Discussion on the Design of Sprayed Eco-Protection for Near-Slope Roads Along Multi-Level Slopes

Abstract

This study proposes a design method for near-slope roads along multi-level slopes that integrates excavation requirements and post-construction ecological restoration through sprayed eco-protection. Firstly, the design principles and procedural steps for near-slope roads are established. The planar layouts of multi-level slopes are categorized, including mixing areas, turnaround areas, berms, and access ramps. Critical technical parameters, such as curve radii and widths of berms and ramps, as well as dimensional specifications for turnaround areas, are systematically formulated with corresponding design formulas. The methodology is applied to the ecological restoration project of multi-level slopes in the Huamahu mountainous area, and a comparative technical-economic analysis is conducted between the proposed design and the original scheme. Results demonstrate that the optimized design reduces additional maintenance costs caused by near-slope roads by 6.5–8.0% during the curing period. This research advances the technical framework for multi-level slope governance and enhances the ecological design standards for slope protection engineering.

1. Introduction

Over the past three decades, ecological slope protection technologies have evolved into a diverse array of methods. Among these, sprayed eco-protection technology has emerged as the dominant approach due to its safety, efficiency, high mechanization, and cost-effectiveness, making it the preferred choice for large-scale, cost-sensitive, and efficiency-sensitive multi-level slope remediation. Near-slope roads for multi-level slopes refer to temporary roads adjacent to slope faces, serving both excavation and subsequent eco-protection construction [1,2]. While technology has matured in construction techniques, machinery, and evaluation methods after decades of application, improper design of near-slope roads remains a critical issue in multi-level slope projects. This is largely attributable to the lack of integrated planning between excavation and ecological restoration phases, which are often handled by separate design entities.

Multi-level slopes are widely found in construction projects such as highways, water conservancy and hydropower facilities, residential buildings, mines, and ports [3]. Platforms on these slopes intercept and accumulate rolling debris, thereby mitigating safety risks associated with falling objects. Beyond this safety function, some platforms serve as pathways for excavation equipment and pedestrians, known as berms [4]. To fulfill traffic requirements, berms at each slope level connect to mixing sites via near-slope roads, collectively forming a temporary road system [5,6]. Designing this system represents a fundamental cross-industry engineering challenge, as most excavated multi-level slopes require stabilization enhancement and ecological restoration [7,8,9]. A significant complicating factor is that excavation design and ecological restoration design are frequently undertaken by different specialized companies, resulting in fragmented responsibility and inconsistent standards for near-slope road planning.

Currently, China lacks comprehensive guidelines for designing temporary road systems on multi-level slopes. For instance, the Technical Code for Building Slope Engineering covers only single-level slope design requirements, excluding multi-level slopes and their associated temporary roads. Although the Technical Standard for Highway Engineering provides some design parameters for temporary roads on multi-level slopes, its applicability is limited by insufficient consideration of operational constraints for medium and large vehicles (e.g., water trucks, hydroseeders, excavators), which leads to unreasonable parameters such as the radius and width of the berms [10]. Internationally, while standards such as Hong Kong’s Geotechnical Manual for Slopes (GEO Publication No. 1/2023) address temporary access roads in slope works, they primarily focus on safety protocols rather than integrated design methodologies for multi-level systems [11]. Similarly, the US Mine Safety and Health Administration (MSHA) regulations mandate temporary road specifications for mining benches but lack provisions for ecological restoration phases [12]. The EU Directive on Management of Waste from Extractive Industries (2006/21/EC) emphasizes slope stability yet omits standardized temporary road design for multi-tier remediation [13]. The disconnect between excavation and eco-restoration designers further compounds these challenges globally, since near-slope road requirements often fall outside their respective scopes. Consequently, engineers face significant difficulties when designing this system due to the fragmented regulatory landscape.

To meet the traffic needs of multi-level slopes during both the excavation and ecological restoration phases, this paper first proposes the overall design steps and detailed methods for road-related parameters, including planar layouts, widths, gradients, and minimum curve radii. The proposed approach is then applied to the multi-level slopes in the Huamahu Airport project, followed by a comparative analysis between the new design and the original scheme.

