CN102628767B - Device and method for testing mechanical properties of pile-soil contact surface - Google Patents

Abstract

The invention discloses a device for testing the mechanical properties of the pile-soil contact surface, which is composed of a sealed pressure chamber, a hollow cylindrical soil sample, a solid cylindrical concrete pile sample, etc. The pile sample is prefabricated, and its diameter is the same as that of the hollow cylindrical soil sample. The inner diameters are equal, and the two are closely fitted; the lower end of the concrete pile sample is placed on the base through a spring group, and the upper end is connected to the stress loading system through a dowel bar, and a stress sensor and a displacement sensor I are set on the dowel bar; the outer side of the concrete pile sample It is a hollow cylindrical soil sample. Filter paper and permeable stone are placed on the lower end of the soil sample and placed on the base, and filter paper and permeable stone are placed on the upper end of the soil sample and connected to the displacement sensor II; After the consolidation is completed, static and dynamic loads are applied to the pile sample, and the axial deformation and pore water stress of the pile and soil are measured; the invention has a simple structure and is easy to implement, and can be used to measure the pile-soil contact surface under static and dynamic loads mechanical properties.

Description

Device and method for testing mechanical properties of pile-soil contact surface

technical field

The invention belongs to the technical field of civil engineering, and in particular relates to a test device and a test method for the mechanical properties of pile-soil contact surfaces.

Background technique

In recent years, pile foundations have been widely used in the foundation engineering of highways, bridges and civil buildings, so that there are a large number of contact surfaces between piles and soil in this type of foundation. Due to the different properties of the pile and the soil around the pile, the stiffness of the two is different. There are large differences in deformation such as settlement under the upper load; in addition, friction piles such as cast-in-place large-diameter pipe piles increase the pile-side friction by expanding the contact area between the pile and the soil. Therefore, it is of great significance to measure the settlement deformation and pile side friction resistance of the pile-soil contact surface during the pile sinking process and after the construction is completed (under the action of static and dynamic loads). At present, the geotechnical instruments used to measure the mechanical properties of the pile-soil contact surface at home and abroad are mainly direct shear instruments and simple shear instruments. In actual engineering, since most piles are embedded in the soil, the piles are subjected to the surrounding soil pressure and the top of the pile. Due to the upper load, the pile has drainage and non-drainage conditions during construction and use. The direct shear instrument and the simple shear instrument cannot simulate the actual stress state of the pile-soil well. The geotechnical triaxial instrument can apply the surrounding pressure and axial pressure respectively, conveniently measure the axial deformation and volume deformation of the soil, and can simulate the drainage and non-drainage conditions. Therefore, the geotechnical triaxial instrument is used to study the pile-soil contact surface The mechanical properties are more in line with the actual working conditions. Due to the limitations of the traditional pressure chamber structure, etc., the static and dynamic triaxial instruments in China are mainly used to study the mechanical properties of a single soil, and cannot carry out the measurement and experimental research of the pile-soil contact surface.

Contents of the invention

The invention provides a pile-soil contact surface mechanical characteristic test device and a test method aiming at the defects that the existing geotechnical instruments cannot carry out test research on the pile-soil contact surface well.

The technical scheme that the present invention solves technical problem adopts is:

A device for testing the mechanical properties of a pile-soil contact surface, the structure of which includes: a sealed pressure chamber, a hollow cylindrical soil sample, and a solid cylindrical concrete pile sample, and is characterized in that: the solid cylindrical concrete pile sample is prefabricated, and its diameter is the same as that of the hollow cylindrical The inner diameters of the soil samples are equal, and the two are closely attached; the lower end of the concrete pile sample is placed on the base through a spring group, and the upper end is connected to the pressure loading system through a dowel bar, and a stress sensor and a displacement sensor I are set on the dowel bar; The outside of the pile sample is a hollow cylindrical soil sample. The filter paper and permeable stone are placed on the base at the lower end of the soil sample, and the filter paper, permeable stone, top cover and displacement sensor II are placed on the upper end of the soil sample in sequence.

