Report test programme geocontainers

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REPORT TEST PROGRAMME

GEOCONTAINERS

BY

VAN OORD ACZ

MARINE ENGINEERING DEPARTMENT

All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, or stored in any retrieval system of any nature, without the written permission of the copyright holder and the publisher,

application for which shall be made to the publisher.

Copyright VAN OORD ACZ B.V. - NICOLON B.V. November 1 995

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SUMMARY AND CONCLUSIONS

This report presents the results of the test programme to investigate the dumping of geocontainers at relatively large water depths.

The test programme was executed by Van Oord ACZ in April 1994 in the sand pit at Kel<erdom, near Nijmegen, The Netherlands.

In the test programme 4 geocontainers with a theoretical volume of 368 m'^ were dumped at water depths with a maximum of 20 m.

fill material volume of fiii water depth

[clay/sand] (m^J [m]

Geocontainer 1 sand 170 18

Geocontainer 2 sand 130 13

Geocontainer 3 clay 135 16

Geocontainer 4 clay 160 20

The test programme has a triple purpose:

(i) To develop an appropriate execution method to dump geocontainers accurately at large water depths without failure.

(ii) To investigate the behaviour of geocontainers during dumping and determine the infiuence of the fill material, filling grade and water depth.

(iii) To set up a theoretical model to simulate the behaviour of geocontainers during dumping.

Present report starts with a detailed description of the test programme including the geocontainers, the instrumentation, the execution method and the equipment. Further, the test results are discussed in detail. The test results are based on the

measurements of the velocity and the pressure inside the geocontainer during the dump a the visual inspection of the geocontainer after the dump by divers.

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dump and the inside pressure and tensile force in the geotextile during the impact on the sub soil, has been simulated by means of a theoretical model.

The main conclusions are as follows;

(i) During the test programme 2 geocontainers failed. This means a rate of success of 50%.

The geocontainers failed at the confection seams.

The reason for the failure of the first geocontainer was the incorrect longitudinal distribution of the sand material inside of the geocontainer. Also the impact on the sub soil caused failure of the geocontainer due to the non-horizontal landing. The fourth geocontainer failed during the release from the split barge. The reasons were the quick release together with the high degree of filling with clay.

(ii) Geocontainers 1 and 2 rotated during the dump.

The reason for rotation of the geocontainer was the unequal distribution of the sand fill in cross direction.

(iii) The behaviour of the geocontainer filled with sand differed from the clay filled geocontainer. The clay container is released much quicker from the split barge than the sand container.

(iv) The instrumentation to measure the fall velocity and the pressure inside the geocontainer during the dump was successful,

(V) The theoretical models to simulate the fall velocity and the impact on the sub soil

have been calibrated with the test results.

The simulation of the fall velocity of the geocontainers give reasonable results. The theoretical model to simulate the impact on the sub soil give indicative results only.

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In order to optinnize the installation of geocontainers by means of dumping the following recommendations are made:

(i) The geocontainer has to be filled in longitudinal direction in such a way that the middle part of the geocontainer will be released as first. This prevents a non-horizontai longitudinal orientation during the dump.

(ii) The fill material has to be equally distributed in cross direction in order to avoid rotation in cross direction during the dump of the geocontainer,

(iii) The split barge has to be fixed during the release of the geocontainer. This is possible by means of spud piles or in deeper water by means of an anchoring system. The fixed position prevents the movement of the split barge which would induce a non-horizontal orientation during the dump and a cross directional rotation.

(iv) More proto-type and model tests have to performed in order to investigate the influence of the relevant parameters on the behaviour of the geocontainer.

Especially, the shape of the geocontainer has to be further investigated during the release from the split barge, the fall and the impact on the sub soil.

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LIST OF CONTENTS

SUMMARY AND CONCLUSIONS 24

LIST OF CONTENTS 5 1 INTRODUCTION 6 2 TEST PROGRAMME 7 2.1 Introduction 2.2 Construction qeocontainers ~^ 2.3 Fill material 8 2.4 Sub soil 8 2.5 Failure modes geocontainer 8

2.6 Instrumentation 9 2.7 Equipment ^ 2.8 Execution method ""^ 2.9 Project organization 3 TEST RESULTS 2 3.1 Introduction ^2 3.2 Geocontainer 1 ^2 3.3 Geocontainer 2 3.4 Geocontainer 3 3.5 Geocontainer 4 ^5 4 THEORETICAL SIMULATION 4.1 Introduction 4.2 Dump velocity

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Nicolon will possibly supply geocontainers to a project in the Far East. In that project, the geocontainers will be dumped at a water depth up to 35 m.

Nicolon has commissioned Van Oord ACZ to execute a test programme.

