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Retaining wall structures Application and construction procedure Retaining wall is a structure that are designed and constructed to withstand lateral pressure of soil or hold back soil materials. The lateral pressure could be also due to earth filling, liquid pressure, sand, and other granular materials behind the retaining wall structure. There are various types of retaining wall structures which are used for numerous goals.

Group 3

1. Hoàng Thị Quỳnh Chi

2. Đỗ Trung Nghĩa

3. Đinh Trí Dũng

4. Chu Hoàng Nam

5. Bùi Chiến Công

6. Nguyễn Đăng Thanh

Typical construction procedure

Introduction

Types of retaining walls

General design steps

I

II

III

IV

 Retaining wall is a structure that are designed and constructed to withstand lateral pressure of soil or hold back soil materials

 The lateral pressure could be also due to earth filling, liquid pressure, sand, and other granular materials behind the retaining wall structure

 There are various types of retaining wall structures which are used for numerous goals

I INTRODUCTION

 1 Mass Gravity/ Semigravity Wall

 2 Mechanically Stabilized Earth Walls (MSE)

 3 Modular Block Walls

 4 Soil Nail Walls

 1 Cantilever Walls

 2 Anchored Walls

GRAVITY

RETAINING

WALLS

 Gravity retaining wall depends on its self weight only to resist lateral earth pressure.

 Commonly, gravity retaining wall is massive because it requires significant gravity load to

counter act soil pressure

 Modern gravity walls include concrete crib walls, gabions, boulders, and large, precast

concrete blocks

II TYPES OF RETAINING WALLS 2.1 MASS GRAVITY RETAINING WALL

Concept

 These walls usually have an average height of three to four meters

 The thickness of the gravity wall shall be at least 50 to 60% of the height of the wall

 They may have to be larger if there is a slope or surcharge on the wall

Structural & Components

 It can be constructed from different materials such as concrete, stone, and masonry units.

II TYPES OF RETAINING WALLS

Materials

2.1 MASS GRAVITY RETAINING WALL

Materials

 Sliding, overturning, and bearing forces shall be taken into consideration while this type of

retaining wall structure is designed

 Stress developed is very low

 These walls are so proportioned that no tension is developed anywhere and the resultant of

forces remain within the middle third of the base

II TYPES OF RETAINING WALLS

Design consideration

2.1 MASS GRAVITY RETAINING WALL

 These walls consist of a volume of materials These materials are stacked together in the making of the walls

 The weight or force of friction that is created by these materials is greater than the force exerted by the soil

 The thickness of the wall at the base exceeds that at the top

 A process known as ‘battering‘ helps the walls to improve stability by leaning back into the retained soil

 Construction of gravity walls demands a high quantity of building materials That is the reason these walls are difficult to build, and get more bulky as they get gravity

Design consideration

 In this type of retaining wall, a small amount of steel reinforcement is used near the back face in order to minimize the size of wall section They are

a blend of the cantilever wall and gravity wall designs

 From the above figure, reinforcement is provided on the back side of retaining wall, where backfill exists

II TYPES OF RETAINING WALLS 2.2 SEMI-GRAVITY RETAINING WALL

Concept

 Special form of the gravity retaining wall

 Therefore, the semi-gravity walls resist external loads with combined resistance offered

by self-weight of structure, vertical soil component of weight above the footing

Concept

 These walls are often constructed of reinforced concrete, un-reinforced concrete, or stone masonry

 The rigid gravity walls develop their soil retaining capacity from their dead weights The semi-gravity walls, such as cast-in place concrete cantilever walls, develop resistance to overturning and sliding from self-weight and weight of soil above the wall footing

 Semi gravity retaining walls can also be constructed with masonry stone It can be used in both cut and fill application

 Semi gravity retaining walls are not used generally in case of deep foundation It is the most economical section in case of low wall heights

II TYPES OF RETAINING WALLS 2.2 SEMI-GRAVITY RETAINING WALL

Structural & Components

 The Gravity Retaining Walls have limited height 3m.

