Method for controlling construction of gravel pile on the basis of pore water pressure

Abstract

A method for controlling construction of a gravel pile on the basis of pore water pressure, comprising: step 1, performing geological analysis to determine construction parameters of the gravel pile; step 2, forming a hole around the position of the pile and mounting a monitoring device; step 3, recording relevant data in the construction process of the gravel pile; step 4, analyzing the relationship between monitored pore water pressure data and the construction parameters; step 5, drilling to inspect the diameters of the gravel pile to determine the relationship between the pore water pressure and the pile diameter; and step 6, guiding the construction on the basis of the value of the pore water pressure. By monitoring the value of the pore water pressure around the gravel pile, relationship curves with key construction parameters of the gravel pile are established, and by drilling to inspect the pile diameter, the relationship between the pore water pressure and the pile diameter is obtained, thereby guiding the vibro-replacement gravel pile construction, improving the uniformity of the pile diameter, enhancing the quality of gravel pile construction, and reducing gravel pile costs.

Description

Method for controlling construction of gravel pile according to pore water pressure TECHNICAL FIELD

[0001] The present application relates to the technical field of foundation treatment construction of offshore backfill land, in particular to a method for controlling construction of gravel pile. BACKGROUND

[0002] Gravel pile method refers to a method for reinforcing foundation when building embankment and other structures on soft foundation. According to the purpose of foundation reinforcement, it can be divided into gravel drainage well method and gravel pile method. Gravel pile method has been widely used in areas lacking well-graded sand. The reinforced foundation soil can meet the requirements of bearing capacity and deformation, and the anti-liquefaction requirement. The gravel pile is a good drainage channel, which can reduce the excess pore water pressure during earthquakes in the future. Therefore, since the gravel pile foundation treatment method was introduced into China, it has been rapidly promoted in the foundation reinforcement of a large number of industrial, civil buildings and water conservancy and transportation engineering, and good results have been achieved.

[0003] Gravel pile method refers to a method for reinforcing foundation by using vibration or impact sinking pipe method, filling sand, gravel, gravel and other materials into the hole formed in the soft foundation and extruding them into the hole to form a continuous and dense pile body with a certain diameter composed of sand and stone. Gravel pile method improves the adverse factors of soil body, mainly through vibration compaction, drainage pressure reduction, pre-vibration effect and reinforcement effect. According to the previous construction experience of gravel pile, since foundation treatment is a concealed engineering, the diameter of gravel pile cannot be directly monitored during construction. At present, the common method is to calculate the diameter of the pile body by the amount of filling, and to detect the diameter of the pile body by drilling after construction. Due to the process characteristics of the gravel pile, the vibration compaction length is 0.5-1m each time, the detection results of the pile diameter are generally in the shape of a gourd, the diameter of the pile body is uneven, and the quality is not easy to control. The method of drilling hole to detect the diameter of the pile needs to drill multiple holes, which is high in cost and long in construction period, and is not suitable for large-area gravel pile detection construction.

[0004] At present, there are similar researches in this field, such as the joint control system and control method of gravel pile construction quality published by Jiang Bingnan et al. (CN 113322930 A), which monitors the soil pressure and pore water pressure around the gravel pile during construction, and determines the compactness, diameter, length and bearing capacity of the gravel pile through detection means such as standard penetration test, side pressure test, composite foundation static load test and radar wave tracing after construction, and compares the data with the main construction parameters of the vibrator during construction, such as compaction current and vibration time. A complex and multi-dimensional relationship curve is established through the above-mentioned many construction parameters (2 items), monitoring data (2 items) and detection data (4 items), the relationship between the detection parameters and the vibration construction process is formed, the construction quality is evaluated, and the construction setting parameters of the gravel pile in the area are determined by analysis. Technical problem

