Vertical drainage structure for improving liquefaction resistance of a driven sand-gravel pile
By setting a grass cushion layer and a perforated steel pipe structure in the gravel piles, the problem of drainage channel blockage during construction is solved, enabling rapid pressure relief and drainage of the gravel piles during earthquakes, improving liquefaction resistance, and making construction simple and economical.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- WUHAN SURVEYING GEOTECHN RES INST OF MCC
- Filing Date
- 2025-07-07
- Publication Date
- 2026-06-02
AI Technical Summary
During the construction of gravel piles, the drainage channels formed by the vibration and the pressure of excess pore water caused by the compression of gravel are easily blocked by fine soil particles, which cannot effectively eliminate the risk of earthquake liquefaction.
The structure employs a grass cushion layer and a perforated steel pipe. The grass cushion layer is spaced at the bottom of the pile and along the pile body. The perforated steel pipe is inserted into the gravel pile. Combined with a U-shaped pipe and a drainage hose, the siphon effect is used to accelerate the discharge of water and ensure unobstructed drainage channels.
It effectively prevents drainage channel blockage during construction, ensures that the sand and gravel piles can quickly release pressure and drain water during earthquakes, improves liquefaction resistance, and has a simple structure and low cost.
Smart Images
Figure CN224314167U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of foundation treatment engineering technology, specifically to a vertical drainage structure that improves the liquefaction resistance of driven gravel piles. Background Technology
[0002] Gravel piles are a widely used technology for soft soil foundation treatment. Their core principle is to use vibration to force gravel into the foundation, forming a dense pile body. This replaces the soft soil, thereby increasing the foundation's bearing capacity, reducing settlement, and improving drainage performance, thus mitigating earthquake liquefaction. However, during construction, due to vibration and gravel compression, and the resulting excess pore water pressure, the pile body forms pressure relief and drainage channels. This often results in sand and grout leakage at the pile head, similar to earthquake liquefaction. After the excess pore water pressure dissipates, fine soil particles fill the voids in the pile body, blocking the drainage channels. Later, during earthquake-induced soil liquefaction, the blocked drainage channels in the gravel piles fail to relieve pressure, drain water, and prevent liquefaction. Summary of the Invention
[0003] The purpose of this invention is to provide a vertical drainage structure that improves the liquefaction resistance of driven gravel piles. The drainage structure prevents fine particles in the soil from moving along the pile body and blocking the drainage channel when pore water dissipates due to vibration construction, thus ensuring the smooth flow of drainage channels during subsequent earthquake liquefaction and achieving an anti-liquefaction effect.
[0004] To achieve the above-mentioned technical objectives, this utility model provides a vertical drainage structure to improve the liquefaction resistance of driven gravel piles, including a gravel pile body. The vertical drainage structure includes a grass cushion layer laid at the bottom of the gravel pile body and above the pile body area, and a perforated steel pipe inserted in the middle of the gravel pile body. The thickness of the grass cushion layer is 8-12cm, and the interval between two adjacent grass cushion layers is 0.8-1.2m. An inverted U-shaped pipe and a drainage hose are provided at the end of the perforated steel pipe that extends out of the gravel pile body.
[0005] A further technical solution of this utility model: the coarse particles of the sand and gravel pile body have a particle size between 20 and 50 mm, accounting for 50% to 60%; the fine particles have a particle size between 5 and 20 mm, accounting for 40% to 50%, and the sand and gravel particle size distribution meets the non-uniformity coefficient of 2 to 5.
[0006] The preferred technical solution of this utility model is as follows: the perforated steel pipe is inserted into the grass cushion layer near the bottom of the sand and gravel pile body, and its insertion end is a closed conical tip, and the diameter of the hole on the perforated steel pipe is smaller than the minimum particle size of the sand and gravel in the sand and gravel pile body.
[0007] The preferred technical solution of this utility model is as follows: the grass cushion layer at the bottom of the gravel pile body is laid after the gravel pile hole reaches the design elevation and is over-excavated by 8-12cm.
[0008] The preferred technical solution of this utility model is that the grass cushion layer of the sand and gravel pile body is laid during the process of pouring sand and gravel materials.
[0009] The preferred technical solution of this utility model is that the area of the grass bedding layer is equal to or greater than the cross-sectional area of the gravel pile body.
