本文選題：嵌巖抗拔樁 + 上覆土軟質(zhì)巖��； 參考：《西南交通大學(xué)》2017年碩士論文

【摘要】：高聳的輸電線路鐵塔承受的荷載十分復(fù)雜,不僅受到上部結(jié)構(gòu)傳來的豎向荷載,還需要承受非常大的上拔力,因此輸電線路工程實(shí)際中常常選用抗拔樁作為基礎(chǔ)。西部山區(qū)的地層特點(diǎn):覆蓋土層主要為粘土,較薄約0～2m,局部可達(dá)4m;基巖主要為軟巖,以砂巖、泥巖、礫巖為主。通常把樁嵌入巖層能夠一定程度提高抗拔承載力,然而目前對上覆土軟巖等截面嵌巖抗拔樁的破壞機(jī)理問題研究較少,所以輸電線路工程中"上土下巖"樁端嵌入基巖的樁基礎(chǔ)上拔承載力設(shè)計計算偏于保守,導(dǎo)致基礎(chǔ)工程量偏大。本文依托昭化—廣元牽引站220kV線路工程和路平—富樂500kV雙回線路新建工程,采用離心模型試驗(yàn)、現(xiàn)場試驗(yàn)和數(shù)值模擬,研究上覆土軟巖等截面嵌巖樁抗拔承載特性,主要的研究內(nèi)容和結(jié)論如下:(1)離心模型試驗(yàn)結(jié)果表明上覆土軟質(zhì)巖嵌巖樁抗拔破壞時樁周巖體破壞模式有圓柱型和復(fù)合型兩種。當(dāng)嵌巖段樁巖界面摩擦粘結(jié)良好時,樁的破壞呈現(xiàn)出復(fù)合型破壞模式.,當(dāng)嵌巖段樁巖界面摩擦粘結(jié)較弱時,樁的破壞呈現(xiàn)出圓柱型破壞模式。(2)上覆土等截面嵌巖抗拔樁達(dá)到極限狀態(tài)后,上拔位移變形迅速增大,荷載—位移曲線會出現(xiàn)明顯的拐點(diǎn),表現(xiàn)為突變型。(3)當(dāng)嵌入軟質(zhì)巖深度不小于1m且上覆土的厚度不大于嵌巖深度時,上覆土極限抗拔力不大于嵌巖樁極限抗拔的10%。上覆土軟質(zhì)巖等截面嵌巖樁極限抗拔承載力隨嵌巖深度呈線性增大。軟質(zhì)巖強(qiáng)度對樁側(cè)阻力的大小影響很大,較軟巖的樁側(cè)摩阻力約為軟巖的樁側(cè)摩阻力2～5倍。上覆土層等截面嵌巖樁極限抗拔承載力隨著巖基強(qiáng)度增大而增大。(4)上覆土軟質(zhì)巖等截面嵌巖樁受上拔荷載作用下巖土分界面位置樁側(cè)阻力會迅速增大,在嵌入軟質(zhì)巖0.5～1.5m范圍左右到達(dá)峰值。隨著上拔荷載繼續(xù)增大,上部軟質(zhì)巖樁側(cè)阻力發(fā)揮發(fā)生一定程度的減弱,下部軟質(zhì)巖樁側(cè)阻力繼續(xù)增大,峰值逐漸往下部移動。達(dá)到極限上拔力時,樁側(cè)阻力最大值發(fā)生在嵌入軟質(zhì)巖2～3m范圍。(5)采用《建筑樁基技術(shù)規(guī)范》按照碎石土計算現(xiàn)場試驗(yàn)軟質(zhì)巖嵌巖樁的極限抗拔承載力,得到的規(guī)范計算結(jié)果與現(xiàn)場試驗(yàn)結(jié)果相差很大,現(xiàn)場試驗(yàn)結(jié)果高于規(guī)范計算值的12.7%～467.8%。若采用《德國樁基規(guī)范》(DIN4014)來計算軟質(zhì)巖嵌巖抗拔樁的極限抗拔承載力,其計算值與本次試驗(yàn)結(jié)果吻合更好。(6)數(shù)值模擬結(jié)果表明,現(xiàn)場試驗(yàn)上覆土軟質(zhì)巖等截面嵌巖樁達(dá)到極限抗拔狀態(tài)后樁周土體發(fā)生內(nèi)部剪切破壞,嵌入軟質(zhì)巖段沿軟質(zhì)巖與樁身表面發(fā)生界面破壞,樁從巖層中被拔出。
[Abstract]:The load on the towering transmission line tower is very complex, which is not only subjected to the vertical load from the superstructure, but also needs to bear a very large uplift force, so the anti-drawing pile is often used as the foundation in the transmission line engineering. The stratigraphic characteristics of the western mountainous area are as follows: the overlying soil layer is mainly clay, the thickness is about 0 ~ 2 m, the local area is up to 4 m, and the bedrock is mainly soft rock, mainly composed of sandstone, mudstone and conglomerate. Usually the pile embedded in rock layer can improve the uplift bearing capacity to a certain extent, however, there are few researches on the failure mechanism of rock socketed pile with soft rock section. Therefore, the design and calculation of the uplift bearing capacity of the pile foundation embedded in the bedrock at the end of the pile end in the transmission line project is conservative, which leads to the large amount of foundation engineering. Based on the 220kV line project of Zhaohua-Guangyuan traction station and the new project of Luping Fulle 500kV double-circuit line, this paper studies the uplift bearing characteristics of rock socketed piles with equal cross-section of overlying soft rock by centrifugal model test, field test and numerical simulation. The main research contents and conclusions are as follows: (1) the results of centrifugal model test show that there are two types of rock mass failure