The test programme has a triple purpose:

(i) To develop an appropriate execution method to dump geocontainers accurately at large water depths without failure.

(ii) To investigate the behaviour of geocontainers during dumping and determine the influence of the fill material, filling grade and water depth.

(iii) To set up a theoretical model to simulate the behaviour of geocontainers during dumping.

The test programme was executed by Van Oord ACZ in April 1994 in the sand pit at Kekerdom, near Nijmegen, The Netherlands. Reference is made to attachment 1 for a location plan.

In section 1, the test programme is explained in detail.

In section 2 the test results, based on the observations and measurements during the execution of the works, are presented and evaluated.

Finally, the simulation of the fall velocity and the impact on the sub soil of the geocontainer is explained in section 3.

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Report test programme

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In this chapter the test programnne is discussed in detail.

First the construction of the geocontainers used in the test programme is described. Then, the 2 possible failure modes during the installation of geocontainers by means of dumping is explained.

To monitor the behaviour of the geocontainers during the dump, the velocity and the pressure inside the geocontainer was measured. The instrumentation used is described in this chapter.

Further, the execution method to install the geocontainers is presented, together with the used equipment.

Finally the project organization of the test programme is listed.

2.2 Construction qeocontainers

In the test programme 4 geocontainers have been dumped. Each geocontainer had a theoretical volume of 368 m^ with the following dimensions:

Reference is made to attachment 2 for a definition sketch.

The geocontainers were fabricated from a polypropylene woven geotextile, GEOLON 120, This geotextile has the following characteristics:

Based on the standard width of the geotextile, the geocontainer was constructed of geotextile sections of 5 m. The seams had a strength of 7 0 % of the tensile strength of the geotextile.

On top of the geocontainer 3 reinforced air vents have been created to decrease the - Length - Width - Height approx. 24.5 m approx. 5.0 m approx. 3.0 m - Mass

- Tensile strength (warp and weft direction) - Young's modulus of elasticity

- O 9 0 - Permeability 630 gr/m^ 120 kN/m 1000 kN/m 170 //m 17 l/m^/s

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expected overpressures inside the geocontainer, which occurs during the dump. Also at the front and rear end such air vents have been constructed. Further two longitudinal expansion seams were made on top of the geocontainer with the purpose to decrease the tensile strain in the geotextile during the dump of the geocontainer.

After filling, the topside is connected to the geocontainer by means of a rope and a handstitch at the front end, the rear end and along one longitudinal side.

2.3 Fill material

The sand and clay used to fill the geocontainers in the test programme originated from the sand pit. The sand material can be roughly described as fine sand. The clay consisted of boulders. Further characteristics of the sand and clay were not investigated.

2.4 Sub soil

The sub soil in the sand pit can be described as silty material. 2.5 Failure modes geocontainer

During the execution, basically 2 failure modes are possible. Failure of the geocontainer is defined as rupture of the geotextile, resulting in direct exposure of the fill material to the environment.

The first failure mode is possible during the release of the geocontainer from the split barge. As the geocontainer is going under water, the air inside the geocontainer is replaced by water. Because the time is too short for the air to escape in relation with the speed of the geocontainer going under water, the air pressure increases inside the geocontainer. The air pressure is equal to the hydrostatic water pressure. The geocontainer will fail because of the internal air pressure when the tensile strength of the geotextile is exceeded.

The second failure mode is possible during the impact of the geocontainer on the sub soil. The kinetic energy of the falling geocontainer has to be dissipated by means of deformation of the geocontainer and the sub soil.

The shape of the geocontainer changes during the impact on the sub soil. The soil inside the geocontainer moves sideways, inducing a decrease in height of the geocontainer. In principle the reshaping of the geocontainer requires an elongation of the geotextile. The duration of the impact is relatively short compared to the time required for the air and water to escape in order to follow the reshaping of the geocontainer, inducing an increase of the pressure inside the geocontainer. The overpressure inside the geocontainer is equally distributed

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throughout the cross sectional area of the geocontainer,

2.6 Instrumentation

In order to monitor the behaviour of the geocontainers during the dump, the fall velocity of the geocontainer and the pressure inside the geocontainer were measured.

The fall velocity was measured at three locations on top of the geocontainer: at the front, in the middle and at the end. At these 3 locations the geocontainer was connected to a

revolution counter by means of a reel and an inextensible steel wire. The reel together with the revolution counter was positioned on the gangway of the split barge.

The pressure inside the geocontainer was measured with three pressure sensors inside the geocontainer. Each pressure sensor was sheltered from the soil by means of a nylon

wrapping in order to measure only the water or air pressure. The sensors had a capacity of 6 bar. The cables of the measurement devices were placed in the gangway of the split barge.

