INSITU TESTS

Written by ayman. Posted in Insitu test



1-Electric cone penetration test shall be carried out in accordance with ASTM D5887.The test shall be continued to the required depth or to refusal.
2-Judging from expected soil conditions, the machine shall have 20 ton thrust capability.
The cone shall be advanced at a constant rate of 2 cm per second while automatically recording the cone tip and sleeve fiction resistances and pore water pressure at 2.5 cm-intervals.
The used rig (TG 73-200 KN) is working with four cylinders diesel engine providing power of 36 HP
The rig is moving on wheels and tracks at speed of 2 Km/hour to set up at the required location. Hydraulic jack will be used for self leveling of the rig and auger will be used with maximum torque of 500 kg m to achieve the fixation on ground surface and to obtain the required reaction load.
The rig capacity is 20 tons at cone penetration rate of 20 mm/sec. The used cone has an apex angle of 60 degrees, projected base area of 10 cm2  and the friction sleeve has the same outside diameter as the cone base with sleeve surface area of 150 cm2. The cone will advanced with the rate of 20 mm/sec while recording cone resistance, lateral friction and pore water pressure data every 20 mm using electrical data acquisition equipment and a portable computer. The test will be continued to the required depth or refusal. If dissipation test is required the penetration will stop at the required depth and the test will be executed until at lest 50%


Geo Group will carry out this field test following BS standards BS 1377 item 3.2 this test is to determine the soil resistance of a penetration of a 90 degrees closed cone under the effect of a dynamic driving in situ. A continuous record will be a provided with respect to depth of the resistance of the cone in contrast to the standard penetration test SPT but there is no soil sampling
The apparatus is the normal hammer (63.5kg) with standard hammering height of 750mm while the cone diameter is 50mm. the record of the blows will be every 10cm of the depth and will be recorded on the standards chart per BS 1377. The max depth required will not be more than 30mor the top of the hard rock layer if encountered. The depth of each test will be dependant on the soil stratification and as directed by owner during testing. The refusal will be set as 25 blows or more for an interval of 10cm.   


Definition of permeability
Permeability is the property of the soil to transmit water and air and is a fundamental property of soil and rock
The coefficient of permeability (k) is generally expressed in m/sec or cm/sec
Permeable soil is soil with k ≥ 10-6  m/sec
Impermeable soil is soil with k ≤ 10-6 m/sec
These tests are very important to determine soil or rock mass permeability and indicate the condition and continuity for fissures, fractures and cracks in the rock. They serve to determine the inject ability of a rock , and are the guide for selecting the method of impermeabilizing a rock layer for dam construction etc…
We must clarify that within a rock the water circulates through fissures, joints and cracks therefore the quantity of water during field permeability test may have considerable variations according to the orientation of the borehole (parallel or perpendicular) to the orientation of these structures, so we have to know the direction of these structures before test.These tests have to be executed with accuracy and according to international standards, since the result of such test is one of the main data for preparation of a bidder

a-PACKER TEST

Use the packer to seal the hole to test a specific down-hole depth interval to determine the permeability of a particular depth interval or soil horizon
The results of a water pressure test are expressed in Lugeon ( uL )
A Lugeon is defined as the water loss of 1 liter/min. per meter length of test section at an effective pressure 1 Mpa.The length of the section to be tested is given by : L >5 D where D is diameter of borehole Packer tests are carried out to assess the variability of a borehole as it intersects various hydrological units.



 Permeability testing

1. Fill out the data entry sheet as shown in fig. .
2. Turn on pump ,open the outlet valve on the flow-meter and close the by-pass valve to allow water to be pumped down inside the drill rods and flow to the bottom of the hole through the tube in the center of the packer. Once the hole is full of water, the water pressure will begin to rise .Adjust
water pressure by the by-pass valve until water pressure (on the water pressure gauge ) stabilizes at the first test pressure(5 x depth kpa)
3. Start stopwatch at the same time you note the reading on the flow-meter.
    Record reading on data sheet(zero reading -liters)
4. Continue to monitor the water pressure and adjust the by-pass valve if required.
5. Record the flow-meter reading after 5 , 10 and 15 min. . If the three readings vary by less than 5% then
 go to the other pressure . If the variation is greater than 5%,continue recording the flow-meter reading every 5 min. ( at the same water pressure) until the variation is less than 5% or after 5 to 6 further readings ,then this is sufficient , go to the second water pressure.
6. Close the by-pass valve slightly to rise water pressure ,reaches to the second test pressure (10 x depth kpa)
7. Record the flow-meter readings same as in step 5
8. Repeat the steps 6&7 at the third test pressure ( 15 x depth kpa) ,the fourth test pressure ( 10 x depth kpa)
and the fifth test pressure (5 x depth kpa) ,then the test is finished.
 In case of a sudden increase of the water quantities pumped into the hole the test must be stopped, since
 this means the hydraulic fracturing of the rock .
Depth -meter sensor must be kept some centimeters above the ground water depth, so that any leakage can be detected through the uprising of the water .
If a leakage of water is detected the test must be interrupted and performed again at a different level.
The results of the test are plotted on graph
Q ( water loss in liter/min/m) versus P ( gauge pressure)
b- Constant &Variable Head Tests
These tests are performed in highly fractured and eroded rocks and are similar to the tests performed in soil layers.
A part of a drill hole is isolated by casing and the test is performed at an unlined section by adding water to maintain a constant head or the rate of fall in water is measured after a slug of water is added to the hole Both methods are not very much in use ,since they suffer from the potential effects of smear and clogging of defects.

