基于凍融循環(huán)作用的基坑變形機理及支護方案優(yōu)化研究
發(fā)布時間：2018-09-17 15:47
【摘要】：隨著城市地下空間開發(fā)與利用,開挖深度大、平面形狀復雜的深基坑數(shù)量不斷增加,而深大基坑經(jīng)常面臨因施工周期長出現(xiàn)越冬的問題.由于現(xiàn)有基坑支護設計規(guī)范中并未考慮凍融作用的影響,依照規(guī)范施工,可能會造成支護結(jié)構和基坑土體的過大變形,甚至破壞失穩(wěn).雖然這一問題已引起人們的重視,但從機理上的研究尚未深入,尤其對于季節(jié)性凍土地區(qū).由于考慮凍融作用的基坑土體應力場-溫度場-滲流場三場間耦合作用與基坑土體支護方案優(yōu)化的研究相對較少,所以研究凍融循環(huán)作用下基坑變形機理及支護方案優(yōu)化是十分必要的.論文以毗鄰沈陽市政府的東森CBD商務廣場二期基坑工程為背景,以凍土力學、熱力學、滲流力學、基坑工程學等相關知識為理論基礎,通過室內(nèi)土工試驗、凍土三軸試驗、土體凍融特性試驗獲得土層基本參數(shù),并總結(jié)了季節(jié)性凍土在凍結(jié)和融化過程中,土體參數(shù)和力學性能隨不同物理狀態(tài)條件(圍壓、凍結(jié)溫度、凍融循環(huán))下各變量(含水率、孔隙比、干密度、壓縮模量、彈性模量、強度等)的變化規(guī)律,為數(shù)值模型的構建和數(shù)值計算提供基本參數(shù)；采用凍融試驗中考慮凍融作用影響所獲得的土層參數(shù),建立考慮凍融作用影響的水熱力三場耦合數(shù)值計算模型,得出考慮凍融作用的基坑變形規(guī)律；設計基坑模型實驗模擬凍融循環(huán)作用下基坑在越冬過程中的溫度環(huán)境,揭示基坑支護在凍融作用下的變形和內(nèi)力規(guī)律,并將模型實驗結(jié)果與數(shù)值計算結(jié)果進行對比,驗證考慮凍融循環(huán)作用影響的水熱力三場耦合模型預測基坑變形規(guī)律的正確性,實現(xiàn)了考慮土體凍融循環(huán)作用的水熱力三場耦合分析,從理論上完成了季節(jié)性凍土區(qū)凍融循環(huán)與水-熱-力耦合作用下基坑變形規(guī)律研究，，對于越冬基坑的支護方案優(yōu)化具有理論和應用價值.通過系統(tǒng)研究沈陽季節(jié)性凍土地區(qū)基坑變形機理及支護方案優(yōu)化,得出以下主要結(jié)論：(1)最佳含水率是含水率在凍融循環(huán)中對壓縮模量影響程度的界限標志：當小于最佳含水率時,首次凍融循環(huán)后壓縮模量降低幅度較大；當大于最佳含水率時,壓縮模量受含水量影響不明顯：隨著凍融循環(huán)次數(shù)的增加,彈性模量先降后增,第1次凍融后的變化幅度最大,經(jīng)歷5-9次凍融循環(huán)后,彈性模量降到最低點,并趨于穩(wěn)定.(2)凍融作用對孔隙比隨著含水率的增大先減后增的規(guī)律基本無影響,凍融后土樣孔隙比減小,干密度的增大會減弱凍融作用對孔隙比影響程度,當干密度增大到一定程度后影響可忽略；試樣含水率隨著凍融循環(huán)次數(shù)的增加緩慢增大趨勢在凍融循環(huán)超過3次后趨于穩(wěn)定；隨著凍融次數(shù)增加,粘聚力c呈現(xiàn)降低的趨勢,而內(nèi)摩擦角φ有增大趨勢；(3)初次凍融循環(huán)對土的結(jié)構性擾動最大,多次凍融循環(huán)后土樣強度有所恢復.當圍壓較小時,凍融后土的強度損失較大,隨著圍壓提高,受凍融影響不明顯；含水率的提高會使應力—應變曲線由硬化型向弱軟化型轉(zhuǎn)化,在高圍壓條件下尤為顯著；凍結(jié)溫度條件對土樣凍融后的破壞強度影響顯著,土樣的破壞強度,在經(jīng)歷5-7次凍融后強度會達到最低值,建議沈陽地區(qū)凍土工程設計時可參考凍融循環(huán)7次時的力學指標；(4)通過基坑模型實驗得出：樁的埋深對腰梁位移影響顯著,整體趨勢為埋深越淺,腰梁位移越大,支護結(jié)構越不穩(wěn)定；在凍融循環(huán)下樁間和樁后土壓力分布隨樁的埋深不同差異顯著：埋深越淺土壓力分布越復雜,隨凍融循環(huán)土壓力不規(guī)則波動；樁間和樁后土壓力隨土溫變化顯著,在凍融循環(huán)前期、中期土溫度較為穩(wěn)定,但土壓力波動明顯；在凍融循環(huán)后期土壓力基本穩(wěn)定,溫度也無較大改變；樁后土壓力分布隨深度不同分布規(guī)律不同.(5)建立了考慮凍融作用的三維數(shù)值模型,對越冬基坑降溫過程進行數(shù)值模擬,從數(shù)值計算結(jié)果云圖中顯示,從0℃降至-10℃的降溫過程的基坑位移量最大,基坑的變形受溫度影響在基坑陽角處最為明顯.整個降溫過程中基坑最大位移量先減后增,但幅度較小.溫度變化對于內(nèi)力的影響相對較小.(6)提出基于凍融作用影響下基坑變形規(guī)律的基坑支護優(yōu)化方案,根據(jù)土體凍融特性試驗,獲得考慮凍融作用后的土層參數(shù),建立考慮凍融作用的數(shù)值分析模型,通過現(xiàn)場監(jiān)測證明變形控制效果較好,對于指導季節(jié)性凍土地區(qū)基坑工程實踐具有一定應用價值和參考意義.
[Abstract]:With the development and utilization of urban underground space, the depth of excavation is great, and the number of deep foundation pits with complex plane shape is increasing. However, deep and large foundation pits often face the problem of overwintering due to long construction period. Although this problem has attracted people's attention, the mechanism research has not been thorough, especially for the seasonal frozen soil area. Because of considering the effect of freezing and thawing, the coupling between stress field, temperature field and seepage field of foundation pit soil and the optimization of foundation pit soil support scheme are comparatively studied. So it is very necessary to study