软土路基处理方法概述 摘要：软土路基的加固有很多种方法，
本文对常用的几种方法从加以解释对其加 固机理,作用,作用范围以及个别的工程实例的阐述
.新型的加固材料以及新工艺 的开发和利用对提高软土路基的加固技术水平所起的重要作用等做以简单的阐 述. 在道路工程中经常会遇到软土路基，
由于高速公路、高速铁路的发展，对地 基的承载能力要求越来越高，天然的软土地基远远不能满足这些高档次的构造物对地基承载力的要求。20 世纪 80～90 年代，由于人口膨胀土地资源日益紧张，同时软土路基加固的技术也有了长足的发展，经济条件有所改善，各种软土加固理论得到了充分的应用与验证，软基加固技术也得到长足发展，在不同的领域里均有涉猎；到 20 世纪 90 年代以后,各种各样的软基处理技术已广泛地应用在各种道路工程中。
地基中常见的软土，一般是指处于软朔或者流朔状态下的粘性土。
其特点是 天然含水量大、孔隙比大、压缩系数高、强度低，并具有蠕变性、触变性等特殊的工程地质性质，工程地质条件较差。选用软土作为路基应用，必须提出切实可 行的技术措施。这种土质如在施工中出现在路基填土或桥涵构造物基础中，
最佳 含水量不易把握，极难达到规定的压实度值，满足不了相应的密实度要求，在通车后，往往会发生路基失稳或过量沉陷。其危害性显而易见,故禁止采用。在软土地基上修筑路堤，特别是桥头引道，如不采取有效的加固措施，就会产生不同程度的坍滑或沉陷，导致公路破坏或不能正常使用即所说的桥头跳车。一般地，除要确保新填筑路基的密实度以减少沉降外，包括原地面的地基总沉降必须达到基本稳定，沉降量大致达到总沉降量的 80%以上时，才容许铺路面。软土地基沉 降严重时，不仅增加填方数量，而且沉降或水平位移对临近填土的桥台、挡土墙、涵洞，甚至对附近的住宅、农田以及路线的技术标准都会产生很大的影响。为此，根据地基土的工程特性，选用适当的处理措施。经过长期的实践，在公路、铁路中形成了多种形式的软土地基处理方法，结合很多的施工企业多年施工经验及有关专家学者的论述进行总结归纳如下：
1 换填垫层法
当软弱土层厚度不很大时，可将路基面以下处理范围内的软弱土层部分或全 部挖除，然后换填强度较大的土或其它稳定性能好、无侵蚀性的材料
(通常是渗 水性好的中粗砂)称为换填或垫层法。此法处理的经济实用高度为
2～3m，如果 软弱土层厚度过大，则采用换填法会增加弃方与取土方量而增大工程成本。
通过 换填具有较高抗剪强度的地基土，从而达到增强地基承载力的目的，满足构筑物对地基的要求。主要加固方法有换填、抛石挤淤、垫层、强夯挤淤几种。垫层法根据材料的不同可分为砂(砾石)垫层、碎石垫层、粉煤灰垫层、干渣垫层、土(灰 土、二灰)垫层。代表方法有砂垫层法及换填法。
砂砾垫层：当路堤高度小于极限高度的 2 倍，软土层较薄，填筑材料比较困难，或雨季施工时，采用砂砾(砂)垫层，在填土与基底之间设一排水面，从而使地基在受到填土荷载后，迅速地将地基土中的孔隙水排出，加快固结速度，提高地基的承载力，减少沉降，防止地基局部剪切变形。要注意控制填土速度，所用的材料为含泥量不大于 5%的洁净中粗砂，或最大粒径小于 5cm 的天然级配砂砾。
换填法：在软土厚度不大于 2m 时，利用渗水性材料(砂砾或碎石)进行置换填土，可以降低压缩性，提高承载力，提高抗剪强度，减少沉降量，改善动力特性，加速土层的排水固结。它的特点是施工工艺简单，但费用比较高。
抛石挤淤：当软土或沼泽土位于水下，更换土施工困难，且厚度小于
3m， 表层无硬壳、基底含水量超过液限、路堤自重可以挤出的软土之上，排水比较困难时，采用抛片石(直径一般不小于 30cm)挤淤的方法。从中部开始抛石，逐渐向两边延伸，挤出淤泥，提高路基强度。
