CN113653025A - Drainage-reinforcement structure for improving stability of soft clay pile body and construction method - Google Patents
Drainage-reinforcement structure for improving stability of soft clay pile body and construction method Download PDFInfo
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Abstract
The invention discloses a drainage-reinforcement structure and a construction method for improving the stability of a soft clay pile body, wherein the drainage-reinforcement structure and a soft clay layer of the soft clay pile body are sequentially stacked, and an inclination angle is formed between the downslope direction and a horizontal plane where the soft clay layer of the soft clay pile body is located; the drainage-reinforced structure comprises a drainage layer and a tensile permeable layer, the tensile permeable layer is arranged in the drainage layer, and a drainage ditch is arranged on one side of the drainage layer. The invention can enhance the friction strength of the rib soil interface, improve the shear strength of the soft clay, make the internal stress distribution of the soft clay pile more uniform, reduce the uneven settlement of the soft clay pile, and further obviously improve the overall stability of the soft clay pile.
Description
Technical Field
The invention belongs to the technical field of soft clay piling, and particularly relates to a drainage-reinforcement structure for improving the stability of a soft clay pile body and a construction method.
Background
Soft clay is defined as follows in geotechnical engineering investigation regulations in soft soil areas (JGJ 83-2011): fine soil which has natural pore ratio of more than or equal to 1.0, natural water content of more than liquid limit, high compressibility, low strength, high sensitivity, low water permeability and high rheological property and can be collapsed by earthquake under the action of larger earthquake force, and the fine soil comprises silt, mucky soil, peat soil and the like. According to the engineering properties and the combination of natural geological and geographic environments, the soft clay in China is divided into three distribution areas: in areas such as North China plain, Bohai Bay and the three river plains in the northeast China, the middle and lower reaches of Yangtze river, the Yangtze river basin and the noble plateau of cloud, it can be seen that the soft clay distribution in China is very wide and the types of the areas are many.
In recent years, with the acceleration of urbanization process and large-scale development and construction of underground space in China, a large amount of soft clay is generated in foundation excavation processes of various buildings, structures, pipe networks and the like in coastal and coastal river regions. The method for transporting soft clay generated by excavation to a receiving field for filling is the main mode for disposing the soil in China at present. Taking Hangzhou as an example, soft clay discharged in Hangzhou subway construction at present is mainly transported to a wharf of a middle station by a vehicle and then transported to more than 20 accepting places of nearby counties and cities such as Deqing, Changxing and the like by a ship for absorption and landfill. Due to the lack of relevant national standards, the accepting fields usually have the problems of ultrahigh overspeed filling, missing compaction procedures, imperfect drainage and guidance facilities and the like, so that the landslide or collapse accident of the pile body occurs. In 12 and 20 days in 2015, a landslide accident occurs in the red depression slag receiving field in Shenzhen Guangming New region, unstable sliding occurs in waste soft clay of about 270 million cubic meters, so that 33 buildings are buried and damaged, 77 people die, and 8.81 million yuan is directly economically lost. Therefore, a scientific and reasonable soft clay stacking technology is explored, so that the long-term safety and stability of the stack body can be guaranteed, and the relevant national standards can be perfected.
In the soft clay piling project lacking effective drainage facilities, the interior of a pile body is gradually saturated along with the continuous pile height of the pile body, the drainage consolidation process is slow, the shear strength is slowly increased, and when ultrahigh and ultra-high speed piling occurs, a critical failure point is easily reached to cause a landslide phenomenon. For this phenomenon, there are two main approaches to solve: 1) the drainage path is shortened, the consolidation process is accelerated, the compaction degree is increased, and the shear strength of the soft clay is improved; 2) the shear strength of the soft clay pile body is improved by adopting a reinforced earth technology and utilizing the friction occlusion effect between reinforced earth and the good tensile property of the reinforced materials. Currently, the main method for the combined action of the approach 1) and the approach 2) is to lay a composite geotechnical drainage net in a soft clay layer. However, experiments have found that the interface strength between cohesive soil and the composite geotechnical drainage network is very low, even lower than the strength of the filling, and the reinforcement effect cannot meet the engineering requirements generally. The main reasons are as follows: 1) cohesive soil generally has the characteristics of high water content and low permeability, so that the cohesive soil is slow in drainage consolidation, poor in compaction performance and large in creep potential; 2) the ability of the geosynthetic material to laterally confine the soil mass and to withstand tensile deformation is achieved by stress transfer at the interface between the soil and the geosynthetic material, since the soft clay has a high content of fine particles, the shear properties between the soft clay and the geosynthetic material are poor. Therefore, the composite geotechnical drainage net is directly arranged on the soft clay, the friction, bonding and interlocking effects among the reinforced soil are weaker, and the reinforcing effect is not ideal.
