软土地基处理新技术之预应力混凝土管桩（17页）

1、 We are the family!软土地基处理新技术 -预应力混凝土管桩组员：王帅、吕东洋、李鹏飞、原锡栋、杨文瑞一、问题的提出 过去在一般公路通过软土地区，由于线路等级标准不高，路基宽度窄、立交少、纵坡要求不严，且多低路堤，故对路基大部分地段处理工程少，仅对桥头高路堤部位重视些。但从高速公路出现后，因要求全立交、桥涵通道多，路堤高度多超过软土填土极限高度。加之软土中含有大量亲水胶体微粒，土体多呈海棉状结构，因其孔隙比大、含水量多、透水性小、抗剪强度低、压缩性强在路堤高填土的自重作用下，要经过较长时间才能趋地压密稳定、因此其沉降稳定要花费长时间。此外软土结构在大交通量、重载车辆的作用下，路

2、基容易产生侧向膨胀挤出滑动，基底沉降现象也严重，为了增强压密稳定力度和较短时间达到最终沉降，消除侧向滑动位移，以免路堤向两侧膨胀挤出，确保路基及其外侧建筑物或其他农田、虾池、鱼塘的安全，因此必须对软基进行处理。 对软土地基处理方法的几点体会：表层处理法 置换法 加载法 竖向排水法 表层处理法 置换法 加载法 竖向排水法 Thicklayerofsoftsoiltreatmentdesignisdifficultyinthedesignoffoundationtreatmentandisthekeytothesuccessofthewholefoundationtreatmentproject.

3、Atpresentdomestic（国内的）mostlyincoastalareasisrelativelyrare,thecommonlyusedtreatmentmeasuresaresandpile,crushedstonepileandcementmixingpileandCFGpile,vacuumpreloading, prestressed concretepipepileandtheEPSlightweightembankmentandsoon.All kinds of treatments selection mainly depends on its area, the g

4、eological hydrological conditions of treatment segment , the successful local experience ,as well as the Economy of treatment program, etc. The common treatments program in deep soft soil are as follows:1、Cement mixing pile2、CFG pile3、PHC(Prestressed Concrete Piles)4、Vacuum preloading5、EPS embankmen

5、t6、Compacted gravel pilePrestressed Concrete Pile Prestressed concrete piles have commonly closed-ended tubular sections of 400 mm to 600 mm diameter with maximum allowable axial loads up to about 2 700 kN. Normal pile elements can be up to about 20 m long and are usually welded together using steel

6、 end plates. Prestressing concrete piles has several benefits. Tensile stresses, which can be set up in a pile during driving, can be better resisted, and the pile is less likely to be damaged during handling. Bending stresses, which can occur during driving, are also less likely to produce cracking

7、. However, the ultimate strength in axial compression is decreased as the level of prestressing is increased. Therefore, prestressed piles are more vulnerable to damage from striking obstructions during driving. They are also difficult to cut after installation, and special techniques have to be emp

8、loyed. As a result they are most suitable for applications where the pile length is predictable and constant. Prestressed Concrete Pile Prestressed concrete piles require high-strength concrete and careful control during manufacture. Casting is usually carried out in a factory, where the curing cond

9、itions can be strictly regulated. Special manufacturing processes such as compaction by spinning or autoclave curing can be adopted to produce high strength concrete.This type of pile is generally less permeable than reinforced concrete piles and may be expected to exhibit superior performance in a

10、marine environment. Hard steel points (fixed or attachable driving shoes) can be used at the toe of jointed piles for protection when penetrating soils containing boulders, or in weak rock. Construction of prestressed concrete pile1、起吊管桩（Lifting pipe pile） 先拴好吊装用的钢丝绳及索具，然后应用索具捆绑住桩上部约50cm处，启动机器起吊管桩，使

11、桩尖垂直对准桩位，缓缓放下插入土中，回复门架在桩顶扣好桩帽，可卸去索具。桩帽与桩周边应有510mm的间隙，桩帽与桩顶之间应有相适应的衬垫，一般采用硬木板，其厚度为10cm左右。Construction of prestressed concrete pile2、稳桩与压桩（Lifting pipe pile ）当桩尖插入桩位，扣好桩帽（pile cap）后，微微启动压桩油缸，当桩入土至50cm时，再次校正桩的垂直度和平台的水平度，保证桩的纵横双向垂直偏差不得超过0.5%（在不受施工影响范围内，成90方向设置经纬仪各一台校准），然后启动压桩油缸，把桩徐徐压下，控制施压速度，一般不宜超过2m/mi

12、n。Construction of prestressed concrete pile3、 压桩的顺序应根据场地的地形、地质、桩基的设计布置密集程度以及压桩机移动方便等因素决定。 建筑面积较大，桩数较多时，可将基桩分为数段，压桩在各段范围内分别进行。压桩应连续进行，同一根桩的中间间歇时间不宜超过半小时。压桩施工时，应由专人或开启自动记录设备做好施工记录，开始压桩时应记录桩每沉下1m油压表压力值，当下沉至设计标高或两倍于设计荷载时，应记录最后三次稳压时的贯入度。Construction of prestressed concrete pile4、接桩（pile extension ） 接桩采用钢端板焊接法，桩段顶端距地面1m左 右就可接桩，接桩前先将下段桩顶清洗干净，加上定位板，然后把上段桩吊放在下段桩端板上，依靠定位板将上下桩段接直，接头处如有空隙，应采用楔形铁片全部 填实焊牢，拼接处坡口槽电焊应分层对称进行，焊接时应采取措施减小焊接变形，焊缝应连续饱满（满足三级焊缝），焊后清除焊渣，检查焊缝饱满程度。 若桩顶不平，可用麻袋或厚纸垫平。送桩深度一般不宜超过2m，送桩留下的桩孔应立即回填密实。Construction of prestressed