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NATM tunnel design principle in the construction of major and

Construction Technology

NATM Design Principle

design

and

construction

of

two

major

theoretical

and

development

process

Since the 20th century, human space on the ground floor of the growing demand,

thus the underground works of the study of a rapid development. In a large number of

underground

engineering

practice,

it

is

generally

recognized

that

the

tunnel

and

underground

cavern

project,

the

core

of

the

problem,

all

up

in

the

excavation

and

retaining

two

key

processes.

How

excavation,

it

will

be

more

conducive

to

the

stability

and

cavern

facilitate

support

:

For

more

support,

Supporting

how

they

can

more

effectively

ensure

stability

and

facilitate

the

cavern

excavation.

This

is

the

tunnels

and

underground

works

two

promote

each

other

and

check

each

other's

problems.

Tunnels

and

underground

caverns,

and

focusing

on

the

core

issues

with

the

above

practice

and

research,

in

different

periods,

People

of

different

theories

and

gradually established a

system of different theories, Each system

includes

theory and

resolve

(or

are

studying

the

resolution)

from

the

works

of

understanding

(concept),

mechanics, engineering

measures

to

the construction

methods (Technology), a series

of engineering problems.

A

theory

of

the

20th

century

the

1920s

the

traditional

relaxation

theory.

Its

core

content

is

:

a

stable

rock

self-stability,

no

load

:

unstable

rock

may

have

collapsed.

need

shoring

structure

to

be

supported.

Thus,

the

role

of

the

supporting

structure

of

the

rock

load

is

within

a

certain

range

may

be

due

to

relaxation

and

collapse

of

rock

gravity.

This

is

a

traditional

theory,

and

their

representative

is

Taishaji

and

Principe's

and

others.

It

works

similar

to

the

surface

issues

of

the

thinking is still widely used to.

Another

theory

of

the

20th

century

made

the

1950s

the

modern

theory

of

timbering or

rock to their own self-stability

:

unstable rock

loss of stability

is a process, and

if this

process

in

providing

the

necessary

help

or

restrictions

will

still

be

able

to

enter

the

rock

steady

state.

This

theoretical

system

of

representative

characters

Labuxiweici,

Miller-Feiqieer,

Fenner

-

Daluobo

and

Kashitenai

others.

This

is

a

more

modern

theory,

it

is already out of

the

ground

works to consider

the

ideas, and

underground

works

closer

to

reality,

the

past

50

years

has

been

widely

accepted

and

applied.

demonstrated broad development prospects.

Can be seen from the above, the former theory more attention to the findings and

the

results

of

treatment

:

The

latter

theory

is

even

more

attention

to

the

process

and

the control of the process, right from the rock for the full utilization of capacity

. Given

this

distinction,

which

both

theory

and

methods

in

the

process,

each

with

different

performance characteristics. NATM

theory

is

rock

for the

tunnel engineering practice

in the representation method.

2. NATM

NATM

that

the

new

Austrian

Tunneling

Method

short

the

original

is

in

New

Austrian

Tunneling

Method,

referred

to

as

the

NATM.

France

said

it

convergence

bound

or

some

countries

alleged

to

observe

the

dynamic

design

and

construction

of

the basic principles.

NATM the basic points can be summarized as follows :

（

1

）

. Rock tunnel structure is the main loading unit, the construction must fully

protect

the

rock,

it

minimize

the

disturbance

to

avoid

excessive

damage

to

the

intensity

of

rock.

To

this

end,

the

construction

of

sub-section

should

not

block

too

much,

excavation

should

be

used

smooth

blasting,

presplit

blasting

or

mechanical

tunneling.

（

2

）

. In order to give full play to rock the carrying capacity should be allowed to

control

and

rock

deformation.

While

allowing

deformation,

which

can

be

a

rock

bearing ring; The other hand, have to limit it, Rock is not so lax and excessive loss or

greatly reduced carrying capacity.

（

3

）

. In order to

improve the support structure,

the

mechanical properties,

the

construction should be closed as soon as possible, and to become a closed cylindrical

structure.

In

addition,

the

tunnel

shape

with

a

round

should,

as

far

as

possible,

to

avoid the corner of the stress concentration.

（

4

）

.

Construction

right

through

the

rock

and

supporting

the

dynamic

observation,

measurement,

and

reasonable

arrangements

for

the

construction

procedures, changes in the design and construction management of the day-to-day.