[0010] In addition to meeting the requirements of Section 7.2 of the standard "Technical Specification for Foundation Treatment of Buildings JGJ 79-2012", the sand and gravel pile material of this utility model should also be designed to have a particle size distribution with a non-uniformity coefficient between 2 and 5.
[0011] This invention utilizes straw mats as a water-soil separation medium. After construction, a perforated steel pipe is inserted for rapid pressure relief, providing a pressure relief channel for the rapid dissipation of excess pore water. The straw mats can be installed around the entire gravel pile. The purpose of the straw mats is to allow water to pass through smoothly while blocking most soil particles. The straw mats can be replaced with other materials with similar functions. The top of the steel pipe in this invention connects to a U-shaped pipe, utilizing the siphon effect to accelerate water drainage.
[0012] This invention utilizes unevenly graded aggregates in the selection of gravel piles, ensuring rapid drainage while maintaining pile strength. A straw mat is placed at 1-meter intervals between the pile bottom and the pile body, allowing water to pass smoothly while filtering soil particles, effectively preventing blockage of the drainage channel. The structure of this invention improves drainage in gravel piles, prevents soil blockage of drainage channels during construction, and ensures the gravel pile's resistance to liquefaction. Its simple construction, low cost, and rapid adoption make it suitable for widespread adoption. Attached Figure Description
[0013] Figure 1 This is a cross-sectional schematic diagram of an embodiment of this utility model.
[0014] In the diagram: 1-Gravel pile body, 2-Grass cushion layer, 3-Perforated steel pipe, 4-U-shaped pipe, 5-Hose, 6-Water trough. Detailed Implementation
[0015] The present invention will be further described below with reference to the accompanying drawings and embodiments. Figure 1The accompanying drawings are simplified versions of the embodiments and are intended only to clearly and concisely illustrate the embodiments of this utility model. The technical solutions shown in the drawings below are specific embodiments of this utility model and are not intended to limit the scope of the claimed utility model. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without inventive effort are within the scope of protection of this utility model.
[0016] The embodiment provides a vertical drainage structure to improve the liquefaction resistance of driven gravel piles, such as... Figure 1 As shown, the structure includes a gravel pile body 1. The gravel material in the gravel pile body 1 has a coarse particle size between 20 and 50 mm, accounting for 50% to 60%; and a fine particle size between 5 and 20 mm, accounting for 40% to 50%. The gravel particle size distribution meets a non-uniformity coefficient of 2 to 5. The vertical drainage structure includes a grass cushion layer 2 laid at the bottom of the gravel pile body 1 and above the pile body area, and a perforated steel pipe 3 inserted in the middle of the gravel pile body 1. The thickness of the grass cushion layer 2 is 8 to 12 cm, and the interval between two adjacent grass cushion layers 2 is 0.8 to 1.2 m. An inverted U-shaped pipe 4 and a drainage hose 5 are provided at the end of the perforated steel pipe 3 that extends out of the gravel pile body 1. The perforated steel pipe 3 is inserted into the grass cushion layer 2 near the bottom of the gravel pile body 1, and its insertion end is a closed conical tip. The diameter of the hole on the perforated steel pipe 3 is smaller than the minimum particle size of the gravel in the gravel pile body 1. The grass cushion layer 2 at the bottom of the gravel pile body 1 is laid after the gravel pile hole reaches the design elevation, with an over-excavation of 8-12 cm. The grass cushion layer 2 on the pile body 1 is laid during the filling of gravel material. The area of the grass cushion layer 2 is equal to or greater than the cross-sectional area of the gravel pile body 1.
[0017] In this embodiment, in addition to meeting the requirements of Section 7.2 of the standard "Technical Specification for Foundation Treatment of Buildings JGJ 79-2012", the aggregate pile material must also meet the requirement that the particle size distribution has a non-uniformity coefficient between 2 and 5. After 1m of aggregate is poured into the aggregate pile, it is inserted back 2 / 3m and vibrated to compact it. Then, a 10cm straw mat is placed in time, and then aggregate is poured in again with straw mats placed in place for continuous construction until the ground elevation is reached.
