Geotechnical Engineering Design
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"As such, this book is likely to be retained and well thumbed by a student well into their first few years in industry." (The Structural Engineer, 1 February 2016)More details
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Preface xi
About the Authors xiii
About the Companion Website xv
1. Introduction to Engineering Geology 1
1.1 Introduction 1
1.2 Structure of the Earth and geologic time 1
1.3 Formation and classification of rocks 2
1.3.1 Igneous rocks 3
1.3.2 Sedimentary rocks 3
1.3.3 Metamorphic rocks 4
1.4 Engineering properties and behaviors of rocks 4
1.4.1 Geotechnical properties of rocks 4
1.4.2 Comparison of the three types of rocks 6
1.5 Formation and classification of soils 6
1.5.1 Soils formation 6
1.5.2 Soil types 7
1.5.3 Residual and transported soils 8
1.6 Maps used in engineering geology 9
1.6.1 Topographic maps 9
1.6.2 Geologic map 9
Homework Problems 12
References 14
2. Geotechnical Subsurface Exploration 15
2.1 Framework of subsoil exploration 15
2.2 Field drilling and sampling 15
2.2.1 Information required before drilling and sampling 15
2.2.2 Drill rigs 17
2.2.3 Drilling methods and augers 17
2.2.4 Soil sampling methods 23
2.3 Geotechnical boring log 29
2.4 In situ field testing 29
2.4.1 Standard penetration test (SPT) 29
2.4.2 Cone penetration test (CPT) 34
2.4.3 Vane shear test 35
2.4.4 Flat plate dilatometer test 36
2.4.5 Inclinometer test 37
2.4.6 Groundwater monitoring well 38
2.5 Subsurface investigations using geophysical techniques 39
2.5.1 Ground penetration radar (GPR) 40
2.5.2 Electromagnetics in frequency domain and in time domain 42
2.5.3 Electrical resistivity imaging 44
2.5.4 Microgravity 45
2.5.5 Seismic refraction and seismic reflection 45
2.6 Geotechnical investigation report 48
2.6.1 Site reconnaissance and description 48
2.6.2 Subsurface exploration (field exploration) 49
2.6.3 Laboratory testing 50
2.6.4 Geotechnical engineering recommendations 50
2.6.5 Appendix 51
Homework Problems 51
References 56
3. Shallow Foundation Design 57
3.1 Introduction to foundation design 57
3.2 Bearing capacity of shallow foundations 59
3.2.1 Failure modes of shallow foundations 60
3.2.2 Terzaghi's bearing capacity theory 61
3.2.3 The general bearing capacity theory 64
3.2.4 Effect of groundwater on ultimate bearing capacity 67
3.2.5 Foundation design approach based on allowable bearing capacity and the global factor of safety approach 69
3.2.6 Foundation design approach based on allowable bearing capacity and the partial factor of safety approach 71
3.2.7 Bearing capacity of eccentrically loaded shallow foundations 81
3.2.8 Mat foundations 90
3.3 Settlements of shallow foundations 92
3.3.1 Vertical stress increase due to external load 92
3.3.2 Elastic settlement 98
3.3.3 Consolidation settlement 103
Homework Problems 108
References 116
4. Introduction to Deep Foundation Design 118
4.1 Introduction to deep foundations 118
4.1.1 Needs for deep foundation 118
4.1.2 Foundation types 118
4.1.3 Driven pile foundation design and construction process 118
4.2 Pile load transfer mechanisms and factor of safety 120
4.3 Static bearing capacity of a single pile 123
4.3.1 Nordlund method, for cohesionless soil 123
4.3.2 a-method, for undrained cohesive soil 130
4.3.3 ß-method, for drained cohesionless and cohesive soils 134
4.3.4 Bearing capacity (resistance) on the basis of the results of static load tests 137
4.4 Vertical bearing capacity of pile groups 139
4.5 Settlement of pile groups 144
4.5.1 Elastic compression of piles 145
4.5.2 Empirical equations for pile group settlement using field penetration data 145
4.5.3 Consolidation settlement of a pile group in saturated cohesive soil 145
Homework Problems 150
References 152
5. Slope Stability Analyses and Stabilization Measures 154
5.1 Introduction 154
5.2 Overview of slope stability analyses 156
5.3 Slope stability analyses - infinite slope methods 159
5.3.1 Dry slopes 159
5.3.2 Submerged slopes with no seepage 160
5.3.3 Submerged slopes with seepage parallel to the slope face 161
5.4 Slope stability analyses - Culmann's method for planar failure surfaces 163
