ABSTRACT: Susukan Bridge is a bridge located on section II Semarang-Solo Highway,
Gedawang-Penggarong. In the process of bridge construction, soil mass
movement occurs around the abutments (ABT-1) which resulted uneven
horizontal deformation of the Susukan Bridge Abutment (ABT-1) on the right
and left. The objective in this work are to identifying the main causes of
deformation, behavior of slopes, and maximum deformation that can occur at the
Susukan Bridge Abutments (ABT-1).
Data of slope topography, physical properties and soil mechanics, and
technical data of abutments are used as input models in the numerical simulations
performed with the program PLAXIS. Simulations performed with the
idealization of the slopes serve as a 2-D plain strain model. Seven models used in
the simulation include the conditions of the natural slope (Model I), slope by
construction abutment and pier bridge (Model II), cutting the hill (Model III), the
addition of bored pile in construction of abutments (Model IV), embankment on
slope foot (Model V), the operational of bridge (Model VI), and operating with an
earthquake load (Model VII).
The results showed that the natural slope in an unstable condition with safety
factor of 1.154 (rainy season) and 1.368 (dry season) with a potential landslide at
the top to the bottom of the Abutment (ABT-1). Soil mass movement on the slope
are triggered by the construction work of the Abutment (ABT-1) which reduces
the strength of the soil, and olso the excavation at the foot of the slope. Soil mass
movement patterns indicate the type of landslide movement (slide) with a curved
field tends to slip (with the rotational movement). Construction of abutment
secondary bored pile are not effective in raising safety factor of the slope, so that
in this phase slope is in unstable condition with the safety factor of 1.058 in the
rainy season and 1.092 in the dry season. Embankment at the foot of slope can
increase the safety factor from 1.058 to 1.794 in the rainy season and from 1.092
to 2.128 in the dry season. Horizontal deformation of Abutment (ABT-1) in the
wet season and dry season are 44.59 cm and 20.23 cm (Model II), 40.91 cm and
16.33 cm (Model III), 46.33 cm and 19.51 cm (model IV), 48.93 cm and 20.55 cm
(model V), 48.96 cm and 20.97 cm (model VI), and 55.60 cm and 27.1 cm (model
VI). Movement of the abutments (ABT-1) is a combination of rotational (rolling)
and translation movement, where the end of the pile also moves from its position.
The maximum horizontal movement of the abutments is 55.597 cm at the
operational phase with the earthquake loads. Considerable movement of abutments
on the rainy season simulation than in the dry season indicate that groundwater has a
significant influence on the horizontal deformation of the abutment so that specific
solutions are needed to control the ground water on the slope.
INTISARI: Jembatan Susukan merupakan jembatan yang terletak di Jalan Tol
Semarang-Solo seksi II Gedawang-Penggarong. Dalam proses pembangunan
konstruksi jembatan, terjadi gerakan massa tanah si sekitar Abutmen (ABT-1)
yang mengakibatkan Abutment (ABT-1) Jembatan Susukan mengalami deformasi
horisontal yang tidak merata di sisi kanan dan kirinya. Tujuan penelitian ini yakni
untuk mengetahui penyebab utama deformasi, perilaku lereng, serta deformasi
maksimum yang dapat terjadi pada Abutmen (ABT-1) Jembatan Susukan.
Data topografi lereng, sifat-sifat fisik dan mekanik tanah, serta data teknis
abutmen digunakan sebagai input model simulasi yang dilakukan secara numeris
dengan program PLAXIS. Simulasi dilakukan dengan idealisasi lereng menjadi
model 2-D plain strain. Tujuh model dipakai dalam simulasi meliputi kondisi
lereng asli (Model I), lereng dengan konstruksi abutmen dan pilar jembatan
(Model II), pemotongan (cutting) bukit (Model III), penambahan bored pile pada
konstruksi abutmen (Model IV), penimbunan kaki lereng (Model V), operasional
jembatan (Model VI), dan operasional dengan beban gempa (Model VII).
Hasil penelitian menggambarkan bahwa lereng asli dalam keadaan tidak
stabil dengan angka aman sebesar 1,154 (musim hujan) dan 1,368 (musim
kemarau) dengan potensi longsor di bagian atas hingga bawah dari Abutmen
(ABT-1). Gerakan massa tanah pada lereng abutment dipicu adanya pekerjaan
konstruksi abutmen (ABT-1) yang mereduksi kekuatan tanah penyusun lereng,
serta akibat penggalian di kaki lereng. Pola pergerakan massa tanah merupakan
tipe gerakan longsoran (slide) dengan bidang gelincir cenderung lengkung
(dengan gerakan rotasi). Penambahan konstruksi bored pile pada abutmen tidak
efektif memberikan kenaikan angka aman pada lereng, sehingga pada fase ini
lereng belum dapat dikatakan cukup aman terhadap longsor yakni dengan nilai
angka aman 1,058 di musim hujan dan 1,092 di musim kemarau.. Penimbunan
kaki lereng memberikan kenaikan angka aman dari 1,058 menjadi 1,794 di
musim hujan dan dari 1,092 menjadi 2,128 di musim kemarau. Besarnya
deformasi horisontal Abutmen (ABT-1) di musim hujan dan musim kemarau
yakni 44,59 cm dan 20,23 cm (Model II), 40,91 cm dan 16.33 cm (Model III),
46.33 cm dan 19,51 cm (Model IV), 48,93 cm dan 20,55 cm (Model V), 48,96 cm
dan 20,97 cm (Model VI), serta 55,60 cm dan 27,1 cm (Model VI). Gerakan yang
terjadi pada konstruksi Abutmen (ABT-1) merupakan perpaduan antara gerak
rotasi (guling) dan translasi, dimana dasar fondasi tiang turut bergerak dari posisi
semula. Hasil penelitian menunjukkan gerakan horisontal maksimum Abutmen
(ABT-1) yakni sebesar 55,597 cm terhitung sejak abutmen selesai dibangun
hingga fase operasional dengan beban gempa. Besarnya pergerakan abutmen pada
simulasi di musim hujan dibanding di musim kemarau menggambarkan bahwa air
tanah memiliki pengaruh besar pada pergerakan sehingga perlu dilakukan
penanganan khusus untuk kontrol air tanah pada lereng.
