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Soil and rock strength
Published in Burt G. Look, Earthworks, 2023
The CBR is an empirical index test used to inform the pavement design on subgrade and pavement material properties. Due to laboratory testing requirements, the CBR test may not represent the in-situ condition. The soaked CBR test is used to model flood and adverse conditions, which cannot be measured in situ.
Pavement infrastructure (roads and rails)
Published in Buddhima Indraratna, Ana Heitor, Jayan S. Vinod, Geotechnical Problems and Solutions, 2020
Buddhima Indraratna, Ana Heitor, Jayan S. Vinod
The design of flexible pavements is generally based on California Bearing Ratio (CBR) tests results. The CBR value is determined by penetration tests and is defined as the rate of the force per unit area required to penetrate a soil mass with a standard circular solid steel plunger of 50 mm diameter at rate of 1 mm/min to that required for the penetration of standard material. The standard material is usually confined crushed rock (i.e. CBR of 100%). The standards load for 2.5 mm and 5 mm penetration are generally 13.2 kN and 20.0 kN, respectively.
Sustainable Drainage
Published in G.L. Sivakumar Babu, Prithvi S. Kandhal, Nivedya Mandankara Kottayi, Rajib Basu Mallick, Amirthalingam Veeraragavan, Pavement Drainage, 2019
G.L. Sivakumar Babu, Prithvi S. Kandhal, Nivedya Mandankara Kottayi, Rajib Basu Mallick, Amirthalingam Veeraragavan
It should be noted that a high degree of compaction (such as 95% of maximum proctor density) is generally not specified for the subgrade – as that would lead to a reduced permeability of the subgrade soil. A lower compaction level is specified (depending on the desirable permeability), and accordingly a reduced CBR should be considered in the pavement design.
Effect of compaction energy on grain breakage of CDW, local soil and soil-CDW mixtures
Published in International Journal of Geotechnical Engineering, 2022
Thales Brito Da Silva, Natália De Souza Correia, Vinícius De Oliveira Kühn
Figure 5 presents the results of CBR tests with limits established by the Brazilian Transportation Department (DNIT 2006) for use as base, subbase course and subgrade. The CBR values are equivalent to some limits established by AASHTO (2008). In general, the higher the CBR value of a particular soil, the more strength it is to support the pavement. As expected, the soil (Figure 5a) presented low CBR values in both compaction energies, with the higher values for the modified energy. Therefore, the application of this soil is only for subgrade layers, according to minimum CBR criteria (CBR of 2%) of DNIT (2006). In general, research has shown that if a subgrade has a CBR value less than 10, the subbase material will deflect under traffic loadings in the same manner as the subgrade and cause pavement deterioration (Schaefer et al. 2008).
Evaluation of layer coefficient ratios for geogrid-reinforced bases of flexible pavements
Published in Road Materials and Pavement Design, 2022
G. Narendra Goud, B. Ramu, B. Umashankar, S. Sireesh, M. R. Madhav
Three types of subgrades, namely, poor, fair, and good, were considered in the present study to assess the behaviour of model pavement with geogrid reinforcement. Typically, poor, fair and good subgrade soils have California Bearing Ratio (CBR) in the range of 3% to 4%, 5% to 6% and 7% to 9%, respectively. In the present study, locally available soil from IIT Hyderabad Campus, India, was collected and tested for various properties. The specific gravity, liquid limit, plasticity index, and free swell index of subgrade soil were found to be 2.7%, 48%, 24%, and 15%, respectively. To identify suitable test conditions that simulate poor, fair, and good subgrades, the CBR of soil was determined at different moisture contents and compacting the soil using standard Proctor compaction energy equal to 600 kN-m/m3. The CBR value ranged from 3.1% to 7.1% corresponding to moisture contents of subgrade soil ranging from 17.6% to 16.2%. As expected, the CBR value was found to decrease with an increase in moisture content. The resilient moduli of poor, fair, and good subgrades considered in this study were 31, 47, and 62 MPa, respectively, determined in accordance with IRC-37 (2018).
Stabilization of aeolian sand with combined use of geofiber and synthetic fluid
Published in Cogent Engineering, 2019
CBR testing is routinely used in mechanistic design as an indicator of strength and bearing capacity of a subgrade soil, subbase, and base course material in road and airfield pavements. The CBR of a soil is the ratio obtained by dividing the stress required to cause a standard piston to penetrate 2.54 mm, 5.08 mm, 7.62 mm, 10.16 mm, and 12.70 mm into the soil by a standard penetration stress at each depth of penetration (ASTM D 1883). The CBR is an index value comparing the strength of the soil to that of crushed rock (Liu & Evett, 2003). Some general ratings of soils to be used as subgrade, subbase and base courses of roads and airfield runways corresponding to various ranges of CBR values are presented in Table 4 (Asphalt Institute, 1962; Bowles, 1978). The CBR test is an economical and simple tool for measuring strength gain and improvement in soils. CBR tests in this study were performed in accordance with ASTM D 1883. CBR performance of each soil sample was evaluated at each of the penetration depths (i.e., 2.54 mm, 5.08 mm, 7.62 mm, 10.16 mm, and 12.70 mm). For a reliable CBR value, an average of minimum two CBR tests is recommended (Yoder & Witczak, 1975). Thus, in this study two replicate samples were tested for each of the CBR value reported (i.e., each reported CBR value is presenting the average value of the two tests).