EPS Example

Examples of Shanghai-Nanjing Expressway Widening Project

The main line of the Shanghai-Nanjing Expressway is 284.21km long, passing through a vast water network area, and the soft soil foundation along the line is 92.29km long. The expansion of the Shanghai-Nanjing Expressway is mainly based on the splicing and widening of both sides of the subgrade. The two-way four-lane widening is symmetrically widened to 8 lanes, and both sides are widened by 8.25m. After the embankment is spliced on the soft soil foundation, the settlement increment caused by the splicing load is in the shape of an inverted basin for the old embankment, which is the smallest at the center of the road and the largest at the vertical line of the cross-section centroid formed by widening on both sides. This will cause differential settlement between the new and old road shoulders and the center of the old embankment, which can easily lead to cracks in the old roadbed and road surface. In order to reduce the differential settlement, the Jiangsu section widened the test section of the project in the range of K0+000～K0+300, K0+800～K1+440, K1+600～K1+770 (including bridge heads, box heads and general road sections) using EPS As a comparison option, the embankment filling test research is carried out.

3.1 The cross-section structure of the embankment

The filling height of the EPS embankment in the test section is 3～5m. When the slope type is adopted, the average foundation pressure is 40.15～55.02kN/m (including the 1.5m thick edging soil outside the EPS). When the vertical slope is adopted, the average foundation pressure is 26.23～ 28.24kN/m. The design of the EPS embankment of the test section adopts the vertical slope and the new ribbed retaining wall structure in order to give full play to the characteristics of low EPS density, light weight, low embankment settlement, and strong independence. This not only reduces the amount of EPS, does not require foundation treatment, but also reduces the area of secondary land acquisition for highway expansion and saves valuable land resources.

In order to improve the overall performance of the board and facilitate lifting, stiffening ribs are arranged in the middle of the prefabricated board. The thickness of the rib is 10cm, the rib width is 40cm, and the height is 15cm. The total width of the prefabricated plate is 1.8~1.9m. The prefabricated ribs are placed on a special vertical slab foundation, and the prefabricated slabs are connected by cast-in-place. The length of the structural section is 10m, the width of the structural joint is 5cm, and it is closed with asphalt.

In order to prevent the EPS from laterally deforming under heavy load from exerting greater lateral pressure on the prefabricated plate, a gap of 5cm is reserved between the EPS and the prefabricated plate, so that the ribs are not subject to or less lateral pressure. Lay a layer of vertical geotextile at the gap.

A layer of 20cm thick reinforced concrete cover is cast in-situ between the top surface of the EPS and the pavement structure layer to make the EPS evenly bear the upper load. The second-stage concrete between the precast slab and the cast-in-situ cover slab should be placed as far as possible in the later stage of the construction of the pavement structure layer, so that the vertical and lateral deformation of the EPS can be fully utilized, and the distribution of the cast-in-situ cover slab and the superstructure can be reduced. The vertical force in the precast panel.

3.2 Design of anti-collision guardrail

For the embankment with a slope of 1:1.5, the wave guardrail used on general expressways can be used for design. As for the retaining wall structure, when a traffic accident occurs, there is a greater safety hazard. In order to prevent vehicles from rushing out of the road, a bridge-type guardrail with higher safety or a reinforced wave guardrail should be used.

The bridge guardrail can be pre-extended steel bars in the prefabricated slab, and connected with the second-stage concrete of the prefabricated slab and cover plate at the same time. Since a car will produce a strong impact when it hits, there is a risk of pulling the concrete structure section on the top of the EPS out of the pavement structure layer, so it is necessary to check the anti-sliding stability of the concrete cover. According to the test, the bridge guardrail is safe.

3.3 Vertical and horizontal connection

In the filling process of EPS embankment, attention must be paid to the connection between EPS and general filled road sections. A transition section should be set at the longitudinal connection section between EPS and the soil embankment, that is, the EPS block is transitionally connected to the soil embankment in a stepped manner, and the same is true for the horizontal direction. At the same time, EPS blocks should be used for vertical and horizontal staggered paving to facilitate the EPS block. The force and deformation of the body are continuous.

For the adjustment of vertical and horizontal slopes, there are two methods to choose from: one is to use the bottom slope to adjust the slope, according to the actual vertical and horizontal slope of the road, the leveling sand layer at the bottom of the EPS is used to level the slope. In this way, the upper vertical load will obliquely act on the EPS block, and the EPS block will be subjected to a horizontal force component, which is not conducive to the force of the EPS, but the loss is small. In order to improve the stress characteristics of the EPS block, the bottom layer can be laid horizontally. The EPS block on the top is cut into small special-shaped blocks, and the cross slope is adjusted by small steps. This method has good EPS stress conditions and convenient construction. , Is a better slope adjustment program, but the loss is greater.

