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1. INTRODUCTION
1.1 General
Retaining walls are built to retain filled earth with greater height.
They are commonly used in rail and road projects where earth filling is required to maintain track or road level especially in approach bridges.
In buildings also if basements are provided retaining walls are required.
Wing walls and abutments are also acting as retaining walls.
To release unnecessary water pressure building up during rainy season, weep holes are provided in the retaining walls.
At the top on back fill and in front of retaining wall longitudinal drains are to be provided. Back filling near retaining wall is with broken stone gravels or sand so that drainage in longitudinal direction is improved and water pressure on walls is released.
A retaining wall is a structure designed and constructed to resist the lateral pressure of soil when there is a desired change in ground elevation that exceeds the angle of repose of the soil. A basement wall is thus one kind of retaining wall.
Retaining walls are designed to restrain soil to unnatural slopes.
They are used to bound soils between two different elevations often in areas of terrain possessing undesirable slopes or in areas where the landscape needs to be shaped severely and engineered for more specific purposes like hillside farming or roadway overpasses
But the term usually refers to a cantilever retaining wall, which is a freestanding structure without lateral support at its top
These are cantilevered from a footing and rise above the grade on one side to retain a higher level grade on the opposite side.
The walls must resist the lateral pressures generated by loose soils or, in some cases water pressure
Every retaining wall supports a “wedge” of soil.
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The wedge is defined as the soil which extends beyond the failure plane of the soil type present at the wall site, and can be calculated once the angle is known.
As the setback of the wall increases, the size of the sliding wedge is reduced. This reduction lowers the pressure on the retaining wall.
The most important consideration in proper design and installation of retaining walls is to recognize and counteract the tendency of the retained material to move downslope due to .
This creates behind the wall which depends on the of internal (phi) and the cohesive strength (c) of the retained material, as well as the direction and magnitude of movement the retaining structure undergoes.
Lateral earth pressures are zero at the top of the wall and - in homogenous ground - increase proportionally to a maximum value at the lowest depth.
Earth pressures will push the wall forward or overturn it if not properly addressed.
Also, any behind the wall that is not dissipated by a system causes on the wall. The total pressure or thrust may be assumed to act at one-third from the lowest depth for lengthwise stretches of uniform height.
Unless the wall is designed to retain water, it is important to have proper drainage behind the wall in order to limit the pressure to the wall's design value.
Drainage materials will reduce or eliminate the hydrostatic pressure and improve the stability of the material behind the wall.
Retaining walls are normally self-draining.
As an example, the requires international code retaining walls to be designed to ensure stability against overturning, sliding, excessive pressure foundation and water uplift; and that they be designed for a safety factor of 1.5 against lateral sliding and overturning
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1.2 TYPES OF RETAINING WALL
The following two types of RCC retaining walls are commonly used:
Cantilever retaining walls
Counter fort retaining walls
Fig 1 cantilever retaining wall
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Fig 2 counter fort retaining wall
These two types of retaining walls are shown in figure 1.1 and 1.2.it may be
observed that:
In cantilever retaining wall stem, heal slab and toe slab are all acting as cantilever due to pressure from back fill and soil pressure.
In counter fort retaining wall counter forts are provided at regular intervals to strengthen the walls. In this case stem and heal slab act as a continuous slab.
Since stem is strengthened with counter fort they are capable of retaining earth to greater height.
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1.3 OTHER TYPES OF RETAINING WALL
1.3.1Gravity walls depend on their mass (stone, concrete or other heavy material) to resist pressure from behind and may have a to improve stability by leaning back toward the retained soil.
For short landscaping walls, they are often made from stone or segmental concrete units (masonry units).
Dry-stacked gravity walls are somewhat flexible and do not require a rigid footing in areas.
Home owners who build larger gravity walls that do require a rigid concrete footing can make use of the services of a professional excavator, which will make digging a trench for the base of the gravity wall much easier.
Earlier in the 20th century, taller retaining walls were often gravity walls made from large masses of concrete or stone.
Today, taller retaining walls are increasingly built as composite gravity walls such as geosynthetic or with precast facing (stacked steel wire baskets filled with rocks) crib walls (cells built up log cabin style from precast concrete or timber and filled with soil) or soil-nailed walls (soil reinforced in place with steel and concrete rods).
Cantilevered
1.3.2 Buttress on Cantilevered Wall
Cantilevered retaining walls are made from an internal stem of steel-reinforced, cast-in-place concrete or mortared masonry (often in the shape of an inverted T).
These walls cantilever loads to a large, structural footing, converting horizontal pressures from behind the wall to vertical pressures on the ground below.