2. Key Design Parameters and Principles for Near-Slope Roads

The near-slope roads of multi-level slopes primarily consist of temporary unpaved roads, which exclude pavement design and transition curves. However, to ensure traffic safety, the design must comprehensively address three dimensions: Plane layout, longitudinal profile design, and cross-sectional design. Vertical profile: Prioritizes maximum gradient design. Vertical profile design prioritizes maximum gradient specifications. Horizontal design focuses on optimizing the spatial layout of near-slope road systems, with proposed design formulas establishing minimum curve radii for turnaround bends, access ramps, and berms. Longitudinal profile design governs maximum gradient requirements to balance vehicle maneuverability and slope stability. Cross-sectional design incorporates critical parameters including turnaround area widths, berm widths, ramp widths, and drainage arrangements. When designing these parameters, the following overarching principles must be observed:

• Temporality requires a simplified design approach that aligns with the transient nature of near-slope roads.
• Safety provides fundamental guarantees that must be maintained despite the implementation of design simplifications.
• Cost-effectiveness is achieved by accommodating concurrent construction equipment operations, thereby reducing project timelines and costs.
• Integrated design holistically adapts to the on-site slope gradients and elevations.

3. Design Steps for Near-Slope Roads

The specific design steps for near-slope roads along multi-level slopes are illustrated in Figure 1. First, through geological analysis, the selected slope height must meet economical excavation requirements, with rock slopes ranging between 5–25 m and soil slopes between 3–15 m [14,15,16]. Next, designers with extensive engineering experience can determine a compliant slope ratio based on actual site conditions, while less experienced designers must refer to relevant codes, such as Tables 14.2.1–14.2.2 in the Technical Code for Building Slope Engineering or AASHTO standards [17]. Stability analysis is then conducted on the preliminary slope ratio and height; parameters are finalized if stable or revised if unstable. Subsequently, excavation methods and ecological restoration techniques are determined based on the finalized parameters, guiding the selection of construction machinery. The dimensions (length, width, height) and operational efficiency of the machinery dictate key design elements of the near-slope roads, including planar layout, minimum curve radii for berms and access ramps, turnaround area design, and the width and gradient of access ramps.

4. Planar Design of Near-Slope Roads

4.1. Planar Layout Types

Under the premise of satisfying slope ratio and height requirements, the planar layout of berms, access ramps, hairpin turns, and turnaround areas is discussed. Taking the “three-level slope” as an example (as shown in Figure 2), the primary planar layout types are categorized into three:

• Turnaround area + hairpin turn
• Single-side access ramp + turnaround area
• Dual access ramps.

4.1.1. Turnaround Area + Hairpin Turn

As shown in Figure 2a, this planar layout employs a single road to interconnect all slope levels and the mixing area, with a turnaround area designed on one platform as a temporary maneuvering zone. This approach not only meets basic road requirements but also accelerates construction progress. It is primarily suitable for multi-level slopes where the near-slope terrain is relatively steep and the number of slope levels does not exceed three.

4.1.2. Single-Side Access Ramp + Turnaround Area

As shown in Figure 2b, this layout features access ramps on one side of the multi-level slope, connecting berms at all levels to the mixing area, while a turnaround area is designed on the opposite side to accommodate slope-level maneuvering. If platform space permits, multiple turnaround areas can be incorporated at each level, as illustrated in Figure 2c. This multi-branch road system meets road requirements while enabling simultaneous operation of multiple construction equipment. It is primarily suitable for projects with relatively gentle near-slope terrain and tight construction schedules.

4.1.3. Dual-Side Access Ramps

This layout designs access ramps on both sides of the multi-level slope, connecting berms at all levels to the mixing area and forming a closed-loop road system. This enhances the speed and flexibility of multi-equipment operations, as depicted in Figure 2d. It is primarily applicable to multi-level slopes with gentle terrain on both sides, higher slope levels, and large-scale engineering projects.

4.2. Minimum Curve Radius Design

Differences in excavation methods and ecological restoration techniques lead to variations in the required types of construction machinery.

