Geotechnical Framework For Basement Car Park


The aim of this design/investigate task is to design a geotechnical structure for a basement car park. The aim of the job is to maximize the car parking area available by developing a long term retaining structure for a basement car park during structure excavation.

The numerous kinds of retaining composition will be compared and considered first by rational and engineering viewpoint which includes several aspect includes toughness, cost, sustainability and environmental impact.

For design purposes, BS EN 1997 -1 :2004 Eurocode 7 is utilized to design the key retaining framework and momentary works necessary. The design considered Ultimate Limit Express of a structure which takes framework stability into accounts.

Chapter 1 - Introduction

Brief Introduction

A hotel chain wishes to use land previously providing as a car park for a new accommodation block. Car parking space to service this is usually to be constructed under the new composition. Therefore, a geotechnical retaining structure needed to be design to aid the ground during structure and after engineering. A plan view and elevation view of the site is given and also set of requirement for this project receive too.

Project Design

Design of the primary retaining walls

Design of any short-term work necessary

Detail of the Project


This is an urban 'Dark brown Field' site. The previous use was known to be low rise home structures followed by conversion to an automobile parking space. The website is flanked on three factors by open public highway and a table study shows services as suggested in (Figure 1. 1) Site Plan. Considerable site exploration has been performed before. The interpreted geological profile is mentioned in Figure 1 too. The interpreted geotechnical design parameters are summarized in Table 1. 1.

General Arrangement

The proposed program is shown in plan and sectional elevation in Number 1. The brand new extension is usually to be developed on the prevailing airport parking area and includes an extended basement as mentioned.

Construction Restraint

One of the main element constraints concerns the noises and vibration boundaries imposed. The project need is to keep the existing hotel properties around the suggested structure completely operation throughout the building period. The restrictions proposed by the neighborhood authority are given in Stand 1. 2 below.

It is also clear that the basement excavation will impact the rafted groundwork to the original hotel wing. To ensure that the serviceability of this structure is promised it has been deemed essential to limit the lateral deflections of the new basement walls at 20 mm into the excavation.

The engineering site is very close to a general public sewer which works in the highway footpath near one site boundary. Therefore, this aspect had been considered in the ultimate decision for choosing types of retaining structure.

Construction Time Rates And Costs

As in many construction projects the swiftness of construction affects overall cost. In cases like this it is vital that the new hotel is operational in the lowest possible of time. Notional building costs and time rates are mentioned in Desk 3. These characters have been given for the purposes of the project. The over head rate for possession of the site, fixed costs for establishment and use of site area are shown in the Stand 3 too. The engineering sequences is to be assumed that activities above and below surface can be run in parallel but above and below ground activities are sequential.

Chapter 2 - Site/Land Profile

2. 1 Ground Description and Classification

To understand the land profile and the habit of every sole type of dirt can be an important step for a geotechnical engineer prior to starting any design works. Generally, land is kind of nutrient particles developed by the weathering of stones which weakly cemented or uncemented [1]. The void space between your particles contain drinking water and/or air [1]. Weak cementation are anticipated to carbonates or oxides precipitated between the particles or due to organic subject [1].

There is several type of soil. Every type of dirt is classified in various categories by their particle size. The three main type of dirt are Sands/Gravel, Silts, and Clays. Particle sizes in soils can vary from over 100mm to significantly less than 0. 001mm. The particle size distribution of the coarse-grained soil is to be determined by the technique of sieving [1]. The normal size of land ranges is shown in Number 2. 1 below. figure 2. 1. jpg

Basically, the terms 'clay', 'silt', 'fine sand' or 'gravel' are used to vary the sizes of soil and type of soils. Several size usually is made up in a graded combination of particles [1]. For example, it isn't necessarily all clay size allergens are clay mineral debris because clay normally contain particles in both the clay size and silt size ranges where clay is kind of soil possessing cohesion and plasticity [1].

In standard, a cohesive soil is said that if the allergens adhere after wetting and subsequent drying if significant push is then required to crumble the garden soil [1].

