1. DARSHAN INSTITUTE OF ENGINEERING & TECHNOLOGY
CIVIL ENGINERING DEPARTMENT
Prepared By: Sherathiya Anand
Subject : Building Construction
BEARING CAPACITY OF SOIL

2. BEARING CAPACITY OF SOILS
GROSS PRESSURE INTENSITY
NET PRESSURE INTENSITY
ULTIMATE BEARING CAPACITY
NET ULTIMATE BEARING CAPACITY
NET SAFE BEARING CAPACITY
SAFE BEARING CAPACITY

3. METHOD OF MEASURMENT BEARING CAPACITY OF SOILS
PLATE LOAD TEST
PENETRATION TEST
SAFE BEARING CAPACITY VALUES GIVEN IN CODES

4. PLATE LOAD TEST TEST SET-UP BY GRAVITY LOADING BY TRUSS LOADING
TESTING PROCEDURE
INTERPRETATION OF RESULT

7. COHESSIVE
SOIL
LOOSE TO MEDIUM
NON COHESIVE SOIL
PARTLIALLY COHESIVE SOIL
DENSE COHESIVE SOIL

8. PENETRATION TEST 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

9. 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.

10. 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.

11. Test methods and standard
• 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.

15. 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 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).

17. METHOD OF IMPROVING BEARING CAPACITY OF SOILS
INCREASING DEPTH OF FOUNDATION
COMPACTION OF SOIL
VIBRATION
VIBROFLOATION
COMPACTION BY PRE-LOADING
USING SAND PILES
DRAINAGE OF SOIL
CONFINING THE SOIL
GROUTING
CHEMICAL TRATMENT