探析公路软土地基的处理

 

Abstract: because of the highway has a high requirement on the after the completion of the roadbed sedimentation, and subsidence just is one of the major problems of soft soil foundation treatment, therefore, build up the highway on soft soil foundation, if not handled with soft foundation, will often result in the instability of the subgrade or excessive settlement, directly affects the road after the completion of the operation state and its service life. 

 

关键词：公路；软土地基；处理方法

 

Key words: road; Soft soil; Processing method 

 

1 软基处理的几种方法

 

1. Several methods of soft soil foundation treatment 

 

1.1 表层处理法 ①表层排水法。对土质较好因含水量过大而导致的软土地基，在填土之前，地表面开挖沟槽，排除地表水，同时降低地基表层部分的含水率，以保障施工机械通行。为了发挥开挖出的沟槽在施工中达到盲沟的效果，应回填透水性好的砂砾或碎石。②砂垫层法。对于地基上部软土层极薄且含水量大时，在软土地基上敷垫0.5～1.2m左右厚的砂垫层。这样可达到固结软土层，使砂垫层起到上部排水层作用；同时，砂垫层又成为填土内的地下排水层，以降低填土内的水位；在进行填土及地基处理施工时，为施工机械提供良好的通行条件。③敷垫材料法。对于地基土层不均匀，可能发生局部不均匀沉降和侧向变位，可利用所敷垫材料的抗剪和拉抗力，来增强施工机械的通行，均匀地支承填土荷载、减少地基局部沉降和侧向变位，以提高地基的支承能力。敷垫材料主要有化纤无纺布、土工布、玻璃纤维格栅等被广为采用。④添加剂法。对于表层为粘性土时，在表层粘性土内渗入添加剂，改善地基的压缩性能和强度特性，以保施工机械的行驶。同时也可达到提高填土稳定及固结的效果。添加材料通常使用的是生石灰，熟石灰和水泥。石灰类添加材料通过现场拌和或厂拌，除了降低土壤含水量、产生团粒效果外，对被固结的土随着时间的推移会发生化学性固结，使粘土成分发生质的变化，从而促进土体稳定。

 

1.1 surface treatment (1) surface drainage method. In soil is good for moisture content is too large due to the soft soil foundation, before filling, groove surface excavation, surface water, at the same time reduce the moisture content of ground surface part, in order to ensure construction machinery. For digging out of the groove in the construction, achieve the result of blind ditch backfill should be excellent drainage gravel or crushed stone. (2) the sand cushion method. For soft clay foundation top is very thin and big water content, apply on the soft soil foundation mat about 0.5 ~ 1.2 m thick layer of sand cushion. Can achieve consolidation of soft soil layer, so the sand mat layer upper drainage layer effect; At the same time, the sand cushion and fill in underground drainage layer, in order to reduce the water level in the filled soil; During filling and in construction of foundation treatment, provide good traffic conditions for construction machinery. 3. Apply the pad material. For uneven subsoil, the partial uneven settlement and lateral displacement may occur, can apply the pad material by the shear and tensile strength, to enhance construction machinery, filling evenly bearing load, reduce the local settlement and lateral displacement of foundation, in order to improve the bearing capacity of foundation. Apply the cushion materials are mainly chemical fiber non-woven fabric, nonwoven fabric, fiberglass grille, etc widely used. (4) the additive method. Surface layer on surface of cohesive soil, cohesive soil infiltration additives, improve the compression performance of the foundation and strength characteristics, in order to protect driving construction machinery. At the same time also can achieve Gao Tiantu stability and consolidation effect. Adding material usually using quicklime and hydrated lime and cement. Lime class adding material by mixing or factory, in addition to reduce soil moisture content and aggregate effect, on the consolidation of soil chemical consolidation will happen with the passage of time, has brought qualitative changes in the composition of clay, so as to promote the stability of soil. 

 

1.2 置换法 本法是以优质土置换软弱土，确保填土稳定和减少沉降量。施工方法分有人工挖掘置换和借填土自重或用爆炸法将软弱土挤出的强制置换。其施工都比较容易，多数情况下能在短时间内达到所要求的目的。从可靠性来说人工挖掘置换较优。置换材料应采用即使受到水浸也不致降低承载力的粗粒土。但必须进行充分压实。

 

1.2 this law is based on high quality soil replacement soft soil replacement method, ensure the stability of the filled soil and reduce settlement. Construction methods have artificial excavation displacement and lend fill weight or explosion method to soft soil extrusion force displacement. Its construction is easy, in most cases can be required in a short period of time to achieve. From artificial excavation displacement better reliability. Replacement materials should be used even by water immersion does not reduce the bearing capacity of coarse grained soil. But it must be properly compacted. 

