Performance of the bamboo geotextile system ‘GEOBAMTILE’ for road construction on deep soft ground

Infrastructural development faces the dilemma of attempting to construct over deep soft ground. Practical methods to support heavy engineering construction over soft ground has evolved tremendously. Proper ways to treat a depth of softness that extends to a great depth technique are pretty expensive and non-functional. Furthermore, those available methods have their practical limitation during implementation. Bamboo Geotextile System “GEOBAMTILE” is designed to solve a critical contemporary civil engineering problem of supporting hefty construction safely over deep soft subgrade without attracting excessive settlements in due course. This study aims to evaluate the performance of Geobamtile on settlement reduction. Methodology to achieve the objective of the study is by data collection from the site. The next phase continues with construction of road work and analysing the result collected. Based on this study, it is found out that the implementation of Geobamtile reducing the settlement rate of foundation effectively. Compared to the predicted settlement design, the field data result is 88mm to 100mm compare the predicted settlement for the first 100 days is 301mm to 341mm. Soil settlement reaches a relatively constant value despite an increase in backfill height. From this study it shows that Bamboo Geotextile System “Geobamtile” is effective for heavy construction over deep soft ground compare to the predicted settlement design.


Introduction
Road construction over soft ground presents significant challenges to the intending road builder to manage the engineering properties of peat, high water content, high compressibility, and low strength. To construct safe, stable, and serviceable road embankments, the road engineer has to overcome these engineering obstacles (example low bearing capacity and excessive settlement) [1]. Geotextile bamboo fascine mattress [2] is developed during the reclamation of slime ponds in Kuala Lumpur. Geotextile bamboo mattresses have been used to fill over wet peat where drainage cannot be carried out. Bamboo is tied up as a raft and forms as a bamboo grid, then lays upon to act as a buoyant foundation [3]. Square bamboo takes the load from matter accumulation, thus reducing the settlement much better than the other models that do not use bamboo. Square bamboo shapes form an interlock to resist horizontal stress and increase bamboo stiffness; hence, the vertical spread of pressure is evenly distributed. The void part of the bamboo, where air is trapped inside the bamboo, can provide a buoyant effect and because it distributes small embankments loads to soft soil layers [4].
The soft peat soil occurred beneath the road leading to differential settlement and forming the undulating road surface at numerous locations. Such organic soil is prone to moistureinduced ground movement, which poses undesirable challenges to field construction. These soil types cannot bear the load exerted by structure due to its extraordinarily high field moisture content that can be as many as 800%. As a result, the structure sinks into the soft soil, similar to how a person is standing in the mud skins into soft, wet clay [5]. Numerous methods are available to mitigate difficulties arising from the construction of built facilities over these soft soils. These include various methods of soft ground improvement and foundation treatment and reinforced concrete slab supported on piles driven to a set known as "raft pile" that are quite expensive. Various type of reinforcement is commonly used as reinforced. Bamboo is better than geotextile as soil reinforcement [6] a soft clay reinforced with a combination of bamboo and geotextiles as a separator between soft soil with embankment material has much better final settlement than reinforced with geotextiles. The use of bamboo grids as reinforcement can be combined with bamboo piles with raft system has been proven to provide advantages for increase soil bearing capacity such as peat and can reduce the decline of the pile [7]. Bamboo-geotextile composite (BGC) is used as a reinforcement system that will spread load further. The load transferred to underlain soft clay will be much smaller than using geotextile alone or bamboo alone, report Khatib [8]. Irsyam et al. [9] had tried the system using bamboo, which had been utilized in several projects for a coastal embankment on soft clay in Indonesia. It is proven that this system is reliable and durable. On the other hand, the utilization of the bamboo mattress system will distribute the embankment load uniformly. This study is located at Clover Leaf Junction, Cyberjaya, Selangor where the condition of the road is uneven, undulating as a result of soft ground and due differential settlements give rise to a bumpy road. The road surfaces show sign of distress longitudinal cracking, potholes and differential settlements. However, there is no proper guideline on the construction using this Geobamtile technique or bamboo as the reinforcement. Therefore, this research will examine the performance of the Geobamtile . To achieve the aims, bamboo geotextile buoyant system comparatively to the theoretical design allowable for road settlement. With the result, a new alternative for a cost-effective solution for bearing capacity problem of soft clay could be used with more confidence backed by data and guidelines.

