Hồ sơ xử lý nền đất yếu Dự án Đà Nẵng Quảng Ngãi

It should be noted that the actual fill thickness used in the ground improvement by means of the vertical drain consolidation system will be greater since it has to account for the settl

Ministry of Transport (B.GTVT)

Vietnam Expressway Corporation (VEC)

Project Management Unit No 85 (PMU 85)

IDA Credit No / IDA tín dụng số : 4779-VN

Project ID No / Mã dự án: P106235

Consulting Services for / Dịch vụ tư vấn Detailed Design for Da Nang - Quang Ngai Expressway Development Project / Thiết kế kỹ thuật dự án Đường cao tốc Đà Nẵng – Quảng Ngãi

Volume 2.4: Addendum to Main Report and Analysis Report

(Based on instruction of VEC at Letter No 3613/VEC-KTCNMT dated October 23, 2013

/Theo chỉ đạo của VEC tại công văn số 3613/VEC-KTCNMT ngày 23/10/2013)

(Updated in accordance with Approval Decision No.01/QD-VEC of VEC dated 03/1/2014

/ Cập nhật theo quyết định số 01/QĐ-VEC ngày 03/1/2014 của VEC)

January 09 , 2014

The Joint Venture of / Liên danh Tư vấn:

THAI ENGINEERING CONSULTANTS CO., LTD

IDA Credit No / IDA tín dụng số : 4779-VN

Project ID No / Mã dự án : P106235

Consulting Services for / Dịch vụ tư vấn Detailed Design for Da Nang - Quang Ngai Expressway Development Project / Thiết kế kỹ thuật dự án Đường cao tốc Đà Nẵng – Quảng Ngãi

(Báo cáo thiết kế kỹ thuật chi tiết)

Volume 2: Main Report (PKG A3) (Tập 2: Thuyết minh chính (Gói thầu A3))

Volume 2.4: Addendum to Main Report and Analysis Report

of Soft soil treatment (PKG A3) (Tập 2.4: Phụ lục điều chỉnh Thuyết minh và Tính toán

xử lý đất yếu (Gói thầu A3))

(Based on instruction of VEC at Letter No 3613/VEC-KTCNMT dated October 23, 2013

/Theo chỉ đạo của VEC tại công văn số 3613/VEC-KTCNMT ngày 23/10/2013)

(Updated in accordance with Approval Decision No.01/QD-VEC of VEC dated 03/1/2014

/ Cập nhật theo quyết định số 01/QĐ-VEC ngày 03/1/2014 của VEC)

Prepared by (Thực hiện) Checked by (Kiểm tra) Quality Control (KCS) Approved by (Duyệt)

Name (Tên) VECC Yasuhiro Nozue Nguyen Manh Chung Ichizuru Ishimoto

Signature (Chữ ký)

Date (Ngày) January 09 , 2014

(09/1/2014)

January 09 , 2014 (09/1/2014)

January 09 , 2014 (09/1/2014)

January 09 , 2014 (09/1/2014)

THE JOINT VENTURE OF NK-NE-CHODAI-TEC/LIÊN DANH TƯ VẤN

Project Manager/Giám đốc Dự án

Ichizuru Ishimoto

CONTENTS

A MAIN REPORT

Letter of Submission Project Location Map Table of Contents List of Abbreviations 1 GENERAL 3

1.1 Introduction 3

1.2 Scope of Work 4

2 DESIGN METHODOLOGY 5

2.1 General 5

2.2 Design Standards 5

2.3 Design Criteria 5

2.4 Engineering Analysis Method 7

2.4.1 General 7

2.4.2 Soil Replacement with Preloading 10

2.4.3 Theory and Calculation for Vertical Drain 11

2.4.4 Software 19

3 STUDY CONDITIONS 20

3.1 Topographical Conditions 20

3.2 Geotechnical Conditions 20

3.2.1 Outline of the Survey 20

3.2.2 Geotechnical Conditions 22

3.2.3 Soil Properties for Calculation 24

4 ENGINEERING ANALYSIS 35

4.1 General 35

4.2 Review on lateral movement of abutment 35

4.3 Engineering Analysis Results 36

4.3.1 Sectioning 36

4.3.2 Recommendation on Principle for Selection of Soft Soil Treatment Method 36

5 Soft Soil Treatment Design 37

5.1 Basic Design Policy 37

5.2 Result of soft soil treatment design 37

5.2.1 Main line 37

5.2.2 Dung Quat Interchange 44

5.3 Monitoring Instruments 49

5.3.1 Surface Settlement Plates (SSP) 49

5.3.2 Alignment Wood Stakes 50

5.3.3 Inclinometers 50

5.3.4 Electric Piezometers 51

5.3.5 Recording and Monitoring 51

6 Conclusion 55

Volume III : Drawings (Volume J in Road Work Document)

