Chapter 18 Subsoil Exploration Soil Substructure Interaction Lab

Chapter 18 Subsoil Exploration 연세대학교 지반공학연구실 Soil Substructure Interaction Lab.

Introduction Ø What is site investigation (SI)? • Site investigation (SI) or soil exploration is the process of gathering information, within practical limits, about the stratification (layers) and engineering properties of the soils underlying the proposed construction site. • The principal engineering properties of interest are the strength, deformation, and permeability characteristics. Borehole Drilling rig Layers Structure Site Investigation Ground Soil Substructure Interaction Lab.

Introduction Ø Why site investigation (SI)? • Many engineering failures could have been avoided if a proper site investigation had been carried out. The site has a sinkhole risk which might have been discovered in a proper site investigation Sinkhole Soil Substructure Interaction Lab.

Introduction Ø Why site investigation (SI)? • The success or failure of a foundation depends essentially on the reliability of the knowledge obtained from the site investigation. Sophisticated theories alone will not give a safe and sound design. Soil Substructure Interaction Lab.

Soil Substructure Interaction Lab.

시추방법 (a) 수직시추 (b) 경사시추 그림 2. 3 시추 방법 Soil Substructure Interaction Lab.

Subsoil Exploration ▶ The purpose of subsoil exploration include the following : 1. Determining the nature of soil at the site and its stratification 2. Obtaining disturbed and undisturbed soil samples for visual identification and appropriate laboratory test 3. Determining the depth and nature of bedrock, if and when encountered Soil Substructure Interaction Lab.

Subsoil Exploration 4. Performing some in situ field test, such as permeability tests (Chapter 5), vane shear tests (Chapter 9), and standard penetration tests 5. Observing drainage conditions from and into the site 6. Assessing any special construction problems with respect to the existing structure (s) nearby 7. Determining the position of the water table Soil Substructure Interaction Lab.

18. 1 Planning for Soil Exploration ▶ A soil exploration program : 1. Compilation of the existing information regarding the structure 2. Collection of existing information for the subsoil condition – Geologic survey maps – County soil survey maps prepared by the U. S. Department of Agriculture and the Soil Conservation Service Soil Substructure Interaction Lab.

18. 1 Planning for Soil Exploration – Soil manuals published by the state highway department – Existing soil exploration reports prepared for the construction of nearby structure 3. Reconnaissance of the proposed construction site 4. Detailed site investigation Soil Substructure Interaction Lab.

Ø Why planning? • How many borings do we need? • How deep the borings should be? Borehole The more the better, but what about the cost? Soil Substructure Interaction Lab.

Ø Why planning? Planning for site investigation is required to: • Minimize cost of explorations and yet give reliable data. • Decide on minimum depth and spacing of exploration. Depth of Borehole • Decide on quantity and quality depending on type, size and importance of project and whether investigation is preliminary or detailed. Borehole Spacing Soil Substructure Interaction Lab.

Ø Depth of investigation • The estimated depths can be changed during the drilling operation, depending on the subsoil encoun tered. • To determine the approximate minimum depth of boring, engineers may use the following rules: Depth of Borehole • In general, depth of investigation should be such that any/all strata that are likely to experience settlement or failure due to loading. Soil Substructure Interaction Lab.

Ø Depth of investigation Determination of the minimum depth of boring 1. Determine the net increase of stress, under a foundation with depth as shown in the Figure. 2. Estimate the variation of the vertical effective stress, ‘ 0 , with depth. 3. Determine the depth, D = D 1, at which the stress increase ’ is equal to (1/10) q (q = estimated net stress on the foundation). 4. Determine the depth, D = D 2, at which ’/ '0 = 0. 05. 5. Unless bedrock is encountered, the smaller of the two depths, D 1 and D 2, is the approximate minimum depth of boring required. q D ’ 0 ’ Soil Substructure Interaction Lab.

18. 1 Planning for Soil Exploration Guidelines for initial planning of borehole spacing Soil Substructure Interaction Lab.

18. 1 Planning for Soil Exploration Sowers & Sowers (1970) provided a rough estimate of Min. depth of borings for multistory building ▶ Light steel or narrow concrete buildings (18. 1) S is the number of stories. ▶ Heavy steel or wide concrete buildings (18. 2) Soil Substructure Interaction Lab.

18. 2 Boring Methods ▶ The test boring can be advanced in the field by several methods : • • Use of augers (Fig 18. 1) Rotary drilling Wash boring (Fig 18. 4) Percussion drilling Soil Substructure Interaction Lab.