[0018] The present invention will be further described below with reference to specific embodiments. The embodiments pertain to the expansion project of a power plant in the eastern part of Lvsi Port Town, Qidong City, Nantong City, Jiangsu Province. To mitigate the adverse effects of earthquake liquefaction, the surface fill soil and silty sand mixed with silty soil in the raw water, clean water, and coal yard areas of the second phase of the project were treated with L=5m length gravel piles for foundation treatment. Construction was carried out first in the raw water area. During construction, in accordance with specifications and design requirements (selecting particle sizes of 20-100mm), without considering particle size distribution and other control measures, severe sand and grout leakage occurred on-site after the gravel piles were completed. Furthermore, the gravel piles were severely blocked by soil particles after the sand and grout leakage.
[0019] The drainage structure of this utility model is used to control the pile body of gravel piles, specifically as follows: Figure 1 As shown, the aggregate pile material is proportioned by particle size before construction. Coarse particles (20-50mm) account for 50%, while fine particles (5-20mm) account for 50%, resulting in a material non-uniformity coefficient of 4. After the hole depth reaches the design elevation, an additional 10cm is excavated, followed by a 10cm layer of straw mat, then 1m of stone is filled. The vibrator head is then inserted back 2 / 3m to vibrate and compact the material before placing another 10cm straw mat. This process is repeated until the top elevation of the aggregate pile reaches the ground level. After construction, a perforated steel pipe 3 is promptly inserted, with an insertion depth of 5-10cm from the bottom of the aggregate pile. This provides a pressure relief channel for excess pore water pressure. Simultaneously, the top of the steel pipe is connected to an inverted U-shaped pipe 4, utilizing the siphon effect to accelerate the dissipation of excess pore water pressure. The other end of the U-shaped pipe uses a drainage hose to collect the discharged water and drain it into a water trough, preventing backflow into the pile body. After construction using the control method of this utility model, water seeps out from the ground and a small amount of soil particles emerge, indicating that the drainage channel of the pile body is not blocked. This ensures that the drainage channel is unobstructed during subsequent earthquakes, thus guaranteeing the drainage and pressure relief capabilities of the sand and gravel pile against liquefaction.
[0020] The above description is merely one embodiment of this utility model, and while it is quite specific and detailed, it should not be construed as limiting the scope of this utility model. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these all fall within the protection scope of this utility model. Therefore, the protection scope of this utility model should be determined by the appended claims.
Claims
1. A vertical drainage structure for improving the liquefaction resistance of driven gravel piles, comprising a gravel pile body (1), characterized in that: The vertical drainage structure includes a grass cushion layer (2) laid on the bottom of the gravel pile body (1) and the area of the pile body above the bottom of the pile, and a perforated steel pipe (3) inserted in the middle of the gravel pile body (1). The thickness of the grass cushion layer (2) is 8 to 12 cm, and the interval between two adjacent grass cushion layers (2) is 0.8 to 1.2 m. An inverted U-shaped pipe (4) and a drainage hose (5) are provided at one end of the perforated steel pipe (3) that extends out of the gravel pile body (1).
2. The vertical drainage structure for improving the liquefaction resistance of driven gravel piles according to claim 1, characterized in that: The coarse particles of the sand and gravel pile body (1) have a particle size between 20 and 50 mm, accounting for 50% to 60%; the fine particles have a particle size between 5 and 20 mm, accounting for 40% to 50%, and the sand and gravel particle size distribution meets the non-uniformity coefficient of 2 to 5.
3. A vertical drainage structure for improving the liquefaction resistance of driven gravel piles according to claim 1 or 2, characterized in that: The perforated steel pipe (3) is inserted into the grass cushion layer (2) near the bottom of the sand and gravel pile body (1). Its insertion end is a closed conical tip, and the diameter of the hole on the perforated steel pipe (3) is smaller than the minimum particle size of the sand and gravel in the sand and gravel pile body (1).
4. A vertical drainage structure for improving the liquefaction resistance of driven gravel piles according to claim 1 or 2, characterized in that: The grass cushion layer (2) at the bottom of the gravel pile body (1) is a grass cushion layer laid after the gravel pile hole reaches the design elevation and is over-excavated by 8 to 12 cm.
5. A vertical drainage structure for improving the liquefaction resistance of driven gravel piles according to claim 1 or 2, characterized in that: The grass cushion layer (2) of the pile body (1) is laid during the process of pouring sand and gravel materials.
6. A vertical drainage structure for improving the liquefaction resistance of driven gravel piles according to claim 1 or 2, characterized in that: The area of the grass mat layer (2) is equal to or greater than the cross-sectional area of the gravel pile body (1).