Advanced Foundation Engineering. Introduction

Transcription

1 Shahrood University of Technology Department of Geotechnical Engineering Advanced Foundation Engineering Introduction Mohsen Keramati, Ph.D. Assistant Professor 1

2 - Detailed Course Plan Introduction (Geotechnical Properties of Soil) Soil Exploration (Penetration & Geophysics) Shallow Foundation (Bearing Capacity, Settlement & Design) Deep Foundation Well Foundation & Retaining wall Sheet pile Reinforced Earth Reinforced Retaining wall Seismic Design of Retaining wall Slope Stability Soil-Foundation Interaction Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 2

3 - Refrences Principles of Foundation Engineering, Braja M. Das, Eighth Edition Foundation Analysis and Design, Bowles, J, McGraw Hill Book Company Fundamentals of Soil Dynamics, Braja M. Das. Elsevier, New York, USA Geotechnical Earthquake Engineering, Kramer, SL. Pearson Education (Singapore) Pvt. Ltd., Indian Branch, New Delhi, India, Foundation Design Principles and Practices, D. P. Coduto, 2nd ed, Foundations and Earth Retaining Structure, M. Budhu, December 26, Soil Strength and Slope Stability, J. Michael Duncan Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 3

4 - Student evaluation 15%: Classroom practices. 15%: Project. 70%: Final Exam. Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 4

5 - The design of foundations generally requires a knowledge of factors as: The load that is coming on the foundation. The requirements of the local building code. The behavior of soil that will support the foundation system. The Geological condition of the soil. Foundation engineering is a clever combination of soil mechanics, engineering geology, and proper judgment derived from past experience. Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 5

6 - Geotechnical properties of soil Grain-size distribution. Plasticity. Soil classification. Hydraulic conductivity. Effective stress. Consolidation. Shear strength parameters. Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 6

7 - Grain-Size Distribution Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 7

8 - Grain-Size Distribution Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 8

9 - Grain-Size Distribution Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 9

10 - Weight Volume Relationships Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 10

11 - Weight Volume Relationships Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 11

12 - Relative Density In granular soils, the degree of compaction in the field can be measured according to the relative density, defined as: Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 12

13 - Relative Density Cubrinovski and Ishihara (2002) studied the variation of e max and e min for a very large number of soils. Based on the best-fit linear regression lines: Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 13

14 - Atterberg Limits When a clayey soil is mixed with an excessive amount of water, it may flow like a semiliquid. If the soil is gradually dried, it will behave like a plastic, semisolid, or solid material, depending on its moisture content. Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 14

15 - Liquidity Index The in situ moisture content for a sensitive clay may be greater than the liquid limit. In this case, LI >1 These soils, when remolded, can be transformed into a viscous form to flow like a liquid. Soil deposits that are heavily overconsolidated may have a natural moisture content less than the plastic limit. In this case, LI <0 Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 15

16 - Activity Skempton (1953) observed that the plasticity index of a soil increases linearly with the percentage of clay-size fraction (% finer than 2 m by weight) present. Activity is used as an index for identifying the swelling potential of clay soils. Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 16

17 - Soil Classification Systems (Unified) Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 17

18 - Soil Classification Systems (Unified) Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 18

19 - Hydraulic Conductivity of Soil Darcy (1856) proposed the following equation for calculating the velocity of flow of water through a soil: Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 19

20 - Hydraulic Conductivity of Soil In the laboratory, the hydraulic conductivity can be determined by: Constant-head method (more suitable for granular soils) falling-head permeability test method (suitable for soils such as fine sands and silts) Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 20

21 - Effective Stress The total stress at a given point in a soil mass can be expressed as: The effective stress, is the vertical component of forces at solid-to-solid contact points over a unit cross-sectional area. Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 21

22 - Effective Stress where i cr = critical hydraulic gradient. For most sandy soils, i cr ranges from 0.9 to 1.1, with an average of about unity. Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 22

23 - Consolidation In the field, when the stress on a saturated clay layer is increased for example, by the construction of a foundation the pore water pressure in the clay will increase. Because the hydraulic conductivity of clays is very small, some time will be required for the excess pore water pressure to dissipate and the increase in stress to be transferred to the soil skeleton.. Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 23

24 - Consolidation Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 24

25 - Consolidation Skempton (1944) gave an empirical correlation for the compression index in which: Rendon-Herrero (1983) Nagaraj and Murty (1985) Park and Koumoto (2004) Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 25

26 - Consolidation The swelling index is also referred to as the recompression index. In most cases, the value of the swelling index is 1 4 to 1 5 of the compression index. Following are some representative values of Cs/Cc for natural soil deposits: Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 26

27 - Consolidation The one-dimensional primary consolidation settlement (caused by an additional load) of a clay layer having a thickness Hc may be calculated as : Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 27

28 - Shear Strength The shear strength of a soil, defined in terms of effective stress, is The value of c for sands and normally consolidated clays is equal to zero. For overconsolidated clays, c > 0. Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 28

29 - Shear Strength Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 29

30 - Shear Strength Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 30

31 - Shear Strength Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 31

32 - Shear Strength Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 32

33 - Shear Strength Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 33

34 - Sensitivity For many naturally deposited clay soils, the unconfined compression strength is much less when the soils are tested after remolding without any change in the moisture content. This property of clay soil is called sensitivity. The sensitivity ratio of most clays ranges from about 1 to 8; highly flocculent marine clay deposits may have sensitivity ratios ranging from about 10 to 80. Some clays turn to viscous liquids upon remolding, and these clays are referred to as quick clays. The loss of strength of clay soils from remolding is caused primarily by the destruction of the clay particle structure that was developed during the original process of sedimentation. Mohsen Keramati, Ph.D., Department of Geotechnical Engineering, Shahrood University of Technology, 34