孔内强夯法处理湿陷性黄土地基的应用综述

Case study on the application of DDC method for foundation treatment in collapsible loess site

以56个不同湿陷性黄土场地采用孔内深层(超)强夯法(DDC法或SDDC法)在地基处理中案例为背景,针对其应用现状展开统计分析,讨论了湿陷性黄土地基承载力、湿陷厚度、湿陷等级及地域分布特性,分析了DDC工法中采取的填料、夯击能、成孔直径、成桩直径、桩长、布桩方式等施工参数对湿陷性消除、复合地基承载力等地基处理效果的影响程度和规律。结果表明:(1)湿陷土层厚度和湿陷等级逐级递减,DDC工法使用频次较SDDC工法高,且DDC法在湿陷性厚度为5~15 m的Ⅲ级自重湿陷性场地集中应用广泛(。2)DDC(SDDC)工法中最常采用的填料为灰土,占比为60%,处理后的复合地基承载力可提高1.4~4.7倍。(3)DDC法夯击能为800~2 000 kJ/层,成孔和成桩直径分别为0.4 m和0.6 m;SDDC法夯击能为1 000~3 000 kJ/层,成孔和成桩直径分别为1.2 m和1.8 m。(4)DDC法和SDDC法的桩间距基本为2.0~3.0倍成孔直径,布桩方式一般为正三角形,但SDDC法处理深度较DDC法更深,其对湿陷性地基的挤密加固效果更为明显。

Based on the case of 56 different collapsible loess sites using deep(super) dynamic compaction method(DDC method or SDDC method) in foundation treatment, a statistical analysis is carried out on its application condition. The bearing capacity, collapsible thickness, collapsible grade and regional distribution characteristics of collapsible loess foundation are discussed. The influence degree and law of the construction parameters such as filler, ramming energy, hole diameter, pile diameter, pile length, and pile arrangement adopted in DDC construction method on the foundation treatment effects such as collapsibility elimination and composite foundation bearing capacity are analyzed. The results show that:(1) The thickness and grade of collapsible soil layer decrease gradually, and the frequency of DDC method is higher than that of SDDC method. The DDC method is widely used in grade Ⅲ self-weight collapsible site with collapsible thickness of 5 to 15 m.(2) About 60% of the DDC(SDDC) construction method uses lime soil as the filler, and the bearing capacity of the treated composite foundation can be increased by 1.4 to 4.7 times.(3) The tamping energy of DDC method is 800-2 000 kJ/layer, hole forming and pile forming diameter is 0.4 m and 0.6 m, respectively;the tamping energy of SDDC method usually is 1 000-3 000 kJ/layer, diameter of hole formation and pile formation are 1.2 m and 1.8 m, respectively.(4) The pile spacing of the DDC method and the SDDC method is basically 2.0-3.0 times the diameter of the hole. The pile arrangement method is usually equilateral triangle. However, the treatment depth of SDDC method is deeper than that of DDC method. The compaction reinforcement effect of SDDC method is more obvious for collapsible foundation.