硅藻土单桩复合地基动力特性试验研究

Experimental Research on the Dynamic Characteristics of Diatomite Single Pile Composite Foundation

研究目的:当前硅藻土的研究侧重于物化性质和成因机制,对其工程特性研究较少,尤其是桩基处理技术和动力特性的研究更是缺乏。本文分别设计了CFG桩、素混凝土桩和螺杆桩进行天然和浸水工况下的动力特性试验,研究不同桩型的应力传递机制、振动速度、桩身应变和沉降规律,对其桩土作用关系和机理进行深入分析。研究结论:(1)硅藻土结构性较强,不适合扰动土体的成桩工艺;螺杆桩土体扰动大,稳定性差,不建议采用螺杆桩;旋挖素混凝土桩扰动小,成桩质量最优,CFG桩次之;(2)天然工况下,素混凝土桩刚度最大,速度响应最小,螺杆桩动应力和速度响应剧烈,桩身应变较大;浸水后硅藻土结构破坏,桩顶应力集中,单桩复合地基的动应力、速度、沉降和桩身应变均不同程度增加;(3)"上刚-中柔-下刚"的结构体系可消散大部分的激振能量,增加整体稳定性,随着激振频率增大,桩土应力比增加,碎石表层和桩板结构动应力呈指数型上升;(4)本文研究可为硅藻土工程动力特性研究及类似工程提供借鉴意义。

Research purposes:At present,the research of diatomite focuses on its physical and chemical properties and genetic mechanism,but the research on its engineering characteristics is less,especially the research on pile foundation treatment technology and dynamic characteristics.In the paper,the dynamic characteristic tests of CFG pile,plain concrete pile and screw pile under natural and immersion conditions are designed respectively,and the stress transfer mechanism,vibration speed,pile strain and settlement law of different pile types are studied,and the pile-soil interaction mechanism are analyzed in depth.Research conclusions:(1)Diatomite has strong structure and is not suitable for the pile forming technology which the soil is disturbed.Screw pile is not recommended because of its large disturbance and poor stability.The disturbance of rotary excavation plain concrete pile is small,the quality of which is the best,followed by CFG pile.(2)Under natural conditions,the stiffness of plain concrete pile is the largest,the speed is the smallest.The dynamic stress and velocity response of screw pile are intense,the strain of which is large.After immersion,the structure of diatomite is destroyed,the stress on the top of pile is concentrated,and the dynamic stress,velocity,settlement and pile strain of single pile composite foundation increase.(3)The system of"rigid-soft-rigid"can dissipate most of the excitation energy and increase the stability.With the increase of excitation frequency,the stress of the top of pile increases,and the dynamic stress of gravel surface and pile plate structure increases exponentially.(4)The research results can provide a reference for the study on dynamic characteristics of diatomite or similar projects.