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GAZIANTEP UNIVERSITY

CIVIL ENGINEERING DEPARTMENT

Construction Division

Soil Improvement techniques CE-562

Final Exam:

(Two Case studies on Deep dynamic compaction method)

Submitted to:

Doç.Dr. Hanifi ÇANAKÇI

Submitted by:

Handren Salih M.A.Jaf Bzhar Muhedin Muhammad

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CASE HISTORY: Application of Dynamic Consolidation and Dynamic Replacement for

Rehabilitation of a Landfill for a Housing Development Project

* Project Description and Location

Phase 1 of the project comprised of 108 units of single-storey double-storey terrace houses and

102 units of double-storey terrace houses. The site is located at the junction of old limestone and

Kenny Hill formation. It was previously a tin mine and was later used as a rubbish dumping

ground. The overburden therefore consists of poorly compacted household waste whilst the

subsurface soil is loose, with slime layers, due to the mining process. The site was also scattered

with ex-mining ponds.

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* Subsurface Conditions Two series of soil investigation were conducted which include deep boreholes,

cone penetration tests and pressure meter tests. The boreholes were sunk to 30m

depth terminated upon reaching limestone rock. A sample bore log is given in

figure 12. Borehole BH2, which was, located in the middle of the proposed Phase I

area indicates a waste fill down to 8.5m. Generally, the thickness of this waste fill

(mostly household rubbish) is about 5m to 8m. Underlying the upper waste fill,

layers of loose silty clayey sand and clayey silt were found. The water table level

was about 1.5 - 2m below the existing ground level. Figure 13 shows the SPT tests

results.

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* Criteria for Ground Improvement The acceptance criteria for the ground improvement works was:

i) Safe bearing capacity > 120 kN/m²

ii) Differential settlement < 1: 600

These criteria carried with it a performance guarantee valid for 7 years. In addition,

the structural design also includes structural joints at every 2nd house unit along

the terrace row. A shallow foundation design was adopted.

* Design of Treatment, Selection of Plant and Equipment and

Construction Sequence A combined dynamic consolidation and dynamic replacement techniques were

used (figure 14). Before the commencement of compaction work, a full-scale

calibration test was carried out on site. This calibration test consists of heave and

penetration tests. The purpose of the calibration is to:

1) Determine the optimal number of blows for each phase.

2) Determine the required compaction energies and the number of phases of

compaction.

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3) Check that the pounder penetration is not a volume displacement but a real

compaction of the soil.

4) Determine the actual spacing of compaction points to avoid any interference of

heaving in between the points.

Dynamic Consolidation to create “compacted sand raft”

To allow slab-on-grade and for infrastructure

Dynamic Replacement sand columns to support column

Loads; increase bearing capacity and reduce settlement

Based of the results of the calibration tests, dynamic replacement and dynamic

consolidation were used for the structural area while the dynamic consolidation

was used for the infrastructure area (roads and services). The operation parameters

were developed and optimized for the compaction operations as shown in Table 5.

A 165-ton crawler crane (American Hoist 9299) was used for the compaction

works (figure 15). The effective area of compaction includes a periphery strip (or

over width) of 5m beyond the boundary of the houses.

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The construction sequence was as follow:

Step 1: Excavation of upper 2.5m recent rubbish deposits (refuse < 5 years old).

Step 2: Backfill with 2.5m of clean sand as working platform and also as drainage

blanket.

Step 3: Performed dynamic replacement on structural areas (especially below

structural columns) and dynamic consolidation over the entire treatment area

(Phase 1).

Step 4: Performed phase 2 and ironing phase of ground improvement work.

Step 5: Carry out quality control, instrumentation and monitoring works

During and after ground improvement works.

Step 6: Complete sand filling to reach finished platform level with compaction to

90% modified proctor standard.

Step 7: Carried out 2m surcharging for 6 weeks. Settlement monitoring.

Step 8: Surcharge removed and proceeds with construction.