Sometimes cantilevered walls are buttressed on the front, or include a counterfort on the back, to improve their strength resisting high loads. Buttresses are short at right angles to the main trend of the wall. These walls require rigid concrete footings below seasonal frost depth. This type of wall uses much less material than a traditional gravity wall.
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1.3.3Sheet piling
Sheet pile retaining walls are usually used in soft soils and tight spaces.
Sheet pile walls are made out of steel, vinyl or wood planks which are driven into the ground.
For a quick estimate the material is usually driven 1/3 above ground, 2/3 below ground, but this may be altered depending on the environment.
Taller sheet pile walls will need a tie-back, or "dead-man" placed in the soil a distance behind the face of the wall, that is tied to the wall, usually by a cable or a rod.
are them placed behind the potential failure plane in the soil. Anchored
An anchored retaining wall can be constructed in any of the aforementioned styles but also includes additional strength using cables or other stays anchored in the rock or soil behind it.
Usually driven into the material with boring, anchors are then expanded at the end of the cable, either by mechanical means or often by injecting concrete, which expands to form a bulb in the soil.
Technically complex, this method is very useful where high loads are expected, or where the wall itself has to be slender and would otherwise be too weak
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1.4MECHANICALLY STABILIZED EARTH
Mechanically stabilized earth or MSE is soil constructed with artificial reinforcing.
It can be used for retaining walls, bridge abutments, dams,seawalls, and dikes.
Although the basic principles of MSE have been used throughout history, MSE was developed in its current form in the 1960s.
The reinforcing elements used can vary but include steel and geosynthetics.
MSE is the term usually used in the USA to distinguish it from the name "Reinforced Earth", a trade name of the Reinforced Earth Company, but elsewhere Reinforced Soil is the generally accepted term.
MSE walls stabilize unstable slopes and retain the soil on steep slopes and under crest loads.
The wall face is often of precast, segmental blocks, panels or geocells that can tolerate some differential movement.
The walls are infilled with granular soil, with or without reinforcement, while retaining the backfill soil. Reinforced walls utilize horizontal layers typically of geogrids.
The reinforced soil mass, along with the facing, forms the wall.
In many types of MSE’s, each vertical fascia row is inset, thereby providing individual cells that can be infilled with topsoil and planted with vegetation to create a green wall.
The main advantages of MSE walls compared to conventional reinforced concrete walls is their ease of installation and quick construction.
They do not require formwork or curing and each layer is structurally sound as it is laid, reducing the need for support, scaffolding or cranes.
They also do not require additional work on the facing.
In addition to the flexibility of MSE walls in design and construction, seismic testing conducted on a large scale shaking table laboratory at the Japan National Institute of Agricultural Engineering (Tsukuba City), showed that modular block reinforced walls, and even more so geocell retention wall, retain sufficient
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flexibility to withstand large deformations without loss of structural integrity, and have high seismic load resistance.
Using straw, sticks, and branches to reinforce adobe bricks and mud dwellings has happened since the earliest part of human history, and in the 16th and 17th centuries, French engineers used sticks to reinforce dikes.
Reinforcing levees with branches has been done in China for at least a thousand years, and other reinforcements have been universally used to prevent soil erosion.
Modern use of soil reinforcing for retaining wall construction was pioneered by French architect and engineer Henri Vidal in the 1960s.
The first MSE wall in the United States was built in 1971 onState Route 39 near Los Angeles.
It is estimated that since 1997, approximately 23,000 MSE walls have been constructed in the world.
The highest MSE wall built in the United States is 30 m (98 ft) high.
Reinforcement placed in horizontal layers throughout the height of the wall provides the tensile strength to hold the soil together. The reinforcement materials of MSE can vary.
Originally, long steel strips 50 to 120 mm (2 to 5 in) wide were used as reinforcement.
These strips are sometimes ribbed, although not always, to provide added friction. Sometimes steel grids or meshes are also used as reinforcement. Several types of geosynthetics can be used including geogrids and geotextiles.
The reinforcing geosynthetics can be made of high density polyethylene, polyester, andpolypropylene.
These materials may be ribbed and are available in various sizes and strengths.
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2. LITERATURE REVIEW
2.1 The following Conclusions were made by Oana Colt¸ and Anghel Stanciu in 2008
The evolution of conceptual work to support the mass of soil was dictated to both the material and the permanent search for the mobilization of shearing resistance of the soil to ensure its stability.
The most of the use of reinforced soil is in the field of retaining walls.
The walls of reinforced soil behave like any types of retaining walls and they can replace the classical solutions used to make the retaining walls, bridge abutment, etc.
