Shore Pile and Braced Excavation Design

Shore Pile and Braced Excavation

Shore pile and bracing system of deep excavation

সাধারণত আমরা যখন excavation করি সেখানে RCC Shore Pile, steel sheet pile, bracing system, anchoring system এর ডিজাইন সম্পর্কে জানার প্রয়োজন হয় , এই সবগুলো বিষয় নিয়েই এই কোর্স। deep excavation কিভাবে ম্যানেজ করতে হয়, কিভাবে ডিজাইন করতে হয়, কনস্ট্রাকশন এ কি কি সর্তকতা অবলম্বন করতে হয় এই বিষয়গুলো এই কোর্সের মধ্যে আছে। Geotechnical Software দিয়ে shore pile and bracing system ডিজাইন করা সহজ যদি Geotechnical Engineering কিছুটা জানা থাকে ।কিন্তু এই  Software গুলো কেঊ কিনে ব্যবহার করতে চায় না এবং সবাই ব্যবহার করতে পারবে না। তাহলে সমাধান কি ? আপনার কাছে থাকা ETABS , STAAD Pro দিয়েই যাতে ডিজাইন করা যায় সেই technique জানা যাবে এই শর্ট কোর্সে । পুরনো বা নতুন কোন বইতে এই বিষয়গুলো এভাবে গুছানো নেই । আশাকরি সিভিল ইঞ্জিনিয়ারদের উপকারে আসবে এই কোর্সটি ।

Usually, when we do excavation, we need to know about RCC shore pile, steel sheet pile, bracing system, anchoring system and its design. All these topics are included in this course. There will also be more information on how to manage the deep excavation, how to design, what precautions to take in construction. It is easy to design shore pile and bracing system with Geotechnical Software if you have some knowledge of Geotechnical Engineering. But no one wants to buy Software and not everyone can use it. So, what is the solution? Techniques are explained so that you can design shore pile and bracing system using ETABS, STAAD Pro. There is no old or new book where you can find all these together. Hopefully, this course will be beneficial for civil engineers.

What you'll learn

  • Shore pile and bracing system design
  • Instrumentation for Shore pile
  • Manual calculation of Shore pile design
  • FEM modelling of braced excavation
  • Case studies
  • Earth pressure
  • Correlations
  • Sand Boiling, Bottom Heave
  • King post detail

Prerequisite / Eligibility

  • BSc, MSc or PhD in Civil Engineering
  • Level 4 or 4th year student of bachelor’s in civil engineering

Course Teacher

Professor Dr. Jahangir Alam, Department of Civil Engineering, BUET, Dhaka, Bangladesh

Brief Biography of Course Teacher

Education

  • PhD in Geotechnical Earthquake Engineering, the University of Tokyo, Japan, 2005
  • MSc in Civil and Geotechnical Engineering, BUET, Dhaka, Bangladesh, 2002
  • BSc in Civil Engineering, BUET, Dhaka, Bangladesh, 1998

Biography

Professor Dr. Engr. Md. Jahangir Alam is faculty member at the Department of Civil Engineering, BUET, Dhaka-1000, since 1999. He completed his PhD from University of Tokyo in Geotechnical Earthquake Engineering in 2005 as a Monbu-Kagaku-sho Scholar. He was research fellow in Ecole Centrale Paris in 2008. Professor Jahangir did his BSc in Civil Engg with major in Structure and MSc in Civil and Geotechnical Engineering from BUET.

Professor Jahangir has multidisciplinary research interests and has publications in international journals and conferences. His current research topics are “Risk Sensitive Land Use Planning of Mega City”, Physical and Numerical Modeling of Liquefaction Hazard, Mitigation against Seismic Liquefaction, Cyclic Behavior of Non-plastic silt, Reinforced Earth, Earthquake Resistant Foundation in Soft Soil, Climate Resilient Concrete, Climate Resilient Road.

Professor Jahangir was involved in many consultancy projects where he designed/checked high rise RCC buildings, Communication towers, Jetty, Shore Pile, Embankment, Container Terminal, Ground Improvement, Bridge Foundation etc. He supervised many MSc and PhD students. He was involved in pile load testing, pile integrity testing, concrete mix design and development of laboratory and field-testing equipment.

Professor Jahangir actively involved in National and International professional bodies. He is life member and was Treasurer of Bangladesh Society for Geotechnical Engineering (BSGE), which is Bangladesh Chapter of ISSMGE. He is life fellow of Institute of Engineers Bangladesh (IEB). He is life member of Bangladesh Earthquake Society (BES). He was Treasurer of Bangladesh Earthquake Society (BES).

Certificate of Attendance

Certificate of attendance will be awarded after completion of all video lessons and quizzes

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Detail Course Outline

Shore Pile and Bracing System Design in Deep Excavation

  • Basic Definitions: Excavation, Open Excavation, Shoring, Support structure, Trench, Trench Cage, Trench jack, Tunnel.
  • Deep Excavation, shore pile and bracing system: Earth pressure calculation, Shore pile or sheet pile design, Bracing system design, Strut, wale, tie, Capping beam design, King post.
  • Other important issues of deep excavation: Water seepage, Sand boiling, Heaving at base, Connections of bracing system, Foundation information of surrounding structures, Lateral displacement and ground loss.
  • Methods of Analysis and Design of Shore Pile and Bracing System: Limit Equilibrium Analysis, FEM (2D, 3D), conventional design of shore pile and bracing system,
  • Analysis of Staged Construction
  • Failure modes of shore pile and bracing system in deep excavation: Water seepage or leakage, Sand boiling in sand, heaving at base in soft clay, Toe failure (kick out failure), Uplifting of mat during construction, Deep seated slope failure.
  • Stages of planning, design and construction
  • Two Approaches of Basement Construction: Top-down method, Bottom-up method.
  • Excavation in Clay Soil and Sandy Soil.
  • Instrumentation: Inclinometer, Piezometer, Settlement gauge, Deflection measuring devices.
  • Components of bracing system in deep excavation: Shore pile / sheet pile, Wale, Strut, Corner bracing, King post.
  • Bottom-Up Excavation Methods: Sloped open cut method, Vertical wall, Cantilever wall, Anchored wall, Incline Propped wall, Braced wall, shore pile / sheet pile, Raker Shoring
  • Types of Vertical Wall: Braced sheet piling or RCC precast piling, Soldier beam and lagging, Bored-pile walls, Diaphragm-slurry walls.
  • Pile type: Secant Pile, Cantilever Shore Pile or Sheet Pile, Anchored or One Level Braced Sheet Pile.
  • Kingpost Removal and Instrumentation in Braced Excavation

