1、頁丿門頁腳町咆刪除僅供借鑒頁丿門頁腳町咆刪除僅供借鑒高等教育高等教育#1高等教育高等教育#1地基沉降量計算地基變形在其表面形成的垂直變形量稱為建筑物的沉降量。在外荷載作用下地基土層被壓縮達(dá)到穩(wěn)定時基礎(chǔ)底面的沉降量稱為地基最終沉降量。一、分層總和法計算地基最終沉降量計算地基的最終沉降量，目前最常用的就是分層總和法。（一）基本原理該方法只考慮地基的垂向變形，沒有考慮側(cè)向變形，地基的變形同室內(nèi)側(cè)限壓縮試驗中的情況基本一致，屬一維壓縮問題。地基的最終沉降量可用室內(nèi)壓縮試驗確定的參數(shù)（e、E、a）進(jìn)行計算，有：is3=珀一門+芒J令變換后得：式中：S-地基最終沉降量（mm）；e-地基受荷前（自重應(yīng)力作用

2、下）的孔隙比；e1-地基受荷（自重與附加應(yīng)力作用下）沉降穩(wěn)定后的孔隙比H2-土層的厚度。計算沉降量時，在地基可能受荷變形的壓縮層范圍內(nèi)，根據(jù)土的特性、應(yīng)力狀態(tài)以及地下水位進(jìn)行分層。然后按式（4-9）或（4-10）計算各分層的沉降量S。最后將各分層的沉降量總和起來即為地基的最終沉降量：i=(4-11)i-l1）劃分土層如圖4-7所示，各天然土層界面和地下水位必須作為分層界面；各分層厚度必須滿足HW0.4B（B為基底寬度）。i2）計算基底附加壓力p03）計算各分層界面的自重應(yīng)力。和附加應(yīng)力。；并繪制應(yīng)力分布曲線。szz4）確定壓縮層厚度滿足。=0.2。的深度點可作為壓縮層的下限；zsz對于軟土則應(yīng)

3、滿足。=0.1。；zsz對一般建筑物可按下式計算z=B（2.5-0.4lnB）。n5）計算各分層加載前后的平均垂直應(yīng)力p=。；p=。+。1sz2szz6）按各分層的p和p在e-p曲線上查取相應(yīng)的孔隙比或確定a、E等其它壓12s縮性指標(biāo)7）根據(jù)不同的壓縮性指標(biāo)，選用公式（4-9）、（4-10）計算各分層的沉降量Si8）按公式（4-11）計算總沉降量S。頁丿門貝腳町咆刪除僅供借鑒頁丿門貝腳町咆刪除僅供借鑒頁丿門貝腳町咆刪除僅供借鑒頁丿門貝腳町咆刪除僅供借鑒貝眉頁腳可i貝眉頁腳可i鍵刪除僅供借鑒高等教育高等教育#1高等教育高等教育#1高等教育高等教育#1土層I沉降計算探鳳自重應(yīng)為分布曲線分常番線受壓

4、層4-7廿層總和法計算地基沉降童土層I沉降計算探鳳自重應(yīng)為分布曲線分常番線受壓層4-7廿層總和法計算地基沉降童分層總和法的具體計算過程可參例題4-1。例題41已知柱下單獨方形基礎(chǔ)，基礎(chǔ)底面尺寸為2.5x2.5m，埋深2m,作用于基礎(chǔ)上(設(shè)計地面標(biāo)咼處)的軸向荷載N=1250kN，有關(guān)地基勘察資料與基礎(chǔ)剖面詳見下圖。試用單向分層總和法計算基礎(chǔ)中點最終沉降量。解：按單向分層總和法計算(1)計算地基土的自重應(yīng)力。z自基底標(biāo)高起算。當(dāng)z=0m,jD=19.5x2=39(kPa)z=1m,o1=39+19.5x1=58.5(kPa)sz1z=2m，o1=58.5+20 x1=78.5(kPa)sz1z=

