Friday, August 26, 2011
Topic: Exploring the New Idea to Manage the Cost and the Time of Geotechnical Investigation Projects
Geotechnical investigations are performed to evaluate those geologic, seismologic, and soils conditions that affect the safety, cost effectiveness, design, and execution of a proposed engineering project.
Insufficient geotechnical investigations, faulty interpretation of results, or failure to portray results in a clearly understandable manner may contribute to inappropriate designs, delays in construction schedules, costly construction modifications, use of substandard borrow material, environmental damage to the site, post- construction remedial work, and even failure of a structure and subsequent litigation. Investigations performed to determine the geologic setting of the project include: the geologic, seismologic, and soil conditions that influence selection of the project site; the characteristics of the foundation soils and rocks; geotechnical conditions which influence project safety, design, and construction; critical geomorphic processes; and sources of construction materials. A close relationship exists between the geologic sciences and other physical sciences used in the determination of project environmental impact and mitigation of that impact. Those individuals performing geotechnical investigations are among the first to assess the physical setting of a project. Hence, senior-level, experienced personnel are required to plan and supervise the execution of a geotechnical investigation.
Geotechnical investigations are to be carried out by engineering geologists, geological engineers, geotechnical engineers, and geologists and civil engineers with education and experience in geotechnical investigations. Geologic conditions at a site are a major influence on the environmental impact and impact mitigation design, and therefore a primary portion of geotechnical investigations is to observe and report potential conditions relating to environmental impact. Factors influencing the selection of methods of investigation include:
a. Nature of subsurface materials and groundwater conditions.
b. Size of structure to be built or investigated.
c. Scope of the investigation, e.g., feasibility study, formulation of plans and specifications.
d. Purpose of the investigation, e.g., evaluate stability of existing structure, and design a new structure.
e. Complexity of site and structure.
f. Topographic constraints.
g. Difficulty of application.
h. Degree to which method disturbs the samples or surrounding grounds.
i. Budget constraints.
j. Time constraints.
k. Environment requirements/consequences
l. Political constraints.
Most investigators involved in geotechnical projects are faced with the problem of obtaining reliable data within a short time from an enormously complex subsurface medium at minimal cost.
Geotechnical engineering inevitably involves the use of engineering judgment and dealing rational with considerable uncertainty. At the time of designing as part of tender specifications, substantial difference between actual soil profiles and available soil profile is very important. Since time interval between issue of tender document and submission of technical bid is very short, we need to have an estimation of the allowable bearing capacity of soil. Soil investigation is very expensive. Engineering judgment comes from execution and experience comes from bad engineering judgment. Sometimes when we study Geotechnical reports, we perceive that there is the great mistake because the results of Triaxial(U.U) and Shear box(C.D) tests are too much less than the results of S.P.T tests. It can be raised due to below reason.
It seems that they have done Triaxial and Shear box tests on undisturbed samples collected from High Over Consolidation clay (H.O.C clay layers) and it have been caused that undisturbed samples are changed to disturbed samples in Laboratory(the allowable bearing capacity have been calculated in accordance with laboratory tests).
Goals and Objective
Throughout a project’s planning, design, and construction phases, Cost Management is employed as a means of balancing a project’s scope and expectations of quality and budget.
The approach can be summarized as requiring the following three steps:
1. Define the scope, the level of quality desired, and the budget
2. Ensure that the scope, quality, and budget are aligned
3. Monitor and manage the balance of these three components throughout the life of the project.
There are many objectives to conduct this research as follows:
-To identify the scope of geotechnical investigation program
-To analyze the influence of the loading on field investigation
-To optimize the plan for Geotechnical investigation. For instance, sometimes we have to increase the number of Boreholes or Test pits abnormally because of the huge fluctuation of soil profile whereas it is possible we gain the benefits to decrease the number of Boreholes by utilizing of data obtained from other field of study such as Geology, Geophysics, and Hydrogeology and so on.
One of the most crucial goals to decrease the cost and the time of Geotechnical investigation at this research is to use of a new idea or new strategy by mixing ASTM and DIN standards of SPT (Standard Penetration Test) in the field study. In fact, the variation can be minimized if standard practices are followed during the soil investigation.
Scope of Study
The limitation of this research is to prepare the data of soil for insensitive projects such as the buildings less than twenty floors in which we do not need to generate the exact mechanical characteristics of soil, low loading and where Allowable Bearing Capacity of soil is more than 1kg/cm2. For instance, shear strength parameters of soil such as Phi and C can be measured with error and decimal around 0.01 to 0.001 by using of Triaxial tests. But we are not urged to obtain these results for some of the projects while for designing of an earth dam, we should present these parameters with the least error and decimals. The meaning of this reality is the same the quality of designing. As an example, we can change Phi = 45.37 degree to the range of Phi = 32 -42 degree or instead of C = 0.278 kg/cm2, we consider C = 0.2 – 0.25 kg/cm2. Another limitation is related to total statistics result of correlation between ASTM and DIN standard penetration test because it is clear that we proceed to correlate two standards on page by using of energy balancing but we should experience the confirmation of this correlation at the site.
At the first, a geotechnical expert should be fully connected with structure engineer and architectural designer because of checking the types of loading, Code height, Benchmark, Layout and so on. I had an experience in the case of soft saturated clay by using of pre-cast concrete piles. Finally I understood we had the lack of Geophysics and Geology investigation before geotechnical investigation because there was different data from stratum in the distance of less than 5 meter between two points on the ground. In fact, Geomorphology of area was dendrite shape.