2. 2 Borehole Data

A set of borehole data (Amount 2. 4) is given for design purposes. Physique 2. 4. jpg

From the borehole data given implies that water table on the website is 1m below the ground level. From top level to 3m below is some sort of coarse gravel. It really is then followed by soft to solid grey brown slightly sandy clay (alluvium) and combination of soft dark brown very silty clay right down to 6m below walk out. From 6m below ground level to 7. 5m, the earth is covered by loose dark brown clayey silt. It really is then followed by loose to medium dense red brown silty clayey sand with a 4. 5m depth. From 12m to 16m below ground level the ground is included in massive amount gravel.

A simplify stand of dirt in the website is shown in table 2. 1 below for better and clearler understanding.

Borehole Data


0 - 0. 2

Tarmacadam surfacing ( MADE Earth)

0. 2 - 3. 0

Dark grey angular to sub-rounded coarse gravel with ash, concrete and rubble fragments (FILL)

3. 0 - 6. 0

Soft to firm grey brown just a little sandy CLAY with some organic and natural matter (alluvium)

Very soft to soft dark brown very silty CLAY

6. 0 - 7. 50

Loose darkish clayey SILT (alluvium)

7. 50 - 12. 0

Loose to medium dense red-brown silty clayey SAND with infrequent sub-angular fine to medium gravel of sandstone (alluvium)

12. 0 - 16. 0

Loose to medium dense, becoming thick red gray silty very sandy, sub curved GRAVEL (alluvium)

16. 0 - 22. 95

Weathered MARL

Reddy dark brown and grey renewable weathered (iii - iv) weak MUDSTONE

Chapter 3 Types of Retaining Structure

There are several factors that influence the issue of basement design and development. These factors normally are existing problems on the site and cannot be easily changed. Designers somehow need to go for different option when making structure to defeat the constraints. For example, the location of the proposed structure, suggested use of the structure, groundwater, the website surrounding existing framework and services. The sort of basement wall will be then preferred to support soils and groundwater of the basement and to design as financially as you can.

The walling or sheeting picked for this project is to provide short-term soil support for long term substructure building, or it may also serve as ground retention. The walling or sheeting will be chosen after evaluation in conditions of cost and time, constructability and etc. Several methods are the following.

  • Plate and anchor wall
  • King post wall
  • Contigous bored piling
  • Secant piling
  • Steel sheet piling
  • Diaphragm walls
  • Reinforced concrete ensemble in situ
  • Reinforced concrete precast
  • Post-tensioned
  • Soldier piling

3. 1 Short Introduction for each Options

i) Plate and Anchor Wall membrane by underpining

The total excavation depth of basement work is typically fall in the range 8 to 12m as well as the floor conditions are dried out and able to support 1. 5 - 2m face deep[2]. The anchored dish method is an economical temporary wall structure support. Pre-grouting is usually to be found in granular soils where the soils were unable to stand unsupported to this moderate depth [2]. Amount 4. 2. jpg

ii ) Ruler Post Wall

King Post method is usually popular for two following factor which is cheapness of materials by using timber and overall economy method of boring by using power augers. This method require boring holes on wall range at 2 - 3m centre depending on soil strength, depth of excavation and surcharges loads. The hole is then positioned with vertical beam also to be concreted with low fat mix cement at the base of every joist below last formation level [2]. Ruler post wall membrane usually used as a short-term soil support and be utilized in dried up or dewatered soils. Vertical settlements of wall is one of the drawbacks where failing of vertical power transferring to the bottom of pile.

iii ) Contigous Bored Pile Wall

Bored pile wall is usually used as an monetary and efficient way for retaining composition. This techniques is very suitable for profound basements excavation and underground framework where working space is bound. This technique prevent large amount of garden soil excavation and also help control ground actions. Hemorrhoids are usually drills into surface by using constant air travel auger (CFA) with a certain distance distance between hemorrhoids. A maximum amount of piles is usually around 20m depending on earth condition. Contiguous tired pile wall membrane is not suited to site with high drinking water level due to the gaps between hemorrhoids.

