Slope Reinforcement Model Scale Test With X-Block

This study aims to determine the material composition and dimensions of X-block, develop a slope reinforcement model using X-block, evaluate the mechanical behavior of slopes that are reinforced with rock-bound by X-block, and analyze the performance of slope reinforcement using X-block. This research was conducted at Hasanuddin University's soil mechanics and civil engineering structure laboratory. The model scale test was employed in this study. The geometrical speciation of the test box is 150 cm in length, 60 cm in width, and 100 cm in height. The X-block model was produced using concrete with a FC of 25 MPa. The X-block was divided into two types: X-block type 1 and X-block type 2. Tensile strength testing is performed on the X-block. The slopes are made of clay soil and have a slope angle of 70 degrees. The loading test was conducted in three stages: without block, with X-block type 1, and with X-block type 2. The loading test uses a hydraulic pump equipped with a load cell and LVDT. The tensile strength of X-block type 1 is 2.56 MPa, whereas X-block type 2 has a tensile strength of 4.35 MPa. The development of the type X-block design, which is used as a retaining wall material, has shown that it can effectively withstand landslides on the slopes under consideration. The slope safety factor rose dramatically after being reinforced with type X-blocks, reaching 2.73 for both X-block type 1 and X-block type 2.


Introduction
Landslides inflict significant damage and occur in a variety of locations across the world [1]. Landslides cause economic damage and deaths that are understated in certain nations. Catastrophes: Landslides cause more damage than other natural disasters, such as earthquakes, floods, and windstorms [2]. Landslides have also occurred in different places in Indonesia, with negative consequences in a variety of domains, including the ecological, social, and economic. Landslides can happen in many different ways because of the same thing that causes them (e.g., rainstorms, long periods of rain) [3].
Problematic soil (soft soil) usually necessitates the use of a soil treatment technology. One of the soil-reinforcing approaches is the use of wood as a raft foundation material [4]. Landslides can occur as a result of erosion on the surface of a slope. Although erosion is a well-known natural phenomenon, it is sometimes worsened by human activities such as poor land use, deforestation, mining, plantations, farming, poorly managed building and development operations, and road construction [5]. Initial subgrade deformation of the slope's surface layer is common, especially after receiving loads from the construction above it. Slope failure can be caused by land subsidence, particularly in areas prone to settlement, such as clay soil [6]. Reduced slope surface erosion is one of the slope management approaches. Plant medium or vegetative approaches have been used to manage slope surface erosion. The carrying capacity of the subgrade is the key issue for infrastructure construction in soft clay soils, since the subgrade compaction is rather substantial, implying that it will endure longer. This issue can be rectified by strengthening the soil to make it stronger [7,8].
The stability of a building is affected by soil conditions. Soil stabilization must be done both physically and chemically to raise the mechanical strength of the soil. Another type of mechanical soil enhancement is stone columns [9]. In addition to employing plant medium, slope erosion may be controlled with a versatile kind of slope protection known as riprap structures. Retaining walls, the most prevalent of which are gravity-retaining stone walls, are typically built around the borders of streams [10]. Overcoming damage to roads and slopes in distant places is still frequently done with soil-based pavement. This is because bringing in adequate materials is expensive [11]. Based on the aforementioned, it is important to install X-block concrete supports to strengthen the gravity wall construction and prevent failure.

Slope Stability
With a history dating back more than 300 years, slope stability is one of the most significant subjects in engineering geology. Various stability assessment techniques have been developed thus far, including simple assessments, planar failure, limit state criteria, limit equilibrium analysis, numerical methods, hybrid and high-order approaches. The interaction between driving and resisting forces is fundamental to slope stability. Some elements contribute to the pushing force, whereas others contribute to the repelling force. As a result, these controlling parameters are critical for rock slope stability analyses in general, and for failure plane modes in particular. Internal regulatory elements include slope geometry, probable failure region features, surface drainage, and groundwater conditions [12], whereas external influences include rainfall, seismicity, and man-made activities [13]. The intensity of rainfall exacerbates the problem of slope stability [14]. This is obvious since slope failure rises during the wet season. These criteria, when considered together, will be accountable for defining the state of slope stability.
Identification of such slope instability problems during the early stages of engineering structure planning and investigation, particularly road projects, may lead to the development of remedial measures that can be adopted to improve slope stability, or such problem slopes can be avoided if identified during the early planning stages [15]. Deterministic slope stability analysis methodologies are time-consuming and need a thorough grasp of geological and geotechnical issues, as well as a comprehensive comprehension of the probable causes of slope failure. Furthermore, these analytical tools can only be applied to limited regions on a single slope scale [16].
In some circumstances, the existence of an underground aquifer supplied by an upstream hydraulic recharge area may be a risk issue for such activity, as it is responsible for deep piezometric heads that can fluctuate seasonally [17]. Many researches have examined the mechanism of the influence of temperature and saturation on unsaturated clay slope stability in light of clay slope instability induced by ambient temperature and rainfall infiltration in summer and autumn [18,19]. The slope's factor of safety may be calculated by gradually diminishing the soil shear strength until the slope fails. The resultant safety factor is the ratio of the actual shear strength of the soil to the decreased shear strength upon failure. This "shear strength reduction methodology" offers several benefits over slope stability analysis using the slices method. Aside from shear strength, cohesion is among the most crucial elements influencing slope stability [20][21][22].

