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Dr Omar Hamza Foundation Engineering CE 483 2. Site Investigations Copy right reserved to Dr O. Hamza.

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Presentation on theme: "Dr Omar Hamza Foundation Engineering CE 483 2. Site Investigations Copy right reserved to Dr O. Hamza."— Presentation transcript:

1 Dr Omar Hamza Foundation Engineering CE Site Investigations Copy right reserved to Dr O. Hamza

2 Contents – Introduction – Program of site investigation – Planning – Implementation – Reporting CE Foundation Engineering - 2. Site Investigation 2 Dr Omar Hamza

3 Introduction CE Foundation Engineering - 2. Site Investigation 3 What is Site Investigation (SI)? Why Site Investigation? Objectives of Site Investigation Copy right reserved to Dr O. Hamza

4 Introduction What is site investigation (SI)? 4 The design of foundations of structures (such as buildings, bridges, and dams) generally requires information about: Structure Ground Structure Ground CE Foundation Engineering - 2. Site Investigation

5 Introduction 5 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. Structure Ground Site Investigation Borehole What is site investigation (SI)? Layers The principal engineering properties of interest are the strength, deformation, and permeability characteristics. Drilling rig

6 Introduction Why site investigation (SI)? CE Foundation Engineering - 2. Site Investigation 6 Many engineering failures could have been avoided if a proper site investigation had been carried out. Sinkhole The site has a sinkhole risk which might have been discovered in a proper site investigation

7 Introduction Why site investigation (SI)? CE Foundation Engineering - 2. Site Investigation 7 Sophisticated theories alone will not give a safe and sound design. The success or failure of a foundation depends essentially on the reliability of the knowledge obtained from the site investigation.

8 Introduction Objectives of site investigation 8 The knowledge about the ground of the proposed construction site is obtained by Site Investigation, and used to determine: Suitability: of site for the proposed construction? Type of design solution: e.g. type of foundation: shallow or deep. Design parameters: such as strength, compressibility, permeability & other parameters used for geotechnical design Ground or Ground-water conditions: that would affect the design and construction? e.g. expansive soil, collapsible soil, high ground water… Geo-materials: available on site which can be re- used? Effect of changes: How will the design affect adjacent properties and the ground water? Site Investigation

9 Introduction Objectives of site investigation 9 Suitability: of site for the proposed construction? Type of design solution: e.g. type of foundation: shallow or deep. Design parameters: such as strength, compressibility, permeability & other parameters used for geotechnical design Ground or Ground-water conditions: that would affect the design and construction? e.g. expansive soil, collapsible soil, high ground water… Geo-materials: available on site which can be re- used? Effect of changes: How will the design affect adjacent properties and the ground water? Site Investigation Manage the geotechnical risk CE Foundation Engineering - 2. Site Investigation

10 Program of site investigation CE Foundation Engineering - 2. Site Investigation 10 Before Site Investigation The sequence of Site Investigation Dr Omar Hamza

11 Program Before Site Investigation 11 Site Investigation is usually carried out as part of Subsurface Exploratory program. Before conducting the Site Investigation, the program usually include: Desk Study and Site Reconnaissance. Desk Study Collect and review preliminary information about the site, and the structure to be built. Site Reconnaissance Visual inspection of the site. CE Foundation Engineering - 2. Site Investigation

12 12 Collecting general information about the structure, from the architectural and structural design: Structure Ground Information about the Structure –Type, dimensions, and use of the structure, and any special architectural considerations. –the load that will be transmitted by the superstructure to the foundation system –the requirements of the local building code (e.g. allowable settlement) Program Desk Study Before Site Investigation CE Foundation Engineering - 2. Site Investigation

13 13 Collecting general information about the ground, from already existing data such as: geological maps, seismic maps, Ariel Photography, Services records (Gas, Water, Electricity), Previous geo- environmental or geotechnical reports, … etc. at or near site. Structure Ground Program Desk Study Before Site Investigation Information about the ground: –the geological conditions of the ground (e.g. layers, Geological features, Ground water, Flood & Earthquake risk in the area,..). –the historical use of the site – if previously used as quarry, agricultural land, industrial unit with contamination issue, man-made fill/slope, etc. CE Foundation Engineering - 2. Site Investigation

