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1、 工人在用洛阳铲进行石灰桩成孔工人在用洛阳铲进行石灰桩成孔第1页/共50页工人用推土铁钎将洛阳铲带出的土刮除工人用推土铁钎将洛阳铲带出的土刮除第2页/共50页工人在室内进行石灰桩施工工人在室内进行石灰桩施工第3页/共50页石灰桩孔径石灰桩孔径d=300mm，桩间距，桩间距s800mm第4页/共50页 人工洛阳铲人工洛阳铲第5页/共50页 三名工人正在夯填石灰桩三名工人正在夯填石灰桩第6页/共50页 夯填石灰桩所用的夯锤（夯板）夯填石灰桩所用的夯锤（夯板）第7页/共50页 夯填石灰桩所用的夯锤（夯板）夯填石灰桩所用的夯锤（夯板）第8页/共50页 运到施工现场的生石灰块运到施工现场的生石灰块第9页
2、/共50页 运到施工现场的粉煤灰运到施工现场的粉煤灰第10页/共50页工人正在拌合生石灰块与粉煤灰工人正在拌合生石灰块与粉煤灰第11页/共50页 量孔器（测量石灰桩孔径及孔深）量孔器（测量石灰桩孔径及孔深）第12页/共50页 量孔器（测量石灰桩孔径及孔深）量孔器（测量石灰桩孔径及孔深）第13页/共50页 石灰桩法适用于处理饱和黏性土、淤泥、淤泥质土、素填土和杂填土等地基；用于地下水位以上的土层时，宜增加掺合料的含水量并减少生石灰用量，或采取土层浸水等措施。第14页/共50页10.2 10.2 加固原理加固原理10.2 Mechanism of Reinforcement 一、物理加固作用 1
3、挤密作用 （1）成桩中挤密桩间土 （2）生石灰吸水膨胀挤密桩间土 2 桩和地基土的高温效应 3 置换作用 4 排水固结作用 5 加固层的减载作用第15页/共50页二、石灰桩的化学加固作用 1 桩体材料的胶凝反应 2 石灰与桩周土的化学反应 （1）离子化作用（熟石灰的吸水作用）（2）离子交换 （3）固结反应 （4）石灰的碳酸化第16页/共50页 一、设计参数及技术要点 1 桩径 一般为300400mm，当排土成孔时，实际桩径取1.11.2倍设计直径。2 桩长 洛阳铲成孔不宜超过6m，机械成孔管外投料时，不宜超过8m。10.3 10.3 设计计算设计计算10.3 Design Procedure第
4、17页/共50页 3 桩距 可取23倍成孔直径。4 桩体抗压强度 可取350500kPa。5 桩间土承载力 与置换率、施工工艺和土质情况有关。可取天然地基承载力的1.051.20倍。土质软弱或置换率大时取高值。第18页/共50页 6 桩土应力比 可取34，长桩取大值。7 复合地基承载力 复合地基承载力特征值不宜超过160kPa。8 布桩 可仅布置在基础底面下，当基底土的承载力特征值小于70kPa时，宜在基础以外布置12排围护桩。第19页/共50页 9 垫层 当地基需要排水通道时，可在桩顶以上设200300mm厚的砂石垫层。10 桩身材料配合比 生石灰与掺合料的体积比可选用1：1或1：2，对淤泥
5、、淤泥质土、填土可适当增加生石灰用量。第20页/共50页 二、石灰桩复合地基承载力计算 面积置换率m应取膨胀后的桩面积计算，即取1.11.2倍成孔直径。第21页/共50页三、石灰桩复合地基沉降计算 石灰桩复合土层的压缩模量宜通过桩身及桩间土压缩试验确定，初步设计时可按下式估算：式中 Es为天然土的压缩模量（MPa），系数可取1.11.3，成孔对桩周土挤密效应好或置换率大时取高值。第22页/共50页10.4 10.4 施工施工10.4 Construction 一、施工工艺 1 管外投料法 2 管内投料法 3 挖孔投料法第23页/共50页二、施工质量控制 1 石灰材料应选用新鲜生石灰块，有效氧化
6、钙含量不宜低于70，粒径不应大于70mm，含粉量不宜超过15。2 掺合料含水量宜控制在30左右。3 填料时必须分段压（夯）实，人工夯实时，每段填料厚度不应大于400mm。4 施工顺序宜由外围或两侧向中间进行。在软土中宜间隔成桩。5 桩位偏差不宜大于0.5倍桩身直径。第24页/共50页 1 石灰桩施工检测宜在施工后710d后进行；竣工验收检测宜在施工后28d进行。2 施工检测可采用静力触探、动力触探或标准贯入试验。检测部位为桩中心及桩间土，每两点为一组。检测组数不少于总桩数的1。10.5 10.5 质量检验质量检验10.5 Quality Verification Test第25页/共50页 3
7、 石灰桩地基竣工验收时，承载力检验应采用复合地基载荷试验。数量宜为地基处理面积每200m2左右布置一个点，且每一单体工程不应少于3点。4 石灰桩复合地基载荷试验沉降比s/d取0.012。第26页/共50页10.1 IntroductionLime columns,where quicklime is mixed in situ with soft soil,are common in Sweden and Finland,to stabilize soft clay and silt as well as organic soils.In China,lime column is usuall
8、y consists of quicklime or mixture of quicklime and flaysh.And flyash can also be replaced by cinder or other materials.第27页/共50页The method has gradually been improved and new applications have been found.Lime columns have mainly been used to increase the stability and to reduce the settlements of b
9、uildings and road embankments and to increase the stability of trenches for sewer lines,water mains and heating ducts.The diameter and the length have gradually increased and the time required for the installation of the columns has been reduced significantly as well as the costs.第28页/共50页Lime colum
10、ns have also been used to stabilize organic soils,where unslaked lime alone has not been effective.Lime columns have the advantage that the permeability and the ductility are normally high.In addition the ground temperature is increased by the heat generated during the slaking.The increase of the sh
11、ear strength,caused by the reduction of the water content,is usually significant.第29页/共50页Since a large number of factors affect the behavior of lime columns,it is necessary to determine for each site the effect of different stabilizers(e.g.lime,cement,gypsum,industrial waste and different ashes)on
12、compressibility,shear strength and permeability of the stabilized soil.Extensive field and laboratory tests are usually required.第30页/共50页The bearing capacity and the shear resistance of the columns are to a large extent governed by the axial load and by the confining pressure.第31页/共50页10.2 Permeabi
