Effect of rock strength on the degradation of ballast equipped with under sleeper pad

Abstract

Railway ballast aggregates are the components that are dramatically influenced by train passage and lead to track degradation. The current study is conducted to determine the effects of ballast Uniaxial Compressive Strength (UCS) values of ballast parent intact rock core specimens and Under Sleeper Pad Bedding Modulus (USP-BM) on ballast abrasion and degradation and settlement through an extensive laboratory program. For this purpose, At the onset, to investigate the physical and mechanical characteristics of two ballast types, rock core specimens derived from parent intact rocks of Shahriar (S) and Kouhin (K) quarries were classified by implementing a series of standard laboratory tests and UCS test on prepared rock cores. Subsequently, the rock cores were categorized based on UCS values as hard rock core (159 MPa) and considerably hard rock core (285 MPa). Consequently, by adjusting the ballast grading curve according to the Australian TfNSW heavy rail network, various laboratory tests were carried out, an indication of the amount of fine-grained material with a sieve diameter of finer than 75 µm, clay lumps, bulk specific gravity, bulk density, Los Angeles abrasion, Micro-Deval abrasion, water absorption, and flakiness index. In the following, 18 laboratory experiments of the ballast box test were conducted in the absence and presence of soft and stiff USPs with USP-BM of 0.13 and 0.3 N/mm3 under 200,000 loading cycles. Finally, the results of ballast box tests were extracted in the index forms of settlement, estimation of correlation equation of ballast settlement, ballast breakage index (BBI), ballast damping ratio (DR), and ballast stiffness. Results of analysis demonstrate that by changing the USP type from stiff into soft for S ballast quarry type, the values of settlement, BBI and stiffness have declined by 16.6%, 7.9%, and 34.6%, respectively, while DR has increased by 114.66%. On the other hand, these reported percentages have changed due to the increased UCS value of Ballast parent intact rock core specimens in the K ballast quarry type. In the long run, the results delineate that the soft USP is most effective in controlling the ballast stiffness and settlement when focusing on the ballast rock cores' values of UCS.