14 14 Ariel Photograph taken for a site – shows a possible sinkhole

15 Program Site Reconnaissance 15 The Site Reconnaissance is normally in the form of a walk-over survey of the site. Before Site Investigation CE Foundation Engineering - 2. Site Investigation What things do I need to look for? Engineer during Site Visit Dr Omar Hamza

16 Program Site Reconnaissance 16 Important evidence to look for is: Before Site Investigation 1.Stratification of soil: from deep cut, such as those made for the construction of nearby highway or other projects – if any. 2.Slope: signs of slope instability include bent trees, shrinkage cracks on the ground and displaced fences or drains. Stratification of soil Signs of slope instability

17 Program Site Reconnaissance 17 Important evidence to look for is: Before Site Investigation 3.Structures: type of buildings in the area and the existence of any cracks in walls or other problems. You may need to ask local people. Tipping settlement (often without cracks) Differential settlement (with cracks) Indication of possible ground- related problem CE Foundation Engineering - 2. Site Investigation

18 Program Site Reconnaissance 18 Other important evidence to look for is: Before Site Investigation 4.Mining: The presence of previous mining is often signs of subsidence and possibly disused mine shafts. Open cast mining is indicated by diverted streams replaced or removed fence/hedge lines. 5.Hydrogeology: Wet marshy ground, springs or seepage, ponds or streams and Wells. 6.Topography: possible existence of drainage ditches or abandoned debris or other man-made features. 7.Vegetation: may indicate the type of soil. 8.Access: It is essential that access to the site can be easily obtained. Possible problems include low overhead cables and watercourses. CE Foundation Engineering - 2. Site Investigation

19 Program The sequence of Site Investigation 19 Whether investigation is preliminary or detailed, there are three important phases: planning, implementation and reporting. Planning Implementation Reporting In large construction projects, 2 site investigations (SI) are carried out: –Preliminary SI, followed by –Detailed SI. Soil exploration is a requirement for the design of foundations of any project. CE Foundation Engineering - 2. Site Investigation Sequence of Site Investigation

20 20 Planning Implementation Reporting CE Foundation Engineering - 2. Site Investigation Planning Why planning Depth of investigation Spacing of boreholes

21 21 Borehole CE Foundation Engineering - 2. Site Investigation Planning Why planning? How many borings do we need? How deep the borings should be? The more the better, but what about the cost?

22 22 Minimize cost of explorations and yet give reliable data. Decide on quantity and quality depending on type, size and importance of project and whether investigation is preliminary or detailed. Planning for site investigation is required to: Decide on minimum depth and spacing of exploration. Depth of Borehole Borehole Spacing CE Foundation Engineering - 2. Site Investigation Planning Why planning?

23 23 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. The estimated depths can be changed during the drilling operation, depending on the subsoil encoun­tered. To determine the approximate minimum depth of boring, engineers may use the following rules: CE Foundation Engineering - 2. Site Investigation Planning Depth of investigation

24 24 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 = D1, at which the stress increase is equal to (1/10) q (q = estimated net stress on the foundation). Determination of the minimum depth of boring 4.Determine the depth, D = D2, at which / ' 0 = Unless bedrock is encountered, the smaller of the two depths, D1 and D2, is the approximate minimum depth of boring required. 0 q D CE Foundation Engineering - 2. Site Investigation Planning Depth of investigation

25 25 Table shows the minimum depths of borings for buildings based on the preceding rule. Depth of Boring Number of Stories Building width (m) What do you notice about this table? CE Foundation Engineering - 2. Site Investigation Planning Depth of investigation

26 26 There are no strict rules for the spacing of the boreholes. The following table gives some general guidelines for borehole spacing. These spacing can be increased or decreased, depending on the subsoil condition. If various soil strata are more or less uniform and predictable, the number of boreholes can be reduced. What do you notice about this table? Type of project Spacing (m) Planning Spacing of boreholes

27 27 Planning Implementation Reporting CE Foundation Engineering - 2. Site Investigation Overview Boring Sampling Testing Implementation Sequence of Site Investigation