13、lity Since the permeability of the laboratory samples often is different from the in situ permeability,where cracks and fissures in the columns affect the results,it is desirable to determine the permeability from the measured excess pore water pressures in the columns.The permeability can also be d
14、etermined from the settlement rate of,for example,embankments and fills.第32页/共50页The difference between the permeability of the columns and the permeability of laboratory samples has been attributed to cracks and fissures in and around the columns caused by shrinkage.The permeability of lime columns
15、 has been determined in the laboratory by constant and by falling head permeability tests as well as by triaxial and oedometer tests with samples from the columns or with small laboratory samples.The permeability has been found to decrease with time.第33页/共50页Baker et al.(1997)report that the in situ
16、 permeability of lime columns can be up to two orders of magnitude higher than the permeability of laboratory-mixed samples.The permeability as determined in the field was 5110-9 to 35010-9 m/s for lime columns.The permeability of the samples prepared in the laboratory was only 210-9 m/s.The permeab
17、ility was observed to decrease with increasing curing time and with increasing confining pressure.The permeability has also been observed to decrease with time and even when the confining pressure is low.第34页/共50页10.3 Behavior of single columnsTransfer lengthIt is necessary to transfer the load from
18、 the embankment to the columns or past weak sections in the columns.The estimated transfer length is 2d,when the load transfer depends entirely on the shaft resistance.When the dry crust is thin or is poorly developed,the transfer length could be up to 10d.The transfer length decreases with time bec
19、ause of the increase of the shear strength of the soil caused by consolidation.The time required for the consolidation can be large for lime columns due to the low permeability of the stabilized soil.The transfer length can also be large at the base of a floating column wall,when the point resistanc
20、e is low.第35页/共50页The undrained shear strength and the shaft resistance for a normally consolidated clay(OCR=1.0)increase with increasing effective overburden pressure.The transfer length,which depends mainly on the shear strength of the soil around the columns,is 3.2m(4d)for a 0.8m diameter column
21、at an axial load of 200kN(400 kPa)and a shaft resistance of 25 kPa,when the point resistance is zero and 4.1 m when the point resistance is 144 kPa.第36页/共50页Lateral displacement of single columnsThe columns,which are located below an embankment,could be displaced laterally by the high lateral earth
22、pressure in the embankment.However,the lateral displacement of the soft soil and of the columns below an embankment is usually small.A large lateral displacement can be expected,when the stability of the embankment is low and the global factor of safety is less than about 1.5.The lateral displacemen
23、t of the columns has been up to 0.5 m next to a slope or a deep excavation.第37页/共50页10.4 Settlement of buildings and of other structuresSettlement of single columns and of column groupsThe main purpose of soil stabilization in the 1960s and 1970s was to reduce the settlements and the angular rotatio
24、n of relatively light buildings.The bearing capacity of the unstabilized soil without the columns was often sufficient to support up to two-storey buildings without basement when the clay is normally consolidated or is slightly overconsolidated.第38页/共50页Most buildings can accommodate relatively larg
25、e settlements,0.2 to 0.3 m or more,without structural damage provided the differential settlements are not excessive.Embankments can in general accommodate a much larger settlement than buildings,provided the settlements are uniform.The length and the spacing of the columns can be varied to take adv