2 深层密实法 采用爆破、夯击、挤压和振动及加入抗剪强度高的材料等方法，对地基深层的软弱土体进行振密和挤密的地基加固方法称为深层密实法。适用于软土厚 度>3m 的中厚软土的加固，分布面积广的软基加固处理，
其加固深度可达到
30m。
通过振动、挤压使地基中土体密实、固结，并利用加入的具有高抗剪强度的桩体材料置换部分软弱土体中的三相(气相、液相与固相)部分，形成复合地基，达到提高抗剪强度的目的。
主要加固方法：强夯法、土(或灰土、粉煤灰加石灰)桩法、砂桩法、爆破法、 碎石桩法(振冲置换法)、石灰桩法、水泥粉煤灰碎石桩(CFG 桩法)、粉喷桩法、旋喷桩法。代表方法有碎石桩法、强夯法、水泥粉煤灰碎石桩法、粉喷桩法。
强夯法：对于砂土地基及含水量在一定范围内的软弱粘性土地基，
可采用重 锤夯实或强夯。它的基本原理是：土层在巨大的冲击能作用下，土中产生很大的压力和冲击波，致使土体局部压缩，夯击点周围一定深度内产生裂隙良好的排水通道，使土中的孔隙水(气)顺利排出，土体迅速固结。强夯后地基承载力可提高 3～4 倍，压缩性可降低 200%～1000%。其佳夯击能：从理论上讲，在最佳夯击能作用下，地基土中出现的孔隙水压力达到土的自重压力，这样的夯击能称最佳夯 击能。因此可根据孔隙水压力的叠加值来确定最佳夯击能。
在砂性土中，孔隙水 压力增长及消散过程仅为几分钟，
因此孔隙水压力不能随夯击能增加而叠加，
可 根据最大孔隙水压力增量与夯击次数关系来确定最佳夯击能。
兰海高速公路某滑 坡体的堆积破碎泥岩堆积物厚度 4~12M.从土样的土工试验报告可知为低液限黏土含水量 29.8~20.2,凝聚力 13.8~12.2KPA,内摩擦角 13.8~20.2. 挤密砂桩、碎石桩加固法：属于复合地基的一种，当软土层较厚，换填处理比较困难，地基土属于非饱和粘性土或砂土时，采用挤密砂桩或碎石桩加固法，可以使地基土密实，容重增加，孔隙比减少，防止砂土在地震或受震动时液化， 提高地基土的抗剪强度和水平抵抗力，减少固结沉降，使地基变均匀，起到置换、挤密、排水作用，防止地基产生滑动破坏，提前完成沉降，减少沉降差。
3 排水固结法 在软土地基上加压并配合内部排水，加速软土地基的排水，加快软土固结的处理方法称为排水固结法。适用于处理各类淤泥、淤泥质粘土及冲填等饱和粘性土地基。软土地基在附加荷载的作用下，逐渐排出孔隙水，使孔隙比减小，产生固结变形。在这个过程中，随着土体超静孔隙水压力的逐渐扩散，土的有效应力增加，并使沉降提前完成或提高沉降速度。
主要加固方法：堆载预压法、砂井法、袋装砂井、真空预压法、电渗排水法、降低地下水位法、塑料排水板法。
预压处理：分为超载预压、等载预压和欠载预压等，其施工工艺简单，但工期较长，超载预压的时间一般为 6 个月，通常与排水处理地基相结合使用。广州
市新窑南路道路工程就是利用堆载法加固软土路基的.新窑南路道路工程起点为广州大道 K4+600,终点为北山村 K11+700,全长约 7KM.道路沿线地层结构自上而 下分别为:地壳硬壳包括松散状杂填土
,素填土和软塑状耕土,厚度为
0.40~2.20; 软土层包括流塑状淤泥和淤泥质土,厚度为 1.51~9.39,沿线厚度变化大;下伏层包括粘性土和砂层.堆载预压时间从 1995 年到 2003 年,大约 7~8 年. 袋装砂井：对于软土厚度大、路堤稳定、填土高的软土路基，采用袋装砂井， 可增加软土竖直方向的排水能力，缩短水平方向的排水距离，加速软土的强度。
砂袋灌入砂后，砂井可采用锤击法或振动法施工。
它的施工工艺复杂，费用相对 较高，所用的时间较长，可采用矩形或梅花形布桩。
珠江地区某市公路的地质 勘探表明，地基土质分布比较均匀，除表层
1。0m 左右耕植土外，接着为
