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1 This document downloaded from vulcanhammer.net since 1997, your source for engineering information for the deep foundation and marine construction industries, and the historical site for Vulcan Iron Works Inc. Use subject to the fine print to the right. All of the information, data and computer software ("information") presented on this web site is for general information only. While every effort will be made to insure its accuracy, this information should not be used or relied on for any specific application without independent, competent professional examination and verification of its accuracy, suitability and applicability by a licensed professional. Anyone making use of this information does so at his or her own risk and assumes any and all liability resulting from such use. The entire risk as to quality or usability of the information contained within is with the reader. In no event will this web page or webmaster be held liable, nor does this web page or its webmaster provide insurance against liability, for any damages including lost profits, lost savings or any other incidental or consequential damages arising from the use or inability to use the information contained within. This site is not an official site of Prentice-Hall, the University of Tennessee at Chattanooga, Vulcan Foundation Equipment or Vulcan Iron Works Inc. (Tennessee Corporation). All references to sources of equipment, parts, service or repairs do not constitute an endorsement. Don t forget to visit our companion site

2 ENCE 361 Soil Mechanics Site Investigations Part I

3 Site Investigation Plan Planning for Field Investigations Exploration Phase Reconnaissance/Feasibility Preliminary Exploration Detailed Exploration Construction/Post Construction Phases

4 Planning for Field Investigations The initial phase of field investigations should consist of detailed review of geological conditions at the site and in its general environs. This should include a desktop study of available data including remote sensing imagery, aerial photography, and a field reconnaissance. To the extent possible, borings should be supplemented by lower cost exploration techniques such as test pits, probes, seismic refraction surveys, and electrical resistivity surveys.

5 Exploration Activities Before Construction Reconnaissance/Feasibility Preliminary Exploration Detailed Exploration During and After Construction Construction Phase Post Construction Phase

6 Reconnaissance/Feasibility Review of: available topographic and geologic information aerial and satellite photographs data from previous investigations site examination (important!) These investigations reveal difficulties which may be expected in later exploration phases and assists in determining the type, number and locations of borings required

7 Field Reconnaissance Nearby structures should be inspected to ascertain their foundation performance and potential to damage from vibration or settlement from foundation installation. Also, the structure's usages must be looked at to check the impact the foundation installation may have (i.e. a surgical unit, printing company, etc.). On water crossings, banks should be inspected for scour and the streambed inspected for evidence of soil deposits not previously indicated.

8 Field Reconnaissance Note any feature that may affect the boring program, such as accessibility, structures, overhead utilities, signs of buried utilities, or property restrictions. Note any feature that may assist in the engineering analysis, such as the angle of any existing slopes and the stability of any open excavations or trenches. Any drainage features, including signs of seasonal water tables. Any features that may need additional borings or probing such as muck pockets.

9 Exploration Preliminary May include borings to recover samples for identification tests Detailed Borings Disturbed and undisturbed Sampling for laboratory testing Standard penetration resistances (SPT) or other penetrations tests (CPT, pressuremeter, etc.) Test pits, piezometer measurements, pumping tests

10 Results of Inadequate or Nonexistent Investigation

11 Construction/Post Construction Phases Exploration does not end with the start of construction Further evaluation may be required during the construction phase and after completion of the work In some cases (especially environmentally sensitive ones) investigations may go on for years after completion

12 Published Soil and Geological Maps U.S. Geological Survey (USGS) Geological index map Folios of the Geological Atlas of the United States Geological Quadrangle Maps of United States Bulletins, professional papers, circulars, annual reports, monographs Water supply papers Topographic maps Libraries

13 Published Soil and Geological Maps National Oceanic and Atmospheric Administration (NOAA, National Ocean Survey (NOS) Nautical Charts U.S. Department of Agriculture (USDA, Soil Conservation Service Soil maps and reports

14 Published Soil and Geological Maps State Geological Surveys/State Geologist's Office Geological Society of America (GSA) Monthly bulletins, special papers, and memoirs. Geological map Library of Congress Worldwide National Earth- Science Agencies