Chinese patent discloses a loess high fill in mountain-shifting ditch-filling engineering and a construction method thereof (publication No. CN106193062A, published japanese 20161207), which discloses: the loess high fill in the mountain shifting and ditch filling engineering is composed of a lime pile composite ground base layer, a gravel drainage layer and a loess layer from bottom to top in sequence. The gravel drainage layer is formed by sequentially laminating a composite geomembrane, a gravel layer and a three-dimensional composite drainage network from bottom to top; the loess layer is formed by stacking a compacted loess layer and a reinforced loess layer from bottom to top, and the reinforced loess layer is uniformly doped with glass fibers and laid with a plurality of layers of bidirectional geogrids. The technical scheme has the following defects that: the soft clay has characteristics such as moisture content is high, the permeability is poor, shear strength is little, and this technical scheme drainage blanket only sets up in the centre of lime pile composite foundation and soil layer, and does not set up in the soil layer, is unfavorable for soft clay concretion, consequently is not applicable to soft clay pile filling engineering.
The Chinese patent discloses a high-strength steel wire mesh reinforced material filling structure of a road embankment (publication number: CN210507006U, grant date: 20200512), which comprises a high-strength steel wire mesh and filling soil, wherein one end of the high-strength steel wire mesh is bent to form a folded angle, and a mesh surface is reserved on the folded angle to serve as a reverse covering surface; the filling compaction is arranged on the net surface of the high-strength steel wire net, and the reverse covering surface is fixed on the compaction surface of the filling; the high-strength steel wire meshes are laid in a multi-layer overlapping mode, the high-strength steel wire meshes on the upper layer are laid on the reverse covering surface on the lower layer, and each high-strength steel wire mesh is connected through stranded steel wire twisting edges; and a gravel drainage layer is arranged on the second or third high-strength steel wire net from the bottom to the top. The technical scheme has the following defects that: soft clay has characteristics such as moisture content height, permeability are poor, shear strength is little, and rubble drainage blanket sets up on from the bottom up second or third floor high-strength steel wire net, and the steel wire net is not set up to the remaining high-strength steel wire net, is unfavorable for the internal consolidation drainage of soft clay heap, consequently is not applicable to soft clay heap filling engineering.
The Chinese patent discloses a structure for deep reinforcing of soft slope by combining grid mesh pipe and coarse granules and a construction method (publication number: CN110952571B, grant date: 20210427), the structure comprises a hollow mesh pipe shaped grid mesh pipe and a geotube bag arranged in the hollow mesh pipe shaped grid mesh pipe, and coarse granules are filled in the geotube bag. The technical scheme has the following defects that: the grid mesh pipe directly contacts with the soft clay, and the soft clay generally has high fine grain content and water content, so the shearing strength of the interface between the grid mesh pipe and the soft clay is low, and the stability of a side slope is not facilitated.
Disclosure of Invention
Aiming at the technical problems, the invention provides a drainage-reinforcement structure for improving the stability of a soft clay pile body and a construction method.
A drainage-reinforcement structure for improving the stability of a soft clay pile body is sequentially stacked with soft clay layers of the soft clay pile body, and an inclination angle is arranged between the downslope direction and the horizontal plane where the soft clay layers of the soft clay pile body are located; the drainage-reinforced structure comprises a drainage layer and a tensile permeable layer, the tensile permeable layer is arranged in the drainage layer, and a drainage ditch is arranged on one side of the drainage layer.
The drainage layer comprises an upper fine soil layer, a coarse soil layer and a lower fine soil layer, the upper fine soil layer is in contact with the upper soft clay layer, and the lower fine soil layer is in contact with the lower soft clay layer; the tensile permeable layer comprises an upper reinforcing layer and a lower reinforcing layer, the upper reinforcing layer is arranged between an upper fine soil layer and a coarse soil layer, the coarse soil layer is arranged between the upper reinforcing layer and the lower reinforcing layer, and the lower reinforcing layer is arranged between the coarse soil layer and the lower fine soil layer; the drainage ditch is located one side of fine grain soil layer down, and the drainage ditch is linked together with fine grain soil layer down.
