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Environmental protection measures during construction of the prague subway by drill-and-blast tunnelling
Environmental Protection Measures Construction of the Prague Subway by Drill-and-Blast Tunnelling Ludbk BartoS and Bohumir
Siastnq
Abstract--The authors present
recommendations for limiting the effects of blasting during tunnelling operations in urban areas. The paper discusses activities necessary at the planning, design and construction stages, e.g. report ofgeologic conditions, determination ofallowableseismicvibrationsand blastingparameters, monitoring. Criteriaforevaluatingsideeffectsof blastingarediscussed inrelation to both protecting inhabitants from noise and vibration effects; and protecting buildings and infrastructure from seismic and air-blast effects. The authors also present a new system for classifying various types of structures based on their resistance to vibration.
Introduction
W
hen construction began on the Prague subway, drilling and blasting was the prevailing method of tunnel excavation. However, the use of explosives on a large scale in major urban centers may result in undesirable side effects, and raises concerns about environmental protection and general safety. This paper presents technical rules for blasting and the control of side effects, e.g. noise, vibration, in the construction of subways. These technical rules may also be applied to any type of construction involving blasting near urban centers or networks, or under similarly difficult conditions. Problems associated with blasting may arise at various stages of a tunnelling project: (1) At the planning stage. (2) During design. (3) During actual blasting on the site. Seismic prospecting for the area under consideration is carried out as part of the geological exploration of the site. Prospecting surveys and small experimental blasts are conducted in order to generate vibrations, which are recorded on seismographs located on the surface. Such seismic survey results provide the initial data during the project preparation stage. A project report is then prepared to guide excavation by blasting. This plan specifically includes: (1) Assessment of the geologic Present address: Ludck BartoS and Bohumir S‘tastnt, Vjlskumnq tistav iniinierskych stavieb,Botanicka 68A, Brno, Czechoslovakia.
Tunnellmg and Underground Printed in Great Britain.
Space Technology,
During
R&sum&-Les auteurs prkentent
des recommendations pour limiter les ejfets des explosions lors de travaux tunneliers em milieu urbain. L’article discute des activitb ntcessaires lors de la @@aration, de la conception et de la construction (rapport sur les donntes gtologiques, dttermination des vibrations kismiques possibles et paramttres d’explosions, pilotage). Les critbres pour &valuer les effets secondaires d’une explosion sont discutb en fonction de la protection contre le bruit et des vibrations des habitants; de la protection des bhtiments et des structures contre les effets skismiques et d’air propulst. L’auteur prbente un nouveau systtme de classification des structures en fonction de leur rtsistance aux vibrations.
conditions, as they relate to blasting operations. (2) Determination of allowable seismic vibrations for all structures (buildings, urban networks, etc.) close to the construction; and, if possible, determination of allowable acoustic effects. (3) Determination of the fundamental parameters governing blasting operations-specifically, the maximum allowable amount of explosive per delay and per blast. (4) Determination of the blast layout, including blasting patterns and excavation procedures. (5) Outline of the various types of isoseisms and estimate of isoseismic magnitudes, i.e. contours, drawn on a map of the region in the vicinity of the tunnel headings. (6) Measures for the control of blast vibrations and for monitoring the effects of blasting. Observations are carried out during blasting in order to determine the intensity of the undesirable side effects, especially vibrations likely to affect certain structures or other object in the vicinity. These measurements allow values to be determined for the maximum allowable explosive charges and for the corresponding dynamic strains.
from the harmful effects of noise and vibration. (2) The need to protect buildings, the urban infrastructure and other installations from both seismic and air-blast effects of blasting.
Protecting Inhabitants from Noise and Vibration The allowable values for noise and vibration are usually determined by local health standards and any relevant exceptions granted for excavation operations. A detailed discussion of the physiological effects of blast vibrations is beyond the scope of this paper, so we will mention just one example of allowable values for vibrations for frequencies up to 100 Hz. In residential areas, the maximum value allowable for vibration acceleration is 1 m/s* (39 in./s*) during daytime, and 0.089 m/s* (3.5 in./sz) at night. In mixed-use areas, areas, the i.e. industrial-residential corresponding value is 2 m/s* (78 in./s*). Allowable noise levels produced within buildings by excavation operations are 70 dB during the daytime and 50dB at night; outside the buildings, the corresponding values are 100dB during the day and 80 dB at night.