The pile sample is a prefabricated concrete sample, and the side surface of the pile can be defined as different roughnesses according to the engineering reality during prefabrication;

The diameter of described solid cylindrical concrete pile sample is 10cm, high 55cm; The inner diameter of hollow cylindrical soil sample is 10cm, outer diameter 30cm, high 50cm;

The test device for mechanical properties of the pile-soil contact surface can realize stress loading control or strain loading control;

The circular permeable stones and the top cover are arranged sequentially on the upper side of the soil sample, and the circular permeable stones and the base are arranged sequentially on the lower side; the upper top cover can move up and down freely, and the displacement sensor II is placed on the upper side and connected with the shaft. Connected to the deformation measurement system;

The present invention also relates to a testing method of the above-mentioned mechanical characteristic testing device of a pile-soil contact surface, comprising the following technical steps:

(1) Prefabricate solid cylindrical concrete pile samples with different surface roughness according to the actual project;

(2) The lower end of the concrete pile sample is placed on the base through the spring group, and the upper end of the pile sample is connected to the stress loading system through the dowel bar, and a certain axial stress is applied to compress the spring group;

(3) Place the permeable stone and filter paper on the base in turn, place the split valve for sample preparation, put the rubber film on the inside of the sample preparation valve and fix the rubber film with a rubber ring, add the soil sample in three equal parts to the rubber film and place Reach the height required by the corresponding layer to make a hollow cylindrical soil sample;

(4) Place filter paper, permeable stone and top cover in sequence on the upper end of the hollow cylindrical soil sample, tighten the rubber membrane, apply a certain negative pressure to the hollow cylindrical soil sample to make the sample stand up, and remove the split valve for sample preparation;

(5) Displacement sensor I is placed on the top of the pile sample, displacement sensor II is placed on the top cover of the soil sample, and the stress sensor, displacement sensor I, displacement sensor II, pore pressure gauge, etc. are connected to the data acquisition system;

(6) Saturation and consolidation: Select an appropriate method to saturate the soil sample. After the saturation is completed, choose a drainage or non-drainage method according to the test requirements to apply confining pressure to consolidate the soil;

(7) Shearing: After the consolidation is completed, a static (dynamic) axial stress is applied to the upper end of the pile sample, and the test begins; Under the joint action of the axial stress and the reaction force of the spring group at the lower end, the pile sample moves vertically, because the rough pile surface drives the soil on the side of the pile to move vertically, the magnitude of the two movements is different , its value can be obtained by measuring the displacement sensor I and displacement sensor II and taking the difference between them. The volume deformation and pore water stress changes caused by the vertical movement of the soil sample are obtained by measuring the pore pressure and so on. The test stops when the axial displacement (or pore water pressure) reaches the corresponding failure standard;

(8) By analyzing the test data, the stress-strain relationship of the pile-soil contact surface, the relative displacement (settlement) of the pile-soil, the volume deformation of the soil, etc. can be obtained, which can be used for the pile sinking process, the use stage of the pile and the drainage and non-existence of the pile. It provides a reference for the design of pile foundation settlement and pile side friction under the two working conditions of drainage.

Advantage and effect of the present invention are:

By improving the pressure chamber, two materials, the solid cylindrical concrete pile sample and the hollow cylindrical soil, can be placed in the pressure chamber, so that the existing geotechnical instruments can be used to study the behavior of the pile-soil contact surface under static and dynamic loads. mechanical properties;

By improving the pressure chamber, confining pressure can be applied to consolidate the hollow cylindrical soil sample around the pile. After the consolidation is completed, static and dynamic axial stresses are applied to the top of the pile sample, so that the stress state of the sample is closer to the actual working condition;

By setting a spring group at the bottom of the rigid concrete pile sample, when performing static (dynamic) force shearing, applying a monotonic load (cyclic load) on the top of the pile can conveniently move the pile sample up and down;

By prefabricating concrete pile samples with different roughness, the influence of different roughness on the mechanical properties of the pile-soil contact surface can be analyzed;

By controlling the drainage and non-drainage conditions during the test, the mechanical properties of the pile-soil contact surface under the drainage and non-drainage conditions can be simulated;

By analyzing the axial deformation and pore water pressure of the pile and soil, the mechanical properties of the pile and soil, such as the settlement deformation of the pile and soil and the frictional resistance of the pile side, can be obtained;

Static and dynamic loads are applied through stress loading control and strain loading control, which can simulate the static and dynamic pile sinking process in actual engineering and the interaction between piles and soil after construction is completed.