The upper fine soil layer and the lower fine soil layer are filled with fine sand or silt fillers, and the coarse soil layer is filled with medium-coarse sand or fine-medium gravel fillers.
The upper reinforcement layer and the lower reinforcement layer are both made of geogrids or geocell materials with good tensile property and water permeability.
The calculation formula of the thickness of the upper fine-grained soil layer and the thickness of the lower fine-grained soil layer is as follows:
in the formula, hflDenotes the thickness of the upper fine-grained soil layer (2-1) and the lower fine-grained soil layer (2-2), dsiAnd (3) showing the thickness of the shear band in the drainage-reinforcement structure of the ith layer in the soft clay pile body.
The thickness d of the shear band in the drainage-reinforcement structure of the ith layersiDetermining according to an interval in which the shear stress in a reinforcement-soil interface shear stress distribution curve in the process of drawing the reinforcement material is not less than 5% of the peak interface shear stress, wherein the formula of the reinforcement-soil interface shear stress distribution curve is as follows:
in the formula, tau represents the shear stress of the reinforced soil interface; p represents the overburden load of the drainage-reinforcement structure; z represents the distance of the calculation point from the upper reinforced layer or the lower reinforced layer, and is positive upwards and negative downwards.
The calculation formula of the thickness of the coarse-grained soil layer is as follows:
in the formula, hciThe thickness of a coarse-grained soil layer in the drainage-reinforcement structure of the ith layer is shown, k represents the vertical permeability coefficient of the soft clay, B represents the width of the coarse-grained soil layer, L represents the length of the coarse-grained soil layer, and k represents the thickness of the coarse-grained soil layer in the drainage-reinforcement structure of the ith layercRepresents the lateral permeability coefficient of the coarse soil layer filler.
The tilt angle is determined by the following formula:
in the formula, SiIndicates the settlement of the soil layer under the drainage-reinforcement structure of the ith layer in the soft clay pile bodyiThe horizontal distance from the slope intersection point of the drainage-reinforcement structure of the ith layer and the soft clay pile body to the slope top platform is shown, gamma represents the gravity of the soft clay layer (1), q represents the external load of the slope top platform of the soft clay pile body, and EsExpressing the compression modulus of the soft clay, alpha expressing the integral gradient of the soft clay pile body, thetaiShowing the inclination angle of the drainage-reinforcement structure of the ith layer, n showing the number of drainage-reinforcement structures in the soft clay pile body, and HiThe thickness of the i-th soft clay layer (1) is shown.
A construction method of a soft clay pile using the drainage-reinforcement structure for improving the stability of the soft clay pile as described above, comprising the steps of:
s1, laying a fine-grained soil layer on the flat ground;
s2, laying a lower reinforcing rib layer on the lower fine-grained soil layer;
s3, arranging drainage ditches at one sides of the lower fine grain soil layer and the lower reinforced layer close to the slope surface, and communicating the lower fine grain soil layer with the drainage ditches;
s4, paving a coarse-grained soil layer on the lower reinforcement layer;
s5, paving a reinforcement layer on the coarse-grained soil layer;
s6, laying a fine soil layer on the upper reinforcement layer;
s7, paving a soft clay layer on the upper fine-grain soil layer;
and S8, paving the drainage-reinforcement structure and the soft clay layers of each layer in sequence from bottom to top according to the layer number requirement of the soft clay pile body by the method of the steps S1-S7.
The invention has the beneficial effects that: the invention can shorten the drainage path of the soft clay pile body, and further accelerate the drainage consolidation, thereby improving the shear strength of the soft clay; the friction strength of a reinforced soil interface can be enhanced, so that the tensile property of the reinforced layer is fully exerted; the soft clay pile body internal stress distribution can be more uniform, so that the uneven settlement of the soft clay pile body is reduced, and the overall stability of the soft clay pile body is obviously improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic view of the inclination angle of the drainage-reinforcement structure.
Fig. 2 is a schematic structural view of a drainage-reinforcement structure.
Fig. 3 is a schematic diagram of a shear stress distribution curve of a reinforced soil interface.
Fig. 4 is a schematic structural diagram of a soft clay pile.