Protecting Urban Areas from Air Blast and Blast Noise Criteria for Evaluating Side Effects of Blasting Undesirable side effects are considered from two viewpoints: (1) The need to protect inhabitants
Vol. 3, No. 4. pp. 393-397, 1988.
0886.7798/M
$3.00 + .OO
Pergamon Press plr
The maximum allowable value for air-blast pressure on surface buildings is established by considering the most sensitive parts of the buildings, such as windows and other glazed surfaces, and roofs. The maximum allowable value
393
tor the dynamic air-blast pressure is 0.15 kPa. In assessing the effects of blast vibrations on buildings, the authors have devised a new classification system. Construction systems are divided in four main groups: (I) Civil structures, habitations, industrial and office buildings, etc.
(2) Engineering structures (3) Underground structures. (4) U ndergrou nd urban networks and cables. These groups can be further sorted using the group and letter classification system shown in Table 1. This system can be refined to reflect the characteristics of a specific type of con-
struction by assigning complementary numerals as appropriate (see Tal)le 1). By using this classification system--i.e. labelling each spe(ific construction type with one capital letter and one ot two c o m p l e m e n t a r y f i g u r e s - - i t is possible to specify the allowable m a x i m u m vibration characterized by the oscillation velocity in the specific
Table 1. Classification of various types of structures based on their resistance to vibration. Group No. Letter classification and description I
II
III
IV
A:
B:
Small brick (masonry) structures. The plan area of these buildings is a maximum of 200 m2; they are no more than 3 stories tall.
C:
Large buildings made of brick or of treated stone; small structures with a monolithic floor; buildings constructed after 1945, of brick, molded brick or panels.
Second complementary numeral
01: Structures having serious flaws, large cracks in the bearing units; obviously damaged structures.
01: Foundation unknown, partially based on a bank, or based on a slope without a rocky base.
02: Poorly maintained structures characterized by damaged surfaces and numerous microcracks in the structure.
02: Foundation built on a homogeneous layer with a strength greater than 0.15 MPa, and with the water table at least 1 m below the base of the structure.
03: Well-maintained and new structures.
03: Foundation built on a homogeneous layer with a strength greater than 0.6 MPa, and with the water table at least 3 m below the base of the structure.
Same as for Group I
Same as for Group I
Same as First Complementary Numerals
D:
Buildings having a reinforced concrete frame or a steel frame; monolithic concrete structures; buildings erected for service and manufacturing purposes.
E:
Reinforced concrete structures for service and manufacturing purposes; reinforced concrete silos and tanks.
C:
Stone bridges featuring carvings and decorations similar to Group I structure; supporting and protecting walls made of stone or brick; masonry water towers.
D:
Abutments of bridges made of treated stone; monolithic water towers.
E:
Reinforced concrete engineered structures; steel poles.
C:
Coatings made of ceramic and stone; pavings in subway passages.
04: Built more than 15 years ago,
D:
Brick, stone or molded brick masonry in the underground.
05: Built fewer than 15 years ago.
E:
Underground monolithic reinforced-concrete structures; bricked-up galleries and circular- or ovular-shaped monoliths; prefabricated canals and tunnels; tubes more than 80 cm in dia.; underground reinforced concrete walls; anchors/anchor roots.
G:
Piping made of concrete, abestone, sandstone; cable connections; reel boxes on communication cables.
H:
Cast iron or concrete piping; piping made of plastic material.
j-
Multi-conductor cables; concentric communication cables.
K:
394
Historical buildings made of natural stone or masonry (brick), with arched lintels, beams, and even plane vaults above rooms at the ground level and in the basement, These buildings often have richly decorated front facades. Because of their historical significance, they are maintained with special care.
First c o m p l e m e n t a r y numeral
Same as for Group Ill
Steel piping.
TUNNELLINGAND UNDERGROUNDSPACE TECHNOLOGY
04: Piping with internal over-pressure greater than 3 MPa. 05: Piping with internal over-pressure greater than 1.5 MPa. 06: Piping with internal over-pressure less than 1.5 MPa,
Volume 3, Number 4, 1988
Table 2. Distribution o] construction types based on their resistance to shocks.
