Excavation Bracing in the Berlin Method of Subway Construction

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t/.;WfJTT. 932 TT·932

NATIONAL RESEARCH COUNCIL OF CANADA

TECHNICAL TRANSLATION 932

EXCAVATION BRACING IN THE BERLIN METHOD

OF SUBWAY CONSTRUCTION

BY

FRANZ HARMS AND RICHARD BERZ

FROM

BAUTECHNIK, 34 (1); 16 - 20, 1957 AND 34 (3) 89·94, 1957

TRANSLATED BY

D. A. SINCLAIR

THIS IS THE SEVENTY· FIFTH OF THE SERIES OF TRANSLATIONS

PREPARED FOR THE DIVISION OF BUILDING RESEARCH

OTTAWA

•

•

Since the beginning of construction of Canada's first subway, the Yonge Street Subway in Toronto

(1949-1953), it has been the privilege of the

Division of Building Research of the National Researoh Council to cooperate closely with the Toronto Transit Commission on a number of research problems in the field of soil mechanics, foundations, structures,

geology, vibration and acoustics. In brief, the

sub-way construction was used as a "research laboratory· so that experience gained in the course of design and construction of this important and difficult project might become available to other engineers and

specialists in various fields. A number of research

papers have evolved from this research activity. The Division of Building Research has also been anxious to help in making available knowledge and literature from other countries to the Canadian

engineers. It is in this sense that this translation

of a German article on the highly developed excavation bracing systems used 1n the "cut-and-cover" method

(or Berlin method) ｯｾ subway ｣ｯｮｾｴｲｵ｣ｴｩｯｮ is presented. The paper was translated by Mr. D.A. Sinclair of the Translations Section of the National Research Council Library, to whom the Division of Building Research wish to record their thanks.

• • Ottawa, .January 1961 R.F. Legget, Director

•

•

Ti tIe:

Technical Translation 932

Excavation bracing in the Berlin method of subway construction

(Die Baugrubenaussteifung beim Bau von Untergrundbahnen nach der Berliner Bauweise)

•

Authors: Franz Harms and Richard Berz

Reference: Bautechnik, 34 (1): 16-20, ＱｾＵＷ and 34 (3): 89-94, 1957

•

•

1. Introduction

All Berlin subways (underground railways) have been built by

the so-called Berlin method of tunnel construction. In London a

layer of clay, which begins at a depth of 6 to 9 metres, made it possible to use the shield method, and in Paris the presence of a hard gravel and marl layer permitted the use of the Belgian method of tunnel ｣ｯｮｳｴｬｾ｣ｴｩｯｮ (underpinning method with top and bottom

heading). In Berlin, on the other hand, attempts to avoid open

excavations and to apply underground mining methods have been unsuccessful because of the sand and gravel beds.

The Berlin methOd has proved successful both here and abroad in almost sixty years of application, if we disregard the accident at Friedrich-Ebert-Strasse (formerly Hermann-Gorlng-Strasse), which

happened only because of a faulty execution(l). The most important

features of the Berlin method are:

1. Excavation of an open cut which, along main streets, is

completely or partially covered shortly after the start of excavation work by a temporary road deck for resumption of surface traffic;

2. Support of the sides of the excavation with timbered walls;

3. Dewatering of the excavation by lowering the ground water

table.

Since its first application on the Kleist- and Tauentzienstrasse

the Berlin method has undergone many modifications. As applied

tOday it is described 1n the "R1chtllnien fur die Festigkeitsbere-chnung und baullche Durchbildung der Baugrubenaussteifung und-abdeckung fur Tunnelbauten der Stadtischen Schnellbahnen" (Guides to the design calculations and construction details of the

excavation bracing and temporary decking for the tunnel structures of urban ra-pld tran sit systems,) hereafter referred to as RB (2) for Short, which were drawn up by the Senator for Construction and

Housing.

In recent times subway construction has changed considerably

by the use of all sorts of heavy equipment and machines. This

incidentally explains the effort made in the new "Guides" (RB) to reduce to a minimum the number of bracing layers constricting the excavation cross-section and thus to provide only two bracing layers over the cross-sectional area of the tunnel. In addition to this' the struts are to be such that the excavation for the normal double-track tunnel, including the Widening at the curves, can still be constructed without a central support. The criterion for this is to be found in the head support of the struts.

Of fundamental importance in the further development of excavation bracing technique was the new concept that had been formed of the effect of the earth pressure on the excavation walls(3,5). Numerous tests and measurements carried out on

excavation walls from 1934 to 1938 revealed that Coulomb's triangular earth pressure diagram, Which has hitherto been used as a basis for dimensioning, leads to incorrect results. The shore pressures in the upper part of the excavation are underdesigned, while in the lower part they are considerably overdesigned. The simplified, but fairly accurate assumption of an earth pressure diagram having the form of a rectangle equal in area to Coulomb's triangle results in tolerable shore dimensions with fewer shores and increased length.

2. Load AS§¥illPtions

2.1 Unit weights of building materials

•

Steel and steel castings (Gray) cast iron

Brick masonry

Sand and gravel (moist) Sand and gravel (wet)

7.85 t*/m3

7.25 t/m3

1.8 t/m3

1.8 tim3

2.0 t/m 3

The unit weights of various kinds of lumber, according to the values laid down for bridges, are as follows:

Spruce and fir, air dry 550 kg/m3 _{, wet 700 kg/m3 ;}

Pine and larch, air dry 600 kg/m3 , wet 750 kg/m3 ;

Oak and beech, air dry 800 kg/m3 , wet 1000 kg/m3 •

The unit weights given include allowances for small hardware (nails and screws), hardwood parts, and paint or impregnation as well as dirt.

2.2 Earth pressure

The specifications on load assumptions for structures (DIN 1055, sheet 1.3, edition of June 1940) provide for an angle of internal friction of p

=

30° for the calculation of the earth pressure in the case of moist sand and gravel. This value is based on the assump-tion of a cohesionless material in which the angle of internal friction agrees with the angle of repose.

From experience gained in the work on the Berlin subways, and considering the temporary use of the bracing, it is possible to depart from DIN,l055 and take an agle of p

=

37° as the angle of internal friction of moist sand.

This value takes the cohesion partly into account. Thus, for moist sand

Unit weight y

=

1.8 t/m3

Angle of internal friction p

=

37°

Angle of friction at the wall 6

=

0°

p

Earth pressure coefficient _Aa

=

tan2(45° _{- 2)}

=

_0.25.