5、3m，o1=78.5+20 x1=98.5(kPa)sz1z=4m,冬1=98.5+(20-10)x1=108.5(kPa)z=5m,；Z=108.5+(20-10)x1=118.5(kPa)z=6m,o：=118.5+18.5x1=137(kPa)sz1z=7m,o=137+18.5x1=155.5(kPa)sz1（2）基底壓力計算?；A(chǔ)底面以上，基礎(chǔ)與填土的混合容重取Y=20kN/m3。=240kPa=240kPa2.5x2.53）基底附加壓力計算。pyU24019.52.020lU?a4）基礎(chǔ)中點下地基中豎向附加應(yīng)力計算。用角點法計算，L/B=1,。尸4札p0，查附加應(yīng)力系數(shù)表得K.oz

6、isisi5）確定沉降計算深度zn按單向分層總和法公式按單向分層總和法公式考慮第層土壓縮性比第層土大，經(jīng)計算后確定z=7m,見下表。n例題4-1計算表格1z(m)zB/2Ksoz(kPa)osz(kPa)嘰(%)zn(m)000.25002013910.80.1999160.758.521.60.112390.2978.532.40.064251.6298.843.20.040132.24108.529.7154.00.027021.71118.518.3264.80.019315.5213711.3375.60.014811.90155.57.6按7m計6）計算基礎(chǔ)中點最終沉降量。利用勘察資

7、料中的e-p曲線，求貝丿廿貝腳町鍵刪除僅供借鑒貝丿廿貝腳町鍵刪除僅供借鑒貝丿廿貝腳町鍵刪除僅供借鑒貝丿廿貝腳町鍵刪除僅供借鑒高等教育高等教育#1高等教育高等教育#1計算結(jié)果見下表。例題4-1計算表格2b血by(kPa(kPa)(cm)自重應(yīng)力平均值陽（kPa）附加應(yīng)力平均(kPa)b當(dāng)+(kPa)(kPa-1)(kPa)(cm)(cm)039201158.5160.7278.590.29398.551.624108.532.245118.521.7115.50.6b血by(kPa(kPa)(cm)自重應(yīng)力平均值陽（kPa）附加應(yīng)力平均(kPa)b當(dāng)+(kPa)(kPa-1)(kPa)(cm)(

8、cm)039201158.5160.7278.590.29398.551.624108.532.245118.521.7115.50.60.000386137210010010010010010010048.7568.5088.50103.5113.5127.5146.25180.85125.5070.9641.9326.9818.6213.71155.11.950229.6194159.46145.43140.48146.12159.960.710.640.6350.630.630.690.680.60.60.60.60.60.60.000230.000210.000230.000370.0

9、00530.0007244186861774968484393314723044.091.830.920.610.610.590.595.926.847.458.068.659.24二、建筑地基基礎(chǔ)設(shè)計規(guī)范推薦的沉降計算法下面計算沉降量的方法是建筑地基基礎(chǔ)設(shè)計規(guī)范（GBJ7-89）所推薦的,簡稱規(guī)范推薦法，有時也叫應(yīng)力面積法。一）計算原理應(yīng)力面積法一般按地基土的天然分層面劃分計算土層,引入土層平均附加應(yīng)力的概念，通過平均附加應(yīng)力系數(shù)，將基底中心以下地基中z._-z.深度范圍的附加應(yīng)力按等面積原則化為相同深度范圍內(nèi)矩形分布時的分布應(yīng)-力大小,再按矩形分布應(yīng)力情況計算土層的壓縮量，各土層壓縮量的總

