INSITU TESTS! Shear Vanes! Shear Vanes! Shear Vane Test! Sensitive Soils! Insitu testing is used for two reasons:!

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1 In-situ Testing! Insitu Testing! Insitu testing is used for two reasons:! To allow the determination of shear strength or penetration resistance or permeability of soils that would be difficult or impossible to recover in an undisturbed state for laboratory testing, using conventional drilling equipment! To extend the data recovered from expensive boreholes over an extensive area quicker and hence at reduced cost" Shear Vanes! The SHEAR VANE TEST estimates the in-situ (undrained) shear strength of saturated CLAYS! the test is unsuitable for other soil types! The vane consists of four thin stainless steel blades on the end of a set of rods. It is pushed into the clay below the bottom of a borehole! to a depth of ca 3x borehole diameter! Torque is applied to the head of the rods until the clay fails. Shear strength is determined from the size of the vanes and the torque at which the soil fails! at the point of failure the vane rotates and no more torque can be applied! vanes often come with different sized blades for varying soil strengths" Shear Vanes! Shear vanes vary in size from hand operated to machine devices! In some very soft soils the vane may be pushed directly into the soil without a borehole! some vanes are supplied with a vaneless head so that the friction of the rods with the soil can be determined and subtracted from the vane reading! Shear Vane Test! REMOULDED shear strength can be measured by repeating the test after the clay has been rotated through several revolutions" 1

2 SENSITIVE SOILS loss their strength when disturbed or remoulded! their natural structure is damaged or destroyed! Some clays are extremely sensitive to remoulding! eg QUICK CLAYS! quick clays are restricted to previously (Pleistocene) glaciated areas of the northern hemisphere eg Norway! Remoulding for testing is normally done by kneading or shear vane" Penetrometers! Penetrometer tests measure the amount of force needed to drive a probe or sample tube into the ground! Penetration Tests can be divided into two categories:! Dynamic Penetrometers! the cone or sampler is propelled into the ground by a falling weight! Raymond sampler or Standard Penetration Test! Scala Penetrometer! Static Penetrometers! the cone or sampler is propelled into the soil using hydraulic pressure! Dutch cone! Electric cones! Penetration Tests! STANDARD PENETRATION TEST (SPT)! sample is collected! can be used in sandy and some gravelly soils! equipment and technique may affect results! CONE PENETRATION TEST (CPT)! no sample is collected! unreliable in gravelly or rocky soils! less prone to error due to differences in equipment and technique! Standard Penetration Test" Often refered to as the Raymond spoon or SPT test! Carried out by using a drilling rig to bore down to testing depth! eg percussion or hollow stem auger rig! The bit or centre rods are removed and the sampler is then attached to the drill rods! The sampler consists of a 50mm O.D. thick walled steel tube, 675 mm long, fitted with a cutting shoe at the bottom and a non return valve on top" 2

3 Standard Penetration Test! Once the sampler is at the desired depth a 65 kg drop hammer and anvil assembly is screwed onto the top of the drill rods! The sampler is then driven into the soil using a 760mm drop for each blow! the blows for each of three 150mm advances are counted and those for the second and third interval reported as the N value for the soil in blows /300mm! often the blows for six 75mm advances are counted! ignore the blows for the first 2 lots of 75 mm penetration and total the blows for the next 4 lots of 75 mm penetration! The sampler is then recovered, opened and the disturbed sample is obtained for description! Standard Penetrometer Test (SPT)! The sampler is driven 450mm into the soil! The N value is the number of blows to drive it in the last 300m! Automatic hammers with trip devices improve the reliability of the test! This test simulates the driving of a tube pile using a drop weight and was first developed in USA by the Raymond Piling Co. as a means of assessing ground conditions for pile foundations in sands and gravel" N value! SPT Sampler / Raymond Spoon! During the course of a standard penetration test, the number of blows for each 75 mm penetration was recorded as shown.! The standard penetration resistance = N Value = the total of the last 4 readings! (i.e = 53)! Depth (mm) Number of blows The Raymond Spoon unscrews and splits apart for easy removal of the disturbed sample! Ball valve inside! SPT Sampler / Raymond Spoon! Standard Penetrometers! Results vary with equipment and operational techniques! Soil samples can be recovered from the sampler! Most percussion rings can carry out this test without needing other equipment! 3