The output signals from the revolution counters and the pressure sensors were recorded by a computer by means of a A/D converter and in-house developed software. The

measurements were presented on-line on the screen. The data were stored on hard disc and floppies.

2.7 Equipment

The equipment used during the execution of the test programme is listed below:

Split barge with a hold capacity of 240 m"^ and a split opening of 2.5 m. Reference is made to attachment 3 for a definition sketch.

Pusher tug Stand-by vessel Crane vessel Diving vessel Mobile crane Cable crane Dump truck Shovel

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2.8 Execution method

Hereafter the execution method of the test programme is described in detail.

Transportation of the split barge from Sliedrecht to the sand pit Kekerdom by means of a pusher tug and accompanied by a stand-by vessel on monday 1 7th.

Placing of the buffer geotextiles inside the hold of the split barge. The buffer geotextiles are connected to the split barge by means of ropes every 2 meter. The purpose of the buffer geotextiles is to prevent the geocontainer to fail due to sharp edges and other impacts during loading and during release from the split barge. Installing measurement instruments in the gangway of the split barge. Loading of required equipment for data-acquisition system. Loading of required materials for test programme.

Placing of the geocontainer inside the hold of the split barge. Wrinkles are created at the underside of the geocontainer to avoid jamming of the geotextile during passing of the split opening.

Loading of the geocontainer with sand or clay. Sand has been transported from the storage area at Kekerdom to the quay wall by means of a shovel and dump truck. The sand has been loaded inside the geocontainer by means of a crane.

The clay, originating from the sand pit, has been transported from the storage area to the quay wall by means of a hydraulic crane and a dump truck. The clay was loaded inside the geocontainer in the split barge by means of a crane.

Closing of the geocontainer. Along the front, the longitudinal and the rear end the lid of the geocontainer was connected by means of a rope and a hand stitch.

Connecting pressure sensors at the inside of the geocontainer. The sensor was connected to the geocontainer by means of a hand stitch.

Connecting the 3 steel wires to the geocontainer for the velocity measurement. Installation of the data-acquisition system.

Transportation and positioning of the split barge to the dump location with a water depth of approximately 20 m by means of the pusher tug and stand-by vessel. The

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deepest part of the sand pit has been marked with marker buoys by the stand-by vessel.

The split barge was kept in place at the dump location by means of the 2 vessels.

Dumping of the geocontainers. The split opening of the split barge was maximum 2.5 m. The time required for the opening of the split barge equals approximately 20 sec. The fall velocity of the geocontainer and the pressure inside the

geocontainer were measured during the dump.

Disconnecting the 3 steel wires and the cables of the pressure sensors from the split barge and connecting to a buoy.

Positioning of split barge at the quay wall repeating the procedure from item 3 for the next geocontainer.

Inspection of the geocontainer by means of divers. The condition of the geotextile material and the longitudinal seam, plus the shape of the geocontainer were

investigated as much as possible. Recovering of the pressure sensors and the 3 steel wires.

2.9 Project organization

The involved parties in the test programme are listed below, together with their contribution: Nicolon

Van Oord ACZ

- Rijkswaterstaat - De Beijer - Baars - Touwslager - Marine Construct -client -supply geocontainers -engineering test programme -execution test programme -instrumentation

-final reporting

-permission for dumping -supply and loading clay -supply and loading sand -split barge

-pusher tug -stand-by vessel -diving operations

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Project Geocontainers® - Van Oord A C Z - Nicolon

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The results of the dumping of the geocontainers were determined by means of diving inspection after the dumps and by means of measurement of the velocity and inside pressure during and after the dump. The results are summarized in the table below.

material fill filling grade

water depth

failure rotation velocity pressure

[m^l [%] [ml [y/n] [y/n] [m/s] [bar]

Dumpi sand 170 46 18 y y 4.4 0.17

Dump2 sand 130 35 13 n y 3.3 0.35

Dump3 clay 135 37 16 n n 3.6

-Dump4 clay 160 44 20 y y (3.3)

-The filling grade is defined as the amount of fill relative to the theoretical volume of the geocontainer of 368 m"^. The hold capacity of the split barge used in the test programme is 240 m^.

The overpressure was determined based on the pressure measurements. The overpressure is defined as the difference between the maximum pressure and the pressure after the dump.

The draught of the split barge unloaded is approximately 0.5 m. The draught of the split barge for the 4 geocontainers was approximately as follows:

Geocontainer 1 1.7 m Geocontainer 2 1.4 m Geocontainer 3 1.4 m Geocontainer 4 1.6 m

3.2 Geocontainer 1

The first geocontainer was filled with 170 m^ of sand. The sand in the geocontainer was not equally distributed in cross direction. On starboard side the geocontainer was filled more. Attached to the geocontainer were 3 steel wires for the velocity measurement, on top of the

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geocontainer. The steel wires were connected at a distance of approximately 3 m from the front and rear end, and in the middle of the geocontainer. In the middle of the geocontainer, just above the hand made seam, the pressure sensor was attached by means of a hand stitch.