15 Remote Sensing Data

16 Remote Sensing Data

17 Remote Sensing Data

18 Remote Sensing Data

19 Soil Borings, Test Pits and Deep In Situ Tests Soil Borings Test Pits Samplers Disturbed Samples Undisturbed Samples Deep In Situ Tests SPT (Standard Penetration) Test CPT (Cone Penetrometer) Test Menard Pressuremeter Test Marchetti Dilatometer Test

20 Soil Borings

21 Soil Borings

22 Aspects of Soil Borings Depth of borings will vary depending on type of structure, soil types and depth distribution Borings should be extended through unsuitable foundation strata (organic soils, soft fine-grained soils, loose coarse-grained soils, etc.) Borings should be extended into rock where quality of rock is unknown or questionable (limestone is especially important) Check borings should be made where conditions are unknown

23 Test Pits and Trenches Test Pits Test pits are used to examine and sample soils in situ, to determine the depth to groundwater, and to determine the thickness of topsoil. They range from shallow manual or machine excavations to deep, sheeted, and braced pits. Hand-cut samples are frequently necessary for highly sensitive, cohesive soils, brittle and weathered rock, and soil formation with honeycomb structure. Test Trenches Test trenches are particularly useful for exploration in very heterogeneous deposits such as rubble fills, where borings are either meaningless or not feasible.

24 Test Pits

25 Soil Sampling Disturbed Sampling Useful for determination of basic soil type, or when testing itself is used to determine soil properties (such as SPT testing) Undisturbed Sampling Necessary for many laboratory soil tests Can be done with soil borings depending upon the sampler being used Important purpose of test pits is to obtain undisturbed samples

26 Samplers for Disturbed Samples

27 Samplers for Disturbed Samples

28 Samplers for Disturbed Samples

29 Rock Core Drilling Done with with either tungsten carbide or diamond core bits Use a double or triple tube core barrel when sampling weathered or fractured rock Used to determine Rock Quality Designation

30 Samplers for Undisturbed Samples

31 Samplers for Undisturbed Samples

32 Samplers for Undisturbed Samples

33 Insertion of Samplers Impact Standard is to use 140 lb. Weight dropped 30 Used for Standard Penetration Test (SPT) and Dynamic Cone Penetrometer Test Hydraulic pushing Used for tests such as Cone Penetrometer Tests (CPT) Insertion Menard Pressuremeter Test Marchetti Dilatometer Test

34 Standard Penetration Test (SPT) Definition The number of blows required to drive a standard split spoon sampler a distance of 12 inches after an initial penetration of 6 inches is referred to as an "N" value or SPT "N" value. In the U.S., this is the most widely used method of sampling soils, especially when deep foundations are to be installed

35 Standard Penetration Test (SPT) Apparatus Drill Rig to advance sampler to desired elevation Standard 2-inch (O.D.) split barrel (or split spoon) sampler 140 pound (63.6 kg) hammer dropping 30 (0.76 m) in free fall Lifting and dropping apparatus, frequently consisting of two wraps of a rope around the cathead on the drill rig Automatic rig also in use more efficient

36 Standard Penetration Test (SPT) Procedure Clean the boring of all loose material, and material disturbed by drilling. Insert sampler, verifying the sampler reaches the same depth as was drilled. Obtain a consistent 30-inch free-fall drop of the hammer with two wraps of a rope around the cathead on the drill rig. (Cables attached to the hoisting drum should not be used because it is difficult to obtain free fall.)

37 Standard Penetration Test (SPT) Procedure Drive the sampler 18 inches, or until normal maximum resistance (refusal) is reached, using the standard hammer and drop. (Refusal is defined as a penetration of less than 6 inches for 100 hammer blows.) Count and record the number of blows required to drive each 6 inches of penetration.