Flexible Slope Reinforcement
Simple slope reinforcement methods, such as gabions, gravity barriers, and riprap, have been widely employed. Gabions are soil reinforcement structures made of woven steel wire coated with zinc and filled with chipped stones in certain proportions. Gabions have several advantages, including simplicity of construction, structural stability, flexibility, and resistance to water loads [23]. Rock riprap is often employed to protect embankments, steep channels, and other structures from damaging overflow erosion [24]. While the soil nailing system is a technology for improving the soil that is used to stabilize slopes. The soil nailing system's behavior is determined by soil types and nailing parameters such as nail spacing, orientation, length, and technique of installation of nails, soil qualities, slope height and angle, and surcharge loading, among others [25].

Concrete Block Structure
Slope stabilization using concrete blocks is still rather uncommon. Concrete is the most frequently used substance on the planet, with yearly worldwide output estimated to be more than 2 billion cubic meters. Concrete is a hardened substance composed of cement, water, fine aggregate, and coarse aggregate [26]. The application is mainly confined to managing river slopes, although it is nearly never encountered on slopes without drainage and with considerable slope angles.

Material and Methods
The research method utilized will define the subject of study, the equipment and materials used, the research plan, and the analysis of any difficulties encountered during the research process.

Sampling Location
The material applied to set up the slopes is a soft soil type acquired from landslide-prone locations. Figure 1 depicts the site of the land acquisition in Sapaya village, Gowa Regency, South Sulawesi, Indonesia. The coordinates of the sampling site are 5° 21' 44.8" S and 119° 42' 58.7" E.

Materials and Method
An overview with geometric specifications along with other details of the experimental model is shown in Figure 1.

Figure 2. Slope test scheme
The materials employed in this study include laboratory testing standards materials and equipment, which are as follows:  The type of soil that will be utilized to construct the slope is clay soil. First, it is tested in a soil mechanics laboratory to determine gradation, moisture content, the Atterberg limit (liquid limit, plastic limit, plastic index), maximum dry density, soil density, and optimum moisture content  Figure 3 depicts the testing preparation stage, where the observation equipment, such as load cells, LVDTs, and hydraulic pumps, has been correctly prepared. To read the data, use a computer device that is directly linked to the loading device and LVDT.

Testing Stage
The stages of testing carried out are divided into three stages according to the research design.

Basic Test:
The basic test is a clay soil properties test. The purpose of the properties analysis is to investigate the attributes of clay soil which will be utilized in slope test.

Model Test:
The model test is the primary testing stage in this study. The installation of X-blocks type 1 and X-blocks type 2 is done alternately, as indicated in Figure 4. A hydraulic pump is used to power the test model, which is a statically loaded slope test model. This test is performed in three stages: 1. without block, 2. with X-Block Type 1, and 3. with X-Block Type 2.

