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1、 袋装砂井法在桥梁工程软土地基处理中的应用 摘 要:袋装砂井是一种常用的软土地基处理方法。分析了软土地基的工程特性和袋装砂井的优点,阐述了砂井选用和布置要点,概述了袋装砂井的施工工艺。 关键词: 袋装砂井法 软土地基 施工工艺 在江河湖泊附近修建铁路桥梁时,会不可避免地遇到软土地基。在软土地基上修建桥梁时,遇到的比较麻烦的问题是天然地基承载能力不足。而桥梁基础要求地基应有足够的承载力,符合要求的沉陷变形。为了保证持力层有足够的强度,确保桥梁不发生因不均匀沉降而倾斜损毁
2、,就需要对软土地基采取加固措施。在桥梁工程软土地基处理过程中,常用的方法是砂井法或袋装砂井法。该文简要分析软土地基的工程特性和袋装砂井法的施工工艺。 1 软土地基概述 软土是在静水或缓慢流水环境中以细颗粒为主的近代沉积物,是一种呈软塑状态的饱和粘性土,包括淤泥、淤泥质土和部分冲填土、杂填土及其他压缩性土。由上述软土构成的地基称之为软土地基,其广泛分布于我国东南沿海地区和内陆江河湖泊的周围。软土地基主要有以下工程特性:(1)含水量高、空隙比大。一般含水量在3580,空隙比为12。且含水量越大,土的抗剪强度越小、压缩性越大。 (
3、2)抗剪强度低。根据工程试验结果,我国软土的天然不排水抗剪强度一般小于20kPa,其变化范围约在525kPa,有效内摩擦角约为2035,固结不排水剪内摩擦角为1217。(3)压缩性高。一般正常固结的软土层的压缩系数为0.51.5MPa-1,最大可以达到4.5 MPa-1,压缩指数C约为0.350.75。 (4)渗透性小。软土的渗透系数一般约为ix10-6ix10-8cm/s,固结速率很慢。当软土曾厚度超过10m,要使土层达到较大的固结度往往需要5年至10年或者更久。 (5)具有明显的结构性和流动性。软土一般为絮状结构,在荷载作用下,软土承载剪应
4、力的作用产生缓慢的剪切变形,并可能导致抗剪强度的衰减,在主固结沉降完毕之后还可能继续产生可观的次固结沉降。 2 袋装砂井简介 袋装砂井的作用原理与一般砂井完全相同,它的作用原理是:袋装砂井加载预压,使空隙水能就近流入砂井,并通过砂井作为排水通道而排出地面,缩短排水固结时间,增强处理效果。 2.1 袋装砂井的优点 袋装砂井与普通砂井相比具有显著的优点。 (1)袋装砂井能适应软土固结产生的地基变位,在受力时能与地基变形相协调,故砂井的
5、连续性不会受到砂井错位、断颈等影响。 (2)袋装砂井直径大为缩小,目前我国采用直径多为7cm,加固同样面积的土,袋装砂井的用砂量要比普通砂井少得多,能节省费用近半。 (3)袋装砂井施工机具轻便简单、效率高,一般每台班(8h)可打设100根左右。 (4)袋装砂井打设时,排泥量较普通砂井要少,对土体扰动也小,施工比较便捷,对周围影响也小。 2.2 袋装砂井的选用 袋装砂井适用于软土地基处理,特别是用于软土地基中存在连续薄砂层时更为有
6、效;但对于渗透性好的以及含有大量腐殖物的土效果不显著,不宜采用。在选择袋装砂井排水法加固地基时,需要注意原地基的固结状态。如在先期固结压力(原已压密稳定的最大压力)已超过设计堆载压力值时,加载就不可能产生超静水压,砂井即无排水效果;如先期固结压力值达到加载的一部分时,则堆载在该部分作用下砂井亦无排水效果。对于灵敏度高的软土采用砂井法时,要注意其融变性,特别是采用封底钢管冲击法(或振动法)施工时,土体结构受机械扰动而破坏,打井后短期内反会使强度降低。 2.3 砂井布置 普通砂井直径一般为3040cm,护管砂井直径可小到15cm,袋装砂井直径可小到
7、712cm。砂井间距是指相邻砂井中心之间的距离,是影响固结速率的主要原因之一。砂井间距一般为砂井直径的610倍,常用24m。砂井平面布置形式有正方形和正三角形两种。正方形排列时,每个砂井的影响范围为一个正方形;正三角形排列时,每个砂井影响范围为一个正六边形。砂井长度一般为1020cm,具体应用时,需根据软土层的厚度、荷载大小和工程要求而定。一般来说,砂井不一定都要穿过整个软土层,当软土层不厚、底部有透水层时,砂井应尽可能穿透软土层;如软土层较厚或土中夹有砂层时,有否必要将砂井穿透软土层应按工程要求和土质条件等情况而定。在砂井顶部应铺设砂垫层,可作为良好的排水通道,并与各砂井连通,从而将水排至场
8、地以外。砂垫层的宽度应大于堆荷载或建筑物的底宽,并伸出砂井区外边线2倍砂井的直径;施工过程中应保持垫层不受扰动,铺设平整,垫层用砂要求与砂井相同,垫层铺设厚度一般为50cm左右。 3 袋装砂井的施工工艺 袋装砂井与普通砂井的施工工艺基本相同,如砂井的成孔方法、使用的机械设备以及堆载预压等。该文简要介绍其施工工艺。 3.1 施工工序 袋装砂井施工工序分为两种,即现场灌砂成井和预制砂袋直接投放孔内成井。 现场灌砂成井工序为:&n
9、bsp; (1)将钢套管(下端用可开闭的底盖或预制桩靴)打入土中要求的深度(管径较砂袋直径大,一般袋装砂井直径为7cm,导管采用 894.5无缝钢管); (2)将准备好的砂袋,长比砂井长2m,扎好下口后向袋内灌入洁净的粗砂约20cm上下(高度)作为重压,放到套管沉到要求深度; (3)在将砂井放入套管内不能达到要求深度,会有一部分拖留在地面,此时需机械排泥处理,继续下沉达到规定深度; (4)将袋口固定于装砂漏斗,通过振动装砂入袋,砂装满后,卸下砂袋,拧紧套管上盖,然后一般把压缩空气送进套管,一边提升套管直至地面。预制砂袋直接投放孔内成井工
10、序: (11)预先在砂袋里装满砂料,并将上口扎结牢靠,运送到现场,弯成圆形堆放; (2)套管成孔后,随即将预制砂袋投放孔内,拔管成井。 3.2 质量控制 2(1)每根砂井的长度均须露出地面50100cm,伸入砂垫排水层以利于排水通道流畅,如果长度所留很少或多余过多(可能砂袋被拔套管时部分带出)皆应重新施工,以保证成井质量。 (2)采用袋装砂井时,砂袋必须选用透水性和耐水性好以及韧性较强的麻布、再生布或聚丙烯
11、编织布制作。 (3)灌入砂袋的砂,应捣固密实;砂井位置的允许偏差为该砂井的直径;垂直度的允许偏差为1.5。 3.3 堆载预压 一般情况下,预压荷载的大小宜接近设计荷载,必要时可超过设计荷载1020。施加预压荷载,任何情况下作用于地基的荷载不得超过地基的极限荷载,以免地基失稳破坏,在需要施加较大荷载时,应分级加载,并控制加荷速率,使之与地基的强度增长相适应。当达到以下条件时,可以进行卸荷:(1)地面总沉降量达到预压荷载下计算最终沉降量的80以上;(2)理论计算的地基总固结度达到80以上;(3)地面沉降
12、速度已降到0.51.0/d以下。 4 结语 软土地基是铁路工程施工中经常遇到的地质情况,为避免其影响桥梁构造物的稳定性,必须对其进行加固处理。袋装砂井法是一种常用的处理软土地基的方法,它施工简便、节约材料、效果显著,在工程施工中应用较为广泛,并取得了较好的工程效益和经济效益。参考文献: 1郭文,王汝恒,初文荣等. 软土地基的工程特点及震害影响J. 四川建筑,2006,24(4):5960.2杨文渊,徐犇. 桥梁施工工程师手册M. 北京:人民交通出版社,2003.organization system
13、and working mode, the selection of a number of municipal strengthening group to build innovation and strengthen the organization of the basic level organizations advanced model.(seven) the manual work of the Communist Youth League Organization published and League branch of manual work, to promote t
14、he use of two manuals in the citys organizations at various levels. The county committee, directly under the group (work) is under the jurisdiction of grassroots League and group (total) using branch ratio shall not be less than 70%.Three, to further strengthen the groups leadership and team buildin