Group I (Residences, civic and industrial structures) A1 A21, A22, B1 A23, A3, B2, C1 B31, C21, C22 B32, C23, C31, D11 B33, D12, C32, C33 D13, D21, D22, D31, E1 D23, D32, D33, E21, [E22], [E31] E22, E23, E31 E32, E33 [E33]
Group II (Engineering structures)
Group III (Underground structures)
[C1] C1, C21 C22, C31, D1 C23, C32, C33, D2 D23, D31, E1 D32, D33, E21, [E22] E22, E23 E3, F1, F32 [E3], F33
Group IV (Urban underground network and cables)
Frequency range 20-50 Hz
50 Hz 10 15 20 25 35 50 80
[C4] C4, [C5], G4, [D4] C5, D4, [D5] [C5], D5, [E4]
G4 G5, H4, K44, [G4] H5, K54, [G5]
5-7 7-10 10-15 15-20 20-30 30-40 40-60
E4, [E5]
J, K45, K55
60-80
100
E5 E5, F4 [F4], F5
K55, K46, J K56, [J] [K56]
80-120 120-150 150-200
150 200 250
Note: The smaller the values of the vibration velocity, the smaller are the shock frequencies. Values in brackets remain valid under specific conditions.
frequency range. These values are shown in Table 2. In blasting, we define limit values for two m a i n frequency groups of seismic waves: (1) 20-50Hz: typical for surface excavations. (2) Above 50 Hz: typical for blasting in tunnels, galleries, etc. T h e dynamic resistance for types of construction not covered by this classification system must be determined on a case-by-case basis.
works ( G r o u p III) shown in Table 1 are comparable to the corresponding values for surface buildings of similar quality. For example, a reinforced-concrete tunnel l i n i n g ( G r o u p III) is considered comparable to a surface structure of reinforced concrete (Group II). Substantial field experience, both local and foreign, has demonstrated that u n d e r g r o u n d structures have a higher resistance to dynamic vibration effects or shocks than do surface structures of the same material. We believe that, in
order to improve our theoretical and experimental knowledge of the relative resistance, i.e. underground vs surface, so as to arrive at practical conclusions, it will be necessary to pay more attention to the way that seismic phenomena affect structures, as well as to the actual constructed arrangement of tunnel linings in cross-section. T h e current status of such vibration effects studies in Czechoslovakia may be considered in two parts: (1) fundamental studies, based on known results from
Seismic Effects on Underground Structures T h e values for allowable magnitudes of vibration effects on underground
A
|
"~:2) ® ®
® Figure 1. Example o[ the interaction between a wave P and a circular-shaped construction, under the condition ~ < D, where ~ = wavelength, and D = diameter o[ the structure. The physical model is a plexiglass ring in a transparent liquid. (From the archives o[ Dr ]. Koz~k, Csc., Geo[yzikMnlustav, CSA V Prague.) Volume 3, Number 4, 1988
~
,
.
-®
l"1mm
•
J_
.....
I'7
Figure 2. Partial recordings o[ the vertical component o[ movement f l o m the point o[ the experimental, rein]orced-concrete arches (1 and 2), and the concrete support (3), with pillars on which the arches have been adjusted as a whole. The arrows with the letters A and B show where the arches have been adjusted in the experimental section. A =[reely adjusted arch; B =grounded arch. Scale o[ experimental model with respect to [ull-sized underground system o[ chambers is M = 1:1000. The experiment was per[ormed in the L u b e n i k magnesium mine by blasting successive explosive charges having a total weight of approx. 66 tonnes. TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY 395
foreign literature, together with some l i m i t e d e x p e r i m e n t s on models; and (2) studies on actual structures in-situ. W i t h respect to the m e c h a n i s m by which seismic waves affect u n d e r g r o u n d structures, it is assumed that all seismic effects are a form of d e f o r m a t i o n or m o v e m e n t transmitted in the m e d i u m w h e n the seismic waves pass t h r o u g h the tunnel and the l i n i n g (Fig. 1). T h u s , in assessing the stresses related to a particular type of masonry construction, it is theoretically always necessary to consider whether the decisive factor will be: (1) T h e induced stress (see Fig. 1); or (2) O n e of tim c o m p o n e n t s of m o v e m e n t , e.g. displacement, velocity, acceleration of the rock particles. In this sense, the c o n d i t i o n s of transfer of seismic effects from the rock to the structure become the critical factor. T h e f u n d a m e n t a l criterion that, in principle, determines the characteristics of the interaction between the tension wave and the strength of the structure is the ratio between the w a v e l e n g t h and the m a g n i t u d e of the tensile strength. Accordingly, if the l i n i n g can m o v e relative to the s u r r o u n d i n g rock (Fig. 2), the stress in the structure will tend to be m o r e or less the same as the stress in a similar surface structure. In this case, it is reasonable, as a r o u g h estimate of the seismic response of the structure, to use the m e t h o d o l o g y
(a) 1.78(mm) 4 230 ~1'q-100-~1"9~ 140
-
/ 1
AA AB 80ram
2 ~J
3
Figure 3. Study of the influence of the quality of interracial contact on wave transfer. (3a) Distribution for the physical model. (1) Plexiglass prism with coneshaped openings for the sensors A and B (surfaces are polished). (2) Air shock wave acting on the front face of the prism. (3) Sensor with an inserted piezoelectric gauge. (3b-d) Recordings of the stress waves passing through the prism, showing the influence of reflections from the free
surfaces. 3b: Sensors A and B in contact with the oil filter (1 division = 100.10 -6 s; 0.25 MPa). 3c: Sensor B introduced in the dry opening (1 division = 100.10 -6 s; 0.25 MPa). 3d: Sensors ,4 and B introduced in the dry openings (1 division = 100.10 -6 s; 0.25 MPa).
