑遣恢睾系?隨著剪切變形的深入發(fā)展,兩者逐漸趨于一致。非共軸現(xiàn)象對(duì)應(yīng)力-應(yīng)變關(guān)系具有“軟化”作用,即非共軸模型計(jì)算得到的剪應(yīng)力比的增長(zhǎng)速度滯后于共軸模型計(jì)算結(jié)果的增長(zhǎng)速度。與理想彈塑性情況下的計(jì)算結(jié)果相比,非共軸現(xiàn)象對(duì)應(yīng)力-應(yīng)變關(guān)系的影響在應(yīng)變硬化情況下更加明顯。當(dāng)采用應(yīng)力峰值作為密砂的抗剪強(qiáng)度時(shí),需要考慮非共軸模型與共軸模型計(jì)算結(jié)果之間的差異；當(dāng)采用臨界狀態(tài)的殘余強(qiáng)度作為抗剪強(qiáng)度時(shí),非共軸模型與共軸模型計(jì)算結(jié)果之間沒(méi)有差異。靜止側(cè)壓力系數(shù)、豎向應(yīng)力和流動(dòng)法則等因素對(duì)非共軸現(xiàn)象具有顯著的影響。 2.在理想彈塑性、應(yīng)變硬化和應(yīng)變軟化情況下,采用共軸和非共軸模型對(duì)淺基礎(chǔ)地基荷載-變形問(wèn)題進(jìn)行數(shù)值分析,研究了非共軸現(xiàn)象對(duì)地基荷載-位移關(guān)系的影響。研究結(jié)果表明：非共軸現(xiàn)象對(duì)地基荷載-位移曲線具有“軟化”作用,即非共軸模型得到的地基荷載的增長(zhǎng)速度要滯后于共軸模型計(jì)算結(jié)果的增長(zhǎng)速度。隨著淺基礎(chǔ)下方土體單元水平位置的增加,主應(yīng)力方向的旋轉(zhuǎn)越來(lái)越顯著,非共軸現(xiàn)象也越來(lái)越明顯。非共軸現(xiàn)象在淺基礎(chǔ)邊緣下方深度較淺處比較明顯。與理想彈塑性情況下的計(jì)算結(jié)果相對(duì)比,非共軸現(xiàn)象對(duì)地基荷載-位移關(guān)系的影響在應(yīng)變硬化和應(yīng)變軟化情況下更加明顯,在應(yīng)變硬化和軟化模型的基礎(chǔ)上考慮非共軸現(xiàn)象的影響具有實(shí)際意義。研究非共軸現(xiàn)象對(duì)數(shù)值計(jì)算結(jié)果的影響時(shí),需要考慮基礎(chǔ)形式、基礎(chǔ)埋深和偏心距的變化。 3.對(duì)淺基礎(chǔ)地基承載力與變形特性進(jìn)行了離心機(jī)模型試驗(yàn)研究,分析了地基荷載-沉降關(guān)系的特點(diǎn)、地基承載力系數(shù)Nγ與基礎(chǔ)寬度的關(guān)系、以及基礎(chǔ)尺寸效應(yīng)。研究結(jié)果表明：對(duì)于中密砂地基而言,試驗(yàn)所得到的地基豎向荷載-位移關(guān)系曲線沒(méi)有顯著的拐點(diǎn)或曲線斜率突變階段；隨著豎向位移的增加,豎向荷載-位移曲線的初始斜率隨著基礎(chǔ)寬度的增加而增加；將確定地基承載力特征值fak時(shí)所采用的V/D提高到0.015～0.05時(shí),試驗(yàn)結(jié)果與理論公式的結(jié)果比較接近；基礎(chǔ)尺寸效應(yīng)在基礎(chǔ)沉降較大時(shí)比較明顯,試驗(yàn)所得到的Nγ與理論公式結(jié)果比較接近；當(dāng)基礎(chǔ)沉降較小時(shí),基礎(chǔ)尺寸效應(yīng)不明顯,試驗(yàn)所得到的Nγ低于理論公式結(jié)果。對(duì)于密砂地基而言,離心機(jī)試驗(yàn)得到的豎向荷載-位移關(guān)系曲線具有明顯的拐點(diǎn)；地基承載力隨著基礎(chǔ)寬度的增加而增加；地基承載力隨著基礎(chǔ)埋深的增加而增加,該結(jié)論在基礎(chǔ)寬度較小時(shí)比較明顯；達(dá)到地基承載力時(shí)的基礎(chǔ)沉降δ對(duì)于Nq的影響不明顯,δ對(duì)Nγ的影響比較明顯,考慮δ時(shí)的Nγ低于不考慮δ時(shí)的Nγ；基礎(chǔ)形式的變化對(duì)Nγ的影響比較明顯,其對(duì)Nq的影響不明顯。與方形淺基礎(chǔ)的試驗(yàn)結(jié)果相比,圓形淺基礎(chǔ)試驗(yàn)結(jié)果中的基礎(chǔ)尺寸效應(yīng)更加明顯。 4.對(duì)淺基礎(chǔ)離心機(jī)試驗(yàn)進(jìn)行數(shù)值模擬,將數(shù)值計(jì)算結(jié)果與試驗(yàn)結(jié)果進(jìn)行對(duì)比分析。從地基荷載-位移關(guān)系和地基承載力兩個(gè)方面,驗(yàn)證了非共軸模型計(jì)算結(jié)果的合理性。研究結(jié)果表明：當(dāng)基礎(chǔ)沉降較小時(shí),數(shù)值計(jì)算得到的豎向荷載-位移關(guān)系曲線的斜率大于離心機(jī)試驗(yàn)結(jié)果的斜率,共軸模型與非共軸模型的計(jì)算結(jié)果之間的差異不明顯；隨著基礎(chǔ)沉降的增加,非共軸模型與共軸模型計(jì)算得到的荷載-位移曲線之間的差異越來(lái)越明顯,離心機(jī)試驗(yàn)結(jié)果分布在非共軸模型結(jié)果中間。共軸模型計(jì)算得到的地基承載力系數(shù)高于離心機(jī)試驗(yàn)和非共軸模型的結(jié)果,離心機(jī)試驗(yàn)與非共軸模型所得到的地基承載力系數(shù)比較接近。
[Abstract]:In many practical geotechnical engineering problems , such as foundation pit excavation , shallow foundation foundation bearing capacity and deformation characteristic , earthquake or wave load , the change of initial principal stress state caused by rotation of main stress direction is not to be ignored . In the course of rotation of the main stress direction , the main stress direction and the plastic main strain increment direction are not consistent , that is , there is a non - coaxial phenomenon .