 In the 16th Century Cantilever theory was introduced

by Galileo

⇒ Overcome disadvantages of Gravity Retaining Walls

 Cantilever Retaining Walls height up to 7.5m with

Cantilever theory:

 Any components act like cantilever with high rigidity of connection

 Utilizing the weight of the soil to retain itself => More difficult to overturn

 Low thickness leading to sensitive in flexure

Concept

 They consist of a stem and a base slab

 The base includes heel and toe

II TYPES OF RETAINING WALLS 2.3 CANTILEVER RETAINING WALL

Structural & Components

 They consist of a stem and a base slab

 The base includes heel and toe

Dimension:

 Top width stem : 200mm

 Bottom width stem: depends on max moment

 Width of base slab: b = 0.5H ~0.6H w/o surcharge

 b = 0.7H with surcharge

 Thickness of base slab = that of stem

Structural & Components

 Materials: are made from an internal stem of steel-reinforced, cast-in-place or

precast concrete

 The main difference depends on the side of load

II TYPES OF RETAINING WALLS 2.3 CANTILEVER RETAINING WALL

Typical types

2.3 SEMIGRAVITY CANTILEVER RW

 Materials: are made from an internal stem of steel-reinforced, cast-in-place or

precast concrete

 The main difference depends on the side of load

Typical types

 Cantilever retaining walls suffers cracks and curves in their service lives

 => Arrange steel bar in location that in tension

II TYPES OF RETAINING WALLS 2.3 CANTILEVER RETAINING WALL

Reinforcement layout

2.3 SEMIGRAVITY CANTILEVER RW

 Can be used for high back fill soil (7.5m)

 Use much less concrete => Save space

 Can be pre-casted also or casted in place

Disadvantages

 Require more design and careful construction

 Need to control lateral displacement

 Not suitable used near buildings

Advantages & Disadvantages

3m

7.5m

II TYPES OF RETAINING WALLS 2.4 COUNTER-FORT RETAINING WALL

 When the height of earth to be retaining exceeds 5m, the bending moment

developed in the stem, heel and toe slabs are very large which results in large

thickness of structural elements and becomes uneconomical

 Thus, counterfort type retaining wall is adopted for larger heights

Concept

 Counterfort retaining wall consists of a stem, toe slab and heel slab as in case of cantilever retaining wall But it also consists of counterforts are regular interval which divides the stem.

 The stem and heel slabs are effectively fixed to counterforts so that the stem bends horizontally between the counterforts due to lateral earth pressure

 Can be constructed of reinforced or pre-stressed concrete

 Counterfort retaining walls are more economical than cantilever walls for heights above 25 ft

Structural & Components

II TYPES OF RETAINING WALLS

 As cantilever retaining wall, sliding, overturning, and bearing pressure shall be taken into consideration during its design

 Counter fort spacing is equal or slightly larger than half of the counter-fort height

 Counter-fort wall height ranges from 8-12m

Design consideration

2.4 COUNTER-FORT RETAINING WALL

 Mechanically stabilized earth (MSE or reinforced soil) is soil constructed with artificial

reinforcing It can be used for retaining walls, bridge abutments, seawalls, and dikes

 The reinforcing elements used can vary but include steel and geosynthetics

Concept

 A Mechanically Stabilized Earth (MSE) retaining wall is a composite structure consisting of

alternating layers of compacted backfill and soil reinforcement elements, fixed to a wall

facing

 The stability of the wall system is derived from the interaction between the backfill and

soil reinforcements, involving friction and tension

 The wall facing is relatively thin, with the primary function of preventing erosion of the

structural backfill The result is a coherent gravity structure that is flexible and can carry a

variety of heavy loads

II TYPES OF RETAINING WALLS 2.5 MSE RETAINING WALL

Structural & Components

 Facing Elements

 Choosing the right facing type depends on the application, aesthetics, differential settlement, service life, and other factors

Structural & Components

 Soil Reinforcements

 Soil reinforcements have gone through extensive full-scale testing for pullout capacity, tensile capacity, durability, and corrosion

II TYPES OF RETAINING WALLS 2.5 MSE RETAINING WALL

Structural & Components

High-Adherence (HA) Ribbed Reinforcing Strips High-Adherence Ladders GeoStrap® Geosynthetic Reinforcing Strips

 Select Backfill

 Soil : A wide range of soil properties will meet specifications, however the ideal select backfill is open-graded with low plasticity and fines content, such

as sand or crushed stone This allows for easy compaction and fast drainage

Structural & Components

 Select Backfill

 Soil : A wide range of soil properties will meet specifications, however the ideal select backfill is open-graded with low plasticity and fines content, such as sand or crushed stone This allows for easy compaction and fast drainage

 Recycled : Crushed concrete and other recycled material can be used successfully as MSE select backfill

 Lightweight : In cases where the MSE wall must have a significantly reduced load on the foundation, lightweight material can be used such as lightweight aggregate, low density cellular concrete, and foamed glass aggregate