3.4 Drainage problem

Since EPS is an ultra-lightweight material, if it is immersed in water, it will be affected by buoyancy. The upper structure of EPS will be subjected to vertical upward load, causing tensile stress and shear stress in the structural layer at the junction of new and old roadbeds. Longitudinal cracks and dislocation will occur. Therefore, the construction base level of EPS must be higher than the minimum safety distance S of the highest groundwater level, and at the same time, a layer of lime stabilized soil is filled on the construction base surface to completely isolate the influence of groundwater. Then the construction of the drainage sand layer is carried out, and the sand layer has a leveling effect at the same time to facilitate the laying of the EPS block.

For the drainage during the construction period, the main purpose is to prevent rainwater from immersing the EPS block and rainwater from infiltrating into the old subgrade at the junction of the new and old subgrade, causing damage to the old subgrade. For this reason, temporary drainage ditches must be set up at the toe of the slope to prevent water accumulation in the roadbed. After construction, the EPS block and the excavation steps of the old road must be covered with geotextile to prevent rainwater from entering. In order to prevent the intrusion of rainwater into the old roadbed and prevent the sand layer from being eroded by rainwater, the pores between the EPS and the steps should be filled with plain concrete.

Drainage during the operation period is the main factor affecting the quality of its use, so special attention must be paid. In order to prevent rainwater from infiltrating into the embankment through the pavement structure layer, EPS will absorb water for a long time and cause its own weight to increase, so a layer of anti-seepage geotextile is added between the cast-in-place reinforced concrete slab and the top layer of EPS. Subgrade drainage can be drained by setting a 20-30cm sand cushion on the construction base surface, and at the same time, it needs to be connected to the drainage sand layer of the original road and the sand layer at the step. For the vertical structure, since the sand layer cannot be connected to the outside, drainage can be done by embedding PVC pipes or plastic blind ditch. The elevation of the bottom should be 10-20cm above the bottom of the drainage ditch to prevent rainwater from flowing back into the drainage ditch.

In order to give full play to the ultra-light characteristics of EPS and minimize the stress of the foundation, sometimes it is necessary to excavate and replace the foundation. At this time, a horizontal drainage channel should be set up. In order to avoid the side ditch being too deep, a vertical drainage blind can be considered below the side ditch. Ditch to drain the rainwater under the roadbed.

3.5 EPS laying

Since EPS is very light, manual paving is used, and the key is flatness control and firm connection. The EPS block is laid on the construction base surface, and the construction base surface must be kept dry. When the block is laid, tractors and other heavy machinery are not allowed to drive directly on the EPS block. The EPS blocks are laid in staggered layers from bottom to top, and the overall paving quality largely depends on the construction base surface and the laying accuracy of the lowest layer.

The gaps and misalignments between the EPS blocks should be as small as possible. The bottom layer is adjusted by the cushion layer, and the middle layers are leveled with non-shrinkage cement mortar. In order to prevent the EPS blocks from misaligning each other, double-sided claw-type couplings are used between each layer of the block, and single-sided claw-type couplings are used on the top and side surfaces. Between the lowest layer of EPS block and the construction base surface and soil foundation Adopt pin connection.

On the top surface of the top layer of EPS blocks, a layer of reinforced concrete slab is to be poured. It can not only improve the stress characteristics of the EPS, spread the driving load and the upper road structure load uniformly, prevent the damage of the EPS due to stress concentration, but also make the EPS block form a good whole to prevent harmful substances from invading the EPS block.

4. Concluding remarks

As an ultra-lightweight roadbed filler, EPS has been widely used in foreign countries. Practice has proved that EPS has excellent properties such as good heat insulation, light weight, strong independence, etc., and has a good treatment effect on solving roadbed freezing damage, bridgehead jumping, roadbed instability, and new and old roadbed splicing. However, since the domestic use of EPS to build embankments has not been long, and there is a lack of in-depth and comprehensive research on the performance of EPS itself, there are still many problems that need to be solved in the process of use. In summary, the main points are as follows:

(1) At present, domestic EPS is mainly used in the packaging industry and construction industry, and it is still less used in highways. The higher price of EPS limits its large-scale use, and it is yet to be studied to produce EPS products with better performance and cheaper prices.

(2) The performance of EPS under long-term load is lack of in-depth understanding, and the residual deformation and service life after long-term use remain to be seen. The research on the long-term changes of EPS performance under repeated load and impact load should be strengthened, and the changes and development of EPS performance under the combined action of multiple load forms should be studied.

(3) Reference standards should be formulated in time to facilitate quality management during project construction.

As a new type of lightweight engineering material, EPS is increasingly being valued by the engineering community