ObservedPerformance ofHighwayEmbankment over SoftMarine Clay: A Case Study in Wenzhou, China

-is paper presents a case history of observed performance of highway embankment over soft marine clay in Wenzhou, China. During the embankment construction, the changes of ground settlement, ground displacement, and lateral displacement of subsoil with the construction time were monitored and analyzed. -e monitoring results indicate that the ground settlement and lateral displacement of subsoil account for about 75% in the process of embankment construction.-emeasuredmaximum values of ground settlement, ground displacement, and lateral displacement of subsoil are 37.88mm, 21.50mm, and 23.56mm, respectively. After the completion of the embankment construction, the settlement gradually tended to be stable. It is suggested that the monitoring data of settlement and displacement of embankment are smaller than the design requirements, and the embankment stability is also ensured.


Introduction
Wenzhou is located in the southeastern coastal area of China, and the Feiyun River flows through Wenzhou. Most of the areas near the Feiyun River are alluvial deposits formed in Quaternary [1][2][3][4].
Recent composite foundation is widely used for the construction of embankments on soft ground [26,27]. Geosynthetics (such as geotextiles and geogrids) with high tensile strength, low elongation, and high stiffness are laid at the bottom of embankment which form reinforced cushion with gravel to maintain the integrity and continuity of the base [28][29][30]. Reinforced cushion and concrete pile constitute composite foundation of reinforced pile group. e reinforcement effect of geosynthetics on soft soil is mainly reflected in horizontal reinforcement. e reinforcement principle of geosynthetics reinforced cushion is as follows [31,32]: (1) It can increase the integrality and stiffness of cushion and adjust uneven settlement (2) Due to the influence of the increase of cushion stiffness, it enlarges the range of load diffusion and makes the stress uniformly distributed (3) e lateral deformation of the underlying soft soil foundation is restrained In this paper, a case history of observed performance of highway embankment over soft marine clay in Wenzhou, China, was presented. e plain concrete piles were used to support soft soil embankment. e changes of ground settlement, ground displacement, and lateral displacement of subsoil with the construction time were monitored. After the completion of the embankment construction, the settlement gradually tended to be stable. It is suggested that the monitoring data of settlement and displacement of embankment are smaller than the design requirements.

General Situation of Engineering.
e test site was located in the southwest of Zhejiang Province, in the middle and lower reaches of the Feiyun River ( Figure 1). e length and width of the selected line were 364 and 17 m. e expressway was constructed on soft soil. e profile of the main soil is shown in Figure 2. ere is a 1 m thick coarse grained fill overlying a 4 m thick deposit of silty clay; this deposit overlies mud layer that is approximately 6 m thick. Underneath the mud layer is a mucky clay layer that is about 4 m thick followed by a clay breccia layer. e ground water level is at a depth of 2 m. Based on the Unified Soil Classification System (USCS), the three types of soils can be classified as low plasticity clay (CL; [33]). e available detailed test data are shown in Figure 2, including the water content, the void ratio, and the unit weight to a depth of about 16 m below ground level. e mud layer has the characteristics of low strength, high compressibility, and high water content. Its void ratio is greater than 1.5. And its water content is between 50% and 65%, usually higher than the liquid limit. Compared with the mud layer above, the water content of the mucky clay layer is lower than the liquid limit, and the void ratio is between 1 and 1.5.

