桩底复合式后注浆灌注桩的竖向承载特性研究

Study on vertical bearing characteristics of composite post grouting cast-in-place pile at pile bottom

为减小沉降、固化沉渣、提高灌注桩承载力,提出一种灌注桩桩底复合式后注浆工艺,利用安装在桩底的钢板胶囊通过胶囊内外(开-闭-开式)的复合式注浆方式加固桩端周围土体。基于西凌井公路大桥工程进行灌注桩后注浆及静载试验,研究在后注浆过程中注浆压力、注浆量、桩顶位移的实时响应规律,探究桩底复合式后注浆桩的承载特性。利用ABAQUS软件对该工程桩底复合式后注浆灌注桩的承载特性进行数值模拟,并探讨注浆量及注浆体强度对承载力的影响。结果表明:桩底开-闭-开式交替注浆的3次注浆量均达到设计值,稳定时段的注浆压力平均在4.4 MPa左右,桩顶位移累计抬升1.01 mm;复合式后注浆桩比常规桩的极限承载力提高1.9倍左右,同时在桩端以上2.5 d(d为桩半径)左右的范围内,复合式后注浆桩侧摩阻力明显增大,平均侧阻达到189.7 kPa,侧阻增强系数为3.45,侧摩阻力呈“R”形分布;随着注浆量及注浆体强度的增大,起初桩基承载力增长较快,在扩大头半径约为2.5倍的桩半径,弹性模量约为50倍的地基土弹性模量之后,承载力增长幅度较小。

In order to reduce settlement,solidify sediment and improve the bearing capacity of cast-in-place pile,a composite post grouting process at the pile bottom of cast-in-place pile was put out.The steel plate capsule installed at the bottom of pile was used to strengthen the soil around the pile end through the composite grouting method inside and outside the capsule(open-close-open).Based on the post grouting and static load test of cast-in-place pile in Xilingjing highway bridge project,the real-time response law of grouting pressure,grouting volume and pile top displacement in the process of post grouting was studied,and the bearing characteristics of composite post grouting pile at pile bottom were explored.The bearing characteristics of the composite post grouting cast-in-place pile at the pile bottom of the project were numerically simulated by ABAQUS software,and the effects of grouting volume and grouting strength on the bearing capacity were discussed.The results show that the three grouting volumes of open-close-open alternate grouting at pile bottom all reach the design value,the average grouting pressure in the stable period is about 4.4 MPa,and the cumulative displacement of the pile top is raised by 1.01 mm.The ultimate bearing capacity of composite post grouting pile is about 1.9 times higher than that of conventional pile.At the same time,in the range of about 2.5 d(d is pile radius)above the pile end,the side friction of composite post grouting pile increases obviously,the average side resistance reaches 189.7 kPa,the side resistance enhancement coefficient is 3.45,and the side friction presents an“R”distribution.With the increase of grouting volume and grouting strength,the bearing capacity of pile foundation increases rapidly.After the diameter of pile end enlarged head is about 2.5 times of pile diameter and the elastic modulus of pile end enlarged head is about 50 times of that of foundation soil,the bearing capacity increases slightly.