Download Sherathiya Anand 130540106108 Subject : Building Construction

DARSHAN INSTITUTE OF ENGINEERING & TECHNOLOGY
CIVIL ENGINERING DEPARTMENT
Prepared By: Sherathiya Anand
130540106108
Subject : Building Construction
BEARING CAPACITY OF SOIL
BEARING CAPACITY OF SOILS
GROSS PRESSURE INTENSITY
NET PRESSURE INTENSITY
ULTIMATE BEARING CAPACITY
NET ULTIMATE BEARING CAPACITY
NET SAFE BEARING CAPACITY
SAFE BEARING CAPACITY
METHOD OF MEASURMENT BEARING CAPACITY
OF SOILS
PLATE LOAD TEST
PENETRATION TEST
SAFE BEARING CAPACITY VALUES GIVEN IN CODES
PLATE LOAD TEST
TEST SET-UP
TESTING PROCEDURE
• BY GRAVITY LOADING
• BY TRUSS LOADING
INTERPRETATION OF RESULT
COHESSIVE
SOIL
LOOSE TO
MEDIUM
DENSE
COHESIVE NON COHESIVE
SOIL
PARTLIALLY
COHESIVE
SOIL
PENETRATION TEST
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Evolution of SPT
Test methods and standards
Influence of ground conditions on penetration resistance
SPT energy measurement and corrections for SPT
Use of SPT results
Profiling
Soil classification
Determination of geotechnical parameters
Direct design uses
Evolution of SPT
•The Standard Penetration Test, or SPT, is the most widely used in-situ test, in Hong Kong
and throughout the world, as an indicator of the density and compressibility of granular
soils. It is also commonly used to check the consistency of stiff or stony cohesive soils and
weak rocks. Estimation of the liquefaction potential of saturated granular soils for
earthquake design is often based on these tests. Available design methods for both shallow
and deep foundations rely heavily on SPT results.
•The test consists of driving a standard 50-mm outside diameter thick- walled sampler into
soil at the bottom of a borehole, using repeated blows of a 63.5-kg hammer falling through
760 mm. The SPT N value is the number of blows required to achieve a penetration of 300
mm, after an initial seating drive of 150 mm.
•One of the advantages of the test is that it is carried out in routine exploration boreholes
of varying diameters, so that (in contrast with other in-situ tests, such as the Cone
Penetration Test) there is no need to bring special equipment to site.
ADVANTAGE OF SPT
•The Standard Penetration Test was introduced in 1947, and is now in widespread use because of
its low cost, simplicity and versatility.
•The SPT procedure initially arose from a desire to obtain cheap additional information during
small-diameter sampler driving.
•The test is not yet fully standardised, either nationally or internationally.
•Differences in boring, equipment and test procedure are likely to influence the SPT N value.
• The SPT provides a simple, universally applicable, testing method.
• No sophisticated boring or testing rig is required.
•The test has sufficient versatility that it can provide information on hard-to-sample soil and weak
rocks.
Test methods and standard
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a requirement to drill for at least 1 m before carrying out an SPT
a return to a 63.5-kg (140 lb) drive weight
the specification of an anvil mass between 15 kg and 20 kg
a specified maximum overall weight for the drive assembly (or trip hammer) of 115 kg
the introduction of a maximum rod weight of 10 kg/m
the specification of a maximum permitted curvature for bent rods, in the form of a
relative deflection of 1/1000
• maximum blow counts for the seating drive and test drive: In seating drive In test drive
• In HK (GEO 1995), a SPT test should be terminated when any increment of
75 mm penetration cannot be achieved after 100 blows or where the total
number of blows, excluding the seating drive, reaches 200.
• where the penetration under the dead weight of the rods and hammer exceeds 450 mm,
the N value is recorded as zero.
Test procedures in BS 1377: 1990
• BS 1377: 1990 requires that the borehole shall be cleaned using equipment which ensures that the material
in the test section is 'relatively undisturbed'. Common practice in granular soils is to use a full-diameter shell
or bailer. The maximum depth of the shell is rarely checked, but it is common for the driller to lower a
weighted
tape to check the level of the bottom of the hole. The depth of the bottom of the casing is normally estimated
from the number of casing lengths in use and the stick- up at ground level. While the level of the bottom of
the hole can be calculated, the thickness of disturbed soil or material fallen from the sides of the hole will
not be known.
• The split-barrel sampler is then lowered on rods to the bottom of the hole and the trip hammer assembly
connected. The SPT tool penetrates under the dead-weight of the rods and trip hammer, before being driven
the 150 mm of the seating drive. The blows for the seating drive are recorded for two 75 mm increments of
penetration, although this is optional in the current British Standard. It is commonly assumed that the 150
mm seating drive penetrates completely the zone of soil disturbed by the action of boring, but in some cases
(for example, in granular soil) this may not be
so. The sampler is then driven a further 300 mm, sometimes recording the blows for
each of four 75 mm increments of penetration, sometimes for two 150 mm
increments, and occasionally even for a single 300 mm drive. The rate of application
of blows is not standardised, but may typically be about 15-20 blows per minute. The total blows for the last
300 mm of penetration is the penetration resistance, N. When values are obtained using the standard cutting
shoe, the result is recorded either as SPT or as SPT (S) on the driller's daily report. When the solid 60° cone
is in use, the test is recorded as SPT (cone) or SPT(C).
METHOD OF IMPROVING BEARING CAPACITY OF SOILS
INCREASING
DEPTH OF
FOUNDATION
COMPACTION
OF SOIL
VIBRATION
VIBROFLOATION
COMPACTION
BY PRELOADING
USING SAND
PILES
DRAINAGE OF
SOIL
CONFINING THE
SOIL
GROUTING
CHEMICAL
TRATMENT