15、g(a) to strengthen the leagues leadership at all levels of construction. Continue to do a good job of municipal Party Committee Organization Department on the strengthening of the Communist Youth League cadres management opinions implementation. To promote the group counties (autonomous counties, ci
16、ties) Commission and city directly under the group (workers) appointed to carry out the Five team building activities. Improve the League Association Department working mechanism. Conscientiously fulfill the duties of CO, combined with the city group directly under (the) Committee of the general ele
17、ction and the adjustment, actively jointly with the unit where the party organization department good group leadership selection with the work. Do a good job in municipal Party committee assistant committee leadership and leading cadres of the annual assessment work, adhere to and improve the assist
18、ant secretary of the Communist Youth League talk system group To weave individual conversation and collective conversation, to strengthen the committees of all levels, the Standing Committee of the Standing Committee, the establishment of a sound system of central group learning, the system of inves
19、tigation and study, the system of important issues and the reporting system.(two) to strengthen the work of education and training of cadres to conscientiously implement the Central Committee. On the implementation of grassroots cadres training project and opinions on carrying out the mission munici
20、pal CYL Cadres training project implementation opinions, full implementation of the project of the City Youth League cadres training education. Focus on the county grassroots cadres and workers focused on training, the new school system vocational training League cadres, for the Municipal Organizati
21、on Department jointly held the third session of the Communist Youth League system training cadres in party. Focusing on the construction of new socialist countryside, strengthening village cadres and rural construction team group member of the young team, the county organizations at various levels t
22、hroughout the year is expected to train 100 00 rural grassroots cadres, plans to train 1000 village secretary of the village Party branch.(three) actively promote grassroots cadres election work. Under the unified leadership of the party organization, to strengthen grassroots organizations direct wo
23、rk, standardize the election work rules and procedures, in the designated candidate, open competition to democratically elected branch secretary at the same time, actively and steadily the development of Township, streets and other grassroots organizations in the direct election of the pilot work, o
24、n the basis of summarizing the experience and gradually expand the scope of the pilot, and gradually formed a set of measures and cadres election system.(four) to strengthen the cadres testing exercise. To study the development of XX city from 2006 to 2008 cadres testing exercise planning. To select
25、 outstanding cadres to the central mission in Beijing, Shanghai, Guangzhou and other central organs and sending work in developed areas. With the Central Committee the implementation of the western region and ethnic minorities cadres training plan . To carry out the eighth batch of municipal organs
