Name: Khaled Almutairi. Student no: Construction methods and technology. Group 4. Retaining wall

Transcription

1 Name: Khaled Almutairi Student no: Construction methods and technology Group 4 Retaining wall

2 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 1 1. Introduction Technology advancement has transformed our world into a global village where population is increasing day by day and places are going to be jam-packed up with people and traffic. A proper place should be there to keep everything safe and this can be done with proper planning and scheduling like car parking, it is one of the biggest problems now days because population has been increased very fast as compared to previous years and in analogous cars and traffic are also increasing. A proper place should be there to park the cars and this place should be secure and trustworthy so that it can serves for many years and to make it reliable and secure retaining wall is a perception which was presented to make walls reliable. Due to the scarceness of land the requirement of basements for car parking is used to enhance the use of land and in results it increases the complexity of basement being constructed. Deep basement is one of the vital and widespread methods which are used in last ten years to utilize the accessible underground space for car parking. There are many other methods and ways to make a car parking but those are immoderate and congested methods as it depends on the area. Lot of constrictions can be a big obstacle for retaining walls but there are many ways that can curtail these obstacles and can help to make it in a better way. By cutting and filling methods the balanced areas level can be attained. It would be obliging to make a balanced place for on some sites but not for all may be it wouldn t be productive and will be costly for the other sites. Concrete retaining wall is one of the elucidations to sidestep this cost and this method is also help to protect against erosion on vulnerable sites. There are some practical requirements which are necessary for the concrete retaining walls and these requirements are structural consistency, reliability against the exposed environment, approval of water existing system. Entrance is another aspect which is countable in these kinds of structures. Concrete retaining wall gives better results and long-lasting solution because it is done with soil and wide-open to continuous moistening and aeration. Strategy phase and erection phase of retaining walls need a proper care and deep study and it is also needed to monitor the performance. This paper defines in a discerning way like design and construction methods for retaining walls for car parking. This

3 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 2 paper covers:-the background of the topic, Structure and proposed scheme, Exploration and estimation methods. 2. Background Retaining wall is a structure or a design that carries soil or rock which helps in forming a building, structure or area. It delivers the provision for the vertical grade variations and it also prevent down slop movement. Walls can be made of different types of materials such as:-stones Bricks, Concrete, and Steel There are two major phases in designing of retaining walls and one of them is adjacent earth pressure which is used to check the solidity for the entire environment. After appraising this phase there is a need to observe for possible turning the rounds, slope and tolerance to accept the weight. Second phase is to inspect the strength of each component with strengthening of steel and then manufacturing the structure conferring to the tolerance factor and bear qualities. There are numerous types of retaining walls that have been used in the antiquity which include the Gravity retaining walls and cantilever retaining wall. Gravity retaining walls are one of the types that are constructed with plain concrete or stone masonry. It depends on the stability of weight and soil resting on the masonry. Research and experts shows that it is not an efficient method to construct the high walls. Cantilever retaining wall is that which is constructed with the help of strengthened concrete of a thin stem and a base slab. Experts and analysis shows that this type of wall is suitable for the height of 25ft. Research papers and specialists gives the thorough exploration about the retaining walls that it can be failed in different ways like, it may overturn which can make it over, it may slide along its base, it may fail due to the loss of bearing capacity of soil supporting the base, it may undergo deep seated failure; there may be a chance that it goes through excessive settlement. 3. Quality Quality factor can be attained by the following:- Proper planning Requirement gathering

4 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 3 Every project needs to gather proper information regarding the project. If the main objectives and purpose is absent then it would not be possible to get the goals, so to make a retaining wall for car parking, it is the important part to identify the area in which a parking is going to be construct.the next step is to present the design which is explained in the below sections. 3.1 Planning of subsurface investigation As stated in BS8002: 1994 Code of practice for each retaining structures proper info should be collected on the surface and surface water conditions because both factors are very essential while making such kind of designs. These two factors help to retain and support the retaining structure. Correct and precise information is required for planning of surface exploration and laboratory testing which are the essential factors for the designers to make safe and cheaper design for the car parking. For the selection of geotechnical parameters for design of retaining walls, reference can be made to Gue (1997 & 1998) and CIRIA report 104 (1984).