10、和即為地基的計算沉降量。理論上基礎(chǔ)的平均沉降量可表示為貝m貝m腳町咆刪除僅供借鑒貝m貝m腳町咆刪除僅供借鑒高等教育高等教育#1高等教育高等教育#1芒工g；=倘-習(xí)_l)(4-12)i-li-1E.式中：S-地基最終沉降量（mm）；n-地基壓縮層（即受壓層）范圍內(nèi)所劃分的土層數(shù)；p基礎(chǔ)底面處的附加壓力（kPa）；E-基礎(chǔ)底面下第i層土的壓縮模量（MPa）；siz、z分別為基礎(chǔ)底面至第i層和第i-1層底面的距離（m）；ii-1a、a分別為基礎(chǔ)底面計算點至第i層和第i-1層底面范圍內(nèi)平均附ii-1加應(yīng)力系數(shù)，可查表4-1。表4-1矩形面積上均布荷載作用下，通過中心點豎線上的平均附加應(yīng)力系數(shù)az/B1

11、.01.21.41.61.82.00.1.001.001.001.001.001.0000000000.0.990.990.990.990.990.9917888880.0.980.990.990.990.990.9927012220.0.960.970.970.970.970.9737368990.0.930.940.950.950.950.9646736850.0.900.910.920.920.930.9350549350.0.850.870.890.890.900.9068808360.0.810.840.850.860.870.8776055160.0.770.800.810.830

12、.830.8485191940.0.730.760.780.790.800.8195447631.0.690.720.740.760.770.7808394531.0.660.690.710.730.740.7513473431.0.630.660.680.700.710.722136355L/B2.42.83.23.64.05.0101.001.001.001.001.001.001.0000000000.990.990.990.990.990.990.9988888880.990.990.990.990.990.990.9933333330.980.980.980.980.980.980.

13、9800111120.960.960.960.960.960.960.9612233330.930.930.930.940.940.940.9479900000.910.910.910.910.910.910.9102344550.880.880.880.880.880.880.8814567780.850.850.850.850.850.860.8615789000.820.820.820.830.830.830.8316901230.790.790.800.800.800.800.8028134670.760.770.770.770.770.780.7841579020.730.740.7

14、40.750.750.750.757492468頁丿門貝腳町咆刪除僅供借鑒頁丿門貝腳町咆刪除僅供借鑒頁丿門貝腳町咆刪除僅供借鑒頁丿門貝腳町咆刪除僅供借鑒高等教育高等教育#1高等教育高等教育#11.0.600.630.650.670.680.690.710.710.720.720.730.730.73313748819580351.0.570.600.620.640.660.670.680.690.700.700.700.710.71435981276158141.0.540.580.600.620.630.640.660.670.670.680.680.690.6958042734693603

15、1.0.520.550.580.590.610.620.640.650.650.660.660.670.67646093511836051.0.500.530.550.570.590.600.620.630.630.640.640.650.65723871301836161.0.480.510.520.550.570.580.600.610.610.620.620.630.63823761301949381.0.460.490.510.530.550.560.580.590.600.600.610.610.62933761313160622.0.440.470.490.510.530.540.

16、560.570.580.590.590.600.60065983535404062.0.420.450.480.500.510.520.540.550.560.570.570.580.59199205869748512.0.410.440.460.480.490.510.530.540.550.550.560.570.57243649103283072.0.400.420.450.460.480.490.510.520.530.540.540.550.56308194658748642.0.380.410.430.450.460.480.500.510.520.530.530.540.5547

17、4649103305312.0.370.400.420.440.450.460.480.500.500.510.520.530.53541315860962092.0.360.380.410.420.440.450.470.480.490.500.500.510.52629082537649882.0.350.370.390.410.430.440.460.470.480.490.490.500.51717860214427672.0.340.360.380.400.410.430.440.460.470.480.480.490.50816748093206562.0.330.350.370.

18、390.400.410.430.450.460.460.470.480.49916737981195563.0.320.340.360.380.390.400.420.440.450.450.460.470.48026637971195473.0.310.330.350.370.380.390.410.430.440.440.450.460.47137737870084473.0.300.320.340.360.370.380.400.420.430.430.440.450.46258847970195583.0.290.320.330.350.360.370.390.410.420.420.

