*3.3. Improvement before Analysis of Monitoring Data*

Settlement observation was conducted during the period January 2010 to August 2010. In the EK0 + 323 section, the largest settlement, reaching over 129.0 mm, occurred on a road bridge, affecting the speed of traffic and highway safety. In September 2010, asphalt concrete pavement filling was applied, and it was later observed that the roadbed continued

sinking at a larger sedimentation rate (i.e., 9.1 mm/month). On 25 March 2011, the settlement reached its maximum, 219.0 mm. Measurements of the settlement before the application of FCB are shown in Figure 4.

**Figure 3.** Drilling holes on north sides of the embankment. Reprinted with permission from Ref. [18]. Copyright 2021 IEEE Proceedings.

**Figure 4.** Total embankment settlement before improvement with FCB.

As shown in Figure 4, until 25 March 2011, no obvious convergence trend in the subsidence curves was noted, based on the post-construction monitoring settlement data. The reason may be due to tight deadlines resulting in inadequate preloading foundation, making the work required after settlement too large in scope. A settlement prediction formula [21] for EK0 + 323 settlement was used to demonstrate this method. Based on the bridge sections of EK0 + 323 and two settlement observation sections, the settlement prediction results are shown in Table 3. To simplify the forecasting process and meet the requirements of settlement prediction analysis with prediction process, secondary consolidation settlement was not considered.

The settlement prediction results showed that section EK0 + 323 s settlement will be up to 402.2 mm. Not taking into account the largest remaining secondary consolidation, settlement will again lead to vehicle bumping; thus, holes filled with bubbled and mixed FCB were introduced in section EK0 + 323 for improvement.

Following the above-described unloading calculation method, the FCB replacement quantity was 102.4 m3, and the total FCB volume for embankment improvement was separated into 774 lateral holes with diameters of Φ 150 mm (including 719 holes that were 6.0 m deep and 55 holes that were 4.0 m deep).

**Table 3.** Settlement forecast.


*3.4. Effectiveness Analysis of Improvement*

For the FCB improvement of section EK0 + 323, the embankment settlement data based on dynamic monitoring data analysis is shown in Figure 5.

**Figure 5.** Total embankment settlement after improvement with FCB.

Section EK0 + 323 is located on a bridgehead segment, and according to the preconstruction settlement prediction, the remaining post-construction settlement of the left and right sides were 182.9 and 103.3 mm, respectively, until May 2011. As shown in Figure 5, after improvement with FCB on both the left and right sides, the settlements were 57.1 and 44.2 mm after embankment improvement finished (i.e., October 2011), respectively. Comparing the two sites, after initial construction of the section, the settlement exhibited a relatively sharp decreasing trend. The reason was that during the improvement process, the construction disturbance caused an impact on the embankment. The settlement after improvement was approximately 70% of the predicted settlement. Additionally, the average remaining settlement was 43.2 mm, meeting the residual settlement thresholds (i.e., less than the 30.0 cm) of the expressway embankment after improvement.

The results of EK0 + 323 after replacement improvement using the proposed technology revealed a monthly settlement rate of 50%, which was a reduction from the remaining settlement after construction of 70%. After improvement with the lateral hole replacement technology, the remaining settlement met the threshold for the settlement control after construction standards, and effectively suppressed the recurrence of bumping.

## **4. Discussion**

Using FCB to replace the undisturbed soil of embankment on both sides cannot affect the normal operation of the highway. It can avoid economic losses caused by closure. FCB has very good fluidity, so it can be pumped to the designed depth and has a fast construction speed, so the construction period can be greatly shortened.

By calculating the replacement thickness of the embankment by using the formula proposed in this paper, after improving the embankment with this thickness, the settlement of embankment begins to stabilize. The residual settlement of embankment meets the thresholds (i.e., less than the 5.0 cm). Thus, this calculation formula, proposed in this paper, can be used in embankment improvement projects. During the improvement of the embankment, the settlement has a sharply increasing trend. It may be caused by embankment disturbance during the construction period. Thus, embankments should be replaced by the undisturbed soil in the same section, which is used to analyze the impact of construction disturbance. Additionally, monitoring the road surface settlement without embankment improvement, which is used to prove that the decrease in foundation settlement rate is caused by FCB improvement.