5 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e Permeability A faultless examination should be there of soil co-efficient of permeability, which has a foremost effect on the architecture of basement system which is made for the car parking and there is also another factor than can affect the enactment of the system which results in failure of the system. A layer is there in the system that provides the ground water cut off which is known as boulder clays. In this system where the k value is important which define the quantity and rate of the excavation of groundwater is calculated and it presents all these facts and figures. These calculations show that which kind of wall would be construct and how much it should be reduced for the groundwater. Paper and research shows that there are different kinds of methods to find out the K value, such as increase/decrease and constant head tests in boreholes and these should be tested in laboratory on different parameters There is another way to find out the K value which is known as Particle Size Distribution (PSD) analyses and tri axial cell tests in the laboratory It is suggested that a perfect advisor or expert analyst would be allotted this task who can give a proper solution for this particular problem and according to that solutions all the enactments would be designed and can get rid of the problem within the given time interval. Relative exploration is always a good practice for all kind of test which helps to finalize the decision so in this situation it would be advantageous to conduct a relative exploration. 3.3 Stratigraphy It is quite obvious for the basement of car parking that an accurate and perfect determination should be adapted for the basement and it is an essential part of the whole system. To enrich different retaining walls together, than it can make its size double or it may increase the depth of the whole basement. There is some probability that could occur while making this basement for the car parking like, low strength or high permeability which can be caused below the basement level. There is a possibility that existence of bedrock may constrain the utilization of some parameters like sheet pilling or CFA pilling, these are the issues that can proved to be the resistance of the system so to make it adequate and get rid of this issue it is necessary to gather the well and proper information about the depth which makes a fruitful basement for the car parking and it is also be useful for the retaining wall. 3.4 Testing Mechanism Different inquiries like BS5930:1981 explains the general practices and tests. Normally a ground condition is dependent on the number of boreholes which are acceptable with the length of the wall. There is a test available for boreholes predominantly in sedimentary loose or soft deposits named Piezocone test. It would be valuable to conduct the geographical survey for the large sites

6 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 5 to enhance the subsurface exploration. Boreholes have a exact distance from each other which is normally 10m to 50m but it depends on the surface of the ground and it varies from site to site. Normally experts examine the surface from the outside of the site and it should be carried out from the sensitive side of the structure. Most of the communal fields that can be used for designing of retaining wall comprises of rotary wash boring and include standard infiltration test, Pressure meter tests, and collection of disturbed and undisturbed soil sampling for laboratory testing. In a deep retaining wall design there are some important key elements are needed such as Adequate information about the surface water level Seepage pressures Information on existence of any hydrostatic uplift pressure. Prediction of the ground water condition of a particular area can be done with the help of Local geographical information. There is a method or technique which can help to determine or confirm the ground water condition at a specific place is called bore system in which stand pipes or piezometers used to installed and drilled boreholes. It has been determine during the bore operation and in this procedure water is used as flushing medium. After doing the bore process complete it must be closed properly that prevent the collapse of the soil which can causing loosening of subsoil. 4. Evaluation of Foundations One of the major concern while making planning and execution of deep basement it is impact of construction related to ground movements on the adjacent properties and utilities. There are some changes have been noticed in retained side are the stresses revive on the excavation face resulting in horizontal ground movement for equilibrium and it raise in vertical stress due to lowering of water table resulting in both instantaneous and consolidation settlement of the ground. These ground movement that vary away from the excavation can cause buildings to move in different directions and these directions can be change the whole shape of the building and can alter the buildings as shown in the diagram below:

