A Record of Deep Soft Soil with Vacuum Combined with Preloading Chen Xianchun\ Lin Bing bureau2, Zhao Youliang3(1. Jin Liwen Expressway Yongjia Lucheng Command, Wenzhou 325000, China;2.Wenzhou Municipal Engineering Construction and Development Office, Wenzhou, Zhejiang 325000; 3. Wenzhou Traffic Construction Group Co., Ltd., Wenzhou 325000, China) Ming, Vacuum-loaded combined preloading treatment of deep soft ground is a fast, effective and economical reinforcement method.
1 Rumors Vacuum-loaded combined preloading is a method for dealing with deep soft soils. It has obvious advantages for reinforcing deep soft soils. This paper uses engineering examples to illustrate its application.
The Yongtaiwen high-speed company Ruian section of the West Dian interchange D road DK0 500 subgrade soft soil depth (up to 25m) and soft soil moisture content, high compressibility, low bearing capacity, loading height of 3.0 ~ 3.7m, in order to Under the premise of ensuring the stability of the embankment, shorten the construction period, ensure the timely construction of the abutment, and reduce the post-construction settlement. After a study, it was decided to carry out a vacuum combined preloading treatment for the road section. The simple stratum condition of this section is as follows: 1 Plain fill: variegated, mainly composed of block stone, gravel, sand, etc., about 0.6m thick; 2 clay: grayish yellow, plastic ~ hard plastic state, about 1.5m thick; 3 silt: grayish gray, saturated, flow-shaped, with a small amount of shells, thick 22 gravel, gray ~ gray yellow, slightly dense ~ medium dense, about 3.2m thick.
2 Construction Because the vacuum preloading is applied for the first time in the Wenzhou Expressway, and it is constructed in a tunnel with a small width and a large camber, the surrounding environment is complex and therefore has a certain degree of difficulty. Through careful analysis and research, we first conducted supplementary drilling and soil sampling, and then buried observation equipment such as layered sedimentation equipment, inclinometers, and pore water pressure gauges. The pre-construction of vacuum preloading began on December 11: laying of pipelines, laying of sealing membranes, excavation of sealed trenches, installation of vacuum equipment, etc., and formal vacuum was applied on December 26, after which leaks were filled and holes were filled in January. After 3 days, the vacuum degree was maintained above 80 kPa to meet the design requirements.
The beginning of the day is partially filled with earth, and on the 24th of February, a layer of 50cm rock slag is on the entire road. Due to the slower loading, loading was almost concentrated in the last two months, ie, the design elevation was basically reached in late April. According to the loading conditions on the site, the DK0+400 section and the DK0+455 section load were simplified. It was found that due to various reasons, the loading speed did not keep up with the previous period, and the combined preloading period for the vacuum one-load was less than one month. The design is different.
3 Field Observations 3.1 Surface Settlement As of May 14, the surface settlement curves reflected by the three surface sedimentation plates of BM1, BM2 (DK0+455) and BM3 (DK0+400) are as follows, and their cumulative settlement is as follows: BM1 As shown in the graph, the horizontal displacement curve of the settling velocity DK0+400 of the settling plate can be seen from the figure. 3 Stratification Settlement curves of the two sections are shown in the figure. They can be larger than the lower part of the soil from the figure, explaining the effects of plastic L and other reasons, resulting in observation curves of the upper part of the settlement curve L gap water pressure changes are basically the same. The instantaneous settlement rate has increased.
The maximum settling rate reached 41cm/day, far exceeding the 1cm/day of the preload requirement for surcharge preloading. The 2 month phase at 5 months Koda's) water pressure curve, 4m, 14m, 24m! On day 4 and on May 4th, the instantaneous pore pressure in I reached relatively long and the deep soil pore pressure I increased. This is the typical surface sedimentation rate curve from April 1 to May. The daily sedimentation rate is shown in Table 1. It can be seen that after the completion of the surcharge, the sedimentation rate is significantly reduced. After a period of combined preloading, the surface settlement curve tends to be gentle and gradually converge.