26、attachment cadre management, selection, training work. The outstanding cadres to start the National Development Bank XX branch testing exercise.(five) to strengthen the group construction. The main position to play the role of Youth League cadre education and training as the city, in accordance with
27、 the requirements of post training, further curriculum scientifically and rationally, adopt arrangement menu course, basic theory includes group work, focus, hot and difficult issues, to enhance the content and practice; to strengthen the construction of teaching staff, the integration of teachers,
28、establish a quality teacher training team, establish and implement course evaluation system; take delivery of training to the countryside, on-site training, and increase the rural grassroots cadres training efforts.Four, efforts to strengthen the work of young talent(a) to tenth XX young 54 medal in
29、 recognition of the publicity, and actively explore the XX youth service. 54 Medal of institutionalization, standardization and socialization mechanism. Give full play to the XX award in recognition of 54 youth medal Association, Youth Award winner in the 54 chapter, investigation activities. Who wo
30、n the Youth Service medal, dedication to the society to create conditions, build the stage. During the 54, named in recognition of the tenth XX young 54 medal. The association of XX editing of young talent , the exchange of information and communication platform for the XX of outstanding young talen
31、ts.(two) the establishment of municipal Party committee of young talent information database. In accordance with the feasible, effective, classification management, implement step by step principle, the establishment of municipal Party committee of youth talent database; guiding organizations at var
32、ious levels generally established the young talent database, construction of city, county (directly under the Communist Youth League), grassroots organizations three young talent information database the relevant information collection system, and gradually establish the citys young people, the Comm
33、unist Youth League youth talent information network, provide information platform for young talent resource development.Five, take effective measures to strengthen the mission management(a) to strengthen the mission management work. Strengthen the dues collection and management, continue to adhere t
34、o the dues collection regularly reporting system, the annual comprehensive award in recognition of the tour and the tour one vote veto system audit system. Do statistical work in the group. The group service award in recognition of the advanced units, standardization, promoting group management work
35、 institutionalized.(two) to strengthen the organization of research and information exchange efforts. Grassroots carry out research, efforts to form a number of theoretical results. Make full use of the network carrier, to explore the establishment of electronic group service system, promote the wor
36、k of Communist Youth League information.Attachment 4:XX municipal Party Committee Propaganda Department of the Communist Youth League work pointsIn 2006, the Communist Youth League propaganda ideological work XX to Deng Xiaoping theory and the important thought of Three Represents as guidance, study
37、 and implement the partys sixteen and the spirit of the the fifth Plenary Session of the 16th CPC Central Committee implementation of the eight plenary session of the two committee, the citys cultural work conference, the Propaganda Department of the meeting and the the fourth Plenary Session of the