During the release of the geocontainer the front end dropped out of the hold of the split barge first. The geotextile failed inside the hold at a cross directional confection seam on top of the geocontainer. The weight of the already submerged front part of the geocontainer had to be carried by the geotextile still inside the hold. The confection seam failed under this load.

Due to the uneven release of the geocontainer the split barge moved forward.

According to the divers the geocontainer was ruptured in the confection seam at both ends of the geocontainer. This indicated that the confection seam at the front end failed during the impact on the sub soil. The geocontainer landed with a horizontal velocity and a non-horizontal orientation which increases the probability of failure.

The maximum width of the dumped geocontainer was approximately 7 m at the bottom. The maximum height above the bottom level was approximately 1.5 m.

The geocontainer rotated during the dump. From the view point at the rear of the split barge, the geocontainer rotated clockwise. The pressure sensor and the three steel wires were located under the geocontainer. The hand made seam was not detected. The pressure sensor could not be retrieved, because it was lying underneath the geocontainer.

The reason for the rotation was that the centre of the geocontainer was lying more to starboard and that fill material was unequally distributed in cross direction. The starboard side of the geocontainer submerged first. The upward movement of the split barge and the friction with the port side of the geocontainer resulted in rotation of the geocontainer.

The plot of the measured velocity at the 3 locations is attached to this report. It shows that the starting moment of the fall of the locations of measurement is different. This is in accordance with the observations during the release of the geocontainer.

During the fall, the velocities of the 3 locations of measurement were not the same, indicating a non horizontal position.

It is assumed that the moment the geocontainer hits the sub soil is determined in the plots at the moment the maximum velocity is decreasing. In case the steepness of the velocity versus time relation is 0, the maximum equilibrium velocity is reached.

The time needed for the geocontainer to reach the maximum velocity was on average 5.6 s after the start of the fall. The maximum velocity for the middle and rear end of the

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was the equilibrium velocity.

The maximum pressure inside the geocontainer during the impact on the sub soil was 3.0 bar. After the impact the pressure decreased to approximately 2.8 bar. This meant an overpressure of 0.17 bar during the impact on the sub soil.

The time interval between the touch down ( = maximum velocity) and the maximum pressure was 1.3 sec. This time was needed for the total length of the geocontainer to reach the sub soil and for the soil-water-air mass inside to deform and reshape the geocontainer, inducing the overpressure inside the geocontainer.

3.3 Geocontainer 2

The second geocontainer was filled with 130 m^ of sand. The sand fill was better distributed than the first geocontainer: at the front ends more than in the middle. Also in cross direction the sand was placed more equally.

At the front and rear end, on top of the geocontainer two steel wires for the velocity measurement were attached. Also two pressure sensors were attached to the geocontainer, at one third of the length on top of the geocontainer.

According to the divers the geocontainer was not ruptured after the dump.

The width of the geocontainer was the same as the first geocontainer. The height of the geocontainer above the sub soil level ranged from 1 to 2 m. In length direction the

geocontainer was lying in a bent position, with the bend in the middle of the geocontainer. The reason is that one end of the geocontainer first touched the sub soil and because of a horizontal velocity the other end of the geocontainer was pushed aside.

Like the first geocontainer the geocontainer rotated in cross direction, also to the right hand direction. The geocontainer laid upside down. The 2 pressure sensors could not be retrieved.

The plot of the measured velocities is attached to this report. As for the first dump, it shows that the front end of the geocontainer was released approximately 3 s earlier than the rear end. Also the front of the geocontainer touched the sub soil 3 s earlier than the rear end. This might be the reason for the bent position of the geocontainer after the dump.

From the recorded velocity profile it becomes clear that the maximum equilibrium velocity was reached for both locations of measurement after 4.6 s. The maximum velocity was 3.3 m/s for both locations.

The pressure measurements at the front and rear end show both a maximum pressure, which occurred at the same time as the maximum reached velocity started to decrease,

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marking the touch down. The first peak pressure at the front end was relatively small compared to the second peak pressure at the rear end. This can be explained by the fact that the pressure at the front end could escape backwards to the part of the geocontainer which was still falling. The peak pressure in the rear end was 2.5 bar. After the impact the pressure decreased to approximately 2.1 bar. The overpressure due to the impact on the sub soil was 0.35 bar.

3.4 Geocontainer 3

The third geocontainer was filled with 135 m"^ of clay.