In the figure, 1 is a soft clay layer, 2-1 is an upper fine-grain soil layer, 2-2 is a lower fine-grain soil layer, 3-1 is an upper reinforced layer, 3-2 is a lower reinforced layer, 4 is a coarse-grain soil layer, 5 is a drain hole, and 6 is a drain ditch.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
Example 1: a drainage-reinforcement structure for improving the stability of a soft clay pile body is shown in figure 4, wherein the soft clay pile body comprises a plurality of soft clay layers 1, and the lower part of each soft clay layer 1 is provided with the drainage-reinforcement structure; as shown in fig. 1, the drainage-reinforcement structure and the soft clay layer of the soft clay pile are stacked in sequence, and a certain inclination angle is formed between the down-slope direction and the horizontal plane; every drainage-reinforced structure all includes drainage blanket and tensile permeable bed, and the tensile permeable bed sets up in the inside of drainage blanket, and one side of drainage blanket is equipped with escape canal 6, and escape canal 6 is arranged in collecting and the moisture in the soft clay of discharging. The drainage-arrangement of adding muscle structure can show the overall stability ability that promotes soft clay pile body, and this mainly reflects from following three aspects: firstly, the soft clay pile body can shorten a drainage path and accelerate drainage consolidation, so that the shear strength of the soft clay is improved; secondly, the friction strength of a reinforced soil interface can be enhanced, so that the tensile property of the tensile permeable layer is fully exerted; finally, the internal stress distribution of the soft clay pile body can be more uniform, so that the uneven settlement of the soft clay pile body is reduced.
As shown in fig. 2, the drainage layers each include an upper fine soil layer 2-1, a coarse soil layer 4 and a lower fine soil layer 2-2, the upper fine soil layer 2-1 is in contact with the upper soft clay layer 1, and the lower fine soil layer 2-2 is in contact with the lower soft clay layer 1; the tensile permeable layer comprises an upper reinforced layer 3-1 and a lower reinforced layer 3-2, the upper reinforced layer 3-1 is arranged between an upper fine soil layer 2-1 and a coarse soil layer 4, the coarse soil layer 4 is arranged between the upper reinforced layer 3-1 and the lower reinforced layer 3-2, and the lower reinforced layer 3-2 is arranged between the coarse soil layer 4 and the lower fine soil layer 2-2; the drainage ditch 6 is positioned at one side of the lower fine grain soil layer 2-2, and the drainage ditch 6 is communicated with the lower fine grain soil layer 2-2; one side of the drainage ditch 6 is provided with a drainage hole 5, and the lower fine soil layer 2-2 is communicated with the drainage ditch 6 through the drainage hole 5; the side height of the drainage ditch 6 is matched with the corresponding lower reinforcement layer 3-1 and the lower fine grain soil layer 2-2 to facilitate the lateral drainage of water in the coarse grain soil layer 4, and the bottom of the drainage ditch 6 is matched with the bottom of the lower fine grain soil layer 2-2 to facilitate the uniform diversion and drainage of water in the lower fine grain soil layer. Go up fine grain soil layer 2-1 and fine grain soil layer 2-2 down and mainly used vertical water conservancy diversion is from the moisture of soft clay layer 1 exhaust, can also prevent simultaneously that soft clay granule in the soft clay layer 1 from entering into coarse grain soil layer 4 and cause the jam in coarse grain soil layer 4. The coarse soil layer 4 is mainly used for guiding the water drained from the upper fine soil layer 2-1 to the drainage ditch 6 in a side direction so as to facilitate the drainage of the water. The upper reinforcement layer 3-1 and the lower reinforcement layer 3-2 are mainly used for improving the overall rigidity and the overall strength of the soft clay pile body, so that the uneven settlement of the soft clay pile body is reduced, and the stability of the soft clay pile body is enhanced.
The upper fine grain soil layer 2-1 and the lower fine grain soil layer 2-2 are both filled with fine sand or silt filler, and the coarse grain soil layer 4 is filled with medium-coarse sand or fine-medium gravel filler. The upper reinforcement layer 3-1 and the lower reinforcement layer 3-2 are made of geogrids or geocell materials with good tensile property and water permeability, and the upper reinforcement layer 3-1 and the lower reinforcement layer 3-2 are arranged at the interface between a fine soil layer and a coarse soil layer, so that the tensile strength of a reinforced soil interface can be obviously improved, the friction strength of the reinforced soil interface is matched with the tensile strength of the reinforcement layer, and the reinforcement layer is prevented from being pulled out and damaged in a soft clay pile body compared with the traditional mode of arranging the reinforcement layer in a soft clay layer 1.
