j土力学第六章 天然地基承载力.doc
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1、difficult, not hating; blueprints, not rhetoric; words and simple, but full of love, truth, passion, entrepreneurial passion. Take this opportunity, my inspirational quotes Li Dazhaos classic iron specialise in uplifting blend with the article gave everyone, with a view on how to do well under the n
2、ew situation of township and village leaders inspire and help, and also share with you. A good play to create iron shoulders strong arms, to assume the burden be passed; only specific qualities, will it be possible in specific areas to create a world. In my view, village chiefs in the new situation,
3、 we must first have five basic quality. One ambition is to pioneer. Who is handsome. People only high-minded can stimulate the flow of momentum to become brave and persistent, become quiet and powerful. Township and village party leaders, within their respective jurisdictions, political stability an
4、d economic and social development issues, decisions and orientation depends to a large extent because of your. Everybody in village chiefs and the positions, both the trust of the masses, the Organizations trust, more ability to you, fully affirmed the moral and other qualities. Therefore, we must a
5、lways maintain the historical mission and social responsibility, and our ideal tree rooted in the hard work of the soil, with indomitable spirit, indomitable courage to open up a new situation of villages and towns. To have a feeling of closeness to the second. The people and country. Our business f
6、oundation in the peoples blood in the people power people. Advanced decisions of the party cadres to the feelings of the people is an eternal theme. Fan Zhong-yan, called first, and enjoy comfort about others, Zheng Banqiaos also wrote a Ya Chai lay listening to the rustling of bamboo, the suspect i
7、s suffering. Cao County officials, little my, a total turn off. Old of feudal official even has so feelings, alone we is to serving for purposes of people servant does? we more should always hold with on people of deep feelings, heart Department masses of leading visited tea, care masses of emotions
8、 thoughts complained, always insisted put masses of interests put in first, consciously from itself do up, from small do up, from masses most care, and most directly, and most reality of interests problem grabbed, real do love for people by Department, and right for people by with, and Lee for peopl
9、e by conspiracy to. Three with the fame of mind. Non-indifferent not insist your dream, without serenity not go far. Ascension to fame is morality, is the sublimation of the soul. As Township and village, be sure to maintain a normal state of mind, establish a correct viewpoint on power, position an
10、d values and Outlook, as fame is light like water, depending . 50 km, also red and like hundreds of thousands of the KMT military combat, but he went on to collect a variety of newspapers and magazines, and then race against time to pore over. As long as the study of mind, it is not necessary to com
11、e to the library, workshops, into the villages, people learned farming techniques, problem-solving methods, participation in第六章 天然地基承载力第六章 天然地基承载力引言结合第四章的铁道校区的主教学楼案例,启发学生引出地基承载力的计算问题,进一步引出一下概念:天然地基、人工地基、地基承载力、极限承载力、容许承载力。 6.1 地基的破坏形态一、地基破坏的三种形态1整体剪切破坏(general shear failure)基底剪切破坏面与地面贯通,形成一弧形滑动面。密实砂土
12、,基础埋深很浅;或饱和粘土,荷载急速增加的情况下,极易造成整体剪切破坏。2局部剪切破坏(local shear failure)地基中剪切面延伸到一定位置,未扩展到地面。一般性粘土或中密砂土,基础埋深较浅;或基础埋深较大时,无论是砂性土或粘性土地基,最常见的破坏形态是局部剪切破坏。 图6.1 整体剪切破坏 图6.2 局部剪切破坏3冲切破坏(punching shear failure)松砂或其它松散结构的土,易造成冲切破坏。基础边形成的剪切破坏面垂直向下的发展。备 注采用设问法,引出本章要研究的内容。注意三种地基破坏形态的破坏面对比,PS曲线对比。图6.3 冲切破坏第一种在理论上研究较多;第三
13、种在理论上研究得很少,因为作为建筑物地基,很少选择在松砂或其它松散结构的土层上,故无研究必要;第二种破坏形态在天然地基中经常遇到,其理论工作在前一阶段进展较慢,近年来研究已有了突破性进展。二、地基变形的三个阶段地基的变形可分为三个阶段:1. 当P Pa 时,为弹性变形阶段;2. 当Pa P Pk 时,为塑性变形阶段。三、确定地基容许承载力的方法1. 按控制地基中塑性区开展深度的方法。只要地基中塑性区的开展深度小于某一界限值,地基就具有足够的安全储备。2. 按理论公式推求地基的极限荷载Pk再除以安全系数的方法。3. 按规范提供的经验公式确定地基的容许承载力。4. 按原位测试的方法确定地基的容许承
14、载力。备 注介绍冲切破坏研究的进展情况。结合整体剪切破坏的PS曲线对比,介绍后面几节的内容是围绕这四种方法讲解。 6.2 地基临塑压力一、地基临塑压力当地基土中仅个别12个点的应力达到极限平衡时,基底压力称为临塑压力(critical edge pressure)。二、理论公式推导过程1. 计算图式图6.4临塑压力计算图式2. 推导过程 条形基础下任一点N的是由引起的大小主应力和 (6-1) 土体自重在N点产生的应力s1、s3s1 = g (H+Z)s3 = K0 s1 = K0 (H+Z) 为简化计算,假设K0=1,相当于静水压力的受力状态。 备 注采用设问法,师生互动,推导时围绕土中一点的
15、极限平衡方程。 假定N点达到了极限平衡,将s1、s3代入极限平衡方程得: 由上式求得N点的深度: Z = 塑性区的最大深度Zmax 由,得到= =0 y=p/2 -j Zmax = 临塑压力pa。当Zmax=0时,求得pa=0得: 当j=0时,pa=cp+gH所以pa当j=0,H=0时(即地基在表面荷载作用下): Pa=cp备 注讨论:临塑压力与那些因素有关?为什么与基础宽度无关? 6.3 浅基础地基极限承载力的近似解一、普朗德尔的极限承载力理论1.计算图式图6.5 破坏图式2基本假设(1)基底光滑,剪应力为零;(2)地基土自重为零,即g=0,c0、q00,算出地基极限压力;3. 计算(1)极
16、限平衡区sa=ob=on-bn=on-nn1=s1-(pi+s1)sinf=pk-(pi+pk)sinf=pk(1-sinf)-pisinf 式中pi=c.ctgf,sa与深度无关,它在BC上的分布为常数。(2)极限平衡区sp=ob=om+mb=om+mm1=s3+(pi+s3)sinf= =q0(1+sinf)+pisinf sp与深度无关,它在BE上的分布为常数。(3)过渡区对数螺旋线的表达式为:备 注首先介绍本节的公式推导思路,分三步走,循循善诱,娓娓道来。详细讲解计算图式。围绕摩尔应力园讲解。法向应力sa对B的力矩为;法向应力sb对B的力矩为;对数螺旋线上的粘聚力对B点的力矩为由于扇形
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