Volume IV : Quantity

List of Abbreviations

DHWL : Design High Water Level

GOVN : Government of Vietnam

QCVN : Vietnamese National Standards

of Da Nang as an exporting center Construction of this expressway section is essential for the socio-economic development and growth of the central of Vietnam

Beside that, the expressway is a part of the North-South Expressway located in parallel with the existing NH1A and North-South Railway and passing through Danang city, Quang Nam and Quang Ngai provinces in the central region The road starts at the intersection of the Danang Bypass and NH14B in Danang city and ends at the connecting point with the planned City Ring Road at existing NH1A in Quang Ngai province The major socio-economic developments along the expressway are Chu Lai Open Economic Zone in Quang Nam province and Dung Quat Industrial Zone in Quang Ngai province As for the cultural properties, Hoi An Ancient Town and My Son Sanctuary, registered as the world heritage (cultural heritage), are existed along the expressway

The proposed Danang Quangngai Expressway can be divided into two (2) sections according to the funding arrangment; namely JICA portion between Danang to Tamky with length of approximately 65

km followed by World Bank portion from Tamky to Quangngai with length of around 65 km as shown

in Figure 1-1 The route is further divided into thirteen (13) design and construction packages (Packages 1, 2, 3A, 3B, 4, 5, 6, 7, A1, A3, A3, A4 and A5)

Figure 1-1 : Project Facilities Plan Contract Package A3 from km 99+500 to km 110+100, includes embankments over soft ground with

12 bridges across some rivers, cross roads, canals

For Package A3 with embankment height (Ho: defined as the height between the existing and the design profile grade) of 1.2 m to 13.5 m, there will be a need to treat the soft clay for improving the overall stability during construction and for reducing post-construction settlement of the expressway

It should be noted that the actual fill thickness used in the ground improvement by means of the vertical drain consolidation system will be greater since it has to account for the settlement during preloading and additional surcharge for reducing the consolidation or construction time The required fill thickness can be over twice the design embankment height in the thickness of soft ground area

This report summarizes the design methodology and the proposed ground improvement methods for Package A3 from Station Km 99+500 to Km 110+100 only Calculations of the ground improvement design are provided in Volume 4

1.2 Scope of Work

The scope of the geotechnical design for ground improvement work consists of the followings:

• Evaluate the subsoil conditions From the new soil investigation performed, the subsoil conditions in the relevant sections are evaluated with focus on the thickness and the properties of the soft compressible soils close to the ground surface Based on the subsoil conditions in terms of soft soil properties and their thickness, the subsoils along the route have been divided into 48 major geotechnical units in the main line and 33 major geotechnical units in Dung Quat Interchange

• Evaluate and recommend suitable ground improvement methods for each section From the design criteria and other design constraints, the most appropriate methods of ground improvement have been proposed 81 embankment sections have been selected based on the subsoil conditions, the design profile grades and the design criteria etc

• Perform engineering analysis For each section with selected methods, the settlements during construction and operation are estimated, which are required to meet the design criteria Due to the soft nature of the upper soft soils along with loads from the embankment fill, the embankment stabilities under various configurations at the critical sections are checked with minimum factor of safety of 1.2 under the short term conditions (during construction) The stabilities of roadway after completion are also estimated and verified

• Highlight foreseeable construction issues Some important construction issues are also addressed in the report to increase the awareness of avoidable problems

From the soil investigation work conducted, the subsoil conditions and the problematic soils have been identified Soft clay deposit with thickness of 3.0 to 15.5 m has been encountered from Station km 99+500 to km 110+100 With the embankment placed over the soft clay deposit, there is

a need to improve the soft ground by appropriate ground improvement method for increasing the stability during construction and for minimizing the settlement during operation The merits and limitations of various ground improvement methods are presented and discussed in this chapter

