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1、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8090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
2、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
3、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
4、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23m，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
5、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
6、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、
7、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34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
8、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412M.从土样的土工试验报告可知为低液限黏土含水量29.820.2,凝聚力13.812.2KPA,内摩擦角13.820.2.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
9、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
10、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0.402.20;软土层包括流塑状淤泥和淤泥质土,厚度为1.519.39,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78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
11、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
12、安全事故是较常见的，就设计采用7cm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。Overview of Soft Subgrade TreatmentAbstract: The reinforcement of
13、 soft soil roadbed There are many ways, several to explain the reinforcement mechanism of the role, scope, and individual project example elaboration. New reinforcement materials and new technology development and utilization of soft subgrade reinforcement played an important role to do with the sim
14、ple description. When road works are often encountered in soft soil subgrade, the carrying capacity of the foundation have become increasingly demanding due to the development of highway, railway, natural soft ground is far from meeting these high-grade structures are the foundation bearing force re
15、quirements. 1980s and 1990s, due to population expansion of land resources are becoming increasingly tense, soft soil subgrade reinforcement technology has made great progress, and economic conditions have improved, a variety of soft soil reinforcement theory has been fully Application and verificat
16、ion of soft base reinforcement technology has made rapid progress in different areas are covered; to the 1990s, a variety of soft foundation treatment technology has been widely used in various road projects. Foundation in soft soil, usually in soft new moon or under the state of the flow of new moo
17、n of the clay. Which is characterized by the natural water content, void ratio, compressibility factor, low strength and creep, thixotropy, and other special engineering geological properties, poor engineering geological conditions. Selection of soft soil roadbed application must be put forward prac
18、tical measures.Soil, such as in the construction of the base of the embankment or bridge and culvert structures, optimum moisture content is not easy to grasp, is extremely difficult to achieve the required degree of compaction can not meet the density requirements after the opening, often a roadbed
19、 instability or excessive settlement. Its obvious dangers, therefore prohibiting the use. Construction of embankment on soft ground, especially Bridge Approach, if not take effective measures for the reinforcement, it will have varying degrees of collapse slip or subsidence, resulting in road damage
20、 or is not working is known as the Bump. In general, in addition to ensure that the new subgrade Using density to reduce the settlement In addition, the total settlements of the foundations of the original ground must meet the basic stability of the settlement roughly more than 80% of the total sett
21、lement amount, to allow resurfacing. Serious settlement of soft ground, not only to increase the amount of fill, and subsidence or horizontal displacement of the bridge near the filling, retaining walls, culverts, and even the technical standards of the nearby residential, farmland, and the route wi
22、ll have a huge impact .To this end, according to the engineering properties of foundation soil, the selection of appropriate measures to deal with. After a long practice, the formation of roads, railways, various forms of soft ground, combined with a lot of construction companies many years of exper
23、ience in construction and related experts and scholars discussed summarized as follows: 1 replacement cushion methodWhen the thickness of the soft soil, soft soil below the subgrade surface within part or all of the excavation, then change to fill the greater intensity of soil or other stability, no
24、n-erosive materials (usually good water permeability in coarse sand) called Replacement Cushioning. This economical and practical method to deal with the height of 2 to 3m, if the thickness of the soft soil is too large, then using the replacement method will increase the disposable side and dug sid
25、e content and increase the cost of the project. Replacement higher shear strength of soil, so as to achieve the goal of enhanced foundation bearing capacity to meet the requirements of the structures on the foundation. Reinforcement Method Replacement, Stone Fill, cushion, COMPACTED silt several. Cu
26、shioning according to the different materials can be divided into the sand (gravel) cushion, gravel pads, fly ash cushion, the cushion of dry residue, soil (dust, ash) cushion. Representatives of sand cushion method and replacement method. Gravel cushion: when the embankment height is less than 2 ti
27、mes the limit height, soft soil layer is thin, the filling material is more difficult, or rainy season, construction, gravel (sand) cushion between the fill and the basement to set up a drainage face, so that the foundation by filling load in the foundation soil pore water discharge speed to acceler
28、ate the consolidation to improve the bearing capacity of foundations, reduce sedimentation, to prevent the foundation of local shear deformation. Pay attention to controlling the filling speed, the materials used to clean coarse sand with mud is not more than 5%, or maximum particle size less than 5
29、cm natural gradation gravel. Replacement Method: water permeability material (gravel or crushed stone) in the soft soil thickness is not greater than 2m, filling replacement can reduce the compression to increase bearing capacity, shear strength, and reduce the settlement to improve the dynamic char
