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1、 水泥粉喷机水泥粉喷机第1页/共40页 水泥粉喷机水泥粉喷机第2页/共40页 水泥粉喷机水泥粉喷机第3页/共40页 水泥粉喷机底盘水泥粉喷机底盘第4页/共40页 贮灰罐贮灰罐第5页/共40页水泥粉喷机的搅拌叶片水泥粉喷机的搅拌叶片第6页/共40页水泥粉喷机的控制柜水泥粉喷机的控制柜第7页/共40页 三轴水泥搅拌机三轴水泥搅拌机第8页/共40页 水泥土搅拌法分为深层搅拌法（湿法）和粉体喷搅法（干法）。水泥土搅拌法适用于处理正常固结的淤泥与淤泥质土、粉土、饱和黄土、素填土、黏性土以及无流动地下水的饱和松散砂土等地基。当地基土的天然含水量小于30、或地下水的pH值小于4时不宜采用干法。第9页/共40
2、页 水泥浆液搅拌法是美国在第二次世界大战后研制成功的，称（MixedinPlace Pile(简称MIP法）。国内1978年研制出第一台搅拌机械。粉体喷射搅拌法（Dry Jet Mixing Method，简称DJM法）由瑞典人Kjeld Paus于1967年提出设想，1971年制成第一根桩，1974年获得专利。铁道第四勘察设计院1983年开始试验研究，并应用于过程中。第10页/共40页 水泥土搅拌法的优点：（1）最大限度地利用了原土；（2）搅拌时无振动、无噪音和无污染，对周围原有建筑物及地下沟管影响很小；（3）设计灵活，可按不同地基土的性质及工程设计要求，合理选择固化剂及其配方；（4）根据上
3、部结构的需要可灵活地采用柱状、壁状、格栅状和块状等加固形式；（5）与钢筋混凝土桩基相比，可节约钢材并降低造价。第11页/共40页11.1 IntroductionThe use of in situ soil mixing(SM)to improve the engineering and environmental properties of soft or contaminated ground has increased widely since its genesis.This indicates growing international interest and acceptanc
4、e of this relatively new and quickly developing technology.In this method of ground improvement,soils are mixed in situ with different stabilizing binders,which chemically react with the soil and/or the groundwater.The stabilized soil material that is produced generally has a higher strength,lower p
5、ermeability and lower compressibility than the native soil.The most important binders are cements and limes.第12页/共40页SM technology can be subdivided into two general methods:the Deep Mixing Method and Shallow Mixing Method.The more frequently used and better developed DMM is applied for stabilizatio
6、n of the soil to a minimum depth of 3 m and is currently limited to treatment depth of about 50 m.The binders are injected into the soil in dry or slurry form through hollow rotating mixing shafts tipped with various cutting tools.The mixing shafts are also equipped with discontinuous auger flights,
7、mixing blades or paddles to increase the efficiency of the mixing process.第13页/共40页In situ soil mixing is a versatile ground improvement method.It can be used to stabilize a wide range of soils,including soft clays,silts and fine-grained sands.Stabilization of organic soils is also available,but is
8、more difficult and requires carefully tailored binders and execution procedures.However,the engineering properties of the stabilized soil will not only depend on the characteristics of the binder.They will also depend,to a large extent,on the inherent characteristics of each soil and the way it has
9、been deposited,as well as on mixing and curing conditions at a particular worksite.第14页/共40页In this chapter,DMM method with cement binder is outlined.It is not possible to predict the strength of in situ mixed soil with a reasonable level of accuracy.As a consequence of this fundamental deficiency,w
10、hich we are challenged to overcome,it is believed that the development of SM will be continued along a somewhat erratic experimental path,and will be to a large extent dependent on accumulated experiences.第15页/共40页11.2 Historical development and classificationThe roots of deep soil mixing go back to