In some cases it might result a large economy, and sometimes the technology used for reinforced soil, taking in account the flexibility of structures, may be the only possible solution[1]
2.2 The following Conclusion were made by WU Weidong, YAN Deyou, china
The slope engineering is very complicated. It has the characters of discontinuity and uneven, easy to be eroded by rainwater and effected by geological disasters and human activities. All of these factors will make it hard to keep the stability of the slope and affect the project directly.
The project is not suitable to use low concrete strength and big height retaining wall. If gravity retaining wall is needed, we should consider the retaining wall’s type, scope, structural requirements, and shear and aseismatic checking are needed. We should ask a professional design company to redesign the project, and do the construction after the design has been passed.
For the security problems of slope engineering, we must check the shear strength and shock strength combined with hydrological conditions, geological features and actual needs. Also, we should pay attention to the monitor and maintenance on time, try our best to ensure the safety of the project[2]
2.3 Following Conclusions were made by Ammara Nusrat ,M. Akram Tahir, UET, Lahore
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The computer program in combination with the proportioning charts presents an easy and efficient solution to the problem of proportioning and designing the RC retaining walls.
The program is effective even in the absence of such charts. A number of solutions can be saved in the memory or on disk for comparison purpose.
The user-friendly computer program can be used to study the comparative cost of various options for any given problem.
The program may effectively be used both for design and research.[3]
2.4 Following observations were made by K. H. PAIK_ and R. SALGADOy in 2003
The estimation of active earth pressures acting on retaining walls is very important in geotechnical design.
However, unlike the assumption used in the analysis of Coulomb (1776), which is generally used to calculate active earth pressure, the distribution of active earth pressure behind the wall is non-linear, and the earth pressure distribution differs depending on the mode of wall movement (tilting about the top or base of the wall or translation).
This is due to arching effects in the retained soil, which result from the frictional resistance between the wall and the soil.
In this paper, a new formulation is proposed for the nonlinear distribution of active earth pressure on a translating retaining wall considering arching effects, under the assumption that the slip surface in the soil behind the wall is planar and makes an angle of with the horizontal.
In order to check the accuracy of predictions using the proposed equations, the equations were applied to existing test results for five rigid retaining walls with different heights.
Comparison of predicted with measured values showed that the proposed equations produce satisfactory results.
Design charts are also proposed for the modified active earth pressure coefficient and for the height of application of the lateral active force.[4]
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3.METHODOLOGY:
(i)Before selecting the project we have gone through rigorous sessions of internet search, literature reviews and group discussions.
(ii) From various articles of research we have chosen the subject “EFFECT OF VARIATION OF HEIGHT ON DESIGN OF CANTILEVER RETAINING WALL” under the guidance of Proff. Kishor patil.
(iii) In our study we have considered cantilever retaining wall which is a kind of earth retaining structure, is generally designed for horizontal earth pressure.
(iv)During the first phase of the study the design of cantilever retaining wall was carried out for different heights viz. 3m, 4m, 5m, 6m, and 7m.
(v)The data obtained from the design was tabulated and represented in the form of graphs
(vi)All the dimensions, forces, area of steel, and moments for different heights were compared with those of the height of 3m
(vii)The results were discussed among group students and faculty, and the report was finalised
GENERAL DESIGN REQUIREMENTS (I.S.I)
Table 1 Permissible stresses of concrete in tension
Grade of
concrete
Permissible stress in KN/m^2
tension
Shear
Direct Bending
M20
M25
1.2
1.3
1.7
1.8
1.7
1.9
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M30 1.5 2.0 2.2
4.DESIGN
i) DESIGN CONSTANT
ii) DEPTH OF FOUNDATION
iii) CALCULATION OF DIMESIONSION OF RETAINING WALL
iv) CHECK FOR STABILITY
v) FACTOR OF SAFETY AGAINST OVERTURNING
vi) FACTOR OF SAFETY AGAINST SLIDING
vii) PRESSURE DISTRIBUTION
viii) MAXIMUM PRESSURE
ix) DESIGN OF STEM
x) DESIGN OF HEEL SLAB
xi) DESIGN OF TOE SLAB
xii) DETAILS OF REINFORCEMENT
.