For other types of soil corresponding values should be used. The former earth pressure triangle is to be replaced by an

earth pressure rectangle of equal area. The assumption of the

rectangular loads in the lower part of the excavation results in a value of which according to on-the-spot measurements only about 70% is actually present. This difference makes it possible to neglect even a theoretically higher bUilding pressure, which is apprOXimately 60° within the range of the slide angle.

..

•

3. Principles of GalcutatioQ

Be s Lde s the "Gu Lde s" (RB), the following al so apply insofar as they do not conflict with the ITB:

1. Grundlagen fur die Festikeitsberechnung des Tunnelbause der

Stadtischen Schnellbahnen (Principles of design calculation for tunnel construction of urban rapid transit systems), referred to as BT for short(6).

2.

DIN,

1050, 1052, 1073, 1074, 4074, 4420 •

3. Berechnungsgrundlagen fur stahlerne EisenbahnbrUcken (Principles of calculation for steel railway bridges), referred to as 3E for short; published by Deutsche Bundesbah, ｾｰｲｩｬＬ 1955.

4. Strassenverkehrsordnung (StVO).

Bau- und Betriebsvorschriften (Street traffic regulation, sectlon on construction and operation).

5. Verordnung uber den 3au und Betrieb der Strassenbahnen (BOStrab) (Regulation concerning the building and operation of street

railways), with amendments of the 14.8.1953(7).

The guides (RB) are based on a different set of assumptions

from the specifications for bridges. In the first place the Wooden

planking between I-beams demands that special consideration be given to concentrated loads, and secondly the construction methods

result in the concentrated loading of the I-beams, in contrast to

the load reduction that is permissible in the case of bridges. The

loadings are predominantly single beam loadings or group loadings of deck beams, spaced 2 m supported by girders 6 m long.

3.1 Standard loads

According to the StVO (road traffic regulation) the loading of the excavation deck is determined from two standard vehicles chosen in accordance with the admissible maximum loads carried and the heavy trucks constructed for these by the motor industry

( Fig. 1 and 2).

Since a change of loads according to the StVO comes into

effect only on the 1 July 1960, the above assumptions hold for the

tramway loads (Fig. 3) can be applied, but these become invalid if the tramway lanes can be used by heavy trucks as well.' The

division into main, auxiliary and outside lanes (Fig. 4 to 7) is determined on the basis of stationary and moving vehicles for a normal mixed traffic of heavy and light vehicles.

Fig. 4 and 5 show the way in which the vehicles are grouped so as to arrive at the load assumptions for calculating the road deck beams. Fig. 6 and 7 show the arrangement for calculating the central beams.

3.2 Vibration coefficients

The vibration coefficients are included in the standard loads. For the main lanes they are ｾ

=

1.4 for the road-deck beams and

ｾ

=

1.2 for the beams.

3.3 Substitute loads

The loads of the StVO do not exceed a suitable uniformly distributed load (substitute load) of p

=

1.1 t/m2

• In view- of the

BVG (Berliner Verkehrs-Gesellschaft) vehicles also present in the traffic of the city, the uniformly distributed load applied in front of, behind and beside the vehicles (Fig. 4 to 7) is 0.7 t/m2 _plus

the appropriate vibration coefficients. Generally speaking a

traffic of heavier special purpose vehicles in the Vicinity of the underground construction sites can be ruled out.

3.4 ｾ｟ｲ｡ｫｩｮｧ loads

Braking and starting up loads for motor vehicles at the road surface level are to be taken as 1/20 the full load on the roadway at 0.7 t/m2 _{Without a vibration coefficient, taking into account}

the cross-bracings by Which the traffic lines are divided, and which

act as fixed points. However, they must be at least 0.3 times the

weight of the stationary standard vehicles.

TNhere the tramway has its own right-of-way 1/10 the weight of all axles loading the superstructure in the vicinity of a fixed

point should be applied at the level of the top of the rail.

Tram-ways without their own right-of-way are to be treated as roadway surfaces.

..

3.5 Load distribution

In calculating the road deck surface the load distribution

should be determined in accordance with DIN 1073 or 1074. For a

2 em wear of the planking we obtain a distribution height of

3 + 18/2 ｾ 12 em. As a consequence of standardization of the

traffic loading a wheel pressure of only ｾ x p

=

1.4 x 5 ::: 7 t is

involved. From a tire contact area of 0.48 m in one direction and

0.30 m in the other we get a load distribution of 0.72 m and 0.54 m,

respectively. This yields a dead load for the wooden deck covering

of 0.117 tim in qne direction and 0.097 tim in the other.

The maximum moment from block load plus dead load is:

M:=: 2.90 tim Wrequired::: 2400 cm3 Wexisting:=: 4 x 648

=

2592 cm'

3.6 Pressure from bUildings

If buildings of four to five storeys are present then regard-less of their construction a soil ｰｲ･ｳｳｵｾ･ of 4 kg/cm2 _{beneath the}

front walls, or a load of 40 t per ｲｵｮｮｩｾｧ metre of building

front-age should be assumed. To obtain maximum safety a load distribution

below the foundation footing of 30° from the ｨｯｾｩｺｯｮｴ｡ｬ is assumed. 0. 7 Permissible building materials

For decking and planking timber of quality class II, (sawn

timber class A) is required. Used lumber and steel building

materials may be employed after inspection for re-usability.

3.8 Safe stresses

The members require no special protective measures to ensure

their long life, since they serve a temporary purpose. Hence,

departing from DIN 1050, 1052 and 1073, a stress increase up to

20% is permissible.

3.8.1 Wood construction

For the decking, the plank walls, shores and other lumber, the following stresses are permissible:

Bending stress for

Compressive stress

parallel to grain _{permissible 0d}

₌

_{85 + 15}

₌

_{100 kg/cm}2

•

•

•

Compressive stress at right angle to grain

for coniferous wood per!1lissible

°d

=

25 + 5

=

30 kg/em :2

for hardwood _{permissible ad}

₌

_{40 + 8}

₌

_{48 kg/cm:2}

3.8.2 Steel structures

For calculating the decking, the outside and centr9.1 pile beams, and other temporarily installed structural parts of St 37, the following stre$ses apply for bending, compression and tension stresses

permissible a ::: 1400 + 200

=

1600 kg/cm2

in exceptional cases permissible 0::: 1800 kg/cm:2.