[0005] The purpose of the present application is to solve the problems in the process of back calculation of pile diameter by filling amount in the construction process of vibro-replacement stone column, and to provide a method for controlling the construction parameters of stone column according to the pore water pressure. Under the geological conditions of land formed by backfilling of offshore mountain stones, and under the condition that the groundwater level changes constantly due to the influence of tides, the pile diameter of the stone column can be effectively controlled in the construction process only by monitoring a single indicator (pore water pressure), and the relationship curve and formula between the pore water pressure and the pile diameter of the stone column are formed. The pore water pressure of the soil around the vibro-replacement stone column is mainly monitored during the construction process, and the pore water pressure values at the same height position of the pile body fixed distance are related to the two parameters of the vibration time of the vibro-replacement stone column and the compaction current, so as to guide the construction of the stone column and control the pile diameter of the stone column through the pore water pressure monitoring values, thereby improving the overall construction quality of the pile body. Technical solution

[0006] The technical scheme adopted by the present application is: a method for controlling the construction parameters of stone column according to the pore water pressure, characterized by comprising the following steps:

[0007] First step: determining the construction parameters of stone column through geological analysis

[0008] The key construction parameters of the power of the vibro-replacement device, the compaction current and the vibration time are preliminarily determined under the geological conditions of land formed by backfilling of offshore mountain stones, and 7-10 test piles are constructed in a representative area with a thickness of about 10-20m of offshore backfilling stones and a stone particle size of less than 30cm.

[0009] Second step: installing monitoring equipment around the pile position

[0010] A hole is formed at a position 2-4m away from the edge of the test pile, the hole diameter meets the size of the pore water pressure instrument installation, and the construction is carried out according to the designed pile diameter to prevent the pore water pressure sensor from being buried during the construction process of the vibro-replacement stone column. After the hole is formed, the pore water pressure monitoring instrument is installed, and the pressure monitoring instrument is connected with the pressure detection probe and the data processing platform.

[0011] Third step: recording related data during the construction process of stone column

[0012] After the construction preparation is completed, the vibro-replacement test pile construction is formally started, and the key construction data such as the compaction current, the vibration time, the filling amount and the like of different parts of the test pile are monitored in real time by using intelligent equipment, and the change of the pore water pressure values at the same height position is recorded.

[0013] Fourth step: analyzing the relationship between the pore water pressure monitoring data and the construction parameters

[0014] According to the various data indexes collected in the construction process, the relationship between the pore water pressure and the two key construction parameters of the residual vibration time and the compaction current is obtained by systematic arrangement and analysis, and the relationship curve is drawn. Among them, the relationship between the pore water pressure and the residual vibration time,

[0015] Y=27.764ln(x)-3.9429, wherein Y is the pore water pressure, and the unit is kPa; x is the residual vibration time, and the unit is s;

[0016] Among them, the relationship between the pore water pressure and the compaction current,

[0017] Y=35.767ln(x)-124.32, wherein Y is the pore water pressure, and the unit is kPa; X is the compaction current, and the unit is A;

[0018] Fifth step: the relationship between the pore water pressure and the pile diameter of the gravel pile is obtained by drilling detection

[0019] After the construction of the experimental pile is completed, the pile diameter is detected by drilling detection, and the relationship between the pore water pressure and the pile diameter is obtained as Y=28.796X+18.563, wherein Y is the pore water pressure, and the unit is kPa; X is the pile diameter, and the unit is m;

[0020] Sixth step: guiding the construction through the pore water pressure value

[0021] According to the monitoring equipment installed around the pile position in the second step, the calculated pile diameter value is obtained according to the relationship formula between the pore water pressure and the pile diameter through the monitored pore water pressure value in the construction process, the deviation pore water pressure value is calculated by comparing the calculated pile diameter value with the designed pile diameter value, the residual vibration time and the compaction current construction parameters are calculated according to the deviation, and the instruction is sent to adjust the residual vibration time and the compaction current construction parameters, so as to control the construction of the vibroflotation gravel pile, control the size of the pile diameter to meet the standard, and improve the overall quality of the pile foundation construction.

[0022] Preferably, in the third step, the compaction current and the residual vibration time (the value after meeting the requirements) of the experimental pile at different heights and the monitoring value of the pore water pressure corresponding to the height are detected by the intelligent equipment including the current sensor, the depth monitoring sensor, the time recorder and the weighing sensor.

[0023]

[0024] Preferably, in the second step, the monitoring equipment is installed in a hole formed at a position 3m away from the edge of the experimental pile position.