II TYPES OF RETAINING WALLS 2.5 MSE RETAINING WALL

Structural & Components

 The properties and materials of the three major components can vary, and an engineer must choose the most efficient combination of materials based on the wall’s design criteria

 Facing elements are modular precast concrete panels or wire mesh Each facing type offers different advantages when considering criteria such

as aesthetics, durability, construction procedure, and expected settlement

 Soil reinforcements are typically steel or geosynthetic, in the form of strips or ladders All soil reinforcement options have unique characteristics for pullout and tensile capacity, corrosion, and durability

 Select backfill allows for reliable construction and performance of the wall, in which the gradation, plasticity, electrochemical properties, and overall durability should be closely analyzed

Design consideration

 Gabion walls are constructed of steel wire baskets filled with selected rock fragments and tied together Gabions walls are flexible, free draining and easy to construct.

II TYPES OF RETAINING WALLS 2.6 GABION RETAINING WALL

Concept

 The mesh cages reduce some internal movement and forces, and also reduce erosive forces

 Gabion walls are free-draining retaining structures and such as are often built in locations where ground water is present

 It is also used to stabilize steep slopes

 Wire mesh gabions are less expensive than most other construction materials

Concept

 The gabion walls are composed of orthogonal wire cages or baskets tied together and filled with rock fragments

 These wire baskets are also known as gabion baskets The standard height of these baskets may vary from 1 foot to 3 feet Individual wire baskets are filled with rock fragments ranging in size from 4 to 10 inches

II TYPES OF RETAINING WALLS 2.6 GABION RETAINING WALL

Structural & Components

 The minimum embedment for gabion walls is 1.5 feet The ratio of the base width to height will normally range from 0.5 to 0.75 depending on backslope, surcharge and angle of internal friction of retained soil

 The wires used for constructing gabions baskets must be designed with adequate corrosion protection

 Maximum heights are normally less than 21 feet These walls are desirable where equipment access is limited A height of about 18 feet should

be considered as a practical limit for gabion walls Gabion walls have shown good economy for low to moderate heights

 While the shapes and appearance may vary, The internal structure of these gravity walls is made up of one of two types - the front slope wall and the rear slope wall

 To increase stability, it is common to tilt the angle of the walls 6 ° to 10 ° toward the leveling, especially with the steep back walls These two types are shown illustrated in the following figure

Design consideration

 First row of gabion baskets is placed on a foundation made from stone material or concrete, depending on project requirements

II TYPES OF RETAINING WALLS 2.6 GABION RETAINING WALL

Design consideration

 The second row is placed on a way that it is moved from the outer edge toward the back in a certain distance After completing the basket, the space behind the basket is filled with a suitable material up to the height of the upper gabion row.

 On the back face, geotextile is placed in order to seperate fine particles from the stone material of the gabion wall With this the water permeability and filtration mechanism that limits washout is secured

Design consideration

 They are constructed of interlocking individual boxes made from timber

or pre-cast concrete

 Then, the boxes are filled with crushed stone or other coarse granular

materials to create a free draining structure

II TYPES OF RETAINING WALLS 2.7 CRIB RETAINING WALL

Concept

 Crib walls are built using prefabricated units which are stacked and interlocked and filled with free draining material

 Cribs consist of solid interlocking reinforced concrete members called rails and tiebacks (sometimes called stretchers and headers) The rails run parallel with the wall face at both the front and rear of the cribbing and the tiebacks run transverse to the rails to tie the structure together

Structural & Components

 The most common type of crib comprises longitudinal beams (stretchers) and lateral ties (headers) made up into a series of regular shaped cells The lower courses of high walls may be constructed from two or more rows of cells.

II TYPES OF RETAINING WALLS 2.7 CRIB RETAINING WALL

Structural & Components

 The second most common type consists of frames built up to form ‘towers’ with stretchers spanning between them to form ‘fields’ The frames can be filled with reinforced concrete and thereby become suitable for use with ground anchorages

Structural & Components

II TYPES OF RETAINING WALLS 2.8 SOIL NAILING RETAINING WALL

 Soil nailing is a technique used to reinforce and strengthen existing ground

 Soil nailing consists of installing closely spaced bars into a slope or excavation as construction proceeds from top down

 It is an effective and economical method of constructing retaining wall for excavation support, support of hill cuts, bridge abutments and high ways

 This process is effective in cohesive soil, broken rock, shale or fixed face conditions

Concept