2.2 Design Standards

The design was conducted in compliance with the following standards;

in consideration of the following issues:

• Time for preparation works,

• Time for construction of culverts and underpass structures,

• Time for construction of piles and abutments,

• Time for construction of pavement and completion, and

• As consolidation of the underneath soft soil reaching 90% at least

• Near Abutment: Post Construction Settlement ≤ 10 cm in 15 years

• Culvert zone: Post Construction Settlement ≤ 20 cm in 15 years

• Fill Embankment: Post Construction Settlement ≤ 30 cm in 15 years

c Factor of safety The adopted factor of safety against instability during construction is maintained above 1.2 The long term stability of the roadway will be controlled with factor

of safety of no less than 1.4

d Traffic load Traffic load is evaluated in accordance with 22TCN262-2000 from following equations:

l B

G n

Whereas (see Figure 2-1)

n: Number of vehicle,

G: Weight of vehicle (G = 30 ton in case of H30),

B: Width of traffic load (Max 14.3m as designated, 1 side),

l: distance between front wheel and rear wheel (l = 6.6m, in case of H30),

Figure 2-2 Traffic load value and distribution

In summary, the above constraints and criteria have been considered in the design process, which are described in later section

2.4 Engineering Analysis Method

2.4.1 General

There are several methods of improving the properties of soft soils for reducing the post-construction settlement or for increasing the stability of the embankment during and after construction Without any improvement, the fill embankment may suffer from low stability during construction and excessive settlement after operation due to consolidation of the compressible soils It should be kept in mind that most of the ground improvement methods can be rather costly compared with the conventional earthwork Therefore the use of any ground improvement would depend greatly on both technical and financial aspects of the project and it is generally classified into two categories as sliding-prevention method and consolidation acceleration method

Table 2-2 Classification of Soft Soil Treatment Countermeasure

Prevention

of Slope Sliding

• Counter Weight Method

• Reinforcement Geotextile

• Sand Compaction Pile

• Deep Mixing Method

• Replacement Method

• Expandable Polystyrene(EPS) Method

• Stone Column Pile

• Grouting Method

Acceleration of

Consolidated

• Preloading

• Vertical Sand Drain

• Prefabricated Vertical Drain

• Vacuum Consolidation Method

Soft soil was not found in Feasibility Study There is no any reviewing results for reference improvement solution applied

Figure 2-3 presents the ground improvement design flowchart adopted for this package based

on the technical viability and the construction cost, starting with no ground modification, followed by PVD, SD and SCP method

Figure 2-3: Ground improvement design flowchart

The following sections briefly describe the successful ground improvement methods available in this region

2.4.2 Soil Replacement with Preloading

Apart from improving the compressible soils by cementation or by consolidation through VDs, soil replacement can be a possible option as illustrated in Figure 2-4 The principle of the soil replacement is to remove the compressible soils down to required depths, and to replace with suitable compacted fill The depth of excavation will be governed by the long-term settlement

of the remaining compressible soils and the overall stability of the excavated pit It will not be economical and practical to replace the soft compressible soils if the replacement depths are too deep because of the vast quantity in replacement and excavation

Figure 2-4: Typical Soil Replacement Method

These main merits of this method are as follows:

• Ease of construction The soil replacement with preloading method predominately involves earthwork with excavation, fill placement and compaction etc., which can be handed by the earthwork contractor with appropriate construction equipment

Dewatering should be planned if there is a possibility of water flowing into the excavated pit

• Excavation and filling time The excavation and filling time can be adjusted depending on the capacity of the construction equipment and manpower To accelerate the construction, it is possible to increase the construction equipment and manpower

It should be noted that the disposal of the excavated materials has to be considered in the decision making

2.4.3 Theory and Calculation for Vertical Drain

The vertical drain system, including prefabricated vertical drain (PVD) or Sand Drain (SD) has been widely used for treating the soft compressible soils in Vietnam over the last decade The maximum PVD installation depth in Vietnam had reached over 30 m in some projects The improvement via this method had proven to be very effective, but it requires a moderate construction (or preloading) period and/or counterweight berm for stability purpose The primary difference between the PVD and the SD is the material used as the drainage media In