11、 the mid-1950s,when the mixed in Place(MIP)piling technique was developed by Intrusion-Prepakt Inc.,including the US patent of Liver,filed in November 1956.In this method a mechanical mixer was used to mix cementitious grout into the soil for the purpose of creating foundation elements and retaining
12、 walls.The grout was injected from the tip of the mixing tool consisting of a drilling head and separated horizontal blades.Subsequent more intensive use of MIP was observed in Japan for excavation support and groundwater control in the 1960s.Modern deep mixing techniques reflect,however,mainly Japa
13、nese and Scandinavian efforts over the last three decades.第16页/共40页The level of research and development activity in Japan in relation to DMM remains the highest in the world.The study on soil mixing was initiated at the Port and Harbour Research Institute(PHRI)in 1967 in the framework of government
14、-sponsored research work.The in situ soil mixing includes wet and dry deep mixing methods.第17页/共40页11.3 Installation ProcessThe typical installation process consists of positioning the mixing shaft(s)above the planned location,penetration of the mixing tool,verification and improvement of the bottom
15、 soil layer,withdrawal,and movement to a new location if necessary.The details of execution depend on the type of method applied(dry or wet),technical features of the equipment,and the site-specific and functional requirements.第18页/共40页The position and verticality of the shaft is checked first,and z
16、ero adjustments of the logging system are conducted.For on-land application optical survey devices are normally used,whereas for marine operations the use of the Global Positioning System(GPS)has become common.The GPS is also advantageous in the case of large on-land projects,especially those involv
17、ing treatment of very weak superficial soils.第19页/共40页During penetration the mixing tool is delivered to the required depth.In this phase compressed air(dry method),or slurry(wet mechanical mixing),or high-velocity jetting with slurry or water and air(hybrid mixing)is used to support mechanical dril
18、ling.Mechanical penetration may be difficult when the tool hits a hard layer or when the improvement depth is relatively deep,leading to possible damage or deadlock of the tool in the ground.第20页/共40页After the bottom of treatment depth is reached,the mixing tool remains on the bottom rotating about
19、0.5-2 min for complete mixing.This phase is often called bottoming,and serves to ensure sufficient contact of the column(s)with the bearing subsoil.Penetration into the bearing layer should be confirmed by a rapid change of penetration velocity of the tool,requires torque and rotation speed.At this
20、stage the tool can be raised about 0.5 to 1m and lowered again to treat more effectively the transition zone between soft and bearing soils.第21页/共40页The accompanying delivery of the stabilizing agent to the subsoil is operator/computer controlled and linked to the energy of mixing in the specific la
