第 碎石樁PPT課件

1、 振沖碎石地基處理第1頁(yè)/共27頁(yè) 夯擴(kuò)碎石樁 振沖碎石地基處理振沖碎石地基處理第2頁(yè)/共27頁(yè) 碎石振沖置換樁第3頁(yè)/共27頁(yè) 碎石樁地基處理第4頁(yè)/共27頁(yè) 采用振沖法在地基中設(shè)置碎石樁加固地基的方法稱為振沖碎石樁法。振沖碎石樁法適用于處理不排水抗剪強(qiáng)度不小于20kPa的黏土、粉土、砂土、飽和黃土和人工填土地基。 9.2 9.2 振沖碎石樁法振沖碎石樁法9.2 Vibroflotation Stone Column Method第5頁(yè)/共27頁(yè) 9.1.1 Introduction For over 70 years depths vibrators have been used to i

2、mproved the bearing capacity and settlement characteristics of weak soils. Vibro compaction was introduced and developed to maturity by the Johann Keller Company in 1936, which enabled the compaction of non-cohesive soils to be formed with excellent results.第6頁(yè)/共27頁(yè) Vibro compaction has been applied

3、 successfully on numerous sites around the world. Reliable stone column production by vibro compaction in cohesive soils with a high water content is achievable with the aid of a heavy water jet. Water is jetted from the vibrator tip as the vibrator is lowered to the desired depth. Mud flushes loose

4、ned soil and rises to the surface, stabilising the cavity. This is known as the wet vibro replacement method.第7頁(yè)/共27頁(yè) To overcome the limitations of the vibro compaction method, a technique to insert the vibrator into the soil without the aid of simultaneously flushing in water was developed in 1956

5、. After the vibrator is lifted, the temporarily stable cylindrical cavity is filled with coarse material, section by section. The coarse material is then compacted by repetitive use of the vibrator.第8頁(yè)/共27頁(yè) This vibro replacement procedure came to be known as the conventional dry method. Such techni

6、cal developments in dense stone column construction allowed for a greater range of treatable weak natural soils and man-made fills. Vibro replacement continues to be widely used in Europe to improve weak soil. It has a reputation for providing stable ground which allows for safe and economic constru

7、ction of residential and light commercial and industrial structures.第9頁(yè)/共27頁(yè) The conventional dry method utilizes the vibrator to displace the surrounding soil laterally, rather than for primary compaction of the original soil. The crushed stone is pressed laterally into the soil during both the cav

8、ity-filling stage and compaction stage. This produces stone columns that are tightly interlocked with the surrounding soil.第10頁(yè)/共27頁(yè) Groups of columns created in this manner can be used to support large loads. The conventional dry method reliably produces stone columns to depths of 8 m in cohesive s

9、oils that have a shear strength of at least 20 kN/ m2. In very soft nearly liquid soils vibro replacement is not applicable due to the lack of lateral support of the soil. A geotextile coating may be used around the column to ensure filter stability and to activate tensile forces to avoid lateral sp

10、reading of the column. (Geotextile-coated Stone Column Method)第11頁(yè)/共27頁(yè) 9.1.2 Vibro processes During vibro compaction, the motor runs as the depth vibrator is inserted into the soil. The insertion is aided by water flushing. Field experience has shown that penetration is more effective when a larger

11、 volume of water is used, rather than a high pressure. The water flow will expel some loosened sand through the annulus around the vibrator.第12頁(yè)/共27頁(yè) After the initial insertion and compaction processes have been completed at a particular location, the vibrator is moved to the next location and lowe

12、red to the depth specified for compaction.第13頁(yè)/共27頁(yè) 振沖碎石樁復(fù)合地基承載力特征值應(yīng)通過(guò)現(xiàn)場(chǎng)復(fù)合地基載荷試驗(yàn)確定，初步設(shè)計(jì)時(shí)也可用單樁和處理后樁間土承載力特征值按下式估算：第14頁(yè)/共27頁(yè) 等邊三角形布樁 正方形布樁 矩形布樁 s為等邊三角形布樁和正方形布樁時(shí)的樁間距，s1、s2分別為矩形布樁時(shí)的縱向樁間距和橫向樁間距。 skpkspkfmmff)1 ( 22/eddm sde05. 1sde13. 12113. 1ssde第15頁(yè)/共27頁(yè) 對(duì)小型工程的黏性土地基如無(wú)現(xiàn)場(chǎng)載荷試驗(yàn)資料，初步設(shè)計(jì)時(shí)復(fù)合地基的承載力特征值也可按下式估算： 式中