SD system, a column of good permeability sand has to be installed in the soft soils in shortening the drainage path during the preloading process The installation of SD is always time consuming due to the process of preparing the hole and placing the sand In addition, significant effort has to be placed in controlling the quality of the sand and the installation which may vary depending on the sand sources and the contractors

In the VD preloading method, it is usually more economical to construct the embankment in a number of loading stages, benefiting from the gain in undrained shear strength of the improved soils through consolidation during the preloading period The rate of loading (that is, filling of the embankment) can also contribute to some gain in the shear strength of the improved soils Therefore eithers stage loading, slow continuous loading or a combination of two can be adopted in the loading process, provided that there is sufficient construction time for this method of ground modification

The major components in the VD preloading method can be summarized as follows:

layer) in preventing any contamination to the sand mat The geotextile can sometimes be used

as the reinforcing member depending on the design requirements In this case, the geotextile may have to be placed above the VDs preventing the loss of its integrity due to penetration by the VD mandrel during the VD installation

ground for carrying the water out of the VDs during preloading The thickness of the sand mat will depend on the expected rate of settlement, its permeability, and the drainage distance or path etc Typically, a minimum thickness of 0.5 m is used

• VD: The VDs are the primary components in shortening the drainage paths of the soils in the preloading process To reduce the future settlement caused by the consolidation of soils, the VDs are normally installed down to the bottom (close to bottom) of the soft soils or to depth of soft soils where the stress induced from the embankment is sufficiently low The rate

of settlement during preloading is proportional to the spacing of the VDs If the construction time is limited, then shorter VD spacing in triangular grid pattern can be adopted

consolidating the soft soils in the VD improvement area This fill as described earlier, may be placed in stages or at a prescribed filling rate, taking advantage of the gain in the shear strength

of the improved soft soils during preloading process

It should be noted that this method will require a moderate construction time compared with other methods of improvement Nevertheless, the VD preloading method is the most common technique in improving soft soils at present, primarily because of its high performance, low cost and well established construction procedure

(1) Theory and Calculation for PVD and Sand Drain

Due to variation of stress caused by embankment load by distribution depth of soil, a soil layer will be divided into sub-layers with 1~2m in thickness for settlement calculation and settlement

of the soil layer will be summed up from the settlement of the sub-layers

It is possible to calculate consolidation settlement by using original formula as depicted below (hereinafter referred to as ∆e method):

H e

e e

log

P P H e

C

c

∆ + +

o o o

s c

P

P P H e

s c

P

P P H e

C P

P H e

C

+

+ +

0 0

log 1

log

In the sand layer, the following formula can be used for immediately settlement (De Beer method)

o

o i

P

P P H N

P

log 4

.

Where as:

∆P: Pressure caused by embankment,

t C

2 2

2 2

4

1 3 ln 1 )

(

n

n n n

n n

s

h s

d

d k

q

k z L z

F = π 2 −

(2-16) Where as:

pattern),

L: Drainage length,

consolidation being evaluated as follow:

m: Index of increase of undrain shear strength

(2) Theory and Calculation for Sand Compaction Pile

Sand Compaction Pile (SCP) method uses vibration load to penetrate a casing for making sand compaction pile on soft soil It shall contrive increase of bearing capacity, decrease of consolidation settlement, increase of horizontal resistance, uniformity of ground, consolidation drainage effect due to increase density of ground This method is used almost soil condition including sand soil, clay soil and organic soil

Settlement of the composite ground is less than non-treated ground because SCP shares load acting upon the ground and, accordingly, SCP reduces stress acting upon soil Following equation is used to get settlement of the composite ground

s c

P

P c P H e

s c

P

P c P H e

C P

P H e

C

+

+ +

0 0

log 1

log

Soft ground after being treated by SCP will be considered a composite ground comprising of SCP

Where,

µc: Reduction coefficient of stress,

Fv n

c c

) 1 ( 1

1

− +

=

=

σ

σ µ

µs: Increase coefficient of stress,

Fv n

n s

s

) 1 (

σ

σ

=

Cu/p: Ratio of strength increase

Z: Depth to the failure surface

γm' = Average sub water unit weight of composite soil

Friction angle of sand (of SCP) and ratio of stress division depending on replacement ratio is shown in table 2-1 below:

Table 2-1 Friction angle and Ratio of stress division depending on replacement ratio Replacement

Ratio, Fv

Friction Angle of

Ratio of stress division, n

Bishop method as formulated below is recommended for sliding check

w

b u w b C m

Figure 2-6 Sliding check model

In case reinforced geotextile is used, the resistance mobilized from the geotextile will be computed as follow:

Tensile: tensile strength of reinforcing geo-textile (=400KN/200KN is applied)

k: safety factor (=2 for polyester made geotextile as 22TCN262-2000 recommended)

k’: Reservation factor (=0.66 as 22TCN262-2000 recommended)

Figure 2-7 Resistant force mobilized from reinforced geotextile

Quang Nam has a complicated topography, it is gradually low from Western to Eastern, forming

4 ecological regions: high mountain region, midland region, plain region and coastal region; on the other hand it is divided by river valleys of Vu Gia, Thu Bon, Tam Ky… to form sub-areas having specific characteristics of small, narrow belong to river valleys of Vu Gia, Thu Bon, Tam Ky, to be deposited annually by alluvium, people have traditional intensive cultivations of wet rice and short-term industrial crops, food plant

Terrain surface of Package A3 was segmented by the road, dyke and irrigation canal Elevation

of terrain surface changes from 36.0m to 0.6m;

Figure 3-1: Overall Package A3 Route

3.2 Geotechnical Conditions

3.2.1 Outline of the Survey

114 boreholes were drilled down to depth of 40.0m to determine the subsoil conditions The laboratory tests were conducted for soil classification purposes as well as for determining the

stress history of the soft soils through consolidation tests Unconfined compression tests, triaxial compression test were also performed to determine the undrained shear strength profiles of the soft soil layers A geotechnical investigation report has been separated, describing the subsoil conditions in details

Based on Atlas sheet of Hoi An Map (D-49-I) in the scale 1/200.000 of Published by Viet Nam Geology Bureau in 1995 The geological formations can be encountered the section as follows:

quartz-mica schist, mi ca gneiss bearing gamest and sillimanite with interbeds or lenses of amphibolite, 800m thick

granite and pegmatite

biotite granite, two - mica granite, bionite granodiorite bearing muscovite These rocks are white-grey with black spots, of oriented structure and medium-grained hypidiomorphic texture

classic beds It consists of two-pyroxene basalt, plagiobasalt, olivine-augite-plagioclase basalt, olivine-augite basalt and olivine basalt Total thickness is 150m

places mixed with a few boulders Total thickness is 2-5m

granule and a little grit, light-grey, yellow-grey colored and well cemented The thickness is 10-15m

plant humus; 5-25m thick

upper part Pebble and granule have heterogeneous composition; 1.5-10m thick

- Undifferentiated Quaternary (Q): This formation is composed of boulders, pebble, grit, in some places, lateralized clay of motley color; 3-10m thick

Figure 3-2: Geological Map of PKGA3

The route goes through many different geological regions In general, geological condition along package route is very complicate, hard soil and soft soil overlap each other

3.2.2 Geotechnical Conditions

From the new soil investigation data, it is observed that the upper soil layer consists of soft clay

in some position which could be deposited in recent history; therefore the upper soft clay can

be considered to be lightly overconsolidated From the data gathered, the subsoil conditions along the route are divided into 81 geotechnical sections: from Km 99+500 – Km 110+100

The relevant subsoil conditions for soft ground treatment can be divided into seven (7) basic soil layers, including:

the locations), consists of Clayey sand (SC), somewhere is silty clayey sand (SC-SM), poorly graded sand (SP) yellowish grey, ash grey, loose The natural water content is 24.33% in average Void ratio is 0.842 in average This soil is overconsolidated, which is consistent with the age of the deposit There is no any unconfined or triaxial compression test for this layer SPT value N = 1-10 blows/30cm

soft to very soft with thickness of around 6.0m The natural water content is 27.22% in average Void ratio is 0.867 in average This clay is overconsolidated, which is consistent with the age of the deposit SPT value N = 0-4 blows/30cm

organic and cockles, ash grey, dark grey, soft to very soft The natural water content is 50.92% in average Void ratio is 1.519 in average Thickness of the layer changes from