the deformation mechanism of foundation pit under freeze-thaw cycles and the optimization of supporting schemes.Based on the second-stage foundation pit project of Dongsen CBD Business Plaza adjacent to Shenyang Municipal Government, this paper takes the permafrost mechanics, thermodynamics, seepage mechanics, foundation pit engineering and other related knowledge as the theoretical basis, through indoor geotechnical tests, permafrost triaxial. The variation of soil parameters and mechanical properties with various physical conditions (confining pressure, freezing temperature, freezing-thawing cycle), including water content, porosity ratio, dry density, compressive modulus, elastic modulus and strength, during freezing and thawing of seasonal frozen soil is summarized. The construction of numerical model and numerical calculation provide the basic parameters; adopt the soil parameters obtained by considering the effect of freeze-thaw in freeze-thaw test, establish the hydrothermal three-field coupling numerical calculation model considering the effect of freeze-thaw, and obtain the deformation law of foundation pit considering the effect of freeze-thaw; design the foundation pit model experiment to simulate the effect of freeze-thaw cycle. The temperature environment of foundation pit in the process of overwintering reveals the deformation and internal force law of foundation pit support under the action of freezing and thawing, and compares the model experimental results with the numerical results, verifies the correctness of the three-field coupling model considering the effect of freezing and thawing cycles to predict the deformation law of foundation pit, and realizes the freezing-thawing cycle of soil. The deformation law of foundation pit under the action of freeze-thaw cycle and water-heat-force coupling in seasonal frozen soil region is studied theoretically by using the coupled analysis of hydrothermal and mechanical fields. It is of theoretical and practical value to optimize the supporting scheme of overwintering foundation pit. The main conclusions are as follows: (1) The optimum moisture content is the limit sign of the effect of water content on compressive modulus in freeze-thaw cycles: when the water content is less than the optimum, the compressive modulus decreases greatly after the first freeze-thaw cycles; when the water content is greater than the optimum moisture content, the influence of water content on compressive modulus is not obvious: with the increase of freeze-thaw cycles After 5-9 freeze-thaw cycles, the modulus of elasticity decreases to the lowest point and tends to be stable. (2) Freeze-thaw has little effect on the rule that the porosity ratio decreases first and then increases with the increase of water content. The porosity ratio decreases after freeze-thaw, and the effect of freeze-thaw decreases with the increase of dry density. The influence degree of porosity ratio can be neglected