19、430.440.46370958971196603.0.280.310.330.340.350.370.380.400.410.420.420.430.45492169182207723.0.280.300.320.330.350.360.380.390.400.410.410.420.44524381203328943.0.270.290.310.330.340.350.370.380.390.400.410.420.43667503425530163.0.260.290.300.320.330.340.360.370.380.390.400.410.42790835647752393.0.

20、260.280.300.310.320.330.350.360.370.380.390.400.42834168969984523.0.250.270.290.300.320.330.340.360.370.380.380.390.41977491292207854.0.250.270.280.300.310.320.340.350.360.370.370.390.40011824525539184.0.240.260.280.290.300.310.330.340.360.360.370.380.40165268858862424.0.240.260.270.290.300.310.320.

21、340.350.350.360.370.39210602281296764.0.230.250.270.280.290.300.320.330.340.360.350.370.39365046625539104.0.230.250.260.270.290.300.310.320.330.340.350.360.38410580069973544.0.220.240.260.270.280.290.310.320.330.340.340.350.37565035403317984.0.220.240.250.260.270.280.300.310.320.330.340.350.37620589

22、957751334.0.210.230.250.260.270.280.290.310.320.320.330.340.36785034492196774.0.210.230.240.250.260.270.290.300.310.320.330.340.36841589946640224.0.210.220.240.250.260.270.280.300.310.310.320.330.35907135491195775.0.200.220.230.240.260.260.280.290.300.310.320.330.3506379094663022頁丿門頁腳町咆刪除僅供借鑒頁丿門頁腳町咆

23、刪除僅供借鑒頁丿門頁腳町咆刪除僅供借鑒頁丿門頁腳町咆刪除僅供借鑒頁眉頁腳可一鍵刪除僅供借鑒頁眉頁腳可一鍵刪除僅供借鑒咼等教育咼等教育#1咼等教育咼等教育#1高等教育高等教育#1由(4-12)式乘以沉降計算經(jīng)驗系數(shù)V，即為規(guī)范推薦的沉降計算公s式中：V沉降計算經(jīng)驗系數(shù)，應(yīng)根據(jù)同類地區(qū)已有房屋和構(gòu)筑物實測最終沉s降量與計算沉降量對比確定，一般采用表4-2的數(shù)值；表4-2沉降計算經(jīng)驗系數(shù)次基底附加壓力p0(kPa)壓縮模量Es(MPa)2.54.07.015.020.0Po=k1.41.31.00.40.2PoV075f1.11.00.70.40.2注：表列數(shù)值可內(nèi)插;當(dāng)變形計算深度范圍內(nèi)有多層土?xí)r

24、，Es可按附加應(yīng)力面積A的加權(quán)平均值采用，即三)地基受壓層計算深度的確定計算深度z可按下述方法確定：n1)存在相鄰荷載影響的情況下，應(yīng)滿足下式要求：朋；蘭0Q25土丘冕(4-14)i-i式中:Sz-在深度z處，向上取計算厚度為Az的計算變形值；z查表4-3；nn表4-3z取值B(m)22VB44VB88VB1515VB30z(m)0.30.60.81.01.21.5S-在深度z范圍內(nèi)，第i層土的計算變形量。in2)對無相鄰荷載的獨立基礎(chǔ)，可按下列簡化的經(jīng)驗公式確定沉降計算深度z：n玉=5(2.5-0.4n)(4-15)規(guī)范法的具體計算過程可參例題4-2?！纠}42】已知柱下單獨方形基礎(chǔ)，基礎(chǔ)底

25、面尺寸為2.5x2.5m,埋深2m,作用于基礎(chǔ)上(設(shè)計地面標(biāo)咼處)的軸向荷載N=1250kN，有關(guān)地基勘察資料與基礎(chǔ)剖面詳見下圖。試用規(guī)范法計算基礎(chǔ)中點最終沉降量。解：按建筑地基基礎(chǔ)設(shè)計規(guī)范計算，采用下式，計算結(jié)果詳見下表。例題4-2計算表格z/B(m)001.00.82.01.62.43.04.03.24.05.04.86.07.05.67.66.080.25000.23460.19390.15780.13100.11140.09670.08520.08040.23460.38780.47340.52400.55700.58020.59640.61100.23460.15320.08560.

