50th INDIAN GEOTECHNICAL CONFERENCE thigs/ldh/files/igc 2015 pune... · 5 0 th 50th INDIAN GEOTECHNICAL CONFERENCE 17 th–19 DECEMBER 2015, Pune, Maharashtra, India Venue: College

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INDIAN GEOTECHNICAL CONFERENCE

17th

– 19th

DECEMBER 2015, Pune, Maharashtra, India

Venue: College of Engineering (Estd. 1854), Pune, India

ATTENUATION CHARACTERISTICS OF PILE BORING VIBRATIONS

M. R. Khan1, S. J. Shah

2

ABSTRACT

Ground vibrations originating from construction activities are one of the most alarming issues faced by

structural builders, working on the construction of large scale projects down to the buildings erected for

residential purposes. Much more than the structural damages caused on to the adjacent structures, they

create distress to the crowd of population in close proximity to the work sites. The sense of disturbance to

humans is evoked as a very low threshold than is generally estimated during environmental impact

assessments. This is due to the combination of physically experienced vibrations with the noise being

created during the course of action. Construction of pile foundations have become an inevitable part of

the ever-growing civil engineering industry, since present day constructions are progressing with the

motive of satisfying the dreams of humans to touch the skies. These mega structures impose a very large

load onto the ground and demand the load to be transferred to very great depths, necessitating pile

foundations. Bored cast in-situ pile foundations are generally adopted nowadays, since the transportation

of long precast piles is almost impractical through the crowded spaces available these days. Moreover, the

drivability of slender piles into soils is very limited and tedious due to requirement of very high driving

loads. Such high impacts may also result in the failure of foundation, if not installed with utmost care.

Bored cast in-situ piling demands very less complications in the transportation of materials and provides

complete control over the specification and erection of piles at the site. Direct mud circulation technique

is a common method of pile boring used in soft soils. This method requires use of a very heavy cutting

chisel, which is raised and dropped from a predetermined height for cutting into the ground and taking out

the soil contained within. During this drop, the heavy chisel hits the ground with a very high impact,

imparting all the contained kinetic energy of the chisel on to the incident ground mass. This results in

vibration of the ground, with the waves travelling out in the radial direction due to the impact.

Propagation of these vibrations occurs in three mutually perpendicular directions (vertical, radial and

transverse). These vibrations have a general trend to attenuate with increasing distances away from the

point of impact, due to geometric damping of expanding wave front and material damping occurring

within the soil mass. The distances travelled by these vibrations depend upon a large number of factors,

including the weight of hammer, height of drop and the most complex variable, the characteristics of

ground itself. Based on studies that have already been conducted in this regard, standard codes specify the

1Mr. M. Roshan Khan, Department of Civil Engineering, Indian Institute of Technology Bombay, Mumbai, India,

[email protected] 2Dr. Syed Jalaludeen Shah, Department of Civil Engineering, Universal Engineering College, Thrissur, India,

[email protected]

mailto:[email protected]


M. R. Khan & S. J. Shah

maximum intensities of vibrations that the receiving structures or humans may safely be subjected to.

Beyond these limits, vibrations have a destructive attribute and the same must be avoided. Studies are

conducted to find out general trends in attenuation characteristics of vibrations in triple axis directions, in

different soil profiles prevailing at various piling sites. Accelerometers have been used for making

measurements in all the three axes simultaneously and the data is logged onto a computer for analysis.

The readings are measured in terms of peak particle velocities measured in mm/s, which is computed as

the root of sum of squares of vertical, radial and transverse directional vibrations. The variations in peak

ground accelerations are also considered. The effect of depth of boring on the propagation of vibration

has been an important aspect of the study. These results can be used by the piling contractors and

structural builders in practicing sustainable constructions with slightest impacts on the surrounding

environment.

