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3 Collect sludge samples from major rivers and lakes, evaluate their physical and chemical properties, and assess their potential for conversion into foundation-filling materials.. 4 Dev

HANOI UNIVERSITY OF CIVIL ENGINEERING

Pham Tri Thuc

STUDY ON TREATMENT OF DREDGED SLUDGES FROM TYPICAL RIVERS AND LAKES IN HANOI CITY TO GRANULAR MATERIALS FOR FILLING

Major: Geotechnical Engineering

Code: 9580211

SUMMARY OF DOCTORAL DISSERTATION

Hanoi – 2025

Reviewer 1: Assoc Prof Dr Nguyen Đuc Manh

Reviewer 2: Assoc Prof Dr Nguyen Thi Nu

Reviewer 3: Assoc Prof Dr Vu Anh Tuan

The dissertation will be defended in front of the dissertation Evaluation Council, at Hanoi National University of Civil Engineering

At hour, date month of 2025

For further information, please visit the National Library and the Library of Hanoi University of Civil Engineering

INTRODUCTION

1 Research rationale

Hanoi, the country's capital, is rapidly developing its infrastructure and is home to numerous rivers, ponds, and lakes Every year, large amounts of sludge are generated from construction and dredging activities This sludge is often disposed of at authorized and unauthorized sites, occupying significant land, causing pollution, and incurring high disposal costs

Urban infrastructure projects, such as dike upgrades, embankments, and road expansions, require substantial amounts

of materials for leveling and foundation filling These materials are typically sourced from sand or graded soil extracted from mountain quarries or riverbeds However, sand extraction severely impacts geological conditions, ecosystems, land erosion, and traffic safety, especially waterway traffic

With increasing environmental concerns and the pressure on authorized disposal sites, the development of materials from dredged sludge for ground leveling and foundation filling has become crucial

Globally, various solutions have been implemented, such as sludge dewatering and the addition of lime or cement to enhance strength Each approach has its own benefits, limitations, and applications One promising solution under research is producing artificial sand from sludge, which shows great potential as a ground-filling material Its benefits include rapid drainage, lightweight properties, ease of transportation, and compactability However, this method is still new and has not yet been adopted in Vietnam

In response to these practical challenges, the doctoral candidate

has chosen the topic: “Study on treatment of dredged sludges from typical rivers and lakes in Hanoi city to granular materials for filling” This research holds significant scientific value, and

its findings will lay the groundwork for the reuse of dredged

2) Explain the scientific principles behind converting sludge into granular materials

3) Collect sludge samples from major rivers and lakes, evaluate their physical and chemical properties, and assess their potential for conversion into foundation-filling materials

4) Develop a process to produce granular materials from liquid dredged sludge with low additive content

5) Investigate the geotechnical properties of granular materials produced with minimal additives and define their applicable use

3 Research Subjects and Scope

This dissertation focuses on sludge samples from rivers and lakes

in Hanoi’s inner city It uses locally available cement as enhancing additives and high-activity superabsorbent polymers

strength-as adhesives The goal is to develop GFM (Granular Treated Soil for Filling Material), with an emphasis on studying its geotechnical properties with low additive content

Cement-4 Research Methods

The author employs a combination of research methods, including theoretical analysis, literature collection and synthesis, field surveys and evaluations, laboratory experiments, synthesis and analysis of experimental results, and expert consultation

5 Scientific Value and Practical Significance of the Dissertation

5.1 Scientific Value

The author clarifies the scientific basis for producing granular material from liquid sludge and develops a laboratory-scale manufacturing process The study highlights the role of cement

and polymer additives in converting liquid sludge into granular material Additionally, the author explains the stress-strain behavior of the granular material, where soil particles are prone

to breakage and shrinkage, unlike rigid particles such as sand or gravel

5.2 Practical Significance

This dissertation introduces a new method for treating dredged sludge from rivers, ponds, lakes, and other construction activities The process converts the sludge into granular material, GFM (similar to sand), which can be used for ground leveling, road foundations, retaining wall backfill, and more

The research also shows that large amounts of sludge, previously regarded as waste, can be turned into valuable fill material, contributing to environmental protection and reducing the demand for foundation materials in infrastructure development

across the country

6 New Contributions of the Dissertation

The new contributions of this dissertation, based on its scientific and practical significance, are as follows:

1) The author proposed a process for treating fine-grained dredged sludge to produce granular material, GFM (similar to sand), for use as fill and foundation material in construction The process also demonstrates that GFM can be produced with minimal cement and polymer additives, ensuring cost-effectiveness The dissertation identifies the application scope of GFM based on varying additive contents

2) The author highlighted the unique stress-strain behavior of GFM compared to traditional granular materials like sand and gravel Under low stress, GFM behaves similarly to sand and gravel, but under high stress, it acts like cohesive soil

7 Structure of the Dissertation

The dissertation includes an introduction, conclusion, recommendations, three chapters, 12 tables, 98 figures and charts, spanning 128 pages, excluding the appendices