396
TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY
V o l u m e 3, N u m b e r ,t, 1988
and criteria for a similar type of surface construction. T h e data given in Table 1 for G r o u p III should be considered in this way. The degree of correspondence between the movement of the construction and that of the surrounding rock is demonstrated in the examples given in Fig. 2. If the quality of the (interface) connection between the rock and the structural l i n i n g permits the complete transfer, across the interface interstices, of any kind of stress or deformation, the structure behaves in a qualitatively different manner than if the connection is not so complete. T h e lining becomes, in principle, an integral part of the surrounding rock; it is bound to endure the strains transmitted by the rock m e d i u m and to follow its movements faithfully. In this case, the magnitude of the effects of the seismic wave will be determined not by the components of movement, but by the stresses produced by the development of stress concentrations in the material, i.e. lining, rock, around the opening. Today's limited knowledge about the transmission of stress waves from a solid m e d i u m to a solid material (such as a structure) shows that the more solid, i.e. the more rigid, the rock medium, the lower the level of transmitted strains. Using the numerous experiments on
Volume 3, Number 4, 1988
models (such as the examples presented in Fig. 3), it is concluded that, under these conditions, the transfer of stress waves is influenced by the microstructure of the areas of contact (in actuality, the right side of the stope and the wrong side of the lining). In this case, the important parameter for assessing the magnitude of the effects of seismic waves (especially with regard to the o p e n i n g of cracks) is the particle velocity in the stress wave (mass velocity). T h e figures in the literature, e.g. Henrych (1973), Holmerg and Persson (1979) and Weber (1974), for the values of critical velocities for different types of rock show that most of these values are in the range of approx. 1000mm/s (40 in./s) or more, with a possible brittle fracture (under the required conditions for the tensile rupture of the particles). In theory, the values for more resistant structures, e.g. G r o u p II and G r o u p III in Table 1, are smaller than those given above. It is obvious that the allowable strains caused by these dynamic effects on an u n d e r g r o u n d s t r u c t u r e s h o u l d be checked in advance. T a k i n g the a f o r e m e n t i o n e d experiences into account, it is always necessary to give the data regarding the observed or allowable vibration magnitude for underground structures, together with a detailed description of the
lining contemplated for the structure. T h e following possible variation for the internal distribution may be considered: (1) T h e lining is strongly linked to the surrounding rock. (2) T h e l i n i n g is not strongly linked to the surrounding rock (this arrangement is also referred to as a side contact). Cases (1) and (2) may be further subdivided into the following subgroups: (A) Monolithic Concrete (1) Allowing cracks to exist in the (concrete) structure. (2) Excluding cracks in the structure. (B) Erected/Mounted Structures (1) Before creating the monolith and m a k i n g injections for weathertightness. (2) After creating the monolith and m a k i n g injections for weathertighmess. []
References Henrych, J. 1973. Dynamika vybuchu a jeff uziti. Prague: Praha Academia. Holmerg, R. and Persson, P. A. 1979. Design of tunnel perimeter blasthole patterns to prevent rock damage. Tunnels and Tunnelling (March 1979): Weber, P. et al. 1974. Texte provisoire des recommandations concernant l'6tude des effets sismiques de l'explosif. Tunnels et ouvrages souterrains 2 (Mars-Avril 1974).
TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY 397
Siastnq
Abstract--The authors present
recommendations for limiting the effects of blasting during tunnelling operations in urban areas. The paper discusses activities necessary at the planning, design and construction stages, e.g. report ofgeologic conditions, determination ofallowableseismicvibrationsand blastingparameters, monitoring. Criteriaforevaluatingsideeffectsof blastingarediscussed inrelation to both protecting inhabitants from noise and vibration effects; and protecting buildings and infrastructure from seismic and air-blast effects. The authors also present a new system for classifying various types of structures based on their resistance to vibration.
Introduction
W
hen construction began on the Prague subway, drilling and blasting was the prevailing method of tunnel excavation. However, the use of explosives on a large scale in major urban centers may result in undesirable side effects, and raises concerns about environmental protection and general safety. This paper presents technical rules for blasting and the control of side effects, e.g. noise, vibration, in the construction of subways. These technical rules may also be applied to any type of construction involving blasting near urban centers or networks, or under similarly difficult conditions. Problems associated with blasting may arise at various stages of a tunnelling project: (1) At the planning stage. (2) During design. (3) During actual blasting on the site. Seismic prospecting for the area under consideration is carried out as part of the geological exploration of the site. Prospecting surveys and small experimental blasts are conducted in order to generate vibrations, which are recorded on seismographs located on the surface. Such seismic survey results provide the initial data during the project preparation stage. A project report is then prepared to guide excavation by blasting. This plan specifically includes: (1) Assessment of the geologic Present address: Ludck BartoS and Bohumir S‘tastnt, Vjlskumnq tistav iniinierskych stavieb,Botanicka 68A, Brno, Czechoslovakia.
Tunnellmg and Underground Printed in Great Britain.
Space Technology,
During
R&sum&-Les auteurs prkentent
des recommendations pour limiter les ejfets des explosions lors de travaux tunneliers em milieu urbain. L’article discute des activitb ntcessaires lors de la @@aration, de la conception et de la construction (rapport sur les donntes gtologiques, dttermination des vibrations kismiques possibles et paramttres d’explosions, pilotage). Les critbres pour &valuer les effets secondaires d’une explosion sont discutb en fonction de la protection contre le bruit et des vibrations des habitants; de la protection des bhtiments et des structures contre les effets skismiques et d’air propulst. L’auteur prbente un nouveau systtme de classification des structures en fonction de leur rtsistance aux vibrations.
conditions, as they relate to blasting operations. (2) Determination of allowable seismic vibrations for all structures (buildings, urban networks, etc.) close to the construction; and, if possible, determination of allowable acoustic effects. (3) Determination of the fundamental parameters governing blasting operations-specifically, the maximum allowable amount of explosive per delay and per blast. (4) Determination of the blast layout, including blasting patterns and excavation procedures. (5) Outline of the various types of isoseisms and estimate of isoseismic magnitudes, i.e. contours, drawn on a map of the region in the vicinity of the tunnel headings. (6) Measures for the control of blast vibrations and for monitoring the effects of blasting. Observations are carried out during blasting in order to determine the intensity of the undesirable side effects, especially vibrations likely to affect certain structures or other object in the vicinity. These measurements allow values to be determined for the maximum allowable explosive charges and for the corresponding dynamic strains.
from the harmful effects of noise and vibration. (2) The need to protect buildings, the urban infrastructure and other installations from both seismic and air-blast effects of blasting.
Protecting Inhabitants from Noise and Vibration The allowable values for noise and vibration are usually determined by local health standards and any relevant exceptions granted for excavation operations. A detailed discussion of the physiological effects of blast vibrations is beyond the scope of this paper, so we will mention just one example of allowable values for vibrations for frequencies up to 100 Hz. In residential areas, the maximum value allowable for vibration acceleration is 1 m/s* (39 in./s*) during daytime, and 0.089 m/s* (3.5 in./sz) at night. In mixed-use areas, areas, the i.e. industrial-residential corresponding value is 2 m/s* (78 in./s*). Allowable noise levels produced within buildings by excavation operations are 70 dB during the daytime and 50dB at night; outside the buildings, the corresponding values are 100dB during the day and 80 dB at night.