To the geocontainer 3 steel wires were attached on top of the geocontainer. No pressure sensors were attached to the geocontainer.

During the dump operation the split barge was attached to the anchored diving pontoon. This resulted in a steady position of the split barge during the release of the geocontainer. According to the divers the geocontainer was not ruptured.

The dimensions of the geocontainer on the sub soil were the same as the first two dumped geocontainers. As for the second dump, the geocontainer was bent in the middle.

No rotation of the geocontainer was observed. According to the divers the hand made seam was detected intact along the sides of the geocontainer.

The results of the velocity measurement, attached to this report, show that the starting moment of the movement of 3 locations of measurement was the same, indicating a

horizontal orientation of the geocontainer during the release. The maximum velocities of the front and the middle were reached at the same time, after 5.0 sec. The maximum velocities of the geocontainer were 3.6 m/s. From the steepness of the time versus velocity plot it can be concluded that the maximum equilibrium velocity was reached.

3.5 Geocontainer 4

The fourth and last geocontainer was filled with 160 m^ clay.

To the geocontainer 3 steel wires were attached on top of the geocontainer. No pressure sensors were attached to the geocontainer.

During the dump the split barge was not attached to the anchored diving pontoon.

According to the divers the geocontainer was totally ruptured. No shape of a geocontainer could be determined. Observations from the diving pontoon indicated that a large cloud of material was visible around the split barge during the release of the geocontainer. This meant that the geocontainer was already ruptured during the release of the geocontainer.

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As for the third geocontainer the time versus velocity plot shows that the geocontainer was released horizontally from the split barge. For all three locations the maximum velocity was reached at the same time, after 5.0 sec. The maximum velocity was 3.3 m/s, which is the maximum equilibrium velocity, because of the decreasing slope of the plot towards the maximum velocity.

During the dump the difference in depth over the length of the geocontainer was small, with a maximum of 2 m difference between front and rear end.

It has to be stated that the measurement of the maximum velocity was not correct, because the total geocontainer was ruptured during the release of the geocontainer. The relative low velocity can be explained by the loss of material because of the failure during the release.

The reason for the failure during the release is the combination of a quick release of the clay geocontainer together with a high degree of filling. The overpressure in the geocontainer, apparent during the sinking of the geocontainer, is dependent on the degree of filling. A higher degree of filling will increase the pressure. In case of a quick release from the split barge the air has little time to escape which will increase the overpressure.

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The behaviour of the geocontainers during the dump is theoretically simulated. The fall velocity over the water depth has been calculated.

Also a theoretical model is set up to simulate the transformation of the kinetic energy of the geocontainer into the overpressure inside the geocontainer.

The results of the measurements are used to calibrate the theoretical models.

The overpressure inside the geocontainer is translated into a tensile stress in the geotextile.

It has to be emphasized that the presented theoretical models have to be considered as a first step towards more sophisticated theoretical models with which eventually the failure of the geocontainers can be predicted.

From the test results it can be concluded that failure of the geocontainers is dependent on aspects of the execution method that are not incorporated in the theoretical models.

4.2 Dump velocity

The calculation of the velocity is described hereafter.

The acting forces on the geocontainer are the gravitational force, directed downward, and the flow resistance force, directed upward.

The gravitational force:

= Vol ( p ^ - pJ g with:

gravitational force volume of geocontainer specific density fill material specific density water gravitational acceleration [kNl g (kN/m^l [kN/m^] [m/s2]

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The flow resistance force:

with:

= flow resistance force [kN] A = flow catching surface area geocontainer [m^]

= specific density water [kN/m"^] Q = drag coefficient (-] V = velocity of geocontainer [m/s]

The velocity of the geocontainer will increase after the release from the split barge. The increase of the velocity is given in the following formula:

Vol ( p , - p „ )

9-with:

dV = increase of velocity [m/s]

= gravitational force [kN]

Fr = flow resistance force [kN]

Vol = volume of geocontainer [m^]

Ps = specific density fill material [kN/m^

= specific density water [kN/m^

g = gravitational acceleration [m/s^l

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The equilibrium velocity is reached, when the gravitational force equals the flow resi force. This is the maximum velocity.

2 Vol ips - 9' A P»

with;

^max = equilibrium velocity l'^'^' Vol = volume of geocontainer '

= bulk density fill material inside geocontainer [kN/m ] = specific density water [kN/m ] g = gravitational acceleration (rn^s ^ A = flow catching surface area geocontainer [m ]

C h = drag coefficient t"'

Very important with respect to the simulation of the velocity is the cross directional shape of the geocontainer during the dump. The A, Cd and free falling height are determined by the shape of the geocontainer during the dump.

In this theoretical simulation a horizontal orientation of the geocontainer is assumed.