7 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 6 Approximating the magnitude and distribution of the ground movements are the important factors to examine. The skill to handle the structure pressure and utilities to the distortion and noise control as the result of the ground movements should also be assessed. 4.1 Empirical Methods for Retaining walls Skempton and MacDonald (1956) classify a basis on which to assess all the available and allowable parameters that helps to make it settle down. Direction for design has been largely based on their work. 4.2 Selection Type Retaining wall Support system and selection of retaining wall type has been made on basis of different constraints which are mentioned below: New and contiguous properties and facilities for retaining wall Limitations and boundaries level of ground water and its states Site disadvantages and its basic needs and requirements Time and cost of the total work Different variation of plan which provide the flexibility and consistency Experience in local area geography and construction ideas Repairing and keep check and balance on support system in permanent condition Commonly used retaining walls have been showed in the figures and explained about these walls. 4.3 Sheet pile wall

8 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 7 Sheet pile wall is generally used as temporary retaining wall system for car parking. The appropriateness of sheet pile to be used in basement construction is generally prejudiced by the following factors which are mentioned below: Soil conditions and the ease of the pile installation which must be allowed the sheet pile to be easily drive in the with standard penetration test. Depth of excavation There is a need to pass the material through the dovetailing steel if it provide the difference in results It has reliability to change temporary sheet pile after used 4.4 Contiguous Bored Piles Wall Contiguous bored piles wall can be both provisional and permanent wall for excavation. Normally contiguous bored piles wall is valuable in different circumstances like in stiff soil and in a place where the water level is low. There are some benefits of contiguous bored piles that it lessen the cost and it also helps to control the speed where the drilling conditions are conductive. The system has higher capacity to overcome obstacles like rock compared to conventional system. It is needed to add new and transformed work with the surface of the wall. 4.5 Secant Piles Wall The major drawback of contiguous bore piles walls which is the lack of the water tightness has been efficiently overcome by interlocking as in secant piles wall. Other than water tightness, secant piles have similar advantages and drawbacks as contiguous bored piles wall have. This

9 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 8 method comprises with different techniques like boring and concreting primary piles at center to center spacing of slightly less than twice the nominal pile diameter. 5. Structure 5.1 General Design Principles Generally soil has been collected by vertical or near vertical retaining wall and it has a specific pressure around the wall which is fashioned against the soil absorbent. Pressure has a special impact on wall it can cause of sliding of wall and it also can cause to rotate the wall from right to left and left to right so it is essential part to design a wall in such a way that a wall can resist against all these confrontation and forces that can move it in different directions. There are some other factors that also have similar importance and they should also be look after while designing the wall like robustness. Water existing system must be looking after appropriately and they need care. Structure and architecture should be suitable and appropriate for the particular building and it should be approved form the qualified and professional consultants. 5.2 Retaining Wall Systems Reinforced concrete masonry walls The below picture shows the reinforcement of the block which are filled by the concrete footing and it make it reliable for the retaining wall for car parking.

10 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 9 The structure which is presented in the above picture has lot of benefits for the retaining wall and it has zero lot line and different range of possible finishes. Generally it has height of 3m which is considered as a normal height for this structure. All the information regarding concrete masonry wall is available in different guides and there is lot of information is available on different sites which explained its design and structure for the user and user can easily use its design and structure for any particular project. Strengthened concrete walls Cantilever retaining walls has a flexibility that it can be construct with any other technology and techniques like it can be construct or design with the help of reinforced concrete. The figure 6 and figure 7 has shown in the below which shows that wall can be either castinsituor precast.

11 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 10 The front side of the wall which is shown as vertical can be handle in different ways and with the help of new technology we can give some texturing on the wall as shown in the figure 8. There is a way to construct the low height retaining wall with the help of dry stacking and in this process interlocking segmental concrete masonry unit is useful and also fruitful to make it happen. This kind of wall has a property that it treats like gravity wall. Wall can be modified in different shapes like it can be a vertical wall or stepped wall or either it can be made like a slope, all these shapes can be given on the basis of unit used.