Advantages of contiguous pile surfaces are :

Comparative low cost and rate of construction

Low level of reasonable pollution ( low level of vibration)

Pile can be drill in limited spaces

Has the ability to minimize the length between bored stiff pile wall structure and existing wall membrane for small excavation depthcontiguous uninterested pile wall. jpg

iv ) Secant Piles

Disadvantages of contiguous bored to death pile are overcome by using secant hemorrhoids where interlocking method is released. Secant pile surfaces are built by concreting main (girl) hemorrhoids first then supplementary (hemorrhoids) are weary through female piles before concrete reach full power [2]. By this the piles forms overlapping between each other.

Advantages : a)Can be installed in hard earth (cobbles /boulders)

b)Low noise pollution

c) Better wall membrane tightness compare to sheet piles

secant-pilingBig. jpg

v ) Sheet Pile Wall

Sheet Pile wall are made from several piles that interlock each other and is influenced into the garden soil. Most sheet pile wall membrane nowadays is using metallic sheet which fabricated in factory. The usage of sheet pile for non permanent ground support for basement at metropolitan area isn't that popular where noises is the key constraint. Sheet pile may be installed using hydraulic can decrease the noise pollution. Sheet pile wall can be design as cantilever wall membrane or anchored wall membrane is determined by the basement depth and garden soil condition that vary.

Advantages : a) High amount of resistance to driving strains.

b) Sheet can be reuse

c) Simple to install

Disadvantages : a) Sheet pile can scarcely be use as long lasting structure.

b) Installation of hemorrhoids are hard where soil contain boulders and cobblers

c) Noise pollution (High vibration)

vi ) Diaphragm walls

Diaphragm surfaces are strengthened concrete wall created in slurry supported by machine digging a trench in sections of certain length. This slurry can be bentonite slurry where has thixotropic properties [8]. The wall structure is first built in short sections length, by putting in reinforced cages and concreting, then later intermediate sections are excavated to complete the complete wall. There may be 3 type of diaphragm walls in use in industry, which is cast in-situ diaphragm wall structure, precast reinforced diaphragm wall and post-tensioned diaphragm wall.

Advantages : a) Allow effective transfer of vertical insert from the building to subsoil

b) Minimum noises and vibration disturbance

c) Allow structure on limited site area.

3. 2 Evaluation of every option

A table (stand 3. 2) of matrix below is to compare the advantages and disadvantages of several retaining structure. This evaluation results will shows the most suitable retaining wall to create and construct for this project.


Durability is not usually a problem for a momentary wall depending on the soil condition. But when wall is usually to be design as a long term structure, the wall membrane should meet the durability need where wall membrane should reach design life. For instance, durability requirement of concrete wall will depend on the look life, concrete content, water cement percentage, cover of encouragement and also quality of workmanship.


Rigidity means a structure property that does not bend under an applied push in vertical or horizontal load [10]. Different kind of retaining surfaces could maintain different loading. Some wall space are good in resisting vertical launching and does not bend but some walls can only just sustain horizontal push. For example, strengthened diaphragm wall is a lot more rigid than a sheet pile wall. Reinforced concrete diaphragm wall can be design as a long lasting structure that take weight from superstructure above and does not bend in any way. Evaluating 6 types of retaining structure above, Diaphragm walls, contiguous pile wall structure and secant pile wall space are three best on rigidity.

Constructability on Site

Constructability of a composition means a composition to be constructed on site easily from commence to finish by satisfying client's requirement. Constructability also means ease of building. A constructability review must be done before starting any construction process to prevent error, construction wait or cost overrun [11]. The area to construct the proposed structure is limited. Body 1. 1 demonstrates a existing sewer pipe brand is 1m beside the proposed composition on the right in addition to a existing composition 2m definately not the suggested building on the left. One of the project necessity is to minimize the sound of structure in metropolitan area. Selection of excavation is bound to avoid any harm to the prevailing properties. Trench excavation is well suited for this project. Therefore, constructing diaphragm wall membrane is the best answer where diaphragm wall can be built in limited space by using trench excavation, low noise produce and machinery is not big.

