Chapter 5 Groundwater 第五章 地 下 水. Definition of groundwater: Groundwater is that part of...
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Transcript of Chapter 5 Groundwater 第五章 地 下 水. Definition of groundwater: Groundwater is that part of...
chapter 5 Groundwater
第五章 地 下 水
Definition of groundwater:
Groundwater is that part of water which exits in the spac
e of rock’s, soil’ pore below ground surface.
Groundwater is precious natural resource to human bein
g, But it’s a factors of reducing the strength of the rock and
soils. According to the statistics, Nearly 80% engineering g
eological problems were caused by the existing of ground
water. So the study on groundwater is very important for a
geotechnical( 岩土工程 ) engineer.
地下水的基本概念
The main topic of chaper 5
§5-1 The physical properties and chemical
composition of groundwater
§5-2 The classification of groundwater
engineering properties
§5-3 Moving law of groundwater
§5-4 The influence of ground water to
the engineering
§ 5-1 The physical properties and chemical composition of groundwater
一 .The physical properties of groundwater temperature color taste transparent smell radioactivity
Groundwater is a kind of solvent, resolving the soluble co
mposition from rock or soil , so groundwater is full of ions.
1 .The main ion in G
Cation 阳离子 : H+, Na+, K+, Mg2+, Ca2+, Fe2+
Anion 阴离子 : OH-, Cl-, SO42-, NO2, HCO3
-, CO32-,
SiO32-, PO4
2-
HCO3-→bicarbonate CO3
2-→carbonate
SO42-→sulfate Cl→chlorate
SiO32-→silicate PO4
2- →phosphate
二 . Chemical composition of groundwater
O2→oxygen
N2→nitrogen
CO2→carbon dioxide
→from karst area,
→ plant respiration
H2S→sulfate hydrogen
exiting confining
environment
Esp. Oil layer tin:Sn zinc :Zn
copper :Cu
iron :Fe aluminum :Al
manganese :Mn magnesium :Mg
calcium :Ca sodium :Na
potassium :K fluorine :F
chlorine :Cl oxygen :O
sulful :S nitrogen :N
phosphorus :P carbon :C
silicon :Si hydrogen :H
2.The main gas composition
SiO2
Fe(OH)3 hydroxide
Al(OH)3 hydroxide aluminum
chemical combination
The function of colloid and organism on engineering
is indirect, because they may change chemical
composition of G.
3.The main colloid( 胶体 ) and organism in G.
1 According to the temperature
over cold water <0℃
cold water 0-20℃
warm water 20-40℃
hot water 40-100℃
over hot water >100℃
§ 5-2 The classification of groundwater
and its engineering properties
2 According to existing state gaseous state water (气态水)
liquid state water (液态水)
solid state water (固态水)
3 According to the medium of containing water
Karst water( 岩溶水 )
Fracture water (裂隙水) Pore water (孔隙水)
按含水介质的不同,对地下水的分类
Pore water (孔隙水) Fracture water (裂隙水)
free water (自由水)
absorbed water (结合水)
capillary water( 毛细水 )
gravity water (重力水)
Strong absorbed water (强结合水) Weak absorbed water (弱结合水)
4 According to interaction between
water and its medium
Capillary water is
controlled by
capillarity( 毛细作用( surface tension
force )
( 1 ) Capillary Water
wc rdh
4
diameter of soil grain unit weight of water tension farce of surface
dwr
Contact point ofgas, liquid,solid
Column cup
ch
Water table
Capillary rise (hc)
Capillary fringe(zone)
the law of is:
◆ the bigger d, the quicker of the speed of
capillary water
◆The smaller d, the higher the hc of capillary
water, but if d<0.002mm, no capillary water.
◆ silty clay ( 粉质粘土 ) and Clay silt ( 粘质粉土 )
is most obvious medium for capillary water
existing
ch
Ice lens body冰透镜体
Ground frozen expansion 地面冻胀
Ground frozen地面冻胀
沼泽地(湿地) Marshland (salinized soil)
The engineering meaning of capillary water
( 2 ) Gravity Water
The gravity water is only controlled by gravity (in movement)
( 3 ) Absorbed Water
water is extra-molecular( 极性分子 ),and the surface of clay grain have negative charge 负电荷。
Free waterWeak absorbed water
Strong absorbed water
Soil grain
5 According to the storage condition
Air-containing zone
Impermeable layer
Suspending water
Stagnant water
(1) Suspending water (2) Stagnant water stagnant water may have bad influence to engineering in limited areas
◈
(3) Phreatic Water
Movement direction
Phreatic surface
Phreatic water is below the ground surface, above the first impermeable layer, and has free water surface.
毛细带水
潜水
上层滞水
潜水面
地下水的埋藏类型
隔水底板潜水含水
层厚度
潜水埋藏深度
地下水的补给、排泄
潜水面形态的变化规律
受地形和河流位置
的影响
受底板隔水层高度变化
的影响
受含水介质渗透性变化
的影响
Featuresof phreatic water: ① charging: precipitation and river discharging: river, evaporation, spring ② distribution controlled by impermeable layer or permeable layer and topography ③ water level change controlled by weather condition ④ chemical composition depending on the circulating speed of ground water and the composition of Water medium and pollution. ⑤ The influence of phreatic water to engineering --frozen expansion --change the strength of soil or rock
(4) Confined Water(pressure water)
Spring 泉
aquifer含水层
Discharging area 排泄区
Pressure-bearing area 承压区
recharging area补给区
Confined Water 承压水
地下水的埋藏类型
自流区
承压区排泄区补给区
承压水流向
Featuresof pressure water:
① recharge is in striped way
discharge movement is finished by spring,
② distribution
controlled by the distribution of confining layer.
③ water level change
water table change has no obvious seasonal feature
s
④ chemical composition
pollution is hard to recover
⑤ The influence of pressure water to engineering
MH
Hr
rM w
土的重度板的距离:基坑底面距含水层顶
水头高度
:
:
r
M
H
§ 5-3 Moving law of groundwater
QSoils sample
土样
A: 水箱截面积
h1
h2
L
Bucket水箱
截面 1
截面 2
L : 渗透路径h1: 截面 1 水头h2 :截面 2 水头Q: 流量
IAKL
hhAKQ
21
Q: rate of flow (m3/d)
A: cross area (m2)
L: traveling distance
I: hydraulic gradient
K: permeability coefficient
I : to indicate the water head loss in unit traveling Distance.
Darcy law:
sand : Ikv
K indicate the ability of soil (or rock)
permitting water to pass
clay soil : )( 0IIkv
vseepage velocity(m/d)
0I initial hydraulic gradient
which indicate the value of hydraulic gradient when the ground water begin moving.
§ 5-4 The influence of ground water to the engineering
一、 seepage failure (渗透破坏) Quicksand (flowing sand) or piping
wr
I
)( 3/mkNIrG wD
unit weigh of water
hydraulic gradient
DG dynamic water pressure
单位体积土体
水流
▣ Quicksand 流砂The definition of dynamic water pressure
e
dI scr
1
1为流砂发生的条件
▣ piping: (管涌)
Under the action of GD, the fine soil grain will be
carried away through chinks among coarse soil grain
流砂和管涌发生条件
1 diameter of soil grain (d) 0.05—0.005 粉细砂
2 quicksand: houngenous soils
piping: heterogeneous soils
3e
dII scr
1
1
基坑的流砂或管涌 坝基的流砂或管涌
二、 Ground water table lowering cause the settlement of soft ground base
Uplift pressure
HH
h