8.6m 厚的高含水量、高压缩性、低强度，高含粘性的超软弱淤泥。第三层为厚约 1.0m 的贝壳粉砂土；第四层又为
7.6m 厚的淤泥质粘土；以下分别是
0.5m 厚粘土和 3.0m 厚粉细砂。往下为击数（
SPT）大于 19 击的含砾粗砂层，再往下土质更好。
地基土质为 20m 左右深厚的淤泥，含水量高达
85.7%，十字板剪切强度仅
4Kpa， 且淤泥分布深度大致由前方向后方陆域倾斜，前浅后深，前方相对有利。在这样大面积超软弱的淤泥地基上筑路需作软基深层处理，以防止施工期软基沉降缓慢，引起工程完工后仍有较大剩余沉降量，同时不致因加载引起地基失稳破坏。
这一带因软基不当而出现工程质量或安全事故是较常见的，
就设计采用 Ф7cm 袋 装砂井加砂垫层堆载预压排水固结进行软基加固，目的是通过打设砂井使第二、四层淤泥土排水固结后，土质强度获得提高、减少工程投产后的沉降，保证工程的正常使用，满足工程设计要求。
塑料排水板：排水原理与袋装砂井相同，由于是工厂制作，它的质量稳定、重量轻、运输保管方便，施工工艺比较简单，投入劳力少，费用相对较低，并且渗滤吸水性好，具有一定的强度和延伸率，对土的扰动小，预压时间较长，在工程中得到广泛应用，但对于提高土层的抗剪能力不如袋装砂井。
OverviewofSoftSubgradeTreatment
Abstract:ThereinforcementofsoftsoilroadbedTherearemanyways,several
toexplainthe reinforcement mechanism ofthe role, scope,andindividual projectexampleelaboration.Newreinforcementmaterialsandnewtechnology
development
and utilization
of soft subgrade reinforcement played an importantroletodowiththesimpledescription.
Whenroadworksareoftenencounteredinsoftsoilsubgrade,thecarrying
capacityofthefoundationhavebecomeincreasinglydemanding due tothe developmentofhighway,railway,naturalsoftgroundisfarfrommeetingthese
high-gradestructures arethe
foundation bearing forcerequirements. 1980s and 1990s, due to population expansionoflandresourcesare becoming increasingly tense, softsoil subgrade reinforcement technology has made greatprogress,andeconomicconditionshaveimproved,avarietyofsoftsoil
reinforcement
theory has beenfully Applicationandverificationofsoftbase reinforcement
technology has made rapidprogress indifferent areas are covered;tothe1990s,avarietyofsoftfoundationtreatmenttechnologyhas
beenwidelyusedinvariousroadprojects.