Table 1. Common Construction Equipment Data Sheet.

Equipment	Length (mm)	Width (mm)	Height (mm)	Average Operating Speed (Site) (km/h)
Excavator (Light Vehicle)	9625–11,250 (with extended arm)	2990–3245	3100–3500	4–6
Water Truck (Medium/Large Vehicle)	7650–9880	2280–2500	2780–3210	8–10
Earth Mover (Medium/Large Vehicle)	7320–9680	2350–3240	2520–3140	8–10
Loader (Light Vehicle)	5860–6880	1960–2230	2570–2710	4–6
Pickup Truck (Light Vehicle)	4820–5370	1780–1918	1450–1880	10–12
Soil Sprayer (Large Vehicle)	9000–12,000	1500–2600	3800–4500	8–10

provides a data sheet for common construction equipment. During the initial construction phase, multi-level near-slope roads are typically partially leveled to ensure vehicular accessibility and efficiency. In such cases, the road surface is often irregular concrete or gravel, with lateral friction coefficients exceeding 0.3 [18,19]. The design lateral force coefficient (0.10–0.17) accounts for a small proportion of the ultimate lateral friction coefficient [20], ensuring high safety margins that effectively mitigate lateral sliding risks [21]. Additionally, given the low average operating speeds of common equipment listed in Table 1, the design adopts minimum curve radii with single-sided road crowns instead of superelevation.

If berms or access ramps on the multi-level slope include curves, this method can universally apply to determine the minimum curve radius. The formula is as follows (The formulas are derived from AASHTO):

$$R_{min}={\displaystyle \frac{v^2}{127(\mu +i)}}.$$

(1)

where $R_{min}$ is minimum curve radius with a single-sided road crown (m); $i$ is cross slope of the single-sided road crown, taken as 0.015–0.020; $\mu$ is lateral force coefficient, taken as 0.10–0.17.

The minimum curve radius for roads without superelevation but with a single-sided road crown is calculated using Equation (1), with results rounded to the nearest integer and listed in

Table 2. Minimum Curve Radios for Roads with Single-Sided Crowns.

Design Speed/(km·h−1)	12	10	8	6	4
Rmin/m	10	7	5	3	1

. The designed minimum curve radii must comply with Table 4.1.3 in the «Code for Design of Parking Garage Buildings».

5. Longitudinal Profile Design of Near-Slope Roads

To prevent vapor lock and stalling of construction equipment during uphill travel, as well as safety hazards caused by frequent braking during downhill descent, the road gradient design requires special consideration [22,23]. Based on detailed investigations of heavy-duty construction equipment operating on slope roads at construction sites, combined with industry standards and reference literature, and incorporating the types and performance data of common onsite equipment, reasonable maximum gradient limits have been established [24,25]. Key parameters for typical equipment—including excavators, bulldozers, loaders, and their rated load capacities and maximum climbing capabilities—are listed in

Table 3. Maximum Longitudinal Gradients for Roads.

Design Speed/km·h−1	12	10	8	6	4
Maximum longitudinal slope/%	12	13	14	15	16

. Using this data and field survey results, the designed maximum gradient values (see Table 3) ensure safe and efficient operation of construction equipment on near-slope roads.

6. Cross-Sectional Design of Near-Slope Roads

6.1. Components of Berm Cross-Sections

In conventional road design, curbs and greenbelts are used to separate sidewalks from roadways at varying elevations, forming distinct “panel layouts” to ensure traffic safety, pedestrian accessibility, efficient underground utility installation, and drainage [26,27,28]. Based on design practices across China, the “three-panel” and “single-panel” layouts are widely recognized for their effectiveness. The three-panel design typically includes a central divider, flanked by roadways and sidewalks, and is suitable for urban arterial roads or high-traffic areas, effectively segregating motorized and non-motorized traffic to enhance safety and efficiency [29,30]. In contrast, the single-panel design merges roadways and sidewalks onto a single plane, ideal for low-traffic zones such as branch roads or residential streets.