Ground Subsidence or Ground Loss due to Excavation

  • Cause of Ground Subsidence (Ground loss)
  • Reasons of Lateral Movement and Ground Loss
  • How to Prevent Ground Loss: Snug fit of wall against soil, Making Struts Stiffer, Making Wales Stiffer, Making Stiffer Shore Pile, Prestressing Struts, Reducing Elapsed Time between Excavation and Installation of Bracing System, Reducing Elapsed Time between Excavation and Installation of Bracing System, Location of 1st bracing level.
  • Calculation of volume of soil in the lateral displacement zone
  • Estimate the lateral distance of the settlement influence
  • Compute ground loss settlements
  • Effect of excavation width on ground settlement
  • Estimation of ground loss as per Ou and Hseih (2011)

Bottom Heave in Soft Clay

  • Why bottom heave happen?
  • How to prevent bottom heave?
  • Solution for Bottom Heave Before Excavation
  • Solution for Bottom Heave After Excavation

Sand Boiling in Braced Excavation

  • Reasons of sand boiling / piping
  • How to prevent sand boiling?
  • Determining the factor of safety against piping by drawing a flow net
  • Workout example for Factor of Safety Calculation

BNBC guidelines on excavation

  • Excavation
  • Notice to adjoining property
  • Written notice for excavation
  • Shoring, bracing and sheeting
  • Guard rail
  • Entry and exit
  • Placing of construction material
  • Safety regulations
  • Dewatering
  • Slope stability of adjoining buildings
  • Sliding
  • Missing information for excavation in BNBC 2017

Lateral Deflection and Settlement Limit during Braced Excavation

  • Wall movement needed for active condition
  • Limiting values of retaining wall displacements and impact to the adjacent structures
  • Generally acceptable criteria
  • Settlement limit of adjacent ground and building
  • Monitoring plan
  • Recording construction activities
  • Limits of adjacent ground and building settlements due to excavation

Course contents

1
Course contents of Shore Pile and Bracing System Design

Shore pile and bracing system of deep excavation



Contents

1.      Shore pile and bracing system design

2.      Instrumentation

3.      Manual calculation

4.      FEM modeling of braced excavation

5.      Case studies

6.      Earth pressure

7.      Correlations

8.      Sand Boiling, Bottom Heave

9.      King post detail

10.  Braced excavation in soft soil

2
Documents of Shore Pile and Bracing System Design

Shore Pile and Bracing System Design in Deep Excavation

1
Shore Pile and Bracing System Design, Part-1

Shore Pile and Bracing System Design in Deep Excavation




Why do we need?

• It is legal obligation to protect adjacent infrastructures when excavating to any depth



Deep Excavation, shore pile and bracing system

·        Earth pressure calculation

·        Shore pile or sheet pile design

·        Bracing system design

o  Strut, wale, tie

·        Capping beam design

·        King post



Other important issues of deep excavation

•Water seepage*****

•Sand boiling

•Heaving at base

•Connections of bracing system

•Foundation information of surrounding structures



Methods of Analysis and Design of Shore Pile and Bracing System

•Limit Equilibrium Analysis: Manual Calculation

FEM:

2 D

•Modeling Shore Pile / Sheet Pile as Elastic Beam in any FEM Software (ETABS, STAADProetc)

•Modeling Shore Pile / Sheet Pile as Elastic Beam in any Geotechnical FEM Software (Geo5,Geostudio, Plaxis2D etc)


3D

•Modeling soil, shore pile / sheet pile and bracing system in 3D GeotechnicalFEM Software (Plaxis3D, MIDAS etc)



Analysis of Staged Construction

•Shore pile / sheet pile, bracing system and deep excavation need staged construction

•Each stage should be analysed

•Any stage might be critical based on soil and surrounding condition



Analysis of Shore Pile and Bracing System

Limit Equilibrium Analysis

•FoSis calculated from Ultimate Resistance/Applied Load

•Serviceability can not be checked

•Failure means FoS<1.0

•C, phi is required



Finite Element Analysis

•Stress –Strain –Deformation is calculated

•Serviceability can be checked easily

•Failure is identified from excessive deformation or nonconvergence

•C, phi, E and other parameters required



Failure modes of shore pile and bracing system in deep excavation

1. Lateral deflection of shore pile, wale ******

2. Vertical displacement of retained soil

3. Shear or bending failure of shore pile, wale

4. Buckling failure of strut

5. Anchorage failure (anchor rod yielding, passive failure of anchor block / friction failure anchorage length

6. Connection failure of bracing system

7. Water seepage***** or leakage

8. Sand boiling in sand

9. Heaving at base in soft clay

10. Toe failure (kick out failure)

11. Uplifting of mat during construction

12. Deep seated slope failure



Stages of planning, design and construction

•Topographical survey

•Inventory survey (foundation, structure and existing situation of surrounding infrastructures)

•Subsoil investigation

•Analysis and design (meeting criteria of code)

•Construction sequence, safety and instrumentation planning

•Piling, Excavation and Bracing etc.



Two Approaches of Basement Construction

•Top-down method -X

•Bottom-up method



Most favorable situation during excavation

•Unsaturated soil within excavation depth

•Water table is below base of excavation

So, who is the #1 enemy?



Excavation in Clay Soil


Demerit

•Earth pressure is high if soil is soft

•Heave

•Very low soil resistance below dredge line


Merit

•No water seepage



Excavation in Sandy Soil


Demerit

•Water seepage and loss of ground with seepage water

•Sand boiling


Merit

•Better resistance under dredge line



Instrumentation

·        Inclinometer

·        Piezometer

·        Settlement gauge

·        Deflection measuring devices



Components of bracing system in deep excavation

•Shore pile / sheet pile

•Wale

•Strut

•Corner bracing

•King post



why don’t shore pile and bracing system fail in many instances even it is not properly designed?

Answer is: unsaturated soil, tree roots



Basic Definitions

·        Excavation : An excavation means a man made cavity or depression in the earth’s surface formed by earth removal.

·        Open excavation means an excavation in which the width is greater than the depth, measured at the bottom.



