Overview
The new standard across the board test ME (Standard SN 670 317b) has eliminated certain shortcomings of the previous experimental procedure, but were at the same time the time required for testing, and thus their costs significantly increased. The practice of installation check the road with a systematic application of quality management attracts a corresponding inspection efforts. Both factors contribute to increase the control effort.
The aim of this project is to look for ways which can reduce significantly the amount of time and costs without sacrificing quality control activities. The purpose of the examination of the applicability of the light falling weight was offered by some manufacturers in Germany and Denmark. The Light Drop-Weight Tester is fast and simplified (no counterweight needed). Experimental procedure allows the implementation of a dense network of checkpoints with minimal effort and provides an ideal control tool for small construction sites (grave fills, foundation backfilling, etc.).
The scope of this research project is to investigate the possibilities to carry out compaction controls of unbound layers with a much lesser use of time and cost resources in comparison to the standardized plate loading test ME (SN 670 317b) while maintaining the current quality levels.
The research deals in particular with the application of a light falling weight device being manufactured, partially with minor differences in construction and accessories, by a number of suppliers in Germany and Denmark.
Conducting comparative measurements between the load plate test ME and the drop weight test the extent of 6 case weight loads per ME-test on unbound foundation layers at about 100 sites. In 25% of cases of ME-trial comes with a second load on the application and there are there also the specific gravities of the foundation layers identified with the nuclear device.
The totality of the results will be evaluated with the aim of determining a practically applicable correlation, or for the determination of those conditions of application, where the application of small falling weight seems less indicated.
A total of 290 sets of measurement data on sub-base layers from the years 1966 until 2007 have been available for the research project. Of these data, the results of 49 measurement sites have been discarded for various reasons, leaving a total of 241 data sets fort the analysis. The research project was limited to the testing of unbound sub-base layers, which represents the most common application of the plate loading test. The layout of the measurement points was chosen in order to obtain a good comparability of results.
Funding
Results
The light weight deflectometer allows the determination of the bearing capacity of untreated layers at single points similarly to the plate loading test. The ease of use of the device allows the control of the bearing capacity of sub-base layers or of the formation level in very time. The results of the measurement are immediately available. Therefore, the device is particularly suitable as an alternative for compaction controls with intense coverage or for the internal testing by the contractor. The light falling weight tester can be used in all places with difficulty of access, as it is light, can be operated by a single person and does not need a counter-weight as for the plate loading test. Different possibilities of application, low cost characteristics and the direct availability of results make this device particularly suitable for everyday construction site controls.
The light weight deflectometer is an ideal complement to the plate loading test for the determination of the bearing capacity of unbound sub-base layers:
- As opposite to the costly and time consuming plate loading test, the light weight deflectometer allows to carry out a large number of measurements with an easily transportable apparatus which can be operated by a single person alone at low cost. This also contributes to increase the meaningfulness of the statement about the homogeneity of the achieved compaction and the bearing capacity.
- The proposed procedure of determining the mean value of five different individual measurements allows assessing the bearing capacity of a surface of about 2 m2 .
- The results obtained in very timely manner are sufficiently precise for the use of the light weight deflectometer as an alternate or complementary solution for compaction controls with intense coverage or for the internal testing by the contractor.
- The light weight deflectometer can also be used under difficult circumstances, in particular in places where a counter-weight needed for plate loading tests can only be provided with great effort or where the space conditions are inadequate for a correct placement of the reference beams.
Technical Implications
For the unified use of the light weight deflectometer in Switzerland it will be necessary to introduce requirement values for the dynamic deformation modulus Evd specification SN 640 585 and to create a Swiss specification for the application conditions of the device in the standard.
Requirement values for the dynamic deformation modulus Evd can be introduced in the standard specification SN 640 585 for the use of the light weight deflectometer for quality control on smaller construction sites.