Embankment Design and Pile Support Reinforcement.
e starting point of the route was connected to the 56 provincial highway, and the terminal was connected to the bridgehead approach, with a total length of 364 m. e embankment filling height was about 3.0-5.5 m. e embankment was 5.5 m high. e width of the road was 17 m. e side slope of the embankment was 1 V to 1.5 H (V, vertical; H, horizontal). e embankment was supported by cast-in-place circular plain concrete pile that was formed from a low-slump concrete with a minimum of compressive strength of 15 N/mm 2 . e circular plain concrete piles were 19 m in length and were founded on a relatively harder clay breccia layer (Figure 3(a)). It had a diameter of 0.5 m which was formed with the low-slump concrete. e piles were placed in a square grid with a center-to-center spacing of 2 m. e pile caps had a dimension of 1.2 m × 1.2 m × 0.35 m (length × width × height) that were formed from a minimum of compressive strength of 20 N/mm 2 of concrete and reinforcement bar with diameter of 12 mm. Soil-rock mixture was used as the fill material for the embankment. According to the Technical Specifications for Construction of Highway Subgrades [34], the ratio of soil and rock by weight is designed as 6 : 4. Two layers of steel wire mesh were used together with gravels to form a 0.5 m thick load transfer platform as shown in Figure 3(c). e bottom layer of the steel wire mesh was 0.3 m from the base, and the second layer was 0.5 m above the first. e tensile strength of the steel wire mesh was 100 kN/m in both longitudinal and transverse directions. e maximum allowable tensile strain was 3% [35]. e design value of the ultimate pile capacity in this project is about 960 kN, while the allowable pile capacity is about 800 kN. e key construction process of the plain concrete pile is as follows: (1) After surface cleaning, the pile rig was placed according to the designed pile position. Pile rig must be level and stable. e immersed pipe was perpendicular to the ground to ensure that the deviation of verticality was not more than 1%.
(2) e casing pipe was constructed and sunk to the predetermined elevation. During the sinking process of the casing pipe, the current on the ammeter was recorded once per 1 m sinking. e change of soil layer was explained. (3) When the immersed pipe reached the design elevation, the material was fed into the pipe immediately until the mixture was level with the inlet. e mixture was formulated according to the design mix ratio and the concrete slump was controlled between 3 and 5 cm. (4) e immersed pipe should vibrate while pulling out, each pulling 0.5-0.1 m, retaining vibration for 5-10 s. e upward speed of immersed pipe was not more than 1.0 m/min, and it was evenly pulled up. If there was silt or silty soil, the rate of pipe pulling should be slowed down and controlled within 0.5 m/min. Reverse insertion was not allowed in the process of pulling out the casing pipe. If the supply material was insufficient, concrete should be poured while casing pipe is pulled up. With this method, the top standard of pile can reach the design requirement. (5) After the immersed pipe was pulled out of the ground, it was confirmed that the pile reached the design height requirement. e steel reinforcement of pile cap was embedded; then, the casing pipe was moved to carry out the next pile construction.
e piles in this study are friction piles. During the construction of these piles, there exist some problems, such as diameter shrinkage and incline of pile center line. In order to avoid these problems, the casing pipe was used to complete the perfusion of concrete and was pulled out slowly after the completion of the perfusion of concrete; meanwhile, the verticality inspection was also conducted to ensure the verticality of the pile.
Based on the Specifications for Design of Highway Subgrades [34], the factor of safety (FOS) of the embankment is evaluated by simplified Bishop method. e FOS can be determined by the following equations: where W i is the gravity of the soil-slice i (as shown in Figure 4); K i is a factor; α i is the horizontal angle of the soilslice i (see Figure 4); c di is the cohesion of the soil-slice i in ground; φ di is the friction angle of the soil-slice i in ground; W di is the gravity of the soil-slice i in ground; b i is the width of the soil-slice i (as shown in Figure 4); W ti is the gravity of the soil-slice i in embankment; c ti is the cohesion of the soilslice i in embankment; φ ti is the friction angle of the soil-slice i in embankment; and φ i is the friction angle of the soil-slice i. Using the above analytical method, the FOS of this case history can be calculated as 1.8, which is larger than the design requirement, 1.35, and the safety of the embankment construction can also be verified by the measure displacement during the construction.

Monitoring Methods and Technical
Requirements. e settlement of soft foundation was mainly observed by settlement plate. Observation points were laid on the middle line of the subgrade and the edge of the shoulder. Settlement was measured by leveling. Relying on the   was plastic pipe. With the increase of filling soil, the measuring rod and casing were connected correspondingly, and the length of each section was generally 50 cm. A small compactor was used to compact the soil around the settlement plate. When placing the settling plate, the bottom groove of the settling plate should be flat. Sand cushion should be laid under the settling plate. e vertical deviation rate of the connecting rod of the settlement plate and the bottom plate should be no more than 1.5%.
Displacement monitoring adopted displacement pile (surface displacement) and inclinometer tube (deep soil displacement) for dynamic monitoring. e displacement piles were mainly used to monitor horizontal and vertical displacements. Horizontal displacement of measuring point can be achieved by polar coordinate method with high precision total station and prism. Vertical displacement can be observed by high precision level or total station with prism.
e displacement side piles were laid before soft foundation treatment. ey were prefabricated with reinforced concrete. e top of the pile should be pre-embedded with forced alignment facilities. When the displacement piles were placed in excavated soil, the pile body was poured and fixed with concrete from the bottom up to 50 cm. e inclinometer tube was formed by polyethylene casting. e outer diameter of the tube was 71 mm and the wall thickness is 6 mm. It was buried in the deep section of soft soil and the front of bridge head. e burial depth should be no less than 1 m through the soft soil layer. e accuracy of the inclinometer system was not less than 0.25 mm/m, and the resolution was not less than 0.02 mm/500 mm. e monitoring principle of the inclinometer used in monitoring is shown in Figure 5(b). e horizontal deviation of the action point of the pulley under the probe relative to the action point of the upper pulley was calculated by the inclination angle θ measured by the instrument. e calculation formula is as follows: where δ i is incremental value of relative horizontal deviation in Section 1 (the bottom of the inclinometer is Section 1); L i is vertical length of measuring in Section 1; and θ i is relative increment of inclination in Section 1. Assuming that the horizontal deviation of the section is zero, the total horizontal deviation of the inclinometer at the depth of section n is as follows:

Control Standard and Monitoring
Frequency. Based on the Chinese Design Code, JTG D30-2015 [34], the filling rate should be strictly controlled during the filling process of embankment in soft foundation section. e control standard was that the land subsidence rate of the embankment center line was not more than 1.0 cm per day and night. e horizontal displacement rate of slope foot was not more than Advances in Civil Engineering 0.5 cm per day and night. Deep lateral displacement rate was 3 mm per day and night. e settlement of the preloaded road section was less than 5 mm for two consecutive months. e monitoring frequency is summarized as follows: (1) Construction period: at least one observation per floor was required. If the construction was stopped for any reason, it was observed every three days. (2) Preloading period: observation every three days in the first month, observation every seven days from the second month to the third month, and observation every half a month from the fourth month until the pavement is paved. (3) Operation period after construction: a small number of typical sections were taken for follow-up observation once every 1-2 months. e frequency of lateral displacement observation was the same as that of settlement observation until the embankment reached the designed construction elevation.
e filling height at sections A and B was about 5.5 m. e embankment was filled in layers with a thickness of 50 cm. e filling work was divided into four stages. e first stage consisted of two layers of filling with a filling height of 1 m. It took 25 days to fill and 25 days to consolidate the soilrock mixture. e filling height of the latter three stages was 1.5 m with 25 days for filling and 30 days for consolidation. In the process of subgrade filling, the settlement of A and B had similar development law with time (Figures 6(a) and 6(b)). Firstly, when the first stage was filled to 1 m, the maximum accumulative settlement of A1 and B1 was 5.53 mm and 6.02 mm, respectively. In the second stage of filling to 2.5 m, the maximum settlement of A1 and B1 was 13.77 mm and 14.85 mm, respectively. When the third stage was filled to 4 m, the maximum accumulated settlement occurred at A1 and B1, which was 23.72 mm and 26.80 mm, respectively. Up to 5.5 m of filling, the maximum accumulative settlement of A1 and B1 was 26.23 mm and 29.78 mm, respectively. is corresponded to 76% and 78% of the ultimate settlement. e filling height at sections C, D, and E was about 3 m. e filling of three sections was constructed in three stages. Each stage was filled in two layers. e filling time was 25 days and the consolidation time was 30 days with 1 m filling height. When the first stage was filled to 1 m, the maximum cumulative settlement of the three sections was 10.54 mm, 6.15 mm, and 10.72 mm at C1, D1, and E1, respectively. When the second stage was filled to 2 m, the accumulative settlement of C1, D1, and E1 was the largest with 18   Advances in Civil Engineering soil is the largest, which accounted for a considerable part of the total settlement. When the filling height was reached, the load gradually became stable. With the drainage consolidation of foundation soil, the strength of soil gradually increased, and the cumulative settlement-time curve of subgrade tended to be flat. At this time, the settlement was mainly secondary consolidation. And the settlement converged to a stable value which was the final settlement. Figure 5 also shows that the settlement rate of A1, B1, C1, D1, and E1 points increased sharply during filling period and tended to be flat during consolidation period. e maximum settlement rates were 0.42 mm/day, 0.37 mm/day, 0.42 mm/ day, 0.27 mm/day, and 0.45 mm/day, respectively, which were within the control range. e maximum cumulative settlement of each section occurred at the location near the riverside on the left side of the subgrade (Figure 4). According to the site geographic environment and geological conditions, the role of the river had a certain impact on the stability of the embankment [39][40][41]. Based on the Chinese design code, JTG D30-2015 [34], the monitoring results showed that the maximum cumulative settlement and settlement rate did not exceed the control range. It can be seen that the composite foundation composed of plain concrete pile and reinforced cushion plays an important role in improving the stability of embankment. With the increase of filling height of subgrade, the cumulative ground settlement values will become larger, but the settlement rate will be smaller because of the continuous consolidation of soil. Figure 6 shows the change of accumulated surface displacement of each observation point during the observation period. Displacement piles (J1, J2, J3, J4, J5) were buried outside the treatment scope of soft soil roadbed. Moreover, the cumulative displacement of five displacement piles had similar law with time. With the increase of embankment filling height, the cumulative displacement increased gradually. e displacement tended to be stable after the final filling was completed. e ultimate cumulative displacement of each measuring point in the X direction was relatively large, which was 21.5 mm (J1), 17.9 mm (J2), 15.2 mm (J3), 16.3 mm (J4), and 12.0 mm (J5), respectively. e reason may be that, in the direction perpendicular to the route, the lateral soil body of the embankment was not restrained. e filling increased the load, which resulted in large deformation in this direction. As can be seen, the ultimate cumulative displacement in the Y direction was the smallest, which was 2.5 mm (J1), 2.8 mm (J2), 4.3 mm (J3), 3.0 mm (J4), and 2.4 mm (J5), respectively. Because the filling height of the embankment on the section where the displacement pile (J1) was located is about twice that of other measuring points, and the equivalent load was nearly twice that of other measuring points, the accumulated lateral displacement of the ground surface was relatively large. However, due to the reinforcement effect of the pile, there is not much difference between the maximum displacement and the minimum displacement. Figure 7 also illustrates that the displacement pile (J3) may have a steeper curve change rate due to the rapid filling in the filling process, where the displacement rate was relatively large.   With the completion of embankment filling, the load gradually stabilized. Lateral surface displacement also decreased gradually, and the displacement curve tended to be flat. Figure 8 shows the variation of horizontal displacement in the depth of each survey point. It was measured by an inclinometer at 2 m from the foot of embankment slope. e maximum cumulative lateral displacements of inclinometer tubes (F1, F2, and F4) were 23.56 mm, 20.68 mm, and 16.11 mm, respectively, which all occurred at 0.5 mm below the surface. e maximum cumulative lateral displacement of subsoil of the inclined pipe (F3) was 14.01 mm, which occurred at a depth of 3 m below the surface, while the maximum cumulative lateral displacement of subsoil of the inclined pipe (F5) was 14.10 mm, which occurred at a depth of 2 m below the surface. Among them, the cumulative displacement of the inclinometer tube (F2) was the largest, which was mainly related to the embankment filling height. During embankment filling, the maximum cumulative displacement of each measuring point accounted for 75%, 73%, 78%, 76%, and 64% of the final cumulative displacement, respectively. erefore, the process of loading caused large displacement of embankment. It can be seen from the data of each monitoring point that the lateral displacement inside the soil was relatively small. From the bottom of the inclinometer tube to the ground, the lateral displacement of soil increases gradually. And the closer the ground, the greater the displacement. It also shows that the treatment of soft soil subgrade played a vital role in the stability of embankment. Embankment construction or excavation process involves a time-dependent problem due to the dissipation of excess pore water pressure [42,43]. Due to the fact that the pore water pressure indicators were all destroyed because of the carelessness of construction persons during the construction, the time-dependent behavior of this project was not given more focus.