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GIVEN:-
ho = 3meters
q = 200 KN/m2
ϒ = 18 KN/m2
Ø = 30o
µ = 0.6
f y = 415N/mm2
f ck = 20 N/mm2
1. DESIGN CONSTANT
k a = 1−sin Ø1+sin Ø =
1−sin 30o
1+sin 30o = 0.33
2. DEPTH OF FOUNDATION
Df = qϒ
. ka2
Df = 1.21meters
3. DIMESNSIONS OF WALL
TOTAL HEIGHT OF WALL, H = ho + Df
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H = 4.21 meters
WIDTH OF SLAB, b = 0.6 H
b = 2.526 meters
WIDTH OF TOE SLAB =b3 = 0.843 meters
THICKNESS OF STEM = H12 = 0.3508 meters
THICKNESS OF BASE SLAB = H12 = 0.3508 meters
WIDTH OF HEEL = b - b3 -
H12 = 1.3332 meters
HEIGHT OF STEM = H – (b - b3 -
H12 ) = 3.8592 meters
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4. CHECK FOR STABILITY
FIG 3 VERTICAL FORCES
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S.no
WEIGHT(KN) DISTANCE OF C.G FROM TOE
RESISTING MOMENT
1. W 1 = 0.2 × 3.8592× 25 = 19.296
0.842 + 0.1508 + 0.1 = 1.0928
21.086
2. W 2 = 0.5 × 0.1508 × 3.8592 × 25= 7.2745
0.842 + (2×0.1508)/3 = 0.942
6.8525
3. W 3 = 0.3528 × 2.526 × 25 = 22.27952
= 1.263 28.138
4. W 4 = 1.332 × 3.8592 × 18 = 92.5281
0.842 + 0.3508 + 0.666 = 1.8594
172.046
∑W = 141.37792 ∑R = 228.1232
TABLE 2 CALCULATION OF RESISTING MOMENTS
FACTOR OF SAFETY AGAINST OVERTURNING
0.9 × ∑R
∑ M O > 1.4
0.9 × 228.1232
∑ M O > 1.4
M O = PH× H3
PH = 0.5 ϒ × H 2 × k a
= 0.5 × 18 × 4.21 × 4.21 × 0.33 = 52.6405
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M O = 73.8721
0.9 × 228.123273.8721
= 2.7792
2.7792 > 1.4
FACTOR OF SAFETY AGAINST SLIDING
0.9 × µ×∑W
PH × 1.4
0.9 × 0.6 ×141.377
52.6405 > 1.4
1.4502 > 1.4
5.PRESSURE DISTRIBUTION: -
NET MOMENT = M R - M O
= 228.123 – 73.8721 = 154.2509
x = NET MOMENT
∑W
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= 154.2509
141.37792 = 1.09105
e = b2 – x
= 2.526
2 – 1.0910
e = 0.172
6. MAXIMUM PRESSURE
PM AX = ∑W
b (1 + 6 eb )
= 141.37792
2.526 (1 + 60.1722.526 )×
= 55.968 (1.408)
= 78.803
PMIN = ∑W
b (1 - 6 eb )
= 141.37792
2.526 (1 - 6 ×0.172
2.526 )
= 55.968 (0.5914)
= 33.10221
= PMIN+¿ (PMAX−PMIN
b) (b – WIDTH OF SLAB)
= 33.10221 + (78.803−33.1022
2. 526 ) (2.526 – 0.842)
= 33.10221 + 18.092 × 1.684
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= 63.56941 KN
M 2
7. Design of Stem :-
M max= 12
Ka Ɣ H 2 H3
M max= 16×.33×18×3.85423
M max=56.681
Factored moment M u=56.681×1.5
M u=85.35
Depth Of stem :-
Rulimbd2= M u
.138×20×1000×d2=85.35
d=175.85
Area Of Steel Required: -
A st=.5 f ck
f y[1-√1−
4.6∗M u
f ck bd2 ]bd
A st=1377mm2
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Spacing:-
Assume 10mmФ
1000∗AФ
A st
=60mm
Provide 10mmФ@60mmcc .
Distribution Steel: -
.12%Ag
( A¿¿ st)d ¿=.12100×1000×d
( A¿¿ st)d ¿=336
Spacing:-
Assume 8mmФ
1000∗AФ
A st
= 306.33~ 300mm
Provide 8mmФ@300mmcc .
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8.DETAILS OF REINFORCEMENT
FIG 4 SECTIONAL VIEW OF REINFORCEMENT
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FIG 5 LONGITUDINAL VIEW OF REINFORCEMENT
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5.OBJECTIVE
The above mentioned steps are were carried out for different
heights of the retaining wall and their results were compared to
check the effect of changing heights on the structural components
of the retaining wall
The objective behind carrying out this whole project is to note and
observe the effects of the different heights of the retaining wall on
its structural elements which would be shown with the help of a
graphical representation.
