556 INTRODUCTIONThe main characteristics of peat soil are high compressibility, low shear strength, and high moisture content [01]. Such characteristics pose problems if peat soil is used as a subgrade construction. Several methods to improve peat soil include soil replacement, reinforcement to improve soil strength and stiffness, preloading and stage construction, soil improvement, stone columns, piles, and mixing of chemicals such as cement and lime [02]. Sand fi ll on peat soil can improve parametric values of peat soil. Adding the thickness of sand on peat soil will increase the value of subgrade reaction modulus and the modulus of deformation [03]. Deposition of fi ll with better soil types can be performed on peat soil, but its implementation may encounter several problems. Some problems include excessive lateral movement, heave occurring on deposit of soft soil and the formation of mud wave, mixing of fi ll with the very soft soil, and differential settlement, as in [04]. The large deformation took place together with tension cracks and heave when the height of embankment rapidly increased [05]. Secondary settlement can be reduced by surcharging [06]. The effective method to improve peat soil are preloading and surcharging [07]. Preloading consists of applying a load, equivalent to or greater than a total load of a planned structure, over the site prior to constructing the structure which is being partially or fully removed when the required settlement has taken place. Preloading consisting of loading and unloading methods can accelerate peat soil compression [08]. The increase in OCR on loading and unloading methods for high organic soil can reduce the rate of secondary compression [09]. In addition to reducing compression, preloading can also increase the bearing capacity of peat [10]. The Embankment with stage construction and thin layers can be applied to peat soil to allow consolidation and increase shear strength.Reinforcement can contribute to increasing the stability of embankment, that reinforcement and shear strength of peat will resist lateral forces [11]. Reinforcement with slabs without piles only affects the top layer of the surface with a depth of generally not more than the width of the foundation slab [12]. Slabs can be reinforced by piles to support the embankment. Some of the advantages of the piles in supporting embankment include the implementation of embankment construction can be completed in a short time, embankment-supporting piles can reduce total settlement and differential settlement signifi cantly [13]. In addition, the implementation of the piles corresponds to non-uniform geological conditions. Another alternative use of piles on soft soil is the use of nailed-slab system [14], [15], [16]. Piles affect the increase in modulus of subgrade reaction. The height of piles affects the stiffness of nailed-slab system and the reduction of slab defl ection at the load center. The nailed-slab system generated uniform settlement, increased the strength of subgrade support, improved the...
This paper presents the study on the volcanic ash as replacement of cement on compression strength of concrete. Preliminary study at the early stage were conducted with the specifi c gravity and sieve analysis of the volcanic as replacement of cement material of concrete. The cement replacement is made with the weight of the volcanic ash in the cement ratio of 2%, 4%, 6%, and 8%. Compressive strength test of concrete was conducted at the age of 7, 14, and 28 days. The mechanical properties by applying slump value and compressive strength were investigated. The result showed that compression strength value of concrete with volcanic ash are close to the same with the normal concrete mix design. The addition of volcanic ash shows improvement of compression strength of concrete.
Improvement of peat compression and increasing the bearing capacity can be achieved with the embankment load as preloading. The embankment on peat soil has problems such as excessive settlement, horizontal movement, and differential settlement. The stability of embankment is maintained with the installation of the reinforcement system, but the time factor and duration of loading can affect the stability of embankment and excess settlement. It is necessary to study the loading stages that can maximize compression and minimize deflection so that stability can be maintained. The embankment load test was performed on peat soil reinforced with bamboo grid and concrete piles. The model test in the laboratory used the test box measuring 120 cm x 90 cm x 90 cm with a height of the peat soil of 50 cm. The embankment load was distinguished based on the stage and duration of loading. The results showed that multiple stages is better than the single-stage because settlement changes are relatively smaller than the other. The longer load duration provides the opportunity to consolidate the peat layer so that the bearing capacity and the modulus of subgrade reaction increases. The good stage load is obtained in three stages with the addition of the embankment load of 3.02 kPa or 1/3 of the total load every 2 days or 1/3 of the total duration of the load. At this stage and duration, the peat compression and the deflection of reinforcement are smaller than the others.
The compression behavior of peat was investigated by a program of static and dynamic load testing. The comprehensive model tests were conducted in the laboratory to evaluate the effect of loading sequences on the behavior of peat soil. The result test indicated that compression behavior of peat soil was signifi cantly infl uenced by loading sequences and reinforcement of bamboo grids. The compression behavior after the dynamic load appears smaller than before the dynamic load. Reinforcement of bamboo grids can reduce the compressibility of peat soil, especially for one layer and two layers of bamboo grid, while for three layers of bamboo grid resulted in similar settlement for two layers of bamboo grid on the pressure above 9 kPa.
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