CFG樁復(fù)合地基樁土分擔(dān)荷載比

CFG樁復(fù)合地基樁土分擔(dān)荷載比研究摘要：以某工程為例，針對(duì)不同材料構(gòu)成的褥墊層（相同厚度）及同一種材料不同墊層厚度情況進(jìn)行了土壓力盒試驗(yàn)，確定了不同情況下樁土分擔(dān)荷載關(guān)系，并得出了一些有益的結(jié)論。關(guān)鍵詞：CFG樁，復(fù)合地基，樁土應(yīng)力比1、前言CFG樁(CementFly-ashGravelPile)，即由碎石、粉煤灰摻適量的水泥加水拌合，用各種成樁機(jī)具制成的可變粘結(jié)強(qiáng)度樁，近年來(lái)在工程中得到了廣泛應(yīng)用。CFG樁復(fù)合地基由樁、樁間土及褥墊層三部分構(gòu)成，其加固機(jī)理為褥墊層受上部基礎(chǔ)荷載作用產(chǎn)生變形后以一定的比例將荷載分?jǐn)偨o樁及樁間土，使二者共同受力。同時(shí)土體受到樁的擠密而提高承載力，而樁又由于周圍土的側(cè)應(yīng)力的增加而改善了受力性能，二者共同工作，形成了一個(gè)復(fù)合地基的受力整體，共同承擔(dān)上部基礎(chǔ)傳來(lái)的荷載【1】。顯然，不同材料構(gòu)成的褥墊層及同種材料不同墊層厚度樁土分擔(dān)的荷載是不同的，而準(zhǔn)確了解樁土分擔(dān)的荷載比在CFG樁復(fù)合地基工程設(shè)計(jì)中往往是很重要的。本文以某工程為例，針對(duì)不同材料構(gòu)成的褥墊層及同一種材料不同墊層厚度情況進(jìn)行了土壓力盒試驗(yàn)，確定了不同情況下樁土分擔(dān)荷載關(guān)系，并得出了一些有益的結(jié)論。2、場(chǎng)地工程地質(zhì)概況2.1地形地貌該工程場(chǎng)地地貌單元屬長(zhǎng)江北岸I級(jí)階地，現(xiàn)有地形比較平坦。2.2地質(zhì)巖性構(gòu)成擬建場(chǎng)地的地基土主要由人工填積（Qml）層和第四系全新統(tǒng)沖積（Qal4）層構(gòu)成。場(chǎng)地內(nèi)分布的地層，按其特點(diǎn)由上至下分述如下：雜填土：主要由混凝土地坪、粉煤灰、磚塊、房屋老基礎(chǔ)及少量粘性土填成。呈濕的、松散狀態(tài)。該層在整個(gè)場(chǎng)地均有分布，厚度為0.88－1.90m。第四系全新統(tǒng)沖積（Qal4）層：該層具有明顯的二元結(jié)構(gòu)沉積規(guī)律。上部主要由細(xì)粒的粘土、粉質(zhì)粘土及粉土組成，中、下部主要由粗粒組成的粉細(xì)砂、中粗砂，底部為河道形成的I級(jí)階地下卵石層。下臥基巖為泥巖。3、土壓力盒試驗(yàn)概況為了解不同材料構(gòu)成的褥墊層（相同厚度）及同一種墊層材料不同厚度情況確定樁土分擔(dān)荷載關(guān)系，本次試驗(yàn)針對(duì)粗石(70%)＋砂(30%)，砂，瓜米石(70%)＋砂(30%)三種材料組成的200mm厚的褥墊層及300mm、400mm和500mm厚的粗石(70%)＋砂(30%)的褥墊層進(jìn)行了6組土壓力盒試驗(yàn)，如表1所示。表1 土壓力盒試驗(yàn)墊層材料及墊層厚度表序號(hào)樁號(hào)墊層材料墊層厚度(mm))1996粗石(70%)＋砂((30%)2002615砂2003573瓜米石(70%))＋砂(30%)2004174粗石(70%)＋砂((30%)3005438粗石(70%)＋砂((30%)4006365粗石(70%)＋砂((30%)500樁墊層土壓力盒承壓板6897樁墊層土壓力盒承壓板68972543110 a)墊層下 b)墊層上4土中壓力盒41 樁上壓力傳感器1圖1 土壓力盒埋設(shè)示意圖本次試驗(yàn)分別在墊層上下的土層和樁身對(duì)應(yīng)埋設(shè)10個(gè)土壓力盒，如圖1所示。土壓力盒試驗(yàn)采用浙江科學(xué)儀器廠生產(chǎn)的JXR鋼弦式壓力盒。該壓力盒通過(guò)量測(cè)鋼弦的頻率變化得到施加在壓力盒上的壓力值，壓力盒量程為0.4MPa?？紤]到樁上應(yīng)力大，樁上應(yīng)力采用本所自行研制的量程為10MPa壓力傳感器量測(cè)，該壓力JXR型土壓力盒壓力傳感器頻率計(jì)靜態(tài)應(yīng)變儀JXR型土壓力盒壓力傳感器頻率計(jì)靜態(tài)應(yīng)變儀圖2 土壓力盒試驗(yàn)系統(tǒng)示意圖4、試驗(yàn)結(jié)果試驗(yàn)結(jié)果見表2～7及圖3～14。各樁試驗(yàn)結(jié)果表明，隨著荷載的增大，樁分擔(dān)的荷載也逐漸增大。在最大試驗(yàn)荷載作用下（1000kPa），996＃樁承擔(dān)的荷載達(dá)85％，最小的573＃樁也達(dá)74％，表明CFG樁復(fù)合地基中樁承擔(dān)的荷載仍占絕大部分。