5.5 Slope stability analyses - curved failure surfaces 168
5.5.1 Undrained clay slope (f = 0) 168
5.5.2 c - f soil (both c and f are not zero) 171
5.6 Slope stability analyses - methods of slices 173
5.6.1 Ordinary method of slices (Fellenius method of slices) 173
5.6.2 Bishop's modified method of slices 178
5.7 Slope stability analyses - consideration of pore water pressure 181
5.7.1 Bishop-Morgenstern method 181
5.7.2 Spencer charts 189
5.7.3 Michalowski charts 193
5.8 Morgenstern charts for rapid drawdown 194
5.9 Averaging unit weights and shear strengths in stratified slopes 198
5.10 Slope stability analyses - finite element methods 199
5.11 Slope stabilization measures 200
5.11.1 Surface drainage 201
5.11.2 Internal drainage 201
5.11.3 Unloading 202
5.11.4 Buttress and berm 204
5.11.5 Slope reinforcements 204
5.11.6 Soil retaining walls 206
Homework Problems 207
References 211
6. Filtration, Drainage, Dewatering, and Erosion Control 212
6.1 Basics of saturated flow in porous media 212
6.2 Filtration methods and design 214
6.3 Dewatering and drainage 217
6.3.1 Open pumping 218
6.3.2 Well points 218
6.3.3 Deep wells 219
6.3.4 Vacuum dewatering 220
6.3.5 Electroosmosis 220
6.4 Surface erosion and control 223
6.4.1 Surface erosion on embankments and slopes 223
6.4.2 Surface erosion control measures 223
6.5 Subsurface erosion and seepage control methods 227
6.5.1 Subsurface erosion 227
6.5.2 Underseepage control methods in levees and earthen dams 228
6.5.3 Through-seepage control methods in levees and earthen dams 230
Homework Problems 234
References 236
7. Soil Retaining Structures 237
7.1 Introduction to soil retaining structures 237
7.2 Lateral earth pressures 237
7.2.1 At-rest earth pressure 239
7.2.2 Rankine's theory 242
7.2.3 Coulomb's theory 248
7.3 Conventional retaining wall design 250
7.3.1 Factor of safety against overturning 250
7.3.2 Factor of safety against sliding 253
7.3.3 Factor of safety of bearing capacity 254
7.3.4 Retaining wall drainage 256
7.4 Sheet pile wall design 262
7.4.1 Failure modes 262
7.4.2 Preliminary data for the design 263
7.4.3 Design of cantilever walls penetrating cohesionless soils 264
7.4.4 Design of cantilever walls penetrating cohesive soils 275
7.5 Soil nail wall design 280
7.5.1 Initial design parameters and conditions 283
7.5.2 Global stability failure 284
7.5.3 Sliding failure 288
7.5.4 Bearing capacity failure 291
Homework Problems 297
References 304
8. Introduction to Geosynthetics Design 305
8.1 Geosynthetics types and characteristics 305
8.2 Design of mechanically stabilized Earth walls using geosynthetics 308
8.2.1 Design procedures of geosynthetic MSE walls 310
8.3 Design of reinforced soil slopes 322
8.4 Filtration and drainage design using geotextiles 339
8.4.1 Hydraulic properties of geotextiles 339
8.4.2 Filtration and drainage criteria 340
Homework Problems 346
References 352
9. Introduction to Geotechnical Earthquake Design 353
9.1 Basic seismology and earthquake characteristics 353
9.1.1 Seismic faults and earthquake terminology 353
9.1.2 Seismic waves 353
9.1.3 Earthquake characteristics 357
9.2 Dynamic Earth pressures 361
9.2.1 Dynamic active earth pressure 361
9.2.2 Dynamic passive earth pressure 362
9.3 Seismic slope stability 367
9.3.1 Pseudostatic analysis 368
9.3.2 Newmark sliding block analysis 375
9.3.3 Makdisi-Seed analysis 377
9.4 Liquefaction analysis 379
9.4.1 Liquefaction hazard 379
9.4.2 Evaluations of liquefaction hazard 381
9.4.3 Evaluation of CSR 381
9.4.4 Evaluation of CRR 382
Homework Problems 391
References 397
Index 399
Chapter 1
Introduction to Engineering Geology
1.1 Introduction
Engineering geology involves description of the structure and attributes of rocks that are associated with engineering works, mapping, and characterization of all geologic features and materials (rocks, soils, and water bodies) that are proximate to a project and the identification and evaluation of potential natural hazards such as landslides and earthquakes that may affect the success of an engineering project. It is different from geology, which concerns the present and past morphologies and structure of the Earth, its environments, and the fossil records of its inhabitants (Goodman 1993).