13、 n為樁土應(yīng)力比，在無(wú)實(shí)測(cè)資料 時(shí)，可取24，原土強(qiáng)度低取大值，原土強(qiáng)度高取小值。skspkfnmf)1(1 第16頁(yè)/共27頁(yè) 振沖碎石樁復(fù)合土層的壓縮模量可按下式計(jì)算： 式中 Esp復(fù)合土層壓縮模量（ MPa）； Es 樁間土壓縮模量（MPa），宜按經(jīng)驗(yàn)取值，可取天然地基壓縮模量。 n值當(dāng)無(wú)實(shí)測(cè)資料時(shí)，對(duì)黏性土可取24，對(duì)粉土和砂土可取1.53，原土強(qiáng)度低取大值，原土強(qiáng)度高取小值。 sspEnmE)1(1 第17頁(yè)/共27頁(yè)一、干振擠密碎石樁法 它與振沖擠密碎石樁的不同之處是不用高壓水沖。主要適用于地下水位較低的非飽和黏性土、素填土、雜填土和二級(jí)以上非自重濕陷性黃土。二、沉管碎石樁法 可分

14、為管內(nèi)投料重錘夯實(shí)法、管內(nèi)投料振動(dòng)密實(shí)法、先拔管后投料復(fù)打密實(shí)法。9.3 9.3 其他碎石樁法其他碎石樁法9.3 Other Gravel Column Methods第18頁(yè)/共27頁(yè) 三、夯擴(kuò)碎石樁法 夯擴(kuò)碎石樁法適用于非飽和土地基，對(duì)雜填土、素填土地基加固效果很好。四、袋裝碎石樁法 當(dāng)天然地基土的側(cè)限壓力過(guò)小時(shí)，可采用土工織物將碎石樁包上，形成袋裝碎石樁。它具有填料用量少，易于控制填料數(shù)量，樁身密實(shí)度較高，受力性能較好的優(yōu)點(diǎn)，且土工織物袋能起到隔離、過(guò)濾保證排水固結(jié)并防止軟黏土受壓后擠入碎石孔隙的作用，特別適合于在高含水量、低強(qiáng)度的軟黏土中應(yīng)用。第19頁(yè)/共27頁(yè)五、強(qiáng)夯置換碎石樁（墩）

15、法 該法為在地基中設(shè)置碎石墩，并對(duì)地基進(jìn)行擠密，碎石墩與墩間土形成復(fù)合地基以提高地基承載力，減小沉降。第20頁(yè)/共27頁(yè)9.4 9.4 碎石樁復(fù)合地基設(shè)計(jì)碎石樁復(fù)合地基設(shè)計(jì)9.4 Design of Gravel Column Composite Ground 1 樁徑 可按每根樁所用的填料量計(jì)算，常為0.81.2m。樁徑與成樁方法、成樁機(jī)械以及土質(zhì)條件有關(guān)。第21頁(yè)/共27頁(yè) l 2 樁長(zhǎng)樁長(zhǎng)l 樁長(zhǎng)應(yīng)根據(jù)軟弱土層的性能、厚度或樁長(zhǎng)應(yīng)根據(jù)軟弱土層的性能、厚度或工程要求按下列原則確定：工程要求按下列原則確定：l （1）當(dāng)軟土層不厚時(shí)，應(yīng)穿透軟土層；）當(dāng)軟土層不厚時(shí)，應(yīng)穿透軟土層；l （2）當(dāng)軟

16、土層較厚時(shí)，對(duì)按變形控制的工）當(dāng)軟土層較厚時(shí)，對(duì)按變形控制的工程，加固深度應(yīng)滿足砂樁復(fù)合地基變形不超過(guò)地程，加固深度應(yīng)滿足砂樁復(fù)合地基變形不超過(guò)地基容許變形值的要求；基容許變形值的要求；l （3）對(duì)按穩(wěn)定性控制的工程，樁長(zhǎng)應(yīng)不?。?duì)按穩(wěn)定性控制的工程，樁長(zhǎng)應(yīng)不小于最危險(xiǎn)滑動(dòng)面的深度；于最危險(xiǎn)滑動(dòng)面的深度；l （4）在可液化地基中，樁長(zhǎng)應(yīng)按要求的抗）在可液化地基中，樁長(zhǎng)應(yīng)按要求的抗震處理深度確定；震處理深度確定；l （5）樁長(zhǎng)不宜小于）樁長(zhǎng)不宜小于4m。第22頁(yè)/共27頁(yè) 3 布樁范圍 應(yīng)根據(jù)建筑物的重要性和場(chǎng)地條件及基礎(chǔ)形式而定。對(duì)一般基礎(chǔ)，在基礎(chǔ)外應(yīng)擴(kuò)大13排；對(duì)可液化地基，在基礎(chǔ)外緣擴(kuò)大寬度不應(yīng)小于可液化土層厚度的1/2，并不應(yīng)小于5m 。 4 樁間距 應(yīng)根據(jù)荷載大小和原土的抗剪強(qiáng)度確定，可用1.52.5m。 5 樁體材料 可用碎石、卵石、角礫、圓礫等硬質(zhì)材料，含泥量不得大于5%，最大粒徑不宜大于50mm。第23頁(yè)/共27頁(yè) （1）對(duì)粉質(zhì)黏土地基間隔時(shí)間可取2128d，對(duì)粉土地基可取1421d。 （2）樁的施工質(zhì)量可采用單樁載荷試驗(yàn)，檢驗(yàn)數(shù)量為總樁數(shù)的0.5%，且不少于三根。樁體檢驗(yàn)可用重型動(dòng)力觸探