同時(shí)，試驗(yàn)結(jié)果表明樁間土體也充分發(fā)揮了作用。表2996＃樁復(fù)合地基壓力盒試驗(yàn)結(jié)果荷載值(kPa)樁土應(yīng)力比樁承擔(dān)荷載比2#3#4#5#7#8#9#10#Aver(2-55)Aver(7-100)墊層下墊層上25013.8412.0614.1314.2610.0911.8911.3213.4013.5711.670.590.5437524.6222.4625.9025.3116.3621.9017.8021.4024.5719.360.750.6850030.9130.9332.9531.7418.8729.6023.1327.2431.6324.710.770.7162537.6938.2439.8740.9523.0839.4929.2934.0139.1931.470.810.7775042.3242.2643.0945.4024.2844.9830.1939.4743.2734.730.820.7787547.7846.4949.1751.6628.3952.5932.7045.1248.7839.700.850.81100048.8348.5352.3253.6132.5657.4133.7247.2650.8242.740.850.82在墊層厚度相等（200mm）情況下，以粗石(70%)＋砂(30%)為材料的墊層，在試驗(yàn)初期荷載較小的情況下，樁承擔(dān)的荷載最小，而在較大荷載作用下，樁體承擔(dān)的荷載最大；而以純砂為材料的墊層，在試驗(yàn)初期荷載較小的情況下，樁承擔(dān)的荷載最大，并且隨著荷載的增大，樁分擔(dān)的荷載比增加不大。對(duì)于同種墊層材料，在加載初期，厚度不同，樁分擔(dān)的荷載略有不同；在加載后期，厚度對(duì)于樁土分擔(dān)荷載比影響不大。各樁試驗(yàn)結(jié)果表明，樁土應(yīng)力比隨著荷載的增大而逐漸增大。表3615＃樁復(fù)合地基壓力盒試驗(yàn)結(jié)果荷載值(kPa)樁土應(yīng)力比樁承擔(dān)荷載比2#3#4#5#7#8#9#10#Aver(2-55)Aver(7-100)墊層下墊層上25023.1920.9423.1329.0817.2715.9814.7311.3824.0914.840.710.6037521.3820.5622.8027.6016.8016.4714.9311.7823.0915.000.720.6250021.3621.6623.9227.6217.1318.1915.5613.0923.6415.990.720.6462522.8724.0226.7928.7217.5819.9416.1814.3925.6017.020.720.6375025.5127.5430.7630.7819.4723.0118.3417.2528.6419.520.750.6687529.1432.2835.7933.3622.2727.5121.7221.5132.6423.250.780.72100032.8637.8839.5636.6124.9432.9225.0625.4536.7327.090.800.75表4573＃樁復(fù)合地基壓力盒試驗(yàn)結(jié)果荷載值(kPa)樁土應(yīng)力比樁承擔(dān)荷載比2#3#4#5#7#8#9#10#Aver(2-55)Aver(7-100)墊層下墊層上25014.9910.7019.2114.386.7810.329.4010.7714.829.320.600.4837514.899.2319.1913.827.339.738.579.0214.288.670.590.4850020.2712.8027.3418.8510.5113.4411.7912.5219.8112.070.680.5662523.8815.9032.6822.2713.3016.8214.5615.9223.6815.150.700.6175028.9121.8539.6827.3916.9020.7618.0321.2229.4619.230.740.6787534.0129.4847.1332.4820.7525.4521.8727.8635.7823.980.780.71100038.5437.3456.2937.5524.4530.6125.8535.7942.4329.180.820.75表5 