Table 1 Surface sedimentation rate Table No. Date Section April 1st April 5th April 6th April 6th 12th April 12th 17th April 17th April 21st 23rd April 23rd April 25 April 25 May 4 May 4 May 6 May 6 May 11 May 11 May 14 3.2 Horizontal displacement Horizontal displacement curves of two sections as shown. It can be seen that the horizontal displacement of the soil surface is large, and the greater the soil depth, the smaller the horizontal displacement. With the loading, the soil will temporarily move outward with respect to the reinforcement zone, but the general trend is to move to the consolidation zone, which is essentially different from the simple surcharge preloading, which ensures the stability of the embankment.
It can be seen that the settlement of the upper soil is obviously due to the drainage distance of the drainage plate and the consolidation of the well resistance soil is faster than that of the lower soil.
3.4 Pore pressure DK0+400 section roadbed, as shown.
The pore pressure of the DK0+400 cross section was at the maximum of April 7 and April 12 respectively. It shows that the shallow soil mass is obviously in the heap, and its dissipation speed is also faster; it is lagging behind, and it dissipates the Mandel effect of pore pressure in the initial stage.
Driving up and down, resulting in a large amount of mud in the pebbles, part of the drain board was blocked. As of May 18, the settlement of the DK0+400 section was 1.351 m, which was 87.16% of the final settlement (1.55 m) under this permanent load. It is the logarithmic relationship between soil settlement and time. As can be seen from the figure, the settlement rate is still relatively large before the April 25 settlement due to the quicker soil addition in the later period. After the April 18th, the addition of soil on the inside caused the sedimentation rate, which tends to decrease, to be somewhat large. After May 4th, the sedimentation rate tends to ease, and it can be seen from the settlement curve that it has a convergence trend.
From the measured data, logarithmic curve fitting method was used to predict the settlement. From the figure, the settlement at the time of June 3 is 1.416m, and the average degree of consolidation is 91.35%. Based on this calculation, the vacuum can be evacuated in about the middle of June, and it can be ensured that the settlement is relatively stable after the vacuum is removed.
On the other hand, in this deep soft foundation, it is assumed that the problem of landslides does not occur during the loading process, and an average consolidation degree of 92.16% is achieved. Vacuum preloading can be completed within 4 months.
Therefore, when using a vacuum-loaded combined preloading method, it should be carried out in a timely manner to ensure a joint preloading period, so that the advantages of this method can be better exerted.
5 Concluding remarks Through the examples of this project, it has been shown that a vacuum-loaded combined preloading treatment of deep soft ground is a fast, effective and economical reinforcement method.
In the process of filling, if there is no vacuum, it is highly likely to cause landslides. Vacuum can ensure the stability of rapid filling.
(Continued on page 15) Surface Settlement Prediction Curve 00 Sectional Horizontal Displacement Curve From the horizontal displacement curve, see the displacement of the soil around the reinforcement zone into the reinforcement zone, and the pure surcharge preload can only be generated outside the reinforcement zone. The horizontal displacement is not conducive to the stability of the roadbed. It is the horizontal displacement curve produced by the top of the inclinometer pipe. It can be seen that the trend of the two is almost the same.
(2) The original design load should be completed within two months after the start of vacuuming. The vacuum combined preload period is approximately two months. However, because of earth-tightness and other objective reasons, the loading is almost concentrated in the last two months. After filling the vacuum for four months, the filling is basically completed, making the vacuum one-load combined preloading period not vacuumed for four months. In the combined preloading period, if the vacuum is stopped at the moment, it is extremely unfavorable to dissipate or settle the stability of the excess pore water pressure. Therefore, the vacuum must be properly extended. According to the design and other engineering experience, the combined preload period 1~ 2 months or so.
Due to the analysis of the reinforcing effect of the car at the site 4 when cleaning the site prior to the vacuum preloading construction, from the perspective of the filling situation, less than two months later, the 2 kPa is piled up and the pile has a 2.5 m high fill. In the next 3 days, 80cm is piled, the daily sedimentation rate is up to 4.1cm/day, and it is very likely to cause landslide hazard if there is no vacuum. Therefore, vacuum can be used to ensure stability during rapid filling.
It is the horizontal displacement along the depth curve from the initial observation to May 14.
(Continued from page 6) Industry Press, 1988
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