1.3m to 7.0m The shear strength of the undisturbed soil from Vane shear test varies from 14.0 to 20.0 kPa SPT value N = 0-4 blows/30cm With high water content, big void ratio value and low shear strength, this soil layer would have to be improved for supporting the roadway as well as for reducing the post construction settlement

soft to very soft Thickness of the layer changes from 1.3m to 7.0m The natural water content is 30.28% in average Void ratio is 0.985 in average The shear strength of the undisturbed soil varies from 14.0 to 20.0 kPa SPT value N = 0-4 blows/30cm With high water content and low shear strength, this soil layer would have to be improved for supporting the roadway as well as for reducing the post construction settlement

organic and cockles, ash grey, dark grey, medium stiff Thickness of around 1.8m to 11.7m The natural water content is 76.69% in average Void ratio is 2.193 in average The shear strength of the undisturbed soil from Vane shear test varies from 17.0 to 31.0 kPa SPT value N = 4-6 blows/30cm This clay is overconsolidated, which is consistent with the age of the deposit With high water content, big void ratio value and low shear strength, this soil layer would have to be improved for supporting the roadway as well

as for reducing the post construction settlement

medium stiff The layer thickness varies from 1.8m to 10.8m The natural water content

is 105.05% in average Void ratio is 2.925 in average Strength of unconfined comp test

qu = 19.62kPa SPT value N = 4 – 6 blows/30cm

varies from 1.5m to 5.2m Strength of unconfined comp test qu = 27.96kPa SPT value

N = 4 – 6 blows/30cm The natural water content is 29.02% in average Void ratio is 0.928 in average

In summary, the upper soft clay layer will dominate the ground settlement; therefore it has to

be treated in supporting the roadway embankment The soil layers under above soil layer in each section are much stiffer; they will be the bedrock layers

It will consider all such parameters as soil strata – thickness, homogeneousness, etc., Following are only principles in general for sectioning according to the soil condition:

- Soft soil thickness changes over 3m, and/or

- There is a seam/lens of sandy soil detected in soft soil layer

the footing preventing lateral flow of the abutment and negative friction phenomenon 3.2.3 Soil Properties for Calculation

According to the soil investigation data, the subsoil is relatively uniform comprising of soft to medium clay, distributes from the ground surface to the depth of 15.5m approximately Sandy soil was some time detected but only as seams The soft soil, which will mostly affect to the stability of the embankment, was stratified into soil 3a1, 4a1, 4a2, 4a3, 4b1, 4b2, 4c and 5a in the Soil Investigation Report The following content will be the evaluation of soil values of these soils for soft soil treatment design

(Please refer to Soil Investigation Report for PKGA3 prepared by Thang Loi Jsc for more detailed)

Figure 3-4: Unit weight of layer 4a2, 4a3, 4b1, 4b2

Figure 3-5: Unit weight of layer 4c, 5a, 5b, 6

From the above figure, the following values will be recommended:

(3) Initial Undrain Shear Strength

Initial undrain shear strength of soft soil (Co) will be evaluated from the following basis:

- Field vane shear test (FVST): in situ Co value will be directly estimated from FVST being conducted during embankment boring,

- Triaxial test, UU-diagram (UU Test): Co value is also directly evaluated from this laboratory UU

test conducted on undisturbed samples,

- Unconfined Compression test (UC Test): Co value is evaluated from equation

For a reliable Co value for design, the analysing Co value will also be refered to the following basis:

- Standard penetration test (SPT): following empirical relationship will be used to estimate Co value from N of SPT testing

) ( 100

Table 3-2 : Relationship between Consistancy, Unconfined Compressive Strength of Clays,

and N value of the SPT

Consitancy

Unconfined Compressive Strength

Data range and Co typical value of these testing is shown in figures 3-6, 3-7

Figure 3-6: Shearing strength of layer 3a1, 4a2 from Vane shear test

Figure 3-7: Shearing strength of layer 4a3, 4b1 from Vane shear test

Table 3-3 : Summary selected Co value from the testing data and recommendation

As for soil 3a2, 3a3, 3b1, 3b2 which were detected as Clayey Sand (SC), Silty Sand (SM) and will behave mostly like sandy soil, in which internal friction angle will be critical for the soil strength