Protecting Urban Areas from Air Blast and Blast Noise Criteria for Evaluating Side Effects of Blasting Undesirable side effects are considered from two viewpoints: (1) The need to protect inhabitants
Vol. 3, No. 4. pp. 393-397, 1988.
0886.7798/M
$3.00 + .OO
Pergamon Press plr
The maximum allowable value for air-blast pressure on surface buildings is established by considering the most sensitive parts of the buildings, such as windows and other glazed surfaces, and roofs. The maximum allowable value
393
tor the dynamic air-blast pressure is 0.15 kPa. In assessing the effects of blast vibrations on buildings, the authors have devised a new classification system. Construction systems are divided in four main groups: (I) Civil structures, habitations, industrial and office buildings, etc.
(2) Engineering structures (3) Underground structures. (4) U ndergrou nd urban networks and cables. These groups can be further sorted using the group and letter classification system shown in Table 1. This system can be refined to reflect the characteristics of a specific type of con-
struction by assigning complementary numerals as appropriate (see Tal)le 1). By using this classification system--i.e. labelling each spe(ific construction type with one capital letter and one ot two c o m p l e m e n t a r y f i g u r e s - - i t is possible to specify the allowable m a x i m u m vibration characterized by the oscillation velocity in the specific
Table 1. Classification of various types of structures based on their resistance to vibration. Group No. Letter classification and description I
II
III
IV
A:
B:
Small brick (masonry) structures. The plan area of these buildings is a maximum of 200 m2; they are no more than 3 stories tall.
C:
Large buildings made of brick or of treated stone; small structures with a monolithic floor; buildings constructed after 1945, of brick, molded brick or panels.
Second complementary numeral
01: Structures having serious flaws, large cracks in the bearing units; obviously damaged structures.
01: Foundation unknown, partially based on a bank, or based on a slope without a rocky base.
02: Poorly maintained structures characterized by damaged surfaces and numerous microcracks in the structure.
02: Foundation built on a homogeneous layer with a strength greater than 0.15 MPa, and with the water table at least 1 m below the base of the structure.
03: Well-maintained and new structures.
03: Foundation built on a homogeneous layer with a strength greater than 0.6 MPa, and with the water table at least 3 m below the base of the structure.
Same as for Group I
Same as for Group I
Same as First Complementary Numerals
D:
Buildings having a reinforced concrete frame or a steel frame; monolithic concrete structures; buildings erected for service and manufacturing purposes.
E:
Reinforced concrete structures for service and manufacturing purposes; reinforced concrete silos and tanks.
C:
Stone bridges featuring carvings and decorations similar to Group I structure; supporting and protecting walls made of stone or brick; masonry water towers.
D:
Abutments of bridges made of treated stone; monolithic water towers.
E:
Reinforced concrete engineered structures; steel poles.
C:
Coatings made of ceramic and stone; pavings in subway passages.
04: Built more than 15 years ago,
D:
Brick, stone or molded brick masonry in the underground.
05: Built fewer than 15 years ago.
E:
Underground monolithic reinforced-concrete structures; bricked-up galleries and circular- or ovular-shaped monoliths; prefabricated canals and tunnels; tubes more than 80 cm in dia.; underground reinforced concrete walls; anchors/anchor roots.
G:
Piping made of concrete, abestone, sandstone; cable connections; reel boxes on communication cables.
H:
Cast iron or concrete piping; piping made of plastic material.
j-
Multi-conductor cables; concentric communication cables.
K:
394
Historical buildings made of natural stone or masonry (brick), with arched lintels, beams, and even plane vaults above rooms at the ground level and in the basement, These buildings often have richly decorated front facades. Because of their historical significance, they are maintained with special care.
First c o m p l e m e n t a r y numeral
Same as for Group Ill
Steel piping.
TUNNELLINGAND UNDERGROUNDSPACE TECHNOLOGY
04: Piping with internal over-pressure greater than 3 MPa. 05: Piping with internal over-pressure greater than 1.5 MPa. 06: Piping with internal over-pressure less than 1.5 MPa,
Volume 3, Number 4, 1988
Table 2. Distribution o] construction types based on their resistance to shocks.
