天津外环线调线工程软土地基水泥搅拌桩加固施工技术

目录摘要··········································································I第1章前言······································································11.1工程概况···················································································11.2工程地质、水文概况····································································11.3水泥深层搅拌桩技术的特点···························································1第2章软土地基处理和水泥搅拌桩原理·····································22.1软土地基处理技术·······································································22.2水泥搅拌桩原理和作用·································································2第3章试桩·········································································4第4章施工准备···································································5第5章施工工艺及施工控制····················································65.1施工工艺流程·············································································65.2设计参数要求·············································································65.3施工工艺···················································································6第6章质量保证措施·····························································86.1质量控制措施·············································································86.2质量控制要点·············································································96.3质量检验措施·············································································106.4施工质量管理措施·······································································106.5冬季施工保证措施·······································································116.6质量保证措施·············································································11第7章质量检测···································································137.1质量检测方法·············································································13第8章安全及环保要求··························································148.1安全要求···················································································148.2文明生产及环保要求····································································15参考文献···············································································16I摘要水泥搅拌桩是进行软基处理的一种有效形式。本文结合本人这几年工作的经验以及所见、所闻介绍了水泥搅拌桩施工中试桩、施工准备、施工工艺流程、设计参数及要求、施工控制、质量检验等控制环节。其是采用水泥等材料作为固化剂,通过深层搅拌机械对淤泥、淤泥质土、粘土、亚粘土等进行深层搅拌,提高地基土承载力。关键字：软基处理水泥搅拌桩施工控制1第1章前言水泥搅拌桩多用于软土层的地基加固处理工程中，其基本原理是基于水泥加固土的物理化学反应过程，可通过专用机械设备将水泥喷入处理的软土地基内，并在喷注过程中上下搅拌均匀，使水泥与土发生水解和水化反应，生成水泥水化物并形成凝胶体，将土颗粒或小土团凝结在一起形成一种稳定的结构整体，这就是水泥骨架作用，同时，水泥在水化过程中生成的钙离子与土颗粒表面的钠离子进行离子交换作用，生成稳定的钙离子，从而进一步提高土体的强度，达到提高地基承载力的目的。