1.2 Structure of the Earth and geologic time
The Earth is divided into three main layers: crust, mantle, and core (Figure 1.1). The crust is the outer solid layer of the Earth and comprises the continents and ocean basins. The crust varies in thickness from 35 to 70 km in the continents and from 5 to 10 km in the ocean basins. It is composed mainly of aluminosilicates. The mantle, a highly viscous layer about 2900 km thick, is located beneath the outer crust. It includes the upper mantle (about 35-60 km thick) and the lower mantle (about 35-2890 km thick) (Jordan 1979). The mantle is composed mainly of ferro-magnesium silicates. Large convective cells in the mantle circulate heat and may drive the plate tectonic processes. Beneath the mantle and at the center of the Earth are the liquid outer core and the solid inner core. The outer core is an extremely low viscosity liquid layer, about 2300 km thick, and composed of iron and nickel, with an approximate temperature of 4400 °C. The inner core is solid, about 1200 km in radius, and is entirely composed of iron, with an approximate temperature of 5505 °C (Engdahl et al. 1974). The Earth's magnetic field is believed to be controlled by the liquid outer core.
Fig. 1.1 Structure of the Earth.
Geologic time is a chronological measurement of the rock layers in the history of the Earth. Evidence from radiometric dating indicates that the Earth is about 4.57 billion years old. The geologic time scale is shown in Figure 1.2. The rocks are grouped by age into eons, eras, periods, and epochs. Among the various periods, the Quaternary period (from 1.6 million years ago to the present) deserves special attention as the top few tens of meters of the Earth's surface, which geotechnical engineers often work with, developed during this period (Mitchell and Soga 2005).
Fig. 1.2 Geologic time scale.
1.3 Formation and classification of rocks
The main rock-forming minerals are silicates, and the reminders are carbonates, oxides, hydroxides, and sulfates. There are three major categories of rocks: igneous rocks, sedimentary rocks, and metamorphic rocks.
1.3.1 Igneous rocks
Igneous rocks are formed due to igneous activities, i.e., the generation and movement of silicate magma. There are two kinds of igneous rocks: extrusive or volcanic rocks that are formed by cooling of lava from volcanic eruption, and intrusive or plutonic rocks that are formed by the slow cooling of magma beneath the surface. Cooling below the Earth's surface is slow and results in large crystals, whereas cooling on the surface is rapid and results in small crystal size. Therefore, the extrusive rocks are usually fine-grained, and the intrusive rocks are coarse-grained. The intrusive rocks are found in many great mountain ranges that were brought to the surface due to erosion of the overlying material and relative tectonic plate movements. The main intrusive rock type is the light-colored granite. The main extrusive rock type is the dark-colored basalt. Coarse-grained intrusive rocks generally have lower strength and abrasion resistance as compared to fine-grained extrusive rocks (West 1995). Figure 1.3 shows Half Dome in the Yosemite National Park, California; Half Dome is an igneous rock.
Fig. 1.3 Igneous rock in the Yosemite National Park, California, USA.