38、 15th CPC Central Committee permanent mission spirit, closely around 11th Five-Year XX the goal of full implementation of Scientific Outlook on Development, emancipating the mind, seeking truth from facts, keep pace with the times, close to reality, close to life, close to the young, persevere grasp
39、 orientation, grasping deepening, grasping construction innovation, further improve the groups propaganda and ideological work ability, unity To guide the majority of members of the youth to achieve the 11th Five-Year planning tasks, the overall construction of a well-off society, building a sociali
40、st harmonious society to make new contributions.One, adhere to the Three Represents important thought and Scientific Outlook on Development education to guide the youth, to further strengthen the ideological and political education of youth(a) armed with youth science theory. Unremittingly with Deng
41、 Xiaoping theory and the important thought of Three Represents armed members of youth education, to promote the study and implement to expand the depth and breadth. To study and implement the important thought of Three Represents with the establishment and implementation of Scientific Outlook on Dev
42、elopment combine with the implementation of the requirements of constructing socialist harmonious society with Scientific Outlook on Development, carry out education as an important part of the theory of armed youth in the new period, strengthen the establishment and implementation of Scientific Out
43、look on Development education, educate and guide the youth to fully understand the great significance of establishment and implementation of Scientific Outlook on Development, in-depth understanding of the Scientific Outlook on Development era back The king, the practice foundation, basic connotatio
44、n, historical status, spirit and practice requirements, a profound understanding of Scientific Outlook on Development with Marxism Leninism, Mao Zedong thought, inheriting and developing relationship between Deng Xiaoping theory and the important thought of Three Represents, to help young people est
45、ablish and consciously practice Scientific Outlook on Development. Persist in learning, grasping the backbone, grasp the practice, grasp the opportunity. Catch club, effective way to grasp the network, with the group of cadres, young students and young backbone fronts as the focus, to promote the wo
46、rk of the armed youth theory to develop in depth, to help the youth continue to firm ideals and beliefs, to build a powerful spiritual pillar. To carry out the study and implementation of the partys sixteen session of the five Eight plenary session of the two plenary session of the Central Committee
47、 and the party spirit, to the citys Youth League members thinking into the spirit of the meeting, to achieve the goal of national consciousness and XX economic and social development in 11th Five-Year period. Contribute to help and guide the youth to a profound understanding of the significance and
48、main task of building a socialist harmonious society, actively join the construction of socialist harmonious society.(two) to strengthen the ideological and moral construction of teenagers. Thoroughly implement the central spirit of the document No. 8, No. 16 and the program for Improving Civic Morality to minors and students as focus groups, to strengthen and improve the ideological and moral construction of minors and the ideological and political education of college students. Make full use of the spirit and the spirit of the
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