Soil Condition

The soil profile is required to consider when designing retaining composition. Some structure's construction is hardly to process when the soil has cobbles or boulders. Most of the structure is suitable to be constructs upon this project site as a result of clayey ground from walk out to the very least depth of 12m. Only once primary design for retaining structure with required depth over 12m into gravel covering, retaining framework like diaphragm wall is not that suitable due to the stability of wall.

Water Table

Ground drinking water on site are mainly from rainfall or groundwater move through ground from waterways and seas [2]. By lowering the groundwater within the excavation depth and composition depth by dewatering process will raise the strength of garden soil as the pore normal water pressure is reduced. Groundwater control is essential to prevent any leakage of normal water in to the basement car park or cause instability of framework, for example, floor heave. Retaining wall membrane usually works as a groundwater take off. Several alternative ways of groundwater cut-off are:

To lower the groundwater by short-term dewatering process where earth movement is to be considered.

Temporary sump pumping is usually to be done is surface is sufficiently impermeable

Excavation is to be done under water and so long lasting wall is usually to be construct under water by tremie concreting techniques.

Diaphragm wall will serve as a good normal water barrier compare to sheet pile or secant piles where sheet pile might corrode and water will flow through the space between secant pile.

Depth of wall

Designer must consider the depth of your retaining framework can be construct. Some structure is cheaper to be built-in deeper depth compare to shallow depth. Stand 3. 1 shows the different type of keeping structure that may be construct up to the maximum height of wall structure in order for the structure to remain steady and safe.

Storage of Materials

Proper storage space of recycleables is very important for a building. Raw materials like support cages, cement, sand, and etc. would have to be on site on time to prevent any hold off of construction. For example, metallic sheet and support cages both are created in large size and needed large space to store up. Therefore, it will probably be worth to consider this problem when choosing a retaining framework.

Environmental Impact

Environmental impact is one developer to be consider when framework is build in metropolitan area. The decision of wall can affect the environmental during construction, during in use and demolition [12]. Three main triggers to environmental impacts:-

During Installation

Noise and vibration when boring pile. (sheet piling)

Number of vehicle used.

Use of sustainable materials (Guidewall construction for diaphragm wall structure)

When used

Effects on groundwater around the wall.

End of life

Ease of removal

Ability of materials to be reused

3. 3 Final Decision

Diaphragm wall is to be used for my design job.


Chapter 4 Diaphragm Wall

4. 1 Preplanning and Design

For making purposes and engineering of diaphragm wall surfaces, a number of item require to be considered in preplanning and design of diaphragm wall membrane.

Excavation Sequence

The collection of excavation from ground level to the basement walls is to be well planned to minimize rig movement and avoid changing places and moving of pipework from panel to -panel of panel excavation. Earth dump pick up truck, slurry removal vehicle, cranes and concrete mixing up trucks, and to allow healing of cement in completed sections are all parts of engineering and excavation sequence that needed to be well designed.

Guide Trench Construction

The successful of trench excavation for diaphragm wall structure depends upon the temporary guide wall membrane. The guide walls must be design and create to be powerful to avoid any motion due to extreme loads from excavation rig service cranes or keeping support cages and response from stop end jacking systems. In a few building, reuseable precast concrete guide wall structure have been used and be interlocked each other by bolted to guarantee the same standard of rigidity as in-situ cast concrete wall structure [2].

Panel Size

Diaphragm wall is to be constructed by the -panel trench excavation first. The panel length typically will vary from a minimum of one get bite (trench excavation machine grab width) to a multiple of get bites which will prolong to 7m. A grab bites fluctuate between 2. 3 and 2. 8m depending on machine used. The -panel length include two stop ends for the primary sections (Stop ends will be talked about on following webpages). Secondary sections are those sections dug between two concreted sections. The panel length is bound to a certain period, and therefore -panel size, this is to ensure that sufficient cement can be fill up the whole -panel within concreting period in a day. This requires maximum daily working time and concrete supply into account. -panel size more depends on designer and service provider decision.

