本文選題：紅土　切入點(diǎn)：雙向循環(huán)荷載　出處：《西北農(nóng)林科技大學(xué)》2017年碩士論文

【摘要】：紅土在我國(guó)地震頻發(fā)的南方熱帶、亞熱帶地區(qū)廣泛分布,對(duì)該地區(qū)紅土的動(dòng)力特性進(jìn)行研究就顯得十分必要,這對(duì)其工程抗震設(shè)計(jì)具有積極的意義。在以往的動(dòng)三軸試驗(yàn)研究中,學(xué)者通常忽略地震縱波產(chǎn)生的拉壓動(dòng)荷載作用,將地震荷載簡(jiǎn)化為一水平剪切動(dòng)荷載,在單向振動(dòng)荷載作用下進(jìn)行試驗(yàn),并用最大剪切面上的應(yīng)力來模擬地震荷載的作用。這種簡(jiǎn)化方法在深源地震或震級(jí)較小的地震中是可行的,但是在淺源地震或震級(jí)較大的地震中忽略地震縱波產(chǎn)生的拉壓動(dòng)荷載的影響,是不合理的和偏于不安全的。目前,學(xué)者對(duì)雙向動(dòng)荷載作用下土體的動(dòng)力特性研究主要集中在砂土、軟黏土和黃土等土類,對(duì)紅土的研究也多數(shù)為在單向振動(dòng)荷載作用下的試驗(yàn)研究,在雙向動(dòng)荷載作用下對(duì)紅土的動(dòng)強(qiáng)度特性研究還較為少見,鑒于此,本文利用SDT-20型微機(jī)控制電液伺服土動(dòng)三軸儀對(duì)紅土進(jìn)行了雙向振動(dòng)三軸試驗(yàn),探究紅土在雙向循環(huán)荷載作用下的動(dòng)強(qiáng)度特性,主要分析了固結(jié)圍壓、含水率、軸向動(dòng)荷載幅值、側(cè)向動(dòng)荷載幅值以及軸向與側(cè)向動(dòng)荷載間的相位差等因素對(duì)紅土動(dòng)強(qiáng)度特性的影響,探究不同的受力狀態(tài)下紅土動(dòng)強(qiáng)度的變化規(guī)律。通過本文試驗(yàn)分析,主要得出以下結(jié)論:(1)在相同含水率、相位差、側(cè)向循環(huán)荷載幅值條件下,單向和雙向動(dòng)三軸試驗(yàn)中,固結(jié)圍壓對(duì)重塑紅土動(dòng)強(qiáng)度的影響規(guī)律一致,即在同一循環(huán)振次下,固結(jié)圍壓越大,紅土的動(dòng)強(qiáng)度越大。且隨著固結(jié)圍壓的增大,相鄰兩個(gè)動(dòng)強(qiáng)度曲線的間距越來越小,動(dòng)強(qiáng)度增大的幅度越來越小,增大的趨勢(shì)也越來越緩慢。(2)不管是在單向還是雙向循環(huán)荷載作用下,含水率對(duì)紅土動(dòng)強(qiáng)度的影響均表現(xiàn)為在相同破壞振次下,紅土動(dòng)強(qiáng)度隨含水率的增大而減小,且隨著含水率的增大,動(dòng)強(qiáng)度曲線間距越來越小,動(dòng)強(qiáng)度降低的速率和幅度也越來越小,最后趨于穩(wěn)定,含水率對(duì)土體動(dòng)強(qiáng)度的影響也越來越不顯著。(3)在同相位試驗(yàn)中(υ=0°),同一循環(huán)振次下,紅土的動(dòng)強(qiáng)度隨側(cè)向循環(huán)荷載幅值的增大而增大,且雙向循環(huán)荷載下的動(dòng)強(qiáng)度明顯高于單向循環(huán)荷載下的值。在變相位試驗(yàn)中,紅土的動(dòng)強(qiáng)度隨側(cè)向循環(huán)荷載幅值的變化規(guī)律整體表現(xiàn)為“正弦”變化現(xiàn)象,即是當(dāng)相位差υ在0°~90°范圍內(nèi)時(shí),相同循環(huán)振次下,動(dòng)強(qiáng)度隨側(cè)向循環(huán)荷載幅值增大而增大;當(dāng)相位差υ在90°~270°范圍內(nèi)時(shí),動(dòng)強(qiáng)度隨側(cè)向循環(huán)荷載幅值增大而減小;當(dāng)相位差υ在270°~360°范圍內(nèi)時(shí),動(dòng)強(qiáng)度隨側(cè)向循環(huán)荷載幅值增大而增大。在υ=90°、270°時(shí),隨著側(cè)向循環(huán)荷載幅值增大,動(dòng)強(qiáng)度變化規(guī)律均表現(xiàn)為先增大后減小,動(dòng)強(qiáng)度變化趨勢(shì)由隨側(cè)向循環(huán)荷載幅值增大而增大的趨勢(shì)向隨側(cè)向循環(huán)荷載幅值增大而減小的趨勢(shì)過渡。(4)相位差在0°~360°范圍內(nèi)增大時(shí),紅土動(dòng)強(qiáng)度以相位差180°為轉(zhuǎn)折點(diǎn),先減小后增大。υ=180°時(shí)的動(dòng)強(qiáng)度較υ=0°時(shí)的動(dòng)強(qiáng)度有明顯的衰減,在同一固結(jié)圍壓下,側(cè)向循環(huán)荷載幅值越大,衰減率越大;而在相同的側(cè)向循環(huán)荷載幅值下,固結(jié)圍壓越大,衰減率越小。在小圍壓、大側(cè)向循環(huán)荷載幅值以及相位差為180°的條件下,雙向動(dòng)荷載作用對(duì)土體的穩(wěn)定極為不利,實(shí)際的工程抗震設(shè)計(jì)中,應(yīng)給予足夠的重視和充分的考慮。(5)在單向循環(huán)振動(dòng)三軸試驗(yàn)中,cd隨含水率的增大而減小,而υd在含水率大于最優(yōu)含水率時(shí)隨含水率增大而增大;在雙向無相位差的同相位試驗(yàn)中,cd和υd均隨含水率的增大而減小,而側(cè)向循環(huán)荷載幅值對(duì)cd和υd的影響表現(xiàn)為側(cè)向循環(huán)荷載幅值越大,cd越小,而υd卻越大。
[Abstract]:Red in China's earthquake prone southern tropical and subtropical regions are widely distributed, it is very necessary to research the dynamic characteristics of the laterite area, which is of positive significance to the engineering design. In the past three triaxial test research, scholars usually ignore the earthquake wave generated by the tensile and compressive load. The seismic load is simplified as a horizontal shear load, test in one-way vibration load, and the maximum shear stress on the surface to simulate seismic loads. This simplified method is feasible in the deep earthquakes or smaller magnitude earthquakes, but in shallow earthquakes or large magnitude earthquake ignore the seismic wave produced by tension and compression load