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*Penetration Test (CPT)

Forty-one locations of PMT test were carried out i.e. 8 locations before compaction

works, 12 locations after phase 1, 9 locations after phase 2 and finally 12 locations

after the final ironing phase. From the results, it can be shown that there is an

increase of the pressure limit Pl and pressure meter modulus Em down to about 6-

7m

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*Enforced Settlement

The enforced settlements obtained were:

Phase 1: 0.29m

Phase 2: 0.21m

Ironing phase: 0.10m

The total enforced settlement was about 0.6m which represent about 13-14% of the

total of the remaining rubbish deposit after excavation of the upper 2.5-3m.

* Bearing Capacity The pressure meter test is a type of load test which in particular yields the limit

pressure Pl that corresponds to the failure of the soil. Experience and theory have

shown that the ultimate bearing capacity of a foundation is proportional to Pl

value. The factor of proportionality so-called the bearing factor K is a function of

the relative depth and the foundation shape. The bearing capacity is calculated

according to the D60AN manual for Interpretation and Application of Pressure

meter Test Results to Foundation Design (Sol Soils No: 26 - 1975) - Rule 4 based

on equivalent limit pressures. The equivalent limit pressure Ple defined as the

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geometric mean of the Pl values obtained near to the level of the foundation is

given by:

Ple = 3 _ {Pl1 * Pl2 * Pl3} ………. (5)

Where

Pl1 is the mean of the limit pressures measured from 0 to 2m depth

Pl2 is the limit pressures measured from at 3m depth

Pl3 is the limit pressures measured at 4m depth The bearing capacity (q) is then

calculated using equation (6) below with a bearing factor of K = 0.8 and a factor of

safety of 2.5.

q = {Ple * 0.8}/2.5 ………. (6)

The calculated safe bearing capacity before compaction works varies from 90

kN/m² to 160 kN/m². After compaction works the calculated safe bearing capacity

varies from 320 kN/m² to 500 kN/m² with mean value of 410 kN/m². The bearing

capacity is increased by a factor of 3.3.

* Settlement

Estimation of settlement is carried out using the Schmertmann’s method based on

the cone penetration tests results. The calculated settlement due to a load of 120

kN/m² on a square footing of 1.65 x 1.65m ranges from 8mm to 19mm with a

mean value of 12mm after compaction works. A similar calculation is carried out

using the pressure meter results. The estimated total settlement after compaction

works ranges from 5mm to 11mm with a mean value of 8mm. To obtain the

maximum differential settlement between two footings, the worse possible

conditions of loading combined with the results of the pressure meter tests is used.

The calculation is based on the following details:

Shape of footing: square

Size of footing: 1.65m x 1.65m

Maximum distance between footings: 2.5m

The computed maximum differential settlement is 1:544.

* Surcharge Surcharge was carried out after the compaction works to: -

(i) Consolidate the presence of any cohesive layer below the rubbish deposit.

(ii) Reduce the potential differential settlement.

(iii) Reduce future secondary compression. It was however, primarily used as a

simple load test. A surcharge of 2m fill was placed for 6-7 weeks until the time-

settlement behavior reached at least 70% degree of consolidation according to

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Field measurements of the settlement plate. The settlement readings taken from 12

sets of settlement plates vary from 4mm to 30mm. Out of the 12 readings, 8

readings have settlement less than 15mm, 3 readings have settlement less than

25mm and only 1 reading has exceeded 25mm. The average value is 13mm.

The 1st phase of the project was completed in 1990. Occupation of the houses was

almost immediate and until today (1999) there is no structural defect reported.

Figure 18 shows the completed structure after 7 years upon completion

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* CONCLUSION

From the various case histories cited in this paper, the dynamic consolidation

technique is applicable for densifying landfill to allow for additional storage space.

Furthermore, it is also possible when it combines with dynamic replacement

technique to permit developments such as housing projects to be carried out over

landfill sites as in any ground improvement projects; instrumentation and

monitoring still play a very important role in the success of the works.

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2- A case study on soil improvement with heavy dynamic compaction

ABSTRACT: In this paper, soil improvement works by means of heavy dynamic

compaction method performed for the foundation subsoil of Carrefour’s

Hypermarket and Trade Center in Bursa, Turkey is given as a case study. In order

to increase the bearing capacity of the foundations subsoil’s as well as to regulate

the total and differential settlements underneath the foundations Heavy Dynamic

Compaction (HDC) together with High Energy Pillars (HEP) is implemented.

