本文關(guān)鍵詞：巖溶地區(qū)高層建筑剛性樁復(fù)合地基—筏板基礎(chǔ)體系的受力性能研究　出處：《華南理工大學(xué)》2015年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 高層建筑 剛性樁復(fù)合地基 褥墊層 筏板 FDM-DEM 巖溶

【摘要】：巖溶地質(zhì)占我國面積的35%,多集中在廣東、廣西、湖南、四川等人口密集省份。高層建筑可有效滿足人口密集地區(qū)的住房需求,但對地基基礎(chǔ)安全性要求高。巖溶地質(zhì)構(gòu)造十分復(fù)雜,隱伏土洞、溶洞廣泛存在,給工程建設(shè)帶來許多難題。因此,如何保證巖溶地區(qū)高層建筑地基基礎(chǔ)安全穩(wěn)定,是十分重要的課題。剛性樁復(fù)合地基-筏板基礎(chǔ)具有承載力高、施工方便、成本較低等優(yōu)點,經(jīng)過工程實踐證明,十分適用于巖溶地區(qū)高層建筑。本文通過大量試驗及理論研究,解決了剛性樁復(fù)合地基荷載分配和沉降計算問題,揭示了褥墊層作為散體材料的特殊性質(zhì)及其對上部結(jié)構(gòu)抗震性能的影響,得到了筏板受力變形規(guī)律,解釋了正常使用狀態(tài)下筏板鋼筋應(yīng)力較小的真正原因,從而形成了完整的樁-土-墊層-筏板-上部結(jié)構(gòu)力學(xué)性能體系。總結(jié)起來,本文對以下內(nèi)容進(jìn)行了深入研究和探討:(1)針對粵北5個典型巖溶場地高層建筑項目進(jìn)行了54根剛性樁單樁復(fù)合地基現(xiàn)場靜載試驗。5個工程涵蓋了常見的地質(zhì)條件和復(fù)合地基方案,包括:1)淺層6m淤泥質(zhì)土+CM樁復(fù)合地基;2)10m厚卵石層+長螺旋樁復(fù)合地基;3)淺層高承載力粉質(zhì)粘土+PHC管樁復(fù)合地基;4)淺層低承載力中砂+PHC管樁復(fù)合地基;5)埋深淺且傾角大基巖+載體樁復(fù)合地基。測量得到剛性樁復(fù)合地基受荷沉降及淺層樁間土應(yīng)力的變化規(guī)律,統(tǒng)計得到沉降、土應(yīng)力、樁土應(yīng)力比、土承擔(dān)荷載比例等關(guān)鍵指標(biāo)的變化范圍。(2)假設(shè)樁、土受荷沉降符合“雙曲線”模型,利用褥墊層中的力平衡和位移協(xié)調(diào)條件,推導(dǎo)出剛性樁復(fù)合地基沉降、土應(yīng)力、樁對墊層刺入量等的解析計算方法。利用它對樁、土、墊層、復(fù)合地基受荷沉降進(jìn)行了參數(shù)分析,得到了規(guī)律性結(jié)論。(3)應(yīng)用離散元(DEM)方法模擬褥墊層顆粒,實現(xiàn)了有限差分-離散元(FDMDEM)耦合計算方法。首先進(jìn)行3種常用褥墊層材料的物理力學(xué)性質(zhì)試驗,得到密度、空隙率、壓縮模量等宏觀指標(biāo)。利用PFC2D程序進(jìn)行自然堆積和側(cè)限壓縮數(shù)值試驗,標(biāo)定顆粒細(xì)觀參數(shù)的取值。使用FISH語言編制命令流,在PFC2D和FLAC之間傳遞變量,實現(xiàn)耦合計算,從細(xì)觀尺度揭示褥墊層顆粒的受荷運(yùn)動規(guī)律。以褥墊層材料、厚度hc,樁徑d、樁距D,樁間土變形模量E和樁端土變形模量Eb作為因素,進(jìn)行耦合模型數(shù)值正交試驗,通過級差和方差分析得到各因素對承載力極限值fspu、樁刺入量Δ、樁土應(yīng)力比N、樁承擔(dān)荷載百分比Rp的影響規(guī)律,給出它們的區(qū)間估值以及選用原則。(4)對不同厚度、不同材料褥墊層進(jìn)行單調(diào)及循環(huán)加載下的剪切試驗。單調(diào)加載下得到水平力峰值歸一化系數(shù)μn和滑動位移umax;循環(huán)加載下得到褥墊層受剪的“三折線”骨架曲線,以及其中彈性段、塑性段、滑移段關(guān)鍵指標(biāo)的計算公式。采用“三折線”骨架曲線模擬褥墊層滯回性能,針對不同高度、不同型式有無褥墊層結(jié)構(gòu)進(jìn)行罕遇地震下彈塑性時程分析。對比兩種情況下結(jié)構(gòu)的宏觀指標(biāo),得到褥墊層對上部結(jié)構(gòu)抗震性能影響的定量結(jié)論。(5)針對一實際高層建筑進(jìn)行筏板鋼筋應(yīng)力、淺層地基土應(yīng)力、整體沉降長期監(jiān)測,發(fā)現(xiàn):1)上部結(jié)構(gòu)完成3~5層之前,筏板鋼筋應(yīng)力增長很快,之后基本不變;2)結(jié)構(gòu)封頂時,鋼筋應(yīng)力僅有5~20MPa,從澆筑筏板到結(jié)構(gòu)封頂,鋼筋應(yīng)力變化在50MPa以內(nèi),遠(yuǎn)低于其強(qiáng)度設(shè)計值。(6)采用數(shù)值模擬方法,分析了地基模型、上部結(jié)構(gòu)剛度、筏板底摩擦力以及受拉區(qū)混凝土對規(guī)則受力筏板計算彎矩和變形的影響規(guī)律。建立實測項目的剛性樁復(fù)合地基-筏板-上部結(jié)構(gòu)整體模型,進(jìn)行施工模擬。對比實測結(jié)果,統(tǒng)計受拉區(qū)混凝土應(yīng)力,分析施工過程中筏板溫度、剛度的變化規(guī)律,證明了筏板鋼筋應(yīng)力由“急劇增長”到“緩慢變化”的原因是:1)上部結(jié)構(gòu)完成3~5層之前,筏板剛度較小,以整體彎曲為主,彎矩增長快;2)筏板混凝土水化過程中與鋼筋的粘結(jié)沒有完全形成,彎矩主要由鋼筋承擔(dān)。鋼筋應(yīng)力較小的原因是:1)混凝土收縮對鋼筋產(chǎn)生了-40~-20MPa的初始壓應(yīng)力;2)結(jié)構(gòu)封頂時,筏板受拉區(qū)混凝土并未開裂,承擔(dān)了很大一部分彎矩,但這部分安全儲備不可缺少。