 

1.3 加载法 加载法是为了预先促进软土地基沉降，增加地基强度，以防止设置在填土上或邻接填土的路面和构造物或者埋入填土内的构造物发生有害沉降而导致破坏。促进地基固结沉降的方法有：在地基上增加总压办法；减少土中的间隙水压提高有效应力法等。前者用填土荷载时，一般为填土加载法，后者又可分通过井点，竖井等的降低地下水法和在地表面铺砂，覆盖不透水膜使之形成真空，依靠大气压力加载来促进固结的大气压加载法。采用填土加载法时，须注意地基的稳定状态。而降低地下水法和大气压加载法则不必担心地基遭到破坏，但受到地基适应性的限制且工程费用大，一般不采用。上述方法，都很少单独采用。

 

1.3 load loading method is to promote the soft soil foundation settlement in advance, increase the strength of foundation, in order to prevent the setting on the fill or adjacent surfaces of the filled soil and the structure filling or embedded within the harmful settlement in construction and cause damage. Methods are: to promote the foundation consolidation settlement increase total pressure on foundation; Reduce gap pressure increase in the soil effective stress method, etc. Filling with load, the former general to fill load method, which in turn can be divided by well point, shaft, etc to reduce underground water and spread sand, in the earth's surface covered impervious membrane forming a vacuum, depend on atmospheric pressure loading to promote consolidation of atmospheric pressure loading method. When filling load method is adopted, must pay attention to the foundation of the steady state. And reduce the underground water and atmospheric pressure loading rules don't have to worry about the foundation is destroyed, but is limited by the adaptability of foundation and engineering cost, is generally not used. The above method, is rarely used alone. 

 

1.4 砂井排水法 砂井排水法根据砂井的施工方法不同，可分为打入式、振动式、螺旋钻式、水射式及袋装式等。

 

1.4 sand Wells drainage sand Wells drainage method according to different construction method of sand drain, can be divided into type, vibration type, spiral drill, water and bag type, etc. 

 

本法很少单独使用，多与加载法或缓速填土法并用，对层厚大，均质的粘土地质最为有效；对泥炭质地基效果稍差。粘性土层固结所需时间t与垂直方向最大排水距离D的平方成正比。很清楚，粘土层越厚，所需固结时间就越长。

 

This law is rarely used alone, with the method of loading or slow filling method, and the layer thickness, homogeneous clay geology is the most effective; Effect of peat quality foundation is a bit poor. Cohesive soil consolidation needed time t and the maximum vertical drainage is proportional to the square of the distance D. It is clear that clay layer is thicker, the longer time will elapse for consolidation. 

 

 

 

2 施工现场常用处理软土路基方法

 

2 methods dealing with soft soil subgrade construction site 

 

在施工中经常碰到的情况多数不是软土地基，因为如果有软土地基一般情况在设计时应该根据地质资料，提出处理方法。多数情况是有局部地段地质情况和原来设计不同，出现局部地基承载力达不到设计要求，或者由于局部地段含水量过大（原有排水系统不畅，原有地基土质渗水性不好）造成地基软弹（翻浆，弹簧土地段）。根据出现的这些情况一般常用的方法主要有：①换填。②抛石填筑。③盲沟。④排水砂垫层。⑤石灰浅坑法。

 

Often encountered in the construction of most is not soft soil, because if there is a general situation of soft soil foundation when the design should be according to the geological data, the processing method is put forward. Most of the time there is a local area geology and the original design is different, a local foundation bearing capacity can not meet the design requirements, or local area due to moisture content is too large (the original drainage not free, and the original foundation soil water permeability is bad) caused by foundation soft shells (pumping, spring land section). According to appear these conditions commonly used methods are: (1) for filling. (2) the ripped-rock embankment. 3. The blind ditch. (4) drainage sand cushion. 5. Lime method of a shallow pit. 

 

3 实际施工中软土地基的处理

 

3 construction of soft soil foundation treatment 

 

3.1 挖除换填碎片石方法 对于深度不太大的软基工程，在路堤范围内，将需要处理的软土挖除，动力触探合格后，用碎片石换填，可采用分段挖除，分段分层回填的方法。用于换填的石料强度应不小于15MPa，分层厚度不宜大于30cm，石料最大粒径不应大于层厚的2/3。依据规范，分层回填的碎片石应碾压合格，表面石块嵌挤紧密无松动，用镐刨不动，一般采用激震力320kN以上的压路机强震碾压无轮迹。

 

3.1 invisible fill in pieces of stone, a method for soft foundation engineering depth is not too big, within the scope of the embankment, will need to deal with soft soil invisible, after qualified, dynamic or fragments of stone for filling, can use segmented invisible, segmentation of the stratified backfill method. Used for replacement of stone strength should not be less than 15 mpa, layering thickness should not be greater than 30 cm, stone maximum particle size should not be more than two-thirds of layer thickness. According to the specification, stratified backfill fragments of stone should be rolling qualified, surface rocks embedded no loose to close, with picks plane, generally USES the shock force of more than 320 kn roller rolling wheel track without strong earthquakes. 