The thicknesses of the upper fine soil layer 2-1 and the lower fine soil layer 2-2 are both at least more than half of the thickness of a shear band of the reinforced soil interface, wherein the shear band refers to the deformation thickness of the contact surface of the reinforced layer and the fine soil layer or the reinforced layer and the coarse soil layer during drawing, and therefore the calculation formulas of the thicknesses of the upper fine soil layer 2-1 and the lower fine soil layer 2-2 are both:
in the formula, hflDenotes the thickness of the upper fine-grained soil layer 2-1 and the lower fine-grained soil layer 2-2, dsiThe thickness of the shear band in the drainage-reinforcement structure of the ith layer in the soft clay pile body is shown, in this embodiment, the thickness d of the shear bandsiThe thickness of the shear band is taken.
The thickness d of the shear band in the drainage-reinforcement structure of the ith layersiThe determination is performed according to an interval in which the shear stress in the shear stress distribution curve of the reinforced soil interface in the process of drawing the reinforced material is not less than 5% of the shear stress of the peak interface, as shown in fig. 3, the reinforced layer above the shear stress distribution curve of the reinforced soil interface is taken as a central axis, which is similar to normal distribution, and because the normal distribution generally takes 95% as a confidence level, the interface shear stress of the reinforced soil interface only falls on the curve, 5% of the shear stress of the peak interface is taken as a boundary, and an interval not less than 5% of the shear stress of the peak interface is taken as a confidence interval, which is a value range of the thickness of the shear band.
The formula of the reinforced soil interface shear stress distribution curve is as follows:
in the formula, tau represents the shear stress of the reinforced soil interface; p represents the overburden load of the drainage-reinforcement structure; z represents the distance between a calculation point and the upper reinforcement layer by 3-1, and is a positive value when going up and a negative value when going down, namely the interface shear stress of different z values (the point corresponding to each z value is the calculation point) within the range of 0 axis from the upper reinforcement layer to the plus reinforcement layer, wherein the positive direction is when going up and the negative direction is when going down, and the distance from the plus reinforcement layer to the minus reinforcement material is 0.40 m.
The thickness of the coarse soil layer 4 at least meets the requirement of lateral water diversion, so the thickness of the coarse soil layer 4 is determined according to the following formula:
in the formula, hciRepresent the thickness of coarse grain soil layer 4 among the drainage of ith layer-reinforced structure, k represents the vertical osmotic coefficient of soft clay, B represents the width of coarse grain soil layer 4, L represents the length of coarse grain soil layer 4, in this embodiment, the length of the top of taking the coarse grain soil layer is for the meterCalculating length, kcThe lateral permeability coefficient of the coarse soil layer 4 filler is shown.
The inclination angle is an included angle between the drainage-reinforced structure along the slope direction and the horizontal direction and is required to meet the requirement of lateral water diversion, and the calculation formula of the inclination angle is as follows:
in the formula, SiIndicates the settlement of the soil layer under the drainage-reinforcement structure of the ith layer in the soft clay pile bodyiShowing the horizontal distance from the slope intersection point of the i-th drainage-reinforcement structure and the soft clay pile body to the slope top platform, gamma showing the gravity of the soft clay layer 1, q showing the external load of the slope top platform of the soft clay pile body, and EsExpressing the compression modulus of the soft clay, alpha expressing the integral gradient of the soft clay pile body, thetaiShowing the inclination angle of the drainage-reinforcement structure of the ith layer, n showing the number of drainage-reinforcement structures in the soft clay pile body, and HiThe thickness of the i-th soft clay layer 1 is shown.
