CHAPTER 1: SUB-STRUCTURE •
Lecture 1 - Soil investigations
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Lecture 2 - Choice of foundation in relation to soil condition
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Lecture 3 - Shallow foundations: pad, strip & raft
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Lecture 4 - Basic understanding of piling deep foundations
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Lecture 5 - Basement construction waterproofing
SOIL INVESTIGATION
SOIL INVESTIGATION •
A thorough & comprehensive SI is an essential preliminary to the design & construction of a civil engineering works.
•
The size & type of project will influence the scope of SI.
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SI needs to be completed prior to the design stage of a project.
OBJECTIVE 1.
To assess the general suitability of the site & environs for the proposed works.
2.
To enable an adequate, economic & safe design to be prepared, including the design of temporary works.
3.
To plan the best method of construction; to foresee & provide against difficulties & delays that may arise during construction due to ground conditions.
4.
To determine the changes that may arise in the ground, either naturally or as a result of the works; and the effect of such changes on the works, on adjacent works and on the environment in general.
5.
Where alternatives exist, to advise on the relative suitability of different sites, or different part of the same site.
SCOPE OF S.I
• • • • • •
Desk study Site reconnaissance (learn about the strength) Detailed site exploration & sampling Laboratory testing of samples In-situ testing Reporting results
DESK STUDY This is essentially the collection of a wide variety of information relating to the site. a)
Maps
b)
Drawings
c)
Details of existing & historic development
d)
Local Authority information
e)
Geological maps
f)
Detail of utilities & services
g)
Ownership of adjacent property
h)
Information (soil condition & structure) from adjacent projects
i)
Aerial photograph; etc.
SITE RECONNAISSANCE An early examination of the site by appropriate experts is most desirable; geologist, land surveyor, hydrologist etc. Information to be collected: a) Overall site layout b) Topography c) Basic geology d) Detail of access; etc. Local conditions to be examined: e) Climate f) Stream flows g) Groundwater conditions; etc.
DETAILED SITE EXPLORATION & SAMPLING a)
b) c) d) e) f)
Investigation of detailed geology & sub-surface soil conditions using surface survey, trial pits, boreholes, sounding etc. Survey of groundwater conditions over a significant period of time. Examination of existing & adjacent structures for sign of cracking or settlement. Location of underground structures & cavities Location of underground services Provision of samples for further examination & laboratory test.
LABORATORY TESTING OF SAMPLES
• • • • • •
Tests on samples submitted by the site team. Test on soils for classification, quality, permeability, shear strength, compressibility etc. Tests on rock cores & samples for strength and durability. Tests on constructional materials. Tests on groundwater. Chemical & petro graphic analyses.
REPORTING RESULTS SI report shall contains: 1. 2. 3. 4. 5. 6. 7. 8.
Detailed background of site (type of soil, groundwater level, contour, vegetation etc) – geological map Location of existing underground services Low & high tide (especially water front area) Site memoirs (flood, land slide etc) Soil classifications Points of sampling Analysis of soil conditions – soil bearing capacity Recommendations
METHODS OF S.I. MACKINTOSH TRIAL
PITS BOREHOLES
PROBE & HAND AUGER
MACKINTOSH
PROBE
Introduction:
Preliminary investigation Hammer weight = 5kg Drop height = 280mm Depth < 12m or 400 blows/300mm
Use:
Localised soft area or weak layer Determine hard layer or shallow bedrock Preliminary subsoil information Assist in interpolation between Boreholes
ď ś MACKINTOSH PROBE Limitations: Shallow depth (deeper depth in coarse materials give misleading results)
Human Errors are high: Varies in drop height or exerting force will give misleading results. Wrong counting, unless use mechanical counter
.
Precautions: Drop of hammer should be a free fall & consistent drop height Components & apparatus properly washed & oiled.
MACKINTOSH PROBE - Assembling
1/4
MACKINTOSH PROBE - Connection & Jointing
2/4
3/4
4/4
HAND AUGER
Usually use together with JKR probe.
To determine the type of soil & ground water.
More than 5 meter depth.
Limitation:
Disturbed sample often get mixed.
Limited use.
Link video
SOIL INVESTIGATION
TRIAL PITS
Safety Precautions: Stability of sides or slopes. Barricades if the pit needs to be left overnight for further testing. Backfill & compact properly after use.
Excavation of soil by using: Hand (Stone breaker & scoop) if less than 2m depth. Wheeled backhoe – 2m-4m depth. Hydraulic excavator – 4m-6m depth.
Use: Assessment of the shallow ground condition. Allow collection of bulk & block samples. Allow plate bearing test & JKR probe test inside the pit (In-situ Testing)
SOIL INVESTIGATION
TRIAL
PITS Temporary DHO Office
1.2 m
3m (max)
1.8m (Max. depth excavated) for Sample no. 1
– Bagh, Pakistan
TRIAL
PITS – Bagh, Pakistan
DEPTH : 0 TO 0.3 METER – SOFT WITH GRAVEL
TRIAL
PITS – Bagh, Pakistan
DEPTH: 0.3 TO 0.6 METER – SOFT WITH GRAVEL
TRIAL PITS – Bagh, Pakistan
DEPTH: 0.6 TO 0.9 METER
BOREHOLES Sometimes called DEEP BORING. The details of boring, sampling & testing are describe in BS 5930:1981 Borehole usually includes boring, sampling, in-situ testing & water table observation. Depth usually < 100m. Drill through all soils & hard core. The best method of SI. Two types of boreholes: Rotary Drilling By circulating fluid (water betonies or air foam). Most common method. Wash Boring (motorized hand boring) Utilises the percussive action of a chisel bit to break up materials & flush to the surface by water or drilling fluid pumping down the hollow drill rods
ď ś Rotary Drilling
WASH BORING
BOREHOLES
BOREHOLES
END OF LECTURE THANK YOU