28 Overview 28 Boring Trial pits Boreholes Sampling Soil Sampling Rock Sampling Testing In-situ tests Laboratory tests The implementation phase of site investigation usually includes three important aspects: CE Foundation Engineering - 2. Site Investigation Implementation

29 29 Boring Trial pits Boreholes Sampling Soil Sampling Rock Sampling Testing In-situ tests Laboratory tests CE Foundation Engineering - 2. Site Investigation Boring Implementation

30 30 Trial pits CE Foundation Engineering - 2. Site Investigation Trial pits are shallow excavations - less than 6m deep. The trial pit is used extensively at the surface for block sampling and detection of services prior to borehole excavation. For safety ALL pits below a depth of 1.2m must be supported. Backhoe Pick and shovel DepthExcavation Method 0-2mBy Hand 2-4mWheeled Back Hoe 4-6mHydraulic Excavator Trial Pit 6m > depth Boring Implementation

31 31 Boreholes CE Foundation Engineering - 2. Site Investigation 1.Auger Boring 2.Wash Boring 3.Rotary Drilling 4.Percussion Drilling Borehole The right choice of method depends on: –Ground condition: presence of hard clay, gravel, rock. –Ground-water condition: presence of high ground-water table (GWT). –Depth of investigation –Site access Boreholes may be excavated by one of these methods: Boring Implementation

32 32 This is the simplest of the methods. Hand operated or power driven augers may be used. Suitable in all soils above GWT but only in cohesive soil below GWT. Hand operated augers Power driven augers Post hole auger Helical auger 1. Auger Boring Boreholes Boring Implementation

33 33 A casing is driven with a drop hammer. A hollow drill rod with chopping bit is inserted inside the casing. Soil is loosened and removed from the borehole using water or a drilling mud jetted under pressure. Wash boring is a very convenient method for soil exploration below the ground water table provided the soil is either sand, silt or clay. The method is not suitable if the soil is mixed with gravel or boulders. 2. Wash Boring CE Foundation Engineering - 2. Site Investigation Boreholes Boring Implementation

34 34 In this method a heavy drilling bit is alternatively raised and dropped in such a manner that it powders the underlying materials which form a slurry with water and are removed as the boring advances. Possibly this is the only method for drilling in river deposits mixed with hard boulders of the quartzitic type. 3. Percussion Drilling CE Foundation Engineering - 2. Site Investigation Boreholes Boring Implementation

35 35 In this method a rapidly retaining drilling bit (attached to a drilling rod) cut the soil and advance the borehole. 4. Rotary Drilling 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. Drilling bit Drilling rod Rotary Head Movement transmitter CE Foundation Engineering - 2. Site Investigation Boreholes Boring Implementation

36 36 Boring Trial pits Boreholes Sampling Soil Sampling Rock Sampling Testing In-situ tests Laboratory tests CE Foundation Engineering - 2. Site Investigation Sampling Implementation

37 37 Soil sampling Soil samples are recovered carefully, stored properly to prevent any change in physical properties, and transferred to laboratory for testing. CE Foundation Engineering - 2. Site Investigation Sampling Implementation Samples from each type of soils are required for laboratory testing to determine the engineering properties of these soils. Soil Sampling equipment? Disturbed vs Undisturbed?

38 38 Soil Sampling equipment There is a wide range of sampling methods such as Split-spoon, Thin- walled Tube. The choice of method depends on: the requirement of disturbed or undisturbed samples Type of soil discovered at site (Gravel, Sand, Silt, Clay) Split-spoon Sampler Soil sampling Sampling Implementation Soil Sample advancement

39 39 Soil sampling Sampling Implementation Soil Sampling equipment

40 40 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. CE Foundation Engineering - 2. Site Investigation Soil sampling Sampling Implementation Disturbed vs Undisturbed

41 41 It is nearly impossible to obtain a truly undisturbed sample of soil. The quality of an "undisturbed" sample varies widely between soil laboratories. So how is disturbance evaluated? Quality of samples is evaluated by calculating Area Ration A R : Sampling tube soil The thicker the wall of the sampling tube, the greater the disturbance. Outer Diameter Inner Dia. Good quality samples A R <10%. CE Foundation Engineering - 2. Site Investigation Soil sampling Sampling Implementation Disturbed vs Undisturbed