1.3.2 Sedimentary rocks
Sedimentary rocks are formed by the accumulated and hardened deposits of soil particles and weathered rocks transported by wind, streams, or glaciers. The accumulated deposits are hardened due to overburden pressure and cemented by minerals such as iron oxide (FeO2) and calcium carbonate (CaCO3). Among sedimentary rocks, the most widespread are shale, sandstone, limestone, siltstone, mudstone, claystone, and conglomerates. They all display the characteristic stratification resulting from the gradual accumulation of layers of compacted and cemented deposits. The three main rocks that comprise 99% of sedimentary rocks are shale (46%), sandstone (32%), and limestone (22%) (West 1995). Sedimentary rocks are extremely diverse in their texture and mineral composition due to their diverse origin, transportation, and formation environment. Shale, claystone, and mudstone usually have low strength and low abrasion resistance and can be problematic in engineering works. Figure 1.4 shows Grand Canyon National Park, Arizona. The Grand Canyon is mainly composed of sedimentary rocks, which were eroded by the Colorado River for millions of years leading to the current formation of the Canyon.
Fig. 1.4 Sedimentary rocks in the Grand Canyon National Park, Arizona, USA.
1.3.3 Metamorphic rocks
Metamorphic rocks are formed when igneous or sedimentary rocks are subjected to the combined effects of heat and pressure, resulting in compaction, cementation, and crystallization of the rock minerals; the extreme pressure and heat transform the mineral structure. The metamorphic rocks commonly encountered in nature include marble, slate, schist, gneiss, and quartzite. These rocks include foliated and nonfoliated rocks. The layering within metamorphic rocks is called "foliation." The foliated metamorphic rocks include slates, phyllites, schists, and gneisses. The nonfoliated metamorphic rocks include marble (which is metamorphosed limestone) and quartzite (which is metamorphosed sandstone). Foliated metamorphic rocks exhibit directional properties. Strength, permeability, and seismic velocity of metamorphic rocks are strongly affected by the direction of foliation (West 1995). Figure 1.5 shows metamorphic rocks in Marble Canyon in Death Valley National Park, California.
Fig. 1.5 Metamorphic rocks in Marble Canyon, Death Valley National Park, California, USA. (Photo courtesy of Benjamin T. Adams.)
1.4 Engineering properties and behaviors of rocks
1.4.1 Geotechnical properties of rocks
The geotechnical properties of rocks include basic properties, index properties, hydraulic properties, and mechanical properties (Hunt 2005).
Rocks can be categorized into intact rock specimens and in situ rock mass, and their basic properties and index properties are tested accordingly. Intact rock specimens are fresh to slightly weathered rock samples that are free of defects. The in situ rock mass may consist of rock blocks, ranging from fresh to decomposed, separated by discontinuities.
- The basic properties of intact rocks include specific gravity, density, porosity, hardness (for excavation resistance), and durability and reactivity (for aggregate quality). The basic property of rock mass is its density.
- The index property tests for intact rocks include the uniaxial compression test, point load index test, and sonic velocities that provide a measure of the rock quality.
The index properties of rock mass are the sonic-wave velocities and the rock quality designation (RQD).
- The hydraulic property of rock is its permeability.
- The mechanical properties of rocks are the rupture strength and deformation characteristics. The rupture strength includes the uniaxial compressive strength, uniaxial tensile strength, flexural strength, triaxial shear strength, direct shear strength, and borehole shear test.
1.4.2 Comparison of the three types of rocks
Typically, igneous and metamorphic rock formations are hard and durable. Sedimentary rock formations can also be sound and durable; however, when compared to igneous and metamorphic rocks, more inconsistencies are expected in sedimentary rocks because of the presence and inclusion of foreign materials at the time of formation or because of weak bonding and cementing. Shale and mudstone generally soften when soaked in water, settle significantly under load, and yield under relatively low stresses. Such weak rocks can provoke unpredictable difficulties in excavations and foundations.
1.5 Formation and classification of soils
1.5.1 Soils formation
Soils are formed by the weathering of rocks. Weathering is a process that breaks down rocks into smaller pieces due to mechanical, chemical, and biological mechanisms. All types of rocks are subjected to weathering.
Mechanical weathering
The following physical mechanisms contribute to mechanical weathering:
- Temperature: It includes extremely high or low temperatures that cause the shrinking and expansion of rocks.
- Pressure: It includes high overburden stresses in the subsoil or in the ocean floor.
- Unloading: When the overburden stress that exerts on rocks is removed,...