'rhe deflection due to traffic loading must not exceed f ::: 1/400

of the beam span. In calculating the steel piles and road deck

beams it 1s necessary to include a deduction for two screw holes of 21 or 25 mm diameter in order to make possible the installation of any bracings that may be necessary at any point without exceeding the permissible stress.

For screwed joints without fitting 4 D (formerly St 38.13) the following figures apply in accordance with the BE of 1st April, 1955:

Permissible shearing stress 't"a ::: 1400 kg/cm:2

Permi ssible bearing stress a1 ::: 2800 kg/cm:2

Permissible tensile stress a

z = 1000 kg/cm2

3.8.3 Road deck cross-beams

The cross-beams are to be calculated as beams on two supports. The number of joining screws required should be determined for

1.2 times the value of the total bearing pressure. If the

cross-beams are used in place of braces for strengthening the excavation they should also be calculated for buckling •

3.8.4 Lower girders

Lower girders over the central pile beams normally have a length of 6.00 m and are also to be calculated as beams on two

4. Construction Details 4.1 ｐｩｬｾ

For outer piles (up to 15 m in length) in normal sandy soil

I-beams can be used. For outer piles of more than 15 m in length

and in curves of less than 200 m radius with an excavation depth of more than 9.0 m, and also for all central piles, wide-flange profiles should be used.

The length of the piles depends on the depth of the excavation and the depth of penetration below the excavation floor.

1.80 Depth of penetration in m IP-beams IP-beams 1.50 3.00 with p < 25° 1.50 3.00 Excavation depth of 6 to 13 m Outer piles Central piles Over 13 m or in unfavourable ground

Outer piles Central piles in sump holes 1 m deeper

to the top road surface is less than 2.25 m the sleepers/are to be wedged in using I-beams; for IP-beams the smaller figure obtained from the lower beam height is sufficient.

3.8.5 Splicing of parts sUbject to bending stress

For splices of parts subject to bending stress the moment of inertia of the splices covering the joint must be at least equal

to that of the parts joined. Each part must also be separately

covered (see also under 4.4).

3.8.6 Connecting and splicing of cross-bracings

The diagonals.of the cross-braclngs are to be connected accord-ing to their net cross-section F

n, or according to their full

cross-section divided by the buckling coefficient, F/w. Diagonals which

are subject to only small stresses and are designed according to practical considerations are to be spliced in accordance with the most practical principles.

•

f

•

Where only one layer of shores is used the pile should be

calculated as a fixed-end beam. In general double the penetration

depth is then required.

4.1.1 Outer piles

The outer piles should be placed as much as possible at equal intervals so that no rotation of the beams occurs due to unequal

earth pressures. They should be driven in such a way that the

shores can be installed in a straight line and at right angles to

the tunnel axis or to the central piles. The reason for this is to

keep the stress on tqe central piles due to the shoring forces to a minimum.

The standard outer pile spacing is 2.00 m. In curved tunnel

sections this distance is to be maintained on the outside of the curve, in the case of intermediate walls at the centre of the wall. On the inside of the curve the interval should be reduced so that

the shores can be installed in radial direction. The spacing of

the central wall openings is to be chosen so that the shores will fall into the openings.

For the outer piles on straight stretches and in curves of more than 200 m diameter 1-34 beams are to be used, except at station entrances, where 1-28 to 1-32 will suffice. In curves of

less than 200 m diameter and an excavation depth of more than 9.00 m,

IP-28 beams are to be provided. To ensure tightness of the

construc-tion the IP-beams should whenever possible be pulled again. To determine the maximum permissible shore spacing in the

vertical direction for the given pile section, the diagram for pile sections in Fig. 8 can be used. The use of the table is illustrated in the following examples.

1. Total shore pressure

=

27.0 t

vertical shore interval

h_s

=

3.80 m for three supports of the pile h

s

=

1.80 m for four supports of the pile

•

•

2. Total shore pressure

=

16.0 t

h_s

=

3.80 m for three supports of the pile

h = 3.75 m for four supports of the pile

s

Section I-26

ｾＮＱＮＲ Standard position central ｰｬｬｾ

The central piles (Fig. 9) should be driven at spacings three times the normal spacing of the outer piles, in any case 6.00 m apart and as far as possible not in a straight line between the

outer piles. The shores or struts can then be carried past the

central piles. In exceptional cases the central piles can be placed at 4.00 m intervals.

In case of extremely high loads or unfavourable soil conditions the compressive forces may no longer be supported safely by the

wall friction of the pile ends in the soil. Then supplementary posts

should be installed on either side of each central pile. Whether

this post should be set up below the last or second-last shoring position, depending on the progress of excavation, is to be

determined from case to case. In every case the effects of the

load should be checked continuously.

Underpinning or the transfer of load of the central piles is carried out first at the tunnel floor and later at the tunr.el

celling. When the tunnel floor is concreted, conical holes of at

least 1.50 x 1.50 m should be left at the central piles. After the

concrete has set the pile should be supported on the finished

tunnel floor to the side of the hole. The transfer of load from the central pile can be accomplished most simply in the manner of

Fig. 11, rather than Fig. 10, omitting the two slanting braces. The pile is then cut about 20 cm below the waterproofing layer and about

20 em below the upper edge. This piece is then removed, the

pro-tective coating, the waterproofing and the steel reinforcement are set in the hole, and after two steel angles have been fastened to the new pile end the hole is filled up with concrete (Fig. 10 and 11). The temporary support will be removed only when the central pile is dismantled. When the tunnel ceiling is constructed a hole is left

with steel sections resting on timber crib work constructed on the completely finished and waterproofed tunnel ceiling (Fig. 12 and

13). The central pile is cut off below the support, the lower part

is removed and the ceiling is closed at this point, waterproofed

and the protective coating applied. A block is concreted to the

protective coating, the plan area of which is to be so dimensioned that the permissible compressive stress in the waterproofing of 1 kg/cm2 _{will not be exceeded. The pile is to be protected against}

bonding of the concrete inside the concrete block so that the pile can later be easily lifted out.

The supporting and blocking of the piles should only proceed in small steps corresponding to the progress of backfilling.

4.1.3 Central piles 2.00 m ｡ｰｾｲｾ

Where a wider floor span results from a particular track arrangement and the central piles are included in a wall they

should be driven at intervals of 2 m.

4.1.4 End walls

End walls, i.e., vertical walls consisting of piles with planks

between them should be avoided if possible. When they cannot be

avoided the earth pressures, including that resulting from eXisting or expected vertical loads, against the end wall must be transferred to the outer walls and not to any central walls (Fig. 14).