42 42 Area Ration A R = = Samples collected in Split-spoon Sampler is usually classified as disturbed. What is the Area Ration? CE Foundation Engineering - 2. Site Investigation Soil sampling Sampling Implementation Disturbed vs Undisturbed

43 43 Core drilling equipment? Core recovery parameters? Rock samples are called rock cores, and they are necessary if the soundness of the rock is to be established. CE Foundation Engineering - 2. Site Investigation Sampling Implementation Rock Sampling (Coring)

44 44 Coring is done with either tungsten carbide or diamond core bits. Rock sampler is called core barrel which usually has a single tube. Double or triple tube core barrel is used when sampling of weathered or fractured rock. Core barrel: (a) Single-tube; (b) double-tube (a) (b) Inner barrel Outer barrel Core barrel Rock Coring bit Drill rod Diamond Drill Bit Rock core Rock Rock Sampling (Coring) Sampling Implementation Core drilling equipment

45 45 Cores tend to break up inside the drill barrel, especially if the rock is soft or fissured. Core recovery parameters are used to describe the quality of core. Length of pieces of core are used to determine: – Core Recovery Ratio (R r ) – Rock Quality Designation (RQD) Rock cores CE Foundation Engineering - 2. Site Investigation Sampling Implementation Rock Sampling (Coring) Core drilling equipment

46 46 10 Assuming the following pieces for a given core run: L i = L 100% (Core run) RrRr ( L i 10 cm ) (Core run) Recovery Ratio, R r Rock Quality Designation, RQD Rock Sampling (Coring) SamplingImplementation Core drilling equipment Core recovery (lengths of intact pieces of core)

47 47 So Rock Quality Designation (RQD) is the percentage of rock cores that have length 10 cm over the total drill length (core run). RQD may indicate the degree of jointing or fracture in a rock mass. e.g. High-quality rock has an RQD of more than 75%. RQD is used in rock mass classification systems and usually used in estimating support of rock tunnels. Core recovery parameters CE Foundation Engineering - 2. Site Investigation Rock Sampling (Coring) Sampling Implementation

48 48 Class Example Work out R r and RQD for the following core recovery (intact pieces), assuming the core run (advance) is 150 cm. What is the rock mass quality based on RQD? CE Foundation Engineering - 2. Site Investigation Rock Sampling (Coring) Sampling Implementation Core recovery parameters

49 49 Total core recovery L = 125 cm Core recovery ratio: R r = 125/150 = 83% On modified basis (for pieces 10cm), 95 cm are counted, thus: RQD = 95/150 = 63 % RQD = 50% - 75% Rock mass quality is Fair Solution: CE Foundation Engineering - 2. Site Investigation Rock Sampling (Coring) Sampling Implementation Core recovery parameters ? ? = ? L i L 100% = L i L

50 50 Boring Trial pits Boreholes Sampling Soil Sampling Rock Sampling Testing In-situ tests Laboratory tests CE Foundation Engineering - 2. Site Investigation Testing Implementation

51 51 In-situ tests Introduction Groundwater measurements Standard Penetration Test (SPT) Cone Penetration Test (CPT) Testing Implementation Plate Load Test (PLT) Pressure-meter Test (PMT) Flat Dilatometer Test (DMT) Vane shear test (VST) PLT In Borehole Piezometer

52 52 Introduction Definition: In-situ tests are carried out in the field with intrusive testing equipment. If non-intrusive method is required, then it is better to use geophysical methods which use geophysical waves – i.e. without excavating the ground. Advantage of in-situ testing (against lab testing) It avoids the problems of sample recovery and disturbance some in-situ tests are easier to conduct than lab tests In-situ tests can offer more detailed site coverage than lab testing. Testing standards American Society for Testing and Materials (ASTM) British Standard (BS) CE Foundation Engineering - 2. Site Investigation : In-situ tests Testing Implementation