Wall-Slab Development Joints

Joints between basement flooring surfaces slabs and wall membrane is usually to be design carefully because the joints can transfer vertical shear and bending moment that could cause instability of structure and basement. Bend out pubs and Threaded-end couplers are both used in the joints.

Reinforcement cage

The depth of diaphragm wall structure has resulted in the size of reinforcement cages. These cages are usually fix off-site and delivered to site when is needed. The maximum length of cages is restricted because of transportation of long and large cages.

Slot for Tremie Tubes

A tremie tube can be used to ensure concrete is placed in correct position which no parting of aggregate occurs during concreting pouring concrete throughout of wall space. Therefore, support cage is usually to be made to allow sufficient access for tremie pipes. For some structure of diaphragm with large sections, two tremie is to be used to maintain the concreting rate of 60 to 80m3 each hour.

4. 2 Structure Sequence

End Of Construction

Site Clearing

Top Down Basement Construction

Diaphragm Wall membrane Construction

Site Preparation

4. 3 Work to be Done

4. 3. 1 Site Preparation

Basement and retaining wall construction methods involve a high amount of mechanization. A clear working space give maximum flexibility for equipment, materials and personnel, hence maximize the working speeds increasing construction period. Therefore, several steps are needed to be done before any construction work progress. For instance, temporary street should be provided to achieve an instant tempo of structure in moist or dried up weather.

Traffic Management

Local government bodies are highly matter on the traffic management especially in urban area. Construction in central of metropolitan area might lead to serious traffic congestion scheduled to decrease moving structure vehicles and parts of street are occupied by equipment. A just a little highway way will be transformed on A designated in body 4. 2 below to provide access for engineering vehicle in to the site. On highway marked A in figure 4. 2, the road is usually to be assumed that is a typical single lane carriageway. Therefore, the road period will be marginally reduced near by the construction site. An alternative road for vehicle towards junction is usually to be suggested to local authorities to prevent any traffic congestion. Clear barricades and highway indication will be provided along the street closure.

Location of Underground Services

Site prep in urban area includes tracing and clear marking of existing services includes underground cell phone, power cables, drinking water and sewer pipe, gas pipe, etc.

Underground services is to be assumed to provide in any circumstances. Trench excavation is much more likely to come across underground service when confronted with excavation parallel to the type of excavation [13]. Many serious crashes have been triggered by men or machines when underground services are struck, penetrated or during excavation. Electric distress may derive from striking electricity cords during excavation.

On this project, it is plainly shown on figure 1. 1 a 1200mm diameter concrete sewer pipeline is merely 1m from the side of proposed structure. A sewer pipeline bursting could cause contamination of the ground and odour smell to near by citizens. Many sewer pipes are under high pressure too.

As a remedy, first, a confirmation of sewer tube location is to be done on site. Once the documents are obtained, it will be kept on site and become accessible to personnel. Furthermore, building of diaphragm wall uses trench excavation techniques, which highly decrease the chance of striking the sewer pipe.

Any other services includes telecommunication cords, gas tube and electric tube that are not shown in physique 1. 1 given will be examine on site before excavation.

Existing Building

Building located around the site are needed to be protected from damage and dirt-staining. Cleaning and retaining existing building in the end of construction can be expensive. In figure 1. 1 implies that there is existing 3 storey with raft groundwork building 2m away from basement wall membrane. Before any excavation start, careful inspection is usually to be done to the prevailing building to determine whether there are any existing breaks due to settlement or any destruction on external wall structure of building. Breaks and damage is usually to be saved down and photographed as a facts to prevent any boasts from house owner.