4.2 Planks and shores

4.2.1 Planks of the outside walls

As excavation proceeds planks are inserted between the piles

of the outside walls. They must be thick enough to transfer the

earth pressures to the piles. The accompanying charts (Fig. 15) are

used to determine the required thicknesses. The use of the charts

is illustrated by the following examples:

1. s

=

2.15 m; be

>

9 m; t

=

9.60 m planks 8 cm (no pressure from buildings)

2. s

=

2.00 m; be

=

6 m; t

=

9.80 m planks 8 em

&

The planks between the piles on installation should

pe

pre-stressed by hardwood wedge strips so that the earth behind them will not yield and cause damage to other structures, especially pipes under pressure.

If standard I-beams are used for the piles, a standard wedge strip is adequate, since the flanges of these profiles are sloped. However, if wide-flange beams are used as piles the wedge strips must be levelled on the excavation side in order to ensure adequate pressure of the planks when the wedge strips are driven into

place (Fig. 16 and ＱＷＩｾ If the outer piles are pulled after back-filling a guard plate should be placed between the pile and the protective concrete layer so that the concrete protective layer will

not be torn loose with the waterproofing. The top metre of the

vertical protective layer of B 120 concrete is provided With a

steel wire mesh. If the piles are not pulled this reinforcement of

the wall protective layer is unnecessary. If very fine sand is

present (quicksand) the gaps between the planks which do not close tightly should be covered With 1.5 x 3 em strips.

4.2.2 Size of shores

The shore dimensions are based on the following horizontal pressure components: Earth pressure: e_b

=

ｾ

•

0.45 t/m2 ; t

=

4.45 e_t m Traffic pressures: e v

=

ｾ

.

0.275 t/m2; 1.10 0 1 v

=

1.80

=

.6 m

Pressure from buildings: _{e c}

₌

0.45

u'

tim2

c ii'_c

₌

ii_c

-

t'

.

c' t'_c

₌

+1.61 m

..

,

u c

₌

_3(2b2.22 . P c + 0.60) m 14.8

-

5.75 m·

,

=

4.00 m·

,

=

con st. ;

=

10.00 m·

,

=

9.45 m·

,

=

3.50 m·

,

=

32 cm;

=

2.00 m·

,

=

12.95 m·

,

=

6.00 m·

,

=

con st. ;

=

10.00 m·

,

=

14.40 m·

,

=

4.00 m·

,

=

36 cm; b c e v 1 t_c h s ¢ s (2) t b c e v 1 t c h s ¢

The accompanying dimensioning table (Fig. 8; cf. Bautechn.

1957, p.19), is used to determine the required shores. The use of

the table is tllustrated by the following examples:

(I) t

s

=

2.00 m.

4.2.3 Construction of shores (struts)

If a shore cannot be placed horizontally or at right angles, the shore end should be secured against slipping by providing steel sections or timber supports in both directions wherever the angle

of slip is more than 5°. The standard outer pile interval in the

horizontal direction is 2.0 m corresponding to the standard outer

pile interval. The vertical distance between shores should not

exceed about 3.25 m, for peripheral shoring 4.00 m and in exceptional cases down to 10.00 m depth, 4.50 m, using an allowable stress of 0e

=

1800 kg/cm2_{• As far as possible, however, peripheral shoring}

should be avoided.

4.2.4 Vertical position of shores

The shore position should be chosen high enough above the construction joint in the wall below it so that the application of the waterproofing will not be hindered by the junction point of the

•

steel reinforcement, i.e., where

d = 20 mm steel rods with 1.40 m interval d

=

26 mm steel rods with 1.65 m interval are used.

On the other hand the second construction joint of the wall must be at least 42 d below the top of the roof slab.

Where the vertical position is restricted a distance from a point about 20 cm ｢･ｬｯｾｬ the construction joint to the shore of about 1.10 m is reQuired where the shore is above the [-section.

This is necessary to a!low a proper waterproofing joint. In the

case of a shore directly on the (-section 0.80 m is sufficient (Fig. 18).

The vertical level of the shores should also be chosen so that they will not have to be changed on account of existing cables and

pipes. If the road deck beams are also used for shoring, thereby

eliminating the top shores, the buckling length of the I-sections should be reduced by longitudinal shores

>

¢

20 em at the centre when

A exceeds 200. For cantilever action of the piles above the top

shoring position, with a steel stress of a

=

leOO kg/cm2 a canti-lever length of about2.0J rn is obtained. If these stresses were to be exceeded by more than 12.5% for a comparatively long time due to the construction work it would be necessary to install temporary shores at the top end.

4.2.5 Support of shores

On the central piles all shores should be supported in the

[-sections which are bolted directly to the piles. The space

between the two (-sections at the supporting position of the shores should be filled With a suitable piece of round timber which is specially secured against dropping.

On the outer piles the shores should be supported in a

[-section which spans at least two bays and is bolted to the pile • The shores should be secured in position by two hardwood wedges

driven simultaneously. So that the wedges will not be weakened by

the provision of holes for the heads of bolts, hardwood liners of

15 mm thickness should be inserted between them. The purpose of the

continuous [-section are: to ensure the correct ｳｰ｡｣ｬｮｾ of the outer wall piles, to prevent rotation of the piles, to distribute the earth pressure more uniformly on to the shores, and, in certain

cases, also to act as supports for the road deck beams. This is

assuming the standard shore spacing according to 4.2.2 (Fig. 18

and 19). At the lowest shoring position in exceptional cases beam

claws can be used (Fig. 20 and 21) instead of the continuous [-sections for supporting purposes when local considerations or rapid progress in construction make this desirable, provided opposite piles allow vertical shoring; otherwise it will be

necessary to use [-sections here as well. If the piles, especially

IP-sections, are strong enough to permit spans up to 4.50 m,

particularly where there are [-sections exactly perpendicular to the axis of the tunnel, the [-steel beam can also be placed below the

shoring position. For wedging up the shores hardwood wedges of at least 2.5 em average thickness should be used.

4.3 Diagonal bracing (Fig. 22)

The arrangement and design of the bracings should be determined in the shoring plan (Fig. 19, 23, 25, 26). The first principle is that all measures for securing the tunnel excavation depend on the

weakest point of the shoring construction. The type of construction

is evident from the figures. Fig. 24 shows the excavation without transverse bracing.