Keywords: Ground vibrations, Direct mud circulation piling, Peak particle velocity

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ATTENUATION CHARACTERISTICS OF PILE BORING VIBRATIONS

M. R. Khan, Ph.D. Research Scholar, Indian Institute of Technology Bombay, [email protected]

S. J. Shah, Professor, Universal Engineering College, Thrissur, Kerala, [email protected]

ABSTRACT: Vibrations due to pile boring activities impose serious concern in safe and sustainable construction

practices. Propagation and attenuation characteristics of these vibrations in various soil profiles are studied in detail

using accelerometers that quantify the vibrations in terms of peak particle velocities and accelerations. The analysis

is done considering vibration components in triple axes directions and the general trends are studied both in

component levels and as resultant particle velocities and accelerations. Based on the standardized safe permissible

limits, piling contractors need to ensure environment friendly pile boring sequences, inflicting meagre deteriorating

effects on the proximate structures and least discomfort to the population in vicinity.

INTRODUCTION

Direct Mud Circulation (DMC) is a common

technique used for pile boring in marine soils and

soft soils. The method employs a cutting chisel for

boring, which emanates vibrations during impact

on the ground. These pose serious effects on to the

surroundings and need to be observed critically. A

study was conducted for analyzing the general

trends in propagation of vibration characteristics in

the triple axes (vertical, radial and transverse) and

the results were quantified in terms of Peak Particle

Velocities (PPV) and Peak Ground Accelerations

(PGA).

DIRECT MUD CIRCULATION TECHNIQUE

Boring of piles by DMC involves the use of

various machineries and equipments including

power winch, tripod, drilling chisel, DMC rods,

lifting head, flushing head, concrete mixer,

concrete funnel, tremie pipes, etc for boring the

soil and concreting of piles. Drilling chisel is the

cutting tool used for penetrating the layers of soil

for their subsequent removal. The drilling chisels

are available in a variety of sizes and weights,

which are selected in projects based on the

diameter of piles and the characteristics of soil,

respectively. The DMC rods are connected through

threads for making the drilling chisel reach the

desired depth of boring and also connect onto the

water lines provided inside the chisel. During

flushing procedures, their function is to carry the

suspension of bentonite to the bottom of hole.

Fig. 1 Drilling chisel with casing

Figure 1 shows the photograph of a casing with the

drilling chisel, which is initially used at shallower

depths for preventing caving-in of bore-holes. The

walls of bore-hole at greater depths are stabilized

by a vertical pump system, as shown in Fig. 2. In

the pump system, a suspension of bentonite is

pumped down into the bottom of the bore hole

through drill rods and it overflows at the top of

casing. The system in general should have the

capacity to maintain a velocity of 410-760 mm/s to

float the cuttings.

An additional weight rod was connected to the

chisel when boring was supposed to be past soils

with higher penetration resistance, like lateritic

soils. There was no requirement of a weight rod

attachment when boring was done in clayey soils.




Fig. 2 Vertical pump system for mud circulation

Concrete funnel is used for pouring in concrete

during the concreting of pile and tremie pipes are

connected at the bottom of concrete funnel to carry

the concrete mix down to the location of

concreting. These are also connected through

threads for varying the height of operation.

Course of piling

After insertion of casing, pile boring is done using

pile chisel as the cutting tool. Chisel is dropped

down straight and then rotated at place to scrape

out the soil to be removed out.

The dropping down of chisel from specified height

onto the ground is the main source of ground

vibration in DMC piling. In this study, vibration

characteristics of the adjacent soil during pile

chisel drops have been the matter of interest.

FIELD MONITORING OF VIBRATION

The information on absolute levels of ground

vibration associated with chisel boring in DMC

piling was collected at various sites in Kerala with

different soil profiles. Piling vibrations were

measured using four accelerometer modules, which

were placed at ground level during the complete

pile boring sequence until the depth of hard stratum

to rest the pile was encountered. Accelerometer

modules had been placed at measured distances of

2.5, 5, 7.5 and 10 m from the point of pile boring

horizontally at ground level, as given in Fig. 3.

Fig. 3 Monitoring Scheme Adopted for Field Study

The accelerations in triple-axes directions were

collected for every point of measurement and

corresponding velocity components were

calculated using a processing microcontroller. The

PPV is then calculated from the three components

of velocity obtained and similarly, triple-axes

accelerations give the resultant PGA.

Monitoring at Piling Location 1

The information on vibration levels was collected

at the site of construction of a commercial complex

in Cochin, Kerala by the method of DMC.