Step 1: hammer the 30 cm diameter ring at least 15 cm into the soil .Use the timber to protect the ring from damage during hammering.
Keep the side of the ring vertical and drive the measuring rod into the soil so that approximately 12 cm is left above the ground.
Step2: start the test by pouring water into the ring until the depth is approximately70-100mm.
Step3: record the clock time when the test begins and note the water level on the measuring rod.
Step4: after 1-2 minutes, record the drop in water level in the ring on the measuring rod and add water to bring the level back to approximately the original level at the start of the test . Record the water level.
Step5: continue the test until the drop in water level is the same over the same time interval.
Take readings frequently (eg.every1-2 minutes) at the beginning of the test , but extend the interval between readings as the time goes on (e.g. every 20-30 minutes)

The vane shear test is an in- situ geotechnical testing methods used to estimate the undrained shear strength of fully saturated clays without disturbance. The test is relatively simple, quick,  and provides a cost-effective way of estimating the soil shear strength; therefore, it is widely usedin geotechnical investigations. Under special condition, the vane shear test can be also carried out in the laboratory on undisturbed soil specimens; however, the use of the vane shear test in in-situ testing is much more common.



Dead Load Reaction
A suitable load for test ( Loader , Excavator…etc) shall be provided to serve as the dead load necessary to provide reaction for the hydraulic jack.
Hydraulic Jack and Pump Assembly
The system consists of a hydraulic jack, hose, pump and pressure gauge. The total assembly is able to withstand  a maximum required pressure
Bearing Plate
Three circular steel plates 25 mm in thickness with different diameters .
Settlement Gauges
Three analogue dial gauges will be used to measure the settlement of the bearing plate. Each gauge has an accuracy of 0.001 inches.  The three gauges will be supported on a reference beam
The reference beam shall be independently supported on two steel supports located 2.4 m from the center of the loaded area.


Hole Preparation:


To obtain suitable measures drilling operations will be carried out with special care to avoid caving along the hole walls.
At the end of the boring operations a rigid plastic pipe of PVC will be installed inside the hole, inner pipe diameter 80-100mm. Pipe thickness will be 5mm.
The annulus between pipes and hole walls will be carefully grouted starting from the hole bottom.
Grout will be formed by water-cement- bentonite (100-30-6 parts in weight respectively). The hole will be grouted from the bottom through a small diameter plastic tube lowered bed together with the PVC pipe.
Withdrawal of the temporary steel casing will be carried out of the end. Water-Cement-bentonite mixture is added to compensate the volume of the casing being extracted.
The top of the PVC pipe will be protected by a manhole cover.
A concrete impact block 500mm x 500mm x 500mm nominal dimensions will be cast on site with the nearest side approximately 500mm from the top of the borehole between 200mm and 250mm of the block will be below ground cast directly against the sides of the excavation No form work will be used below ground level.




Ground Penetrating Radar (GPR)
The velocity of electromagnetic radiation is dependent upon the
material through which it is traveling.  GPR uses this principle to analyze the reflections of radar signals transmitted into the ground by a low frequency antenna.  Signals are continuously transmitted and received as the antenna is
towed across the area of interest, thus providing a profile of the subsurface material interfaces.
Penetration is commonly on the order of 3 to 30 ft. GPR is limited by the contrast in the properties of adjacent material. In addition to having sufficient velocity contrast, the boundary between the two materials needs to be sharp. For instance, it is more difficult to see a water table in fine-grained materials than in coarse-grained materials because of the different relative thicknesses of the capillary fringe for the same contrast. See ASTM D 6432.


Hole Preparation:

To obtain suitable measures drilling operations will be carried out with special care to avoid caving along the hole walls.
At the end of the boring operations a rigid plastic pipe of PVC will be installed inside the hole, inner pipe diameter 80-100mm. Pipe thickness will be 5mm.The annulus between pipes and hole walls will be carefully grouted starting from the hole bottom.
Grout will be formed by water-cement- bentonite (100-30-6 parts in weight respectively). The hole will be grouted from the bottom through a small diameter plastic tube lowered bed together with the PVC pipe.Withdrawal of the temporary steel casing will be carried out of the end. Water-
Cement-bentonite mixture is added to compensate the volume of the casing being extracted.
The top of the PVC pipe will be protected by a manhole cover.
A concrete impact block 500mm x 500mm x 500mm nominal dimensions will be cast on site with the nearest side approximately 500mm from the top of the borehole between 200mm and 250mm of the block will be below ground cast directly against the sides of the excavation No form work will be used below ground level.