As follows, taking soft clay generated by excavation of a foundation pit in a certain area of China as an example, the basic characteristics are shown in table 1. The soft clay stacking height is 5.0m, the stacking gradient is 1:3, the length of the slope top platform is 2m, the width and the length of the slope bottom of the soft clay stacking body are about 17m, and the slope top platform has no external load. The drainage-reinforcement structure is totally set to 5 layers from bottom to top, and the thickness of each soft clay layer 1 is 1.0 m. The fine-grained soil layer filler adopts fine sand with good gradation, the coarse-grained soil layer filler adopts clean coarse sand, and the reinforced layer adopts a geogrid with good tensile property and water permeability. Wherein, the transverse saturation permeability coefficient of the coarse sand is 5 multiplied by 10-5m/s。
TABLE 1 basic Soft Clay Properties
Determination of the thickness of two fine-grained soil layers: according to the natural density of the soft clay, the covering loads of the 5-layer drainage-reinforcement structure from bottom to top are respectively 84.5kPa, 67.6kPa, 50.7kPa, 33.8kPa and 16.9 kPa. The shear stress distribution curve of the reinforced soil interface shown in fig. 3 is obtained by calculation according to a shear stress distribution curve formula of the reinforced soil interface, and the peak values of the shear stress are 27.46Pa, 24.30Pa, 19.86Pa, 14.90Pa and 9.65Pa respectively. The shear stress value in the standard reinforced soil interface shear stress distribution curve of the shear band is not less than 5% of the peak interface shear stress, namely 1.373Pa, 1.215Pa, 0.993Pa, 0.745Pa and 0.483 Pa. The shear band thicknesses are therefore 0.12m, 0.22m, 0.55m, 0.68m and 0.74m from bottom to top; the thickness of the fine soil layer of the drainage-reinforcement structure is not less than 0.06m, 0.11m, 0.28m, 0.34m and 0.37m from bottom to top, because the thickness of the fine soil layer is at least half of the thickness of the shear band at the reinforced soil interface.
Determining the thickness of the coarse-grained soil layer: the thickness of the coarse-grained soil layer is only related to the permeability coefficient, the calculated length and the permeability coefficient of the soft clay, the calculated lengths L of the 5-layer drainage-reinforcement structure from bottom to top are respectively 17m, 14m, 11m, 8m and 5m, and the thickness of the coarse-grained soil layer from bottom to top is respectively 0.19m, 0.16m, 0.13m, 0.09m and 0.06 m.
Determining the inclination angle theta of the drainage-reinforcement structure: according to the natural density of the soft clay, the uniformly-coated and uniformly-distributed loads borne by the 5-layer drainage-reinforcement structure from bottom to top are respectively 84.5kPa, 67.6kPa, 50.7kPa, 33.8kPa and 16.9 kPa. The 1 st layer of drainage-reinforcement structure is laid on the foundation from bottom to top, so that the inclination angle theta is formed1Is 0 deg.. The deformation of the soil layers under the other 4 layers of drainage-reinforcement structures is 0.124m, 0.217m, 0.279m and 0.310m respectively. The lengths l from the intersection point of the drainage-reinforcement structure and the slope to the intersection point of the uniformly distributed load and the vertically triangular distributed load are respectively 12m, 9m, 6m and 3m, and the inclination angles theta of the 4 layers of drainage-reinforcement structures are calculated to be not less than 0.59 degrees, 1.38 degrees, 2.66 degrees and 5.90 degrees and are respectively taken as 0.60 degrees, 1.40 degrees, 2.70 degrees and 5.90 degrees.
In summary, the thickness of the fine-grained soil layer, the thickness of the coarse-grained soil layer, and the dip angle of the 5-layer drainage-reinforcement structure are shown in table 2.
TABLE 2 drainage-ribbing structural parameter values
Example 2: a construction method of a soft clay pile using the drainage-reinforcement structure for improving the stability of the soft clay pile according to embodiment 1, comprising the steps of:
and S1, laying fine sand with good gradation on the flat ground to form a lower fine soil layer 2-2, wherein the thickness and the inclination angle of the lower fine soil layer 2-2 are shown in the table 2 in the example 1.
S2, laying a layer of geogrid with good tensile property and water permeability on the lower fine-grained soil layer 2-2 to form a lower reinforcement layer 3-2.
S3, arranging a drainage ditch 6 on one side, close to the slope, of the lower fine grain soil layer 2-2 and the lower reinforcement layer 3-2, and communicating the drainage ditch 6 with the lower fine grain soil layer 2-2;
the drainage ditch 6 can be determined according to the Water and soil conservation engineering design Specification (GB 51018-2014): the drainage ditch is preferably of a trapezoidal or rectangular section, and the width and the depth of the bottom of the drainage ditch section are not preferably less than 0.40 m. The inner slope of the trapezoidal drainage ditch is preferably 1: 1.0-1: 1.5. The drainage ditch 5 with the diameter of 50mm is arranged at the joint of the drainage ditch and the lower fine-grained soil layer, so that accumulated water at the bottom of the lower fine-grained soil layer can be drained into the drainage ditch timely and smoothly.
