CIVL451

IN SITU TESTING METHODS

• In situ tests can provide a better insight to soil

behavior and should be relied on to a greater

extent.

• Some in-situ tests that can improve the quality

of prediction of foundation behavior are

discussed below.

The following types of ground conditions are

examples of those where in situ testing is either

essential or desirable

• Very soft or sensitive clays

• Stoney soils.

• sands and gravels.

• Weak, fissile or fractured rock.

In situ tests may be classified according to purpose

• penetration resistance;

• strength and/or compressibility, or

• in situ permeability. • in situ permeability.

• Wholly empirical interpretation. No fundamental analysis is possible. Stress paths, strain levels, drainage conditions and rate of loading are either uncontrolled or inappropriate. (Examples: SPT, CPT.)

• Semi-analytical interpretation. Some relationships between parameters and measurements may be developed, but in reality interpretation is semi-empirical, developed, but in reality interpretation is semi-empirical, either because both stress paths and strain levels vary widely within the mass of ground under test, or drainage is uncontrolled, or inappropriate shearing rates are used. (Examples: plate test, vane test.)

• Analytical interpretation. Stress paths are controlled, and similar (although strain levels and drainage are not). (Example: self-boring pressuremeter.)

SPT

• Test has significantly changed since design

• correlations were made (1940-1960s)

• Terzaghi & Peck, 1948

• Engineer must use N60-values to properly use

• those correlations• those correlations

• N60-values rarely shown on boring logs

• Using only N-values leads to overly

• conservative and expensive designs

• SPT is a dynamic test—may not model soil’s

• behavior to static structure loads

• Correlations between SPT N value and soil or weak rock properties are wholly empirical, and depend upon an international database of information.

• Because the SPT is not completely standardized, these correlations cannot be considered particularly accurate in some cases, and it is therefore important that users in some cases, and it is therefore important that users of the SPT and the data it produces have a good appreciation of those factors controlling the test, which are:

• variations in the test apparatus;

• the disturbance created by boring the hole; and

• the soil into which it is driven.

SPT Hammer Types and Approximate

Energies

• a) Automatic Hammer ~95% eff.,

• b) Safety Hammer ~60% eff.,

• c) Donut Hammer ~45% eff.

• (photos from GeoServices Corp.)

• Procedure (ASTM D 5778)

• Standard cone consists of a 60o pointed tip • Standard cone consists of a 60o pointed tip with

• projected area of 10cm2

• Friction sleeve has a surface area of 150 cm2

• Cone is pushed vertically at a constant rate of

• 2 cm/sec

Pressuremeter

• This is an advanced state-of-the-art test.

A probe with a rubber membrane is lowered into the borehole and expanded under pressure. The pressure-volume relationship is pressure. The pressure-volume relationship is correlated to various engineering properties of the soils. The prediction of soil bearing capacity and settlement from pressuremeterdata is more realistic than other available methods.

Inflatable cylinder is expanded

radially in a borehole

Pressure applied to the

borehole wall and the volume

change of the pressuremeter

are recordedare recorded

This information is used to

estimate soil modulus, shear

strength (drained or

undrained), and horizontal

stress conditions

Pressuremeter Test Schematic

Pressuremeter Test Setup

The field curve and calibration data

(air calibration and pipe calibration) are

presented together with the corrected

pressure versus volume curve.

Typical Results of Pressuremeter Test

• The pressuremeter data may be correlated to the

various soil properties. Table presents the typical values

• of limit pressure for different types of strata.

Range of Limit Pressure for Different Soils

The advantages of the pressuremeter

tests are:• In-situ stress-strain behavior of soil and rock can be evaluated

• There is minimum disturbance to in-situ conditions,hence quality of results is superior

• In weathered rocks, where core recovery is poor, pressuremeter test is the only test, which can give realistic data

• Bearing capacity analysis and settlement analysis for

shallow foundations and pile capacity analysis using

pressuremeter data gives more realistic estimate ofpressuremeter data gives more realistic estimate of

actual soil behavior.

The disadvantages of this technique are:

• In sandy strata, where boreholes collapse, it may be

difficult to conduct the test

• Test cannot be conducted in bouldary strata

• In fractured rocks, the membranes may get damaged

TYPICAL INFORMATION

Po – lift off pressure

Pf – yield pressure

Pl – limit pressure

Field Vane Test

FIELD VANE TEST

Used primarily for clays

Inserted in borehole for

deeper tests

Inserted to a depth 4 times

the borehole diameter

Rotated by hand with

torque measuring device

Torque measurements

taken frequentlytaken frequently

• Dilatometer Test

• Calibrated static deformation test

• Performed at 0.1 to 0.2m intervals (nearcontinuous)

• Low volumetric and shear strain induced during

• penetration—measures significance of lateral

• stress• stress

• Accurately measures deformation modulus,

• drained friction angle in sands and undrained

• shear strength in clays

• Test Repeatability Error: 5-15%

• Easy to use from drill rig, barge, even row boat

WAVE PROPAGATION SEISMIC

SURVEY

• Mechanical Wave Measurements

– Crosshole Seismic Tests (CHT)

– Downhole Seismic Tests (DHT)

– Seismic Refraction– Seismic Refraction

• Electromagnetic Wave Measurements

– Ground Penetrating Radar (GPR)

– Surface Resistivity (SR)

– Magnetometer Surveys (MT)

• WAVE PROPAGATION SEISMIC SURVEY

• Why use these tools?

• Determination of site stratigraphy

• Identification of abrupt changes in soil or

• rock formations• rock formations

• Measurement of dynamic properties in

• situ

• Identification of cavities in karst regions

• Identification of underground obstructions

• (Arman et al. 1997)

WAVE PROPAGATION SEISMIC

SURVEY