本文選題：淤泥質(zhì)黏土　切入點：單向固結(jié)　出處：《中國地質(zhì)大學(xué)（北京）》2014年碩士論文

【摘要】：淺海相沉積軟土廣泛分布于我國沿海地區(qū)，不同程度地影響工程建設(shè)。淤泥質(zhì)黏土是最為常見的海積軟土，其主要特點是天然含水率和孔隙比大、重度小、塑性指數(shù)較大，宏觀性質(zhì)方面表現(xiàn)出強度低、承載力小、滲透性小、壓縮性高等特征，同時還具有明顯的次固結(jié)特性。軟土的次固結(jié)特性和微觀結(jié)構(gòu)對其宏觀力學(xué)性質(zhì)有重要影響，因此導(dǎo)致工程建設(shè)出現(xiàn)沉降量過大、變形不滿足要求以及長期變形不穩(wěn)定等問題。 基于上述情況，本文以天津濱海南港地區(qū)埋深約7米的原狀海積淤泥質(zhì)黏土作為試驗和研究對象，進行分級加荷和預(yù)固結(jié)分別加荷兩種單向固結(jié)試驗以及微觀試驗，探討其在不同加荷方式下的次固結(jié)變形特征，并通過微觀試驗分析次固結(jié)過程中微觀變化與宏觀力學(xué)特性的關(guān)系。結(jié)合地基預(yù)壓工程測試實例對試驗結(jié)果進行分析，得出了一些對軟土地區(qū)工程建設(shè)尤其是地基預(yù)壓有指導(dǎo)作用的結(jié)論和建議。本文主要研究成果如下： （1）本次研究的淤泥質(zhì)黏土先期固結(jié)壓力pc為63kPa，超固結(jié)比OCR約為1，屬于傳統(tǒng)觀念的正常固結(jié)土。單向固結(jié)試驗結(jié)果表明其主次固結(jié)分界點的時間約在150～200min。相對于加荷比η，固結(jié)壓力p對次固結(jié)特性影響更大。當(dāng)固結(jié)壓力p從較小值逐漸增加，，次固結(jié)系數(shù)逐漸增大，當(dāng)p接近2pc時次固結(jié)系數(shù)達(dá)到最大，其后隨著固結(jié)壓力p進一步增大，次固結(jié)系數(shù)逐漸減小，當(dāng)p400kPa后，次固結(jié)系數(shù)減小趨緩。 （2）微觀結(jié)構(gòu)試驗揭示了淤泥質(zhì)黏土初始狀態(tài)的微觀結(jié)構(gòu)以及在次固結(jié)過程中微觀結(jié)構(gòu)的變化，并獲得了主要微觀形態(tài)參數(shù)的時效規(guī)律。 （3）研究了次固結(jié)過程中次固結(jié)系數(shù)和壓縮模量的變化規(guī)律。結(jié)果表明，在相同的應(yīng)力水平下，隨著荷載作用時間延續(xù)，次固結(jié)系數(shù)都有減小的趨勢且衰減逐漸變緩，壓縮模量都有增大的趨勢但沒有明顯數(shù)值規(guī)律。基于次固結(jié)系數(shù)的衰減性，在前人研究基礎(chǔ)上，對常規(guī)次固結(jié)沉降計算公式進行了分析和改進。 （4）將上述試驗結(jié)果與軟土地基預(yù)壓工程實踐綜合分析研究，認(rèn)為在地基極限承載力范圍內(nèi)，適當(dāng)?shù)某d預(yù)壓可以使軟土提前發(fā)生一部分次固結(jié)變形，工后次固結(jié)沉降會減少；采取有效的降、排水措施以快速消除土中的超靜孔隙水壓力，減少土體中的孔隙以降低連通率，可使次固結(jié)系數(shù)一定程度減小，也有利于控制工后次固結(jié)沉降。
[Abstract]:Shallow marine sedimentary soft soil is widely distributed in coastal areas of China, which affects engineering construction to varying degrees. Silt clay is the most common marine soft soil. Its main characteristics are high natural moisture content and porosity ratio, small degree of gravity and large plastic index. The macroscopical properties show the characteristics of low strength, small bearing capacity, low permeability, high compressibility, and obvious secondary consolidation properties. The secondary consolidation characteristics and microstructure of soft soil have important influence on its macroscopic mechanical properties. As a result, the settlement of engineering construction is too large, deformation does not meet the requirements and long-term deformation instability and so on. Based on the above situation, this paper takes the silt clay of the undisturbed sea with a depth of about 7 meters in Tianjin Binhai South Port as the test and research object, and carries out two kinds of unidirectional consolidation tests and microscopic tests, respectively, of graded loading and preconsolidation. The characteristics of secondary consolidation deformation under different loading modes are discussed, and the relationship between microscopic changes and macroscopic mechanical properties in the process of secondary consolidation is analyzed through microscopic tests. The test results are analyzed by combining with the test examples of foundation preloading engineering. Some conclusions and suggestions for soft soil engineering construction, especially foundation preloading, are obtained. The main research results of this paper are as follows:. 1) the preconsolidation pressure (PC) and the overconsolidation ratio (OCR) of the silt clay studied in this study are about 63 KPA and 1, respectively, which belong to the traditional normal consolidation soil. The results of unidirectional consolidation test show that the time of the primary and secondary consolidation boundary is about 150 ~ 200 min. The consolidation pressure p has a greater effect on the secondary consolidation characteristics than 畏. When the consolidation pressure p increases gradually from the smaller value, The secondary consolidation coefficient increases gradually, the secondary consolidation coefficient reaches the maximum when p is close to 2pc, and then decreases with the consolidation pressure p increasing, and the secondary consolidation coefficient decreases slowly after p400kPa. (2) the microstructure of the silt clay is revealed by the microstructure test, and the change of the microstructure during the secondary consolidation process is revealed, and the aging law of the main microscopic morphology parameters is obtained. The variation of secondary consolidation coefficient and compression modulus during secondary consolidation is studied. The results show that the secondary consolidation coefficient decreases and the attenuation gradually decreases with the extension of loading time at the same stress level. Based on the attenuation of secondary consolidation coefficient, the conventional formula of secondary consolidation settlement is analyzed and improved on the basis of previous studies. 4) based on the comprehensive analysis of the above test results and the practice of soft soil foundation preloading engineering, it is concluded that in the range of ultimate bearing capacity of foundation, appropriate overload preloading can make soft soil occur part of secondary consolidation deformation ahead of time, and the secondary consolidation settlement will be reduced after construction. Effective reduction and drainage measures are taken to quickly eliminate the excess pore water pressure in the soil and reduce the porosity in the soil to reduce the connectivity. The secondary consolidation coefficient can be reduced to a certain extent and the secondary consolidation settlement can be controlled.
【學(xué)位授予單位】：中國地質(zhì)大學(xué)（北京）
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TU447

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