第24卷第4期水利水电科技进展2004年8月
用覆盖层土的浮重与渗透力计算基坑下承压水降深
葛孝椿
(安徽省・水利部淮河水利委员会水利科学研究院, 安徽蚌埠 233000)
摘要:通过对渗透力基本概念的分析, 指出用覆盖层土的浮重与覆盖层内渗透力计算基坑下承压水
降深比用覆盖层湿土重与层底水压力计算合理. 通过两种方法比较说明, 在基坑渗透稳定安全系数等于1, 后一种方法中覆盖层用饱和土重计算时两者是一致的; 但是, 在基坑渗透稳定安全系数大于1时, 通常前者计算的基坑下承压水降深小于后者; 当基坑下承压水降深一定时, 前者求得的基坑渗透稳定安全系数大于后者. 合理, 宜于采用, . 关键词:基坑降水; 承压水降深; 渗透力; 蚌埠闸中图分类号:TU46+3 文献标识码:A(2004) 04Ο0012Ο02 , , 的计算, 压水位. 计算基坑下承压水降深(以下简称降深) 的常用方法是将承压水层顶面以上到基坑底面之间的湿土重与承压水层顶面的水压力之比作为基坑渗透稳定安全系数(以下简称安全系数) . 但是, 当安全系数不等于1时, 上述计算方法与渗透力作用的概念并不相符, 而用覆盖层土的浮重与覆盖层内渗透力计算降深比较合理. 下面介绍两种降深(或安全系数) 的计算方法
, 并对两种方法进行比较, 最后通过蚌埠闸扩建工程降深的计算, 进一步说明两者计算结果的差异. 为了说明方便, 将承压水层顶面以上到基坑底面之间的弱透水土层简称为覆盖层(见图1) .
间的单位水平面积湿土重为(h p -h s ) ρc g , 其中h p 为基坑底面高程, 即基坑开挖后覆盖层顶面高程; h s 为砂层顶面高程, 即覆盖层底面高程; ρc 为覆盖层湿土密度; g 为重力加速度.
覆盖层底面水压力等于承压水层顶面水压力, 单位水平面积上水压力为(h -h s ) ρw g , 其中h 为基坑承压水降后水位; ρw 为水的密度. 安全系数k 为承压水层顶面以上到基坑底面之间的单位水平面积上湿土重与承压水层顶面水压力之比, 即
() ρ(1) k =
(h -h s ) ρw 基坑降水前的承压水位与式(1) 计算的安全系
数满足要求的承压水降后水位h 之差即为降深. 式
(1) 适用于覆盖层为绝对不透水层或底部存在绝对
不透水隔层的情况, 但在实际工程中这种情况难以见到. 1. 2 按覆盖层土的浮重与覆盖层内渗透力计算安全系数———方法2
图1 基坑降水示意图
1 两种计算方法及其比较
1. 1 按覆盖层湿土重与层底水压力计算安全系数
由于覆盖层土体内存在孔隙, 下面又有承压水, 因此覆盖层土体内总会受到渗透力的作用. 基坑开挖前, 覆盖层在地基承压水的长期作用下, 一般已处于稳定渗流状态, 基坑开挖仅使渗透力进行调整; 又由于水利工程基坑开挖面大, 历时较长, 因此可按稳定渗流考虑. 覆盖层单位水平面积土体的浮重为(h p -h s ) ρg , 其中ρ为覆盖层土体的浮密度. 覆c ′c ′
———方法1
如图1所示, 承压水层顶面以上到基坑底面之
) , 男, 江苏南京人, 教授级高级工程师, 从事堤坝变形、作者简介:葛孝椿(1936—渗流和稳定分析研究.
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盖层内平均竖向渗透比降j 为
j =
h p -h s
重, 将会产生渗流破坏. 为了保证新闸基坑施工安全, 并且确保老闸不致因承压水位降低而产生有害沉降, 必须降低砂层承压水水头, 进行砂层承压水降深计算. 2. 2 按方法1计算安全系数及降深
根据文献[1]得蚌埠闸扩建工程基坑降水设计
33
中的h s =-110m , ρc =1192g/cm , ρw =110g/cm , Δh =h p -h s . 由于安排非汛期施工最低部工程, 所以承压水位(降前) 设计值用1615m , 由建筑物各部位底部高程确定的h p 见表1, 根据各种基坑承压水降后水位h , 对不同部位的h p 代入式(1) 求得相应的安全系数k , 见表1.