4.3.1 Vertical lonitudinal bracing {Fig. 23)

The central piles are subjected to vertical forces from the dead load of the shoring system, and, When the excavation is covered by a deck, also from the dead load of the deck, as well as from traffic and possibly also from the equipment being used in

construction. The central piles also have to take some horizontal forces in the longitudinal direction because the shoring system is not always straight-lined and because of deceleration and

acceleration of vehicles on the deck. Dischinger(S) in his report on the serious cave-in during the building of the Berlin North-South S Route, pointed out that here, as in most construction

•

accidents, the cause lay in a lack of stability. The dangers from

having the piles too short had not been fully realized and while precautions had been taken to prevent vertical displacements,

nothing had been done to prevent horizontal movement. In this

connection it is again emphasized that in all excavation shoring operations the joints should be protected against displacement in all directions by diagonal bracing.

Diagonal braces should be installed between the central piles

for protection against longitudinal displacement. The steel

cross-｢ｾ､｣ｩｮｧ should be placed between the upper shore levels in every

second central pile bay in the case of three to four shore levels, and over the entire length of the excavation in the case of five or more shore levels (Fig. 23).

To transfer the longitudinal forces from the diagonal braclngs of the upper part of the centre wall to the ground, at certain

intervals two central piles should be reinforced down to the floor

of the excavation by structural steel cross-bracings. These should

be installed: on straight stretches and at curves with a radius

> 500 m,

with single piling, in every eighth or sixth bay, with double or more pile rows, in every fourth bay; on curves of < 500 m radius

with single piling, in every fourth bay,

with double or more central pile rows, in every third bay on curves of < 250 m radius,

with single centre piling, every third bay,

with double or more central pile rows, in every second bay. At transitions from single to two or more central pile rows and where central piles are staggered, the end bays are to be provided with structural steel cross-bracing from top to bottom. In case of normal cQnstruction this cross-bracing can be omitted in

the bottom part. In general one full bracing in the second bay 1s

4.3.2 Horizontal and vertical bracinr; (Fi;;. 19, 25, 26)

In excavations without central piles, ｢ｲｾ｣ｩｮｧ is not generally

necessary. On curves of less than 250 m radius the use of bracing

should be decided upon from case to case. In order to use the

outer walls for absorbing the horizontal longitudinal forces occurring in the central piles, one horizontal bracing should be installed at one shoring level next to a vertically reinforced central pile bay, in deeper excavations this should be done at two

shoring levels. The bracing should be independent of the shores.

These bracings should'be placed wherever possible above the tunnel ceiling so that they interfere as little as possible with the work on the tunnel and can remain in place until the tunnel is finished. In excavations with single central piles the bracings will be in

the form of a cross-brace (Fig. 25). In the case of two rows of

central piles the bracing must be designed as a double-braced

construction (Fig. 26). The horizontal bracing should be installed

every eighth central pile bay and should be made of structural steel.

A vertical bracing should be installed between the first and second shore levels in combination with the horizontal transverse bracing in every eighth cent raL pile l--ay (Fig. 19).,

The horizontal and vertical bracing should be made of

structural steel. Under difficult local conditions the arrangement

of the transverse bracing should be determined individually.

4.4 Connections and joints

For the connections and joints of structural steel sections,

4D bolts and standard holes should be used. The bolt threads should

not extend into the holes. The holes should not be flame-cut but

must be drilled, for 20 mm bolts with a diameter of 21 mm and for

24 mm bolts with a diameter of 25 mm. The joints in the channel

walls must not be made at the piles but must be placed in the spaces

between the piles and the road deck supports. The connections should

be calculated for tension (each with two 20 ｭｾ bolts) and for

•

•

taken into account separately. If at the same time they carry the road deck see Sec. 3.8.5.

Welded joints may also be used if made by approved welders. In order to keep down the number of types of bolts at the building site, only 20 mm" (4D) and 24 mm (4D) bolts should be specified for the bolted joints, which should be calculated from case to case.

4.5 Road deck (Fig. 27)

4.5.1 Road deck beams

ｔｨｾ road deck beams should be laid directly on the uppermost channel sections of the outer walls, always near the piles, and

bolted down tightly. The allowable distance from the pile must be

calculated. If possible wide flange beams should be used when the road deck carries streetcars (Fig. 28 to 32, showing details at

points 1-8). In excavations with one or ｾｯｲ･ central pile rows the

road deck beams should generally be placed in staggered arrangement on the cross-beams of the central rows and should be supported on the channel sections of the outer walls acjacent to the piles, so

that each beam represents a girder on two supports (Fig. 28). Where

the deck beams extend across two bays they can be made continuous, as girders on three supports.

The uppermost channel sections and the cross-beams of the central rows also accommodate the head shores, which are used only for a half-open excavation (Fig. 29) and in the region of the

bracings (Fig. 23). If the road deck beams are also used as shores

for the excavation and if the load on the cantilevering end of the pile is 1800 kg/m2 _{(point 1 and 2 in Fig. 28, point 5 in Fig. 30)}

they should be fitted with knee-braces or horizontal channel sections.

4.5.2 Bracing against deceleration ｦｯｲｾ

For transmitting the deceleration forces due to braking of

vehicles to the outer walls, except in the case of narrow excavations up to 6 m in width where the continuous road deck beams transmit

•

intervals of not more than 30 m in the region of the horizontal

bracings. Their position will depend on the local conditions. For

example, brake force bracing should be provided near rail sWitches and near bus stops, since this is where braking occurS most

frequently and regularly. These bracings are made of angle steel

sections bolted to the bottom flanges of three road deck beams as diagonals so that these road deck beams and angle sections together form a horizontal lattice bracing (points 1 to 4 in Fig. 28 and 29). Adjacent beams should be forced to contribute by providing a

longi-tudinal stiffening of not less than 20 em diameter timbers laid parallel to the tunnel axis at half the height of the I-beams whenever the beams by themselves no longer suffice for the

trans-mission of the braking forces to the outer walls. The bolted

joints between the road deck beams and the cross-beams serve

primarily to absorb the brake forces. In the zone of the brake force bracing the three beams should also be stiffened near the supports

With round timbers of 20 em diameter. In any case the brake forces

should be transmitted to the fixed points which are formed from the horizontal and vertical bracings. the braking forces being considered

as an additional load. If possible, therefore, one of the brake

force bracings should be placed directly above the fixed point; if this should lead to too complicated connections then the braking force should be carried directly downwards by diagonals.

4.5.3 Expansion joints

If continuously welded embedded rails have to be exposed the traffic authorities should be urged to provide expansion joints in order to prevent the rails from buckling.

