On the characteristics of highway roadbed and soft soil treatment measures

Abstract: In the soft soil to build roads, if not the actual situation and deal with the construction of embankment, embankment instability tend to occur or excessive subsidence problems, leading to damage to road surface can not even work properly. In this paper, I participate in a number of engineering practice, analysis highway construction in the characteristics of soft soil roadbed, features, and made a number of soft soil roadbed can effectively improve the quality of technical measures.

Keywords: road; soft soil roadbed, characteristics and measures
As China's economic system reform, transportation economy has entered a new era of development, while improving the quality of the highway requirements the quality of the road, embankment quality plays a vital role in the construction process, such as do not attach importance to the subgrade treatment, will directly affect the operational status of the road after the completion of its life.

First, the characteristics of soft soil roadbed
Mud and silt soil on the project referred to as soft soil, also refers to the high compression of the soft soil, the main components of soft soil and silt particles, often into the floc structure, high water content. Porosity ratio, poor permeability, low shear strength, high sensitivity in the effect of load, the foundation bearing capacity is low, the accident prone to instability. Foundation settlement deformation, differential settlement is also large, and stable settlement lasted longer. Therefore, in the soft subgrade in the design and construction process, must be studied in detail to grasp the nature of soft soil and soil characteristics (particularly strength and deformation of soft soil dynamic change and take appropriate engineering measures to prevent the embankment collapse, instability and abutment damage, pavement cracking, Bump and so on.

Second, the reinforcement of soft soil roadbed effective measures
(A play on the sand wells in the roadbed
Sand Sand, also known as drainage wells, for thickness greater than 5m when the soft soil subgrade, sand drain diameter is generally normal 30 ~ 40cm, maximum depth of effective treatment is 18m. Sand is the use of piling equipment or high pressure water jetting and blasting methods in the foundation law arranged in a certain hole, and poured in the eyes of these holes, the coarse sand to form sand column, affecting the rate of consolidation is one of the main sand drain spacing, which is adjacent to Sand Center the distance between the sand drain spacing is generally 6-10 times the diameter of the sand drain, often 2-4m. sand wells to determine the length of the soft soil by the thickness, load size, and engineering requirements may be, generally 10 -20cm. Sand layout in the form of a square and triangle two. In general, wells in the sand to the top of the sand cushion shop, well connected with the sand, this site can be drained to the outside. Sand layer must be greater than the width of the bottom width of the building, and well out of the sand area outside the line of 2 times the diameter of sand wells, the construction process, cushion sand with sand sand the same wells, laying flat to a thickness of about 50cm. 
Sand Wick, for soft soil thickness, embankment stability, high soft soil roadbed fill. Sand Wick diameter as small as 7 ~ 12cm, maximum effective treatment depth 18m. Sand Wick soft soil can increase the vertical straight direction of the drainage capacity, reduce the horizontal drainage distance, accelerate the strength of soft soil. sand bags poured into the sand, the sand drain method can be used to hammer or vibration construction method and it's complex construction process, the cost is relatively high, the use of a longer time. well if the well diameter sand generally too small for the construction, it is now widely used mesh fabric Sand Wick, low cost wells than sand, and will not operate due to construction on the occurrence of errors or foundation level and vertical deformation and loss of continuity.

Sand Wick is the drainage of deep soft soil of the vertical body, set it for the clay foundation can play the role of replacement. At the same time by filling pre-press to form vertical drainage channels, with sand cushion, or preloading surcharge preloading and other methods to drain into the groundwater from the three-way drainage, pore water dissipation, but also can effectively prevent or additional load caused by the dissipation of excess pore water pressure increased speed up consolidation of the foundation, speed up the settlement.

(B Sand, Construction Sand Wick Notes
1 to conduct pre-construction test drilling, according to the design depth, repeated many times, finally to determine the scope of the sand deep wells, the specific depth of the sand wells range in depth to determine by actual measurement.

2 for raw materials testing. Sand bags, sand must be tested and qualified before being used.