S4, laying coarse sand on the lower reinforcement layer 3-2 to form a coarse soil layer 4, wherein the thickness and inclination angle of the coarse soil layer 4 are shown in table 2 of example 1.
S5, laying a layer of geogrid with good tensile property and water permeability on the coarse-grained soil layer 4 to form an upper reinforcing rib layer 3-1.
S6, paving a layer of fine sand with good gradation on the paved upper reinforced layer 3-1 to form an upper fine grain soil layer 2-1, wherein the thickness and the inclination angle of the upper fine grain soil layer 2-1 are the same as those of the lower fine grain soil layer 2-2 in the step S1;
and the lower fine soil layer, the lower reinforced layer, the coarse soil layer, the upper reinforced layer and the upper fine soil layer are sequentially paved from bottom to top to form a paved drainage-reinforced structure.
S7, paving 1 m-thick soft clay on the upper fine-grain soil layer 2-1 to form a soft clay layer 1.
And S8, sequentially laying the reinforcement structure and the soft clay layer on each layer according to the thickness and the inclination angle of the upper fine soil layer, the coarse soil layer and the lower fine soil layer changed according to the layer number of the drainage-reinforcement structure until the soft clay pile body reaches the designed elevation.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. A drainage-reinforcement structure for improving the stability of a soft clay pile body is characterized in that the drainage-reinforcement structure is sequentially stacked with soft clay layers (1) of the soft clay pile body, and an inclination angle is formed between the drainage-reinforcement structure and a horizontal plane where the soft clay layers (1) are located along the slope direction; the drainage-reinforced structure comprises a drainage layer and a tensile permeable layer, the tensile permeable layer is arranged in the drainage layer, and a drainage ditch (6) is arranged on one side of the drainage layer.
2. The drainage-reinforcement structure for improving the stability of a soft clay pile according to claim 1, wherein the drainage layer comprises an upper fine soil layer (2-1), a coarse soil layer (4) and a lower fine soil layer (2-2), the upper fine soil layer (2-1) being in contact with the upper soft clay layer (1), the lower fine soil layer (2-2) being in contact with the lower soft clay layer (1); the tensile permeable layer comprises an upper reinforced layer (3-1) and a lower reinforced layer (3-2), the upper reinforced layer (3-1) is arranged between an upper fine soil layer (2-1) and a coarse soil layer (4), the coarse soil layer (4) is arranged between the upper reinforced layer (3-1) and the lower reinforced layer (3-2), and the lower reinforced layer (3-2) is arranged between the coarse soil layer (4) and the lower fine soil layer (2-2); the drainage ditch (6) is positioned on one side of the lower fine grain soil layer (2-2), and the drainage ditch (6) is communicated with the lower fine grain soil layer (2-2).
3. The drainage-reinforcement structure for improving the stability of a soft clay pile according to claim 2, wherein the upper fine soil layer (2-1) and the lower fine soil layer (2-2) are filled with fine sand or silt filler, and the coarse soil layer (4) is filled with medium-coarse sand or fine-medium gravel filler.
4. The drainage-reinforcement structure for improving the stability of a soft clay pile according to claim 2, wherein the upper reinforcement layer (3-1) and the lower reinforcement layer (3-2) are made of geogrids or geocell materials having tensile and water permeability properties.
5. The drainage-reinforcement structure for improving the stability of a soft clay pile according to claim 2, wherein the thickness of the upper fine soil layer (2-1) and the lower fine soil layer (2-2) are calculated by the formula:
in the formula, hflDenotes the thickness of the upper fine-grained soil layer (2-1) and the lower fine-grained soil layer (2-2), dsiAnd (3) showing the thickness of the shear band in the drainage-reinforcement structure of the ith layer in the soft clay pile body.
6. The drainage-reinforcement structure for improving the stability of soft clay piles as claimed in claim 5, wherein the thickness d of the shear band in the drainage-reinforcement structure of the ith layer is larger than that of the shear band in the drainage-reinforcement structure of the ith layersiDetermining according to an interval in which the shear stress in a reinforcement-soil interface shear stress distribution curve in the process of drawing the reinforcement material is not less than 5% of the peak interface shear stress, wherein the formula of the reinforcement-soil interface shear stress distribution curve is as follows:
in the formula, tau represents the shear stress of the reinforced soil interface; p represents the overburden load of the drainage-reinforcement structure; z represents the distance of the calculation point from the upper reinforced layer (3-1) or the lower reinforced layer (3-2), and is positive upwards and negative downwards.