4.5.4 Decking of roadways

According to the Street Traffic Regulation the road decking for standard loads consists of 12 x 18 ern timbers which shall be butted

only over the beams, and 5 ern thick wooden planks laid over them. In exceptional cases only, e.g. at double street intersections, hardwood planks should be used. As soon as t::e planks are worn down 2 ern by the traffic they should be re91aced. At transition points from road decking to pavement protective angle pieces

50 x 50 x 5 should be installed which enclose the plank ｳｵｲｦｾ｣･ｳ

(see details of Fig. 28 - 32).

The squared timbers should be laid longitudinally with no gaps

between them. They should be kept from moving by angle steels every

30 m. The lateral space between timbers should be 1 cm. These

gaps should be maintained by liners.

4.5.5 ｄ･｣ｫｩｮｾ of sidewalks

If the excavation extends under the sidewalks the squared

timbers should be arranged as shown in Fig. 32, even though this is not required for the normal sidewalk load, since this will take care

of the possibility of vehicles running up over the curb. Wooden

planks 5

bm

thick suffice for decking. The sidewalk edges should be provided with 50 x 50 x 5 angles.

4.5.6 Decking of streetcar ｴｲ｡ｾｫｳ

If ordinary rails are used the streetcar tracks should be laid on sleepers as shown in Fig. 28 and 29. The sleepers are carried on longitudinal girders which are wedged firmly between road deck beams

and rest on tho bottom flanges. If I-beams are used as road deck

beams, adequate supporting surfaces for the longitudinal beams

should be provided, if necessary by welding 125 x 300 x 10 mm bearing

plates or capped I-section flanges. The sleepers should be secured

on the longitudinal beams and the latter in turn should be fastened to the road deck beams by brackets, round-timber props and angles

to prevent their displacement in any direction. To prevent

dis-placement of ralls special shackles or protecting clamps should be installed at intervals of not more than 30 m, the connections of

which should be calculated. All wedges, liners and shims should be

fastened down.

5. Concluding Remarks

The instructions which have come into use since 1953 have proved effective especially with regard to the required safety in the excavation work on the Seestrasse-Kurt-Schumacher-Platz section of sUbway line C, so ｴｨｾｴ no critical circumstances have arisen

,

•

satisfactory as shown by the acceptance of that section of the subway.

On the 3rd of May 1956, this 2.4 km section with the three stations of Rehberge, Afrlkanische Strasse, Kurt-Schurnacher-Platz (Fig. 33) was opened to traffic after a building period of 2 1/2 years.

The following figures give some idea of the scope of the operations: 26,000 m of piles were driven, 14,000 m2 _{of road}

decking was laid, 40,000 m2 _{of planking and 35,500 m of shores were}

installed: 230,000 m3 _{of ground were excavated, 108,000 m}2

protective coating with 82,700 m2 of 3-, 1- and 5-ply waterproofing were applied and 65,200 m3 _{of concrete were placed with 3400 tons}

of reinforcement steel. The aggregate consisted of 40% of West

Berlin gravel sand, and 60% of crushed brick, added in grain sizes

3 - 7, 7 - 15 and 15 - 30 mm. The quality of the concrete was B 225.

In lowering the ground water the 136 unde rwat.er- pumps lifted about 15 million m3 _{of water.}

..

..

References

1. Bousset, J. Betrachtungen zum Einsturzungluck beim Bau der

Nordsud-S-Bahn in Berlin (Observations on the cave-in during construction of the North-South S-line in Berlin). Bautechn. 1937. p.333 •

2. RB: Innerdienstliche Anweisung des Senators fur Bau- und

Wohnungswesen Berlin VII F (Internal directive of the Senator for Construction and Housing, Berlin VII F).

3. Spilker, A. Mitteilung uber die Messung der Krafte in einer

Baugrubenaussteifung (Report on the measurement of forces

in an excavation bracing). Bautechn. 1937. p.16.

4 0 Ohde, J. Zur Theorie des Erddruckes unter besonderer

BerUck-sichtigung der Erddruckverteilung (On the theory of earth pressure with special reference to the earth pressure

distribution). Bautechn. 1938. pp.150, 176, 241, 331,

480, 570 and 753.

5. Lehmann, H. Die Verteilung des Erdangriffs an einer oben drehbar

gelagerten Wand (The distribution of the earth pressure

against a wall hinged at the top). Bautechn. 19420 p.273.

-: Der Einfluss von Auflasten auf die Verteilung des

Erdangriffs an Baugrubenwanden (The influence of vertical loads on the distribution of the earth pressure against

excavation walls). Bautechn. 1943. p.2l.

6. BT: Innerdienstliche Anweisung des Senators fur Bau- und

Wohnungswesen Berlin VII F (Internal directive of the Senator for Construction and Housing, Berlin VII F).

7. BOStrab: Reichsgesetzblatt 1937, Part I, No.123 of 16.11.1937

and Reichsverkehrsblatt, 1940, ed.B. No.47 of 14.11.1940.

8. Dischinger, F. Die Ursachen des Einsturzes der Baugrube der

Berliner Nordsud-S-Bahn in der Hermann-Goring-Strasse (The causes of the cave-in of the excavation of the Berlin North-South S-line in Hermann-Goring Street) •

Bauing. 1937. p.107.

8t 8t 8t Fig. 2

rr---

---:1

ｾ I : Sl ...- I • I l I I

Heavy truck; standard load for 24 ton truck

Fig. 3

Streetcar; standard loads for types TED 52 and TM 3 Fig. 1

Heavy truck; standard load for 16 ton truck

...

• -26-lane F1g. 4 lane

I

•

Road deck beams. Load 1nclud1ng streetcar

lane

Fig. 5

;leary l-Iei'JYY'

ir<Jek Street. c er: trtJc.k

U TED.5.2.- ;}I/-r:----1 - - - , - - - , -- - : l I I I I I I I I I I I I I I I I I I I I I I I Fig. 6 lane lane lane lane lane

Road deck longitudinal beams. Load including streetcar

•

p lleavy lr14(..k 14-r;- - - - --; I I I I 1 I I I p Fig. 7 lane lane

I

1':

(;J

I

Pile interval s

Total shore press.Excavation shore ｣ｲｯｳｳＭｳ･｣ｴｩｯｾ

70t ! 20 : JO "0 5 0 ' 60 lfJ &J 70t Z() JO 40 SO :J 7(1 I/O 10f0 r-, 1\ -, I r-, I'\: r-, t 1\ r-, - I'- r-, II'\. r-, I, I'" I _I-.. I\; r-, r-, I I r-' ....u _.r- r-I

"

I'\. _.J:::. f ·v. I .. ,LV _{"'-'. "V :>p so - 70 3.} ｯＬＮＮＮｾ " z ｾ ... -ｾＢＧｉＭ ｦＬＭｾ ':'- " " , -m ｾ ｾ ｾ _II I ::f-_i·."b

.-V V 1:;- l.- n l3 . '\.7\) - 't

.

