CHAPTER 2
SITE INVESTIGATION
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2.1 |
General Aspects of Site Investigation |
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2.2 |
Pre-investigation and Details of Investigation |
2.1 GENERAL ASPECTS OF SITE INVESTIGATION
In the planning, design and construction of GRS-RW, an investigation is conducted to cover the topology, geology, underground water, and environmental conditions of the site.
The individual items, details and procedure of investigation should be considered with reference to the type, scale and significance of a project.
The site investigation is conducted to obtain relevant information used for planning, design and construction of GRS-RW. The information is also used for subsequent maintenance and repair of GRS-RW.
2.2 PRE-INVESTIGATION AND DETAILS OF INVESTIGATION
The site investigation program is composed of the following items:
1. Pre-Investigation
a) Literature Review
b) Surveying
2. Site Investigation
a) Soil Foundation
b) Backfill Soil
c) Construction-Related Issues
The literature review and surveying give the topology, geology, soil conditions, etc., of the GRS-RW construction site. The potential construction problems are revealed. A detailed investigation of the site will be made upon careful studying of available information.
1. Pre-Investigation
a) Literature review
It allows brief information of the site to be obtained. The various types of information obtained during this stage allow a site investigation to be done smoothly after revealing potential construction problems. The information may be obtained from the topographical maps, geology maps, aerial photographs, previous reports of investigation, construction records, etc.
b) Surveying
Surveying is conducted mainly to confirm if the site situation is similar to that obtained from the literature. The topography, deformation of existing structures (settlement, cracking) and underground water conditions (water level, flow out) are some of the items to be looked into.
2. Site Investigation
Site investigation is conducted based on the results of pre-investigation.
a) Soil Foundation
Boring may have to be conducted to understand better the geological conditions of the foundation. The standard penetration test is used to obtain the strength of the foundation. The depth of investigation should be extended up to a firm soil layer that does not exhibit sign of instability, settlement and liquefaction. For the sites where potential problems have been revealed during pre-investigation, sounding, sampling and soil testing are required to obtain additional information. Table 2.1 gives the types of sounding under different soil conditions and Table 2.2 gives the related laboratory tests. Note that some of these devices may be common only to the Japanese practice.
Table 2.1 Types of Sounding
a. Standard Penetration Test
b. Large-Scale Dynamic Cone Penetration Test
c. Automatic Sounding
d. Cone Penetration Test
e. Double-Tube Cone Penetration Test
f. Swedish Sounding
g. Medium Dynamic Cone Penetration Test
h. Portable Cone Penetration Test
i. Vane Shear Test
Notations:
1: effective method
2: very effective method
a) Soft Soil Layer Underlying Sandy Soil Layer
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a |
b |
c |
d |
E |
f |
g |
h |
i |
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gravel sand layer (large gravel and stone) more than 3 m thick, N>30 |
1 |
1 |
1 |
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sand layer (coarse sand with gravel) more than 3 m thick, N>30 |
2 |
2 |
1 |
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sand layer (small gravel) more than 3 m thick, N=10~30 |
2 |
2 |
2 |
2 |
2 |
1 |
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sand layer (small gravel) less than 3 m thick, N=10~30 |
2 |
2 |
2 |
2 |
2 |
2 |
1 |
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b) Continuous Soft Clay Layer
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a |
b |
c |
d |
e |
f |
g |
h |
i |
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average N value between 2 to 4 |
1 |
1 |
2 |
2 |
2 |
2 |
2 |
1 |
1 |
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average N value between 1 to 2 |
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2 |
2 |
1 |
2 |
2 |
2 |
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N close to 0 (rammer settles by own weight) |
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1 |
1 |
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1 |
2 |
2 |
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N close to 0 (rod settles by own weight) |
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1 |
2 |
Table 2.2 Analysis and Related Soil Testing
Notations:
1: most frequently used
2: frequently used
3: used if necessary
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Stability |
Settlement |
Liquefaction |
Remarks* |
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Test to determine density |
1 |
1 |
2 |
JIS A 1202 |
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Test to determine water content |
1 |
1 |
2 |
JIS A 1203 |
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Tests to determine liquid and plastic limits |
1 |
1 |
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JIS A 1205 |
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Test to determine soil gradation |
1 |
1 |
1 |
JIS A 1204 |
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Test to determine fine contents |
2 |
2 |
1 |
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Tests to determine max and min relative density |
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1 |
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Test to determine bulk unit weight of soil |
1 |
1 |
1 |
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Unconfined compression test |
1 |
1 |
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JIS A 1216 |
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Triaxial compression test (consolidated undrained test) |
1 |
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Cyclic triaxial test |
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3 |
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Consolidation test |
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1 |
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JIS A 1217 |
* JIS is given here as reference. ASTM, BS or other standards may be considered as necessary.
b) Backfill Soil
The soil suggested for the GRS-RW construction should be tested in the laboratory. The relevant laboratory tests are given in Table 2.3. The judgment on applicability of the soil for construction is discussed in Chapter 4.
Table 2.3 Laboratory Tests for Backfill Soil
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Laboratory Test |
Testing Standard* |
Remarks |
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Test to determine water content |
JIS A 1203 |
natural state |
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Test to determine soil gradation |
JIS A 1204 |
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Tests to determine liquid and plastic limits |
JIS A 1205 |
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Test to determine unit weight |
JIS A 1214 |
natural state |
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Compaction test |
JIS A 1210 |
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Slacking test** |
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* The JIS is given here as reference. The ASTM, BS or other standards may be considered as necessary.
** For soft and fractured rock
3. Construction-Related Investigation
The investigations related to construction should be the items that may hinder the construction time. The following items are included in the investigation:
a) Soil topography and geology
b) Climatic conditions
c) Site conditions and land-use
d) Construction environment
e) Obstacles and buried structures