7. The drainage-reinforcement structure for improving the stability of a soft clay pile according to claim 2, wherein the thickness of the coarse soil layer (4) is calculated as follows:
in the formula, hciThe thickness of a coarse-grained soil layer (4) in the drainage-reinforcement structure of the ith layer is shown, k represents the vertical permeability coefficient of the soft clay, B represents the width of the coarse-grained soil layer (4), L represents the length of the coarse-grained soil layer (4), and k represents the thickness of the coarse-grained soil layer (4)cRepresents the lateral permeability coefficient of the coarse soil layer (4) filler.
8. The drainage-reinforcement structure for improving the stability of a soft clay pile body according to claim 1, wherein the inclination angle is calculated as follows:
in the formula, SiIndicates the settlement of the soil layer under the drainage-reinforcement structure of the ith layer in the soft clay pile bodyiThe horizontal distance from the slope intersection point of the drainage-reinforcement structure of the ith layer and the soft clay pile body to the slope top platform is shown, gamma represents the gravity of the soft clay layer (1), q represents the external load of the slope top platform of the soft clay pile body, and EsExpressing the compression modulus of the soft clay, alpha expressing the integral gradient of the soft clay pile body, thetaiShowing the inclination angle of the drainage-reinforcement structure of the ith layer, n showing the number of drainage-reinforcement structures in the soft clay pile body, and HiThe thickness of the i-th soft clay layer (1) is shown.
9. A construction method of a soft clay pile using the drainage-reinforcement structure for improving the stability of the soft clay pile according to claim 2, comprising the steps of:
s1, laying a fine-grained soil layer (2-2) on the flat ground;
s2, laying a lower reinforcing rib layer (3-2) on the lower fine-grained soil layer (2-2);
s3, arranging drainage ditches (6) on one sides, close to the slope, of the lower fine grain soil layer (2-2) and the lower reinforced layer (3-2) and communicating the lower fine grain soil layer (2-2) with the drainage ditches (6);
s4, paving a coarse-grained soil layer (4) on the lower reinforced layer (3-2);
s5, paving a reinforcement layer (3-1) on the coarse-grained soil layer (4);
s6, paving a fine soil layer (2-1) on the upper reinforcing rib layer (3-1);
s7, paving a soft clay layer (1) on the upper fine-grained soil layer (2-1);
and S8, paving the drainage-reinforcement structure and the soft clay layers (1) of each layer in sequence from bottom to top according to the layer number requirement of the soft clay pile body by the method of the steps S1-S7.
10. The construction method of a drainage-reinforcement structure for improving the stability of a soft clay pile according to claim 9, wherein the thickness of the upper fine soil layer (2-1) and the lower fine soil layer (2-2) are calculated by the following formula:
in the formula, hflDenotes the thickness of the upper fine-grained soil layer (2-1) and the lower fine-grained soil layer (2-2), dsiThe thickness of a shear band in the drainage-reinforcement structure of the ith layer in the soft clay pile body is represented;
the coarse-grained soil layer (4) thickness calculation formula is as follows:
in the formula, hciThe thickness of a coarse-grained soil layer (4) in the drainage-reinforcement structure of the ith layer is shown, k represents the vertical permeability coefficient of the soft clay, B represents the width of the coarse-grained soil layer (4), L represents the length of the coarse-grained soil layer (4), and k represents the thickness of the coarse-grained soil layer (4)cRepresents the transverse permeability coefficient of the coarse soil layer (4) filler;
the calculation formula of the inclination angles of the upper fine soil layer (2-1), the lower fine soil layer (2-2) and the coarse soil layer (4) of each drainage-reinforcement structure is as follows:
in the formula, SiIndicates the settlement of the soil layer under the drainage-reinforcement structure of the ith layer in the soft clay pile bodyiThe horizontal distance from the slope intersection point of the drainage-reinforcement structure of the ith layer and the soft clay pile body to the slope top platform is shown, gamma represents the gravity of the soft clay layer (1), q represents the external load of the slope top platform of the soft clay pile body, and EsExpressing the compression modulus of the soft clay, alpha expressing the integral gradient of the soft clay pile body, thetaiShowing the inclination angle of the drainage-reinforcement structure of the ith layer, n showing the number of drainage-reinforcement structures in the soft clay pile body, and HiThe thickness of the i-th soft clay layer (1) is shown.
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