Supervision in Chile

The site investigation was in Valparaiso Region, Chile. It was carried out by a local site investigation contractor and technically supervised by the client�s engineering representatives. Liquefaction potential 28 boreholes were required. Lankelma was brought in when 2 of these showed a liquefaction potential at approximately 20m and the SPT values produced were unsatisfactory. Lankelma was chosen to supervise the job due to our engineers� field experience with different combined CPT and drilling systems and environments, backed up by interpretation and data processing knowledge. The site is in a seismically active zone, a cause for extra concern, also, a cause for confusion as seismic activity usually causes compaction of granular soils, particularly at these depths. CPTs were required to be carried out at these locations, from the base of the boreholes, down a further 20m. The local site investigation contractor had never carried out CPTs before and had only recently purchased a �Memo-cone� acoustic system for the purpose of these works.
Modified drilling rig The drilling rig was modified to carry out the cone penetration testing. Firstly a small frame was welded on to allow the fixing of a microphone unit. Next, the top of the casing was modified to support the pushing rods. This utilisation method is similar to that used on drilling ships. In this situation, where data is not transmitted through a cable within the push rod ^[1] , the cone contains a memory system that logs the data as the test is being carried out. It is then downloaded from the cone when back on the surface. The data is concurrently transmitted real-time, acoustically, up the rods where it is picked up using a microphone push head. The microphone is connected to the logging computer which displays the results real-time on the computer screen.
Snapped rod The first CPT of the project resulted in the cone snapping from the CPT rod at the crossover. At first it was thought that it may have been pushed too hard. Once the cone had been recovered it was noted that the crossover section had been over-machined, leaving the metal on the crossover dangerously thin. The cone was damaged during the retrieval process and had to be replaced. Test results confirmed there is a problem with liquefaction on the site and remediation will be necessary. The tip resistance values fell well below those required. The local site investigation contractor carried out a very professional operation regarding the performing of the CPTs. All members of their team were diligent in the preparation of the cone before each test. There were teething problems on the first location. This was mainly down to problems with the equipment, not to the operation of it. ^[1] CPT specific rigs use a coiled rod system in which the cable is pre-threaded through the push rods and connected to the cone.