表1 按方法1计算与基坑承压水降后水位h
相应的安全系数
h p /m 6619盖710抛石槽710堤基清淤715下游引河910上游引河915堤基回填1010
[***********]10151110
作用于覆盖层单位水平面积土体的渗透力(方向向上) 为j (h p -h s ) ρw g =(h -h p ) ρw g.
安全系数k 为覆盖层单位水平面积上土体浮重与渗透力之比, 即
k =
() ρ′(h -h p ) ρw
(2)
1. 3 两种计算方法比较
当安全系数k =1时, 从式(1) 可得:
ρh p -h s =(h -h s )
ρc
(3)
由于基坑顶面高程低于承压水水位, 所以ρc 可用饱
和密度代替, 故有ρ+ρc =ρc ′w , 代入式(3) 并整理得
() ρ′(4) =1(h -h p ) ρw 可见, 当k =1时, 式(4) 即式(2) , 说明在k =时, 上两种方法是一致的. 但是, 在k , 推导不能成立, . , 若(h -h s ) /ρ2) 求得的安全c >(h -h p c 系数k 大于用式(1) 求得的; 反之, 则用式(2) 求得的小于用式(1) 求得的. 在覆盖层土的饱和密度约等于2倍浮密度, 以及ρ≈ρc ′w 的情况下, 可由上述不等式推求得:当(h p -h s ) >(h -h p ) , 即用式(2) 求得的安全系数k 大于1时, 用式(2) 求得的安全系数k 大于用式(1) 求得的; 反之, 则用式(2) 求得的小于用式(1) 求得的. 下面用蚌埠闸扩建工程降深的计算来说明两种计算结果的差异.
h 时的安全系数k
18. m 16511. 0m 10. 0m 9. 0m
[***********][***********][***********][***********]11481163
[***********][***********][***********]922117
施工组织设计采用k =1110, 从表1中可见, 消
力池是控制情况, 所需要的承压水降后水位h =1110m , 所以降深为1615m -1110m =515m. 2. 3 按方法2计算安全系数及降深
覆盖层土的ρ=0192g/cm 3, 其余数据同前, 但c ′是代入式(2) 求安全系数k , 计算结果见表2. 从表2可见, 仍为消力池控制, 所需要的承压水降后水位为1215m , 所以降深为1615m -1215m =4. 0m.
表2 按方法2计算与基坑承压水降后水位h
相应的安全系数
项目名称消力池闸底板铺 盖抛石槽堤基清淤下游引河上游引河堤基回填
h p
2 两种计算方法计算实例比较
2. 1 蚌埠闸扩建工程简介
蚌埠闸枢纽位于淮河干流, 蚌埠市以西, 涡河河口以下. 该枢纽由节制闸(简称老闸) 、电站、船闸和分洪道等建筑物组成, 其作用是蓄水灌溉, 兼有航运、发电和供水等功能. 根据淮河正阳关—蚌埠近期河道整治规划, 需扩大蚌埠闸(老闸) 的规模, 减少设计过闸落差, 因此对该闸进行扩建.
蚌埠闸扩建工程位于老闸北端与淮北大堤之间, 主要建筑物为新闸. 新闸同老闸轴线一致, 共12孔, 每孔净宽10m. 闸底板高程为9. 0m , 消力池底部高程为614m (均为黄海高程, 下同) . 闸址原地面高程为15. 0～1715m , 地基砂层承压水水位为1615～1810m , 砂层厚约27m ; 砂层以上为17m 厚的粉质黏土. 基坑开挖到闸底板和消力池底部高程时, 砂层承压水对覆盖层产生的向上渗透力远大于覆盖层浮
Δh
/m 1810m
/m [**************]
[***********][**************]74
[***********][**************]7
不同h 时的安全系数k
1615m 1310m 1215m 1210m 1110m 1010m [***********][***********][***********][***********][***********][***********][***********][***********][***********][***********]5510610112
910m [***********]21
从两种方法计算结果可见, 方法2计算的降深比方法1小115m ; 如果降深仍取方法1计算值515m , 则从表2中可得用方法2计算的安全系数为1148, 比方法1求得的大.