when the dry density increases to a certain extent; the water content of samples increases slowly with the increase of freeze-thaw cycles, and tends to be stable after more than three freeze-thaw cycles; the cohesion c decreases with the increase of freeze-thaw cycles, while the internal friction angle increases; (3) the initial freeze-thaw cycles. When the confining pressure is small, the strength loss of the soil after freezing and thawing is large, and with the increase of confining pressure, the influence of freezing and thawing is not obvious; the increase of water content will make the stress-strain curve change from hardening to weakening, especially under high confining pressure. Temperature conditions have a significant impact on the failure strength of soil samples after freeze-thaw, and the failure strength of soil samples will reach the lowest value after 5-7 freeze-thaw cycles. It is suggested that the mechanical indicators of freeze-thaw cycles for 7 times can be referred to in the design of Permafrost Engineering in Shenyang area. (4) Through the foundation pit model test, it is concluded that the depth of pile has a significant impact on the displacement of waist beam, and the overall trend. The shallower the buried depth is, the greater the displacement of the waist beam is, and the more unstable the supporting structure is; the difference of the earth pressure distribution between piles and behind piles is significant with the depth of the piles under freeze-thaw cycles: the more complex the earth pressure distribution is, the more irregular the earth pressure fluctuates with the freeze-thaw cycles; the earth pressure between piles and behind piles varies significantly with the soil temperature; at the early stage of the freeze-thaw cycles, in the middle stage of the freeze- The soil temperature in the period of freezing-thawing is stable, but the earth pressure fluctuates obviously; the earth pressure is basically stable and the temperature does not change greatly at the later stage of freezing-thawing cycle; the distribution law of the earth pressure behind the pile is different with the depth. (5) A three-dimensional numerical model considering the freezing-thawing effect is established to simulate the cooling process of overwintering foundation pit. The figure shows that the displacement of the foundation pit is the largest when the temperature is lowered from 0 C to - 10 C, and the deformation of the foundation pit is most obvious at the sunny corner of the foundation pit. According to the freeze-thaw characteristic test of soil, the soil parameters after considering the freeze-thaw effect are obtained, and the numerical analysis model considering the freeze-thaw effect is established. The field monitoring shows that the deformation control effect is better, which has certain application value and reference significance for guiding the foundation pit engineering practice in seasonal frozen soil area.