1.2 Current Status of Dredged Sludge Recovery in Hanoi and Other Major Cities in Vietnam

1.3 Some Solutions/Technologies for Treating Dredged Sludge into Construction Materials Worldwide and in Vietnam

A common method involves collecting liquid dredged sludge and mixing it with additives like cement, lime, fly ash, or paper pulp

1.4 Some Factors Affecting the Technical Properties of Fill Material Made from Sludge Combined with Cement

1.5 Scientific Basis of the Solution for Treating Liquid Sludge into Granular Material

The principle of treating liquid sludge into granular material is presented in figure 1.34

Figure 1.34 Principle of Granulation from Liquid Sludge

1.6 Evaluation of the Selection of Solutions for Treating Dredged Sludge from Some Rivers and Lakes in Hanoi into Granular Fill Material

CHAPTER 2 STUDY OF SLUDGE CHARACTERISTICS, MANUFACTURING METHODS, AND FACTORS AFFECTING THE TREATMENT OF SLUDGE INTO

GRANULAR FILL MATERIAL 2.1 Sludge Sampling and Storage for Experimentation 2.2 Some Basic Physical and Chemical Properties of Sludge

H 2 O Clay

H 2 O

H 2 O

Polymer

Samples from Selected Rivers and Lakes in Hanoi

2.2.1 Experimental Methods

2.2.2 Some Physical Properties of Sludge Samples

a) Initial Moisture Content of Sludge Samples

b) Liquid Limit of Sludge Samples

c) Plastic Limit of the Sludge Samples

Figure 2.5 Initial moisture content and Atterberg limits of some

dredged sludge samples

a) Hoan Kiem lake sludge sample

b) West lake sludge sample

c) Nhue river sludge sample

Figure 2.8 Particle gradation of sludge samples from Hoan

Kiem lake, West lake, and Nhue river

Figure 2.9 Organic content of sludge samples from West Lake,

Hoan Kiem Lake, and Nhue River

2.2.3 Some basic chemical properties of the sludge samples

The author analyzes the chemical components that significantly impact the sludge treatment process, with results presented in Figures 2.10, 2.14, and 2.15

Figure 2.10 pH level of the sludge samples from Hoan Kiem Lake,

West Lake, and Nhue River

a) Hoan Kiem Lake sludge samples “H”

b) West Lake sludge samples “W”

Figure 2.14 Content of oxides in the sludge samples from Hoan

Kiem Lake and West Lake

a) Hoan Kiem Lake sludge samples

b) West Lake sludge samples

Figure 2.15 Heavy metal content in the sludge from Hoan Kiem

Lake and West Lake

2.2.4 Evaluation of the potential for treating sludge from several rivers and lakes in Hanoi to produce construction materials

2.3 Study on the potential for granulation of liquid sludge at

following the sequence

shown in Figure 2.20: Figure 2.20 Laboratory Mixing

Hình 2.23 The Effect of Cement on the Particle Composition of GFM

Liquid ludge

Free water removal

Mix with cement Mix with polymer

Curing

Hình 2.24 The Effect of Polymer on the Particle Composition of GFM

2.4 Mechanism of Formation and Strength Development of GFM Soil Particles

Hình 2.28 Image at 5,000x Magnification

CHAPTER 3 GEOTECHNICAL CHARACTERISTICS AND APPLICATION SCOPE OF GRANULAR FILL MATERIAL PRODUCED FROM DREDGED SLUDGE WITH LOW

CEMENT AND POLYMER CONTENT

3.1 General Introduction

3.2 Materials and Experimental Content

3.3 Some Basic Physical Properties of GFM Materials

The author determined the basic physical properties of GFM samples in the laboratory, with results shown in Figure 3.3:

a) Unit Weight of GFM Samples

b) Particle Density of GFM Samples

c) Void Ratio of GFM Samples

Hình 3.3 Some Basic Physical Properties of GFM Samples

3.4 Strength of GFM Material from Uniaxial Compression with Lateral Expansion Test

3.4.1 Experiment to Determine the Main Oxide Components

(5-a) Relationship between Compressive Strength with Lateral

Expansion and Axial Strain

Hình 3.7 Results of Uniaxial Compression with Lateral Expansion at Different Cement Contents

a) Relationship between Compressive Strength and Axial Strain Hình 3.8 Results of Uniaxial Compression with Lateral Expansion at Different Polymer Contents

Hình 3.9 Effect of Mixing Method on Compressive Strength

Hình 3.11 Optimum Moisture Content for Compaction of Soil Samples

3.6 CBR Bearing Capacity of GFM Material

3.6.1 Materials and Experimental Method

3.6.2 Experimental Results

Figure 3.14 shows that the pressure resistance of the sample increases proportionally with the cement content The change in pressure is relatively distinct when the cement content increases from (5%, 7%, to 10%)