4 Dutch Cone Penetrometer! The Dutch Cone penetrometer measures penetration resistance as the hydraulic pressure required to advance a specially designed cone through the soil a distance of 200mm! The results are plotted as profiles of point resistance and in case of the 10 tonne machine friction capacity versus depth.! One of the big advantages of the Dutch cone penetrometer is the continuous nature of the readings obtained" (Dutch) Cone Penetrometer! Three different driving devices are currently in use in NZ:! 2.5 tonne medium sounding penetrometer! uses a hand wound rack and pinion system to push a two piece mantle cone into the soil.! 10 tonne capacity motorised deep sounding penetrometer! uses a hydraulic ram powered by a small diesel or petrol engine to drive the three part friction cone into the ground.! anchored to the ground by an array of screw anchors! 20 tonne capacity computerised penetrometer! uses an electronic cone and is usually mounted on a fourwheel drive truck! Cone Penetrometer Test (CPT)! The CONE PENETROMETER has a conical head on the end of a string of solid rods fitting inside a string of hollow outer rods! a friction sleeve in the head behind the cone can be advanced independently of the cone! The cone is pushed through the soil hydraulically & the pressure measured! Using the inner rods the cone is first pushed a set distance (50-80mm) into the soil at a uniform rate of 20mm/sec! the sleeve remains stationary! (Dutch) Cone Penetrometer! Total resistance is measured when cone tip & friction sleeve are advanced together! Friction ratio! R f = f sc / Q c x 100" Then the outer rods are pushed downwards (advancing the cone as well), & the test is repeated" Cone Penetrometer Test (CPT)! No borehole is required for the test! A continuous record is recorded! Used to estimate bearing capacity of a soil! corrections & allowable bearing pressures are read from empirical charts! Also called the DUTCH CONE PENETROMETER! Cone Penetrometers are faster and cheaper than drilling and standard penetration testing! Cone Penetrometer Technology! The ELECTRIC CONE is a cone penetrometer with built-in strain gauges which measure Qc & fsc continuously! Other sensors can be included in the cone head, especially for ENVIRONMENTAL INVESTIGATIONS and determination of contaminants and groundwater contaminants! these sensors are used as screening tools with data being confirmed by sampling and laboratory analysis! Ultrasonic transmitters in the cone can be used it enable the cone penetrometer to be used on stiffer soils! Some penetrometers now have directional capability" 4

5 Cone Sensors! Cone Penetrometer plus Soil Samples! No sample is collected during the CPT test! However it is possible to collect small diameter, disturbed soil samples with the same CPT pushing equipment immediately AFTER the CPT test! Thus soils can also be entered on the CPT log! Scala Penetrometer! The SCALA PENETROMETER is a small hand operated cone penetrometer used in:! simple site investigations of low cost structures (eg houses)! some roading investigations! some airport runway investigations! Charts are available to correlate Scala penetrometer soundings with! Acceptable Bearing Pressure (ABP)! California Bearing Ratio (CBR)! Scala Penetrometer! First used for testing road subgrades prior to placement of aggregate layers as a simpler version of the California Bearing Ratio or CBR test! It has been adopted as a means of foundation soil assessment in NZS 3604: 1984! The test consists of driving a steel cone of end area mm 2 into the ground using a drop hammer of 9 kg falling a distance of 500mm! The penetration (distance) which results from each blow is recorded and reported as the penetration / blow = e" Scala Penetrometer! Borehole Visual Inspection! Geologists & engineers can be lowered down large boreholes with diameters of 0.75m or greater to directly examine and log subsurface conditions & soil stratigraphy, & to take bulk samples where necessary! boreholes may have a diameter from m! holes may be unlined, lined with steel mesh, or cased in steel pipe (with observation & inspection windows)! Holes for visual inspection may be excavated using large-diameter solid stem augers or bucket augers! 5

6 Borehole Visual Inspection! The geologist or engineer is lowered down the borehole in an aluminium cage or on a swinglike stand! equipment taken includes geological hammer and compass & sampling tools! a safety harness is essential! the hole must be well ventilated & kept free of hazardous gases! Advantages of Visual Inspection! Downhole logging of bucket auger borings provides valuable geologic structural and lithologic details! Especially useful in landslide investigations as it allows measurement of dip & strike of bedding, fracture, and shear planes as well as slickenside bearings on landslide surfaces! Bulk samples of shear surfaces can be taken for laboratory testing such residual shear strength of remoulded samples" 6