【學位授予單位】：遼寧工程技術大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TU753
本文編號：2246393
[Abstract]:With the development and utilization of urban underground space, the depth of excavation is great, and the number of deep foundation pits with complex plane shape is increasing. However, deep and large foundation pits often face the problem of overwintering due to long construction period. Although this problem has attracted people's attention, the mechanism research has not been thorough, especially for the seasonal frozen soil area. Because of considering the effect of freezing and thawing, the coupling between stress field, temperature field and seepage field of foundation pit soil and the optimization of foundation pit soil support scheme are comparatively studied. So it is very necessary to study the deformation mechanism of foundation pit under freeze-thaw cycles and the optimization of supporting schemes.Based on the second-stage foundation pit project of Dongsen CBD Business Plaza adjacent to Shenyang Municipal Government, this paper takes the permafrost mechanics, thermodynamics, seepage mechanics, foundation pit engineering and other related knowledge as the theoretical basis, through indoor geotechnical tests, permafrost triaxial. The variation of soil parameters and mechanical properties with various physical conditions (confining pressure, freezing temperature, freezing-thawing cycle), including water content, porosity ratio, dry density, compressive modulus, elastic modulus and strength, during freezing and thawing of seasonal frozen soil is summarized. The construction of numerical model and numerical calculation provide the basic parameters; adopt the soil parameters obtained by considering the effect of freeze-thaw in freeze-thaw test, establish the hydrothermal three-field coupling numerical calculation model considering the effect of freeze-thaw, and obtain the deformation law of foundation pit considering the effect of freeze-thaw; design the foundation pit model experiment to simulate the effect of freeze-thaw cycle. The temperature environment of foundation pit in the process of overwintering reveals the deformation and internal force law of foundation pit support under the action of freezing and thawing, and compares the model experimental results with the numerical results, verifies the correctness of the three-field coupling model considering the effect of freezing and thawing cycles to predict the deformation law of foundation pit, and realizes the freezing-thawing cycle of soil. The deformation law of foundation pit under the action of freeze-thaw cycle and water-heat-force coupling in seasonal frozen soil region is studied theoretically by using the coupled analysis of hydrothermal and mechanical fields. It is of theoretical and practical value to optimize the supporting scheme of overwintering foundation pit. The main conclusions are as follows: (1) The optimum moisture content is the limit sign of the effect of water content on compressive modulus in freeze-thaw cycles: when the water content is less than the optimum, the compressive modulus decreases greatly after the first freeze-thaw cycles; when the water content is greater than the optimum moisture content, the influence of water content on compressive modulus is not obvious: with the increase of freeze-thaw cycles After 5-9 freeze-thaw cycles, the modulus of elasticity decreases to the lowest point and tends to be stable. (2) Freeze-thaw has little effect on the rule that the porosity ratio decreases first and then increases with the increase of water content. The porosity ratio decreases after freeze-thaw, and the effect of freeze-thaw decreases with the increase of dry density. The influence degree of porosity ratio can be neglected when the dry density increases to a certain extent; the water content of samples increases slowly with the increase of freeze-thaw cycles, and tends to be stable after more than three freeze-thaw cycles; the cohesion c decreases with the increase of freeze-thaw cycles, while the internal friction angle increases; (3) the initial freeze-thaw cycles. When the confining pressure is small, the strength loss of the soil after freezing and thawing is large, and with the increase of confining pressure, the influence of freezing and thawing is not obvious; the increase of water content will make the stress-strain curve change from hardening to weakening, especially under high confining pressure. Temperature conditions have a significant impact on the failure strength of soil samples after freeze-thaw, and the failure strength of soil samples will reach the lowest value after 5-7 freeze-thaw cycles. It is suggested that the mechanical indicators of freeze-thaw cycles for 7 times can be referred to in the design of Permafrost Engineering in Shenyang area. (4) Through the foundation pit model test, it is concluded that the depth of pile has a significant impact on the displacement of waist beam, and the overall trend. The shallower the buried depth is, the greater the displacement of the waist beam is, and the more unstable the supporting structure is; the difference of the earth pressure distribution between piles and behind piles is significant with the depth of the piles under freeze-thaw cycles: the more complex the earth pressure distribution is, the more irregular the earth pressure fluctuates with the freeze-thaw cycles; the earth pressure between piles and behind piles varies significantly with the soil temperature; at the early stage of the freeze-thaw cycles, in the middle stage of the freeze- The soil temperature in the period of freezing-thawing is stable, but the earth pressure fluctuates obviously; the earth pressure is basically stable and the temperature does not change greatly at the later stage of freezing-thawing cycle; the distribution law of the earth pressure behind the pile is different with the depth. (5) A three-dimensional numerical model considering the freezing-thawing effect is established to simulate the cooling process of overwintering foundation pit. The figure shows that the displacement of the foundation pit is the largest when the temperature is lowered from 0 C to - 10 C, and the deformation of the foundation pit is most obvious at the sunny corner of the foundation pit. According to the freeze-thaw characteristic test of soil, the soil parameters after considering the freeze-thaw effect are obtained, and the numerical analysis model considering the freeze-thaw effect is established. The field monitoring shows that the deformation control effect is better, which has certain application value and reference significance for guiding the foundation pit engineering practice in seasonal frozen soil area.
【學位授予單位】：遼寧工程技術大學
【學位級別】：博士
【學位授予年份】：2015
【分類號】：TU753
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