（

5

）

.

To

lay

waterproof

layer,

or

is

subject

to

bolt

corrosion,

deterioration

of

rock properties,

rheological, swelling caused by the

follow-up

to

load,

use composite

lining.

（

6

）

. Lining

in principle, and

the early rock deformation Supporting

the basic

stability

of

the

conditions

under

construction.

rock

and

supporting

structure

into

a

whole, thereby improving the support system of security.

NATM

above

the

basic

elements

can

be

briefly

summarized

as

:

disturbance, early spray anchor, ground measurements, closed tight.

3

．

Points

（

1

）

.

Rock

cavern

excavation

is

affected

by

that

part

of

rock

(soil)

body,

the

rock is a trinity : have a load bearing structure, building materials.

（

2

）

.

Tunnel

construction

is

in

the

rock

stress

is

of

special

architectural

environment, which can not be equated with the construction on the ground.

（

3

）

. Tunnel structure rock + = bracing system.

II. The new Austrian highway construction in the basic method

NATM

one

of

the

characteristics

is

the

scene

monitoring,

measurement

information

to

guide

construction,

through

the

tunnel

construction

measure

receipts

and

excavation

of

the

geological

observation

for

prediction

and

feedback.

And

in

accordance

with

the

established

benchmark

for

measuring

the

tunnel

construction,

excavation

section

steps

and

sequences,

Supporting

the

initial

parameters

for

reasonable adjustments to guarantee the safety of construction, a tunnel rock stability,

the

quality

of

the

project

and

supporting

structure

of

the

economy

and

so

on.

The

author

of

commitments

(Chengde)

Chek

(Chifeng)

East

Maojingba

Tunnel

NATM

basic

construction

method

for

investigation

concluded,

synthesis

of

a

new

highway

tunnel

Natm

the

selection

of

different

types

and

the

basic

characteristics

of

the

construction methods and tips.

1. A tunnel construction

method of choice tunnel construction

method of choice,

mainly

based

on

the

engineering

geological

and

hydrogeological

conditions

Construction, rock

type, buried deep tunnel, the

tunnel section size and

length

lining

types, Construction should be the premise of safety and engineering quality at the core,

and

with

the

use

of

the

tunnel

function,

the

level

of

construction

technology,

Construction

machinery

and

equipment,

time

requirements

and

economic

feasibility

of factors to consider in selection.

2.

New

Austrian

Tunneling

Method

program

New

Austrian

Tunneling

Method

used all methods can be divided into sections, Division level and the three major types

of excavation method and some changes in the program.

(1)

Full-face

method.

That

whole

section

excavation

method

is

based

on

the

design

of

an

excavation

face

excavation

molding.

Excavation

order

is

its

full

face

excavation, steel bracing, pouring concrete

lining. Often choose to IV-VI Class

Rock

Hard Rock Tunnel, which can be used blasting deep hole.

Excavation

whole

section

of

the

law

is

a

larger

space

operations,

introducing

supporting

large

mechanized operations,

improving

the speed and process

small,

less

interference and

facilitate

the construction organization and

management.

Excavation

is

due

to

shortcomings

in

the

larger,

lower

relative

stability

of

rock,

and

with

each

cycle of the relatively

large workload,

it requires the construction

units should

have a

strong excavation, transport and slag out and support capability, Maojingba VI : Class

V rock used in the full-face excavation to achieve the desired results.

Full- face excavation face, drilling and blasting construction more efficient use of

deep focus to accelerate the excavation blasting speed, and the rock blasting vibration

frequency

less conducive to a stable transfer

rocks.

The drawback

is every deep

hole

blasting

vibration

larger.

Therefore

require

careful

drilling

and

blasting

design

and

strict control of blasting operations.

Full-face

excavation

method

is

the

main

process

:

the

use

of

mobile

carts

(or

platforms),

the

first

full-face a bored,

and

installed a

line, and

then drilling

platform

car outside 50m back to a safe place and then detonate, Blasting to

make a shape out

after drilling Jardine car again moved to the excavation face in place, began a cycle of

drilling

and

blasting

operations,

Anchor

sprayed

simultaneously

supporting

or

after

the first arch wall lining.

(2) step

method. Step

method of design

is

generally divided

into sections on the

half- section

and

the

lower

half

section

two

excavation

molding.