modes around piles: cylindrical type and composite type during uplift failure of soft rock socketed pile with overlying soil. When the pile-rock interface friction bond is good, the pile failure presents a composite failure mode, and when the pile-rock interface friction bond is weak in the rock socketed segment, The failure of the pile shows a cylindrical failure mode. (2) after the pile reaches the limit state, the uplift displacement increases rapidly, and the load-displacement curve will appear obvious inflection point. When the depth of embedded soft rock is not less than 1m and the thickness of overlying soil is less than that of embedded rock, the ultimate uplift resistance of overlying soil is less than 10% of the ultimate uplift resistance of rock-socketed pile. The ultimate uplift bearing capacity of rock socketed piles with the same cross section of overlying soft rock increases linearly with the depth of rock socketed. The strength of soft rock has a great influence on pile side resistance, and the pile side friction of soft rock is about 2 or 5 times that of soft rock. The ultimate uplift bearing capacity of rock socketed piles with equal cross-section of overlying soil increases with the increase of the strength of rock foundation. (4) under the action of uplift load, the pile side resistance at the interface of rock and soil will increase rapidly under the action of uplift load on soft rock socketed pile with soft rock overlying soil. The peak value is reached in the range of 0.5 ~ 1.5 m of embedded soft rock. With the increasing of uplift load, the lateral resistance of the upper soft rock pile decreases to a certain extent, and the side resistance of the lower soft rock pile continues to increase, and the peak value gradually moves to the lower part. When the ultimate uplift force is reached, the maximum of pile side resistance occurs in the range of 23m embedded soft rock. The Technical Specification for Building pile Foundation is adopted to calculate the ultimate uplift bearing capacity of soft rock socketed pile in situ test according to the gravel soil. The result of the standard calculation is quite different from that of the field test, and the result of the field test is higher than that of the calculated value of the code, which is 12.7% and 467.8%. If the German Specification for pile Foundation (DIN4014) is used to calculate the ultimate uplift bearing capacity of soft rock socketed pile, the calculated value is in better agreement with the test results. In the field test, when the rock socketed pile with equal cross section of overlying soft rock reaches the state of ultimate pull-out, the internal shear failure occurs in the soil around the pile, the interfacial failure occurs along the interface between the soft rock and the pile body in the embedded soft rock section, and the pile is pulled out from the rock stratum.
【學(xué)位授予單位】：西南交通大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM75

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