53 53 Groundwater measurements Why Groundwater: Groundwater conditions are fundamental factors in almost all geotechnical analyses and design studies. Types of Groundwater measurements: Determination of groundwater levels (GWT) and pressures. Borehole instrumented with Piezometer is used for this purpose. Measurement of the permeability of the subsurface materials, particularly if seepage analysis is required. The test called Pumping test. Piezometer CE Foundation Engineering - 2. Site Investigation : In-situ tests Testing Implementation Ground water level Standpipe

54 54 Standard Penetration Test (SPT) This empirical test consists of driving a split- spoon sampler, with an outside diameter of 50 mm, into the soil at the base of a borehole. Drivage is accomplished by a trip hammer, weighing 65 kg, falling freely through a distance of 760 mm onto the drive head, which is fitted at the top of the rods. The split-spoon is driven three times for a distance of mm (6 in) into the soil at the bottom of the borehole. The number of blows required to drive (only) the last two mm are recorded. The blow count is referred to as the SPT-N. 760 mm mm (6 in) x 3 times The first one does not count Falling Hammer Definition Drive head Slit spoon CE Foundation Engineering - 2. Site Investigation : In-situ tests Testing Implementation

55 55 Relatively quick, simple, reasonably cheap, and suitable for most soils. good correlation between SPT-N and soil properties. provides a representative soil sample for further testing. Disadvantage SPT does not typically provide continuous data Limited applicability to soil containing cobbles and boulders. Samples obtained from the SPT are disturbed. SPT N blow require correction Advantage CE Foundation Engineering - 2. Site Investigation Standard Penetration Test (SPT) Testing Implementation : In-situ tests

56 56 Corrections are normally applied to the SPT blow count (N) to account for: –Energy loss: during the test (about only 60% of energy remains) –Equipment differences: hammer, sampler, borehole diameter, rod Corrections for energy and equipment The following equation is used to compensate for these factors: ( ) ( ) (usually ) ( ) Standard Penetration Test (SPT) Testing Implementation : In-situ tests Usually this correction is made by the Site Investigation operator. 60%

57 57 Corrections for overburden pressure Standard Penetration Test (SPT) Testing Implementation : In-situ tests C N = overburden pressure correction factor In granular soil (sand, gravel) the SPT blows are influenced by the effective overburden pressure at the test depth: Many equations have been suggested for C N – see Page 86, (Dass text book). For example:

58 58 Standard Penetration Test (SPT) Correlation between N and friction angle There are many equations suggested. The figure shows the correlation with the angle of shearing resistance of sand (according to Pecks, 1974). Testing Implementation : In-situ tests Angle of shearing resistance (degree) Corrected SPT N blow

59 59 The following are the recorded numbers of SPT blows required for spoon penetration of three 152.4cm (6 in) in a sand deposit: Class example Standard Penetration Test (SPT) Testing Implementation : In-situ tests Depth from ground surface (m) SPT blows (blow/ 6 in)3, 4, 57, 9, 107, 12, 118, 13, 1410, 14, 15 The ground water table (GWT) is located at a depth of 4.5m. The wet unit weight of sand above GWT is 18 kN/m 3, and the saturated unit weight of sand below GWT is kN/m 3. Draw a sketch of the foundation showing the given details of the soil. Determine the standard penetration number (SPT-N) at each depth. What is the corrected (SPT-N) value? (use Seeds equation). Determine the friction angle at depth 4m below the footing. (Use Pecks Equation or Chart). Note. Assume the above SPT blows are corrected for energy and equipment.