Deep excavation Vs Open excavation

Deep excavation: An excavation in soil or rock more than 4.5mis called deep excavation

Open excavation: It means an excavation without any retaining system by providing suitable slope 1:2 or 1:1, when surrounding allows



Basic Definitions

Shoring: is an assembly of structural members designed to prevent earth or material from falling, sliding or rolling into an excavation.

 

Support: structure means a temporary or permanent structure or device designed to provide protection to workers in an excavation, tunnel or shaft from cave-ins, collapse, sliding or rolling materials and includes shoring, bracing, piles, planks and trench cages.


Trench means an excavation that is deeper than its width measured at the bottom. (long -deep –narrow)


Trench Cage means a steel support structure designed to resist the pressure from the walls of a trench and capable of being moved as a unit.

 

Trench Jack means a screw or hydraulic jack used as a brace for a temporary support structure.


Tunnel means a generally horizontal excavation that is more than a meter long and located underground.



Necessity of deep excavation

1.      Mega structures like dams, power stations

2.      Building with multiple basements

3.      Tunnel construction

4.      Basement required for high rise building to increase overturning stability

5.      Nuclear waste containment

6.      Utility lines under road



Bottom-Up Excavation Methods

1.      Sloped open cut method

2.      Vertical wall / shore pile / sheet pile

·        Cantilever wall / shore pile / sheet pile

·        Anchored (tieback) wall / shore pile / sheet pile

·        Incline Propped (Raker) wall / shore pile / sheet pile

·        Braced wall / shore pile / sheet pile



Sloped open cut method

·        Sloped open cut method: Does not use retaining walls or struts. The construction site is excavated with sloped sides.

·        Digging with slope and backfilling are necessary

·        Preferable when excavation is not too deep



Cantilever wall

Cantilever method: Require construction of retaining walls without bracing system



VARIOUS WALLS FOR BRACED EXCAVATIONS

Types of Vertical Wall

• Braced sheet piling

• Braced RCC precast piling

• Soldier beam and lagging

• Bored-pile walls

(a) intermittent,

(b) contiguous,

(c) secant

• Diaphragm-slurry walls



How to make water tight

·        Sheet piling

·        Jet grouting in contiguous bored pile

·        Shotcretingwith wiremeshin bored pile

·        Secant pile

·        DIAPHRAM WALL / SLURRY WALL



Watertight by bored pile and shotcreting

• Shotcretingis done from the ditch after excavation

• Wire mesh may be used if needed

• Weep holes may be kept with proper dewatering management



Watertight by Secant pile

Secant wall construction sequence:

1. Drill and cast female piles (soft primary piles without rebar)

2. Drill and cast male (secant) piles



SECANT PILE

Secant piles are reinforced with either steel rebar or with steel beams. Primary (female) soft piles are installed first without rebar. Then secondary (male) piles constructed in between primary (female) piles once the concrete gains necessary strength. Pile overlap is typically in the order of 80 mm and can go in depths of up to 45 meters. (Baxter, 2012)



Advantages & Disadvantages of using secant piles

The main advantages of secant pile walls are:

·        Increased wall stiffness compared to sheet piles.

·        Can be installed in difficult ground(soft soil, loose sand etc)

·        Used in high water table conditions.


The main disadvantages of secant pile walls are:

·        Verticality tolerances may be hard to achieve for deep piles.

·        Total waterproofing is very difficult to obtain in joints.

·        Increased cost compared to sheet pile



DIAPHRAM WALL / SLURRY WALL

·        The continuous diaphragm wall (also referred to as slurry wall) is a structure cast in a slurry trench by tremieconcrete.

·        The trench is initially supported by bentoniteor polymer based slurries.



DIAPHRAM WALL / SLURRY WALL

A) Trenching under slurry,

B) End stop inserted (steel tube or other),

C) Reinforcement cage lowered into the slurry-filled trench,

D) Concreting by tremiepipes



Short Term Critical

·        Shallow foundation

·        It applies a total stress increase to the clay subsoil, and positive pore pressures are induced



Idealized wall movements

Active: Rigid structure rotates away from soil about its base. Eventual soil failure involves a small mass of soil, which is partly supported by the shear stresses on the failure plane. Pressures are low.


Passive: Rigid structure rotates toward the soil about its base. Eventual soil failure involves a large mass of soil, with shear strength acting against the wall. Pressures are high.


Earth pressure at rest: Structure is rigid, does not move, and can be placed in the soil without allowing any lateral soil movement. Lateral pressures existing in the soil before wall installation are applied to the wall



Ka or Ko

·        It is dangerous to assume passive pressure as resistance, because, to develop passive pressure need sufficient wall movement. Rather apply support spring at passive side.

·        Same applies to active pressure.

·        In reality, it is in between Kaand Ko.

·        So, K = (Ka+Ko)/2




LIMIT EQUILIBRIUM ANALYSIS



Cantilever Shore Pile or Sheet Pile

·        Cantilever pile may not fail totally, But excessive lateral deformation may pose danger to adjacent structures

·        Pile must be embedded into sandy soil and stiff / hard clay



Alternative Solution of Anchored or Braced Shore Pile or Sheet Pile


Pressure distribution below dredge level

• Generally, there is a point of contra-flexure in the wall some distance below dredge level

• For very dense sands, the point of contra-flexure may be at, or slightly above, dredge level

• For loose sands, it will be lower



Steps of analysis

1. Calculate EI of shore pile / sheet pile. Define the beam section in software so that model EmIm= EI/s. Beam finite elements length should be 0.5-1.0 m

2. Compute pressure diagram using Effective unit weight and K =(Ka+Ko)/2 uptopile tip and take minimum Pressure = 0.2(H+q)

3. Add water pressure to earth pressure at both sides

4. Run analysis to get shear force, BM diagram and R1, R2 reactions

5. Calculate resultant force (Pp) of passive earth pressure below dredge line

6. Check that R2 < 0.5Pp

7. Use R1 to design bracing system

8. Use SF and BM of shore pile to design shore pile




CONVENTIONAL DESIGN OF SHORE PILE AND BRACING SYSTEM



Steps for design of shore pile and bracing system

·        Compute the lateral pressure using peck’s apparent pressure diagram

·        Determine strut forces

·        Design the struts, sheeting, wales



Limitations

1. They apply to excavations having depths greater than about 6 m.

2. Embedment length is tends to zero.

3. They are based on the assumption that the water table is below the bottom of the cut.

4. Sand is assumed to be drained with zero pore water pressure.

5. Clay is assumed to be undrained and pore water pressure is not considered.

6. Not applicable for layered soil



Cut in sand

σa= 0.65 γH Ka

Where,

γ= unit weight

H = height of the cut

Ka= Rankine active pressure coefficient

= tan2(45 –ϕ’/2)