Foundationinsoftsoil,
usuallyinsoftnewmoonorunderthestateoftheflowofnewmoonofthe
clay. Which
is characterized by the
natural water content, void ratio, compressibility factor, low strength and
creep,thixotropy,andother special engineeringgeologicalproperties,poorengineeringgeologicalconditions.Selectionofsoftsoilroadbedapplicationmustbeputforwardpracticalmeasures.Soil,suchasintheconstructionofthebaseoftheembankmentorbridgeandculvertstructures,optimummoisturecontentisnoteasytograsp,isextremelydifficulttoachievetherequireddegreeofcompactioncannotmeet thedensityrequirementsaftertheopening,oftenaroadbedinstabilityorexcessivesettlement.Itsobviousdangers,thereforeprohibitingtheuse.Constructionofembankmentonsoftground,especiallyBridgeApproach,ifnottakeeffectivemeasuresforthereinforcement,itwillhavevaryingdegreesof
collapse sliporsubsidence,resultinginroaddamage or is not working is knownastheBump.Ingeneral,inadditiontoensurethatthenewsubgrade
UsingdensitytoreducethesettlementInaddition,thetotalsettlementsofthe
foundations oftheoriginalgroundmustmeetthebasic stability of the settlement roughlymorethan80%ofthetotalsettlement amount,to allow resurfacing.Serioussettlementofsoftground,notonlytoincreasetheamount
offill,andsubsidenceorhorizontaldisplacementofthebridgenearthefilling,
retainingwalls,culverts,andeventhetechnicalstandards of the nearby residential, farmland, and the routewill havea huge impact.To this end, according
totheengineering properties offoundation soil, theselection of appropriatemeasurestodealwith.Afteralongpractice,theformationofroads,
railways,variousformsofsoftground, combined with alot ofconstruction companiesmanyyearsofexperienceinconstructionandrelatedexpertsand
scholarsdiscussedsummarizedasfollows:
1replacementcushionmethod
Whenthethicknessofthesoftsoil,softsoilbelowthesubgradesurfacewithin
partoralloftheexcavation,thenchangetofillthegreaterintensityofsoilor
otherstability,non-erosivematerials(usuallygoodwater permeability in coarsesand)calledReplacementCushioning.Thiseconomicalandpractical
methodtodealwiththeheightof2to3m,ifthethicknessofthesoftsoilistoo
large,then usingthe replacement methodwillincrease the disposable side anddugsidecontentandincreasethecostoftheproject.
Replacementhighershearstrengthofsoil,soastoachievethegoalof
enhancedfoundationbearingcapacitytomeetthe requirements of the structuresonthefoundation.
ReinforcementMethodReplacement,StoneFill,cushion,COMPACTED
siltseveral.Cushioningaccordingtothedifferentmaterialscanbedividedinto
thesand (gravel)cushion, gravel pads, flyashcushion,the cushion of dry residue,soil(dust,ash)cushion.Representativesofsandcushionmethodandreplacementmethod.
Gravelcushion:whentheembankmentheightislessthan2timesthelimit
height,softsoillayeristhin,thefillingmaterialismoredifficult,orrainyseason,
construction,gravel(sand)cushionbetweenthefillandthebasementtosetup
adrainageface,sothatthefoundationbyfillingloadinthefoundationsoilpore
waterdischargespeedtoacceleratetheconsolidationtoimprovethebearing
capacity
offoundations, reduce sedimentation,
toprevent thefoundation of localsheardeformation. Payattentionto controlling the fillingspeed, the materialsusedtocleancoarsesandwithmudis notmore than 5%, or maximumparticlesizelessthan5cmnaturalgradationgravel.
Replacement Method: water permeability
material (gravel or crushed stone)inthesoftsoilthicknessisnotgreaterthan2m,fillingreplacementcan
reduce thecompression to increase bearing
capacity, shear strength,and reduce thesettlementtoimprove
the dynamiccharacteristics accelerate soil consolidation by drainage. Itischaracterized by the constructionprocessis simple,butthecostisrelativelyhigh.