60 Z, mSPT blowN 60 (kPa) CNCN N 1.53, 4, 54+5=91.5x18 = o 37, 9, = , 12, , 13, 14? 7.510, 14, Only the last 2 sets of blows count Solution Standard Penetration Test (SPT) Testing Implementation : In-situ tests =18 kN/m 3 sat =19.8 kN/m Z Corrected

61 61 The corrected SPT N blow can be approximately correlated to many important engineering properties of soil such as shear strength & compressibility. This equation shows the correlation with untrained shear strength Su (or Cu) of clay. (also with OCR = Over Consolidation Ratio). CE Foundation Engineering - 2. Site Investigation Standard Penetration Test (SPT) Testing Implementation : In-situ tests Correlation between N and untrained shear strength In Clay

62 62 The table shows the correlation corrected SPT-N with untrained shear strength Su (or Cu) of clay (according to Terzaghi et al. 1996) CE Foundation Engineering - 2. Site Investigation Standard Penetration Test (SPT) Testing Implementation : In-situ tests Correlation between N and untrained shear strength

63 63 CE Foundation Engineering - 2. Site Investigation Standard Penetration Test (SPT) Testing Implementation : In-situ tests Class Example shown below the Figure

64 64 Standard Penetration Test (SPT) Testing Implementation : In-situ tests Solution Z, mN 60 (kPa) C u (kPa) (MPa) OCR x x( ) = x0.29 x = /1000= x(5/ 0.038) = x( ) = OCR av = C u -av =

65 65 Standard Penetration Test (SPT) Correlation between N and Relative Density Dr correlation between N 60 and Relative Density of Granular Soil Testing Implementation : In-situ tests CE Foundation Engineering - 2. Site Investigation Copy right reserved to Dr O. Hamza For Clean sand only General

66 66 Standard Penetration Test (SPT) Testing Implementation : In-situ tests CE Foundation Engineering - 2. Site Investigation Very loose Loose Medium Dense Correlation between N and Relative Density Dr

67 67 Standard Penetration Test (SPT) Testing Implementation : In-situ tests Correlation between Modulus of Elasticity and Standard Penetration Number The modulus of elasticity of granular soils (E s ) is important parameter in estimation the elastic settlement of foundation. An approximate estimation for E s was given by Kulhawy and Mayne (1990) as:

68 68 Cone Penetration Test (CPT) called also "Dutch cone test or Static Penetration test. The test method consists of pushing an instrumented cone, with the tip facing down, into the ground at a slow controlled rate. Cone: 60 degree apex cone, Dia = 36 mm. Definition Cone CE Foundation Engineering - 2. Site Investigation Testing Implementation : In-situ tests Measures Cone or Tip resistance (q c ) or (q t ) Sleeve friction (f s ) Water Pore pressure (u b ) Friction Ratio, F r = qcqc fsfs q c or q t fsfs Hydraulic push at rate 20 mm/s Cone Rod (36 mm dia.) Other variables e.g. Shear wave velocity (v s )

69 69 Cone Penetration Test (CPT) CE Foundation Engineering - 2. Site Investigation Testing Implementation : In-situ tests Soil profile (stratigraphy): soil type identification Estimation of geotechnical parameters (strength, compressibility, permeability) Evaluation of groundwater conditions (pore pressure) Geo-environmental: distribution and composition of contaminants Applications: Sample data Sleeve friction, f s Tip resistance, q c Pore Pressure, u Clay Clay & Silt Silty Clay Clay & Sand Friction Ratio, F r

70 70 Cone Penetration Test (CPT) Testing Implementation : In-situ tests –High in granular soil –Low in cohesive soil –Low in granular soil –High in cohesive soil Friction Ratio F r Point resistance q c Soil Identification: However, the cone/tip (q c ) and sleeve (f s ) resistance increase with increasing overburden stress 0 for accurate identification, normalization of q c & f s by overburden stress is required. Classification Chart (Robertson et al., 1983)

71 71 Cone Penetration Test (CPT) CE Foundation Engineering - 2. Site Investigation Testing Implementation : In-situ tests Inability to penetrate through gravels and cobbles Newer technology = less populated database than SPT Lack of sampling Disadvantages: Borehole is not necessary Almost continuous data (reading every 10mm) Elimination of operator error (automated) Reliable, repeatable test results Advantages:

72 72 Cone Penetration Test (CPT) CE Foundation Engineering - 2. Site Investigation Testing Implementation : In-situ tests In Sand: the drained friction angle Correlation with shear strength where: q c = the cone (tip) (point) resistance 0 & 0 = effective and total overburden pressure, respectively N K = Bearing factor depends on type of cone (varies from 11-20) OCR = Over Consolidation Ratio In Clay: undrained shear strength c u (Ricceri et alls. 2002)

73 73 Cone Penetration Test (CPT) Testing Implementation : In-situ tests Class example: Correlation with shear strength Use equation proposed by Ricceri et alls

74 74 Cone Penetration Test (CPT) Testing Implementation : In-situ tests Solution: Depth, mq c (MPa) (kPa)q c / (Rad) (deg) x 16 = / 24 = x180/ =40 o av = av = / 6 Note. tan -1 is inverse tangent, the angle returned is in Radian.