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性能, 但索引的创建是以浪费存储空间为代价的, 若在一个经常修改的数据域上建立索引, 则效果适得其反, 最终将造成系统性能的下降和存储空间的浪费. 通过分析, 可得使用索引的几个原则:①为经常出现在检索条件中的数据域建立索引, 如果数据域是经常一起出现在检索条件中, 那么建立复合索引; ②为了提高多表连接效率, 对经常用于表连接操作中的数据列应建立索引, 如果是多域连接则建立复合索引; ③在利用外键连接的表中, 外键上也应该建立索引.
c. 调整内存分配及相关的初始参数. 正确分配
动器上的多个文件, 使回滚段与数据字典、用户数据、
索引等分离开来, 减少I/O 的竞争. 同时独立使用回滚段, 可以减少用户数据表空间碎片的产生.
4 结 语
清江防洪与梯级调度仿真系统前期开发已经完成, 应用程序设计采用C ++, 界面设计采用VC ++, 各计算子系统利用Oracle 提供的Pro 3C 访问数据库,GIS 与三维仿真显示利用ODBC 访问数据库. 多次系统联合调试结果表明, 数据库管理子系统能为多个子系统提供有效的数据服务, 下一步的工作是继续完善功能, 进一步提高系统的性能. 参考文献:
[1]萨师煊北京:高等教育出版社,
R M odern client/server DBMS architectures
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[3]邵佩英. 分布式数据库系统及应用[M].北京:科学出版
内存资源可以改善高速缓存性能, 减少S Q L 语句的分析, 减少内存的分页和交换. 主要调整库缓冲区、数据字典缓冲区和缓冲区高速缓存的内存分配.
d. 优化磁盘I/O. 磁盘的I/O 速度对整个系统的性能有较大的影响, 将文件分散存储在不同的可用磁盘上, 这样事物处理所执行的磁盘访问不妨碍对相应的事务日志登记的磁盘访问, 从而减少对数据文件和事务日志文件的竞争, e. 优化回滚段. (, insert ,update ) 务开始以前的状态, 能力, 因而即使数据库其他部分设计得再好, 但如果回滚段设计得不合理, 仍将会严重影响系统的性能. 为回滚段建立一个独立的表空间数据, 可以包括在不同驱(上接第13页)
社,1998. 12.
[4]郭生练, 杨金星, 郭井. 水库调度综合自动化系统[M].武
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(收稿日期:2003Ο11Ο18 编辑:熊水斌)
4 结 论
a. 对承压水以上覆盖层为绝对不透水层, 或者
其底面存在绝对不透水隔层的情况, 按方法1计算安全系数或降深是正确的. 但是, 覆盖层通常为黏性土层, 土体内存在孔隙, 相对于承压水层而言均为弱透水层, 因此, 实际工程中难以出现上述情况.
b. 覆盖层为弱透水土层时, 按方法2计算降深比按方法1计算合理.
c. 当(h -h s ) /ρ时, 按方法2c >(h -h p ) /ρc ′
计算的降深比按方法1计算的小; 在降深一定时, 按方法2计算的安全系数比按方法1计算的大. 当安全系数等于1时, 两者一致.
d. 按方法2计算降深, 且(h -h s ) /ρc >(h -h p ) /ρ时, 所采用的最小安全系数可适当加大; 但c ′
3 用方法2计算的最小安全系数取值范围
鉴于方法2比方法1合理, 一般(h p -h s ) >(h -h p ) 时计算的安全系数比方法1大, 因此, 用方法2计
算时可将安全系数适当提高. 就像用圆弧滑动条分法
分析边坡稳定一样, 简化毕肖普法考虑了条块间作用力, 比瑞典法合理, 但是计算的稳定安全系数比瑞典法大, 规范(S D J218Ο84) [2]规定了用瑞典法计算的最小安全系数, 而用简化毕肖普法计算时, 安全系数提高5%～10%.由于简化毕肖普法比瑞典法合理, 因而新规范(S L274Ο2001) [3]则规定用简化毕肖普法计算安全系数, 而用瑞典法计算时, 安全系数减小8%, 说明新规范比老规范突出了较合理的简化毕肖普法. 能否参照这种精神确定两种降深计算方法的最小安全系数值得探讨. 目前G B5007Ο2002《建筑地基基础设计规[4]范》附录W 规定, 用方法1计算的最小安全系数为111, 所以用方法2计算的最小安全系数宜大于111, 但应小于新规范(S L274Ο2001) [3]中81214节规定的安
控制部位宜小于115. 参考文献:
[1]周国林. 深井降水在蚌埠闸扩建工程施工中的应用[J].
