Analisis Data Lendutan Perkerasan dengan Program Backcalc untuk Sistem Struktur 2-Lapisan
DOI:
https://doi.org/10.5614/jts.2003.10.1.4Keywords:
Lendutan maksimum, Cekung lendutan, Pemodelan struktur perkerasan, Modulus perkerasan, Back calculation, Program backcalc.Abstract
Abstrak. Data lendutan masih umum digunakan dalam proses evaluasi kondisi struktur perkerasan, khususnya karena pengukuran lendutan dapat dilakukan secara non-destruktif. Lendutan maksimum (dmax) dan cekung lendutan yang terjadi akibat beban roda kendaraan secara teoritis dapat mencerminkan kondisi struktur perkerasan yang dinyatakan dengan modulus (E) dan konstanta poisson (μ). Makin besar nilai dmax yang terjadi, maka nilai E struktur perkerasan akan makin rendah, dan sebaliknya. Sedangkan, cekung lendutan akan menentukan distribusi nilai E untuk masing-masing lapisan perkerasan, dimana nilai E untuk lapisan yang lebih atas biasanya akan lebih besar dibandingkan dengan nilai E untuk lapisan dibawahnya. Pengaruh nilaiμ terhadap hubungan antara nilai dmax dan nilai E umumnya dianggap tidak signifikan. Back Calculation merupakan proses perhitungan balik untuk mendapatkan modulus perkerasan berdasarkan data lendutan dengan mempersamakan cekung lendutan teoritis terhadap cekung lendutan yang diukur di lapangan. Namun, dari literatur dan dari hasil analisis yang telah dilakukan, cekung lendutan teoritis ternyata sulit untuk dapat dibuat tepat sama dengan cekung lendutan survai kecuali di beberapa titik pada cekung lendutan yang sengaja dijadikan target dalam melakukan proses konvergensi. Makalah ini mendiskusikan proses Back Calculation hanya untuk struktur perkerasan yang dimodelkan sebagai sistem struktur dua-lapisan dengan menggunakan program komputer BackCalc. Untuk sistem struktur dua-lapisan, konvergensi umumnya terjadi pada titik lendutan maksimum dan pada titik belok dari cekung lendutan. Disamping itu, lendutan maksimum diketahui lebih berkorelasi dengan modulus perkerasan, sedangkan lendutan titik belok lebih berkorelasi dengan modulus tanah dasar.Abstract. Deflection is still used in pavement condition evaluation, particularly because it can be measured in a non-destructive way. Maximum deflection (dmax) and its respective deflection bowl caused by the wheel load theo-retically reflect structural conditions of a pavement, expressed in terms of modulus (E) and poisson ratio (μ). The higher the value of dmax, the smaller the modulus will be. Meanwhile, deflection bowl dictates the distribu-tion of the modulus for each pavement layer, where upper layers normally have higher modulus. The effect of poisson ratio on the relationship between deflection and pavement modulus is usually assumed to be insignificant. Back calculation is a process whereby pavement modulus is to be back calculated from deflection data, in such a way, that the resulting theoretical deflection bowl is to be matched with the measured deflection bowl. However, from the literature and from the analysis carried out in this research, it was found that it would be quite difficult to obtain a perfect match between the two deflection bowls, except at few deflection points at which convergences were exercised. This paper discusses back calculation for pavement structures modeled as a two-layered system by using com-puter program BackCalc. For two-layered systems, in general, convergences occurred at the maximum deflec-tion point and at the inflection point of a deflection bowl. Whereas, maximum deflection was found to correlate better with pavement modulus, and deflection at the inflection point correlated better with subgrade modulus.
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