The invention has a simple structure, and the improved pressure chamber can be directly used on the existing geotechnical instrument, is easy to implement, and can be used to measure the static and dynamic deformation characteristics of the pile-soil contact surface.

The advantages and effects of the present invention will be further described in specific embodiments.

Description of drawings

Fig. 1 structural representation of the present invention;

1—pressure chamber; 2—hollow cylindrical soil sample; 3—solid cylindrical concrete pile sample; 4—spring group; 5—stress sensor; 6—displacement sensor I; 7—displacement sensor II; 8—dowel rod; 9—filter paper; 10—permeable stone; 11—base; 12—base; 13—top cover; 14—rubber film.

Detailed ways

As shown in Figure 1, a pile-soil contact surface mechanical properties testing device, its structure includes a sealed pressure chamber (1), a hollow cylindrical soil sample (2), a solid cylindrical concrete pile sample (3), is characterized in that The solid cylindrical concrete pile sample (3) is prefabricated, and its diameter is equal to the inner diameter of the hollow cylindrical soil sample (2), and the two closely fit; the lower end of the concrete pile sample (3) is placed by the spring group (4) On the base (11), the upper end is connected to the pressure loading system through the dowel bar (8), and the stress sensor (5) and the displacement sensor I (6) are set on the dowel bar (8); the outer side of the concrete pile sample (3) It is a hollow cylindrical soil sample (2). The filter paper (9) and the permeable stone (10) are placed on the lower end of the soil sample (2) and placed on the base (12). The filter paper (9) and the permeable stone ( 10), the top cover (13) and the displacement sensor II (7); the stress sensor (5), the displacement sensor I (6), and the displacement sensor II (7) are connected to the data acquisition system.

A test method for a test device for mechanical properties of a pile-soil contact surface, comprising the following technical steps:

1. Prefabricate solid cylindrical concrete pile samples with different surface roughness according to the actual project (3);

2. Place the lower end of the concrete pile sample (3) on the base (11) through the spring group (4), and connect the upper end of the pile sample (3) to the stress loading system through the dowel bar (8), and apply a certain axial The stress causes the spring set (4) to compress;

3. Place the permeable stone (10) and filter paper (9) on the base (11) in sequence, place the sample preparation split valve, put the rubber membrane (14) on the inside of the sample preparation valve and fix the rubber membrane (14) with a rubber ring , put the mass of the soil sample in thirds into the rubber film (14) sequentially and reach the height required by the corresponding layer to make a hollow cylindrical soil sample (2);

4. Place the filter paper (9), permeable stone (10) and top cover (13) in sequence on the upper end of the hollow cylindrical soil sample (2), tighten the rubber film (14), and apply a certain amount of water to the hollow cylindrical soil sample (2). The negative pressure of the sample makes the sample stand up, and the sample preparation split valve is removed;

5. Displacement sensor I (6) is placed on the top of the pile sample (3), displacement sensor II (7) is placed on the top cover (13) of the soil sample (2), and the stress sensor (5), displacement sensor I ( 6), Displacement sensor II (7), pore pressure gauge, etc. are connected with the data acquisition system;

6. Saturation and consolidation: Select an appropriate method to saturate the soil sample. After the saturation is completed, select a drainage or non-drainage method according to the test requirements to apply confining pressure to consolidate the soil sample (2);

