第 碎石桩学习.pptx

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1、振冲碎石地基处理第1页/共27页夯扩碎石桩振冲碎石地基处理振冲碎石地基处理第2页/共27页碎石振冲置换桩第3页/共27页碎石桩地基处理第4页/共27页 采用振冲法在地基中设置碎石桩加固地基的方法称为振冲碎石桩法。振冲碎石桩法适用于处理不排水抗剪强度不小于20kPa的黏土、粉土、砂土、饱和黄土和人工填土地基。9.2 9.2 振冲碎石桩法振冲碎石桩法9.2 Vibroflotation Stone Column Method第5页/共27页9.1.1 Introduction For over 70 years depths vibrators have been used to improved

2、 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页/共27页 Vibro compaction has been applied successf

3、ully 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 loosened soil and

4、 rises to the surface,stabilising the cavity.This is known as the wet vibro replacement method.第7页/共27页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.After the vibra

5、tor 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页/共27页 This vibro replacement procedure came to be known as the conventional dry method.Such technical developments in d

6、ense 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 construction of residential an

7、d light commercial and industrial structures.第9页/共27页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 cavity-filling stage and comp

8、action stage.This produces stone columns that are tightly interlocked with the surrounding soil.第10页/共27页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 soils that have a shear streng

9、th 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 spreading of the column.(Geotextil

10、e-coated Stone Column Method)第11页/共27页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 volume of water is used,rather than

11、a high pressure.The water flow will expel some loosened sand through the annulus around the vibrator.第12页/共27页After the initial insertion and compaction processes have been completed at a particular location,the vibrator is moved to the next location and lowered to the depth specified for compaction

12、.第13页/共27页振冲碎石桩复合地基承载力特征值应通过现场复合地基载荷试验确定，初步设计时也可用单桩和处理后桩间土承载力特征值按下式估算：第14页/共27页 等边三角形布桩 正方形布桩矩形布桩s为等边三角形布桩和正方形布桩时的桩间距，s1、s2分别为矩形布桩时的纵向桩间距和横向桩间距。第15页/共27页 对小型工程的黏性土地基如无现场载荷试验资料，初步设计时复合地基的承载力特征值也可按下式估算：式中 n为桩土应力比，在无实测资料 时，可取24，原土强度低取大值，原土强度高取小值。第16页/共27页 振冲碎石桩复合土层的压缩模量可按下式计算：式中 Esp复合土层压缩模量（MPa）；Es 桩间土

13、压缩模量（MPa），宜按经验取值，可取天然地基压缩模量。n值当无实测资料时，对黏性土可取24，对粉土和砂土可取1.53，原土强度低取大值，原土强度高取小值。第17页/共27页一、干振挤密碎石桩法 它与振冲挤密碎石桩的不同之处是不用高压水冲。主要适用于地下水位较低的非饱和黏性土、素填土、杂填土和二级以上非自重湿陷性黄土。二、沉管碎石桩法 可分为管内投料重锤夯实法、管内投料振动密实法、先拔管后投料复打密实法。9.3 9.3 其他碎石桩法其他碎石桩法9.3 Other Gravel Column Methods第18页/共27页 三、夯扩碎石桩法 夯扩碎石桩法适用于非饱和土地基，对杂填土、素填土地基

14、加固效果很好。四、袋装碎石桩法 当天然地基土的侧限压力过小时，可采用土工织物将碎石桩包上，形成袋装碎石桩。它具有填料用量少，易于控制填料数量，桩身密实度较高，受力性能较好的优点，且土工织物袋能起到隔离、过滤保证排水固结并防止软黏土受压后挤入碎石孔隙的作用，特别适合于在高含水量、低强度的软黏土中应用。第19页/共27页五、强夯置换碎石桩（墩）法 该法为在地基中设置碎石墩，并对地基进行挤密，碎石墩与墩间土形成复合地基以提高地基承载力，减小沉降。第20页/共27页9.4 9.4 碎石桩复合地基设计碎石桩复合地基设计9.4 Design of Gravel Column Composite Groun

15、d 1 桩径 可按每根桩所用的填料量计算，常为0.81.2m。桩径与成桩方法、成桩机械以及土质条件有关。第21页/共27页 l 2 桩长桩长l 桩长应根据软弱土层的性能、厚度或桩长应根据软弱土层的性能、厚度或工程要求按下列原则确定：工程要求按下列原则确定：l （1）当软土层不厚时，应穿透软土层；）当软土层不厚时，应穿透软土层；l （2）当软土层较厚时，对按变形控制的工）当软土层较厚时，对按变形控制的工程，加固深度应满足砂桩复合地基变形不超过地程，加固深度应满足砂桩复合地基变形不超过地基容许变形值的要求；基容许变形值的要求；l （3）对按稳定性控制的工程，桩长应不小于）对按稳定性控制的工程，桩长

16、应不小于最危险滑动面的深度；最危险滑动面的深度；l （4）在可液化地基中，桩长应按要求的抗震）在可液化地基中，桩长应按要求的抗震处理深度确定；处理深度确定；l （5）桩长不宜小于）桩长不宜小于4m。第22页/共27页 3 布桩范围 应根据建筑物的重要性和场地条件及基础形式而定。对一般基础，在基础外应扩大13排；对可液化地基，在基础外缘扩大宽度不应小于可液化土层厚度的1/2，并不应小于5m。4 桩间距 应根据荷载大小和原土的抗剪强度确定，可用1.52.5m。5 桩体材料 可用碎石、卵石、角砾、圆砾等硬质材料，含泥量不得大于5%，最大粒径不宜大于50mm。第23页/共27页 （1）对粉质黏土地基间

17、隔时间可取2128d，对粉土地基可取1421d。（2）桩的施工质量可采用单桩载荷试验，检验数量为总桩数的0.5%，且不少于三根。桩体检验可用重型动力触探进行随机检验。对桩间土可用标准贯入、静力触探等进行检验。9.5 质量检验9.5 Quality Verification Test第24页/共27页（3）复合地基竣工验收，应采用复合地基载荷试验，数量不应少于总桩数的0.5%，且每个单体工程不应少于3点。第25页/共27页思考题思考题(Problems)（1）按施工方法不同，碎石桩分为哪几种？（2）振冲碎石桩复合地基的承载力如何计算？（3）振冲碎石桩施工质量如何控制？（4）振冲碎石桩复合地基如何进行质量检验？第26页/共27页感谢您的观看！第27页/共27页