1. A proper preparation of the cone and other material is inevitable prior to a CPTU test.

Transcription

1 PREPARATION FOR CPTU Procedure for saturation of a piezocone for CPTU 1. A proper preparation of the cone and other material is inevitable prior to a CPTU test. 2. GeoMil Equipment recommends to saturate (de air) the filters which will be used in a silicon oil (viscosity of for example 50 cs) or glycerin. In cases where these liquids cannot be used, a vegetable type of oil (for example sunflower or olive oil) or de mineralized water can be used. 3. It is necessary to maintain the filters in a sufficient amount of liquid under vacuum for at least 24 hours. The filters are sufficiently saturated when no more air bubbles appear to come out of the filters. After saturation, store the filters in an airtight container, in sufficient liquid. 4. In addition, saturate approx. 0.5 to 1 liter of the same liquid. This can be used for the preparation of the cone. Store this liquid in an airtight container as well. 5. Prior to the test, the cone should be checked and properly cleaned. Take off the tip and the retaining ring and put the cone upside down in a vice. 6. Mount the saturation funnel on the cone and fill it with the saturated liquid. Try to avoid possible air bubbles in the saturation chamber, or remove these where possible. Important: Never remove the compensation bush or friction sleeve when you fill the cone with the liquid. This will heavily damage the electronics inside the cone. 7. Put the retaining back in position. 8. Take one of the filters out off the container, preferably with a spoon such that the filter remains fully in the liquid. Put the filter in position on the cone. 9. Screw the tip on the cone hand tight is sufficient. 10. Put a condom over the cone and roll it over the sleeve as far as possible. 11. The saturation liquid can now be poured back into the container. If necessary, the liquid can be filtered first. 12. The cone is now prepared for the test. 13. It is necessary to replace the filter after each test and to follow the above procedure from point 5. in full. Westbaan MC Moordrecht The Netherlands Telephone + (31) Fax + (31)

2 Required items - Excicator bowl (new) or Erlenmeyer flask with rubber plug (old) - Electric vacuum pump - Saturation fluid (silicon oil) - Plastic storage containers - Stainless steel funnel - Latex condoms - Small ladle - Syringe - Sintered filters (brass for multiple use or plastic for one time use) Recommended: Vice, latex gloves, cleaning cloth or paper 1. De aeration of filters and silicon oil - Make sure that the silicon oil is de aerated prior to using it for saturating the Piezocone elements. Place one plastic container filled (50%) with silicon oil in the excicator and apply the vacuum pump for 24 hours. Then make sure that the de aerated silicon oil will not be exposed to air. - Put several P filters into the second plastic container and poor sufficient (preferably de aerated) silicon oil on top (all filters must be submersed in the oil). - Place the container in the excicator, close the cover and apply the vacuum pump. - The filters are sufficiently saturated when no more air bubbles escape from the filters. Advise: The filter de aeration will be accelerated when dropping the filters into the silicon oil after the excicator had been vacuumed for some time. For doing so, place the filters on a thin wire, laid across the container rim. Shake the excicator gently after vacuum had been created so that the filters drop into the oil. - After saturation you can keep the filters in the container (probably to be filled with more de aired silicon oil) for transport. Plastic filters kept in silicon oil swell with time. This may lead to a slightly increased diameter reducing the effective local friction during a CPT! 2. Preparing the Piezocone - Prior to the test, the cone should be checked and cleaned properly. Remove the tip and retaining ring and put the cone top up in a bench vice. Clean the visible cone interior with a soft cloth. Make sure that the friction sleeve and compensation push are mounted. Don t remove the compensation bush, otherwise oil will enter the cone electronics causing serious damage! - Slide the saturation funnel over the cone and fill it with de aerated silicon oil. Try to avoid possible air bubbles in the pore pressure chamber of the cone. Existing bubbles can be removed with the syringe. - Place the clean pore pressure tip, the retaining ring and one filter ring into the oil filled funnel The presaturated filter ring is best taken with the ladle from the storage container and put into the funnel. - Saturate the dead volume of the pore pressure tip by sucking oil with the syringe through one of the channel openings. - Mount the retaining ring, filter ring and pore pressure tip into proper position.

3 Mounting the Piezoelements must be done while these are fully submersed under silicon oil! Wearing latex gloves will keep your hands free of oil. - Submerse a Latex condom into the oil and unroll it over the cone tip and friction sleeve as far as possible. - Release the cone from the vice and pour the silicon oil back into the storage container. - Remove the funnel by sliding it downwards and clean the cone from excess oil with a cloth. Take of your latex gloves to prevent the cone from slipping your hands. - Firmly re tighten the cone tip by hand, not by using a wrench. - The Piezocone is now ready for CPTU testing.

4 Saturation of filters for Piezocones Required: Vacuum pump Flask or Excicator bowl with evacuation valve Rubber plug hook HDPE hose to vacuum pump HDPE Filters Rubber plug Hose to vacuum pump Valve - open Valve - closed Hook holding the filters Filters Silicon oil Filters in oil after flask has been evacuated Step A Fill flask with silicon oil; Put filters on hook; Plug flask; Connect hose from evacuation valve to vacuum pump ; Create vacuum and evacuate (the flask might be moderately heated while evacuating). Step B Close evacuation valve; Shake the flask so that the filters fall into the silicon oil; Filters will saturate with silicon oil automatically; If necessary evacuate again; Fill the filters together with the evacuated silicon oil in the (Piezocone) mounting funnel; Mount the filter and tip to the cone by using the mounting funnel of the saturation kit and keep all parts constantly under silicon oil.

5 Assembling the pore pressure elements under oil Funnel Silicon Oil Filter ring Tip for pore pressure Retaining ring air bubble Funnel shaft with seals Compensation bush Friction sleeve CPTU cone mounted in funnel for assembling the pore pressure tip and filter under oil Step A Mount funnel in a vice; Put cone through funnel shaft into the funnel; Never remove friction sleeve or compensation bush when saturating!!! Fill funnel with de-aired silicon oil; Put de-aired filter ring, retaining ring and tip into funnel (preferably together with de-aired oil); All under oil covering! Remove remaining air bubbles (e.g. with a syringe); Place retaining ring and filter ring on tip screw; Screw tip into the threaded bore of the cone body. Step B Take funnel out of the vice; Dispose silicon oil into an appropriate container;. Cover tip and filter with a diaphragm (e.g. condom; Apply cone as soon as possible and avoid de-saturation before cone is applied; If necessary, fill pushing hole (probably enlarged by casing) with water to avoid de-saturation of the filter elements before water saturated soil layers are penetrated. Dispose HDPE filter rings after each sounding; Use brass filter rings if necessary; Dispose filter rings, larger in diameter than friction sleeve.