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