Excavation

order

is

its

first

half excavation arch bolt

jet concrete bracing, arch

lining, the central

part of

the

second

half

of

excavation,

sidewall

of

excavation,

concrete

wall

jet

bolt

support

and

lining.

The

more

applicable

to

the

II,

III

and

soft

joint

development

of

the

surrounding rock, which were used Tim change program.

Long-step

method

:

The

next

stage

distance

away,

on

the

general

level

above

50m

ahead,

Construction

can

be

assigned

to

the

Department

of

next

larger

machine

with

parallel

operations,

when

mechanical

deficiencies

can

be

used

interchangeably.

When

the case of a

short

tunnel,

the

upper section

will be all dug

later, and then dug

under

the

section,

the

construction

of

which

less

interference,

single

process

can

work.

Short

step

method

:

on

the

stage

length

5-50m

apply

to

Ⅱ

,

Ⅲ

rock

can

be

shortened Invert closing time, Supporting

improve early stress conditions, but

larger

construction

interference,

in

the

event

of

Soft

Rock

need

to

consider

carefully,

Auxiliary

shall

be

applied

measures

to

stabilize

the

excavation

excavation

face,

in

order to ensure the safety of construction.

Ultrashort

step

method

:

The

only

step

ahead

3-5m,

section

closed

faster.

The

method

used

for the

high

level of

mechanization of

various rock section,

in the event

of

the siege soft rock when required careful consideration.

Auxiliary shall be applied

measures

to

stabilize

the

construction

excavation

face

to

ensure

the

safety

of

construction.

Excavation

level

of

character

is

the

first

step

to

using

light

excavation

drilling

machine drill a

hole, rather than through

large drilling platform car.

Two step

method

of excavation operations with sufficient space and a

faster rate of construction. Level

is

conducive

to

the

stability

of

excavation

face.

Especially

Excavation

in

the

upper,

lower operational safety. Three step method of excavation is the next shortcomings of

operations

interfere

with

each

other.

It

should

be

noted

at

the

bottom

of

the

upper

operational stability, level of excavation will increase the number of country rock.

(3)

Segment

excavation

method.

Excavation

Law

Division

can

be

divided

into

five changes in the program : Excavation Division level, from top to bottom hole lead,

heading advance on the excavation, single (double) and lateral pit method. Excavation

will

be

conducted

Section

Division

excavation

by

the

Ministry

of

shape,

and

to

advance some of excavation, it may be called derivative ahead excavation pit method.

Law

Division

level

:

general

application or soil collapse easily

lots of

soft rock,

with its advantages - stage method, height can be lengthened, the two-lane tunnel for a

hole-fold,

cycling

Road

Tunnel

-

hole

2

times;

rather

than

single

(double)

PENDANTS Heading a

high degree of

mechanization, can accelerate

the progress of

the projects.

The next heading advance excavation method (that is guided pit wall first arch) :

This

Act

applies

to

Ⅱ

,

Ⅲ

rock.

in

the

soft

ground

tunneling,

to

be

adopted

next

general

guide advance excavation pit wall

first arch Act. Its advantages are

: Heading

advance

excavation,

the

use

of

proven

geological

conditions

in

advance

to

facilitate

change

in

the

method.

Face

to

facilitate

started

procedures

applicable

to

the

labor

arrangements

for the

use of small

machinery and construction.

The drawbacks

:

The

next

section

will

guide

small,

slow

construction

and

construction

processes

more,

construction and management difficult.

Unilateral-arm

pit

Law

:

rock

instability,

the

tunnel

span

larger,

ground

subsidence

is

difficult

to

control

when

using

this

method.

Its

characteristics

are

:

a

positive step and arms Heading Act advantages.

Bilateral

arm

Heading

law

:

in

large-span

shallow

tunnels,

surface

subsidence

require strict, especially poor rock used. Advantages of this method are : Construction

of safe, reliable, but slow construction, high cost.

Ⅲ

. Example projects

Built on loose sand gravel stratum of Beijing Subway allowed back of the tunnel

is

a

typical

example.

The

tunnel

is

located

in

the

main

street-256,

358m

long,

the

largest

excavation

section

9m

high,

14.5m

wide

coverage

stratigraphic

top

of

the

tunnel

only

minimum

thickness

9.0m.

Tunnel

boring

machine

of

excavation,

strengthen

the

grid

arch

shotcrete

initial

support

and

advance

small

catheter

care,