1 INTRODUCTION

In this paper, soil improvement works by means of heavy dynamic compaction

method performed for the foundation subsoil of Carrefour’s Hypermarket and

Trade Center in Bursa, Turkey is given as a case study. The project site covers

approximately 100,000 m2 area, on which a Hypermarket, Trade Center and a

Parking structure together with future extension zones and slab-on-grades are

Constructed. A soil improvement with dynamic compaction method is

implemented underneath the foundations and slab-on-grades for the structures

named as Block A, B and C with a total improvement area of approximately

78,500 m2. The planned structures are named as “Hypermarket – Block A”, “Trade

center and parking structure– Block B” and future extensions as “Block C”.

General layout of the site is given in Figure 1. Block A consists of a single storey

hypermarket structure covering and area of 20,400 m2. Block B consists of trade

Centre and closed parking structure located on a base area of 48,500m2. Block B

has a basement level of height 4.0 m. The rest of the structures in the site are

designed without basements. The finished grade elevations for structures, slab-on-

grades and open parking areas are designed at elevation +112 m. The finished

grade elevation of basement within closed parking structure is +108 m and

designed as a partial basement underneath Block B. A quality control program is

implemented during the soil improvement works. This case study presents the

design, construction and performance of the implemented soil improvement by

means of heavy dynamic compaction/dynamic replacement. The geotechnical

modeling based on soil Investigation data is presented and the performance of the

implemented soil improvement is evaluated based on the quality control/quality

assurance testing.

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Figure 1. General layout of the site

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2 LOCAL GEOLOGY AND SUBSOIL CONDITIONS

The subject site is located at about 5 km west of Bursa on the main highway from

Bursa to Izmir. The site is located in an area basically covered with the alluvial fan

deposits of the river Nilüfer flowing north, where the river reaches the flat alluvial

plain of Bursa. The site was previously utilized as a borrow area and after being

abandoned was further utilized as damp area for excavated material of various

origin. As a result, the site contained depressions as deep as 14 m from the present

ground elevations, whereas some part of the site was covered with uncontrolled

fills formed by damped material of debris, blocks, bricks, concrete, clay and

excavated material of various origin. The thickness of uncontrolled old fills

reaches to maximum 14 m. Occasional parts of the site are covered with alluvial

deposits formed by mixtures of clay, sand and gravel down to maximum 15 m

depth. Below these depths native soil is the Neogene aged deposits of clayey sand-

sandy clays. The subject site is located in the first degree earthquake zone in

Turkey with the highest seismic ity. Three main zones are identified within the site

based on soil investigations. These are, natural ground, uncontrolled old fill, and

excavated empty zones. Natural ground areas are undisturbed natural ground

located approximately at elevations +110 m and +112 m. The subsoil is composed

of sandy gravely alluvial soil underneath a topsoil cover. The thickness of the

sandy gravel layer is in the order of 12 m to 15 m and hard sandy clays are

encountered below this layer. Uncontrolled old fill areas consists of uncontrolled

fills damped at the site in time from excavated material of various origin ,

including topsoil, debris and blocks. Alluvial sandy gravel layer is not encountered

in these areas during soil investigations. Excavated areas are the zones of

excavated parts of the former borrow area with elevations ranging between +100 m

and +104m. The subsoil in these zones consists of sandy gravel layer to a limited

depth which was utilized as borrow material and clay-sandy clay layer underneath.

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3 FOUNDATION ENGINEERING DESIGN

3.1 Foundation system

Block A and partially Block B was designed to be located on uncontrolled old fills,

and part of Block B was designed to be located on the previously excavated zone.

For the foundations of the structures the depressions within the site are filled

partially with the excavated uncontrolled fill material and partially with the

imported material in order to achieve a graded level for foundations. The view of

site to backfilling together with the utilized dynamic compaction equipment is

given in Figure 2.