Piles to be erected were of 0.8 m diameter and the

boring equipment being a pile chisel of 0.8 m

diameter, weighing 0.8 tonnes. No additional

weight rod was connected to the chisel since

sufficient advance of boring was achieved with the

weight of chisel itself in the clayey soils. The drop

height was maintained between 0.5-0.75 m. The

profile of layers of soil was obtained by the rotary

drilling of a bore-hole at the piling location, as

given in Table 1.

The horizontal variation of triple-axes ground

velocities and accelerations for various depths of

boring at the site are as given in Figures 4-15.

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Table 1 Soil Profile at Piling Location 1 Depth below Ground (m)

Visual description of

soil

Thickness of layers (m)

1.6 Silty clay with sand

1.6

5.7 Silty clay 4.1 8.8 Sandy clayey silt 3.1 13.6 Silty clay 4.8 14.8 Clayey sand 1.2 27.7 Silty clay 12.9 33.7 Lateritic clay 6.0 37.6 Silty clay with

decayed organic matter

3.9

39.9 Clayey sand 2.3 45.8 Clay with sand 5.9 46.7 Sand 0.9 47.6 Silty (weathered

rock) 0.9

49.6 Hard rock -

Figures 4 and 5 show variations of vertical particle

velocities.

Fig. 4 Variation of Vertical Particle Velocities with

Horizontal Distance at Location 1 (GL-25 m)

The variations of radial particle velocities with

horizontal distances are as shown in Figures 6

and 7.

Fig. 5 Variation of Vertical Particle Velocities with

Horizontal Distance at Location 1 (30-50 m)

Fig. 6 Variation of Radial Particle Velocities with



Fig. 7 Variation of Radial Particle Velocities with


Figures 8 and 9 show the variations of transverse

particle velocities with horizontal distances for

different depths of boring.

Fig. 8 Variation of Transverse Particle Velocities

with Horizontal Distance at Location 1 (GL-25 m)

Fig. 9 Variation of Transverse Particle Velocities

with Horizontal Distance at Location 1 (30-50 m)

The variations in triple-axes ground accelerations

are given in Figures 10-15. Figures 10 and 11 show

the variation of vertical ground accelerations with

depths.

Fig. 10 Variation of Vertical Ground Accelerations


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Fig. 11 Variation of Vertical Ground Accelerations


Figures 12 and 13 represent the variation of radial

ground accelerations with horizontal distances at

various depths.

Fig. 12 Variation of Radial Ground Accelerations


Fig. 13 Variation of Radial Ground Accelerations


Figures 14 and 15 show the variation of transverse

ground accelerations with horizontal distances for

different depths of boring.

Fig. 14 Variation of Transverse Accelerations with



Fig. 15 Variation of Transverse Accelerations with


From the measured values of triple-axes vibration

velocities and accelerations, resultant PPV and

PGA were calculated. The variation of these values

with boring depths, at different points of

measurements are presented in Figures 16 and 17.

Fig. 16 Variation of PPV with boring depths at

different monitoring points in Location 1

Fig. 17 Variation of PGA with boring depths at



Vibration monitoring was next done at the site of

pile boring for a residence apartment in Cochin.

Piles to be erected were of 0.5 m diameter and the

boring equipment consisted of a pile chisel of

diameter 0.5 m connected with a weight rod on top,

weighing a total of 1.2 tonnes together. The drop

height varied between 0.5-0.75 m. Table 2 gives

soil profile obtained by rotary drilling at location of

pile boring.



soil


1.5 Top soil 1.5 10.1 Hard laterite 8.6 10.4 Soft rock 0.3 11.4 Hard rock -

Vibration measurements were done with the same

monitoring scheme adopted for site 1. Similar to

the first site, velocities and accelerations were

measured in vertical, radial and transverse

directions and the resultant PPV and PGA values

were computed. Figures 18 and 19 show the

variation of PPV and PGA with boring depths, at

different points of data measurements considered.

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Vibration characteristics associated with pile

boring were then measured at the site of

construction of another residence apartment

located near the marine coast of Cochin.