However, due to width constraints and functional requirements of berms, the single-panel cross-section is recommended for berms. This design optimizes limited space, ensures safe passage for construction equipment and personnel, and facilitates the installation of underground utilities and drainage systems. As shown in Figure 3, the cross-sectional diagram of a multi-level slope berm illustrates key elements, including berm width, cut-off walls, edge walls, and drainage ditches, all of which collectively ensure functional performance and safety.

6.2. Dimensional Design of Turnaround Areas

The size of a turnaround area must comprehensively account for vehicle dimensions and required turning width. Specifically, the longitudinal direction of the turnaround area defines its length, while the transverse direction determines its width. To ensure smooth turning and parking of vehicles, the length of the turnaround area should exceed the maximum design vehicle length by 10–15%. This additional length provides sufficient space to avoid jamming or collisions during maneuvers. For width calculations, Equations (2) and (3) are applied, incorporating factors such as vehicle wheelbase, track width, and turning radius to ensure the width meets turning requirements (The formulas are derived from AASHTO). This design approach enhances both the operational efficiency and safety of turnaround areas.

$$R=L/2(1-cos\sigma )$$

(2)

$$D=w+2R(1-cos\sigma )$$

(3)

where $R$ is turning radius (m); $\sigma$ is maximum steering angle (°); $w$ is maximum vehicle width (m); $L$ is turnaround area length (m); $D$ is turnaround area width (m).

6.3. Berm Width Design

Under the premise of designing the berm’s road crown as a single-sided road crown, the berm width must satisfy the height differential and cross slope requirements between crown points to ensure effective drainage and safe vehicular conditions [31,32]. Considering that berm width impacts slope stability, which varies with ascending/descending angles, and that most berms require vehicular access during initial construction phases, the designed width should not be excessively narrow. An additional width (30–40% of the maximum operating vehicle width) must be reserved to accommodate edge walls and cut-off walls [33]. The calculation employs the maximum vehicle width and follows Equation (4). This approach ensures berms meet drainage and vehicular requirements while maintaining slope stability and operational safety (The formulas are derived from AASHTO).

$$\mathrm{a}=\mathrm{w}·(1+\mathsf{\delta })$$

(4)

where $a$ is berm width(m); $\mathsf{\delta }$ taken as 0.30~0.40.

6.4. Access Ramp Width Design

As primary routes for construction equipment to ascend and descend slopes, access ramps require appropriately designed widths to ensure safe operation. To guarantee safety, the design references the maximum vehicle width and reserves an additional width of 20–30% of the vehicle’s body width, calculated using Equation (5) [33]. This approach ensures the ramp width accommodates equipment movement while providing sufficient safety margins, thereby securing safe and efficient travel for construction equipment on near-slope roads (The formulas are derived from AASHTO).

$$\mathrm{W}=\mathrm{w}·(1+\mathsf{\gamma })$$

(5)

where $w$ is access ramp width(m); $\gamma$ taken as 0.20–0.30.

6.5. 3D Coordinate Design for Alignment Markers

Once the height, gradient of each slope level, planar layout of near-slope roads, and key parameters are finalized, the 3D coordinate calculation for alignment markers can proceed. To ensure the temporary road alignment is broadly accurate, the design of alignment markers must adhere to strict tolerance limits, with each marker containing precise 3D coordinate information (X, Y, Z). Straight Segments: Markers are placed at start and end points to clearly define the road direction. Curved Sections: Markers are positioned at start, end, and midpoints to ensure smooth transitions between the curvature of access ramps and berm curves. Given the temporary nature of near-slope roads, coordinates are accurate to 0.1 m [34]. This marker design ensures construction precision and efficiency, while facilitating safe and uninterrupted operation of construction equipment.

7. Original Design Scheme

7.1. Engineering Cases

7.1.1. Location and Transportation

As shown in Figure 4, the project is located 16 km southeast of the main city of Echeng at 126°, and the administrative division belongs to Shawo Township, Echeng District, Ezhou. The geographic coordinates of the center of the project area are: east longitude 115°01′20″; north latitude 30°19′09″. The project area is 4.5 km away from Yang Ye Avenue in the east, 7 km away from the entrance of WuE Expressway in the west, 15 km away from the water transport terminal in Yanxi Town in the north, bordering on the Yangtze River Golden Waterway in the north, and Huamahu National Aquatic Germplasm Resource Reserve in the south, with the core of the Reserve at a straight line distance of about 100 m. The project area is located at the center of Shawo Township, Ezhou City.