[0025] Preferably, in the second step, the PVC sleeve is buried to prevent hole collapse.

[0026] Preferably, the fourth step: because the lateral impact force is generated during the compaction of the experimental pile, and because there is groundwater in the stratum, the pore water pressure in the soil increases at the same height as the pile diameter expands during the pile compaction process; according to the pore water pressure value, the vibration time and the compaction current data collected during construction, the system is arranged and analyzed.

[0027] Preferably, the sixth step: during construction, the pore water pressure is monitored, the calculated pile diameter value is obtained from the pore water pressure and pile diameter relationship formula, the calculated pile diameter value is compared with the designed pile diameter value, if the calculated pile diameter value is less than the designed pile diameter value, the pore water pressure required to reach the designed pile diameter value is calculated, and the corresponding vibration time and compaction current are calculated through the pore water pressure and vibration time formula and the pore water pressure and compaction current formula respectively, and the vibration operation instruction is issued, if the calculated pile diameter value is greater than or equal to the designed pile diameter value, the operation instruction for continuing the construction of the previous gravel pile is issued, and the overall engineering gravel pile construction is completed. Beneficial effects

[0028] The present application first proposes a method for controlling the construction of gravel piles by pore water pressure, that is, by monitoring the value of the pore water pressure around the gravel pile, a relationship curve between the pore water pressure and the key parameters of the gravel pile construction is established, the relationship between the pore water pressure and the pile diameter is obtained by drilling to detect the pile diameter, so as to guide the vibration and impact gravel pile construction, improve the uniformity of the pile diameter, and improve the construction quality of the gravel pile.

[0029] 1. During the construction of the vibration and impact experimental pile, the pore water pressure data around the pile site is monitored in real time, and the relationship between the pore water pressure and the compaction current and the vibration time is established.

[0030] 2. The pile diameter is detected by drilling, the relationship between the pore water pressure and the pile diameter is established, and the vibration and impact gravel pile construction is guided by the pore water pressure value. The uniformity of the gravel pile diameter is improved, and the overall construction quality of the pile foundation is improved.

[0031] The present application proves that in the case of land reclamation by backfilling mountain stones on the sea, the gravel pile diameter is effectively controlled by monitoring the pore water pressure index alone, the power of the vibrator, the compaction current and the vibration time are controlled, the uniformity of the pile body is improved, the overall quality of the pile foundation construction is ensured, the amount of gravel filler is saved by about 5%, and the cost of a single gravel pile is reduced by 2.3%. BRIEF DESCRIPTION OF DRAWINGS

[0032] Fig. 1 is a curve graph of the relationship between the vibration time and the excess pore pressure.

[0033] Fig. 2 is a curve graph of the relationship between the compaction current and the excess pore pressure.

[0034] Fig. 3 is a curve graph of the relationship between the pile diameter and the excess pore pressure.

[0035] Figure 4 is a comparison chart of pile diameters before and after improvement. Best mode of the present application

[0036] In the foundation treatment construction of the land area backfilled at sea, the land area geology formed by the backfill of mountain stones is that the mountain stone material is granite with a particle size less than 30 cm and a strength greater than 45 MPa. The geological characteristics are that the land area formed by the backfill of mountain stones has a certain water permeability, and the groundwater level changes due to the influence of tides. At the same time, considering the use requirements of the upper structure in the later period, the bearing capacity of the foundation needs to be met. It involves the construction of vibroflotation stone piles, and the method of controlling the stone pile construction according to the pore water pressure is adopted, which specifically includes the following steps,

[0037] First step: geological analysis to determine the construction parameters of stone piles

[0038] Before construction, according to the geological exploration data, analyze various geological parameter indexes, combine with the clear technical parameters of the design, test pile length, pile diameter, compactness and other key indexes, select a representative area with a backfill stone thickness of about 10-20 m and a stone particle size of less than 30 cm to construct 10 test piles, so that the data obtained are universal and applicable, to guide the subsequent large-area stone pile construction. In this example, the test pile length is 20 m, the design pile diameter is 1.0 m, and the key construction parameters such as vibroflotation equipment and filling amount, compaction current and vibration time are determined.