Piles to be erected were of 1 m diameter. Boring

was done using a pile chisel of 1 m diameter

weighing 1 tonne and no weight rod was connected

since the advance was optimally achieved in the

clayey soil. The drop height was maintained in the

regular range of 0.5-0.75 m. Table 3 gives the soil

profile obtained by rotary drilling at piling

location.



soil


1.1 Filling laterite 1.1 3.6 Loose clay 2.5 6.0 Silty clay with

shell dust 2.4

9.5 Silty clay 3.5 15.0 Clay 5.5 16.5 Clayey sand 1.5 22.0 Lateritic clay

with sand 5.5

35.8 Clay with sand 13.8 45.3 Decayed wood 9.5 47.8 Stiff clay 2.5 50.2 Fine little sand

with clay 2.4

56.4 Decayed wood 6.2 63.0 Stiff clay 6.6 65.0 Stiff clay with

silt -

Similar to piling locations 1 and 2, vibration

monitoring was done, with the same monitoring

scheme. The vertical, radial and transverse

components of velocities and accelerations were

measured and the resultant PPV and PGA values

were computed.

The variation of PPV and PGA with boring depths,

at different points of data measurements are shown

in Figures 20 and 21.






Peak Particle Velocities (PPV)

The measured PPV values were found to have a

general trend to attenuate with horizontal distance

away from impact point of boring, for all the

depths of boring. It was found that the values of

particle velocities were higher at lower depths from

ground and then start reducing with increased

depths from ground surface up to certain depths.

The values were found to again increase when

boring approached soil layers with higher

resistance to penetration of chisel and then rising

substantially high when the depth of boring was

approaching stronger and hard rock strata.

Peak Ground Accelerations (PGA)

The values of PGA were found to be generally

attenuating with horizontal distance away from

impact point of boring, for all the depths of boring

considered. It was found that the values of particle

accelerations were higher at lower depths from

ground and then start reducing with increased

depths from surface of ground up to certain depths.

The values were found to again increase highly

when the boring was approaching stronger rock

strata. Rate of decrease of PPV and PGA was

found to be highest in rock strata, where the

initially high peaks were found to be decaying

significantly to lower values with distances away

from the point of piling.

Triple-axes Vibration Characteristics

Considering the components of the vibration

characteristics in triple-axes separately, the vertical

particle velocities and accelerations were found to

be greater than radial or transverse components,

with the radial characteristics generally being

greater than transverse in most cases. For higher

distances away from piling point, radial

characteristics were approximating to transverse

values.

Correlation between Vibration Characteristics

and SPT-N Value

A general trend in correlation between ground

vibration characteristics and SPT-N value has been

observed during field monitoring of vibration. The

characteristics appear to be directly related to the N

value, meaning that the vibration characteristics

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have an analogous increase when the penetration

resistance of soil is higher (higher SPT-N value).

With a lower resistance to chisel penetration in

some layers of soil (lower SPT-N value), the

characteristic values are also found to be lower.

A sample set of velocity and acceleration readings

changing with the depth of boring is considered for

the piling site 1 at an accelerometer position of 7.5

m. The values are as given in Table 4, with the

SPT-N values of respective layers of soil also

mentioned.

Table 4 Variation of vibration characteristics with SPT-N value at various depths in one sample point Depth from Ground (m)

SPT-N value

PPV (mm/s)

PGA (m/s

2)

G.L. 4 0.322125 0.305008 05 3 0.253782 0.146521 10 6 0.293043 0.179451 15 11 0.493264 0.322125 20 11 0.784494 0.343623 25 18 1.122268 0.561134 30 30 1.315976 0.514566 35 19 0.971912 0.485956 40 44 1.254734 0.920872 45 38 1.460321 1.104593 50 50+ 1.854329 1.429365

However, an absolute equated correlation between

the ground acceleration/velocity and SPT-N value

is beyond the scope of this study, since the drop

heights were considerably varied at site when

changes in the soil strata were encountered. When

boring was done in soils having lower penetration

resistance, the drop height was lowered since

sufficient driving rate was attained even with lower

energy of impact. However, when tougher soil

layers were encountered, the drop height needed to

be increased, imparting more energy for driving to

suffice rate of penetration. Due to this, there is no

benchmark impact energy corresponding to chisel

drops, with which one can compare the readings.