治淮,2002(12) :33～34. [2]S D J218Ο84, 碾压式土石坝设计规范[S].[3]S L274Ο2001, 碾压式土石坝设计规范[S].[4]G B5007Ο2002, 建筑地基基础设计规范[S]
(收稿日期:2003Ο11Ο25 编辑:熊水斌)
全系数下限值115, 因为土石坝为永久性建筑物, 而基
坑降水是临时性施工措施. ・32・
ADVANCES IN SCIENCE AN D
TECHN OLOG Y OF WATER RESOURCES
Measures for sustainable development and utilization of w ater resources in G uanzhong area/ZH OU Wei 2bo
(College o f
Environmental Science and Engineering , Chang ’an Univer sity , Xi ’an 710054, China )
V ol. 24N o. 4
Aug. 20th 2004
Abstract :An analysis is made on the current situation of water res ources development and utilization in G uanzhong area , and s ome problems are pointed out , including the low efficiency of water utilization , overmining of groundwater , aggravation of water pollution , and aging , out of repairing and insufficiency of water supply facilities. From the angle of sustainable development of national economy and s ociety and sustainable utilization of water res ources , s ome measures are proposed , such as actively developing water saving technology to im prove the utilization ratio of water res ources , practicing management by unified netw ork , groundwater mining , and protection of water pollution remediation , wastewater into res ources , and im plementing the project of water diversion from s outh area to north area of the province.
K ey w ords :water res ources ; sustainable utilization ; G uanzhong area
W ater resources optim al allocation model for northw estern irrigation area/ZH AO Dan , et al (State
K ey Laboratory o f Water Resources and Hydropower Engineering Science , Wuhan Univ. , Wuhan 430072, China )
of water shortage will reach 15. 446million m 3, 21. 003million m 3, and 36. 279million m 3.
K ey w ords :optimal allocation of water res ources ; planning for irrigation area ; water saving ; eco 2environmental water demand ; Nanyang canal irrigation area
Stability analysis of N o. 2compound landslide on the right tail w ater bank of Ankang H ydropow er Station/ZH U Y ue 2ming , et al (College o f Water Conservancy and
Engineering ,
210098, China ) Hydropower
Univ. ,
Nanjing
:factors influencing the landslide , including the of main rock faults , concrete anti 2slide , seepage , nonlinearity of material structure , and earthquake 2induced inertial force , the stability and safety of three typical surfaces of the landslide with or without rein forcement by anti 2slide piles , on which slip 2induced cracks might occur , are calculated under three kinds of load combination by use of the finite element calculation m odel and the limit equilibrium method for rigid body analysis. The results show that the landslide is in the steady state , but the daily safety m onitoring of the landslide should still be em phasized.
K ey w ords :finite element method ; structural surface of rock fissure ; slope stability ; anti 2slide pile ; seepage C alculation of dew atering depth of confined w ater under foundation pits by use of submerged w eight of overburden soil and seepage force/GE X iao 2chun
(Water Conservancy Research Institute , Anhui &Huaihe Water Conservancy Commission , Bengbu 233000, China )
Abstract :Aiming at the serious water shortage and eco 2environmental problems in northwestern arid and semi 2arid regions , an ecology and water saving oriented water res ources optimal allocation m odel is developed for the irrigation area based on the idea of system analysis , and a multi 2objective simulation calculation method is proposed with consideration of the factors of water 2saving , water right , and ecological environment. With the Nanyang canal irrigation area as an exam ple , a reas onable scheme for water res ources optimal allocation is educed. The application shows that , with the development of s ocial economy , the shortage of water res ources is getting m ore and m ore serious , and that the v olumes of water res ources the irrigation area can provide for industrial and agricultural development and residents ’life are 56. 415million m 3, 57. 967million m 3, and 56. 572million m 3respectively at current , 2010, and 2030, but the v olume
Abstract :An analysis of the basic concept of seepage force shows that , for calculation of the dewatering depth of confined water , it is m ore reas onable to use the submerged weight of overburden s oil and the seepage force acting on it than to use the wet weight of overburden s oil and the water pressure at the bottom of the layer. The com paris on of the tw o methods shows that , when the safety factor of seepage stability equals one , the calculated results of the tw o methods con form to each other if the weight of the saturated s oil of overburden layers is used for calculation in the latter method ; however , if the safety factor is larger than one , normally , the dewatering depth calculated by the former method is less than that by the latter method. Furtherm ore , it is
・69・
concluded that , for a certain dewatering depth , the safety factor of seepage stability obtained by the former method is larger than that by the latter one. Therefore , the former method is m ore suitable for calculation of the dewatering depth of con fined water. H owever , the safety factor of seepage stability should be properly increased.
