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Soils and their Implications to Development
Transcript of Soils and their Implications to Development
The CPD aims to show clients what characteristics and conclusions can be drawn from even basic knowledge of the soils present at a site and how to get that data
* from a clients
Q. What is Geotechnical Investigation?
Team Exercise 1
As a group - choose someone to fill in your answer sheet
Say hello to your Geosphere representative
Answer the questions
Scores will be checked and the winning team will get prizes!
Soils and the Implications t Development
A. Obtaining data about earth materials
Q. How do you Investigate (i.e. get the data)?
A. From Desk based sources and physical intrusive siteworks
Q. What kind of data do you obtain?
A. Engineering properties of earth materials
Q. What do we use the data for?
A. Developing predictions of how the earth will interact with proposals
The Earth interacts with anything that is put on top of it
2 key words to be aware of......
Prediction means results are interpreted and a factor of safety (conservativeness?) added.
What is an acceptable risk and what is unacceptable?
That interaction needs to be mitigated against
Q. Where do Geotechnical Investigations Fit?
There is a lot of cross over between GEO and ENVIRO so they are worth doing at the same time:
Nearby or historic planning condition data
Made Ground depth
Confirmation of anticipated geology
Window Sampling / Trial Pitting
SOURCES - FREE ON INTERNET*
Cable / Rotary Boreholes
Confined / unconfined
Flow, gradient, soakage
All - shallow / deep / desk
Roll up your sleeves - to start understanding geotechnical issues we need to have idea about:
Team Exercise 2
Geology focuses on ROCKS
What are the three main rock types?
IGNEOUS - volcanic
SEDIMENTARY - deposition
METAMORPHIC - altered
Which are we concerned with in this part of the country?
- so get rid of 90% of all geology
Now we have got rid of most geology - sedimentary soils can be split in to three main groups - identify the main soil component of the samples provided.
Team Exercise 2
How does the detailed information on soils we find get back to client within our reports?
These form the basis of our interpretation - they tell us what testing we will do and how we will adjust our assessment of how soils and structures interact.
PART B - ENGINEERING LOGS
They are produced to a set of rules - BS:5930, and its one of the first things you learn as a consultant.
With you Geosphere Representative as a guide - look at the samples, and classify them roughly using BS:5930.
Only columns 1 to 3 and 9 need to be identified.
Team Exercise 2
Now in groups see if you can identify the primary and secondary components of Sample D.
Desk Based Sources
The BGS will tell you what kind of geology to expect at any particular area - it is a digitized geology map of the UK. It is free to use and a great resource:
Team Exercise 3
In groups, using the BGS data, supervised by your Geosphere Representative - find the anticipated geology for the three sample sites.
SITE A - SUPERFICIAL - Split between RTD and Peat
BEDROCK - Newhaven Chalk Formation
SAMPLE A - Dark orange brown slightly gravelly slightly silty medium to coarse SAND.
RESULT : ????????????????????
SITE B - SUPERFICIAL - None
BEDROCK - London Clay Formation
SITE C - SUPERFICIAL - Kesgrave
BEDROCK - Red Crag Formation
How do you apply this knowledge?
You can look at the anticipated geology for a site at early stages of the project
Superficial and bedrock or just bedrock?
You know what you are expecting in relation to any investigation you have done.
You can even do this in the field on your own sites at any stage of a project.
Team Exercise 4
You are looking for some basic geological information for the Brightwell Barns Estate complex in preparation for additional development. The development is a low rise residential property with low loadings.
Answer the questions then complete the practical.
Q1 - Investigation type - SHALLOW
What does all this data MEAN? and how does any of what you have said benefit me?
Thats all well and good but for the real money shot lets answer one more question - cast your mind back to samples A, B and C.
One of these is the odd one out - Which?
Sample B is the odd one out as it is cohesive and rather than granular.
If the geology is complicated you have to spend more money than if it is uncomplicated. A t the front end how much would you expect a geotechnical testing (laboratory analysis) budget vary between a simple and complicated site?
Simple - £300 / Complicated - £1000+
It will also help identify if the scope of investigation proposed is sufficient or in many cases scoped by non-specialists - over the top.
Small site - £2k / Large Site - £20k
To cut all the jargon and simplify foundation design to its most basic elements:
The more cohesive the underlying soils, the greater the interaction overlying structure.
This increased interaction (system complexity) means that more conservative predictions are made and more stringent (expensive) foundations solutions are recommended based on anticipated risk.
The reason for this is due to the wide range in physical variations that cohesive (clay) soils can exhibit - for example:
Cohesive soils can.........?
......be soft or extremely stiff
....dessicated (dry) or saturated
...have internal structures (fissures, lenses).....
..........expand and contract...........
.....shear and tear..........
......move and flow................
......have an aggressive chemical environment........
The other big variable......
What is the other issue that will affect shallow or deep soils?
The presence and depth of groundwater will also largely affect foundation design.
How does groundwater affect soils?
...destabilization of overlying strata......
Soils affect the development of a site based on the COMPLEXITY of INTERACTIONS with proposed plan.
This is PREDICTED based on DESK BASED and GEOTECHNICAL INVESTIGATIVE data.
The scale of GEOTECHNICAL INVESTIGATION is determined by the proposals and soil type - it is also an ITERATIVE process.
In general, the presence of COHESIVE soils and GROUNDWATER increase the COST, TYPE and SCALE of foundations for any particular proposal.
This can be prepared for at very EARLY stages of the development process with MINIMAL KNOWLEDGE as we have shown in this course.
For your time.
We will thank you even more for work supplied.
Please consider us when you next require any of the services we provide.
We are going to jump ahead a little to the practical site of geotechnical investigation.......
you don't even necessarily need to get your hands dirty.......
Q5 - Primary and Secondary soil components noted.
Q4 - Sample of natural soils required - not topsoil or Made Ground
Q3 - Expecting to find - Sand and Gravels
Q2 - Investigation Method - window sampling / trial pitting
SAMPLE C - Well graded poorly sorted fine to coarse angular to sub-rounded GRAVEL
SAMPLE B - Stiff brown grey mottled slightly silty slightly sandy slightly gravelly fissured CLAY.
Lets also find out what the scores were so we can identify the winning team!