[0039] Second step: hole formation and installation of monitoring equipment around the pile position

[0040] Hole formation at a distance of 3 m from the pile position (four sides around the pile), construction with a hole diameter of 5 cm, to prevent the pore water pressure sensor from being buried during the vibroflotation construction process, the hole diameter meets the size of the pore water pressure instrument installation, and measures are taken to protect the monitoring equipment by burying a PVC sleeve at the position of the pore water monitoring equipment. After the hole formation is completed, the pore water pressure monitor is installed, and the pressure monitor is connected with the pressure monitoring probe and the data processing platform (existing mature equipment platform).

[0041] Third step: record relevant data during the construction process of stone piles

[0042] After the construction preparation is completed, the vibroflotation test pile construction is formally started, and the digital and intelligent equipment is used to monitor the key construction data such as compaction current, vibration time, filling amount, etc. at different positions in real time, and record the pore water pressure value changes at the same height position.

[0043] Through digitalization (including current sensor, depth monitoring sensor, time recorder and weighing sensor), the compaction current and vibration time at different heights of the test pile are detected, and the monitoring values of the pore water pressure at the corresponding height are obtained (slightly different according to different geological parameter indexes. However, the overall trend is the same).

[0044]

[0045] Fourth step: analysis of the relationship between pore water pressure monitoring data and construction parameters

[0046] Because the vibration experiment pile will produce lateral impact in the process of compaction, and because of the existence of pore water in the stratum, the pore water pressure in the soil will change significantly during the process of pile compaction. According to the various data collected during the construction process, systematic analysis is carried out, and the relationship between pore water pressure and two key construction parameters, namely, the relationship between pore water pressure and vibration time and the relationship between pore water pressure and compaction current, is obtained. Among them, the relationship between pore water pressure and vibration time,

[0047] Y=27.764ln(x)-3.9429, where Y is the pore water pressure, unit kPa; x is the vibration time, unit s;

[0048] The relationship between pore water pressure and compaction current,

[0049] Y=35.767ln(x)-124.32, where Y is the pore water pressure, unit kPa; X is the compaction current, unit A;

[0050] And draw the relationship curve, the relationship curve between vibration time and excess pore pressure is shown in Figure 1; the relationship curve between compaction current and excess pore pressure is shown in Figure 2.

[0051] Fifth step: obtain the relationship between pore water pressure and pile diameter

[0052] After the construction of the experimental pile, the pile diameter is detected by drilling and exploring, and the relationship between pore water pressure and pile diameter is obtained, Y=28.796X+18.563, where Y is the pore water pressure, unit kPa; X is the pile diameter, unit m; The relationship curve between pile diameter and excess pore pressure is shown in Figure 3.

[0053] Sixth step: guide the construction through the pore water pressure value

[0054] According to the second step of installing the monitoring equipment around the pile position, in the construction process, the calculated pile diameter value is obtained according to the relationship formula between the pore water pressure and the pile diameter through the monitored pore water pressure value, the calculated pile diameter value is compared with the designed pile diameter value, the deviation pore water pressure value is calculated, the residual vibration time and the compaction current construction parameters are calculated according to the deviation, and the residual vibration time and the compaction current construction parameters are adjusted. If the calculated pile diameter value is less than the designed pile diameter value, the residual vibration time and the compaction current are calculated through the pore water pressure and the residual vibration time formula and the pore water pressure and the compaction current formula. Since the residual vibration time and the compaction current directly affect the diameter of the gravel pile, the change of the diameter of the gravel pile will be reflected by the change of the pore water pressure value. Therefore, increasing the residual vibration time and the compaction current will inevitably increase the pore water pressure value of the gravel pile, so as to achieve the goal of increasing the diameter of the gravel pile. If the calculated pile diameter value is greater than or equal to the designed pile diameter value, the previous gravel pile construction can be continued. Industrial applicability

[0055] Therefore, in the construction process, only the monitored pore water pressure value is used to compare the calculated pile diameter value with the designed pile diameter value according to the relationship formula between the pore water pressure and the pile diameter, and the residual vibration time and the compaction current construction parameters are adjusted according to the deviation, so as to control the construction of the vibroflotation gravel pile, ensure that the pile diameter meets the design requirements, and improve the overall quality of the pile foundation construction.