K ey w ords :foundation pit dewatering ; dewatering depth of con fined water ; seepage force ; Bengbu sluice E nhanced assumed strain (EAS ) element 2based analysis of thin plates on elastic foundations/LI Wen 2hu , et al (College o f Water Conservancy and Hydropower Engineering , Hohai Univ. , Nanjing 210098, China ) Abstract :The E AS element method is used to discretize the thin plate on the elastic foundation. Under the assum ption that the contact forces on the interface of the plate and foundation are in the distributive form , the relationship between the distributed force on the surface of foundations and nodal displacement is according to the theoretical s olution of the nodes in the semi 2in finite space horizontal forces. of com patibility of force equilibrium between the plate and the , FE M equations are formulated with displacements at nodes on the middle surface of the plate taken as unknown variables. An exam ple is given to verify the rationality of the E AS element for analysis of thin plates and to show the necessity of taking the distributed force on the interface between plates and foundations into account.
K ey w ords :E AS element ; distributed reaction force ; semi 2infinite foundation ; G auss integral ; finite element Experimental project of environmental protection vegetation on gangue dike slope of H uaihe River/SH U Y i 2ming , et al (College o f Water Conservancy and
Engineering , 210098, China ) Hydropower
Hohai
Univ. ,
Nanjing
plants in green for a long period. Practice shows that the experimental project has g ood effect on environmental and ecological protection.
K ey w ords :gangue dike slope ; 32D geonet ; environ 2mental protection vegetation ; Huaihe River
N ew technique for bank protection on N anjing reach of Yangtze River/X U X i 2rong , et al (College o f Water
Conservancy and Hydropower Engineering , Hohai Univ. , Nanjing 210098, China )
Abstract :Based on the current situation of regulation w orks for bank protection on Nanjing reach , the mechanism of different structural types for bank protection is analyzed. Simulation experiments are performed on several structural types , the riprap , tetrahedron frame structure , hinged mattress , and s o on. A on shows that the has g ood effect on water , stability , flow deceleration , and of sediment deposition , and is m ore suitable for water 2sediment condition of Nanjing reach.
K ey w ords :bank protection ; rock riprap ; tetrahedron frame structure ; hinged fascine mattress ; Nanjing reach of Y angtze River
Database design for simulation system of Q ingjiang River flood control and cascade dispatching/LI Y a , et al (College o f Hydropower and Information Engineering ,
Huazhong Univer sity o f Science and Technology , Wuhan 430074, China )
Abstract :An introduction is given to the key points for design of experimental project of environmental protection vegetation covered with 32D geonet on a gangue dike slope on the Huaihe River in Huainan diggings , and the techniques for construction , as well as the categ ory selection and management of vegetation. The pavement of 32D geonet on the dike slope can prevent the erosion of thin layer of s oil and plant seeds ; the mixing s owing of plant seeds of the pioneer type and artery type is fav orable for the formation of lawns and en forcement of the slope ; and the effective management measures can keep the
Abstract :An introduction is given to the design scheme for the database , in which the inner coding 2outer coding trans form technique is adopted for code management , and perfect tables for predicted result are designed , s o as to ensure the correctness of input and output data and reliability of the operation of the system. Besides , the redundant technique is applied and multi 2database operation m ode is developed to im prove the efficiency of the system. Furtherm ore , s ome functional m odules , including database management , code management , data reorganization , and data query , are designed for the database system. Finally , s ome measures , such as the rem oval of redundant data , establishment of index mechanism , and adjustment of E MS mem ory and initial parameters , are taken for optimization of the database performance of the system.
K ey w ords :flood control and dispatching system ; Oracle database ; simulation ; code ; redundant database ; Qingjiang River
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