DEPARTMENT OF CONSTRUCTION MANAGEMENT

PROJECT COVER SHEET

STUDENT NAME: DC

STUDENT NUMBER: C 123

COURSE/ YEAR DT117/4

SUBJECT: Advanced Construction

Technology

PROJECT TITLE: Deep Basement Excavation

LECTURER:

FOR OFFICE USE ONLY:

DATE DUE: 10th February 2016

DATE RECEIVED:

RECEIVED BY:

REPEAT PROJECT?

MARKS:

Introduction

The construction site for the prophase of the project will be a multi-story commercial dwelling with

deep basement carpark located in city centre at Smithfield where there is a high level of water content

as it is in close proximity to the river Liffey, lack of space due to other buildings, traffic level are high

and one way system is the only option. The design team have proposed ‘type C drained cavity’ basement

that will consist of ‘secant piling system that has to be delivered in accordance with the project schedule.

Project management has to plan for the following in relation to deep basement construction:

The first thing a CM will do is find out the ground conditions/cut-off points on the Smithfield project

determining the water levels below ground and depth of the required excavation. Also problems that

may be incurred during a city centre project are existing underground services such as water mains and

drainage. Cat-scan will be carried out to locate these services that will allow for additional measures

that may be necessary such as diversion of services. (DEEPEX, 2015)

Specific management plans

All basement projects are to include traffic management plan regards to impact on traffic surrounding

the site showing the impact for the construction schedule and surrounding services such as ambulances,

buses etc. and demolition management plan (CDMP) showing materials handling and storage,

establishment of welfare facilities for the workers on the site a clear construction sequence illustrated

with sketches and detailed diversion of working swears. (personal.cityu)

Project Scheduling

As time equals money quality of planning and scheduling of highly efficient working programme will

be vital for success of a safe on time project without any disturbances to works that may set back the

project to the completion date or require more resources that were not planned for. The project will

require layout and planning of the site accommodation and phasing/sectioning of the job. (teckrackher,

n.d.)

Associated risk and safety

(ADSC, 2015) Health and safety plan will have to be made stating the nature of the work, method

statement of the project, and risks associated with the project. Potential unforeseeable problems during

the construction process of deep basement construction are:

1. The effect of water ingress or pressure on the stability of bored pile walls and excavations

2. Collapse or failure of excavation walls

3. Disturbance of adjoining buildings and structures

Such risks will have to be eliminated by putting in place corrective measures such as:

1. To eliminate the effect of water egress predictability of conditions during the construction

period will be made. Temporary pumping and measures to prevent flooding will be installed.

Monitoring of water levels during construction period to predict potential risk.

2. To prevent the collapse of the basement wall anchors and tiebacks will be used to retain the

wall in place. Available expertise skill will be needed to calculate the vertical loads and lateral

loads to determine if the piles will be able to carry out their function additional shoring can be

placed against the excavated piles.

3. Disturbance to adjoining buildings can be eliminated through public relations and minimization

of the noise control during specified hours. Sprinkler systems will be used to eliminate

construction debris. (ADSC, 2015)

Introduction to Secant piles

The following section will focus on the construction methods used to

deliver Secant pile deep basement from site management perspective.

Secant pile walls are formed by drilling intersecting (one pile with

another) reinforced concrete piles. The research shows that secant

piles are reinforced with either steel rebar or with steel beams.

Primary (female) piles are installed first with secondary (male) piles

constructed in between primary (female) piles once the concrete

gains sufficient strength. Pile overlap is typically in the order of 8 cm

and can go in depths of up to 45 meters. (Baxter, 2012)

Construction procedures of secant pile wall

The secant pile wall will be set out with the piles distances centre-to-centre spacing and is drilled in two

stages. 1st stage involves drilling and placing of primary piles and 2nd stage will involve drilling the

secondary piles in-between the primary wall. (Concrete-group, 2016)

The guide wall will be excavated which is a precast concrete wall to secure the wall alignment

but is not necessary.

The male piles are bored through the female piles before the concrete has achieved its full

strength.

Once the Rebar is placed and poured the levelling of the excavation can begin. First the guide

wall is removed.

Once the wall is excavated to a depth of 2 meters ground anchors may be used.

Ground anchors

Ground anchors are used for installation that is capable of

transmitting an applied tensile load to a load bearing

section which may be a soil or rock to provide resistance to

structural movements. The advantage of ground anchors is

that excavation can stay unobstructed. The ground anchors

will be installed at an angle in the concrete pile. The hole

will be bored where the rebar will be placed and then

injected with concrete. The end of the anchor will be cut

and a cap put on top. (Ergun, 2008)

Ground water barriers

To achieve a water tightens it will be necessary for the CM

to build a skin wall to the sides of the piles. First step is by

cleaning the piles from any remaining spoil. Next shotcrete

will be pumped to the wall. Then waterproof membrane will

be placed on the wall by screwed to the main structure of

the wall. Once the membrane will be on polyethylene

studded sheets will be overlapped to seal the secant pile

wall. Then reinforced concrete levelled walls will be made

to cover the drainage system where it will be poured over

drainage pipe located 20cm from the wall. 50mm concrete

blinding will provide clean working surface for positioning

the mesh floor slab so the concrete can be poured pour.

Advantages of using secant piles

The main advantages of secant pile walls are:

1. Increased wall stiffness compared to sheet piles.

2. Can be installed in difficult ground.

3. Used in high water table conditions.

4. Columns can be as close as 5m from existing

buildings. (Wong, 2002)

The main disadvantages of secant pile walls are:

1. Verticality tolerances may be hard to achieve

for deep piles.

2. Total waterproofing is very difficult to obtain in

joints.

3. Increased cost compared to sheet pile.