7.1.2. Climatic Characteristics

Ezhou City is located in the mid-latitude region, belongs to subtropical continental monsoon climate, monsoon climate is obvious, cold in winter and hot in summer, four distinct seasons, abundant rainfall, abundant sunshine, long frost-free period. The average annual temperature of the project area is 17 °C, the average temperature of the coldest month in the past years is −2.5 °C, and the average temperature of the hottest month is 30 °C; the average annual precipitation of the project area is 1270 mm, and the rainfall of 1 h for one year in 10 years is 54.9 mm, and that of 24 h for one year in 10 years is 171.2 mm; the average relative temperature of the project area is 76.6%, and the rainy season is April to September, and the rainfall is more than 65% of the whole year. The average evaporation is 1450 mm; the average wind speed is 2.4 m/s, the maximum wind speed is 27 m/s, and the number of windy days is about 40 d. The prevailing wind direction is east and north throughout the year, of which the dominant wind direction is east in summer, and the dominant wind direction is north in winter, and there are obvious seasonal changes of the wind direction; the frost-free period is about 268 d throughout the year, and the average number of sunshine hours in the past years is 2013 h, and the maximum depth of permafrost is 3 cm.

7.1.3. Geological and Vegetation Characteristics

Mountain No. 1 is divided into northern and southern blocks by a connecting channel, with the northern block adjacent to the airport runway exhibiting rugged terrain due to engineering excavation, categorized into baseplate zones (elevation: 22–24 m, level with the airport ground) and platform areas (elevation: 30–33 m) located northwest. The platform, connected to the baseplate via access roads, has sparse vegetation. The southern block features a central mining pit (depth: ~12 m, elevation: 23.5 m) and a western high-elevation platform (~67 m) retaining original landforms with dense vegetation, while other excavated areas are barely vegetated. Stratigraphically, the site comprises anthropogenic fill (Q^ml) concentrated in the eastern southern block (≈20% of the area) and Quaternary Upper Pleistocene slope deposits (Q^{dl + el}) in the northwest, underlain by exposed Yanshanian quartz monzonite bedrock. Figure 5 illustrates the site’s geomorphology.

7.2. Design Comparison

In compliance with the Technical Code for Building Slope Engineering, the steep western slope of Hill No. 1 was reconstructed using a benched excavation-filling approach involving 87,254.25 m³ of cut material and 7823.45 m³ of fill, with 10-m high benches connected by 5-m wide berms at an approximate slope angle of 30° (Figure 6). Following slope trimming, exposed cut surfaces received hydroseeding with imported soil matrix, while berms were vegetated with topsoil and grass seeding, supported by a newly installed sprinkler irrigation system throughout the 3-year maintenance period.

As illustrated in Figure 7, the yellow zones represent soil spray-seeding areas, blue linear sections denote berms, blank areas indicate non-greened regions, red lines mark near-slope roads, and blue lines signify drainage ditches. Key design parameters include:

Berm curve radii: Rm21 = 1 m, Rm22 = 7 m, Rm31 = 9 m, Rm32 = 44 m, Rm33 = 10 m, Rm34 = 23 m.

Access ramps: Designed with a width of 5 m, gradient of 12%, and curve radii of R1 = 30 m, R2 = 25 m, R3 = 35 m, R4 = 21 m, R5 = 12 m, R6 = 4 m.

Drainage ditches: Feature internal dimensions of 0.6 m × 0.5 m, masonry thickness of 0.3 m, and double-sided masonry construction in baseplate zones, adhering to the «Code for Design of Irrigation and Drainage Engineering».

This configuration ensures precise alignment with ecological, structural, and hydraulic requirements while maintaining operational efficiency.