ϕ’= effective fiction angle of sand


Apparent pressure diagram (Peck, 1969)



PRESSURE ENVELOPE FOR CUT IN LAYERED SOIL

Sometimes, layers of both sand and clay are encountered when a braced cut is being constructed. In this case, Peck (1943) proposed that an equivalent value of cohesion (ϕ = 0) should be determined according to the following formula



Solution for Layered Soil by Bowels

1. Compute pressure diagram using Effective unit weight, Kaand Ko

2. Make negative pressures to zero

3. Compute resultant Ra and Ro. Calculate avgR

4. Using avgR, make an idealized rectangular or trapezoidal pressure diagram

5. Add water pressure to the idealized pressure diagram



DESIGN OF VARIOUS COMPONENTS OF A BRACED CUT


Strut Design

• In construction work, struts should have a minimum vertical spacing of about 2.75 m or more

• Struts are horizontal columns subject to axial force and bending. The load-carrying capacity of columns depends on their slenderness ratio, which can be reduced by providing vertical and horizontal supports at intermediate points

• For wide cuts, splicing the struts may be necessary

• For braced cuts in clayey soil, the depth of the first strut below the ground surface should be less than the depth of tensile crack, zc


Step-1

• Depending on the soil, assume one of the three apparent-pressure envelopes.

• Draw the pressure envelope next to the wall of the excavation.

• The struts are labeled A, B, C, and D, carrying compressive forces PA , PB , PC, and PD. They are placed at horizontal spacing of s.

• The connection between the strut and the sheet pile (or soldier beam) is assumed to be a hinge (i.e., carrying no moment) at all strut levels, except for the top and the bottom ones.

• Only the ends of struts B and C act as hinges. Some designers assume hinges at all levels except for the top.


Step-2

•Each beam has two unknown strut loads, which can be determined from equilibrium considerations.

•the strut loads per unit length of the excavation are A, B = B1+B2, C = C1 + C2, and D.


Step-3

With center-to-center horizontal strut spacing of s, the strut loads can be summarized as follows

PA = As (A = reaction per m, s = spacing of strut horizontally)

PB = Bs= (B1+B2)s

PC = Cs = (C1+C2)s

PD = Ds


Step-4

Design strut section using the strut forces



Design of Wale Section

To compute the maximum bending moment and shear of wales, the wales can be Viewed as simply supported beams with struts as supporting hinges, or Viewed as continuous beam


• Wales conservatively treated as pinned at the struts

• Maximum moment for wales, which occur at the mid span are

At level A, Mmax= A*s2/8

At level B, Mmax= (B1 + B2)*s2/8

At level C, Mmax= (C1 + C2)*s2/8

At level D, Mmax= D*s2/8

• Now determine the section modulus S = Mmax/ σall



Case Study of Braced Cut and Apparent Pressure Diagram

Lambe(1970) provided data on the performance of three excavations for the subway extension of the MBTA in Boston (test sections A, B, and D), all of which were well instrumented.


The construction of the south half of the National Plaza in Chicago required a braced

cut 21.43 m deep.

Swateket al. (1972) reported the case history for this construction.


The area of actual pressure diagram = 2933 kN/m.

Area of Peck’s pressure diagram = 5280 kN/m

Peck’s pressure envelope gives a lateral earth pressure of

about 1.8 times that actually observed in this case.


So, this method is sometimes unsafe and sometimes conservative


This method is dangerous in the subsoil condition of Bangladesh where piles need to be embedded below dredge line



MODIFIED CONVENTIONAL METHOD OF SHORE PILE AND BRACING DESIGN,

Proposed by Professor Jahangir Alam, Department of Civil Engineering, BUET, Dhaka


Applicable to

• Any depth of excavation

• Water table

• Layered soil and

• Embedment



Solution for Layered Soil in Modified Method

1. Compute pressure diagram using Effective unit weight and K =(Ka+Ko)/2 uptopile tip and Minimum Pressure = 0.2H+q

2. Compute resultant R from pressure diagram

3. Using R, make an idealized rectangular pressure diagram

4.  Consider water pressure diagram at both side

5.Draw passive pressure diagram and calculate Pp using FS=2.0

6. Apply Pp at D/2 distance from pile tip

7. Determine P1, P2…. Using simple beam model in ETABS



Simple FEM Model of Braced Shore Pile using ETABS or Any Structural FEM Software

In reality soil behavior is nonlinear, here it is modeled as nonlinear. If the lateral deflection is kept with code defined limit, the soil behavior is approximately linear



Steps of Simple FEM modeling

1. Calculate EI of shore pile / sheet pile. Define the beam section in software so that model EmIm= EI/s. Beam finite elements should be 0.5-1.0 m

2. Compute pressure diagram using Effective unit weight and K =(Ka+Ko)/2 uptopile tip and take minimum Pressure = 0.2(H+q)

3. Add water pressure to earth pressure

4. Estimate k1, k2…. below dredge line.

5. Assume strut sections and compute s1, s2….. Per unit length of wall

6. Run analysis to get shear force, BM diagram and s1, s2… and k1, k2… reactions

7. Rs1, Rs2… shall be used to design strut and re-calculate s1, s2……

8. Rk1, Rk2….. Shall be summed up to get total passive resistance Rt. Rt< (Pp –Pa)/FS [FS = 1.5-2.0]. If this criteria does not satisfy, increase D.

9. Modify the model for s1, s2, …. And k1, k2…. And RUN again

10. Solve all the stages similarly

11. Check deflections with code limits

12. Take the SF and BM to design the shore pile section



Estimate soil spring as per Chinese Standard

• Ref: JGJ 120-2012 (Technical specification for retaining and protection of building foundation excavations).

• Chinese Standard


Kh =m(z-h)

m = proportional coefficient of modulus of subsoil reaction [kN/m4]

z = depth of the calculation point from the original ground [m]

h = depth of excavation at current stage of construction [m]

•modulus kh is linear with depth

•Proportional coefficient m should be determined from pile test with horizontal load.


If there are no test data, Chinese standard JGJ 120-2012 suggest an empirical formula to estimate this coefficient.