12 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 11 These units are accessible in different shapes and color all depends on the mod and a design as shown in the below figure. These kinds of unit are famous for DIY installations because they are very easy to install and erect. All the information and details are kept in segmental concrete gravity retaining walls which are available from the concrete masonry association. In this industry there are different suppliers like local suppliers should be contacted for specific system details else they do it as feel better it all depends on their experience and practices.

13 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e Dry-stacked segmental concrete masonry with Soil Reinforcement walls Wall can be similar or can be different from each other. Wall have similar look and feel if we associate it with the wall of concrete masonry walls, but there are different walls which are having similar attributes would be constructed by connecting the masonry walls but there is no constraint of height so it could be constructed by connecting the masonry units which may consists of horizontal geo synthetic soil reinforcement placed in the backfill behind the wall unit as shown in the figure 11. These walling units are in dissimilar shapes and color so all concrete masonry units can be mold in different shapes, texture and colors as shown in figure 12. These walls also have property of gravity. These walls are a gravity system. Research and experts shows that in earlier era the segmental walls have been used in which they utilize the soil mass behind the wall to cover the resist the lateral soil forces. This could be done with the help of reinforced soil knowledge which is introduced later and it is very useful to cover and protect the wall from all the forces. It is also a delicate matter to construct the wall there should be proper engineering mechanism and technique used and it should be done with the help of engineering supervisor who is competent. Again the full description and detail of this system is available in Segmental Concrete Reinforced Soil Retaining Walls Design and Construction Guide which is provided by the Concrete Masonry Association. Local suppliers should be contacted for specific system details otherwise they do it as feel better it all depends on their experience and practices. 5.4 Crib walls Crib wall is another type of wall that can be designed and constructed with the help of precast concrete material which is shown in the figure. Figure shows that this type of wall has spaces in it and these spaces between the units are filled with the gravel which helps to make a system free

14 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 13 draining. This design can be constructed with a low budget which means that these are economical and can be constructed for wide range with different heights. These type of walls can be modified and enhanced by different parameters and measurements like we can use different colors of concrete and also can use the landscaping, we can also plant vines over the top of the wall, we can give a soften look to these walls as shown in figure Concrete-sleeper walls There is additional type of wall named precast concrete sleepers span that has a design like a horizontal line between vertical precast concrete post that are enhanced into the ground as shown in the figure 15. These types of walls consist of different posts which are usually fit in to the bored inside concrete pier. This type of wall is very strong and contains the piled system that is relies on the improved strength of the post and steeper that can help to resist against different type of forces. This type of wall can be constructed with a low budget and has zero lot line construction. This type of wall can also be constructed with different colors and also can use different textures.

15 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e Design and retaining walls for car parking GROUNDWATER While scheming the retaining wall for car parking then designer always thing about the ground water which can create obstacles in a basement projects, groundwater has a potential to flow through the retaining walls that can damage the wall and it also can go through the basement floor. Most of the cases it can be found very bad for the retaining wall because it can create uncertainty of the retaining wall or basement floor. It is important to examine the ground level and ground water existence that how much level of ground water is there and what kind of strength it holds that can damage the wall because it can effect on soil and rock that can made a wall strong but if there is a ground water accessible with high potential then it can be affect for these material. There are different levels of ground water and these levels can be named as Upper stratum Lower streamer Both are affected for the retaining wall. The activities which are held near the ground water can affect the level of water like those activities can minimize the level of ground water. Basement retaining wall has been built and designed in such manners that it can cut off the total and near total ground water level by using pumping system. Pumping system is very useful to throw out the ground water from the basement. If the pumping system is used for the basement then it would discharge ground water very effectively. In this process there is a basic need to maintain a proper arrangement to discharge the ground water from the basement; it required an expert or permission letter from the local government to discharge the water from the basement. This method is not so useful because local authorities restrict the user to discharge the water at certain level like there is a limitation to discharge the water from the basement. In this whole process the k value play an important role it has substantial effect on the volumes of ground water which is