In this paper , the non - coaxial phenomenon and its influence on stress - strain relationship are studied . The non - coaxial phenomenon and its influencing factors are studied by numerical simulation of single shear test of sand and soil . The rationality of non - coaxial model calculation results is verified by the results of centrifugal test . The main research contents and conclusions are as follows :

1 . A non - coaxial constitutive model is established by applying the non - coaxial theory of corner structure to the traditional elastic - plastic co - axial constitutive model . The influence of non - coaxial phenomenon and its effect on stress - strain relationship is studied .
When the residual strength of the critical state is adopted as the shear strength , there is no difference between the non - coaxial model and the calculation result of the coaxial model . The static side pressure coefficient , the vertical stress and the flow rule have significant influence on the non - coaxial phenomenon .

2 . Under the condition of ideal elastic - plastic , strain hardening and strain softening , the influence of non - coaxial phenomenon on the load - displacement relationship of foundation is studied . The results show that the non - coaxial phenomenon has a ' softening ' effect on the foundation load - displacement curve .

3 . The characteristics of foundation load - settlement relations , the relationship between foundation bearing capacity coefficient N 緯 and foundation width , and the basic dimension effect are analyzed . The results show that the vertical load - displacement relation curve of the foundation obtained by the test has no obvious inflection point or curve slope mutation stage for medium - dense sand foundation .
As the vertical displacement increases , the initial slope of the vertical load - displacement curve increases with the increase of the base width ;
When the V / D used in determining the characteristic value fak of the ground - bearing capacity is increased to 0.015 - 0.05 , the experimental results are close to the results of the theoretical formula .
The basic dimension effect is obvious when the foundation settlement is large , and the N 緯 obtained by the experiment is close to the result of the theoretical formula .
When the foundation settlement is small , the foundation size effect is not obvious , the N 緯 obtained by the experiment is lower than the theoretical formula result . For the dense sand foundation , the vertical load - displacement relation curve obtained by the centrifuge test has obvious inflection point ;
the bearing capacity of the ground is increased along with the increase of the basic width ;
The bearing capacity of the foundation increases with the increase of the buried depth of the foundation , and the conclusion is more obvious at the base width .
The effect of 未 on Nq is not obvious . The effect of 未 on N 緯 is obvious , and the N 緯 at 未 is lower than that when 未 is not considered .
The effect of the change of the basic form on the Nq is not obvious . Compared with the experimental results of the square shallow foundation , the basic dimension effect in the results of the circular shallow foundation test is more obvious .

4 . The numerical simulation of shallow foundation centrifuge is carried out , and the numerical results are compared with the experimental results . The results show that the slope of the vertical load - displacement relation curve obtained by numerical calculation is greater than that of the centrifuge test results when the foundation settlement is small , and the difference between the coaxial model and the non - coaxial model is not obvious ;
With the increase of the foundation settlement , the difference between the non - coaxial model and the load - displacement curve calculated by the coaxial model is more and more obvious , and the results of the centrifuge test are distributed among the non - coaxial model results . The coefficient of the ground - bearing capacity calculated by the coaxial model is higher than that of the centrifuge test and the non - coaxial model , and the centrifuge test is close to the ground - bearing capacity coefficient obtained by the non - coaxial model .

【學(xué)位授予單位】：大連理工大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2013
【分類號(hào)】：TU41

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