The shape of the geocontainer during the release can be schematized by the following factors; - Filling of geocontainer, Af - Split width, Bq - Height of geocontainer, h^

T \

7 " I \ o p e n i n g • b p 1 i i i i i i i

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The change of shape during the dump and impact is schematized as follows;

..•'-;A:-:v|c,^;r.-/,.:,

After start of the opening of the hold of the split barge the underside of the geocontainer starts moving through the opening of the split barge. A part of the geocontainer is hanging under the split barge. At a certain width of the split opening the whole geocontainer falls through the opening and the falling speed increases rapidly. From this moment the geocontainer is free falling.

The falling height of the geocontainer is defined as the difference between the underside of the split barge and the river bed. The free falling height is smaller, namely the distance between the underside of the geocontainer and the- river bed at the moment the speed of the geocontainer starts to increase rapidly. The free falling height is important in order to

determine if the geocontainer reached its equilibrium velocity before touch down. During the tests the free falling heights could not be determined.

Therefore the free falling height is approximated. It is assumed that just before the

geocontainer is free falling the whole volume of fill is hanging in the geocontainer under the split barge. Assuming a rectangular shape of the geocontainer passing the split opening of 2.5 m the height of the geocontainer (he) can be calculated. The draught of the split barge just before the geocontainer left the hold was approximately 1.0 m.

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The following free falling heights have been derived;

Geocontainer Depth he Free falling height

1 18m 2.8m 14,2m

2 13m 2.2m 9.8m

3 16m 2.3m 12.7m

4 20m 2.7m 16.3m

It has to be stated that this is only true in case the geocontainer is released from the split barge in horizontal orientation over the whole length. If this is not the case the free failing height decreases.

The cross sectional shape of the geocontainer during the various stages of the dump depends on the following factors;

- geometry of the hold of the split barge - split width

- opening speed of hold - perimeter of geocontainer - filling grade of geocontainer - type of fill material (clay or sand) - bulk weight of the fill material

The change of shape of the geocontainer during the release, the fall and the impact could not be determined during the test programme.

Japanese model tests give an impression of the shape of the geocontainer during dumping, although the conditions of the model tests are unknown and therefore the results cannot b( translated to the proto-type tests without precaution.

As the shape of the geocontainer is not known during the dump the fiow catching area of the geocontainer and the drag coefficient Cd are not known.

Based on a length of 24 m and a maximum width of 3.5 m A is approximated to 84 m2. The initial Cd value is approximated to 1.2.

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File no Page Rev-dd c:\..\rep_2.wp5 2 2 / 3 0 November 1995

The bulk density of the fill nnaterial inside the geocontainer incorporates the dry bulk density of the fill material, the water contents in the geocontainer and the air inside the geocontainer on top of the soil which acts as buoyancy,

During the test programme the bulk density inside the geocontainer was not assessed. Due to water in the hold of the split barge during the filling the lowest part of the soil in the geocontainer is saturated. The amount of soil which is saturated was not measured.

Also the buoyancy of the air on top of the soil in the geocontainer was not determined. Based on the available information the bulk density of the fill material inside the

geocontainer is approximated to 1,600 kg/m3 for sand and 1,500 kg/m3 for clay.

The gravitational acceleration is 9.81 m/s2.

The specific density of the water is 1,000 kg/m3.

In the table below the results of the velocity measurements and calculations are presented.

It is assumed that the equilibrium velocity is reached for all geocontainers. The earlier presented free falling heights were larger than the distance required to reach the equilibrium velocity.

Geocontainer density fill volume fill velocity measured velocity calculated [kg/m^l [m^l [m/s] [m/sl 1 1600 170 4.4 4.5 2 1600 130 3,3 3.9 3 1500 135 3.6 3.6

The fourth velocity is not compared because the geocontainer failed already during the release of the geocontainer.

The calculated equilibrium velocities agree reasonably with the measured velocities for the approximated values of the density, drag coefficient (Cd) and flow catching area (A). As both the Cd and A are not known exactly a sensitivity analysis has been performed. The measurement results have been usee in order to calibrate the Cd and A values. For 3 different flow catching areas A the corresoonding drag coefficients have been assessed.

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Project Geocontainers® - Van Cord A C Z - IVIicolon

File no Page Rev-dd o:\..\rep_2.wp5 2 3 / 3 0 November 1 9 9 5

Also for 3 different Cd values the corresponding A values have been determined.

The results are presented below.

A [m2] Cd [-]

dump 1 dump 2 dump 3

60 1.8 2.3 1.7

84 1.3 1.7 1.2

108 1.0 1.3 1.0

Cd (-1 A [m2]

dump 1 dump 2 dump 3

1.0 108 140 102

1.2 90 117 85

1.4 77 100 73

In practice the velocity of the geocontainer is influenced by several factors that are not incorporated in the model, such as:

- rotation of the geocontainer

- non-horizontal orientation during the dump

Further research is necessary on the shape of the geocontainer during dumping in order to assess the drag coefficient, flow catching area and free falling height.