Design principles
"GEOBAMTILE" is designed base on a soil structure integration system where the two influence of the behaviour of the soil immediately beneath and around the foundation on the response of the substructure subjected to either static or dynamic loads. In-situ soils are commonly anti-strip and non-homogeneous and display markedly nonlinear, irreversible, and time-dependent characteristics.  Figure 1 showing a case where the building embankment is directly above the subgrade without any reinforcement. This condition is purely a geotechnical problem that involves consolidation (expulsion of water), essentially a time-dependent process. The primary consolidation settlement depends on time to achieve the designed settlement and surcharging.  Comparison between Case 1, an embankment built over soft subgrade with reinforcement, and Case 2, embankment built over soft subgrade with existences of Geobamtile sandwich in-between layer. Deformation of Case 1 will involve the primary consolidation and secondary compression to the foundation, where is time dependency to Case 2. On the other hand, case 2 deformation is based on structural beam deflection caused by soil displacement and post-construction creep soil movement. This deformation is not time-dependent compare to Case 1. The natural effect of Case 2 is immediate to the foundation while Case 1 is long and unceasing.

Methodology
Research methodology proceed with data collection from the site. The next phase continues with construction work and then analysing the result collected. Analysis settlement is based on M.Hetenyi Uniform Dead Load Formula and derive base on theory applied M. Hetenyi in Beams on elastic Foundation to predict settlement.

Soil properties
Based from the data collected from the site, the soil condition from the first 6 meters is underlined by soft to very soft sandy CLAY and very loose silty SAND. Fibrous material is suspect to be peat is also found at the first 6m layer of soil. Thus, it is postulated that the very soft top 6m subsoil could be the significant factor contributing significantly towards the settlement problem.

Design of bamboo geotextile (GEOBAMTILE)
The design of bamboo grid frame/geotextile buoyant system shall be designed and analysed as a bamboo beam subjected to uniform dead load and is supported continuously over subgrade as an elastic foundation, a method which have been describe in "M.Hetenyi Beam on Elastic Foundation" theory. Based on Figure 4 and Figure 5, Bamboo culms is placed 300mm between centre to centre in both ways, horizontal and vertical and then tied up to form a bamboo grid. Bamboo grid then placed on site and layer up with geotextile to provide significant pressure minimization cum efficient pressure distribution. Hence the road structure is lay upon the bamboo grid to the finish level. Geobamtile application on site is shown in the following sequential step, Figure 6 (a) prefabricated bamboo-grid frames are manufactured on site as a large "raft foundation" formed by tying together rounded matured bamboo culms each of 5m length approximately by galvanised iron wires in a criss-cross manner to form into grid network. Then, Geobamtile frames laid on excavated site then overlapping length recommend is about 0.5m to 0.6m as Figure 6 (b). Afterward as Figure 6 (c), the geotextile as separator will unrolled to over the huge single bamboo-grid frame to separate from backfill material. Figure 6 (d), initial backfill carried out by tipping in reverse position to avoid direct contact of the wheel on the geotextile. The backfill of the soil then compacted to avoid loose material as Figure 6 (e). Once the backfill is finished as Figure 6 (f) the construction of road sub-base or loading will commence to proceed with the rest of the project.
Settlement plates are installed in areas where significant settlement is predicted. Settlement plate used to examine settlement that is occurring, is occurring at predicted rates and magnitudes, has occurred to a magnitude of interest, is substantially complete or is not occurring. Then settlement plate reading is monitored during construction and after construction.