21、yers of treated soil.In general,injection of the stabilizing agent can take place during penetration,withdrawal and restroking;however two main injection methods are distinguished:the penetration injection method(top-bottom process)the withdrawal injection method(bottom-top process)第22页/共40页Penetrat
22、ion injection is typically used for on-land applications of the wet-method because the slurry helps to lubricate the mixing tool and assists in breaking up the soil into smaller pieces.Normally,100 per cent to about 80 per cent of the total slurry volume is used in this stage.This method is also ben
23、eficial to the homogeneity and strength of the manufactured column because the native soil is mixed twice with the binder.第23页/共40页Withdrawal injection is typically used for the dry-method,with usually the whole amount of binder delivered to the soil during this phase.However,if very high binder con
24、centration is needed to reach the design strength,part of the stabilizer may be injected during penetration phase and the rest during withdrawal of the mixing tool.第24页/共40页The sequence of mixing operations will need to be adjusted to suit each sites specific conditions,but,in general,the most effic
25、ient sequence is to work the stabilization machine within its radius of operation as much as possible before it is moved.第25页/共40页11.2 11.2 加固机理加固机理11.2 Mechanism of Reinforcement1 水泥的水解水化反应2 土颗粒与水泥水化物的作用 （1）离子交换和团粒化作用 （2）硬凝反应3 碳酸化作用第26页/共40页11.3 11.3 室内试验室内试验11.3 Laboratory Test 软土地基深层搅拌加固法是基于水泥对软土
26、的作用，而目前这项技术的发展仅经过二十余年，无论从加固机理到设计计算方法或者施工工艺均有不完善的地方，有些还处于半理论半经验的状态，因此应该特别重视水泥土的室内外试验。第27页/共40页 （1）固化剂 宜选用强度等级为32.5级以上的普通硅酸盐水泥，水泥掺量宜为1220。（2）桩长 宜穿透软弱土层到达承载力相对较高的土层。湿法加固深度不宜大于20m，干法加固深度不宜大于15m。11.4 11.4 设计计算设计计算11.4 Design Procedure 第28页/共40页 （3）桩径 常用桩径500700mm。（4）承载力 初步设计时按下式估算：式中 Ra单桩竖向承载力特征值（kN）；Ap桩
27、的截面积（m2）；桩间土承载力折减系数。第29页/共40页 当桩端土未经修正的承载力特征值大于桩周土的承载力特征值的平均值时，可取0.10.4，差值大时取低值；当桩端土未经修正的承载力特征值小于或等于桩周土的承载力特征值的平均值时，可取0.50.9，差值大时或设置褥垫层时均取高值。单桩竖向承载力特征值应通过现场载荷试验确定。也可由下两式估算，取小值。第30页/共40页 式中 与搅拌桩桩身水泥配比相同的室内加固土试块（边长70.7mm的立方体）在标准养护条件下90d龄期的立方体抗压强度平均值（kPa）；桩身强度折减系数，干法可取 0.200.30，湿法可取0.250.33；up 桩的周长（m）；
28、第31页/共40页 n 桩长范围内所划分的土层数；qsi桩周第i层土的侧阻力特征值。对淤泥可取47kPa；对淤泥质土可取612kPa；对软塑状态的黏性土可取1015kPa；对可塑状态的黏性土可取1218kPa；li 桩长范围内第i层土的厚度（m）；qp 桩端地基土未经修正的承载力特征值（kPa），可按现行国家标准建筑地基基础设计规范GB 50007的有关规定确定；第32页/共40页 桩端天然地基土的承载力折减系数，可取0.40.6，承载力高时取低值。（5）垫层 应在基础和桩之间设置200300mm厚褥垫层，其材料可选用中砂、粗砂、级配砂石等，最大粒径不宜大于20mm。（6）布桩 桩可只在基础平
29、面范围内布置，独立基础下的桩数不宜少于3根。第33页/共40页 （7）沉降计算 水泥土搅拌桩复合地基的变形包括复合土层的平均压缩变形与桩端下未加固土层的压缩变形。复合土层压缩变形可按下式计算：第34页/共40页 Ep水泥土搅拌桩的压缩模量，可取（100120）fcu（kPa），对桩较短或桩身强度较低者可取低值。桩端以下未加固土层的压缩变形可按等代实体基础法进行计算。第35页/共40页 水泥土搅拌法的施工步骤为：（1）搅拌机就位、调平；（2）预搅下沉至设计加固深度；（3）边喷浆（粉）、边搅拌提升直至预定的停浆（灰）面；（4）重复搅拌下沉至设计加固深度；（5）根据设计要求，喷浆（粉）或仅搅拌提升直
30、至预定的停浆（灰）面；（6）关闭搅拌机械。11.5 施工施工(Construction)第36页/共40页 一、施工质量检验 （1）成桩7d后，采用浅部开挖桩头，目测检查搅拌的均匀性，量测成桩直径。检查量为总桩数的5。（2）成桩后3d内，可用轻型动力触探（N10）检查每米桩身的均匀性，检验数量为总桩数的1，且不少于3根。11.6 11.6 质量检验质量检验11.6 Quality Verification Test 第37页/共40页 二、竣工验收检测 （1）竖向承载水泥土搅拌桩地基竣工验收时，承载力检验应采用复合地基载荷试验和单桩载荷试验。（2）载荷试验宜在成桩28d后进行。检验数量为总桩数的0.51，且每项单体工程不应少于3点。（3）水泥土搅拌桩复合地基的沉降比取0.006。第38页/共40页思考题思考题(Problems)（1）水泥土搅拌法分为哪两种方法？这两种方法各适用于何种情形？（2）水泥土的物理和力学性质与天然土体相比有哪些提高？（3）水泥土搅拌桩复合地基的设计与灰土挤密桩、石灰桩复合地基的设计有何区别？（4）如何进行水泥土搅拌桩的施工质量控制？（5）水泥土搅拌桩复合地基如何进行质量检测？第39页/共40页感谢您的观看！第40页/共40页