Hình 3.14 Relationship Between CBR Index and Dry Unit

Weight of Soil

slightly and remaining stable over time

Hình 3.17 The CBR index at the 65 blows/compaction per

layer for each saturation-drying cycle

Figure 3.18 illustrates that the particle size changes only slightly after two cycles of saturation and drying, each cycle lasting 60 days, indicating the high durability of the GFM material However, further research is needed on its long-term durability for practical use

a) GFM material after 120 days of water saturation

b) Particle size distribution of GFM after 60-day and 120-day

saturation cycles Hình 3.18 Determination of the dissolution characteristics of

Figure 3.20 displays the e-log(σ) compression curve of GFM

samples, divided into three distinct stages, unlike the compression curve of pure clay Figure 3.21 shows that in GFM material, particles with weak bonds break and separate into smaller particles The drainage of water from the closed voids occurs over time, resulting in the deformation behavior of the GFM samples, as shown in Figure 3.22

Figure 3.20 Compression settlement curves of GFM material samples

Figure 3.21 Particle composition before and after compression

of GFM samples

Figure 3.22 Strain-time curves (e-log(t)) of GFM samples

3.9 Strength and Deformation of GFM Material from CD Triaxial Compression Test

3.9.1 Materials and Testing Methods

b) GFM samples with 7% cement content

c) GFM samples with 10% cement content

d) Medium-grained sand in dense state and stiff plastic clay

under conventional consolidation

Figure 3.28 Volumetric change over time during the consolidation phase of GFM samples

a) GFM samples with 5% cement content

b) GFM samples with 7% cement content

c) GFM samples with 10% cement content

Hình 3.29 Relationship between stress and strain during the

shear loading process

a) Effect of cement content

b) Effect of polymer content

Figure 3.30 Effect of additive content

a) Relationship between internal friction angle and cement

content in GFM samples

d) Relationship between cohesion and polymer content in GFM samples Figure 3.31 Internal friction angle and cohesion of GFM samples

3.10 Proposed Applications of GFM Material

Based on a synthesis of technical requirements for fill and embankment materials from current standards, this section presents the proposed applications of GFM material, as shown in Table 3.7 The research results indicate that GFM material possesses technical properties that meet the requirements for infrastructure fill materials, road embankments, or backfill material for retaining walls

Table 3.7 Application Scope of GFM Material

Require

d Value

Test Result

-re fill material

- Backfill material for retaining walls

Bulk density,

γw (g/cm 3 ) >1.2 1.646 Percentage of

particles passing through the 0.14 mm sieve (%)

< 20 < 10

Fineness

Soil internal friction angle,

t material

- Backfill material for retaining walls

Bulk density,

γw (g/cm 3 ) >1.2 1.646 Percentage of

particles passing through the 0.14 mm sieve (%)

< 20 < 10

Fineness

CBR (%) ≥ 4 5.54÷11.8 Swelling

within the load impact range (%)

Based on these findings, the application scope of GFM material with minimal additives was proposed The following conclusions are summarized from the research results:

1) The sludge treatment method proposed by the author is applicable to sludge from specific rivers and lakes in Hanoi (characterized by high fine particle content, high water content, significant SiO₂ content, and oxide and heavy metal levels within permissible limits per QCVN 07:2009/BTNMT), as well as similar sludge and soils

2) Manufacturing potential with minimal additives: Liquid sludge can be processed into granular material using cement and polymer If the sludge's moisture content is lower than the plastic

limit, polymer may not be required for granulation For sludge with moisture above the liquid limit, a higher polymer content (over 0.5%) is needed When moisture is between the plastic and liquid limits, 0.25% to 0.5% polymer and 5% to 10% cement are sufficient for effective granulation

3) Physical properties of GFM material: GFM is a granular material with a particle density ranging from 2.55 to 2.61 g/cm³,

a low bulk density of 1.63 to 1.70 g/cm³, and a high void ratio between 1.22 and 1.49 It has excellent drainage characteristics,

is lightweight, and easy to transport, making it ideal for use as fill material or embankment soil behind retaining walls

4) Mechanical properties of GFM material:

Strength characteristics from unconfined compression tests: GFM samples show ductile deformation when the cement content is between 5% and 10%, transitioning to brittle deformation at 15% to 20% A small polymer content (0.1% to 0.3%) has minimal impact on strength, while higher polymer content (up to 1%) reduces strength

Compaction characteristics: GFM material has a low maximum dry unit weight, making it lightweight Its compaction capability

is not significantly affected by moisture content and it shows good drainage properties

CBR load-bearing capacity: At 5% cement content, GFM samples achieve CBR values between 2.4% and 5.97%, suitable for fill material or subgrade layers for roads, except for high-standard pavement layers (A1 classification per TCVN 9436-2012) Increasing cement content to 7%–10% raises the CBR value to 5.54%–11.79%, making it suitable for subgrade material

in roads of various grades (III, IV, I, II) as per TCVN 9436-2012 Deformation characteristics: GFM material exhibits distinct deformation behavior Its compression curve consists of three segments with varying slopes The slope is low below 50 kPa, increases up to 200 kPa, and reaches its peak beyond 200 kPa The material shows creep deformation, especially at lower