Vb= horizontal displacement of sheeting structure at the ditch bottom [mm]; (min 10 mm)


AccordingtoCSN731004:


According to Matlock and Reese


Correlation between Modulus of Elasticity (Es) and N60


Linear Distribution (Bowles):

Themodulusofsubsoilreactionatadepthzisprovidedby:

r= reduced width of pile[m],which is given the 2nd equation mentioned above

d= pile diameter[m]

β= angle of dispersion–is input with respect to the angle of internal friction in the range of φ/4~φ

K=soil parameter (modulus) according to Bowles [MN/m3]

?ℎ=k.(0.308+1.584?/?)?/(??)

r = d+2d.tanβ



Calculating spring constant of struts

S1 = P/d = (EA/L)/s

L = half of the width of excavation

S = horizontal spacing of struts

EA/L is for the width s



Modeling section of shore pile

•Calculate EI of one pile

•Model EmIm= EI/s

•Calculate depth of a rectangular beam of width 1 m or 1 ftwhich must have EmIm



MODELING BRACING SYSTEM IN FEM SOFTWARE




Kingpost Removal and Instrumentation in Braced Excavation

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Shore Pile and Bracing System Design, Part-2
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Shore Pile and Bracing System Design, Part-3
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Shore Pile and Bracing System Design, Part-4
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Shore Pile and Bracing System Design, Part-5
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Shore Pile and Bracing System Design, Part-6
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Shore Pile and Bracing System Design, Part-7
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Shore Pile and Bracing System Design, Part-8
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Limit Equilibrium Analysis, Part-1
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Limit Equilibrium Analysis, Part-2
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Limit Equilibrium Analysis, Part-3
12
Anchored or One Level Braced Sheet Pile
13
Conventional Design of Shore Pile and Bracing System, Part-1
14
Conventional Design of Shore Pile and Bracing System, Part-2
15
Conventional Design of Shore Pile and Bracing System, Part-3
16
FEM Model of Braced Shore Pile, Part-1
17
FEM Model of Braced Shore Pile, Part-2
18
FEM Model of Braced Shore Pile, Part-3
19
FEM Model of Braced Shore Pile, Part-4
20
Kingpost Removal and Instrumentation

Ground Subsidence or Ground Loss due to Excavation

1
Ground Loss due to Excavation, Part-1

Ground Subsidence or Ground Loss due to Excavation



Cause of Ground Subsidence (Ground loss)

1.     Vertical ground settlement in a perimeter zone outside the excavation due to lateral movement of shore pile or sheet pile

2.     Top most issueLateral displacement and ground loss (ground subsidence)



Reasons of Lateral Movement and Ground Loss

  1. Elapsed time between excavation and the placement of wales and struts.
  2. Soft soil under the dredge line which cannot resist lateral movement soil
  3. Deflection of strut, wale or shore pile
  4. Heaving or sand boiling
  5. Wrong location of 1st bracing
  6. Gap between wale and shore pile



How to Prevent Ground Loss


1. Snug fit of wall against soil

1.     The wall must fit snugly against the sides of the excavation.

2.     This criterion is critical when the wall is placed against the earth face after some depth of excavation


2. Making Struts Stiffer

The struts, Rakers or tiebacks must allow a very limited amount of lateral displacement.

These are all elastic members with an  so some movement toward the excavation always occurs as the equivalent “spring” stretches or compresses under the wall load.


3. Making Wales Stiffer

The wales must be sufficiently rigid that displacements interior from the anchor points are not over 1 to 3 mm more than at the anchors.

This criterion assumes the wales are in close contact with the wall sheeting, so the assumption of a uniform wall pressure is valid.


4. Making Stiffer Shore Pile

Vertical sheeting or piles should be stiff enough so that large amounts of wall bulging into the excavation do not occur between brace points.

This restriction either puts minimum limits on the stiffness of the wall facing (or sheeting) or limits the vertical spacing of the wales or both


Prestressing Struts

The struts or rakers should be slightly pre-stressed by constructing the brace point so that a hydraulic jack and/or wedges can be driven between the wale and strut both to force the wales against the wall and to compress the strut or raker.

The system of jacking and/or wedges usually requires periodic adjustments during construction to maintain the necessary strut pre-stress


6. Reducing Elapsed Time between Excavation and Installation of Bracing System


7. Penetration of Shore Pile or Sheet Pile into Soil below Dredge Lin

If a hard layer of soil lies below a clay layer at the bottom of the cut,

 the piles should be embedded in the stiffer layer. This action will

greatly reduce lateral yielding and ground loss.

This is specially important for subsoil condition of Bangladesh


8. Location of 1st bracing level

The location of the first bracing level can be estimated by making a cantilever wall analysis

•     This approach is applicable for all soils

•     For cohesive soils, the depth should not

exceed the depth of the potential tension crack ht

If crack occurs and fills with water

it may create excessive lateral pressure thus d1 < ht 


Location of 1st bracing level

  1. The formation of tension crack will increase

·  lateral pressure against the lower wall

  1. it acts as a surcharge
  2. if the crack fills with water the

·  lateral pressure increases considerably

  1. Water will soften the cohesive

·  soil and reduce the shear strength


Install struts as early as possible


Where lateral movement and resulting ground subsidence

can be tolerated, the depth to the first bracing level

in sandy soils may be where the allowable

bending stress in the sheeting is reached

from a cantilever wall analysis


Install bracing system before

bending stresses in sheeting are too large



Approximately, vertical subsidence at edge is half or equal of lateral movement of wall

Based on the best practice in UK,

Lateral deformation of wall in deep excavation is of the order of

H/300 to H/100;

Although these values are dependent on: ground condition, adjacency and type of the adjacent structure

The regulation used in UK is CIRIA C580



Moormann (2004)

·       Maximum Horizontal Deflection of Sheet Piles, δ_(H (max))

For 40% of excavation in soft clay, , 0.5% ≤ δ_(H (max)) / H ≤ 1%.

The average value of / H is about 0.87%.



Moormann (2004) analyzed about 153 case histories dealing mainly with the excavation in soft clay (that is, undrained shear strength, c < 75 kN/m2).


         Maximum Vertical Movement [ δ_(H (max))]

δ_(H (max))∕ H ≈ 0.1 to 10.1% with an average of 1.07% (soft clay)

δ_(H (max))∕ H ≈ 0 to 0.9% with an average of 0.18% (soft clay)

δ_(H (max))∕ H ≈ 0 to 2.43% with an average of 0.33% (noncohesive soil)


Location of , that is, x’ (Figure 19.28)

For 70% of all case histories considered, x’  0.5H

However, in soft clays, x’ may be as much as 2H.