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6.TABLES
TABLE OF DIMENSIONS
TABLE NO. 3
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TABLE OF FOFCES
TABLE NO.4
TABLE OF DESIGNS
TABLE NO. 5
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TABLE NO.6
TABLE NO.7
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7.GRAPHS
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GRAPH NO.1 HEIGHT V/S P(max) P1
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GRAPH NO. 2 HEIGHT V/S P(min)
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GRAPH NO. 3 HEIGHT V/S Mu FOR STEM
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GRAPH NO.4 HEIGHT V/S AST FOR STEM
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GRAPH NO. 5 HEIGHT V/S AST FOR HEEL SLAB
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GRAPH
NO. 6 HEIGHT V/S Mu FOR HEEL SLAB
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GRAPH NO. 7 HEIGHT V/S AST TOE SLAB
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GRAPH NO. 8 HEIGHT V/S Mu FOR TOE SLAB
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8.RESULT
Up to the height of 5 m the graph seems smooth but after that sudden changes
are observed which shows that upto the height of 5 m we can make cantilever
retaining wall.
But after 5m of height we have to provide counter fort retaining wall.
There are different possibilities of failure of cantilever retaining wall after the
height of 5m.
The construction become uneconomical due to sudden increase in ast after 5m
of height
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9. DISCUSSION
With the help of the various tables and graphs laid down after the calculations
involved in the design of retaining walls with various different heights we have
come to know that the height of the wall has a deep impact on the various
structural elements of the retaining wall.
In the design we haven’t used any kinds of counter forts to keep the design
simple and easy for comparison purposes.
All the necessary checks have been carried out to ensure a safe design.
The methodology involved for the design purposes have been same for all the
heights.
The main objective for preparing the graphs was to choose directly the most
stable and economical size for a design.
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10. CONCLUSION
The procedure we carried out as shown above helps us to calculate the variation
in the values of structural elements of the retaining wall.
The graphs laid down with the help of the calculated values shows us the variation in the structural elements.
This helps us to create a safe, efficient and economical design.
The graph shows that the structural elements of the retaining wall vary linearly with the height of the retaining wall
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11. FUTURE SCOPE
As we all know that the most important and crucial part of any project is
the future aspect it incorporates, at the same time keeping in mind the present
scenario of the market.
Our project mainly emphasizes on “effect of height on different
parameters of retaining wall”.
From the study we concluded that while designing a retaining wall there
was a tremendous variation in the value of area of steel
We concluded that as compared to ordinary short retaining wall overall
price of the had increase ordinary long retaining wall tremendously.
For a Civil Engineer the biggest challenge is to make the structure safe
and at the same time economical.
In future, we will emphasize on the estimation of the cost of structure,
keeping in mind the strength and safety of the earthquake resistant retaining
wall
In future we will also lay emphasis on making the design of earthquake resistant retaining wall software oriented and we will emphasize on the fact that the potent software for the design of earthquake resistant retaining wall should make the design economical, safe and the software would be user friendly
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12.REFERENCES
[1] BULETINUL INSTITUTULUI POLITEHNIC DIN IAS¸ I Publicat de Universitatea Tehnic˘a ,,Gheorghe Asachi” din Ias¸I Tomul LIV (LVIII), Fasc. 4, 2008 SectiaCONSTRUCT¸ II. ARHITECTUR˘AEVOLUTION OF THE STABILITYWORK FROM CLASSIC RETAININGWALLS TO MECHANICALLY STABILIZED EARTHWALLS BY OANA COLT¸ and ANGHEL STANCIU [2] EASTERN ACADEMIC FORUMAnalysis on the Collapse Reasons of a Multi-use Building’s Retaining Wall in KangdingWU Weidong, YAN Deyou ,School of Civil Engineering and Architecture, Southwest Petroleum University, China, 610500
[3] DESIGN OF CANTILEVER RETAINING WALLSAmmara Nusrat, UET, LahoreM. Akram Tahir*, UET, Lahore32ndConference on OUR WORLD IN CONCRETE & STRUCTURES: 28 - 29 August 2007,SingaporeArticle Online Id: 100032040The online version of this article can be found at:http://cipremier.com/100032040
[4] Paik, K. H. & Salgado, R. (2003). Ge´otechnique 53, No. 7, 643–653643
Estimation of active earth pressure against rigid retaining wallsconsidering arching effects
K. H. PAIK and R. SALGADO
B.C. PUNAMIA , DESIGN OF R.C.C
S.S. BHAVIKATTI, DESIGN OF R.C.C
PILLAI AND MENNON, R.C.C
IS Code 456:2000
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