Results and Discussion
According to the findings of the soil characteristics test, the soil used as a medium for building slopes has a silt composition of 55.28 percent, a cohesiveness value of 0.91 kg/cm 2 , and an internal shear angle of 25.06 o. Loading tests on untreated slope results in collapses or avalanches. Soil movement begins at the top of the slope and extends to a depth of 500 mm. As indicated in Figure 5, the maximum landslide depth is 200 mm at the top of the slope and the smallest depth is 35 mm at a height of 400 mm from the slope's foot. This avalanche is classified as a block slide based on the type of movement. Based on its pace, this avalanche falls within the category of rapid avalanche.   Figure 6 shows a horizontal and vertical comparison of the deformation of the reinforced slope against the unreinforced slope. The load reached 7.4 kN just before the slope surface collapsed, generating a horizontal deformation of 20 mm. Meanwhile, the X-block types 1 and 2 barely move 1 mm under the same force. The load as an extrinsic element and the nature of the soil as an intrinsic component create the landslide. Slippage occurs as a result of the applied load causing high shear stress. Soil properties with low cohesion and low soil density are intrinsic factors for landslides. The graph above depicts the phenomena of land subsidence followed by landslides, which is a description of landslides induced by the constant rise in load via hydraulic pumps. The maximum load that the slope could withstand before a landslide occurs is 7.4 kN, or equivalently 120 kPa. Figure 6 also illustrates that reinforcing the slopes using X-block types 1 and 2 is quite effective. With a load of 7.4 kN, the horizontal deformation (h) to slope height (H) ratio is 0.001 for both X-block types. While the vertical deformation (v) to slope height (H) ratio is X-block type 1 of 0.012 and X-block type 2 of 0.016. Figure 7 depicts a comparison of horizontal and vertical deformations under the ultimate load. The ultimate load without reinforcement is 7.4 kN, the utmost load with reinforcement using X-block type 1 is 18 kN, and the ultimate load with reinforcement using X-block type 2 is 16 kN. The horizontal deformation without reinforcement is 20 mm, the horizontal deformation with reinforcement using X-block type 1 is 40 mm, and the horizontal deformation with reinforcement using X-block type 2 is 50 mm. The unreinforced vertical deformation is 24 mm, 115 mm for X-block type 1, and 123 mm for X-block type 2. The vertical and horizontal deformation graphs presented above can be used to examine slope characteristics reinforced using X-blocks. It demonstrates that the slope condition is still stable while being constantly loaded up to a load of 18 kN for X-block type 1 and a load of 16 kN for X-block type 2. Because the weight of X-blocks and stones as a unit provides a resisting force, slope stability improves with their strengthening. Furthermore, the self-compacting action of stone material with X-blocks is becoming denser, which increases the stiffness attributes of the reinforcement. The safety factor produced by the strengthening of X-block types 1 and 2 is 2.73. (Greater than the standard of 2). Deformation varies from a maximum height of 800 mm to a height of 200 mm, with X-block type 2 experiencing higher deformation than X-block type 1 at each height variance. Table 2 shows the amount of deformation at different heights.   Figure 9 depicts the horizontal and vertical deformation to slope height ratios at maximum load for each X-block. The obtained findings reveal that the horizontal deformation ratio of an X type 1 block is 0.050, that of an X type 2 block is 0.063, and that the vertical deformation ratio of an X type block is 0.050. The value for X-block type 1 is 0.144, while the value for X-block type 2 is 0.154. Based on these values, the horizontal deformation value is quite minimal when compared to the height of the slope. This also shows that X-Block type 1 performs better as slope reinforcement than X-Block type 2 since it has a lower horizontal and vertical deformation ratio.

Figure 9. Ratio of horizontal and vertical deformation to slope height
As shown in Figure 10, the rise in slope stability based on the ratio of the X-block reinforcement's ultimate load ratio and the load just before failure is 2.4 for the X-block type 1 reinforcement and 2.2 for the X-block type 2 reinforcement. The value of this ratios indicates that the X-type blocks 1 and 2 could sustain a load twofold the failure load. This number also demonstrates that X-Block type 1 is more effective than X-Block type 2.

Conclusion
Based on the analysis of the slope testing results, it is possible to infer that the results of the creation of the type Xblock design, which was used as a retaining wall material, were capable of efficiently resisting landslides on the slopes under consideration. Based on the results, the horizontal deformation value is quite minimal when compared to the height of the slope. This also shows that X-Block type 1 performs better as slope reinforcement than X-Block type 2 since it has a lower horizontal and vertical deformation ratio. The rise in slope stability based on the ratio of the X-block reinforcement's ultimate load ratio and the load just before failure is 2.4 for the X-block type 1 reinforcement and 2.2 for the X-block type 2 reinforcement. This ratio indicates that the X-type blocks 1 and 2 can withstand a load twice as great as the failure load. This number also demonstrates that X-Block type 1 is more effective than X-Block type 2. As a result, the safety factor increased by 2.73 after being strengthened with type X beams for both X-block type 1 and Xblock type 2. In general, X-block utilization in slope stability should be widely considered due to its capability of increasing the slope load capacity, especially in areas with very soft soil and high slopes.

Data Availability Statement
The data presented in this study are available in article.

Funding and Acknowledgment
The author wishes to convey a heartfelt gratitude and appreciation to BPPDN (Domestic Postgraduate Education Scholarship). The authors would also like to thank the supervising lecturers who gave direction and advice so that this study could be finished appropriately, as well as all colleagues at Hasanuddin University Indonesia's Geotechnical Laboratory who were engaged in this research from start to finish.

Conflicts of Interest
The authors declare no conflict of interest.