Sand Wick sand bags to good use and water permeable and resilient linen, cloth or recycled woven polypropylene production. Sand must be sifted, dry up the sand, filling sand should be two irrigation two vibration, and shop to labor, to ensure full filling sand bags and sand are dry sand.

3 holes. Drilling when drilling by the test requirements. Once you reach the bearing layer, immediately shut down, and measure the hole depth, and make the depth record. Drilling is completed, and then measure the distance to the ground at the mark, with length minus the distance is the hole depth. sand well as vertical, individual maximum deviation <1.5%
4 Installation of sand bags. The length of sand bags and sand to the same depth of wells, to be promptly cut off the excess part of the Install can not produce back to the band, as have pulled back flush with the conduct. Sand bags buried promptly after the installation is complete , sun exposure and sand bags to prevent aging. Links to free download http://www.hi138.com (c) Vibro deal with weak foundations
Vibro composite foundation is an economic, rapid reinforcement of the foundation, the soil of the technical measures currently used widely, not only can be applied to sand, silt, clay, fill, and miscellaneous factors such as soil fill can also be used to reinforce some of the soft soil and mud through drift gravel layer, or reinforcement of a good soft soil under the soil. vibro stone pile length and pile diameter reinforced sections according to the actual thickness of soft soil circumstances, the pile diameter is generally 30 ~ 80cm. Pile holes are generally equilateral triangle and square.

Vibro construction methods have varied, but commonly used method is vibro-method it is using a horizontal vibration can produce tubular machinery and equipment, starting in the high-pressure water pump below the red edge vibration, the vibrator high-frequency vibration, the vibrator is designed to sink into the soil depth in the soft clay foundation hole, the clearance hole, the hole can be from the ground to fill in the paragraph by paragraph and other materials gravel or pebbles into a pile, each filling the role of both the vibration is vibration dense crowd, until the ground, resulting in the formation of a foundation in a very dense pile to form a pile composite foundation and the original soil composition, greatly improving the foundation bearing force, and reduce the compression. vibro-replacement method is applicable to the soil is mainly clay, sand can also be manufactured in the rubble pile, but the compaction effect is much larger than Replacement. gravel pile composite foundation pile throughout the the soft soil, when a certain hard layer, the pile plays the role of stress concentration, when the pile has not reached a relatively hard layer, the pile fabric from all the stress and the role of diffusion, while coarse-grained material formed as composite foundation The gravel pile, so I can play a role in accelerating drainage and consolidation.

(D Construction Notice of composite foundation
1 order of construction
Vibro-pile construction sequence is "from the inside out", this sequence has the advantage of displacing part of the soft soil, the system easy to pile in soft soil with higher compression in the construction, the best way to use the interval construction so can reduce the system between the pile during pile soil disturbance.

2. Vibro way of filling
Carved into the pile hole filling Kong Houli pile system. Packing there are two ways The first one is the intermittent filling method, the operation is relatively complex, suitable for small engineering manual cart fill. This construction process is to make the hole vibrator mouth, into the filler to the hole, and then the next vibrator to fill in the vibro-compaction, to a certain construction requirements, such a construction process repeated until the pile is completed the system, the second is a continuous filler method, easy to operate, for mechanized operations. Construction process is not made orifice vibrator, put on only 30 ~ 50cm, left off the already dense pile-up times, ie stone backfill the hole continuously until the second pile vibro-compacting to meet the design requirements, and then on to mention 30 ~ 50cm, continuous vibro-packing density, repeat the above steps, bottom-up system, paragraph by paragraph, until the pile holes.

Third, the conclusion
In summary, to improve soft subgrade of roads is to build a good quality of the underlying soft soil embankment road, soft soil is often encountered in the construction of geological conditions, after the opening of its relationship with the operations and the use of road life, but also on the individual areas of transport economy. Sand Wick law and vibro are two common methods of soft soil reinforcement, with the construction of these two methods are simple, saving material, reliable quality , the effect is significant advantages, so applications in the construction of more extensive view of soil types, characteristics of diversity, dealing with soft subgrade There are many technical measures, this article is no longer listed.

References:
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