The transient method for measuring the thermal resistivity is based on the fact that not only the ultimate temperature rise will depend upon the Thermal resistivity of the material in which the heated body, but also the rate of the temperature rise will depend upon the thermal resistivity of the Material in which the heated probe is immersed.In this method the transient needle or the transient thermal probe is used. The transient thermal probe is a metallic tube which is internally heated by an electrical resistance and its temperatures are measured by two thermocouples which are fixed to the timer surface of the probe at two different positions. The probe has six terminals two for the heater and four for the two thermocouples.
The probe is immersed into the soil. Good contact between the probe and the soil is necessary to give accurate results.
The transient thermal probe method is relatively quick method for measuring thermal resistivity and diffusivity of soil.


Methodology:
The soil resistivity measurements were executed applying Wenner configuration, where the energizing current "I" is injected into the ground through two current electrodes AB, and the potential difference, (∆V) resulting due to the passage of the energized current through the ground is picked up applying another two intermediate electrodes MN. The four electrodes are arranged in straight line Fig (1) , the current electrodes AB were separated by fixed distance, '3a\ while the potential electrodes are situated at point distance "a", "2a", "3a" and "4a" from the source
respectively. The apparent resistivity of the soil applying such array can be determined applying me following equation:
pa=K(∆V/I)


The Flat dilatometer, or DMT, is an in-situ device used to determine the soil in-situ lateral stress and soil lateral stiffness and to estimate some other engineering properties of subsurface soils. It is a relatively simple test and its use in geotechnical investigations becomes more and more common.
ASTM D6635-01 Standard Test Method for Performing the Flat Plate Dilatometer
 


The principle  of a pumping test  is that  if we pump water  from a well  and measure the discharge of the well and the drawdown in the well and in piezometers at knowndistances  from the well, we can  substitute these measurements  into  an  appropriate well-flow equation and can calculate the hydraulic characteristics of the aquifer
Before a pumping test is conducted,  geological and hydrological information  on the
 following should be collected:
- The geological characteristics  of the subsurface (i.e. all those  lithological,  strati- graphic, and structural features that may influence the flow of groundwater)
- The type of aquifer and confining beds
- The thickness and lateral extent of the aquifer and confining beds:
  The aquifer may be bounded laterally by barrier boundaries of impermeable material
   (e.g. the bedrock sides of a  buried  valley, a fault,  or simply lateral  changes
    in the lithology of the aquifer material)

 

The boreholes will be carried out in accordance with French standard  NFP 94-110 (July 1991) which is the conclusion of the general noticeD 60(edition 07177) of the Studies Center Louis Menard combined with the experience gained in this domain. As a rough guide, the standard ASTM D 4719 should be consulted. It is not enough drawn up regarding of the preparation of a satisfactory borehole and the drilling procedures.
The pressure meter boreholes will be executed in accordance with the methods of execution for drilling pressure meter boreholes as per French standard NFP 94-110
The pressure meter boreholes below the water ground level will be executed using bentonite in case of collapsed boreholes walls.
The borehole is drilled so as to minimize wall disturbance and keep a cavity diameter compatible with the probe size.

{slider 14.Trial Pits }
Open test pits, are accessible and afford the most complete information of the ground penetrated. They are generally used for investigations up to 3 m below ground level: they can be hand or machine dug,  according to the nature of soils and to the methods of excavation used, upon Contractor’s judgement.
During excavation the following operations will be performed:
     -soil logging;
     - “pocket penetrometer”  measurements at 20 cm vertical spacing;
      - samples carving, from the bottom or sides of pits.
A representative 1-2 kg sample shall be carved from any tropical layer. Cohesive samples shall be properly waxed, packed and preserved in order to avoid any disturbance .The measured soil strengths, the locations of  samples, the depths to water table and the amounts of ground water percolating shall be reported on the pit logs.


California bearing ratio (CBR) is a penetration test for evaluation of the mechanical strength of road subgrades and base courses.
The test is performed by measuring the pressure required to penetrate a soil sample with a plunger of standard area. The measured pressure is then divided by the pressure required to achieve an equal penetration on a standard crushed rock material. The CBR test is described in ASTM Standards D1883-05 (for laboratory-prepared samples) and D4429 (for soils in place in field), and AASHTO T193. The CBR test is fully described in BS 1377 , Soils for civil engineering purposes.
The CBR rating was developed for measuring the load-bearing capacity of soils used for building roads. The CBR can also be used for measuring the load-bearing capacity of unimproved airstrips or for soils under paved airstrips. The harder the surface, the higher the CBR rating. A CBR of 3 equates to tilled farmland, a CBR of 4.75 equates to turf or moist clay, while moist sand may have a CBR of 10. High quality crushed rock has a CBR over 80. The standard material for this test is crushed California limestone which has a value of 100.
 

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