26、antage of the increase of the compression modulus and of the undrained shear strength with depth.第39页/共50页The settlement of embankments and structures,which are supported by single columns or by column groups,is usually checked by assuming that the axial deformations of the columns are the same as t
27、he deformations of the unstabilized soil between the columns.The settlement of a column group is governed by the weighted average compression modulus of the columns and of the unstabilized soil between the columns when the shear strength of the column is low.Test results indicate that the behaviour
28、of the stabilized soil is similar as that of an overconsolidated clay.The settlements are also affected by the stress increase in the columns.第40页/共50页The stress distribution in lime columns has been investigated by Liedberg et al.(1996)using the computer program PLAXIS.The analysis shows that the t
29、ransfer length is small for soft columns,only a few pile diameters.The main difficulty has been to estimate the modulus of elasticity for the columns and the compression modulus for the unstabilized soil.第41页/共50页The soil is remoulded during the installation,up to 0.4 to 0.3 m below the columns,whic
30、h will increase locally the settlement below the columns.There the stress increase depends on the transfer length and on the remoulded shear strength of the unstabilized soil.The settlement and the settlement rate of the soft soil below the column block is generally calculated from the stress increa
31、se as determined by the 2:1 method.However,the stress increase and the settlements could then be overestimated by as much as 27 per cent.It is usually assumed that the total load is transferred to the bottom of the reinforced block without spreading.第42页/共50页The settlement of a column group is usual
32、ly calculated by assuming that the axial deformations of the columns are the same as the deformations of the unstabilized soil and that the behavior is similar to that of an overconsolidated clay.第43页/共50页The settlement of a column group,s,is governed by the weighted average modulus of elasticity of
33、 the columns and of the compression modulus of the unstabilized soil between the columns.Where is the thickness of the different layers,is the stress increase from,for example,an embankment and is the area ratio.It should be noted that decreases with time due to creep.第44页/共50页Due to the large varia
34、tion of the compression modulus and of the difference between laboratory prepared samples and the in situ compression modulus,it is recommended that the settlements should be calculated for probable maximum and minimum values of the different parameters.第45页/共50页It is also important to monitor the s
35、ettlements and the settlement rate during the construction to determine if preloading will be required to reduce the total and the differential settlements and the time required for the consolidation.第46页/共50页 Holm et al.(1983)and Edstam(1996)have reported that the settlements have been only 40 per
36、cent of the calculated settlements based on a compression modulus determined by oedometer tests.第47页/共50页The settlement of a column group depends mainly on the modulus of elasticity of the columns and on the pre-consolidation pressure.Mainly the modulus of elasticity for the upper part of the column
37、s is important since the compression modulus of the unstabilized soil increases rapidly with increasing depth when the clay is normally consolidated or is slightly overconsolidated.The difference between estimated and observed settlements increases in general with increasing length of the columns.第48页/共50页思考题思考题（Problems）（1 1）石灰桩的适用范围是什么？可应用于何类工程？（2 2）石灰桩的物理加固作用有哪些？（3 3）如何设计石灰桩复合地基？（4 4）如何计算石灰桩复合地基的沉降？（5 5）石灰桩有哪些施工方法？（6 6）石灰桩处理地基后，如何进行质量检测？第49页/共50页感谢您的观看！第50页/共50页