本文選題：地表超載　切入點：有限土體　出處：《清華大學》2013年碩士論文

【摘要】：緊鄰既有建筑的基坑開挖過程中對變形控制非常嚴格，同時坑周土體寬度有限使得很多支護方案在這里都不適用，因此對這類基坑支護進行研究具有重要意義。本文在前人已有研究成果基礎(chǔ)之上，通過理論分析與數(shù)值模擬相結(jié)合的研究方法，針對這一類基坑支護設(shè)計時遇到的幾個問題進行了系統(tǒng)的研究。論文前半部主要研究各種不同情況下的土壓力計算方法，隨后在此基礎(chǔ)上對緊鄰既有建筑基坑的支護設(shè)計進行了探討。具體的研究工作包括以下幾個方面： （1）通過理論分析和數(shù)值模擬對現(xiàn)行規(guī)范中有關(guān)坑邊局部荷載引起支護結(jié)構(gòu)上土壓力的規(guī)定進行了較深入的討論，分析了土體參數(shù)c和φ對附加土壓力彈塑性解的影響，發(fā)現(xiàn)其與靜止土壓力系數(shù)的正比例關(guān)系；針對土體分層情況，利用有限元法分析了附加土壓力的分布形式；針對基坑周邊建筑物荷載的作用，分析了基礎(chǔ)埋深對附加土壓力的影響。利用正態(tài)分布曲線擬合了下臥土層的附加壓力，并在此基礎(chǔ)上推出了計算地表超載引起擋土結(jié)構(gòu)上附加土壓力的簡化公式。 （2）基坑擋土結(jié)構(gòu)與既有建筑基礎(chǔ)間形成有限土體，此時土壓力的計算不能采用通常情況下的朗肯理論或庫倫理論。通過對擋土墻與既有建筑基礎(chǔ)間的有限土體進行完整的受力分析，考慮了既有建筑基礎(chǔ)與有限土體間的法向及切向相互作用力，建立了求解有限土體主動土壓力的計算公式，并進行了適當?shù)暮喕�。通過與有限元結(jié)果對比證實本文給出的簡化公式形式較為簡捷，精度較高。在應(yīng)用公式的過程中要考慮位移的因素以及中主應(yīng)力對強度參數(shù)的影響，本章對這些問題也進行了討論。 （3）分析了水對土壓力的影響，包括滲流對土壓力的影響，以及非飽和土與飽和土強度差異引起土壓力的不同。 （4）由于錨桿的設(shè)置受到限制，常使護坡結(jié)構(gòu)的橫向支護不足，尋找其他措施以減小變形成為這類基坑支護需關(guān)注的重點。通過三維數(shù)值模擬各種不同的支護方案，，發(fā)現(xiàn)了一些減小變形的方法：上部土釘墻支護并適當放坡可有效減小護坡樁的懸臂長度；雙排樁對這類基坑支護有一定的優(yōu)勢；充分利用周邊建筑原來的支護系統(tǒng)等等。對樁徑的選取、放坡的深度也進行了討論。提出一種新型的支護方案，通過限制樁頂彎曲達到減小變形的目的，經(jīng)有限元驗證其效果不錯。
[Abstract]:The deformation control is very strict in the excavation of the foundation pit adjacent to the existing building, and the limited width of the soil around the pit makes many supporting schemes not applicable here, so it is of great significance to study this kind of foundation pit support.In this paper, based on the previous research results, through the combination of theoretical analysis and numerical simulation, several problems encountered in the design of this kind of foundation pit support are systematically studied.The first half of the paper mainly studies the calculation methods of earth pressure under different conditions, and then discusses the supporting design of the foundation pit adjacent to the existing building.Specific research efforts include the following:1) through theoretical analysis and numerical simulation, the regulations of soil pressure on supporting structure caused by local load on pit edge in current code are discussed in depth, and the influence of soil parameters c and 蠁 on the elastoplastic solution of additional earth pressure is analyzed.It is found that it is proportional to the coefficient of static earth pressure, the distribution form of additional earth pressure is analyzed by finite element method in the case of soil stratification, and the effect of building load around foundation pit is analyzed.The influence of the foundation depth on the additional earth pressure is analyzed.The additional pressure of the underlying soil is fitted by the normal distribution curve, and a simplified formula for calculating the additional earth pressure on the retaining structure caused by the surface overload is derived.2) a finite soil mass is formed between the retaining structure of foundation pit and the foundation of existing buildings, and the calculation of earth pressure can not be done by Rankine's theory or Coulomb's theory.Through the complete force analysis of the limited soil mass between the retaining wall and the existing building foundation, considering the normal and tangential interaction between the existing building foundation and the limited soil mass, a formula for calculating the active earth pressure of the finite soil is established.A proper simplification is carried out.By comparing with the finite element results, it is proved that the simplified formula given in this paper is simple and accurate.The factors of displacement and the effect of intermediate principal stress on strength parameters should be considered in the application of the formula. These problems are also discussed in this chapter.3) the influence of water on soil pressure, including the influence of seepage on soil pressure, and the difference of soil pressure caused by the strength difference between unsaturated soil and saturated soil are analyzed.(4) due to the limitation of bolt setting, the transverse support of slope protection structure is often insufficient, so finding other measures to reduce deformation has become the focus of attention for this kind of foundation pit support.Through three dimensional numerical simulation of various support schemes, some methods to reduce deformation are found: the upper soil nailing wall support and proper slope placement can effectively reduce the cantilever length of slope protection piles, and double row piles have certain advantages to this kind of foundation pit support.Make full use of the original supporting system of surrounding buildings and so on.The selection of pile diameter and the depth of slope are also discussed.A new support scheme is proposed, which can reduce the deformation by limiting the bending of the pile top.
【學位授予單位】：清華大學
【學位級別】：碩士
【學位授予年份】：2013
【分類號】：TU753

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