Braja M Das (2006) stated a soil exploration program for a given structure can be broadly divided into four phases:
1. Compilation of the existing information regarding the structure
2. Collection of existing information for the subsoil condition in which the useful information can be obtained from the following sources:
a. Geologic survey maps
b. Country soil survey maps prepared by the U.S. Department of Agriculture and the Soil Conservation Service
c. Soil manuals published by the state highway department
d. Existing soil exploration reports prepared for the construction of nearby structures
Information gathered from the preceding sources provides insight into the type of soil and problems that might be encountered during actual drilling operations.
3. Reconnaissance of the proposed construction site
4. Detailed site investigation
We have spacing of boring and the depth of Boreholes. In this research we will take a debate about them mentioned by Sowers (1970) and the American Society of Civil Engineers (1972) by utilizing the loading of construction and Bossinesq method and Vertical stress of soil layers.
On the other hand, Bowles (1996) mentioned that the standard penetration test, developed around 1927, is currently the most popular and economical means to obtain subsurface information (both on land and offshore). It is estimated that 85 to 90 percent of conventional foundation design in North and South America is made using the SPT. This test is also widely used in other geographic regions. The method has been standardized as ASTM D 1586 since 1958 with periodic revisions to date.
In this research, I am willing to present you how we should select and collect data and use them accompanied by mixed standards of DIN (Germany) and ASTM (USA) to manage a geotechnical investigation project in which we will have the minimum cost and time. In fact, the questions are: Do we actually need to do expensive laboratory tests such as three-axial, Sheer Box or Consolidation for all of the projects? What are the controlling factors to design a comprehensive program for field investigation and laboratory tests? I have brought here two samples which are real projects conducted in Iran.
Geotechnical Investigation Plan
Here are other sources for this research as follows:
ü Using of reference books such as Bowles and Braja M Das
ü Using of ASTM (American Standard)
ü Using of DIN (Germany Standard)
ü Using of Internet to collect secondary
ü Using of Actual projects fulfilled in Iran as sample
Significant of Research
The most important significant of this research is to examine a new idea as a strategy and applications of it to decrease the time and the cost of geotechnical projects.
In the matter of fact, this research have revealed the actual applications of the light hammer of DIN that it can used for SPT tests in which we had have cut-fill and have to recognize the boundaries of loose and hard soil at the site. Sometimes, we cannot use from heavy hammer of ASTM for SPT.
Data collection and analysis of discussion
Sometimes alluviums or loose fill (made-up gravel) have been laid unconformity on geology formations included: out crops, folded rock stratums that their geomorphology have been shown in shape of up and down (roughness).
Therefore the logs of two bore holes, which have very low distance between them, are not compatible together. It is possible, one of them encounter to rock layer in depth of 1m but another bore hole come in contact with this rock layer in depth of 10m.
One of the best ways to specify this problem is to use of German Light S.P.T equipment (DIN 4094). The specifications of this equipment are as follows:
D =22 mm Rod diameter
D*=35.6 mm Point diameter
a =60 degree Point angle
W = 10 kg Hammer mass
H = 50 cm Free falling height
A = 10 cm2 Point area
In this research I am willing to exchange number blows of DIN 4094 to ASTM-D1586 in accordance with energy equilibrium’s principle where we will be able to use all correlation Tables of SPT test (N) which are covered by ASTM -D 1586 . Two record samples, which are real projects conducted in Iran, exactly have been examined. The reasons behind to select these projects by me are as follows:
- Jahan project was only investigated by 5 Bore holes while the area of the site was about 400000 m2.Of course, 12 test pits with average depth of 1.1 m were excavated to confirm an Index layer. Maximum depth of Boreholes was equal to 15m.
- Khavar Dasht project was investigated by 6 test pits while the area of the site was only 1500 m2 exactly the opposite of Jahan project. There were 3 zones at the site and maximum depth of Boreholes was equal 10m. And so the cost and time for each status (ASTM method and DIN method) have been calculated and compared.
Finally, data collection and analysis of discussion are included as follows:
ü Using of the balance of energy to exchange the result of SPT by DIN method to SPT by ASTM method
ü Using of tables and graphs of ASTM method for the result of DIN method
ü To illustrate the method of SPT test by DIN in Test pits
ü Using of SPT results instead of Engineering Lab tests such as Three-axial or shear Box
ü To obtain Allowable Bearing Capacity of the soil
ü To calculate the cost and the time for at least two actual geotechnical projectReferences
1. American Association of State Highway and Transportation
Officials, 444 N. Capitol St., N.W., Washington, DC 20001.
2. American Society of Civil Engineers, New York, NY
Journal of Geotechnical Engineering Division (1974-)
Journal of Soil Mechanics and Foundation Division, ASCE
3. AASHTO (1990), Standard Specifications for Highway
Bridges, 14th ed., 420 pp.
4. Baguelin, F, et al. (1974), "Self-Boring Placement
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be available from Engineering Foundation, NY),
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Penetration Tests for Design Practice," Proc. 1st
ISOPT, vol. 1, pp. 263-296 (huge number of references
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Test Practice," 14th PSC, ASCE, pp. 949-967.
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Posted by Gholamreza Soleimani at 11:46 PM