75 75 Plate Load Test (PLT) Testing Implementation : In-situ tests The test essentially consists in loading a rigid steel plate at the foundation level and determining the settlement corresponding to each load increments. The ultimate bearing capacity is then taken as the load at which the plate starts sinking at a rapid rate. Plate load test is a field test to determine the ultimate bearing capacity of soil.

76 76 Laboratory tests CE Foundation Engineering - 2. Site Investigation Testing Implementation

77 77 Basic physical properties tests (Moisture content, Specific gravity, Soil Indexes,..) Particle size test (sieving, Sedimentation) Direct shear box test Unconfined compression test Triaxial test Consolidation test Permeability test Other lab tests: Chemical test (pH, contamination,..) CE Foundation Engineering - 2. Site Investigation Laboratory tests Testing Implementation

78 78 Planning Implementation Reporting CE Foundation Engineering - 2. Site Investigation Preparation of Borehole Site Investigation Report Reporting Sequence of Site Investigation

79 79 CE Foundation Engineering - 2. Site Investigation Reporting Preparation of Boring Logs Initial information: Name and address of the drilling company, Drillers name, Job description and reference number, boring information (number, type, and location of, and date of boring). Example of a typical boring log

80 80 CE Foundation Engineering - 2. Site Investigation Subsurface stratification: which can be obtained by visual observation of the soil brought out by auger, split-spoon sampler, and thin-walled Shelby tube sampler. Groundwater: Elevation of water table and date observed, use of casing and mud losses, and so on Reporting Preparation of Boring Logs

81 81 CE Foundation Engineering - 2. Site Investigation 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. Reporting Preparation of Boring Logs

82 82 The following borehole is part of a site investigation (SI) carried out over a proposed location of a bridge. Assess the subsoil conditions and ground-water conditions based on the borehole data. In particular write about: Soil layers: types, description, depth… Soil properties: shear strength properties -based on SPT. Ground water depth Reporting Preparation of Boring Logs Class example Copy right reserved to Dr O. Hamza

83 83 CE Foundation Engineering - 2. Site Investigation

84 84 CE Foundation Engineering - 2. Site Investigation When: After the completion of all of the field and laboratory work, a site investigation report is prepared. Why: for the use of the design office and for reference during future construction work. The report is also called soil exploration report or Geotechnical Factual report. Reporting Site Investigation Report What should be included in the site investigation report?

85 85 CE Foundation Engineering - 2. Site Investigation The report should contain descriptions of the followings: Purpose & Scope of the investigation Site & Structure: site location, existing structures, drainage conditions, vegetation,… and information about the structure. Factual Details of field exploration: boreholes, samples, and testing. For each type, quantities, method, tools should be presented. Geological setting of the site (variation of depth and thickness of layers as interpreted from the borings) Subsoil and water-table conditions, (soil parameters as interpreted from the testing results). Design analysis & recommendations: type of foundation, allowable bearing pressure, settlement estimation, and any special construction procedure; alternatives design solution. Conclusions and limitations of the investigations Reporting Site Investigation Report Usually given in another report (Geotechnical Design Report)

86 86 CE Foundation Engineering - 2. Site Investigation The following graphical presentations must be attached to the report: 1.General map showing site location 2.A plan view of the location of the borings with respect to the proposed structures and those nearby 3.Boring logs (including in-situ tests results and samples) 4.Laboratory test results 5.Other graphical presentations (geotechnical cross section based on the boring logs, photos of the field work and soil samples,…) Reporting Site Investigation Report

87 87 Geotechnical cross section based on the boring logs Reporting Site Investigation Report


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