effect is not reasonable and safe. At present, research on the dynamic characteristics of the soil under the load of the two-way dynamic mainly concentrated in the sand, soft clay The Loess and other soil types, the research on clay for the most experimental research in one-way vibration load, in the two-way dynamic loading under the dynamic strength characteristics of clay are rare, in view of this, this paper uses SDT-20 type microcomputer controlled electro-hydraulic servo soil three triaxial instrument for the two-way vibration of three axle test the red soil, the dynamic strength properties of clay in the inquiry under the bidirectional cyclic loading, the main analysis of the moisture content, confining pressure, axial dynamic load amplitude, lateral load amplitude and axial and lateral load dynamic phase difference between the influence factors on the dynamic strength properties of clay, explore the changes of different stress state the dynamic strength of clay. Through this analysis, we draw the following conclusions: (1) the rate of phase difference, in the same water, lateral cyclic load amplitude under unidirectional and bidirectional three triaxial test, consolidation confining pressure on remolded red Consistent effect of soil strength, which is in the same number of cycles, the greater the confining pressure, the dynamic strength of clay is greater. And with the increasing of confining pressure, dynamic strength curve of the two adjacent space more and more small, the dynamic range is more and more small intensity increases, the increasing trend is becoming more slowly. (2) whether it is in a one-way or two-way cyclic loading. The effect of moisture content on the dynamic strength of clay were performed in the same vibration times, the dynamic strength increases with the content of clay decreases with water content increasing, the dynamic strength curve of space more and more small, moving rate the amplitude and intensity decreased more and more small, finally stabilized, influence of water content on soil dynamic strength has become increasingly significant. (3) in the same test phase (=0 degrees), the same number of cycles, the dynamic strength of clay increases with the lateral amplitude of cyclic load, and bidirectional The dynamic strength under cyclic load was significantly higher than that of unidirectional cyclic loading. In the test phase, the dynamic strength of clay's overall changes with the lateral cyclic load amplitude is the sine change phenomenon, that is when the phase difference V at 0 DEG ~90 DEG range, the same number of cycles, dynamic the strength increases with the increase of the lateral amplitude of cyclic load; when the phase difference V at 90 DEG ~270 DEG range, the dynamic strength with the lateral amplitude of cyclic load increases; when the phase difference V at 270 DEG ~360 DEG range, the dynamic strength increases with the increase of lateral cyclic load amplitude. At =90 DEG, 270 degrees, with lateral cyclic load amplitude increases, the change rule of dynamic strength increased first and then decreased, the dynamic strength change trend with the lateral amplitude of cyclic load by increasing the amplitude of cyclic load to side with increasing trend (4) phase transition. 鍦，

本文編號(hào)：1716601