Overhead Obstruction

The most typical overhead obstruction is high anxiety electricity cables local the site. Most engineering vehicle are high. There's a danger when extra tall vehicle go by those overhead wires and cause unwanted incident. Therefore, a clearance is usually to be done between your overhead cables and ground. For example, an average "goal post" protection will be erect over the entry to the website. Body 4. 3 below shows typical "goal post" protection. physique 4. 3. jpg

Public Safety

It is important to taking care about public security. Any pedestrian is not allowed to enter building site. A warning sign is to be displayed around the boundary site and obstacles is to be set up along perimeter of structure.

4. 3. 2 Diaphragm Wall Construction

Construction of diaphragm wall uses trench excavation supported by slurry. The slurry is normally bentonite and normal water.

Diaphragm wall surfaces are made in the following steps :

1) Pretrenching to remove obstruction

2) Guidewall construction

3) Trench excavation (panel excavation)

4) Endstop placement

5) Panel desanding

6) Encouragement cages placement

7) Concreting work (Tremie approach)

8) End Stop removal

9) Excavation of Intermediate Panel

10) Support cages placement

11) Concreting work with remaining sections (Tremie technique)

12) End of Diaphragm wall membrane construction

4. 3. 2. 1Detail steps

Pretrenching to remove obstruction

Pretrenching is a process to remove dirt by available excavation to a certain depth, typically 1-2 m depth for guidewall engineering. Additionally it is a purpose for getting rid of shallow obstruction and provide secure support for the guidewall.

GuideWall Construction

Guide wall is usually to be constructed after pre-trenching process. There are several purpose of creating guidewall, these include:

To prevent the collapsing of dirt near trench excavation surface.

As a template for wall structure excavation and panel layout

To give a temporary helps for reinforcement cage. (by having down the cage during concreting work)

To provide support for end-stop joint. (restrain end-stop)

To support Tremie Pipe

To provide a guide elevation for placing props, slabs, etc.

For this task, the guidewall is to be designed with reinforce concrete and be made from grade M20 grade strengthened concrete. The length between both guidewall will be thickness of diaphragm wall plus a tolerance of 50mm. The dimensions of guidewall (one area) will be 300mm(w) x 1000mm(d).

Trench Excavation (Panel excavation)

Construction of diaphragm wall uses trench excavation method which create a vertical strip in land that can collapse easily. Special excavation equipment are being used to excavate the soil. Several kind of machinery is utilized in construction field nowadays. These equipment can be cable connection hug or Kelly attached and the digging technicians can be cable tv or hydraulic run. physique 4. 7 2. pdf

The excavation is to be excavated in "panels". The panel length varies typically from a minimum of one grab bite (trench excavation machine pick up width) to a multiple of grab bites which will stretch to 7m. A pick up bites fluctuate between 2. 3 and 3m depending on machine used. amount 4. 8. jpg

The trench excavated is usually to be recognized by bentonite slurry. Bentonite is actually clay of montmorillonite group, so when added with normal water it sorts an impervious slurry with large viscosity. The slurry will produce large lateral pressure to wthhold the vertical soil. In case of granular soils, the bentonite slurry will penetrates in to the sides under positive pressure and forms jelly. When bentonite slurry is fills in impervious clay, it will not penetrate into the soil but form a layer of slim film to gives durability helping vertical soils. The bentonite slurry is to be placed continuously in to the trench throughout excavation.

For this task, Kelly Grab is to be used for excavation. The depth and width of excavation will be discussed in following chapters. The -panel span and bentonite slurry density is usually to be designed and results will be shown in following section too.

End stop Placement

Endstops are positioned in both -panel fronts to supply the concrete at each vertical edge of panels with a predetermined condition. The shape of stop ends can be a tube or special keyway end can stop. End stop can be place directly into be long term or temporary.

For this task, a short-term cylinder end stop is to be used. The end stops will be removed by vertical removal soon after the concrete has been poured. Somehow, a wait of few hours is allowed to be able to permit the concrete to gain some early strength and able to stay vertical. The timing and removal of end puts a stop to will be judge by the website contractor and be carefully seen. If end stops is extract out before the cement is steady (gained sufficient durability to remain vertical), there is a risk that the cement will slump.

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