[Abstract]:Karst in China accounts for 35% of the area, mostly concentrated in Guangdong, Guangxi, Hunan, Sichuan and other densely populated provinces. High-rise buildings can effectively meet the housing needs in densely populated areas, but the safty of the foundation requirements. Karst geological structure is very complicated, concealed soil cave, karst caves exist many difficulties the construction of the project. Therefore, how to ensure the high-rise building foundation in karst area safety and stability, is a very important subject. The rigid pile composite foundation raft foundation with high bearing capacity, convenient construction, low cost, through the engineering practice, very suitable for high-rise buildings in karst area. Through a lot of experiments and theoretical research. To solve the problem of load distribution of rigid pile composite foundation and the settlement calculation, reveals the cushion as special properties of granular material and the upper structure seismic performance, the raft The force and deformation, explains the reinforced raft under normal state should be the real reason smaller force, thus forming a complete system of upper structure mechanical properties of pile soil cushion and raft. To sum up, this paper discusses and studies the following contents: (1) according to the 5 typical North Guangdong karst area high-rise building project of 54 rigid pile composite foundation static load test on site.5 Engineering covers the common geological conditions and composite foundation scheme, including: 1) 6m shallow silty soil +CM pile composite foundation; 2) 10m thick gravel + long spiral pile composite foundation; 3) shallow high bearing capacity of silty clay +PHC pile composite foundation; 4) shallow low bearing sand +PHC pile composite ground force; 5) the shallow depth and steep bedrock + carrier pile composite foundation. The measured variation of load and settlement of shallow soil stress between piles under rigid pile composite foundation, statistics The settlement, soil stress, pile-soil stress ratio, the variation range of soil load bearing proportion and other key indicators. (2) assume that pile and soil under loading settlement accords with hyperbolic model, using the cushion of force equilibrium and displacement compatibility conditions of rigid pile composite foundation is deduced, the soil stress. Analytical calculation on the cushion pile penetration method. The use of it on the pile, soil and cushion composite foundation load settlement parameters were analyzed, obtained the conclusions. (3) the application of discrete element method (DEM) simulation of cushion particles, the finite difference discrete element (FDMDEM) coupling the first 3 kinds of calculation methods. The physical and mechanical properties of cushion layer materials commonly used test, obtained density, void ratio, compression modulus and other macroeconomic indicators. The natural accumulation and unconfined compression numerical tests using the PFC2D program, the calibration value of micro parameters of particles. The programmed with FISH command stream in PFC2D And FLAC transfer between variables, coupling calculation, from the meso scale reveal cushion particles bearing movement. With