تقييم جهاز فحص الاختراق الديناميكي المحمول في تحديد معامل رد فعل التربة المرن للترب الرملية

Evaluating Performance of Portable Dynamic Cone Penetrometer in Characterizing Subgrade Reaction Modulus of Sandy Soil

Abstract

The rigid pavement is a system consists of different layers that are capable to resist traffic loading. The traffic loading is transmitted through the pavement layers then finally reaches to the subgrade that works as supporting platform for the pavement. The subgrade reaction modulus (ks), which characterizes the reaction of soil layers when subjected to loads, has been calculated by using the plate load test (PLT). The PLT requires a specialized engineering team, high cost and time to conduct the test. This study presents an experimental and theoretical work to predict the subgrade reaction modulus of sand soils through developing simple and reliable statistical models based on dynamic measurements obtained from performing the in-place dynamic cone penetrometer test.
To achieve the aim of this work, three testing techniques were carried out including: dynamic cone penetrometer (DCP), plate load test (PLT) and sand replacement test (SRM). These tests were implemented to assess geotechnical engineering characteristics of subgrade sand soils collected from three roadway projects located at Karbala, Iraq. To evaluate the effect of compaction process on subgrades’ performance, three compaction levels were considered in preparing laboratory testing model using three number of compactor passes (NOP).
Soil parameters obtained from the DCP were California bearing ratio (CBR), penetration index (DCPI) and bearing capacity (q), while those determined from performing the PLT test include: subgrade reaction modulus, maximum settlement, and Young’s elastic modulus. Finally, the SRM were carried out to assess: moisture content, dry density, and degree of compaction.
The results of experimental work showed that the highest value of degree of compaction is (98.85%) for (18 NOP) and the lowest value is (87.43%) in for (10 NOP), the values of ks ranged from 135 to 230 kPa/mm, DCPI value varied from 14.5 to 26 mm/blow, CBR ranged from 8 to 13.5%, q ranged from 105.45 to 149.42 kPa. These results were statistically analyzed and related with each other to find the best fit regression model to predict ks.
The statistical models are classified into three groups:1st group: models based on DCP Measurements, 2nd group: models based on basic soil properties, and 3rd group: models based on DCP and basic soil properties. The statistical analysis results exhibited that the ks can be predicted based on DCP measurements and physical properties measurements (DC, Cc, Cu) with significant R-squared equals to 88%. The finding of statistical analysis proved that DCP devices can be used as a non-destructive tool for field assessing the subgrade reaction modulus quickly and accurately.