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饱和软土高效固化剂及固化土强度特性研究 2018-06-01

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申请上海交通大学博士学位论文
饱和软土高效固化剂及固化土强度特性研究
(国家自然科学基金资助项目:51379122)
(上海市科委资助项目:15DZ1204500)

饱和软土高效固化剂及固化土强度特性研究
摘要
饱和软土存在含水率高、强度低、压缩性大及常规无机胶凝材料固化处理效果欠
佳等问题,工程中常用的解决方法是加大固化剂(水泥)掺量,导致工程成本增加,
同时不利于环境友好。软土固化处理后,工程师常根据现场检测和经验公式计算得到
的预期力学性能制订后续施工方案。但目前常用的固化土强度计算公式,准确度较低
且同一公式无法适用于不同类型的土,从而引发因固化土强度估算不准确导致的工
程安全隐患等问题。本文从软土固化处理的基础理论出发,研究高效水泥基软土固化
剂,对固化剂各组分作用开展量化分析,并提出了软土有机质的反活性系数,借助固
化土体基本物理性质指标的测试、分析结果,建立固化有机质土强度综合计算模型。
基于以上研究,获得的主要创新性成果如下:
(1)以上海饱和软黏土为对象研究一种水泥与外加剂复合无机高效软土固化剂
及其作用机理:在提高土pH 值、改善固化土早期强度和中后期火山灰效应的基础上,
结合化学沉淀理论,选定水玻璃、氯化钙与氢氧化钠作为外加剂改善饱和黏土及淤泥
土的固化效果,确定氯化钙与氢氧化钠比例为1:1 的复合激发剂,通过正交试验得到
水泥基高效固化剂的基准配比为水泥:助剂:复合激发剂=5:1:2。掺入12%高效固化剂
的固化土强度,基本与掺入20%水泥的固化土的各龄期强度相当。掺入高效固化剂
的固化土中有更多的蜂窝状水化硅酸钙凝胶(C-S-H)生成,说明C-S-H 的形态、数
量及结构对固化土强度均有较大影响。
(2)提出外加剂的火山灰系数,量化分析外加剂对固化土强度的作用:将外加
剂(助剂和复合激发剂)看作火山灰物质并定义其火山灰系数,其作用相当于外掺一
定量的水泥。当量水泥量可由火山灰系数与外加剂掺量的乘积获得。基于水土灰比模
型,多元拟合得到各龄期的助剂火山灰系数(k1)和复合激发剂火山灰系数(k2)。
发现外加剂火山灰系数随养护龄期不断变化,k1 随龄期的增加而降低,k2 随龄期的
增加而增大,其原因为助剂主要起早强作用,而复合激发剂的中后期火山灰作用更显
著。外加剂作用的量化分析为改善水泥固化土的效果提供设计参考,建立固化土强度
综合计算模型提供理论依据。
(3)研究粉煤灰的作用机理,基于分散与填充(P&D)系数分析粉煤灰对固化
土强度的作用:固化土中难觅粉煤灰微米级以下微球体,证实了粉煤灰的火山灰与填
充作用。此外,粉煤灰还将胶凝水化产物-土颗粒的大团簇分散为一些小团簇,有利
于形成更多、更稳定的骨架结构,因此可知粉煤灰在固化土中的作用与水化产物生成
量密切相关。将粉煤灰看作外掺一定量的高效固化剂,当量固化剂量可由P&D 系数
与粉煤灰掺量的乘积获得,其大小与固化剂用量和龄期密切相关,随龄期的增加大体
呈现增加趋势,但增加速率有所降低。
(4)量化腐殖酸对固化土强度的影响,考察固化材料用量与腐殖酸含量对固化
土体物性指标的影响,建立固化有机质土的强度综合计算模型:基于腐殖酸反活性系
数的计算,可得到固化有机质土的当量水泥总量(Cfh)与有效固化剂掺量(Cec)。固
化土体一定龄期孔隙比(etH)可表示为土体初始物性指标、Cec 和养护龄期的函数。
分析固化有机质土强度与etH/Cfh 的关系,最终建立基于土体基本物性参数的固化有
机质土强度计算模型;测试了高效固化剂混掺粉煤灰固化滩涂淤泥各龄期的强度,同
经固化有机质土强度计算模型得到的计算结果对比,可知强度计算模型用于滩涂淤
泥仍具有较高的准确性。
关键词:饱和软土;高效固化剂;再造有机质土;强度特性;计算模型