[0056] Compared with the traditional vibroflotation gravel pile construction, about 5% of the gravel filler is saved, and the cost of a single gravel pile is reduced by 2.3%. The comparison of the pile diameters before and after the improvement is shown in FIG. 4. The traditional pile diameter detection result generally presents a gourd shape, and the pile body diameter is uneven. The pile diameter detection result of the present application presents a cylindrical shape, and the pile body diameter is basically uniform.

Claims

1. A method for controlling construction of a gravel pile according to pore water pressure, characterized by, The method comprises the following steps: First step: geological analysis to determine the construction parameters of the gravel pile The geological conditions of the land area formed by backfilling offshore mountain stones are analyzed to preliminarily determine the key construction parameters of the vibrator power, compaction current and vibration time, and 7-10 test piles are constructed in a representative area with a thickness of 10-20 m of offshore backfill stones and a stone particle size of less than 30 cm; Second step: installation of monitoring equipment around the pile site A hole is formed at a position 2-4 m away from the experimental pile site, the hole diameter meets the size of the pore water pressure instrument installation, and the construction is carried out according to the designed pile diameter to prevent the pore water pressure sensor from being buried during the vibration and compaction of the gravel pile. After the hole is formed, the pore water pressure monitoring instrument is installed, and the pressure monitoring instrument is connected with the pressure detection probe and the data processing platform; Third step: record relevant data during the construction of the gravel pile After the construction preparation is completed, the vibration test pile construction is formally started, the key construction data of the compaction current, vibration time and filling amount at different heights of the experimental pile are monitored in real time by using intelligent equipment, and the pore water pressure value change at the same height is recorded; Fourth step: analyze the relationship between the pore water pressure monitoring data and the construction parameters According to the data indexes collected during the construction, the system is analyzed and arranged to obtain the relationship between the pore water pressure and the vibration time and the compaction current, and the relationship curve is drawn to obtain the relationship formula of the pore water pressure and the vibration time, Y=27.764ln(x)-3.9429, wherein Y is the pore water pressure, and the unit is kPa; x is the vibration time, and the unit is s; The relationship formula of the pore water pressure and the compaction current is obtained, Y=35.767ln(x)-124.32, wherein Y is the pore water pressure, and the unit is kPa; x is the compaction current, and the unit is A; Fifth step: drill hole to detect the pile diameter of the gravel pile to obtain the relationship formula After the construction of the experimental pile is completed, the pile diameter is detected by drilling and exploring to obtain the pile diameter value at each position, and the relationship formula of the pore water pressure and the pile diameter is obtained, Y=28.796X+18.563, wherein Y is the pore water pressure, and the unit is kPa; X is the pile diameter, and the unit is m; Sixth step: guide the construction by the pore water pressure value According to the second step, the monitoring equipment is installed around the pile position, and in the construction process, the calculated pile diameter value is obtained according to the relationship formula between the pore water pressure and the pile diameter through the monitored pore water pressure value, the deviation pore water pressure value is calculated by comparing the calculated pile diameter value with the designed pile diameter value, the remaining vibration time and the compaction current construction parameters are calculated and adjusted according to the deviation, and the operation instruction of vibration is sent out, if the calculated pile diameter value is less than the designed pile diameter value, the required pore water pressure to reach the designed pile diameter value is calculated, and the corresponding remaining vibration time and compaction current are calculated through the pore water pressure and remaining vibration time formula and the pore water pressure and compaction current formula respectively, and the operation instruction of the previous gravel pile construction is sent out, so as to control the construction of the gravel pile, control the size of the pile diameter to meet the standard, complete the overall engineering gravel pile construction, and improve the overall quality of the pile foundation construction.