用水泥搅拌桩处理软弱地基效果显著，处理后可很快投入使用。1.1工程概况本文涉及的水泥搅拌桩位于第五标段WK11+250.260—WK11+489.525，软基处理平均长度239m，宽度47.2m，水泥搅拌桩5098根，总长40784m，桩径0.5m，桩横向桩距为1.6m，纵向桩距为1.39m，成等边三角形布置。1.2工程地质、水文概况本文涉及水泥搅拌桩为鱼塘处理，桩位岩层主要为素填土、粉质粘土、粉土、粉砂土等。1.3水泥深层搅拌桩技术的特点1.适用范围广。水泥深层搅拌桩技术适用于淤泥、淤泥质土、粉质粘土、粉土等软土地基，目前在粉砂土地基中最大施工深度达19米。2.处理可靠，渗透系数小。采用双排梅花型的布置形式，处理更加可靠，水泥土28天龄期的抗渗系数小于a*10-7cm/s。3.施工机具简单。所用的施工机具比较简单，目前市场上有生产。4.充分利用软土。由于利用深层搅拌机就地将土体和水泥固化剂强制进行搅拌，充分的利用软土，避免了大量挖掘和弃土。5.对周围环境无污染。在加固过程中对周围土体无扰动，施工时无振动、无噪间，对周围环境无污染。2第2章软土地基处理和水泥搅拌桩原理2.1软土地基处理技术软土地基处理的目的是利用换填、夯实、挤密、排水、胶结、固结和加筋等方法对地基进行加固，从而提高地基的抗剪切强度、降低地基的压缩性、改善地基的透水性和地基的动力特性以及改善特殊土的不良地基特性等。目前高速公路软土地基的处理方法有：置换法、排水固结法、固化法、振密挤密法、加筋法等，其中置换法是用物理力学性质较好的岩土材料置换天然地基中部分或全部软弱土体，以形成双层或复合地基；排水固结法是指土体在一定何在作用下排水固结，空隙较小、抗剪切强度提高；灌入固化法是向土体中灌入水泥、石灰、或其它化学固化浆材，在地基中形成增强体；振密挤密法是采用振动或挤密的方法使土体密实；加筋法是在地基中设置强度高、模量大的筋材。无论何种地基处理方法，其目的都是提高地基承载力，减少工后沉降。各种软基处理方法有着各自的特点及适用条件，大量的工程实践表明，对于工期较紧的工程，利用水泥土搅拌法处理软土取得过良好的效果，但处理费用相对较高。而对于一些工期不紧的工程建设中，排水固结法也是常用的软土地基处理方法，因为它的处理费用相对要比水泥土搅拌桩低得多。现在工程一般均是工期很紧，特别是高速公路的建设，因此水泥土搅拌桩在高速公路软土地基处理中使用量较大。2.2水泥搅拌桩原理和作用水泥搅拌桩，也称旋喷水泥搅拌桩，适用于处理淤泥、淤泥质土、泥炭土和粉土土质。分为干法和湿法（在此只讲湿法）。湿法以水泥浆为搅入料，搅拌均匀，易于复搅，只是水泥土硬化时间较长。湿法搅拌必须采用双向搅拌桩。水泥搅拌桩是软基处理的一种有效形式，是利用水泥作为固化剂的主剂，搅拌桩基将水泥浆喷入土体兵充分搅拌，使水泥与土发生一系列物理化学反应，使软土固结而显著提高基础强度，从而提高软土地基承载力，达到提高加载速率的作用。固化剂水泥主要由硅酸三钙(3CaO·SiO2)、硅酸二钙(2CaO·SiO2)、铝酸三钙(3CaO·Al2O3)、铁铝酸四钙(4CaO·Al2O3·Fe2O3)等矿物质组成。这4种矿物成分的主要特征如下：硅酸三钙(3CaO·SiO2)的水化速度较快，水化热较大，且主要在早期放出。强度较高，3能不断得到增长，是决定水泥标号高低的最主要矿物。硅酸二钙(2CaO·SiO2)的水化速度最慢，水化热最小，且主要在后期放出。早期强度不高，但后期增长率较高，是保证水泥后期强度增长的主要矿物。铝酸三钙(3CaO·Al2O3)的水化速度极快，水化热最大，且主要在早期放出，硬化时体积减缩也最大。早期强度增长率很快，但强度不高，后期几乎不增长。铁铝酸四钙(4CaO·Al2O3·Fe2O3)的水化速度也较快，仅次于铝酸三钙。水化热中等，强度较低。固化剂水泥和软土中的水发生强烈的水解和水化反应，反应原理如下：2(3CaO·SiO2)+6H2O-3CaO·2SiO2·3H20+3Ca(OH)22(3CaO·SiO2)+4H2O-3CaO·2SiO2·3H20+Ca(OH)23CaO·Al2O3+6H2O-3CaO·Al2O3·6H2O4CaO·Al2O3·Fe2O3+2Ca(OH)2+10H2O-3CaO·Al2O3·6H2O+3CaO·Fe2O3·6H2O水泥经水化作用后，生成新的化合物为：氢氧化钙、水化硅酸钙、水化铝酸钙、水花铁酸钙等水化物，有的自身继续硬化形成水泥骨架，有的则因与活性的土进行离子交换和团粒反应、硬凝反应和碳酸化作用等，通过机械搅拌，将土颗粒粘结在一起，使土颗粒固结、结团、形成网状的结构，从而改善土的物理力学性质、达到加固软土地基的效果。4第3章试桩1.深层搅拌水泥桩适用于处理淤泥、淤泥质土、泥炭土和粉土。当用于处理泥炭土或地下水具有侵蚀性时，应通过试验确定其适用性。冬季施工时应注意低温对处理效果的影响。2.深层搅拌桩施工是藉搅拌头将水泥浆和软土强制拌和，搅拌次数越多，拌和越均匀，水泥土的强度也超高。但是搅拌次数越多，施工时间也越长，工效也越低。试桩的目的是为了寻求最佳的搅拌次数、确定水泥浆的水灰比、泵送时间、泵送压力、搅拌机提升速度、下钻速度以及复搅深度等参数，以指导下一步水泥搅拌桩的大规模施工。3.每个标段的试桩不少于5根，且必须待试桩成功后方可进行水泥搅拌桩的正式施工。试桩检验可采取7天后直接开挖取出，或至少14天后取芯，以检验水泥搅拌桩的搅拌均匀程度和水泥土强度。5第4章施工准备1.确定水泥掺入量为60kg/m，水灰比选用0.6，钻进、提升时管道工作压力0.1-0.2Mpa，喷浆时管道工作压力0.4-0.6Mpa，钻进速度≤1.0m/min，提升速度≤0.5m/min。2.平整场地：清除施工场地上的障碍物及杂物（包括树根、草皮、垃圾等）将原地