18. 2 Boring Methods Soil Substructure Interaction Lab.

Boreholes Auger Boring • This is the simplest of the methods. Hand operated or power driven augers may be used. Power driven augers • Suitable in all soils above GWT but only in cohesive soil below GWT. Hand operated augers Post hole auger Helical auger Soil Substructure Interaction Lab.

18. 2 Boring Methods Soil Substructure Interaction Lab.

18. 2 Boring Methods Soil Substructure Interaction Lab.

18. 2 Boring Methods Soil Substructure Interaction Lab.

Boreholes Rotary Drilling • In this method a rapidly retaining drilling bit (attached to a drilling rod) cut the soil and advance the borehole. • When soil sample is needed the drilling rod is raised and the drilling bit is replaced by a sampler. • This method is suitable for soil and rock. Movement transmitter Rotary Head Drilling rod Drilling bit Soil Substructure Interaction Lab.

18. 2 Boring Methods Wash boring Soil Substructure Interaction Lab.

18. 3 Common Sampling Methods ▶ Methods of sample collection : • Sampling by Standard Split Spoon (Fig 18. 5, Fig 18. 6~7) • Sampling by Thin Wall Tube (Fig 18. 8) • Sampling by Piston Sampler (Fig 18. 9) Soil Substructure Interaction Lab.

18. 3 Common Sampling Methods Split-spoon sampler Soil Substructure Interaction Lab.

18. 3 Common Sampling Methods Soil Substructure Interaction Lab.

Soil sampling Disturbed vs Undisturbed • Two types of soil samples can be obtained during sampling: disturbed and undisturbed. • The most important engineering properties required for foundation design are strength, compressibility, and permeability. These tests require undisturbed samples. • Disturbed samples can be used for determining other properties such as Moisture content, Classification & Grain size analysis, Specific Gravity, and Plasticity Limits. Soil Substructure Interaction Lab.

18. 3 Common Sampling Methods Thin-wall tube Soil Substructure Interaction Lab.

18. 3 Common Sampling Methods Piston sampler Soil Substructure Interaction Lab.

18. 4 Sample Disturbance ▶ The degree of disturbance of the sample ; area ratio, (18. 6) where outside diameter of the sampler inside diameter of the sampler ▶ A soil sample can generally be considered undisturbed if the area ratio is less than or equal to 10% Soil Substructure Interaction Lab.

18. 4 Sample Disturbance ▶ Standard split-spoon sampler : ▶ Shelby tube sampler : Soil Substructure Interaction Lab.

표준관입시험 (SPT) 시험장비 시험전경 Soil Substructure Interaction Lab.

표준관입시험 (SPT) 그림 2. 15 표준관입시험의 모식도 Soil Substructure Interaction Lab.

표준관입시험 (SPT; Standard Penetration Test) N치의 보정 (구조물 기초설계기준, 2009) Soil Substructure Interaction Lab.

18. 5 Correlations for Standard Penetration Test ▶ The unconfined compression strength of clay soils can be approximately correlated to the standard penetration number, N Soil Substructure Interaction Lab.

18. 5 Correlations for Standard Penetration Test ▶ For clays of a given geology, a reasonable correlation between can be obtained Soil Substructure Interaction Lab.

18. 5 Correlations for Standard Penetration Test ▶ Note that the notation is the atmospheric pressure (in the same unit as ) ▶ Based on data shown in Fig 17. 9, the reported regression (17. 8) Soil Substructure Interaction Lab.

18. 5 Correlations for Standard Penetration Test ▶ Empirical relationships has proposed to convert to a standard effective overburden pressure of (17. 9) where corrected standard penetration number correction factor field standard penetration number Soil Substructure Interaction Lab.

18. 5 Correlations for Standard Penetration Test ▶ Correlation of Liao and Whitman (1986) (SI unit) (18. 10) where effective overburden pressure in ▶ Correlation of Skempton (1986) (SI unit) (18. 12) ▶ Correlation between and Soil Substructure Interaction Lab.

18. 5 Correlations for Standard Penetration Test Soil Substructure Interaction Lab.

18. 5 Correlations for Standard Penetration Test Cubrinovski and Ishihara (1999) (18. 14) ▶ The angle of friction of granular soils, has been correlated to the standard penetration number (Peck, Hanson, and Thornburn) (deg) (18. 15) Soil Substructure Interaction Lab.

18. 5 Correlations for Standard Penetration Test ▶ Kulhawy and Mayne (1990) provided a correlation for versus (18. 16) Example 18. 1 18. 2 18. 3 Soil Substructure Interaction Lab.