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Project Geocontainers* - Van Oord A C Z - I^Jicolon

File no Page Rev-dd c:\..\rep_2.wp5 2 4 / 3 0 " November 1 9 9 5

4.3 Impact on sub soil

A theoretical model is set up to simulate the transformation of the kinetic energy of the geocontainer into the overpressure inside the geocontainer. During the impact of the geocontainer on the sub soil the kinetic energy will be dissipated. The contributions to the dissipation are:

internal friction and cohesion of the soil inside the geocontainer, during deformation of the soil inside the geocontainer;

tensile strain of the geotextile; expansion seams;

settlement of the sub soil;

friction between sub soil and geotextile;

escape of air-water through the geotextile during the impact; escape of air-water in length direction: 3 dimensional effects.

A theoretical model is set up to simulate the transformation of kinetic energy into overpressure inside the geocontainer.

The shape of the geocontainer during the dump before and after the impact on the sub soil is schematized as follows:

During the impact on the sub soil the geocontainer is reshaped from a vertically orientated ellipse into a horizontally orientated ellipse. In the derivation of the theoretical model it is

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File no Page Rev-dd c;\..\rep_2.wp5 2 5 / 30 November 1995

assumed that the geocontainer during the impact is cylinder shaped.

Also it is assumed that the mass inside the geocontainer is equally distributed throughout.

Just before touch down the whole geocontainer has a certain kinetic energy depending on its velocity.

with:

E|^in = kinetic energy [Nm] M = mass of geocontainer [kg]

V = fall velocity of geocontainer [m/sl

The kinetic energy is (partly) absorbed by the strain of the geotextile. The following formula is valid for 1 m width of the geocontainer.

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Project Geocontainers® - Van Gord A C Z - Nicolon

File no Page Rev-dd c:\..\rep_2.wp5 2 6 / 3 0 November 1995 with:

Egbs = absorbed energy by strain geotextile E = elasticity modulus of geotextile

I = perimeter of geocontainer [m] F = tensile force in geotextile [N/m]

[Nm] [N/m]

The inside pressure results in a tensile force of the geotextile. Assuming a cylinder shaped geocontainer and a constant pressure along the perimeter the formula presented below is valid (for a cross section of a cylinder with 1 m width).

-5>

\

F = a with;

F = tangential force in cylinder [N/m]

Qq = inside pressure [N/m2] a = radius of cylinder ( = l/2rr) [m]

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File no Page Rev-dd c:\..\rep_2.wp5 27 / 3 0 November 1 9 9 5

Following from the above presented formulas, the energy absorbed by the strain of the geotextile over the full length of the geocontainer can be presented as follows:

E = ^

(4)

Qo a' L

with:

^ a b s = absorbed energy by strain geotextile [Nm]

E = elasticity modulus of geotextile [N/m]

1 = perimeter of geocontainer [ml

qo = inside pressure [N/m2]

a = radius of cylinder [m]

L = length of geocontainer [m]

Only a part of the total kinetic energy will be translated into strain of the geo

with:

^kin = kinetic energy [Nm]

^ a b s = absorbed energy by strain geotextile [Nm]

K = dissipation factor [-]

The above formulas result in the formula presented below. Vol p E

1 L

with:

Qo = overpressure inside the geocontainer [N/m^] Vol = volume of fill inside the geocontainer [m^l

P = density of the fill material [kg/m^

V = velocity at the touch down [m/s]

E = stiffness modulus of the geotextile (N/ml

L = length of geocontainer [m]

a = radius of the geocontainer ( = \l2n) [m]

1 = perimeter of geocontainer [m]

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Project Geocontainers* - Van Oord A C Z - Nicolon Title Report test programme

File no Page Rev-dd c:\..\rep_2.wp5 2 8 / 3 0 November 1 9 9 5

With the test results the theoretical model can be calibrated by means of the K-factor. For the first 2 dumps of the geocontainers, filled with sand, the K-factor is determined, according to the above given formula.

Geocontainer 1:

1 7 0 1 , 6 0 0 4 . 4 ^ 1 , 0 0 0 , 0 0 0

16 2 4 . 5 2 . 5 5 2

For the first geocontainer the result of the calibration is: K = 0.40. This would mean that 4 0 % of the theoretical increase of the pressure is apparent. This would mean that more than 60% of the kinetic energy is dissipated in another way.