the cushion material, thickness HC, pile diameter D, pile spacing D, pile-soil deformation modulus of pile end soil deformation modulus of E and Eb as factors, the orthogonal numerical coupling model test. Through the analysis of variance and differential fspu of various factors on the ultimate bearing capacity of pile penetration value, Delta, pile-soil stress ratio N, influence of pile bearing load percentage of Rp, given their interval estimation and selection principle. (4) of different thickness, shear test and monotonic under cyclic loading with different materials the cushion under monotonic loading. The peak stress level obtained normalized coefficient n and sliding displacement Umax; cyclic loading under cushion shear "three line" and the skeleton curve, wherein the elastic section, plastic section, calculation formula of slip segment key indicators. The "three line "The skeleton curve simulation of cushion hysteretic behavior, according to different height, different types have no cushion structure under rare earthquake elastic-plastic time history analysis. A comparison of two case of macro index structure, quantitative conclusions effect of cushion on the upper structure seismic performance. (5) for a high-rise building for the raft reinforcement stress, shallow soil stress, the overall settlement of long-term monitoring, it is found that: 1) before the completion of the upper structure of the 3~5 layer, the raft reinforcement stress increases quickly, after basically unchanged; 2) cap structure, the steel stress is only 5~20MPa, from pouring raft to the cap structure, reinforced the stress changes within 50MPa, its strength is far lower than the design value. (6) using the method of numerical simulation analysis of foundation model, stiffness of superstructure, raft bottom friction force and bending moment calculation and the deformation of the raft concrete tensile force on the rules established. The overall model test project for rigid pile composite foundation raft superstructure, construction simulation. Comparing the measured results, statistical concrete tensile stress analysis of raft temperature in the construction process, variation of stiffness, stress that the raft reinforced by the "rapid growth" to "slow change" the upper structure is: 1) before completion of 3~5 layer, smaller raft rigidity, overall bending moment, rapid growth; 2) bonded concrete hydration process in the raft board and reinforced the not fully formed, moment is mainly borne by the steel reinforced stress. The smaller is: 1) produced -40~-20MPa the initial stress of reinforced concrete shrinkage; 2) cap structure, raft concrete in tension zone did not crack, assume a large part of the moment, but this part of safety is indispensable.

【學(xué)位授予單位】：華南理工大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TU470

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