3a2 Silty, clayey sand (SC-SM) 8.7 -

C (kPa)

Soil

(4) Factor of Increase of Undrain Shear Strength

Undrain shear strength of soft soil will be increase due to consolidation with a factor called

“Factor of Increase of undrain shear strength” – m, which is basically evaluated from Triaxial test,

There are only 3 CU triaxial tests in this package Therefore, the relation between shear strength

Su (Su = qu/2, Su from VST, Su = N/16) against Po, equation by triaxial compression test m=sinφ/(1-sinφ) and equation by laboratory test result of Skemton m=0.11+0.0037*Ip are recommened to use The relation between Su and Po is shown in figures 3-8, 3-9

Figure 3-8 : m evaluate from qu (UC) against Po for Layer 4a2, 4a3, 4b1, 4b2

Figure 3-9 : m evaluate from Su (VST) against Po for Layer 3a1, 4a2, 4a3, 4b1

Table 3-4 Summary selected Factor of Increase of Undrain Shear Strength

mtan(φCu) sinφφ /(1-sinφφ )

0.11+

0.0037*Ip

3a2 Silty, clayey sand (SC-SM) -

Soil

-

-

-0.28-

0.080.27

4a2 Clay (CH)

(5) Pre-Consolidation Condition and Consolidation Soil Parameters

Pre-consolidation of the soil is evaluated from Over Consolidation Ratio (OCR) and is shown as following figures:

Figure 3-10 : OCR against depth for Layer 3a1

Figure 3-11 : OCR against depth for Layer 4a1, 4a2, 4a3

Figure 3-12 : OCR against depth for Layer 4b1, 4b2, 4c

Figure 3-13 : OCR against depth for Layer 5a

In general the soil in this package is over consolidated (OCR>1)

Testing curves of compression, consolidation coefficient and permeability of soil 3a1, 4a1, 4a2, 4a3, 4b1, 4b2, 4c, 5a and 6 from consolidation test are summarized in following figures 3-14, 3-15, 3-16, 3-17, 3-18, 3-19, 3-20, 3-21 as well as typical values thereof, which will be recommended for design for the respective soil

Figure 3-14 : Testing curves and typical value of soil 3a1

Figure 3-15 : Testing curves and typical value of soil 4a1

e-logP Cv-logP (x10-3 cm2/sec) Kv-logP (x10-7 cm/sec) 12.5 25 50 100 200 400 800 6.25 18 35 71 141 283 566 6.25 18 35 71 141 283 566 0.869 0.850 0.824 0.790 0.745 0.699 0.651 2.807 2.750 2.589 2.432 2.238 2.026 1.885 4.233 2.207 1.429 0.916 0.542 0.268 0.130

e-logP Cv-logP (x10-3 cm2/sec) Kv-logP (x10-7 cm/sec) 12.5 25 50 100 200 400 800 6.25 18 35 71 141 283 566 6.25 18 35 71 141 283 566 1.070 1.024 0.955 0.876 0.788 0.694 0.599 1.219 1.190 1.081 1.054 0.945 0.937 0.914 3.729 2.023 1.384 0.780 0.388 0.206 0.101

Figure 3-16 : Testing curves and typical value of soil 4a2

Figure 3-17 : Testing curves and typical value of soil 4a3

Figure 3-18 : Testing curves and typical value of soil 4b1

e-logP Cv-logP (x10-3 cm2/sec) Kv-logP (x10-7 cm/sec) 12.5 25 50 100 200 400 800 6.25 18 35 71 141 283 566 6.25 18 35 71 141 283 566 1.603 1.525 1.418 1.284 1.134 0.977 0.808 2.237 2.165 1.966 1.763 1.530 1.369 1.317 9.956 5.300 3.392 1.973 1.018 0.518 0.296

Cv-logP (Layer 4a2 <5m)