Geocontainer 2:

1 3 0 1 , 6 0 0 3 . 3 2 1 , 0 0 0 , 0 0 0

16 2 4 . 5 2 . 5 5 2

For the second geocontainer the dissipation factor K is 1.17. The reason for this higher value can be that in the first geocontainer overpressure could escape because the geocontainer was ruptured before reaching the bottom of the sand pit.

In theory the dissipation factor cannot exceed 1. This could mean that the schematizations in the model are too rough.

Once again it is stated that this theoretical model is a first step towards a more

sophisticated model. Therefore it is necessary to perform more tests in order to increase the validity of the model.

Possible reasons for the non-validity of the model could be: No cylinder shape of the geocontainer

The fill of the geocontainer is not equally distributed over the cross sectional area The measured pressure is not present throughout whole geocontainer at one time but more locally

The short term elasticity of the geotextile is larger than 1000 kN/m 0 . 1 7 . 1 0 ^ = K

\

0 . 3 5 . 1 0 ^ = K ^

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Project Geocontainers® - Van Cord A C Z - Nicolon File no c:\..\rep_2.wp5 Page 2 9 / 3 0

Title Report test programme Hev-dd November 1 9 9 5

The tensile force in the geotextile can be derived from the inside pressure in the geotextile.

F = a with:

F = tangential force in cylinder [N/m]

Qo = inside pressure [N/m2] a = radius of cylinder ( = l/2;r) [m]

I = perimeter of geocontainer [m]

For the first geocontainer an overpressure of 0,17 bar results in a tensile force of 43 kN/m. The second geocontainer had to withstand an overpressure of 35 kN/m^, which results in a tensile stress of 89 kN/m.

The tensile strength of the seams of the geocontainer are approximately 70% of the tensile strength of the geotextile: 7 0 % of 120 kN/m = 84 kN/m.

It has to be stated that the calculated tensile forces are impact loads. The short term tensile strength o f t h e geotextile is larger than 120 kN/m.

Both tensile forces are below the tensile strength of the confection seam.

Geocontainer 2 did not fail during the impact on the subsoil, which could be expected from the above calculation bearing in mind that the short term ultimate tensile force is higher than the 84 kN/m.

Geocontainer 1 failed at the front end during the impact on the sub soil although the tensile force theoretically does not exceed the tensile strength. From the observations during the test it can be concluded that the geocontainer failed because of a reason which is not incorporated in the theoretical model, which is described in section 3.

It should be stated that the theoretical simulation models are rough schematizations. These models can only be used to give an indication.

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File no Page Flev-dd c:\..\rep_2.wp5 30 / 3 0 November 1995 ATTACHMENTS 1 D u m p location Kekerdom 2 Definition sketch geocontainer 3 Definition sketch split barge

4 Measurements of velocity and pressure during dump 5 Calculated velocity for geocontainer 2

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HYDRAULIC ENGINEERING

GEOCONTAINER

THE GEOCONTAINER IS A SPECIALLY DESIGNED VERY LARGE SAND CONTAINING BAG FITTING INTO A SPLIT-BOTTOM BARGE.

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TEST PROGRAMME GEOCONTAINERS - Van Oord ACZ - Nicolon

DUMP 1 - SAND - 170 m3 - Depth 18 m

85 90 95 100 105

Time [sec

_ 0 _

Vel - front _g_ Vel - middle Vel - rear Pres - middle

file: c:\123r34\data\o&o\geocon\datac_l l.wk3 — graph: dLimp_l

V O A C Z - Engineering Department

(35)

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HYDRAULIC ENGINEERING

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TEST PROGRAMME GEOCONTAINERS - Van Oord ACZ - Nicolon

DUMP 1 - SAND - 170 m3 - Depth 18 m

85 90 95 100 105

Time [sec

_ 0 _

Vel - front _g_ Vel - middle Vel - rear Pres - middle

file: c:\123r34\data\o&o\geocon\datac_l l.wk3 — graph: dLimp_l

V O A C Z - Engineering Department

TEST PROGRAMME GEOCONTAINERS - Van Oord A C Z - Nicolon

D U M P 2 - SAND - 130 m3 - Depth

13

m

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2

20

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30

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Time [sec]

0 _ Vel - front Vel - rear Pres - front Pres - rear

file: c:\123r34\data\o&o\geocon\datac_12.wk3 — graph: dump_2

V O A C Z — Engineering Department

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TEST PROGRAMME GEOCONTAINERS - Van Oord ACZ - Nicolon

DUMP 3 - CLAY - 135 m3 - Depth 16 m

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30

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file: c:\123r34\data\o&o\geocon\datac_13.wk3 — graph: dump_3

V O A C Z — Engineering Department

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TEST PROGRAMME G E O C O N T A I N E R S - Van Oord A C Z - Nicolon

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