CONCLUSIONS

Accelerometers were used for the measurement of

vibration characteristics at various sites and data

measurements were done in terms of PPV and

PGA for studying the variation of the vibration

characteristics propagating away from the impact

point of piling at different depths. PPV was found

to have a general trend to attenuate with horizontal

distance away from impact point of chiseling for

all the depths of boring. The velocities were higher

at the ground level and start to reduce with increase

in depths from ground surface. The same rises

again considerably when boring approached soil

strata having higher resistance to chisel

penetration. PGA was also found to be generally

attenuating with horizontal distances away from

impact point of boring for various depths of boring.

The values of PGA were higher at lower depths

from ground and then start reducing with increased

depths from surface of ground up to certain depths.

The values were found to again increase highly

when boring was approaching soil with greater

penetration resistance or the stronger rock strata.

Maximum measured values of PPV and PGA were

associated with chiseling in hard rock strata. The

rate of attenuation of PPV and PGA was found to

be highest in the rock strata, where the initially

high peaks decayed significantly with increase in

distance away from the chiseling point. Vertical

vibration components were found to be greater

than the radial or transverse components. The

radial vibration characteristics were found to be

generally higher than transverse components in

most of the measurements. At higher distances

away from the point of boring, radial values

approximated to transverse readings. Vibration

characteristics appeared to be directly related to the

SPT-N value, meaning the vibration characteristics

had an analogous increase when penetration

resistance of soil is higher. When boring was done

at sites with soils having higher resistance to

penetration, weight rod attachments were done to

the chisel to attain a higher weight of drop. This in

turn transferred higher energies to the ground,

resulting in greater values of velocities and

accelerations. Monitoring of ground vibrations is

indispensably required for piling monitoring and

controlling to minimize damages to adjacent

structures.


REFERENCES

1. Amick, H. and Gendreau, M. (2000).

“Construction Vibrations and their Impact on

Vibration-sensitive Facilities”, Proc. of

Construction Congress 6, ASCE, Orlando,

Florida, 758-767.

2. Athanasopoulos, G. A. and Pelekis, P. C.

(2000). “Ground Vibrations from sheetpile

Driving in Urban Environment: Measurements,

Analysis and Effects on Buildings and

Occupants”, Soil Dynamics and Earthquake

Engineering, Elsevier, 19(5), 371-387.

3. Department of Environment and Conservation

NSW. (2006). “Assessing Vibration: a

technical guideline”, Environmental Issues,

<http://www.environment.nsw.gov.au> (March

17, 2012).

4. Hwang, J. H., Liang, N. and Chen C. H. (2001).

“Ground Response during Pile Driving”,

Journal of Geotechnical and Geoenvironmental

Engineering, ASCE, 10(1), 939-949.

5. IS 14884 (2000). “Mechanical Vibration and

Shock - Vibration of Buildings - Guidelines for

the Measurement of Vibrations and Evaluation

of their Effects on Buildings”, Bureau of Indian

Standards, 1-25.

6. Jaksa, M. B., Griffith, M. C. and Grounds, R.

W. (2002). “Ground Vibrations Associated

with Installing Enlarged Base Driven Cast-in-

Situ Piles”, Australian Geomechanics, 37(1),

67-73.

7. Masoumi, H. R., Degrande, G. and Lombaert,

G. (2006). “Prediction of Free Field Vibrations

due to Pile Driving using a Dynamic Soil–

structure Interaction Formulation”, Soil

Dynamics and Earthquake Engineering,

Elsevier, 27(2), 126–143.

8. Shah, S. J. and Khan, M. R. (2012).

“Development and Application of a Vibration

Measuring System to Monitor Piling”, Proc. of

Indian Geotechnical Conference on Advances

in Geotechnical Engineering, IIT Delhi, New

Delhi, 1, 452-455.

50th INDIAN GEOTECHNICAL CONFERENCE thigs/ldh/files/igc 2015 pune... · 5 0 th 50th INDIAN GEOTECHNICAL CONFERENCE 17 th–19 DECEMBER 2015, Pune, Maharashtra, India Venue: College

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