- Lolita Misjune
Contents (Jump to)
Objectives of the site investigation
Benefits of a Desk Study and ground investigation
Introduction
The land on which development takes place has the fundamental influence on the behaviour of the structure which it supports and risks to which the future owners, users and occupiers will be exposed. The adequate investigation of any site is essential to the design of safe and economic foundations and to the detection of any contamination which may be present, with the associated responsibilities for control, protection or removal.
Objectives of the site investigation
- To find out if the site and environment are suitable for target it has been determined.
- To provide adequate economical and commercial requirements as well as temporary works design.
- Plan and investigate the best way of construction and what materials are necessary.
- Predict physical or chemical changes which may occur during work process in site.
- If there are several possible ways suggest best.
- Design ways which may cause failure.
Procedure
The sequence of a site investigation is as follows:
Planning
- Desk Study
- Site Reconnaissance/ Walk over survey
Desk study/Preliminary information
An important part in soil investigation is desk study. Collecting preliminary information is invaluable in assessing the requirements of a ground investigation for both environmental and geotechnical purposes. Well performed desk study helps in formulation of investigation work, pointing explicit places of contamination or geotechnical parameters. A well, executed desk study can help to formulate investigation work, targeting specific areas of contamination or geotechnical parameters, concluding in a cost effective and aimed investigation.
Site assessment
- Site inspection
- Ground investigation
- Preliminary ground investigation
- Assessment
- Main ground investigation
- Laboratory testing
Benefits of a Desk Study and ground investigation
- Mitigate/minimise risk
- Understanding of potential variations in ground conditions
- Can lead to economical design of foundations / geotechnical structures
- Reduce likelihood of unforeseen ground conditions
- Reduce chances of delays on site
- Quantify / qualify risk
- Accurate forecast of budgets
In ground investigation it is possible to design and conduct geotechnical and environmental investigation. Ground investigation work is conducted closely together with clients and engineering team to discuss and provide a cost effective program of exploratory work.
There is wide range of exploratory methods available for site ground investigation.
- Trial Pitting
- Window Sampling and Dynamic Probe Testing
- Cable Percussive Boreholes
- Rotary Drilled Boreholes
- Laboratory Testing
- Site work is followed by both geotechnical and chemical testing.
For ground investigation in given situation could be used Cable Percussive Boreholes.
These are appropriate for most projects. Cable percussive boreholes are a usual method of site investigation. This method offer a cost effective way of drilling within a range of soils varying from low strength alluvium to very stiff over consolidated clays, very weak to weak rock and dense granular soils. Cable percussive boreholes are also proficient of proceeding boreholes in different Made Ground soils, containing engineered fill and landfill materials where obstructions may come across. Using this method can be achieved 50m borehole.
Drilling and trial pitting are normally carried out for a number of reasons, such as:
- to establish the general nature of the strata below a site
- to establish the vertical or lateral variability of soil conditions
- verify the interpretation of geophysical surveys
- to obtain samples for laboratory testing
- to allow in situ tests to be carried out
- to install instruments such as piezometers, or extensometers.
In-situ test
That testing is valuable for soil property information, gaging groundwater pressure, gathering moisture content data and other important data points.
In-situ soil testing can be done in a variety of different ways. Depending on place and aim of analysis each test has its own benefit. That is very important for cost effectiveness and data preciseness to determine what test is appropriate for you.
In the UK in situ testing is carried out when:
- Good quality sampling is impossible (for example, in granular soils, in fractured rock masses, in very soft or sensitive clays, or in stoney soils)
- the parameter required cannot be obtained from laboratory tests (for example, in situ horizontal stress);
- when in situ tests are cheap and quick, relative to the process of sampling and laboratory testing (for example, the use of the SPT in London clay, to determine undrained shear strength); and most importantly,
- for profiling and classification of soils (for example, with the cone test, or with dynamic penetration tests).
Options for In-Situ Soil Testing Procedures
- Astandard penetration test
- Acone penetration test
- A piezocone penetrometer probe
- A flat plate dilatometer test
Etc.
Cone penetration test
However, the most precise anddetailed in-situ soil testing for determining a wide variety of technical data is Cone Penetration Testing (CPT), for this reason I would carry on this test in given situation.
This test is dynamic, cost effective and has been broadly accepted as a simplified solution that provides useful information.
Laboratory testing
Laboratory testing is part of the physical survey. As an essential part of site investigation, the need for laboratory tests will often dictate the type and frequency of sample to be taken, and will therefore control the method of forming boreholes
In laboratories can be done wide variety of tests which can`t be done in site, however economical side of investigation has an important role. For example more complex tests require a longer testing time and for reasons of time and economy these tests are carried in laboratories. During test can be measured both – direct properties of soil or “index properties” used to deliver useful information about the soil without taking any direct measurements of property.
Laboratory tests are such as
- Atterberg limits
- California bearing ratio
- Hydraulic conductivity tests
- Expansion Index test
- etc
In given example one used was falling head permeameter test, from results of that were calculated hydraulic conductivity and permeability cofficient.
Calculations
After performing permeameter test in order to find the vertical permeability of the sand were calculated coefficient of permeability and hydraulic conductivity.
L: the height of the soil sample column A: the sample cross section a: the cross section of the standpipe Δt: the recorded time for the water column to flow though the sample h1= hydraulic head on specimen at time t1, cm,
h2= hydraulic head on specimen at time t2, cm
Nd: number of potential drops
Nf: number of flow channels
Nd=11-1=10
Nf=3*2=6
Soil profile
In soil science and assessment key concept is soil profile. Knowing soil profile helps to investigate processes that have taken in soil development, assess soil features and types of soil which appear and is foundation for their classification.
Scientists have developed methods to define the various components and characteristics of the soil profile. Soil profile helps to predict how the soil might be used By using common terminology, soil profile descriptions are valuable for deciding how the soil might be used and/or predicting how the soil might react to its intended use.
Soil profiles, a more scientific test, evaluate three critical aspects of the soil that may have the potential to cause an on-site sewage system to malfunction. The texture of soil in area of the proposed on-site sewage system The presence or absence of water saturated soils The depth to an impervious soil layer (rock) All three parameters are used to design the most appropriate on-site system for your property.
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Bag samples of the predominant soil types encountered shall be collected from selected soil profile borings to provide specimens for engineering classification, moisture-density (standard or modified Proctor), and California bearing ratio (CBR) testing. These samples also consist of soil cuttings generated by the augering process. Care should be exercised not to combine different soil types for the same bag sample. Samples that will be used for a combination of classification, moisture-density, and CBR testing shall be a minimum of 50 pounds.
One of methods of determining soil profile is cone penetration method. CPT truck is fast and low-cost method to conduct subsurface examination. Results are available directly, allowing on the fly mapping of stratigraphy and other subsurface features.
A CPT sounding is made by pushing a small probe into the ground. Typically, a 3.6-centimeter-diameter probe (cone) is pushed into the ground to depths ranging from 15 to 30 meters. The cone is advanced downward at a constant velocity of 2 centimeters per second, using hydraulic rams that apply the full 23-ton weight of the CPT truck to push the probe rods to depth. In typical CPT soundings, the resistance to penetration is measured. Continuous measurements are made of the resistance to penetration of the tip and the frictional sliding resistance of the sleeve of the cone.
Report
- Preliminary report or feasibility study
- Planning of main Preliminary report
- Financial report (Return of investment)
- Final report
Lolita Misjune
March 2015
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