Result and analysis
The data present are based on observation at site via four nos of settlement plates installed at four instrumentations SP1, SP2, SP3 and SP4 at the site project located at Cyberjaya, Selangor. From Fig. 8, the relationship of soil settlement versus time derived at SP 1, SP 2 , SP 3 and SP 4 shown significantly almost same pattern that is, initially, the settlement tends to increase rapidly during the first 14 days period, it decreases drastically after along the path and appears to plateau off. Closer examination showed that the period of increase of the settlement rate lasted between 28 to 41 days. This signifies a relatively short period to achieve a steady-state for soil settlement. According to Marto [10] the BGC system can reduce the settlement of foundation effectively compared only using the geotextile (TS 40). This is due to the effect of the bamboo properties, which can make the BGC float and as a result to provide the buoyancy effect to support the load. According to Krishna [12], raft foundations increase load-bearing capacity; by distributing the load to a greater area and therefore the stresses on soil became lesser. In comparison, the shallow raft foundations reduce the settlement effectively.

Comparison between predicted settlement result and field data result
The current application of bamboo Geobamtile is design as bamboo beam subjected to uniform dead load and is supported continuously over subgrade as an elastic foundation using "M.Hetenyi Beam on Elastic Foundation" theory. The amount of settlement is calculated base on theoretical analysis method known as 'Hetenyi Beam on Elastic Foundation'.
The amount of theoretically predicted settlement represents total settlement consist of two parts i) immediate settlement that take place during construction ii) cumulative settlement that take place within seven (7) years after completion of construction(postconstruction). Post-construction consolidation process will begin when all the deflection of bamboo Geobamtile, and equivalent soil settlement occurs upon completion of the construction process.
Geobamtile floated on the soft subsoil foundation to afford an equilibrium built up and maintained between the weight of the structures constructed and designed base on a soil structure integration system where the influence behaviour of the soil immediately beneath and around the foundation on the response of the sub-structure subjected to either static or dynamic loads. In-situ soils are commonly antistrip and non-homogeneous and display markedly non -linear, irreversible and time-dependent characteristics. Force above and the in-situ strength of the soft ground whereby the combined system comes into balanced at all stages of the construction.  As tabulated in Table 1, the maximum settlement for seven years post-construction is 401mm. It is assumed theoretically that immediate settlement after construction of settlement, the soil settlement will take about 75% to 85% of the maximum settlement that is around 301mm to 341mm during the first 100 days. As shown in tabulated data Table 2, maximum settlement for the first 100 days of postconstruction at average 85 mm to 163 mm. Compared to the predicted settlement design, the maximum settlement for the first 100 days is 301mm to 341mm. This data provides the effective performance of Geobamtile to the foundation. The existence of bamboo Geobamtile as an interlayer would convert into a soil-structure interaction problem where in-situ soils are anti-strip and non-homogeneous irreversible. The embankment causes immediate settlement due to deflection of the beam, causing displacement of the soil below it. The embankment received equilibrium by the buoyant force of soft subgrade and weight of the embankment. A study by Othman [11] Geobamtile gave much better improvement to the soft soil than unreinforced embankment and High Strength Geotextile Reinforce embankment. The square pattern of Geobamtile formed an interlock to resist horizontal shear stress and increase the stiffness of bamboo, hence distributing vertical pressure evenly. Another contributing factor was due to the hollow section nature of bamboo gave buoyancy effect and therefore distributed small embankment load to the soft layer.

Conclusions
Based on the result of settlement plate monitoring at SP 1, SP 2, SP3 ,and SP4 and analysis carried out on these data produced the following conclusions though they may not be conclusive drawn.
1. From all the four nos time versus soil settlement relationship derived, they indicate that initial stage, soil settlement increases linearly and curvilinearly with time. However, subsequently, three possible observations may result: i. Continue to increase throughout the monitoring period. ii.
Decreases linearly and or curvilinearly with time and occurred with an increase in backfill height or a decrease in backfill height. 2. From soil settlement versus time relationship derived, it is realized that the soil displacement tends to increase with time. Closer examination showed that the period of increase of settlement last between 28 to 41 days or approximately. If this observation will persist and realizable in practice, these results will impart positive prediction for the project regarding the subgrade settlement performance. Geobamtile, compared to the other method, eliminated the high cost of material and reduced the excavation and project duration time. Based on the performance of this project, it is recommended Geobamtile be part as an alternative method for construction over heavy deep soft ground.