StoneFill:Whenthe softsoil ormarshsoil located underwater, replace thesoilconstructiondifficulties,andthethicknessislessthan3m,thesurface
withoutahardshell,thesubstratewatercontentoverliquidlimit,embankment
abovetheweightofthesoftsoilthatcanbe
squeezed out, drainage more difficultwhenusingcaststonetablets(diametergenerallylessthan30cm)to
squeezethedepositionmethod.Startfromthemiddleoftherubble,gradually
extendingtothesides,outofmud,toimprovethesubgradestrength.
2deepcompaction ，
Theuseofblasting,compacting,extrusionandvibrationandjointhehigh
shearstrengthofmaterials,etc., the foundation of deep soft soil density vibration and compaction ofthe foundation reinforcement method is called deepcompaction. For soft soilthickness> 3m thick softsoil reinforcement, distributionofawideareaofsoftReinforcementprocessing,hasconsolidated
itsdepth is up to 30m.Vibration, squeezing
ground Turkey body dense consolidation, and added with high shear strength of the
pile material
replacementofpartof thesoftsoil of the three-phase (gas, liquidand solid phase)portiontoformacompositefoundation,toimprovetheshearstrength
ofpurpose.
Mainreinforcement methods:dynamiccompaction,
soil(ordust,fly ash pluslime)piles,sandpiles,blasting, gravel pile (vibration and substitution method),limepiles,cement,flyashgravelpilepile(CFG),theDJMFrance,jet
groutingpiles.Onbehalfofrubblepiles,dynamiccompaction,cementandfly
ashgravelpiles,DJMFrance.
Thedynamiccompactionmethodcanbeusedtohammercompactionor
dynamiccompaction:sandfoundationandthewatercontentinarangeofsoft
clayfoundation.Itsbasicprincipleis:thesoilunderthehugeimpactinthesoil
toproduce a lot ofpressure and shockwave, resulting in the soil of local compression, tamping points around within a certain depth toproduce the fissuresgooddrainagechannel,sothatthesoilporewater(gas)discharged
smoothly, the rapid consolidation of soil. Dynamic compaction, foundation bearingcapacity can beincreased 3-4 times,compression can be reduced from200%to1000%.
Goodramisabletohit:Intheory, thebest tamping canfunction inthe foundation soilpore waterpressurereaches the soil
weight pressure, such tampingenergyknownasthebesttamping energy. Therefore,according to thesuperposition of thepore water pressure value
to determine the best tampingenergy.Insandysoil,the growth and dissipation of pore water pressureofonlyafewminutes,theporewaterpressurecannotbewiththe
tampingcanincreaseandoverlay,
the maximum
pore water pressure incrementandthenumberoftampingrelationstodeterminethebesttamping
can.Seahighwaylandslideaccumulation of broken mudstone deposits thicknessof4~12Mfromthesoilsamplesofthesoiltestreportshowsthatfor
lowliquidlimitclaycontaining.Water 29.8to20.2,thecohesiveness 13.8 ~ 12.2KPAinternalfrictionangleof13.8~20.2.
Sand compaction piles, rubble pile reinforcement method: a kind of
compositefoundation,thicksoftsoilreplacementtohandlethemoredifficult,
thefoundationsoilisunsaturatedcohesivesoilorsand,sandcompactionpiles
orbrokenShizhuangreinforcement method,thefoundationsoilcompacting bulkdensityincreased,poreslessthantopreventliquefactionofsandinthe
earthquakeorbyvibrationandimprovethefoundationsoilshearstrengthand
the levelof resistance,reducing the consolidation settlement, so that the foundationtochangeuniform,playreplacement,compaction,drainageandto
prevent the foundation to produce sliding failure, completed
ahead of the settlementtoreducethedifferentialsettlement.
3drainageconsolidationmethod
Pressureonthesoftgroundandinlinewithinternaldrainage,accelerate
the drainage of the soft ground, speed up the processing of soft soil consolidation known as drainage consolidation method. Forsaturated cohesivesoilfoundationinhandlingalltypesofmud,siltclayandredfill.