Group I (Residences, civic and industrial structures) A1 A21, A22, B1 A23, A3, B2, C1 B31, C21, C22 B32, C23, C31, D11 B33, D12, C32, C33 D13, D21, D22, D31, E1 D23, D32, D33, E21, [E22], [E31] E22, E23, E31 E32, E33 [E33]
Group II (Engineering structures)
Group III (Underground structures)
[C1] C1, C21 C22, C31, D1 C23, C32, C33, D2 D23, D31, E1 D32, D33, E21, [E22] E22, E23 E3, F1, F32 [E3], F33
Group IV (Urban underground network and cables)
Frequency range 20-50 Hz
50 Hz 10 15 20 25 35 50 80
[C4] C4, [C5], G4, [D4] C5, D4, [D5] [C5], D5, [E4]
G4 G5, H4, K44, [G4] H5, K54, [G5]
5-7 7-10 10-15 15-20 20-30 30-40 40-60
E4, [E5]
J, K45, K55
60-80
100
E5 E5, F4 [F4], F5
K55, K46, J K56, [J] [K56]
80-120 120-150 150-200
150 200 250
Note: The smaller the values of the vibration velocity, the smaller are the shock frequencies. Values in brackets remain valid under specific conditions.
frequency range. These values are shown in Table 2. In blasting, we define limit values for two m a i n frequency groups of seismic waves: (1) 20-50Hz: typical for surface excavations. (2) Above 50 Hz: typical for blasting in tunnels, galleries, etc. T h e dynamic resistance for types of construction not covered by this classification system must be determined on a case-by-case basis.
works ( G r o u p III) shown in Table 1 are comparable to the corresponding values for surface buildings of similar quality. For example, a reinforced-concrete tunnel l i n i n g ( G r o u p III) is considered comparable to a surface structure of reinforced concrete (Group II). Substantial field experience, both local and foreign, has demonstrated that u n d e r g r o u n d structures have a higher resistance to dynamic vibration effects or shocks than do surface structures of the same material. We believe that, in
order to improve our theoretical and experimental knowledge of the relative resistance, i.e. underground vs surface, so as to arrive at practical conclusions, it will be necessary to pay more attention to the way that seismic phenomena affect structures, as well as to the actual constructed arrangement of tunnel linings in cross-section. T h e current status of such vibration effects studies in Czechoslovakia may be considered in two parts: (1) fundamental studies, based on known results from
Seismic Effects on Underground Structures T h e values for allowable magnitudes of vibration effects on underground
A
|
"~:2) ® ®
® Figure 1. Example o[ the interaction between a wave P and a circular-shaped construction, under the condition ~ < D, where ~ = wavelength, and D = diameter o[ the structure. The physical model is a plexiglass ring in a transparent liquid. (From the archives o[ Dr ]. Koz~k, Csc., Geo[yzikMnlustav, CSA V Prague.) Volume 3, Number 4, 1988
~
,
.
-®
l"1mm
•
J_
.....
I'7
Figure 2. Partial recordings o[ the vertical component o[ movement f l o m the point o[ the experimental, rein]orced-concrete arches (1 and 2), and the concrete support (3), with pillars on which the arches have been adjusted as a whole. The arrows with the letters A and B show where the arches have been adjusted in the experimental section. A =[reely adjusted arch; B =grounded arch. Scale o[ experimental model with respect to [ull-sized underground system o[ chambers is M = 1:1000. The experiment was per[ormed in the L u b e n i k magnesium mine by blasting successive explosive charges having a total weight of approx. 66 tonnes. TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY 395
foreign literature, together with some l i m i t e d e x p e r i m e n t s on models; and (2) studies on actual structures in-situ. W i t h respect to the m e c h a n i s m by which seismic waves affect u n d e r g r o u n d structures, it is assumed that all seismic effects are a form of d e f o r m a t i o n or m o v e m e n t transmitted in the m e d i u m w h e n the seismic waves pass t h r o u g h the tunnel and the l i n i n g (Fig. 1). T h u s , in assessing the stresses related to a particular type of masonry construction, it is theoretically always necessary to consider whether the decisive factor will be: (1) T h e induced stress (see Fig. 1); or (2) O n e of tim c o m p o n e n t s of m o v e m e n t , e.g. displacement, velocity, acceleration of the rock particles. In this sense, the c o n d i t i o n s of transfer of seismic effects from the rock to the structure become the critical factor. T h e f u n d a m e n t a l criterion that, in principle, determines the characteristics of the interaction between the tension wave and the strength of the structure is the ratio between the w a v e l e n g t h and the m a g n i t u d e of the tensile strength. Accordingly, if the l i n i n g can m o v e relative to the s u r r o u n d i n g rock (Fig. 2), the stress in the structure will tend to be m o r e or less the same as the stress in a similar surface structure. In this case, it is reasonable, as a r o u g h estimate of the seismic response of the structure, to use the m e t h o d o l o g y
(a) 1.78(mm) 4 230 ~1'q-100-~1"9~ 140
-
/ 1
AA AB 80ram
2 ~J
3
Figure 3. Study of the influence of the quality of interracial contact on wave transfer. (3a) Distribution for the physical model. (1) Plexiglass prism with coneshaped openings for the sensors A and B (surfaces are polished). (2) Air shock wave acting on the front face of the prism. (3) Sensor with an inserted piezoelectric gauge. (3b-d) Recordings of the stress waves passing through the prism, showing the influence of reflections from the free
surfaces. 3b: Sensors A and B in contact with the oil filter (1 division = 100.10 -6 s; 0.25 MPa). 3c: Sensor B introduced in the dry opening (1 division = 100.10 -6 s; 0.25 MPa). 3d: Sensors ,4 and B introduced in the dry openings (1 division = 100.10 -6 s; 0.25 MPa).