In the original design scheme, the curve radii of some berms and access ramps were inadequately designed, only accommodating the movement of excavation equipment, as shown in Figure 8c,d. During the spray-seeding phase, due to these suboptimal radii, the sprayer could only operate from the third-level slope platform for upward seeding. To maintain efficiency, extended spray pipes and additional labor were required, increasing spraying costs, as illustrated in Figure 8e,f. For post-construction maintenance, despite excavation and widening of the ramp curves to allow water trucks to park at the first-level slope entrance, the vehicles remained unable to freely access the berms, necessitating manual hose connections for watering. This reduced watering efficiency, raised labor costs, and slowed construction progress, as depicted in Figure 8a,b.

7.3. Current Design Scheme

7.3.1. Determination of Single Level Slope Height and Slope Rate

The current design adopts the original slope height (10 m) and ratio (1:1.75), as validated in Chapter 1 for compliance with economical excavation, minimum ecological restoration, and slope stability requirements. The parameters remain unchanged to leverage prior feasibility assessments and ensure continuity in structural integrity.

7.3.2. Determination of Excavation Methods, Ecological Restoration Techniques, and Primary Construction Equipment

For implementation, backhoe excavators are utilized for slope excavation, while ecological restoration integrates soil spray-seeding on slope surfaces and grass planting on berms. The selection of construction equipment, aligned with these methods, is detailed in

Table 4. Main Construction Equipment Data Sheet for Current Design.

Installations	Lengths (mm)	Height (mm)	High Degree (mm)	Average Travel Speed (Site) (km/h)
Excavator (Sany SY245H-S) (Light Vehicle)	8825 (length at arm extension)	3190	3220	4
16 m3 Water Truck (Large Vehicle)	9250	2500	3040	10
6 m3 Earth Mover (Medium Vehicle)	7670	2550	2520	8
1.5 m3 Loader (Light Vehicle)	5860	1960	2570	6
Pickup Truck (Isuzu D-MAX) (Light Vehicle)	5370	1918	1880	12
Soil Sprayer (Large Vehicle)	12,000	2500	4000	10

, ensuring operational synergy between excavation efficiency and ecological sustainability.

7.3.3. Layout Design

Based on the topographic survey of the construction site, the multi-level slope exhibits denser contour lines at the lower-left section (indicating steeper near-slope terrain) and sparser contour lines at the upper-right section (indicating gentler near-slope terrain). Referencing the planar layout schemes in Figure 2, the current design incorporates:

• A hairpin turn and access ramp between the second-level berm and fourth-level platform in the lower-left area.
• A turnaround area on the third-level berm.
• A single-side access ramp in the upper-right area, as marked by red lines in Figure 9.

7.3.4. Curve Radius Design

The curve radii for access ramps (R), hairpin turns (Rh), and berms (Rm) in Figure 9 are designed to meet the minimum radius criteria for roads with single-sided crowns (without superelevation). Using the maximum average operating speed of construction equipment from Table 4—specifically the pickup truck (Isuzu D-MAX) at 12 km/h—and applying Equation (1) with data from Table 2, the preliminary calculations yield R_min = 10 m and cross slope (i) = 2.0%. However, per Table 4.1.3 of the «Code for Design of Parking Garage Buildings», the minimum turning radii for large vehicles like soil sprayers and 16 m³-water trucks should fall within 9–10.5 m. Consequently, the final design adopts R_min = 11 m and i = 2.0%, with detailed curve radius data summarized in

Table 5. Curve Radius Design.

Parameter	R1 (m)	R2 (m)	R3 (m)	R4 (m)	R5 (m)	R6 (m)	Rm21 (m)	Rm22 (m)	Rm31 (m)	Rm32 (m)	Rm33 (m)	Rm34 (m)	Rh (m)
radius of a curve	30	25	18	35	21	12	14	12	12	44	16	23	20

.

7.3.5. Longitudinal Gradient Design for Access Ramps

Given the numerous slopes along the access ramps in Figure 9, the longitudinal gradient design is critical. The gradient is determined primarily by the climbing capabilities of construction equipment. Using the average operating speed (12 km/h) of the pickup truck (Isuzu D-MAX) from Table 4 and referencing Table 3, the design adopts a gradient of 12%.