26、05060.0330.02320.01620.0146Esi(kPa)(cm)(cm)4418686177496848439331472304350004.271.800.890.590.600.590.570.034.276.076.967.558.158.749.319.34z/B(m)001.00.82.01.62.43.04.03.24.05.04.86.07.05.67.66.080.25000.23460.19390.15780.13100.11140.09670.08520.08040.23460.38780.47340.52400.55700.58020.59640.61100

27、.23460.15320.08560.05060.0330.02320.01620.0146Esi(kPa)(cm)(cm)4418686177496848439331472304350004.271.800.890.590.600.590.570.034.276.076.967.558.158.749.319.34頁眉賈腳可一頁眉賈腳可一鍵刪除僅供借鑒頁丿門貝腳町咆刪除僅供借鑒頁丿門貝腳町咆刪除僅供借鑒高等教育高等教育#1高等教育高等教育#1按規(guī)范確定受壓層下限，zn=2.5（2.5-0.41n2.5）=5.3m；由于下面土層仍軟弱，在層粘土底面以下取Az厚度計算，根據(jù)表4-3的要求，取Az

28、=0.6m,則z=7.6m,計算得厚度Az的沉降量為0.03cm，滿足要求。n由&=弓-=5淤kPa,并假定/；=朋查表4-2得沉降計算經(jīng)驗系數(shù)2=1.17。那么，最終沉降量為:s=憶=1.17x9.34=10.98cm根據(jù)對粘性土地基在局部（基礎(chǔ)）荷載作用下的實際變形特征的觀察和分析，粘性土地基的沉降S可以認(rèn)為是由機(jī)理不同的三部分沉降組成（圖4-8），亦即*+迅+$(4-16)式中：S-瞬時沉降（亦稱初始沉降）；dS-次固結(jié)沉降（亦稱蠕變沉降）。S-固結(jié)沉降（亦稱主固結(jié)沉降）；cS-次固結(jié)沉降（亦稱蠕變沉降）。瞬時沉降是指加載后地基瞬時發(fā)生的沉降。由于基礎(chǔ)加載面積為有限尺寸，加載后地基中會有

29、剪應(yīng)變產(chǎn)生，剪應(yīng)變會引起側(cè)向變形而造成瞬時沉降。固結(jié)沉降是指飽和與接近飽和的粘性土在基礎(chǔ)荷載作用下，隨著超靜孔隙水壓力的消散，土骨架產(chǎn)生變形所造成的沉降（固結(jié)壓密）。固結(jié)沉降速率取決于孔隙水的排出速率。次固結(jié)沉降是指主固結(jié)過程（超靜孔隙水壓力消散過程）結(jié)束后，在有效應(yīng)力不變的情況下，土的骨架仍隨時間繼續(xù)發(fā)生變形。這種變形的速率取決于土骨架本身的蠕變性質(zhì)。一)瞬時沉降計算瞬時沉降沒有體積變形，可認(rèn)為是彈性變形，因此一般按彈性理論計算，按式(4-17)求解。亀乂筈A1-/)(4-17)式中：s沉降系數(shù)，可從表4-4中查用；p0-基底附加應(yīng)力；卩一泊松比，這時是在不排水條件下沒有體積變形所產(chǎn)生的變形量，所以應(yīng)取卩=0.5；E不排水變形模量，常根據(jù)不排水抗剪強(qiáng)度C和E的經(jīng)驗關(guān)系式(4-18)uuu氏-(300-1250)(7,(4-1S)上式中的低