콘관입시험 (CPT) *전기 마찰콘관입시험기 (ASTM, 1992) *역학적 마찰콘관입시험기 (ASTM, 1992) Soil Substructure Interaction Lab.

현장베인전단시험 그림 2. 24 현장베인전단시험 Soil Substructure Interaction Lab.

공내재하시험 (a) PMT (b) DMT 그림 2. 25 딜라토미터 시험기 Soil Substructure Interaction Lab.

18. 6 Other In Situ Tests ▶ Vane Shear Test (see Chapter 11) ▶ Borehole Pressure Meter Test Soil Substructure Interaction Lab.

18. 6 Other In Situ Tests Soil Substructure Interaction Lab.

18. 6 Other In Situ Tests ▶ For the pseudoelastic zone (18. 17) where modulus of elasticity of soil Poisson’s ratio Cell volume corresponding to pressure (that is, the cell pressure corresponding to the beginning of zoneⅡ) Slope of straight-line plot of zoneⅡ (18. 18) Soil Substructure Interaction Lab.

18. 6 Other In Situ Tests ▶ Relationship between the (18. 19) where shear modulus of soil (18. 20) ▶ The at-rest earth pressure coefficient, (18. 21) where, represents the in situ lateral pressure Soil Substructure Interaction Lab.

18. 6 Other In Situ Tests ▶ Cone Penetration Test Soil Substructure Interaction Lab.

18. 6 Other In Situ Tests ▶The relationship between and can be approximated (after Kulhawy and Mayne, 1990) as (18. 22) ▶ Schmertmann (1970) gave a simple correlation for sand as ; (18. 23) Soil Substructure Interaction Lab.

18. 6 Other In Situ Tests ▶ Trofimenkov (1974) gave correlations for modulus in sand & clay ; (for sands) (18. 24) (for clays) (18. 25) Soil Substructure Interaction Lab.

18. 7 Rock Coring ▶ It may be necessary to core rock if bedrock is encountered at a certain depth during drilling. ▶ It is always desirable that coring be done for at least 3 m. Soil Substructure Interaction Lab.

Rock Sampling (Coring) Rock samples are called “rock cores”, and they are necessary if the soundness of the rock is to be established. • Core drilling equipment? • Core recovery parameters? Soil Substructure Interaction Lab.

18. 7 Rock Coring Soil Substructure Interaction Lab.

Rock Sampling (Coring) Core drilling equipment • Assuming the following pieces for a given core run: Rr Recovery Ratio, Rr Core recovery (lengths of intact pieces of core) (Core run) Rock Quality Designation, RQD 10 = (Core run) S Li L 100% ( L i ≥ 10 cm ) Soil Substructure Interaction Lab.

18. 7 Rock Coring Soil Substructure Interaction Lab.

18. 7 Rock Coring Soil Substructure Interaction Lab.

18. 8 Soil Exploration Report ▶ Exploration report : 1. Scope of investigation 2. General description of the proposed structure for which the exploration has been conducted 3. Geologic conditions of the site 4. Drainage facilities at the site 5. Details of boring 6. Description of subsoil conditions as determined from the soil and rock samples collected 7. Groundwater table as observed from the boreholes 8. Details of foundation recommendations and alternatives 9. Any anticipated construction problems 10. Limitations of the investigation Soil Substructure Interaction Lab.

Ø Preparation of Boring Logs Initial information: Name and address of the drilling company, Driller’s name, Job description and reference number, boring information (number, type, and location of, and date of boring) Example of a typical boring log Soil Substructure Interaction Lab.

Ø Preparation of Boring Logs Subsurface stratification: which can be obtained by visual observation of the soil brought out by auger, splitspoon sampler, and thinwalled Shelby tube sampler. Groundwater: Elevation of water table and date observed, use of casing and mud losses, and so on Soil Substructure Interaction Lab.

Ø Preparation of Boring Logs In-situ tests: Standard penetration resistance and the depth of SPT Samples: Number, type, and depth of soil sample collected; in case of rock coring, type of core barrel used and, for each run, the actual length of coring, length of core recovery, and RQD. Soil Substructure Interaction Lab.

18. 8 Soil Exploration Report ▶ Graphic presentation also need to be attached to the soil exploration report ; 1. Site location map 2. Location of borings with respect to the proposed structure 3. Boring logs 4. Laboratory test results 5. Other special presentations Soil Substructure Interaction Lab.

Ø Site Investigation Report Geotechnical cross section based on the boring logs Soil Substructure Interaction Lab.