, _{ｉｾ , "} ｾ '1".k W ,'I; "'C - _ｌＯＧｾ ,

..

rj) 1 I...- , . I .. .. . t:'_l- ' -ｾＮ ｾＬ "> , , i- _{ｾＭ v} ; , ei!> I ₅ , t- I...;; _{ｾｾ｜ｩ 1--' v} II t _, ｾ j I 1.(.ｾ , 1...- ｾｐ ｾ

_ＢＢｾ

I-J 1/ II _{v t} r I " ....'_. ＭＭｾ t ....' ,.-- _{· V ' ·} 1/ r-r-_t- r ｾｉ .t I _{V V 17 1/} I t> l..-f i> I ., _I ｾｦｚＬＮｾ '» _ｾ｢Ｍ ｾｾ ｾＢｊＹ ｦＭｾｾ［ｬ b--f::::_ｨｾ

n

. <:r (!!' ｾ --1/ ,--1/ 1/ b 1/ , ,/7 I t> f7

,

, 1/ '0 If

Shore pressure for one pile

1 I 2

Total shore ｰｲ･ｳｳＮｾｩｬ･ section (0 = 1500 kg/em)

J ? n I ..."" .. - - - e __ _ 7-' '::' ( (: c -.. E· c ,. .-c • c. r: ｾ '--=. c, -, Shore pressure/m2 e rev ...r:: 7t{m.1 Z 3 t 'I J Q Ｎｾ Earth press. e_t =e t'+ e I-v ' vntbout bldg. press. c

with traffic Dress. accord. to ｾｴｖｏ

For 4 and more supports

For 3 supports

r-,x) for 1-24 - 1-30 and IP-24 and IP-30 the dashed part of curve holds only in the case of 3 supports o t • 7 _{3 ｾ 5 6} 1 b _ｺｾＭ I I' ｾ , '-.: 12 J' 'ｾ 1\ I.i_c I I _r-, 'i I , j' , fi-l I" J' I 1 , 1\ - - -. 5'fra'fl" ... re s ,e:\!t'I 2. \ ,. ; I 7 I \\l!tf1out 1 r,ar'rL 1\ ) ) , r I I 6' -n ｾＧＯ I", H QJ. :>' CJ H QJ, u' m "-', ;'" ;::S Ull "C. (\\ a ;"7

5',

H (1), .0 ｾｃｩ +> ｾＧＲ o .9 Distance of building be 4 .'i 5 7 8 with pressure from building +) examples DT U TTit I I TTl

ｾ

T

ｲＺｪｾ

1-1

r8

_I" L H 1-_1ｾｾＭｮｈＭＭｗｕＭｬＭＭ -iOJ- -ｩ＼ＺＺＫＧＭＫＭｬＭＭＧｾ L... ｾｾ ｾ I i -i \: 1--1 ｮｴＺＧ､Ｚ｜ＺＡＭ｜Ｍｐ＾ｊＮＮｊ［ＺＧ［ｶ＿ＭｾＮ I, I I -ｾＬＬＺＭＫＭＫＭＫＭ

--, 1-.:1" --+-H I " "

ＱＧｾ

ｾ

r-, f--\ <, q I' Tt t::! 77 f--ｾ

t:

\

r

I _L\' _9':::: i i " , F : , ｾＬｉＮ ｾ , -I , \ '"f:;:

ＱＷｩｾ

-+

I 1\ , , ' t : : : '7 'I \1 ) 1 T ,U_L..!...J\1 _{""ll--. T} ..1 J' 1

'0"

_ro 0 , ｾＮ traffic load distance of buLlding de'Jth of foundation ｾ I, o H QJ' . .0 shore len gth , .c vertical shore ｾＬ ､ｩｳｴ｡ｾ｣･ ｾ

pile spac ing horizontal shore interval ...., 1 Trtlrr.c. loa.d. Pv ye SI-.,e/

ｾ

, I_{- - -} '"'M'"_::-r-

"'n

.l

ｾ

I ＢＧｾＧｴ

::!/

ｾ I ｉｉＮｾ '! ｾ '1o...:l I t,-. IｾｊｉＭＬ［［ＧｉＱＭＱ r.I m 1.::Jr«: III .> I

j

I' , ' , [ ---l I' I I I

ｊﾷＯＱｓｬｴﾷｾ

III' I, (¥ ＱｾＺｾＱＱｾＡＺ :-- t, I t ＿Ｌｾｉ :

"';:1)'>

ｾｩ

_{ｾＭ］ＭＭ［ＭＭ］}

i

l' (;

"::1,,' , I.

m

8 , --I 1 I :- .9 , ' - ｬ･ｭ｡ｾ ｾｉ <: _ L -ｾｾＬｾｾ - --fｉｾＭ ｲＭｾｩ r::f-- II, "co, ＭＭＭｃｲＭｾＭＭ･ ..-;-!I ｾＭ r-I

, 'tL"

7 --1';--,' ｾ Determination ｾｾ of rnaximum shore ez

pressure 0 ro , depth below ｾ , surface ｾＬ u). t b c t c <:> ｾｶ 1 h_s = s U c Fig. 8

Design diagrams for determining shore and pile sections

r

j

: Section A-A

A

ｾｐＮｬＸ

Central pilelowest shore

ｉＢＧ］］ｾ］ｗ］ｾ］］］Ｍｉ

Fig. 11

Underpinning of a central pile on the floor in the vicinity of supplementary cross-bracing

ｊ

Ｚ ｴＮＺ ｣ｴ ｩ ｏ ｾ

oN;:'/ ---'::: , ＭＭｾ

.'

Fig. 12 A-A

Underpinning of a central pile on the ceiling

A

r

I

.Central pile _{Section A-A}

Fig. 13

Underpinning of a central pile on the ceiling in the vicinity of supplementary cross-bracing

Head pile wall

Fig. 14

35 J

Z,5

Without building pressure, with traffic load

accord-ing to StVO tm: 15 Z 5 11! l J

- .-.\ <§'2 .-i;' 'tc ｾｇＯ Ｎｾ 6 _XI 7 _1',

,

_c(C. \'J , I \ I I XZ G 2 _I \ I I (.