Considering the presence of distributed loads of various intensity and slab-on-

grades within the planned structures, the soil improvement with dynamic

compaction is then implemented for the whole site from the graded level with

subsoil being composed of uncontrolled old fill, uncontrolled new fill and natural

ground. In order to increase the bearing capacity of the foundations subsoils as

well as to regulate the total and differential settlements underneath the foundations

Heavy Dynamic Compaction (HDC) together with High Energy Pillars (HEP) are

implemented. The areas between the foundations for slab-on-grades are also

improved by means of Heavy Dynamic Compaction (HDC) and Dynamic

Compaction (DC). The selected improvement scheme was the most economical in

comparison to other alternatives based on the summarized conditions. The

foundations of structures were designed as spread footings tied with tie -beams in

two directions located on the improved soil.

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3.2 Dynamic compaction as a soil improvement

The dynamic compaction for soil improvement of the subject site was implemented

by MENARD Soltraitement and quality control/quality assurance testing during

construction was carried out by ZETAS Zemin Teknolojisi A.S. Initial soil

investigations for the site was performed by ZETAS Zemin Teknolojisi A.S.

(1998) composed of rotary boreholes with systematic SPT and pressuremeter

testing. The SPT-N values varied between N=10 to refusal, revealing the presence

of large cobbles and blocks within the uncontrolled fill. Based on grains size

analysis of the retrieved representative samples percent passing No.200 sieve

varied between %8 and %98, indicating the variable nature of the encountered soils

within the site. In order to be able to follow the soil improvement, prior to soil

improvement works six boreholes of 15 m depth with systematic pressuremeter

testing at every 1.0 m were performed in different subsoil conditions that will

represent the site. Pressuremeter test results revealed that the limit pressure values

as low as Pl=2.5 bar, with %70 of the Pl values below 5 bars. Consequently,

pressuremeter tests results are in agreement with the soil investigations results

indicating a heterogeneous nature of the subsoil. Consequently, heavy dynamic

compaction (HDC) together with high energy pillars (HEP) was selected as soil

improvement. Dynamic compaction is a soil improvement method employed to

increase the mechanical properties of subsoils at greater depths. The technique was

first developed and pioneered by Menard 1976). In this method, a heavy ponder is

dropped on soil surface from various heights with free drop within a grid-wise

manner and hence subsoil is compacted by means of the energy delivered to the

soil surface. The basic equipment consists of a heavy mobile crane and ponders

with various weight. The special cranes are utilized which can drop a 40 tonnes

weight from 40 m height, which can deliver a 1600 ton.m energy with a single

drop. The effective depth of soil improvement, D during dynamic compaction is

directly proportional with the energy delivered (weight, W and drop height, H) for

each drop and can be estimated with the following expression.

0.5 (WH)1/2 < D < 0.8 (WH)1/2 (1)

Accordingly, the effective depth of soil improvement D, for a weight of 40 tonnes

dropped from 40m height would be in the range of 20.0m < D < 32.0m, which was

in excess of the total thickness of the uncontrolled fills present within the subject

site. Therefore, a weight of W=20 tonnes from a drop height H=20m was

implemented for the subject site achieving an improvement depth in the range of

10.0m < D < 16.0m for an energy level of 400 ton.m.

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With this kind of soil improvement average settlement of the ground surface of a

soil treated by dynamic consolidation shows that the density is increasing (usually

around 5%). This increase in density corresponds to a much greater increase in

relative density Dr (20% or more). Method of High Energy Pillars – HEP is a

dynamic replacement method similar to dynamic compaction. In this method, the

ponders are dropped repeatedly on a replaced granular soil layer, which force a

large diameter densified granular soil column into the soil and combines the

advantages of dynamic compaction with the stone columns and permits the transfer

of impact energy to deeper soil layers.

4 DETAILS OF SOIL IMPROVEMENT

4.1 Heavy Dynamic Compaction (HDC) HDC is applicable either on unsaturated soil or granular soil under groundwater table. The basic

Principle consists of transmission of the high energy impacts to the surface of ground which is

initially compressible and with low bearing capacity. In unsaturated soil

conditions, the HDC results a quick decrease in void ratio of the soil and an

instantaneous settlement of ground under impact. Ponders weighing from 18 tons

to 25 tons were dropped in free fall from heights ranging between 15 m to 25 m

based on heave and penetration tests performed at various parts of the site prior to

Commencement of work. The craters formed by the drop of pounder at the

predefined grid of ponder prints were back filled with soil of the platform, hence

resulting the an average settlement of site as well as densification. The

performance of two different trail areas based on the improvement characteristics

according to pressure meter tests enabled to determine the grid of tamping and the

number of blows per print.