ESTIMATION OF GROUND LOSS AROUND EXCAVATIONS as per Peck (1969)


ESTIMATION OF GROUND LOSS AROUND EXCAVATIONS as per Caspe (1966)

  1. Obtain lateral deflection profile of wall
  2. Numerically integrate the wall deflections to obtain the volume of soil in the displacement zone
  3. Compute or estimate the lateral distance of the settlement influence.
  4. Compute the surface settlement profile



Calculation of volume of soil in the lateral displacement zone


Vs = volume of soil in the lateral displacement zone

Use average end areas, the trapezoidal formula, or Simpson's one-third rule


estimate the lateral distance of the settlement influence


Compute ground loss settlements


Example 14-2. Using the values Provided by Caspe, verify the method just given. Figure E14-2 displays data from Caspe and as Plotted on Peck’s settlement curve. The excavation was 15.85m (52 ft) wide and 11.58 m (38 ft) deep. The upper 4.25 m was sand backfill with the remaining depth being a soft to stiff clay with an undrained  = 00. Displacements were taken on 1.2-m (4-ft) distances down the wall to the drwdge line, and Caspe estimated the remaining values as shown on the displacement Profile.

Solution. Caspe stared by computing the total settlement depth based on Hw = 11.58 m + Hp = B = 15.85 m (  = 00) = 27.43 m = D. Integrating the wall Profile from 0.6 m to -26.83 m (27.43 – 0.6) using the average end area formula, we obtain.


Vs = ((30.5+5.0)/2+ 33.0+35.6+49.6+45.7+⋯+18.0+12.7 ) x 1200

= 807900 mm3 → 0.8079 m3 ( per meter of wall width)

At the wall face vertical displacement is

Sw = (2x 0.8079)/26.23 = 0.0616 m → 62 mm  (Peck ≈50 mm)



Effect of excavation width on ground settlement


Ground loss profile by Ou and Hseih (2011)


Estimation of ground loss as per Ou and Hseih (2011)

 

δ = (- 0.636√(d/H_e ) + 1) δ_(Vm,) if d /H_e ≤ 2 and    (1)

δ = (- 0.171√(d/H_e ) + 0.342) δ_(Vm,) if 2 ≤ d/H_e ≤ 4 and    (2)


1.     Find Vs from lateral deflection profile

2.     Find max settlement by equating with Vs

3.     Find settlement profile using following equations


δ_V = (- 0.636√(d/H_e ) + 1) δ_(Vm,) if d /H_e ≤ 2 and    (1)

δ_V = (- 0.171√(d/H_e ) + 0.342) δ_(Vm,) if 2 ≤ d/H_e ≤ 4 and    (2)

2
Ground Loss due to Excavation, Part-2
3
Ground Loss due to Excavation, Part-3

Bottom Heave in Soft Clay

1
Bottom Heave in Soft Clay

 Bottom Heave in Soft Clay





Why bottom heave happen?

•       Soft clay under dredge line and

•       Insufficient shore pile embedment

•       The clay may flow beneath the wall and into the excavation

•       It produces heave if sufficient soil is removed that the resisting overburden pressure is too small



How to prevent bottom heave?

•     Increase the shore pile embedment and penetrate into hard soil layer



Solution for Bottom Heave Before Excavation

•     Before excavation

•     Proper subsoil investigation

•     Check FS against heave

•     Increase embedment to increase FS

•     Use RCC shore pile instead of sheet pile



Solution for Bottom Heave After Excavation

•     After excavation

•     Insert new sheet pile from bottom of excavation

•     Casting thick lean concrete after excavating soft clay, starting from middle to end


factor of safety of long braced excavations against bottom heave



FS = q_ult/q = cN_c/(γH+q- cH/B') = cN_c/(γ+q/H- c/B')H



For rectangular braced cut

FS = (cN_c  (1 +0.2 B'/L-))/(γ+q/H- c/B')H



Chang (2000) modified the FS equation as

 FS = (5.14_c  (1 + 0.2B"/L)+cH/B')/(γH+q) 

B' = T if T ≤B/ √2

B' = B/ √2 if T > B/ √2

B'' = √2 B'


TABLE 19.5 Calculated Factors of Safety for Selected Case Records Compiled by Bjerrum and Eide (1956) and Calculated by Change (2000)


FS = (5.14_c  (1 + 0.2B"/L)+cH/B')/(γH+q)            


Bjerrum and Eide (1956) compiled a number of case records for the bottom heave of cuts in clay. Chang (2000) used those records to calculate FS 

Sand Boiling in Braced Excavation

1
Sand Boiling in Braced Excavation

Sand Boiling in Braced Excavation





Reasons of sand boiling / piping

•            Sand and water level difference



How to prevent sand boiling?

1.      Remedies Before Excavation

a.      Drive the piling deeper to increase the length of the flow path L

2.      Remedies after excavation

a.      Grouting at boiling locations

b.      Stone dumping

c.      Casting lean concrete



Determining the factor of safety against piping by drawing a flow net


The factor of safety against piping may be expressed as     FS = ( icr)/i(max(exit) )       

imax(cxit) = ( h/N_d )/a = h/(N_c a)   

FS = ( i_cr)/i_(max(cxit))         i_cr = (G_(s )- 1)/(e-1)   

 

Where icr = critical hydraulic gradient.

The relation for icr can be given as                   i_cr = (G_(s )- 1)/(e-1)   

The magnitude of icr varies between 0.9 and 1.1 in most soil, with an average of about 1. A factor of safety of about 1.5 is desirable.


Workout example for Factor of Safety Calculation

In Figure 10.20 lct / h =4.5m, L1 = 5m, L2 = 4m, B = 5m,

and L3 =∞, Determine

The factor of safety against piping Use Figure 10.22 and 10.23.