7. Shearing: After the consolidation is completed, a static (dynamic) axial stress is applied to the upper end of the pile sample (3), and the test begins; the soil sample (2) is only subjected to the confining pressure at the beginning of the test without axial stress effect, the soil remains stationary; under the joint action of the axial stress and the reaction force of the lower end spring group (4), the pile sample (3) moves vertically, due to the rough surface of the pile sample (3), the pile test Sample (3) drives the soil on the side of the pile to move vertically. The magnitude of the two movements is different, and its value can be obtained by measuring the displacement sensor I (6) and the displacement sensor II (7) and taking the difference between the two. The volume deformation and pore water stress changes caused by the vertical movement of the soil sample (2) are obtained by measuring the pore pressure and the like. The test stops when the axial displacement (or pore water pressure) reaches the corresponding failure standard;

8. By analyzing the test data, the stress-strain relationship of the pile-soil contact surface, the relative displacement (settlement) of the pile-soil, the volume deformation of the soil, etc. can be obtained, which can be used for the pile sinking process, the use stage of the pile, and drainage and non-drainage. The design of pile foundation settlement and pile side friction resistance under the two working conditions provides a reference.

Claims (2)

1. a stake mechanics characteristic of soil contact face proving installation, is comprised of sealing load chamber, hollow cylinder soil sample, solid cylinder concrete-pile sample, it is characterized in that: the diameter of concrete-pile sample equates with the internal diameter of hollow cylinder soil sample, and both fit tightly; Concrete-pile sample lower end is placed on base by groups of springs, and upper end is connected with stress loading system by transmission rod, and strain gauge and displacement transducer I are set on transmission rod; Concrete-pile sample outside is hollow cylinder soil sample, and soil sample lower end is placed filter paper, permeable stone and is placed on pedestal, and soil sample upper end is placed filter paper, permeable stone, top cover and displacement transducer II successively; Strain gauge, displacement transducer I, displacement transducer II are connected with data acquisition system (DAS) respectively;

The diameter of described solid cylinder concrete-pile sample is 10cm, high 55cm; The internal diameter of hollow cylinder soil sample is 10cm, external diameter 30cm, high 50cm.

2. the method for testing of a kind of Pile-soil contact face mechanical property testing device according to claim 1, its technical step comprises:

(1) by the filled circles column concrete-pile sample of the actual prefabricated different surface roughness of engineering;

(2) concrete-pile sample lower end is placed on base by groups of springs, stake sample upper end is connected with stress loading system by transmission rod, applies certain axial stress and makes groups of springs compression;

(3) on base, place successively permeable stone and filter paper, place sample preparation and split valve, rubber membrane is enclosed within to sample preparation and splits valve inner side and with rubber band, rubber membrane fixed, soil sample quality trisection is added in rubber membrane successively and reach the desired height of equivalent layer and make hollow cylinder soil sample;

(4) in hollow cylinder soil sample upper end, place successively filter paper, permeable stone and top cover, tighten rubber membrane, hollow cylinder soil sample is applied to certain negative pressure sample can be stood, remove sample preparation and split valve;

(5) displacement transducer I is placed on a sample upper end, and displacement transducer II is placed on soil sample top cover, presses meter to be connected with data acquisition system (DAS) in strain gauge, displacement transducer I, displacement transducer II, hole;

(6) saturated and fixed: choosing suitable way, to carry out soil sample saturated, after saturated completing by test demand select draining or not drainage pattern apply confined pressure and make soil solidifying;

(7) shear: after fixed completing, in stake sample upper end, apply quiet, moving axial stress, on-test; Soil sample is only subject to confined pressure effect not to be subject to axial stress effect when on-test, and it is motionless that the soil body keeps; Under the acting in conjunction of axial stress and lower end groups of springs counter-force, stake sample is vertically being moved, because driving the stake side soil body, stake rough surface stake sample produces vertical movement, what the two moved varies in size, and the measurement that its value can be by displacement transducer I and displacement transducer II the difference of getting the two obtain; Soil sample produces the vertical variation that causes cubic deformation and pore water stress mobile time and by measured hole, presses and obtain; When axial displacement reaches corresponding criterion of failure, test and stop;

(8) analytical test data, can obtain the strain-stress relation of Pile-soil contact face, the cubic deformation of the relative displacement of Pile Soil, the soil body.

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