30、acteristics accelerate soil consolidation by drainage. It is characterized by the construction process is simple, but the cost is relatively high. Stone Fill: When the soft soil or marsh soil located underwater, replace the soil construction difficulties, and the thickness is less than 3m, the surfa
31、ce without a hard shell, the substrate water content over liquid limit, embankment above the weight of the soft soil that can be squeezed out, drainage more difficult when using cast stone tablets (diameter generally less than 30cm) to squeeze the deposition method. Start from the middle of the rubb
32、le, gradually extending to the sides, out of mud, to improve the subgrade strength.2 deep compaction，The use of blasting, compacting, extrusion and vibration and join the high shear strength of materials, etc., the foundation of deep soft soil density vibration and compaction of the foundation reinf
33、orcement method is called deep compaction. For soft soil thickness 3m thick soft soil reinforcement, distribution of a wide area of soft Reinforcement processing, has consolidated its depth is up to 30m.Vibration, squeezing ground Turkey body dense consolidation, and added with high shear strength o
34、f the pile material replacement of part of the soft soil of the three-phase (gas, liquid and solid phase) portion to form a composite foundation, to improve the shear strength of purpose. Main reinforcement methods: dynamic compaction, soil (or dust, fly ash plus lime) piles, sand piles, blasting, g
35、ravel pile (vibration and substitution method), lime piles, cement, fly ash gravel pile pile (CFG), the DJM France, jet grouting piles. On behalf of rubble piles, dynamic compaction, cement and fly ash gravel piles, DJM France. The dynamic compaction method can be used to hammer compaction or dynami
36、c compaction: sand foundation and the water content in a range of soft clay foundation. Its basic principle is: the soil under the huge impact in the soil to produce a lot of pressure and shock wave, resulting in the soil of local compression, tamping points around within a certain depth to produce
37、the fissures good drainage channel, so that the soil pore water (gas) discharged smoothly, the rapid consolidation of soil. Dynamic compaction, foundation bearing capacity can be increased 3-4 times, compression can be reduced from 200% to 1000%. Good ram is able to hit: In theory, the best tamping
38、can function in the foundation soil pore water pressure reaches the soil weight pressure, such tamping energy known as the best tamping energy. Therefore, according to the superposition of the pore water pressure value to determine the best tamping energy. In sandy soil, the growth and dissipation o
39、f pore water pressure of only a few minutes, the pore water pressure can not be with the tamping can increase and overlay, the maximum pore water pressure increment and the number of tamping relations to determine the best tamping can. Sea highway landslide accumulation of broken mudstone deposits t
40、hickness of 4 12M from the soil samples of the soil test report shows that for low liquid limit clay containing.Water 29.8 to 20.2, the cohesiveness 13.8 12.2KPA internal friction angle of 13.8 20.2. Sand compaction piles, rubble pile reinforcement method: a kind of composite foundation, thick soft
41、soil replacement to handle the more difficult, the foundation soil is unsaturated cohesive soil or sand, sand compaction piles or broken Shizhuang reinforcement method, the foundation soil compacting bulk density increased, pores less than to prevent liquefaction of sand in the earthquake or by vibr
42、ation and improve the foundation soil shear strength and the level of resistance, reducing the consolidation settlement, so that the foundation to change uniform , play replacement, compaction, drainage and to prevent the foundation to produce sliding failure, completed ahead of the settlement to re
43、duce the differential settlement. 3 drainage consolidation method Pressure on the soft ground and in line with internal drainage, accelerate the drainage of the soft ground, speed up the processing of soft soil consolidation known as drainage consolidation method. For saturated cohesive soil foundat
44、ion in handling all types of mud, silt clay and red fill.Soft ground in the role of the additional load is gradually passed to the pore water, the void ratio decreases, resulting in consolidation deformation. In this process, with the gradual diffusion of excess pore water pressure in soil, soil eff
45、ective stress, and settlement in advance or improve the settling velocity. Reinforcement methods: heap preloading method sand wells France, packed sand, vacuum preloading method, electro-osmosis water method, dewatering method, plastic drainage plate method. Preloading: divided into the surcharge pr
46、eloading, set Preloading and less preloading, the construction process is simple, but a longer duration, surcharge preloading time is generally six months, usually used in conjunction with wastewater treatment foundation . New kiln South Road, Guangzhou City, road works is to use a heap load reinfor
47、cement of soft soil roadbed. New kiln South Road road works starting point for Guangzhou Avenue K4, +600, and finish at North Village K11, to +700, total length of about 7KM road along the stratigraphic architecture were as follows: the crust hard shell loose, miscellaneous fill, fill factors, and s
48、oft plastic like cultivated soil, thickness of 0.40 to 2.20; soft layers including the flow of plastic-like silt and silty soil, thickness of 1.51 9.39, along thickness variation; underlying layer of cohesive soil and sand heap preloading time from 1995 to 2003, about 7 to 8 years. Packed sand: soft
49、 soil subgrade for soft soil thickness, embankment stability, high filling, packed sand, increase the soft soil the vertical drainage capacity, shorten the horizontal direction of the drainage distance, accelerate the soft soil strength. Sand bags poured into the sand, sand wells can be used to hammering or vibration method of construction. Complexity of its construction process, the relatively high cost, used for a long time, can be rectan