Solution

We have       2L_(1 )/B = (2(5))/5 = 2

And          B/2L_(2 ) = 5/(2(4)) = 0.625

According to Figure 10.22b. for 2L1/ B = 2 and

B/ 2L2 =0.625,m = 0.033, From

Figure 10.23a, for m = 0.033 and 2L1/B = 2,L2i_(max(cxit))/h = 0.54, Hence.

                  i_(max(cxit)) = (0.54(h))/L_2 = 0.54(4.5)/ 4 = 0.608

And             FS = ( i_cr)/i_(max(cxit))   =   1/0.608 = 1.645

BNBC Guidelines on Excavation

1
BNBC Guidelines on Excavation

EXCAVATION GUIDELINES

BNBC 2017,PART 6, CHAPTER 3




Contents of Chapter 3

The Soils and Foundations Chapter of the Code is divided into the following three distinct Divisions :

•     Division A:

Site Investigations, Soil Classifications, Materials and Foundation Types

•     Division B:

Service Load Design Method of Foundations

•     Division C:

Additional Considerations in Planning, Design and Construction of Building Foundations



DIVISION C

ADDITIONAL CONSIDERATIONS IN PLANNING, DESIGN AND CONSTRUCTION OF BUILDING FOUNDATIONS



3.12 EXCAVATION:

§ Excavation for building foundation or for other purpose shall be done in a safe manner so that no danger to life and property prevails at any stage of the work or after completion.

§ Permanent excavations shall have retaining walls of sufficient strength made of steel, masonry, or reinforced concrete to retain the embankment, together with any surcharge load.

§ Excavations for any purpose shall not extend within 300 mm under any footing or foundation, unless such footing or foundation is properly underpinned or protected against settlement, beforehand.

§ The design and construction of deep excavation work more than 6 m depth or excavation in soft soil or erratic soil must be checked by a competent Geotechnical Engineer.


Excavations for any purpose shall not extend within 300 mm under any footing or foundation, unless such footing or foundation is properly underpinned or protected against settlement, beforehand


Notice to Adjoining Property

Prior to any excavation close to an adjoining building in another property, a written notice shall be given to the owner of the adjoining property at least 10 days ahead of the date of excavation.

§ 1. The protective measures shall incorporate the following:

§ Where the level of the foundations of the adjoining structure is at or above the level of the bottom of the proposed excavation, the vertical load of the adjoining structure shall be supported by proper foundations, underpinning, or other equivalent means.

§ Where the level of the foundations of the adjoining structure is below the level of the bottom of the proposed excavation, provision shall be made to support any increased vertical or lateral load on the existing adjoining structure caused by the new construction.



Written notice for excavation

•     Prior to any excavation close to an adjoining building in another property, a written notice shall be given to the owner of the adjoining property at least 10 days ahead of the date of excavation



Shoring, Bracing and Sheeting

2.    Excavation Work :

1.    Method of Protection :

1.    Shoring, Bracing and Sheeting

With the exception of rock cuts, the sides of all excavations, including related or resulting embankments, 1.5 m or greater in depth or height measured from the level of the adjacent ground surface to the deepest point of excavation, shall be protected and maintained by shoring, bracing and sheeting, sheet piling, or other retaining structures. Alternatively, excavated slopes may be inclined not steeper than 1:1, or stepped so that the average slope is not steeper than forty five degrees with no step more than 1.5 m high, provided such slope does not endanger any structure, including subsurface structures. All sides or slopes of excavations or embankments shall be inspected after rainstorms, or any other hazard increasing event, and safe conditions shall be restored. Sheet piling and bracing needed in trench excavations shall have adequate strength to resist possible forces resulting from earth or surcharge pressure. Design of Protection system shall be checked by a qualified Geotechnical Engineer.


Guard Rail Excavation Work : Method of Protection :

Guard Rail :

A guard rail or a solid enclosure at least 1 m high shall be provided along the open sides of excavations, except that such guard rail or solid enclosure may be omitted from a side or sides when access to the adjoining area is precluded, or where side slopes are one vertical to three horizontal or flatter.



Excavation depth > 1.5 m

Protection or slope 1:1 or stepped cut


Entry and Exit Excavation Work :

•         Every excavation shall be provided with safe means of entry and exit kept available at all times.

•         When an excavation has been completed, or partly completed and discontinued, abandoned or interrupted, or the required permits have expired, the lot shall be filled and graded to eliminate all steep slopes, holes, obstructions or similar sources of hazard.

•         Fill material shall consist of clean, noncombustible substances.

•         The final surface shall be graded in such a manner as to drain the lot, eliminate pockets, prevent accumulation of water, and preclude any threat of damage to the foundations on the premises or on the adjoining property. 


So that workers may escape if they see any danger or guess any failure of protection 


Placing of construction material Excavation Work :

Placing of construction material : Excavated materials and superimposed loads such as equipment, trucks, etc. shall not be placed closer to the edge of the excavation than a distance equal to one and one-half times the depth of such excavation, unless the excavation is in rock or the sides have been sloped or sheet piled (or sheeted) and shored to withstand the lateral force imposed by such superimposed load. When sheet piling is used, it shall extend at least 150 mm above the natural level of the ground. In the case of open excavations with side slopes, the edge of excavation shall be taken as the toe of the slope.



Safety regulations Excavation Work : 

Safety regulations :

• Whenever subsurface operations are conducted that may impose loads or movement on adjoining property, such as driving of piles, compaction of soils, or soil densification, the effects of such operations on adjoining property and structures shall be considered. The owner of the property that may be affected shall be given 48 hours written notice of the intention to perform such operations. Where construction operations will cause changes in the ground water level under adjacent buildings, the effects of such changes on the stability and settlement of the adjacent foundation shall be investigated and provision made to prevent damage to such buildings. When a potential hazard exists, elevations of the adjacent buildings shall be recorded at intervals of twenty four hours or less to ascertain if movement has occurred. If so, necessary remedial action shall be undertaken immediately. On excavation, the soil material directly underlying footings, piers, and walls shall be inspected by an engineer/architect prior to construction of the footing. 



• Except in cases where a proposed excavation will extend less than 1.5 m below grade, all underpinning operations and the construction and excavation of temporary or permanent cofferdams, caissons, braced excavation surfaces, or other constructions or excavations required for or affecting the support of adjacent properties or buildings shall be subject to controlled inspection. The details of underpinning, and construction of cofferdams, caissons, bracing or other constructions required for the support of adjacent properties or buildings shall be shown on the plans or prepared in the form of shop or detail drawings and shall be approved by the engineer who prepared the plans. 



3.13 DEWATERING

All excavations shall be drained and the drainage maintained as long as the excavation continues or remains. Where necessary, pumping shall be used. No condition shall be created as a result of construction operations that will interfere with natural surface drainage. Water courses, drainage ditches, etc. shall not be obstructed by refuse, waste building materials, earth, stones, tree stumps, branches, or other debris that may interfere with surface drainage or cause the impoundment of surface water.



