0 ago language.
The flow of sand is a kind of phenomenon of soil, the primary flow sand soil lose load-carrying capacity, not only the construction conditions deteriorate, will also affect the excavation stability, serious will cause collapse of foundation pit slope, endangering safety. It can be seen that the foundation pit engineering is very important for the treatment of convective sand [1].
1 Introduction to engineering construction.
This paper mainly introduces the general situation of the project and the construction of the concrete including 2 aspects:
1.1 engineering survey.
1.1 1 Engineering geology.
The little elm slope water culvert in tender river floodplain and terrace at the intersection, the terrain was shaped slope. Drilling has revealed the formation is mainly the fourth grade new alluvial layer alQ4 and Pleistocene alluvium alQ3, lithology mainly of high liquid limit clay, poorly graded fine sand, well graded sand. Underground water distribution culvert site mainly of Quaternary pore water, pore water pressure, aquifer permeability, water rich. The soil properties of the water culvert foundation pit of the small elm is shown in Table 1
1.2 1 engineering structure layout.
The small elm slope water culvert is divided into 3 parts, import, hole body and outlet:
1) inlet section and the intercepting ditch is connected by the character of dry masonry walls, wall, a U-shaped groove, wherein, bottom height 169. 10 m, imports of width 1. 75m, height 70 4. M.
Geologic data, the 5, 6 level with good, Heilongjiang Province Water Conservancy Hydropower Investigation Design and Research Institute proposed building foundation can seat in the first layer, according to eliminate the actual situation of the power pool, pool at the bottom of the base is located on the second floor.
2) hole in the body by 9 prefabricated culvert composition, the first two is 1: 5 slope elevation layout by 169. 10 m down to 164. 90 m, middle section is section 5, elevation by 164. 90 m dropped to 164. 64 m, two is 1: 5 slope layout, elevation by 164. 64 m fell to 160. 40 m; hole in the body size of the cross section 1. 50 m x 1. 80 m, hole body thickness of concrete for the 0. 5 m.
Trunk 3) exit from the bottom width is 1. 75 m gradient to wide. 00 m u type wall, bottom elevation of 160. 40 m, the small elm slope water culvert stilling pool Hyman, stilling pool base slab top elevation to 160 40 m, bottom elevation 158. 90 m, Hyman bottom elevation 74 M, dry stone bottom protection, slope protection, little elm slope water culvert and interchange, slope water culvert from the canal passes through the bottom, the canal bottom elevation 168. 61 m, where the channel bottom width of 28. 0 m, the slope of 1: 3, concrete prefabricated lining, door bottom concrete slab size 75 cm x 75 cm x 12 cm; slope concrete slab size 75 cm x 75 cm x 10 cm.
Because this paper focuses on the energy dissipation pool part of the discussion, it will be small elm culvert stress pool engineering layout drawing figure 1 ~ 2
1.2 engineering construction.
2.1 1 engineering construction organization design.
Little elm slope water culvert engineering geological condition is relatively complex. Aiming at the situation of the preparation of the stilling basin is part of the construction organization design and the technical measures to do with brief introduction: in stilling pool base excavation sidelines north, South, East three direction respectively to deploy a eye drains at a depth of 14. 5 ~ 15. 0 M. foundation excavation deep in 7. 0 ~ 11. 0 m, to prevent excavation collapse produces, take the ladder excavation per dig deep 2. 0 m wide horizontal 2. 0 m level settings, and then according to the design of slope excavation. Mechanical equipment put into two excavators, two bulldozer [2].
2.2 1 Engineering Foundation excavation.
Construction and in fire pool based within the scope of a total of 3 wells, the depth of 14. 5 ~ 15 m. retaining pile and the first supporting layer construction is completed, foundation pit precipitation is stable, in on the north side of the foundation pit excavation, finished digging the first layer of soil, two retaining piles starts to water seepage, and in a very short period of time and infiltration water more and more, a large amount of sand. In order to ensure the safety of construction and the next step, the construction was suspended in order to find out the causes of the flow of sand, and to make practical and feasible control measures.
2 cause of the flow of sand.
There are 3 main reasons:
1) from the engineering geological investigation report can see in (- 4. 1 - 10. 7 m) is poorly graded fine sand, and lower soil for the high liquid limit clay soil, the adhesive layer under vertical permeability coefficient is small, for a aquifuge, due to the presence of aquifuge and - 10. 7 m above the water row do not go out, resulting in a the soil to produce a flow of sand to the foundation pit is difficult to continue the excavation.
2) foundation pit on the north side of the original small elm sluice for local villages planting rice water, 5 September limber, resulting in fire power pool soil with the increase of moisture content. Once the soil excavation, it will cause the water in the pit and pit collusion.
3) pit east of about 40 m Nen River diversion canal through, channel bottom elevation is fire pool base 10. 21 m, i.e. trunk channel bottom elevation is 168. 61 m, fire force at the bottom of the pool elevation is 158. 40 m, canal every year in late April 10 in late April, watering, resulting in soil with the increase of moisture content. Disadvantage of foundation pit excavation.
3 engineering treatment measures.
For the construction of the project, it is necessary to stop the flow sand, so we must cut off the external water supply of the foundation pit and reduce the underground water level between each soil layer. After a comprehensive consideration, the following programs:
1) for the foundation pit on the north side of the original small elm drainage sluice seepage influence, in the foundation pit on the north side of things to the drainage ditch, water seepage through the drainage ditch.
2) for excavation of the surrounding soil characteristics, in the elimination of 6 wells to increase the force of foundation pit within the scope of the original foundation, to a depth of 10 m, the other 3 eyes well depth is 14. 5 ~ 15 m. The treatment measures, so that throughout the runoff and the groundwater has been effectively controlled, to stop the flow of sand once again, to ensure the smooth progress of the foundation pit excavation and construction.
4 knot language.
1) of thicker fine, silty sand, underground water is abundant, surrounding a water supply construction of foundation pit, in compiling the construction organization design, to carefully study the geological exploration data, consider the flow of sand damage, flowing sand and the engineering failure to have a full understanding. According to the characteristics of groundwater, to play the corresponding deep wells, reasonable layout of the number of wells and space location, so that effective control of groundwater, so as to avoid the construction of blocked.
2) at the end of the project, the treatment scheme is adopted to avoid the phenomenon of flowing sand again. To provide some reference for similar foundation pit construction.
Reference
[1] Peng Gang. Analysis and treatment measures of the cause of the flow sand in a foundation pit engineering [J]. Shanxi architecture, 2011,37 (04): 58 -59.
[2] Yuan Guangyu. Construction of hydraulic engineering [M]: Second Edition. Beijing: Water Conservancy and electric power press, 1985: 59 -63.