38 Standard Penetration Test (SPT) Interpretation of Results The blows are recorded per 6 of penetration Three (3) consecutive sets of blow counts are taken in a penetration distance of 18 The SPT value in blows/ft (blows/30 cm) is the sum of the second and third blow counts of the last two 6 penetration distances in an 18 total penetration

39 Energy of SPT Ideal Energy of Drop Efficiency E r W s s E r 140lbs2.5'350 ftlbs e E n E r E n ee r

40 Energy of SPT Ideal Striking Velocity of the Weight v r 2gs 12 v r ft sec Actual Striking Velocity of the Weight v 2egs 12 e 1 2 v 12.69e 1 2 n r

41 SPT Efficiency Variations Related to Mechanics of Drop Inadequate stroke of weight Restrictions on free drop of weight Variations in weight Other Variations Incorrect contact of sampler and soil (poor cleaning) Soils unsuitable for split spoon (example: gravel) Poor alignment of impact Poor assembly of split spoon and drill string

42 Errors in SPT Tests

43 Typical Efficiencies of SPT Tests Factor for Country Type Mechanism Typical Efficiency 60% Rod Energy Japan Donut Free-fall 78 78/60=1.30 Donut Rope & 67 67/60=1.12 U.S.A. Pulley with Special throw Safety Rope & Pully 60 60/60=1.00 Donut Rope & Pully 45 45/60=0.75 ArgentinaDonut Rope & Pully 45 45/60=0.75 China Donut Free-fall 60 60/60=1.00 Donut Rope and 50 50/60=0.83 Pully

44 SPT Efficiency Correction Factor e N 60 N m 60 N m ER m N m = blow counts measured with energy of the rig actually used N 60 = blow counts corrected to 60% energy ratio e = efficiency of drop ER m = Correction Factor for Efficiency

45 Overburden Correction Necessary to correct when the confining pressure of the soil increases and affects the drivability of the drill rod

46 Total SPT Correction e N 60 C N N m 60 C N N m ER m N m = blow counts measured with energy of the rig actually used N 60 = blow counts corrected to 60% energy ratio e = efficiency of drop ER m = Correction Factor for Efficiency C N = Correction for Overburden Pressure

47 SPT Correlations Density of Cohesionless Soils Consistency of Cohesive Soils Shear Modulus of Soils

48 Density of Cohesionless Soils SPT N 0-4 Relative Density, % 0-5 Soil Friction Angle, Deg

49 Consistency of Cohesive Soils SPT N Consistency Unconfined Compressio n Strength, kpa 0-2 Very Soft Soft Medium Stiff Stiff Very Stiff >30 Hard >400

50 Shear Modulus of Soils

51 Cone Penetrometer (CPT) Test Originally developed in Europe to address the difficulties of the SPT Test 36 mm diameter penetrometer is usually pushed into the ground instead of impact driven Direct reading of soil resistance both lateral and direct is possible with 280 mm long cone penetrometer Allows considerable data to be obtained in a short time Does not allow for sample recovery

52 Readings on both bearing and shaft friction can be obtained in the two steps of taking the reading Cone Penetrometer (CPT) Test

53 Types Types of CPT Devices Correlations Dutch (Delft) mechanical cone penetrometer Fugro Penetrometer Electrical Cone Penetrometer Piezocone Penetrometer Correlations Soil Classifications Can be used almost directly for pile capacity determinations

54 Dynamic Cone Penetrometer Similar to the cone penetrometer test except, instead of being pushed at a constant rate, the cone is driven into the soil. The number of blows required to advance the cone in 6-inch (150 mm) increments is recorded. A single test generally consists of two increments. Tests can be performed continuously to the depth desired with an expendable cone, which is left in the ground upon drill rod withdrawal, or they can be performed at specified intervals by using a retractable cone and advancing the hole by auger or other means between tests.

55 Dynamic Cone Penetrometer Samples are not obtained. Blow counts can generally be used to identify material type and relative density. In granular soils, blow counts from the second 6-inch (150 mm) increment tend to be larger than for the first increment. In cohesive soils, the blow counts from the two increments tend to be about the same. While correlations between blow counts and engineering properties of the soil exist, they are not as widely accepted as those for the SPT.

56 Questions?