16 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 15 supposed to pump out from the basement. Ground water existence is not only hazardous for that specific building but it can also affect the buildings which are associated with that building because ground water moves around and it makes its own space to flow. This could be happened due to:- The lose associations among the buildings Removal of fines and soil pressure Available moisture inside the wall In this situation piles walls are the best option to use because ground water can cause washout between the piles and behind the wall. Filling between piles can be used to get rid of this problem and it is useful to save the retaining walls from the ground water. 6.1 RETAINED STRUCTURES It is beneficial and performs well everywhere to excavate the basement with single, double and triple basement structure. Therefore it is necessary part to gather the proper information about the retaining buildings and determine whether it is suitable or not for the retaining buildings which are covered in points which are mentioned below: Proper space of retaining wall from the basement All the possible details regarding structure for example the size of the structure, which type would have been adapted, all possible conditions and level Information about dead and load structure Knowledge about all kind of materials and space margins among the wall All the possible geometry and calculations that can help to make a system perfect and flawless Knowledge about all the external sources that can affect the retaining wall like noise and vibration factors The above points help to examine about all the probable events or deflections that can make this project fruitful and also help to settlements of all unwanted and undesired elements that can have big obstacles for this project. 6.2 DESIGN APPROACH According to the design approach which is used for the basement the retaining wall is constructed in parallel with that design and it proceed with various numerical designs. After all investigations and examination is completed the following considerations would be adapted after assessment: Condition of ground Deepness of the basements which is required for the car parking Ground water condition and its cut off options that effect the retaining wall Retaining wall structure and its maintenance and services Space limitation among wall and available plant All the support system that temporary support retaining walls

17 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 16 Estimation budget and events Temporary and constantly retention of the wall Analyze the load that can effect vertically on the wall Assessment of the material like sheets and piles for the wall Working conditions and available space All these requirements are important requirements and based on the above mentioned standards. First all these requirements should be gathered and then further proceed on the design which is based on numerical calculations and assessment. 6.3 Limit States Simpson and Driscoll (1998) is structural designer who present the design in which he stressed on prevention of limit states that can increase the performance of the retaining wall for car parking and it satisfy all the terms and conditions of the retaining wall. This practice can save the damage, economy and all other unsafe situations which may cause the improbability. Retaining walls for car parking should be constructed under some rules and policies and these are ultimate limit state and serviceability limit states. 6.4 Ultimate Limit States Ultimate limit states are the states that cover all the collapse in a wall and it also covers all kind of failures which are related to retaining wall. Ultimate limit states are those associated with collapse or with other similar forms of structural failure. All these states are concerned with the safety measures and safety structures. Some points are mentioned which should be considered: Unbalance of equilibrium and unbalance structure Improbability by the wrong rotation of wall and wrong translation of the wall caused by some external forces Wrong or unbalanced vertical equilibrium of the wall Unbalance structural components such as wall, beam which can be used to make a wall strong Undesirable movement of the retaining wall that can cause the collapse of the structure and it also depend upon the services and maintenance Structural failure due to improper time management and other factors that depends on the time limitations and other fatigue This design has a property of carrying out the investigation of equilibrium. In this design there is a need to suggest safety measures and earth pressure should be calculated which is shown in the diagram 5, in this design classical pressure theory has been used to and it has two types one of them is called active and second one is called passive theory. As mentioned above that improvement in technology has reshaped our methods and make it fast so with the help of computer programming we can make our exploration faster and easier. With the help of computer programs we can easily make changes in geometry, stratigraphy and soil parameters that can help to make this system perfect and without any error. In this system we use limit