174＃樁復(fù)合地基壓力盒試驗(yàn)結(jié)果荷載值(kPa)樁土應(yīng)力比樁承擔(dān)荷載比2#3#4#5#7#8#9#10#Aver(2-55)Aver(7-100)墊層下墊層上25014.1918.6517.148.599.7214.6719.5212.0514.6413.990.590.5837517.4924.0119.8911.0812.4717.6221.4514.8918.1216.610.640.6250020.6628.0322.9313.2515.6520.2424.6218.1721.2219.670.670.6762525.4233.6027.6416.1519.1523.1527.6021.6825.7022.900.730.7175028.1537.3930.1917.9721.6026.0829.5124.4828.4325.420.720.7287532.5041.9733.5620.7125.0028.4831.7527.7432.1928.240.760.75100039.3548.0638.2924.6530.5832.7036.0232.5537.5932.960.790.78表6438＃樁復(fù)合地基壓力盒試驗(yàn)結(jié)果荷載值(kPa)樁土應(yīng)力比樁承擔(dān)荷載比2#3#4#5#7#8#9#10#Aver(2-55)Aver(7-100)墊層下墊層上25015.8413.9112.6917.6410.0910.396.077.1715.028.430.610.4737524.6619.9218.7325.0916.8716.9910.0911.5522.1013.880.690.5950034.5326.8525.7332.7022.5223.2213.9615.4929.9518.800.770.6562540.1631.3529.8835.8425.9127.7216.7118.3134.3122.160.790.6975039.6531.7829.6133.8325.1726.8519.0618.4033.7122.370.770.6987538.6533.9832.0233.3227.4232.0221.5221.0234.4925.500.790.73100039.5736.4735.1236.2426.5835.2824.3922.6736.8527.230.800.74表7365＃樁復(fù)合地基壓力盒試驗(yàn)結(jié)果荷載值(kPa)樁土應(yīng)力比樁承擔(dān)荷載比2#3#4#5#7#8#9#10#Aver(2-55)Aver(7-100)墊層下墊層上25022.6126.0923.0112.8611.4513.118.507.2021.1410.070.670.5037527.4737.7033.4218.2217.8017.3512.3810.9129.2014.610.730.5850028.4242.5931.2419.3223.6322.3914.4913.2830.3918.450.760.6662530.9043.1234.3824.1230.5928.9218.1916.9033.1323.650.790.7275028.9441.3232.8224.2429.1330.8719.5317.1231.8324.160.770.7187532.0842.2533.3826.4529.2430.0319.5117.8433.5424.150.790.72100034.1140.6734.0627.9029.1830.3220.6719.5934.1824.940.770.73圖3 樁分擔(dān)荷載比與荷載關(guān)系試驗(yàn)曲線(996＃樁)圖4 樁土應(yīng)力比與荷載關(guān)系試驗(yàn)曲線(996＃樁)圖5 樁分擔(dān)荷載比與荷載關(guān)系試驗(yàn)曲線(615＃樁圖6 樁土應(yīng)力比與荷載關(guān)系試驗(yàn)曲線(615＃樁)圖7 樁分擔(dān)荷載比與荷載關(guān)系試驗(yàn)曲線(573＃樁)圖8 樁土應(yīng)力比與荷載關(guān)系試驗(yàn)曲線(573＃樁)圖9 樁分擔(dān)荷載比與荷載關(guān)系試驗(yàn)曲線(174＃樁)圖10 樁土應(yīng)力比與荷載關(guān)系試驗(yàn)曲線(174＃樁)圖11 樁分擔(dān)荷載比與荷載關(guān)系試驗(yàn)曲線(438＃樁)圖12 樁土應(yīng)力比與荷載關(guān)系試驗(yàn)曲線(438＃樁)圖13 樁分擔(dān)荷載比與荷載關(guān)系試驗(yàn)曲線(365＃樁)圖14 樁土應(yīng)力比與荷載關(guān)系試驗(yàn)曲線(365＃樁)5、結(jié)論各樁試驗(yàn)結(jié)果表明，樁土應(yīng)力比隨著荷載的增大而逐漸增大。各樁試驗(yàn)結(jié)果表明，隨著荷載的增大，樁分擔(dān)的荷載也逐漸增大。在最大試驗(yàn)荷載作用下（1000kPa），996＃樁承擔(dān)的荷載達(dá)85％，最小的573＃樁也達(dá)74％，表明CFG樁復(fù)合地基中樁承擔(dān)的荷載仍占絕大部分。同時(shí)，試驗(yàn)結(jié)果表明樁間土體也充分發(fā)揮了作用。在墊層厚度相等（200mm）情況下，以粗石(70%)＋砂(30%)為材料的墊層，