2. The method according to claim 1, wherein the third step, the monitoring values of the compaction current and the remaining vibration time at different heights of the experimental pile and the corresponding height of the pore water pressure are obtained by detecting through the intelligent equipment including a current sensor, a depth monitoring sensor, a time recorder and a weighing sensor, and are as follows: The gravel pile depth is 20 m, the remaining vibration time is 10 s, the compaction current is 172 A, the original pore water pressure is 0 kPa, and the excess static pore water pressure is 58 kPa; The gravel pile depth is 19 m, the remaining vibration time is 10 s, the compaction current is 185 A, the original pore water pressure is 0 kPa, and the excess static pore water pressure is 61 kPa; The gravel pile depth is 18 m, the remaining vibration time is 6 s, the compaction current is 98 A, the original pore water pressure is 0.2 kPa, and the excess static pore water pressure is 42 kPa; The gravel pile depth is 17 m, the remaining vibration time is 8 s, the compaction current is 138 A, the original pore water pressure is 10.1 kPa, and the excess static pore water pressure is 55 kPa; The gravel pile depth is 16 m, the remaining vibration time is 10 s, the compaction current is 183 A, the original pore water pressure is 19.8 kPa, and the excess static pore water pressure is 62 kPa; The gravel pile depth is 15 m, the remaining vibration time is 8 s, the compaction current is 131 A, the original pore water pressure is 30.8 kPa, and the excess static pore water pressure is 53 kPa; The gravel pile depth is 14 m, the remaining vibration time is 8 s, the compaction current is 131 A, the original pore water pressure is 41.2 kPa, and the excess static pore water pressure is 52 kPa; The gravel pile depth is 13 m, the remaining vibration time is 6 s, the compaction current is 120 A, the original pore water pressure is 50.2 kPa, and the excess static pore water pressure is 47 kPa; The gravel pile depth is 12 m, the remaining vibration time is 6 s, the compaction current is 100 A, the original pore water pressure is 59.8 kPa, and the excess static pore water pressure is 42 kPa; The gravel pile depth is 11 m, the remaining vibration time is 4 s, the compaction current is 103 A, the original pore water pressure is 71.2 kPa, and the excess static pore water pressure is 38 kPa; The gravel pile depth is 10 m, the remaining vibration time is 6 s, the compaction current is 113 A, the original pore water pressure is 82.1 kPa, and the excess static pore water pressure is 43 kPa; The gravel pile depth is 9m, the vibration time is 8s, the compaction current is 155A, the original pore water pressure is 90.5kPa, and the excess static pore water pressure is 56kPa; The gravel pile depth is 8m, the vibration time is 7s, the compaction current is 135A, the original pore water pressure is 100.5kPa, and the excess static pore water pressure is 52kPa; The gravel pile depth is 7m, the vibration time is 6s, the compaction current is 108A, the original pore water pressure is 110.2kPa, and the excess static pore water pressure is 44kPa; The gravel pile depth is 6m, the vibration time is 6s, the compaction current is 102A, the original pore water pressure is 119.8kPa, and the excess static pore water pressure is 42kPa; The gravel pile depth is 5m, the vibration time is 8s, the compaction current is 138A, the original pore water pressure is 131.1kPa, and the excess static pore water pressure is 55kPa; The gravel pile depth is 4m, the vibration time is 5s, the compaction current is 115A, the original pore water pressure is 140.5kPa, and the excess static pore water pressure is 43kPa; The gravel pile depth is 3m, the vibration time is 9s, the compaction current is 170A, the original pore water pressure is 151.1kPa, and the excess static pore water pressure is 58kPa; The gravel pile depth is 2m, the vibration time is 5s, the compaction current is 117A, the original pore water pressure is 159.5kPa, and the excess static pore water pressure is 44kPa; The gravel pile depth is 1m, the vibration time is 5s, the compaction current is 110A, the original pore water pressure is 170.2kPa, and the excess static pore water pressure is 40kPa.

3. The method according to claim 1, wherein the second step comprises installing monitoring devices in the hole around the pile site, and installing the monitoring devices in the hole 3m away from the pile site.

4. The method according to claim 1, wherein the second step comprises taking measures to prevent hole collapse by embedding a PVC sleeve.

5. The method according to claim 1, wherein the fourth step comprises analyzing the collected pore water pressure values, vibration time and compaction current data during the construction process.

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