Softgroundintheroleoftheadditionalloadisgraduallypassedtothepore
water,thevoidratiodecreases,resultinginconsolidationdeformation.Inthis
process,withthegradualdiffusionofexcessporewaterpressureinsoil,soil
effectivestress,andsettlementinadvanceorimprovethesettlingvelocity.
Reinforcement methods: heap preloading method sand wells France, packed sand,vacuum preloading method, electro-osmosis water method, dewateringmethod,plasticdrainageplatemethod.
Preloading:dividedintothesurchargepreloading,setPreloadingandless
preloading, theconstruction process is simple, but alonger duration, surchargepreloadingtimeisgenerallysixmonths,usuallyusedinconjunction
withwastewatertreatmentfoundation.NewkilnSouthRoad,GuangzhouCity,
roadworksistouseaheaploadreinforcementofsoftsoilroadbed.Newkiln
SouthRoadroadworksstartingpointforGuangzhouAvenueK4,+600,and
finishatNorthVillageK11,to+700,totallengthofabout7KMroadalongthe
stratigraphic architecture were as follows: the crust hard shell loose, miscellaneousfill,fillfactors,andsoftplasticlikecultivatedsoil,thicknessof
0.40to2.20;softlayersincludingthe flowofplastic-like silt andsiltysoil, thicknessof 1.51~ 9.39, alongthicknessvariation;underlyinglayerof cohesivesoilandsandheappreloadingtimefrom1995to2003,about7to8
years.
Packed sand:softsoil subgrade for soft soilthickness, embankment stability,highfilling,packedsand,increasethesoftsoiltheverticaldrainage
capacity,shortenthehorizontaldirectionofthedrainagedistance,accelerate
thesoftsoilstrength.Sandbagspouredintothesand,sandwellscanbeused
tohammeringorvibrationmethod of construction. Complexity
of its construction process, the relatively highcost, usedforalong time, can be rectangularorplum-shaped clothpile.Geological Survey of the PearlRiver areaof acityroadshowthatthe foundationsoil ismore evenly distributed, surface 0maboutCultivate soil,thena8.6mthickhighwatercontent,high compression, low-intensity,
highcontentofviscoussuper-weak
sludge.The thirdlayeristhickand1.0mshellpowdersand;thefourthfloorand7.6mthick
siltyclay;0.5mthickclayand3.0mthicksiltysand.Downfortheblowcount
(SPT)isgreaterthan19hitpebblycoarsesandlayer,andthendownthesoil
better.Thefoundation soil isabout20mdeepmud,upto85.7%moisture content,vaneshearstrengthisonly4Kpaandsiltdistributiondepthofroughly
inclinedbytheformerdirectionoftherearland,theformerlightafterthedark,
infrontofarelativelyfavorable.Roadsneedsuchalargeareaofverysoftsilt
foundations for the deep
processing of soft foundation to
prevent the constructionofsoftfoundationsettlementisslow,causethereisstillalarge
residualsettlementafterthe
completion oftheproject,atthe same timenot causedamage tothefoundation instability due toload. This
area due to improper softfoundation engineering quality orsafety incidents is more common,thedesign Ф7cmpackedsandplussandcushionheaploadPreload
softReinforcementbyplayingsetthesandwellSecond,aftertheconsolidation
ofthefour-story mudsoil drainage,thesoilstrengthimproved, reducing the settlementaftertheprojectputintooperation,toensurethenormaluseofthe
projecttomeetprojectdesignrequirements. PlasticDrainageBoard:DrainagePrinciplesandpackedsandfactoryproduction,itsqualityisstable,lightweight,easytransportationandstorage,constructiontechniquesarerelativelysimple,lessinvestmentinlabor,relativelylowcost,andpercolationwaterabsorption,hasacertainstrength andelongation,soildisturbanceissmall,preloadingalongtime,beenwidelyusedinengineering,butimprovethesoil"sshearcapacitythanpackedsand.