3.14 SLOPE STABILITY OF ADJOINING BUILDINGS

1. Overturning :

a) The possibility of overturning and sliding of the building shall be considered. 

b) The minimum factor of safety against overturning of the structure as a whole shall be 1.5. 

c) Stability against overturning shall be provided by the dead load of the building, the allowable uplift capacity of piling, anchors, weight of the soil directly overlying footings provided that such soil cannot be excavated without recourse to major modification of the building, or by any combination of these factors. 


2. Sliding : 

i. The minimum factor of safety against sliding of the structure under lateral load shall be 1.5. 


ii. Resistance to lateral loads shall be provided by 

a. friction between the foundation and the underlying soil, 

b. passive earth pressure, 

c. batter piles or by plumb piles, 

But note that: 

i. The resistance to lateral loads due to passive earth pressure shall not be taken into consideration where the abutting soil could be removed inadvertently by excavation.

ii. In case of pile supported structures, frictional resistance between the foundation and the underlying soil shall be discounted. 

iii. The available resistance to friction between the foundation and the underlying soil shall be predicted on an assumed friction factor of 0.5. A greater value of the coefficient of friction may be used subject to verification by analysis and test.



Missing information for excavation in BNBC 2017

• Allowable limits of lateral movement of shore pile

• Allowable limit of vertical subsidence of retained soil near excavation

• Instrumentation options for deep excavation


Lateral Deflection and Settlement Limit during Braced Excavation

1
Lateral Deflection and Settlement Limit, Part-1

Lateral Deflection and Settlement Limit during Braced Excavation





Wall movement needed for active condition


Soil and condition ---------Amount of translation

Cohesionless, dense ---------0.001H to 0.002H

Cohesionless, loose ----------0.002H to 0.004H

Cohesive, firm -----------------0.01H to 0.02H

Cohesive, soft ------------------0.02H to 0.05H



Ref-Nagaratnam Sivakugan

There is no code provision that gives deflection criteria of braced sheet piles or ground settlement and I don’t think it would be practical if there was. Every case is different with a different set of parameters and constraints.

The typical procedure is to limit the deflection of the shoring piles/sheet piles in order to control the settlement of the ground at the top.

Unfortunately, a relatively small pile deflection can relate to a large settlement at grade at the top of the excavation. It all depends on the height of the wall and what is behind the wall. For instance, if there is a structure at the top of the excavation the deflection at the top of the wall obviously has to be very small (in the order of ¼ to ½ inches), versus if there is nothing but a field/landscaping, etc. at the top of the excavation.




Moormann (2004)

·       Maximum Horizontal Deflection of Sheet Piles, δ_(H (max))

For 40% of excavation in soft clay, , 0.5% ≤ δ_(H (max)) / H ≤ 1%.

The average value of  / H is about 0.87%.



Moormann (2004) analyzed about 153 case histories dealing mainly with the excavation in soft clay (that is, undrained shear strength, c < 75 kN/m2).


         Maximum Vertical Movement [ δ_(H (max))]

δ_(H (max))∕ H ≈ 0.1 to 10.1% with an average of 1.07% (soft clay)

δ_(H (max))∕ H ≈ 0 to 0.9% with an average of 0.18% (soft clay)

δ_(H (max))∕ H ≈ 0 to 2.43% with an average of 0.33% (noncohesive soil)


Location of , that is, x’ (Figure 19.28)

For 70% of all case histories considered, x’  0.5H

However, in soft clays, x’ may be as much as 2H.



Limiting values of retaining wall displacements and impact to the adjacent structures

Paul Fok, Bian Hong Neo, Chepurthy Veeresh , DazhiWen & Kok Hun Goh

The IES Journal Part A: Civil & Structural Engineering


Volume 5, 2012

BS 8002 recommends the use of mobilisation factors, M, if wall displacements are required to be less than 0.5% of wall height for medium dense or firm soils.

there are considerable numbers of cases where measured wall displacements exceeded the limit of 0.5% of excavated depth and the excavations were carried out successfully.

The criteria should be irrespective of wall displacements where lateral deflection can be higher or lower than 0.5% of the excavated depth.



https://www.tandfonline.com/doi/full/10.1080/19373260.2012.696447?src=recsys&



The failure of Nicoll Highway (A deep excavation failure in

Singapore) proved that deformations exceeding 1% are potentially dangerous.



Generally Acceptable Criteria

•     Lateral deflection < 0.5% of H if there is vulnerable adjacent structures

•     Lateral deflection < 1% of H if there is no vulnerable adjacent structures

•     Ground loss must be estimated and differential settlement of adjacent structure must be assessed to set lateral defection criteria. This shall be different in different sites



BNBC 2017

•     BNBC should define the acceptable criteria of excavations.

•     BNBC should provide set lateral deflection and settlement limits during excavation

Settlement Limit of Adjacent Ground and Building by

Code of Practice for Foundations 2017

(Building Department of Hong Kong)



MONITORING PLAN

Where the construction of a foundation may affect any building, structure, land, street or services, a monitoring plan should be provided. It should contain:

(a) sufficient monitoring stations for the detailed monitoring of movement and vibration in any building, structure, land, street or services;

(b) sufficient piezometers for the detailed monitoring of the ground water conditions;

(c) the frequency at which the readings will be recorded or taken;

(d) the action levels and the contingency measures to be undertaken.



Code of Practice for Foundations 2017

(Building Department of Hong Kong)



Recording Construction Activities

The construction activities on site should also be properly recorded so that they may be correlated with the monitoring readings if necessary. Such correlation can often explain why some apparently abnormal readings are recorded.

The monitoring plan should include a system of three triggering levels, namely the alert, alarm and action levels respectively and the corresponding contingency measures to be carried out when the triggering levels are reached. An example is given in Table 7.1.


Code of Practice for Foundations 2017

(Building Department of Hong Kong)


Example of the Contingency Measures for Three Triggering Levels


1.      Alert: The monitoring should be enhanced by increasing the frequency of monitoring measurements and the number of check points.

2.      Alarm : The method of installation of the pile foundation should be reviewed with the purpose of mitigating the detrimental effects arising from vibration or ground settlement.

3.      Action : The corresponding site works should be suspended. Construction activities should not be resumed until the necessary remedial and preventive measures have been completed satisfactorily.


Code of Practice for Foundations 2017

(Building Department of Hong Kong)

2
Lateral Deflection and Settlement Limit, Part-2
3
Lateral Deflection and Settlement Limit, Part-3

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