STUDY ON THE HIGH-EFFICIENCY STABILIZER FOR
SATURATED SOFT CLAY AND STRENGTH
CHARACTERISTICS OF STABILIZED CLAY
ABSTRACT
To solve the problems of the soft clay with characteristics of high water content, low
strength, high compressibility and poor effectiveness of conventional cementing materials,
different types of admixtures were selected and a Portland cement-based high-efficiency
soil stabilizer was developed by single factor and orthogonal testing analysis. The influence
of the addition of soil stabilizer and fly ash on the fundamental parameters of soft clay was
investigated and the parameters were normalized. And then, the integratedstrengthcalculation
models accounting for the quantitative analysisof the effects of soil stabilizer
and fly ash were established. The mechanical properties of soft clay with different contents
of organic matter stabilized with high-efficiency soil stabilizer and fly ash were tested and
the unti-pozzolanic effect and factors were proposed.And the unti-pozzolanic factors were
calculated by water-soil-stabilizer models. According to the experimental results,
theintegrated strength-calculation models for stabilized organic clay accounting for
fundamental parameters were established. Based on the above study, the following
innovationproducts can be achieved.
(1) A type of Portland cement-based high-efficiency soil stabilizer was developed and
the mechanisms of the stabilizer were studied on Shanghai soft clay. On the basis of the
theory of improving the pH value of the soil, increasing the early term strength and middlelong
term pozzolanic effect, sodium silicate, calcium chloride and sodium hydroxide were
selected to stabilize the soft clay snd silt by chemical precipitation. The composite promoter
was prepared by calcium chloride and sodium hydroxide at the mass ratio of 1:1. The final
formula of the stabilizer (CSCN) was confirmed by orthogonal experiment and the mass
ratio of the Portland cement, sodium silicate and composite promoter is 5:1:2.
Theexperimental results indicate that the compressive strength of the specimens stabilized
with 12% CSCN at different curing ages almost equaled to that of specimens stabilized with
20% cement. The mineral and microstructure characterization indicate that there were more
cellular hydrated calcium silicate (C-S-H) gels produced in the CSCN stabilized specimen.
This observation implied that the strength and structure of the stabilized soil might be
influenced by the amounts, structures and types of C-S-H gels.
(2) The pozzolanic factors were proposed and the the effects of admixtures on
stabilized clay were quantificationally analyzed.Based on the definition of the pozzolanic
materials, the admixtures in the stabilized clay can be regarded as pozzolanic materials.
Hence, the use of the admixtures was assumed as the addition of a certain amount of cement.
And the euqalivent cement of the admixtures could be calculated by the product of the
pozzolanic factors and the content of the admixtures. According to the water-soil-cement
models, the values of the pozzolanic factors of admixtures (k1, k2) could be obtained by
multiple linearregression. In addition, the values of pozzolanic factors varied with curing
time, and the k1 values of the assistant agent decreased with curing time and the k2 values
of the composite promoter increased with curing time. The possible reason for this
phenomenon was that the assistant agent plays a role of early strength agent and the longstrength
pozzolanic effect of composite promoter was more remarkable.
(3) The mechanisms of fly ash in stabilized clay were investigated, andthe pozzolanic
and dispersing (P&D) effects were proposed. The application of fly ash in stabilized clay
had several effects, such as pozzolanic and filling effects. In fact, the C-S-H gels could bond
amounts of soil particles and some big gel-soil clusters were formed. Hence, the dispersing
effect can be explained that the big cluters were dispersed into some small cluters by fly ash
particles. Therefore, the effects of the fly ash in stabilized clay could be influenced by the
amounts of the generation of the C-S-H gels. Fly ash is a type of pozzolanic material, and it
can also be regarded as the addition of a certain amount of CSCN in the stabilized caly. The
equivalent CSCN of fly ash can be achieved by the product of the P&D factors and fly ash
content. The values of kF were determined by the CSCN content and the curing time. The
analysis results indicate that the P&D factors presented an increasing tendendy with curing
time. It’s notable that the increasing rate decreased with curing time.
(4) The influence of organic matter (humic acid) in soft clay on the compressive
strength of stabilized clay was analyzed quantitatively and the integrated strengthcalculation
models for CSCN-fly ash stabilized organic clay on the basis of fundamental
parameters were obtained. Based on the calcution of the unti-pozzolanic factor of humic
acid, the total cement content (Cfh) and effective stabilizer content (Cec) were defined. The
void ratio (etH) of stabilized organic soil at different curing times can be expressed by the
fundamental parameters of the soft clay, Cec and curing time. Based upon the above results,
these fundamental parameters were normalized by defining some variables. The relationship
of compressive strength to etH/Cfh was analyzed, and theintegrated models for calculating
the strength of stabilized organic clay were established. In addition, the compressive
strength of Lianjiang silt stabilized with CSCN and fly ash at different curing ages was
measured. The testing results were compared with the predicted values calculated by the
integrated strength-calculation models. It can be concluded that the strength-calculation
models achieved from Shanghai soft clay is also suitable for silt.
KEY WORDS:Saturated clay, High-efficiency clay stabilizer, Artificial organic soil,
Strength characteristics, The integrated strength-calculation models
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xinli_zhao
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