.

x 5

,

3. ｾＨ｝ I ｾＮ .' .,,9-h I I ｉｾ I 0' 7 19 -₁₁ "W L 4:n1-1

in;

_, 5 ＢＧ［ｾ

'"

7 I

=

depth of foundation

+) not used in tunnel work x) examples With bUilding pressure: ,distance of ｾ o/iJ p. bui Ld Lnz b r <:> c

§

bmiiiJiiijiiDfuJw§ ｾｭ j f 5 6 " tJ 9

ｾＺ

ｾ

(/) I ":.. : mIll

ｾｾＭＭｉＮＭｾ｡ＮＮＮｬ｡ｽＢ

,

!

ｯＮｾ

..,

i

1

ｾＮｾ

0 , I ><. Soil' ｰｾ･ｳｳｵｲ･ｲＮＺＺ OJ below bu Ll.dLng :0" foundation : 7

=

4kg;!em%' :OJ , /I , I 9

=

pile spacing Qj7[,

=

depth below ｾＬ street sur-

tit

face :3IJ (/}

..

;:<:75 o r-l76

=

depth wi th-

277

out ｢ｕｩｬ､ｩｮｧｾＧＸ pressure s t t c b

=

distance of c building Fig. 15

Design chart for determining plank thicknesses for lagging

ｾｾｩｾｗ･､ｧ･ strip ｾｴｾ

-rW"'l,s0;trOO

"'l,50 --zZ8"J'I I •

i

ｾｾ｣ｬＢｲｇＮＮＭＭ

.

I ｾＭＭ＿Ｏ ｾ I • •7 ' • • 'j"

Protective sheet metal

0.5 mm thick, 0.50 m wide Fig. 16

ｉｾｉ ＺＺ［Ｎｾ ｉｾ Wedge strip I . _'1_ I ] 'ＮＬＮＭｾ｣ＮﾷＧ ＢＮｾ <:«:ｾＬ .. + - . •

J.

Protective sheet metal 0.5 mm thick; 0.60 m wide rotective concrete B1201m high ith steel mesh N91

Fig. 17

Wedging of lagging at IP-piles

Point 4

;:=:====::::::::bl

_{I 1,} 'l3ｾｾ

ｬｊｾ

Point 1 _ｾ Point 2 r..: ,: I,) !!? _ｾｉ -...:: , ｾ ｉｾ ｬｴｬｾ _. I':l <::r _ｉｾｾ ,- \", S? _{ｾｴ u ..:..:.} ',> ｉｾｾ _{..; '-} ｉｾ '"" ｾ d,..j.J ｉｾ -9. Point 3 L. , ｾ _! o N --:'''''j/;":»,-YirwiffJ'ft,: , .1 " ｾＭＭＭＭＢ

.

(

ｾ ,1,.- .---, I c' •CＧｾ ( , ' ＮｬｬｉＮｾ

;/

ｾ \ ｾｾ j 1 '," I Ｂｾ /

'f

.

,

.

--ｾｾｾｾｊｉ

k)::? • • Fi'g. 18

Vertical positions of shores

7 Ｘｾ］］］］ｈＺＺ］］］ｾＺ " II IJ Point 5 Point 7 S IDS and hardwood wedges Point 6 Point 9

,,50·50'5 only inU'eI'oa.(､ｾ･ｾ

t;:::;;:::;;::::::;;::::;;::r:;;::::;;:::;;:::;;::::;;:l C 2 0 c l O • • I3Z_ !<flO ao aOO·70070 Fig. 19

Longitudinal ｢ｲ｡｣ｩｮｾ 10m ｢ＡＮＮＮＮＡ］ＡＬＭＭＡＭＭＡＮＮＮＮＮＮｾ］ＭｯｉＧ a 5 h i I ! I J ｝ｾ ｾ

n

｝ｾ

ｾ

tI

;= ;::JJ

I

ｾ -.

-ij

ｉ｟ｾ

) --- --- -- -- - - -" " II " I ' l l I, I' ," I, _{" " .r} (Concrete floor •

..

Fig. 23

Longitudinal bracing for excavation shoring

II II ｾ G !' ,--_"':.=====..ｾＮＺ］ＭＺＺ ＭｾｾｾＢＺＺＮＢＧＮＺｾｾＢＱ I r- --- -- --I I I I I( .,: I r r ｾ II\ I ,r _{_____"J} I II l.. _ _ _ ---- ---II I '- " ' -

...

ＭＭｾ _---...l , Fig. 24

Excavation without lateral bracing

70 Point 10 Point 11 c.JO Wooden shore C.JO cJO H10' L200,7()O,1O , j L200200'76 o ceo-, f\ V V

K

n _1\ L 1'\ 17 __ c

K

1I

t'\ • Fig. 25

Horizontal bracing for excavation shoring in the case of one central pile row

I

'I

I Vl OJ I ｾｐﾷＬ .. Point 4 'I Spacing of lateral / timbersO;fOOl cso-sos . C60 --j ｾ " _{._...}I _-,,7 ..1" '/"0 7C','/'}

L100 II» 108r-ake. force brx-,ng

tr:3 j':' ＮＺＺｾ , I" 2Z/Z6 Cros5lies .'3iJ -ｾＭｾ｟ｾ｟ＢＧＭｾ ?6!.5 -OJOｾ｟Ｍ

Only ,n'lheregIon ofｩＺＮｲｯｾｓＭ

I N/IO , " brac"'9 H I i i ' I i "i": ｾｾ

'"

I 1 ＱｾＯｬｬｊ J j • .",.. / I . I 'I LJ I . ' . [I' " I' I II "fl-J"

ｉｉｾ

Z" fJ 6 0GSO'J ,.·..Ll.,J I' I II l ］ＺｊＮＮ･ｾ zPJD rP'IZ;!i' Fig. 29

Excavation decking for a half open excavation and support of

streetcar line with ordinary rails Zil'.:

'0

1":(;""

ｾ

70/10 10/10

/:1

" / i'J

ＧＺＧｾＧＺＢＢＢＢｃ

1

l'J/11ｾＮ ＢＧｾＢＢＧ］］ＭＮｊＮｾ］ＧｾＢＧＧＧＧＧｾ｟Ｇ｟Ｇ｟ＧＧＺ r---r::-c:... ...' . ' 10/10;; .

10;;

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