Structures and Geotechnics.

COURSEWORK BRIEF
A four-storey concrete framed office building is to be constructed in a town centre location with
a single storey basement to be used for car parking. An outline plan and section of the building
is shown in the figure. Two historic buildings of similar height are located either side of the
site, the nearest is 10m from the perimeter of the new structure. These buildings do not have
any basement and their foundations are unknown at this stage, however anecdotal evidence
suggests they are relatively shallow. An engineering survey of the property, in advance of the
works, suggests there is settlement and possible foundation failure on one of the properties
adjacent to the works. Caution is therefore strongly advised within the design.
Individual Design Criteria is given in the table below. The overall height between level 0 and
level -1, h, of the basement for your design is indicated. Also provided is the column spacing,
L, for the superstructure. This is assumed to be the same in both directions.
The superstructure is a concrete frame with 300mm deep concrete flat slabs at each level
including at roof level. Wind loading should not be considered in the design.
The assignment involves the assessment of the problem and the analysis and design of the
basement wall/slab and any associated temporary works.
Design Criteria
A borehole log has been provided below. The soil conditions should be taken as being
consistent across the whole site.
Table 1.0 Generic Borehole Log
Depth Material Properties of the materials encountered
0.3m Topsoil • N/A
0.3 – 1.7m Made ground • Soil Density (Saturated) 16.0kN/m3
,
• Undrained shear strength (cu) is 25kPa.
1.7 – 10.0m Glacial Till
• Soil Density varies linearly from 16.5kN/m3
to
21.0kN/m3
• Undrained shear strength (cu) varies linearly from
50kPa to 175kPa for the stated depths.
• Drained Friction angle θ’ varies linearly from ~ 23.5o
at the top of the sequence to 30.00 at the bottom. The
associated drained cohesion c’ varies linearly from ~
0.5o at the top of the sequence to. ~ 2.5kPa at the
bottom.
• Structural interface values for undrained and drained
properties shall be assessed as per EC7 Clause 9.5
EC7
• A constant Over Consolidation Ratio of 5 shall be
used throughout the depth of the sequence.
10.0m – 27.5m Medium Dense
sandy Gravel
• SPT profile varies linearly from 12 at the top of the
sequence to 34 at the bottom of the sequence.
27.5 – 30.5m
Weather Rock
head (Upper
formation Basalt)
• Uniaxial compressive strength range 0.6 – 1.0MPa
(Extremely Weak) within the first 3m thereafter the
material becomes Very Weak with a uniaxial
compressive strength range varying from 1 – 5 MPa.
• The rock is a fine gained material and impervious.
General Comments • For the purpose of this analysis, the water-table shall
be taken at 5m below ground level
• All friction angles quoted shall be treated as the
‘constant volume’ condition for assessment
purposes.
• All moduli need for assessment the assessment of
settlements; can be derived from the properties
denoted above using standard published
relationships.
• All engineering judgement calls made as part of
the design sequence must be clearly stated in the
assumptions part of the report.
Sketch of loadings on basement walls and
base
10
Two feasible options for basement
scheme (sketches or short description)
10
Overall assessment of Brief 10
References 10
Part (b) – Basement Design
Wall System Design
A design solution is required for the basement wall system. It must resist all loads applied to
the structure. The works may entail installing a temporary retention system to allow the
construction of the reinforced concrete basement. The design of any temporary (and
permanent) system must be such that it minimise movements in the adjacent ground. All
relevant soil information is detailed in Table 1 (Generic Log). The design shall conform to EC7
Part 1 and the Technical Authority overseeing the works have suggested a minimum
construction surcharge of 10kPa (Characteristic) shall be applied around the perimeter of the
site. Only design approach 1 combination 2 (DA1C2) shall be considered for the works design.
Basement Slab Design
Provide a structural design for a reinforced concrete slab at level -1. Two main loading cases
should be considered.
Remember to state any assumptions and make references to design codes used throughout
your design.
Checklist for structural design
• Calculation of moments & forces
• Equilibrium/flotation check
• Serviceability check – deflection checks only (ignore cracking – examined in
detail in CIV807)
• Slab design ULS uplift
• Slab design ULS down loads
• Basement wall design
• Summary of all reinforcement – a sketch would be best
80% of the coursework mark
Coursework consultation and discussion will take place at the tutorial classes at
12.15pm from week 3 to week 8, inclusive.
Ulster University
School of the Built Environment