18 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 17 equilibrium analysis which can help to maximize the supplement load on the wall and it also help to minimize the soil strength. After all the analysis depth would be measured for enhancement and then factor of unity is applied to this system to avoid the rotational and translation failures. 6.4 Serviceability Limit States Serviceability state is another parameter in which system check whether the exact service performance requirements are achieved or not, like pre-defined limits on the amount of wall failures; in this system tolerance factor has its own prominence which is based on its nearby structure and displacement. It is only worthy if overall stability analysis can be carried out and there are two factors that has exclusive functionality regarding serviceability and these are active and passive parameters. In this process the next phase would be measure the actual wall and all its movements along with the forces that affects the retaining wall for car parking. Normally ground has different components like soil, it exists in the ground and pre-development and these are also along with active and passive limits. It has been analyzed that this system would not reach the active limit and also will not access the passive limit while designers work on this system. As described before that soil will not access the active limit so in this set-up the SLS condition has a greater impact than ULS condition. As explained above that all the forces like shear force, prop loads are measured and these factors are depending upon the soil model which is presented in the ULS phase analysis. It has been finalized and noticed that if the soil will not access its passive limit with its full strength then it would be consider as failure model or there is a need to make a new and reliable model which can be access its full active strength. Research and background studies show that construction activities occur in the form of co-efficient as shown in the figure 6. In this stage the soil cannot strain and it is not been compressed during the formation stage but after this stage the more stresses would be generated for the structure. As shown the below diagram which illustrate the earth pressure for the structure.

19 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e Soil Parameters & Factors of Safety ULS and SLS both are very important for the system. If the calculations of the both are not seamless then it would be create critical situation for overall design so the selection of parameters of soil should be suitable. Both the selection parameters and soil factors should be linked to each other and they can connect with each other. Three approaches were defined regarding design and these approaches take care of all the parameters and safety measures for the retaining wall for car parking. The methods which are defined consist of soil parameter, groundwater pressure and load which are as follow: Moderately Conventional: a calculated and evaluated assessment for the relevant values Worst Credible: the wrong values that would have been chosen by the designer so this method of choosing the value is not suitable for the SLS extents Most Credible: the values which have above 50% probability must be surpassed but this approach is not used for all kind of designs this is only useful for the observational method in which the design would be analyzed on the basis of refractions.

20 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e Conclusion Development in technology has been reshaping the ideas and it can be useful for every field of life whether it should be a medical line or engineering. Retaining wall for car parking is a new and transformed idea to save the place and can be used to park the cars but it should be safer and consistent and there are so many constraints that have been discussed in this paper and there solutions also proposed in this paper. There are different types of retaining walls for car parking has been presented and their methods also discussed. The whole paper shows that a successful design and construction of deep basement for car parking is depending upon the well planned and closely oversaw subsurface investigation workers including the field and laboratory testing mechanism and approval of reliable and qualified engineers or designers. The paper shows that retentive wall for car parking and support system should follow the standards to make it in a better way. There is a need of proper strategies, well defined process, practices and calculated input from the designers which indicate that the system is following the standards. Every stage of the construction starting from setting out and establishing monitoring instruction before any excavation is essential. The construction process should follow the instruction which is approved form the professional experts and analyst which has been discussed in this paper and it should be avoid all the mistakes that can make the system indeterminate especially those highlighted in the paper. Quality assurance system should be appointed to assure that whether the retaining wall for car parking is going in a right direction or not. There are lots of points regarding safety and wrong decisions have been discussed like ground water existence, vertical or horizontal unpredictability, wall color and textural fault and slope issue. Due care meticulousness with full conscience from the design and supervision teams are imperative to ensure success of engineering works in particular for deep excavation which is risky not only to the work but also adjacent structures.

21 R e t a i n i n g W a l l F o r C a r P a r k i n g P a g e 20 Reference BS5930: 1999, Site Investigations (will be superseded by EC7). Eurocode 7: Geotechnical Design. BS8002: 1994, Earth Retaining Structures (will be superseded by EC7). BS8102: 1990, Protection of Structures against Water from the Ground. CIRIA C580, 2003, Embedded Retaining Walls Guidance for Economic Design Institution of Civil Engineers, 1996, Specification for Piling and Embedded Retaining Walls. CIRIA C515: 2000, Groundwater Control Design & Practice Simpson, B and Driscoll, R (1998) Eurocode 7, A Commentary, BRE Caquot, A and Kerisel, J (1948) Tables for Calculation of Passive Pressure, Active Pressure and Bearing Capacity of Foundations