7.3.6. Turnaround Area Design

The size of the turnaround area depends on the vehicle length and turning width. Using the 16 m³ water truck (length: 9250 mm, width: 2500 mm) from Table 4 as the calculation basis and applying Equations (2) and (3), the turnaround area is designed with length = 12 m and width = 11.5 m.

7.3.7. Berm and Access Ramp Width Design

The width of the excavator (Sany SY245H-S) from Table 4 (3.19 m) serves as the primary design parameter. Based on Equation (4), the minimum berm width is calculated as 5 m, while Equation (5) yields a minimum access ramp width of 5 m.

7.3.8. 3D Coordinate Design for Alignment Marker

For straight segments, alignment markers are placed at the start and end points to define the route direction of near-slope roads. In curved sections, markers are added at midpoints to ensure smooth transitions between access ramp curves and berm curves. Adhering to the temporary design principle, coordinates are accurate to 0.1 m. Taking the access ramp–second-level berm–hairpin turn route in Figure 9 as an example, the detailed 3D coordinates are listed in

Table 6. Stake Coordinate Schedule.

Stake	X	Y	Z	Stake	X	Y	Z
K0+000	598,130.3	3,356,104.6	34.7	K0+143	598,057.0	3,356,019.5	55.2
K0+019	598,111.9	3,356,109.7	38.3	K0+149	598,059.0	3,356,011.1	55.3
K0+035	598,098.4	3,356,108.0	43.0	K0+154	598,060.1	3,356,006.2	55.3
K0+051	598,087.9	3,356,096.7	44.2	K0+159	598,058.6	3,356,001.2	55.3
K0+061	598,085.1	3,356,091.6	44.4	K0+239	598,023.0	3,355,941.5	55.2
K0+071	598,083.3	3,356,085.4	44.6	K0+243	598,020.0	3,355,938.4	55.4
K0+081	598,081.3	3,356,077.6	45.8	K0+247	598,016.4	3,355,936.1	55.2
K0+091	598,075.6	3,356,070.6	46.8	K0+291	597,979.5	3,355,905.5	55.2
K0+107	598,064.3	3,356,057.5	49.7	K0+312	597,977.6	3,355,887.0	47.2
K0+123	598,060.3	3,356,039.1	53.2	K0+333	597,993.2	3,355,877.1	44.8
K0+131	598,060.4	3,356,032.5	53.4	K0+364	598,023.9	3,355,885.5	35.2
K0+137	598,058.5	3,356,026.1	53.6

.

7.4. Design Comparative Analysis

7.4.1. Economic Comparative Analysis

As shown in

Table 7. Comparative Analysis of Near-Slope Road Parameters.

	Curve Radii of Access Ramps (R1/R2/R3/R4/R5/R6) (m)	Curve Radius of Hairpin Turn (Rh) (m)	Curve Radii of Second-Level Berms (Rm21/Rm22) (m)	Curve Radii of Third-Level Berms (Rm31/Rm32/Rm33/Rm34) (m)	Berm Width (m)	Gradient of Access Ramps (%)	Width of Access Ramps (m)	Turnaround Area P (Length/Width) (m)
Original Design	-	-	1/7	9/44/10/23	5	-	-	-
Current Design	30/25/18/35/21/12	20	14/12	12/44/16/23	5	12	5	12/11.5

, the two design schemes differ in design parameters such as hairpin turns, turnaround areas, and curve radii of berms. A cost comparison analysis is conducted by calculating and summarizing the excavation and backfilling costs, spraying costs, and maintenance costs for both schemes. The detailed calculations and analytical procedures are outlined below.

①

Excavation and filling Cost Calculation

Original Design: Based on project specifications, the multi-level slope required excavation of 87,254.25 m³ and filling of 7823.45 m³. Market rates for excavation averaged RMB 12/m³, while filling (using on-site Quaternary Upper Pleistocene slope deposits) cost RMB 4/m³. Post-construction maintenance involved excavation and widening of ramp curves (≈300.2 m³). Total cost: RMB 1,081,944.8(USD 150,270.11).