0.000 5.000 10.000 15.000 20.000 25.000

Kv-logP (Layer 4a2 <5m)

e-logP Cv-logP (x10-3 cm2/sec) Kv-logP (x10-7 cm/sec) 12.5 25 50 100 200 400 800 6.25 18 35 71 141 283 566 6.25 18 35 71 141 283 566 1.516 1.463 1.388 1.293 1.175 1.033 0.886 1.987 1.873 1.720 1.517 1.255 1.060 0.997 3.723 3.236 2.159 1.240 0.659 0.347 0.177

Cv-logP (Layer 4a2 >5m)

0.000 2.000 4.000 6.000 8.000 10.000

e-logP (Layer 4a2 >5m)

e-logP Cv-logP (x10-3 cm2/sec) Kv-logP (x10-7 cm/sec) 12.5 25 50 100 200 400 800 6.25 18 35 71 141 283 566 6.25 18 35 71 141 283 566 1.079 1.049 1.007 0.955 0.896 0.828 0.758 2.012 1.937 1.704 1.488 1.270 1.096 1.025 3.731 2.421 1.525 0.837 0.414 0.204 0.106

Kv-logP (Layer 4a3)

e-logP Cv-logP (x10-3 cm2/sec) Kv-logP (x10-7 cm/sec) 12.5 25 50 100 200 400 800 6.25 18 35 71 141 283 566 6.25 18 35 71 141 283 566 2.314 2.195 1.998 1.754 1.487 1.228 0.963 1.328 1.270 1.144 0.970 0.802 0.716 0.693 4.289 3.600 2.809 1.574 0.777 0.372 0.205

Figure 3-19 : Testing curves and typical value of soil 4b2

Figure 3-20 : Testing curves and typical value of soil 4c

Figure 3-21 : Testing curves and typical value of soil 5a

e-logP Cv-logP (x10-3 cm2/sec) Kv-logP (x10-7 cm/sec)

P (kPa) Kv-logP (Layer 5a)

(6) Summary of Soil Value for Soft Soil Treatment Design

According to the analysis being presented above, values of the soil recommended for soft soil treatment design are summarized in the following tables 3-5

Table 3-5 Summary of Soil Parameters Recommended for Soft Soil Treatment Design

Layer No Soil

SPT Valuve ᵞt ᵞsat

C (kPa)

Φ

Φ (deg.) m Cc Cs

Pc (kg/cm2) OCR

Cv x10e-3 (cm2/s)

Cv/Ch

2a Clay (CL) 8.6 1.84 1.92 52.73 0.0 -

2b Clay (CH) 10.0 1.78 1.88 61.31 0.0 -

3a1 Clayey sand (SC) 2.4 1.86 1.91 15.21 0.0 0.200 0.160 0.041 0.65 2.1 2.238 0.5

3a2 Silty, clayey sand

(SC-SN)

8.7 1.86 1.91 0 31.4 - 3a3 Silty sand (SM) 5.5 1.87 1.87 0 29.1 -

6 Clay Sand (SC) 1.82 1.95 18.15 0.0 0.150 0.322 0.095 0.87 1.3 2.810 0.5 L3 b Clay Sand (SC) 1.83 1.92 - 0.0 0.150 0.190 0.053 0.7 1.1 2.542 0.5

The sections improve by the Soil Replacement method are considered carefully and mainly applied for abutment sections or some others with the soft soil thickness is less than 5.0m to avoid the lateral movement to the abutment These abutment sections are narrow, far from each other and unsuitable for any other improvement solution

Around 63 m of the roadway will be improved by the Soil Replacement, 1.35 km will be improved by the Pre-loading method, 2.325 km will be improved by the PVD method, 1.988 km will be improved

by the SD method

The soil parameters used in the engineering analysis are summarized in 3.2.3 The outputs of the engineering analysis for soil improvement are provided in Volume II

4.2 Review on lateral movement of abutment

In the case of embankment on soft soil near abutment, lateral flow may occur in the ground by consolidation Lateral flow can cause some serious problems to the bridge, for example pile foundation of abutment which constructed on soft soil may be damaged due to lateral flow So, lateral flow of abutments in this package need to be checked For checking lateral flow, there are some methods such as lateral flow index, lateral flow judgement index, and stability check against sliding

(a) Large settlement (b) Small settlement