1. Texas Tech University is constructing a new road near the Department of Civil
ID: 1711971 • Letter: 1
Question
1. Texas Tech University is constructing a new road near the Department of Civil and Environmental Engineering building. A project engineer is planning to get the soils from an offsite borrow pit in order to use them as subgrade materials for the roadway pavement. The following laboratory test results for Atterberg limits and sieve-analysis were obtained for the soil sample from the offsite borrow pit. [4 points] Sieve analysis Sieve Size No. 8 (2.36 mm) No. 16 (1.18 mm) No. 40 (0.425 mm) No. 60 (0.250 mm) No. 100 (0.150 mm) No. 200 (0.075 mm) Percent passing by weight 100 99.3 97.9 93.1 77.2 58.6 Atterberg limits Liquid limit (LL) Plastic limit (PL) 29 19 (a) Classify this soil according to AASHTO system including the group index. Show how you arrive at the final classification. (b) According to AASHTO system, is this soil excellent to be used as subgrade materials?Explanation / Answer
a) Given percentage of particles paassing 0.075mm sieve is 58.6 which is gratere than 35% . Therefore the soil is of Silt-Clay general classifictaion
Liquid limit = 29 (<40)
Plastic limit = 19
Plasticity index = 29-19=10(<=10)
Per AASHTO, the soil will be classified as A-4 bvecause it has fall under 40 max liquid limit and 10 max plasticity index
b)No .According to AASHTO, the soil is fair to poor material for use as subgrade
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