Current Design: Due to expanded curve radii for berms and ramps, along with added turnaround areas and hairpin turns, total excavation increased to 87,955.36 m³ (filling unchanged). Total cost: RMB 1,086,758.12(USD 150,938.63).

②

Spraying Cost Calculation

Original Design: Sprayers could not access Level 1 and 2 berms, requiring extended spray pipes and additional labor. Spraying costs rose to RMB 188/m² (Level 2) and RMB 205/m² (Level 1), with a total sprayed area of 11,235.9 m² (Level 1: 2699.5 m², Level 2: 3129.4 m², Level 3: 5407 m²). Total cost: RMB 2,028,472.7(USD 281,732.32).

Current Design: Sprayers accessed all berms freely, maintaining a standard rate of RMB 164/m². Total cost: RMB 1,842,687.6(USD 255,928.83).

③

Post-Construction Maintenance Cost Calculation

Original Design: Water trucks could not access Level 1 and 2 berms, necessitating manual hose connections. Maintenance costs rose to RMB 20/m² (Level 1) and RMB 22/m² (Level 2). Total cost: RMB 203,941.8(USD 28,325.25).

Current Design: Maintenance adhered to the original estimated rate (RMB 15/m²). Total cost: RMB 168,538.5(USD 23,408.13).

Conduct an economic feasibility analysis on the original design and preliminary design by quantifying the impact of ±10% fluctuations in excavation and slope protection costs. As shown in

Table 8. Economic Difference Analysis.

Cost Category	Original Design	New Design	Difference
Baseline Total Cost	USD 460,327.68	USD 430,274.75	USD −30,052.93
Excavation Costs +10%	USD 465,354.72	USD 435,283.38	USD −30,071.34
Excavation Costs −10%	USD 455,300.64	USD 425,266.12	USD −30,034.52
Slope Protection Costs +10%	USD 483,904.95	USD 447,302.23	USD −36,602.72
Slope Protection Costs −10%	USD 436,750.41	USD 413,247.27	USD −23,503.14

, while the current design incurs higher excavation costs, reductions in spraying and maintenance costs yield a total cost reduction of 6.5–8.0%. The proposed near-slope road design not only accommodates excavation equipment but also meets traffic needs for sprayers and water trucks during maintenance, eliminating additional excavation and labor costs and demonstrating economic feasibility.

7.4.2. Safety Comparative Analysis

The original design neglected road layouts for maintenance phases and employed overly simplistic configurations, limiting equipment mobility and causing congestion risks. The current design enhances flexibility, supports simultaneous multi-equipment operations, and improves efficiency while mitigating safety hazards from congestion. Critical safety improvements:

• Curve radii: Original undersized radii hindered large equipment and risked collisions; current radii comply with minimum turning requirements for all vehicles.
• Gradient design: Original steep gradients caused tire slippage; current gradients (e.g., 12%) ensure stable operation.
• Turnaround areas: Original improperly sized areas impeded maneuvers; current dimensions (12 m × 11.5 m) enable safe turning.

In summary, the proposed design advances construction efficiency, cost-effectiveness, and safety compliance, aligning with the industry’s “safety first” principle.

8. Conclusions

This study proposes a design method for near-slope roads in multi-level slope sprayed eco-protection projects, integrating excavation requirements and post-construction ecological restoration needs. The method encompasses planar layout strategies and technical parameters for multi-level slope near-slope roads. Compared to the two-stage design approach, the methodology demonstrates broad applicability in multi-level slope engineering for roads, water conservancy, and mining projects.

9. Prospects

Near-slope road design could integrate intelligent construction equipment and digital management technologies (e.g., BIM, GIS) to dynamically optimize construction paths and machinery scheduling, thereby further enhancing construction efficiency and environmental adaptability. Concurrently, adaptive road parameter design methods based on terrain recognition algorithms should be explored to address complex geological conditions and extreme climate scenarios.

Future research could explore the feasibility of applying the near-slope road design methodology proposed in this study to additional ecologically fragile areas (e.g., karst landforms, high-altitude cold slopes) and conduct engineering validation.