Conclusions
A case study for highway construction over soft marine clay in China is presented in this paper. e obtained results from this study are summarized as follows: (1) e settlement on the left side of the embankment was larger than that on the right side. e final cumulative settlement of each section near the river side was the largest, which was 34.33 mm, 37.88 mm, 24.77 mm, 23.20 mm, and 22.66 mm, respectively. During the embankment filling, the settlement accounted for 76%, 78%, 77%, 73%, and 75% of the final settlement. e maximum settlement rate was 0.45 mm/day. With the increase of embankment filling height, the cumulative settlement has an increase. When the embankment construction was completed, the settlement gradually tended to be stable.
(2) e maximum displacement of the surface at the distance of 2.5 m away from the foot of the embankment was 21.5 mm. e filling height of this section was twice that of other sections, and the load was also nearly twice that of other sections, which makes the lateral displacement of the surface larger. However, due to the reinforcement effect of plain concrete pile and reinforced cushion on roadbed, the observed displacements were not different.

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(3) e maximum cumulative horizontal displacement of each monitoring point was 23.56 mm, which occurred at 0.5 mm below the surface. Moreover, the displacement generated during embankment filling accounted for about 75% of the final displacement. e smallest percentage of other monitoring sites was 64%. It can be seen that the filling had a certain impact on the embankment. e measured settlement and displacement meet the specification requirement, and the monitoring of the process should be strengthened to ensure the safety of the construction.

Data Availability
e data used to support the findings of this study are included within the article.

Conflicts of Interest
e authors declare that they have no conflicts of interest.