 

3.2 对于较深的软基 挖除换填工程量太大，资料显示，施工方采用了粉喷桩。粉喷桩主要是以粉体物质作加固料和原状土进行搅拌，经过理化作用生成具有较高强度的混合柱体，促使整个路堤产生足够的强度。一般采用水泥作为固化剂，最好用Po32.5级普通硅酸盐水泥，要依据施工时间选用水泥初终凝时间合适的水泥，防止未成型即已凝固。试验室应重点对水泥剂量进行监控，重点保证均匀性。我们配制了3%～8%的水泥剂量试验，发现3%水泥几乎不能使软泥固结，6%剂量能满足要求。但是室内配比不能完全代替施工情形，因此应该跟踪检测，应对7d桩监控。对于不合格桩，应在原桩边上补桩，新桩与旧桩净距20cm。如出现较多不合格桩应查找原因，进行改正。

 

Invisible 3.2 for deep soft foundation in filling quantity is too large, the data shows, construction of powder spraying pile is adopted. Powder spray pile mainly powder material for reinforcement material and undisturbed soil mixing, generated by the steric (physical and chemical mixing cylinder has high strength, prompted the embankment have enough strength. Cement commonly used as a curing agent, had better use Po32.5 ordinary Portland cement, according to the construction time chooses at the beginning of cement setting time suitable cement, to prevent the molding namely has solidified. Laboratory should focus on the cement dose monitoring, the key to ensure uniformity. We made up 3% ~ 8% of cement dosage test, found that 3% of cement can hardly make ooze consolidation, 6% dose can meet the requirements. But indoor ratio cannot completely replace the construction situation, so you should tracking detection, monitoring response to 7 d pile. For unqualified pile, the edge should be in the original pile pile, a new pile with old net from 20 cm. Should look for reason, if appear more pile to correct them. 

 

3.3 抛石挤淤 用于存在多处鱼塘和常年积水的洼地。这些地方，软土层位于水下，更换土壤较为困难，或者基底直接落在含水量极高的淤泥中，土壤稠度远超过液限，透水性差、天然含水量大、压缩性高，且这些地方大多为高填方路堤，若对软基不加任何处理或处理不当，往往会导致路基失稳或过量沉降，造成公路不能正常使用。对于厚度较薄，表层无硬壳，片石能沉达底部的泥沼或厚度为3～4m的软土，采用抛石挤淤法效果最佳。当路堤较低且淤泥层较厚时，为增加换土高度，可用挖掘机自一端向另一端或由两端向中间逐段挖除上部3米左右的软泥并外运，挖除段落的长短，以挖掘机能够工作的最大水平距离为准，挖除一个段落后，即可进行抛石。抛挤时，沿路中线向前抛填，再向两侧扩展。当软土地层横坡陡于1∶10时，应自高处向低侧抛投，并在低侧边部多抛投，使低侧边部有2m宽的平台顶面。抛石达到地表常水位以上50mm时，在抛石回填的片石顶面上，铺10～30mm厚碎石垫层（砂砾垫层）并整平压实。整个路段铺筑碎石垫层（砂砾垫层）并平整压实达到要求后，即开始路堤的正常填筑。抛石挤淤时，由于各处沉降不一致，从而在路堤下面残留部分软土，完工后，则会产生不利的不均匀沉降，因而必须注意垫层铺筑后的压实，以使淤泥挤出，减少这种不利影响。

 

3.3 the ripped-rock crowded silting used to exist in fish ponds and water all the year round depressions. These places, soft soil, the sea in replacement of soil is relatively difficult, or basal directly fall in the mud of high moisture content, soil consistency is far more than liquid limit, poor permeability, large natural water content, high compressibility, and most of these places for the high fill embankment, if without any processing or treatment of soft foundation is undeserved, will often result in the instability or excessive settlement of the subgrade, road can't normal use. For thinner thickness, surface crust, flaky can sink to the bottom of the swamp or thickness of soft soil of 3 ~ 4 m, riprap crowded silting method is used to best effect. When low embankment and thick silt, to increase in height, soil available excavator from one end to the other side or by both ends to the middle segment invisible upper 3 meters of mud and sinotrans, invisible, the length of the paragraphs to excavator to work is the greatest horizontal distance, invisible behind a segment, stone can be made. Thrown when squeezed, thrown forward along the center line to fill, to expand on both sides. When cross slope steep in soft soil layer 1:10, should from high to low and toss side, and on the low side and toss more, make the low side of 2 m width at the top of the platform. Riprap and up to the surface water level above 50 mm, often at the top of the riprap backfilling of flaky, spread 10 ~ 30 mm thick gravel cushion (gravel cushion) leveling and compaction. The whole road paving stone cushion (gravel cushion layer) and flat after compaction is achieved, the normal filling embankment as. Riprap crowded silting, due to subsidence, everywhere to remain soft soil under the embankment, when completed, will produce adverse uneven settlement, so must pay attention to cushion paving after compaction, so that the mud extruder, reduce the adverse effect.