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and criteria for a similar type of surface construction. T h e data given in Table 1 for G r o u p III should be considered in this way. The degree of correspondence between the movement of the construction and that of the surrounding rock is demonstrated in the examples given in Fig. 2. If the quality of the (interface) connection between the rock and the structural l i n i n g permits the complete transfer, across the interface interstices, of any kind of stress or deformation, the structure behaves in a qualitatively different manner than if the connection is not so complete. T h e lining becomes, in principle, an integral part of the surrounding rock; it is bound to endure the strains transmitted by the rock m e d i u m and to follow its movements faithfully. In this case, the magnitude of the effects of the seismic wave will be determined not by the components of movement, but by the stresses produced by the development of stress concentrations in the material, i.e. lining, rock, around the opening. Today's limited knowledge about the transmission of stress waves from a solid m e d i u m to a solid material (such as a structure) shows that the more solid, i.e. the more rigid, the rock medium, the lower the level of transmitted strains. Using the numerous experiments on
Volume 3, Number 4, 1988
models (such as the examples presented in Fig. 3), it is concluded that, under these conditions, the transfer of stress waves is influenced by the microstructure of the areas of contact (in actuality, the right side of the stope and the wrong side of the lining). In this case, the important parameter for assessing the magnitude of the effects of seismic waves (especially with regard to the o p e n i n g of cracks) is the particle velocity in the stress wave (mass velocity). T h e figures in the literature, e.g. Henrych (1973), Holmerg and Persson (1979) and Weber (1974), for the values of critical velocities for different types of rock show that most of these values are in the range of approx. 1000mm/s (40 in./s) or more, with a possible brittle fracture (under the required conditions for the tensile rupture of the particles). In theory, the values for more resistant structures, e.g. G r o u p II and G r o u p III in Table 1, are smaller than those given above. It is obvious that the allowable strains caused by these dynamic effects on an u n d e r g r o u n d s t r u c t u r e s h o u l d be checked in advance. T a k i n g the a f o r e m e n t i o n e d experiences into account, it is always necessary to give the data regarding the observed or allowable vibration magnitude for underground structures, together with a detailed description of the
lining contemplated for the structure. T h e following possible variation for the internal distribution may be considered: (1) T h e lining is strongly linked to the surrounding rock. (2) T h e l i n i n g is not strongly linked to the surrounding rock (this arrangement is also referred to as a side contact). Cases (1) and (2) may be further subdivided into the following subgroups: (A) Monolithic Concrete (1) Allowing cracks to exist in the (concrete) structure. (2) Excluding cracks in the structure. (B) Erected/Mounted Structures (1) Before creating the monolith and m a k i n g injections for weathertightness. (2) After creating the monolith and m a k i n g injections for weathertighmess. []
References Henrych, J. 1973. Dynamika vybuchu a jeff uziti. Prague: Praha Academia. Holmerg, R. and Persson, P. A. 1979. Design of tunnel perimeter blasthole patterns to prevent rock damage. Tunnels and Tunnelling (March 1979): Weber, P. et al. 1974. Texte provisoire des recommandations concernant l'6tude des effets sismiques de l'explosif. Tunnels et ouvrages souterrains 2 (Mars-Avril 1974).
TUNNELLING AND UNDERGROUND SPACE TECHNOLOGY 397