4.2 High Energy Pillars (HEP)

HEP method is derived from HDC and same type of equipment is utilized. The tamping energy is

used to create large diameter stone inclusions in a soft soil. These columns are realized by successive

filling and tamping of the pounder print penetrating into soft ground. By means of creating a high

modulus large diameter stone column, the tamping energy can also be penetrated to deeper layers of

the ground through the compacted high modulus pillar resulting a compaction in the deeper layers of

the subsoil beneath HEP.

HEP’s were implemented underneath the footings of the structure composed of selected material

Backfill. The material used in the HEP were calibrated in order to obtained a homogeneous strength

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Stone column or pillar. The material for the execution of pillar was the present granular material

Selected from the site. The total quantity of HEP material was in the order of 38,000 m3. The quality

Of the material was decided by soil improvement subcontractor, where the site material did not meet

The requirements, granular material of equivalent properties were imported to site.

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4.3 Ironing

The last phase of tamping consists of a dense grid of lighter dynamic compaction

in order to homogenise the surface layer.

4.4 Quantities

The soil improvement work included the execution of total of 2048 HEP

underneath the columns of the superstructure based on the column loads. The total

average settlement of the site based on the topographical surveys prior and after

soil improvement could be summarized as:

5 QA/QC TESTING

Quality control/quality assurance of the soil improvement as well as the

performance monitoring of the implemented method is performed by means of a

series of testing. The QA/QC testing includes the following:

Systematic pressure meter testing was performed before and after the soil

improvement randomly below the slab-on-grade areas at every 2500 m2 down to

14 m depth with one test per meter. In addition to slab-on-grade areas, pressure

meter test points below the footings at every 1250 m2 down to 6 m depth with one

test per meter, were performed in order to verify the desired compaction \for HEP

implemented below footings. A typical test result with before and after tests for

HEP location is given in Figure 3.

Two test zones were selected that would represent the soil conditions within the

site. In these test zones heave and penetration tests before the initiation of job in

order to optimize and determine the number of blows per print in different subsoil

types as well as determination of optimum energy delivery. Once the optimum

compaction energy level and number of blows were determined, the HDC and HEP

production and quality control is followed by systematic pressure meter testing.

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Figure 3 – Sample pressuremeter test results before and after soil improvement

Magnetic settlement columns after the compaction in order to monitor, any further

settlement due to foundation and superstructure loads are installed. Magnetic

settlement columns consisting of five different levels of measurement within 20 m

depth. The construction continued upon verification of no additional settlements

based on monitoring data. Seismic tests were conducted by means of measuring

Rayleigh waves before and after dynamic compaction in order to observe the

increase in modulus of the subsoil. By means of measuring wave velocities before

and after compaction and hence determining consequent shear and Young modulus

of subsoil, the increase in modulus values as well as percentage of increase were

observed. Consequently, HEP and HDC are appeared to be very effective method

in terms of performance of structures and the cost for the improvement of

unsaturated granular soils.

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REFERENCES

Menard Soltraitement (2000), “Method Statement and Schedule, HEP, HDC, DC

and PMT, Bursa Carrefoursa

Project”, Paris

Menard Soltraitement (2001), “Soil Improvement of a Filled Area by Dynamic

Consolidation and Dynamic

Replacement Final Report Carrefoursa Bursa”, Paris

Menard, L ve Broise, Y. (1976), “Theoretical and Practical Aspects of Dynamic

Consolidation”, Institute of

Civil Engineers, Ground Treatment by Deep Compaction, London

ZETAS Zemin Teknolojisi A.S. (1998). “Carrefoursa Bursa Hypermarket and

Trade Centre Soil Investigation

and Foundation Engineering Evaluation Report”, Istanbul