CN107103168A - Foundation pit side-wall soil-baffling structure design method - Google Patents

Abstract

The invention discloses a method for designing a retaining structure of a side wall of a foundation pit, relating to a method for designing a retaining structure. In order to solve the problem that the existing retaining structure design model does not consider the beneficial effect of the soil resistance behind the retaining structure on the retaining structure and the effect of the precompressed stress introduced into the soil body at the same time, resulting in the excessive amount of retaining structure materials. The present invention firstly calculates the value of active earth pressure and draws a mark to establish a simplified diagram of the model; then mirrors the pressure value of the active earth pressure P reduced by 3:1 in the simplified diagram of the model to the side of the bolt spring support, removes the pre-pressure and then Remove the soil pressure or soil resistance on the side of the soil; collect the concentrated force according to the sharing interval to determine the vertical row distance of the anchor bolts at the centroid or center point of the trapezoidal line; according to the model diagram of removing the soil side soil pressure or soil resistance Determine the anchor bolt preload concentration formed by the vertical row spacing and the action position to design the equivalent simplified diagram of the anchor preload concentration force; then design the retaining structure according to the vertical foundation beam. The invention is suitable for the soil retaining structure design of the side wall of the foundation pit.

Description

Design Method of Soil Retaining Structure on Side Wall of Foundation Pit

technical field

The invention relates to a soil retaining structure design method.

Background technique

The soil retaining structure on the side wall of the deep foundation pit is used temporarily during the construction period, and its material consumption is too much, and the man-hour cost is no less than that of the underground foundation project. The root cause of the redundant consumption of these resources is that a suitable design method has not been found. The main problem is that the effect of preload cannot be considered during the implementation of the operation. Even if the prestressed bolt support is used, the slippage of the soil wedge due to the stress of the applied preload transmitted from the retaining structure to the soil is not taken into account. There are no quantitative calculation and analysis results. For example, the design model of the anchor retaining structure that is commonly used does not consider: when the anchor at the end of the anchor applies preload to the retaining structure, the beneficial effect of the soil resistance behind the retaining structure on the retaining structure and the simultaneous introduction of soil The precompression stress in the body produces three stress increments on the limit equilibrium slip surface of the soil wedge: normal stress, shear stress, and shear strength increment. Since the horizontal compressive stress is equal and uniformly distributed within the unit body formed by the sliding surface of the soil wedge, there are three stress increments after transformation to balance the self-weight stress increment of the soil in the active limit equilibrium state. The lateral preload can also be regarded as a lateral constraint force, which can constrain the soil to be in an active limit equilibrium state. Due to the inclusion of the soil impedance and shear strength increment behind the retaining structure, the schematic diagram and design method of the existing retaining structure model have been changed.

Contents of the invention

The present invention solves the problem that the existing retaining structure design model does not consider the beneficial effect of the soil resistance behind the retaining structure on the retaining structure and the effect of precompression stress introduced into the soil body at the same time, resulting in excessive use of retaining structure materials.

The method for designing the retaining structure of the side wall of the foundation pit includes the following steps:

Step 1. Calculate the active earth pressure value and draw the mark, and establish the model diagram; in the model diagram, one side of the retaining structure is the soil side, and the other side of the retaining structure is equipped with a number of unidirectional bearing preloaded anchor rods Spring support and anchor rod, one-way bearing preloaded anchor rod The spring support connects the anchor rod to apply a preload Npi1 to the retaining structure;

Step 2: Mirror the pressure value of the active earth pressure P reduced by 3:1 in the model diagram to the side of the bolt spring support, remove the pre-pressure Npi1, and remove the earth pressure or soil resistance on the soil side to obtain the removed soil Simplified model diagram of soil pressure or soil resistance on the side of the body;

Step 3. Knowing that the preload value that the bolt can exert is equal to the trapezoidal line load in the model diagram, the concentrated force Npi2 is collected according to the sharing interval; and then the centroid or center point of the trapezoidal line load is determined to obtain the Row spacing;

Step 4, according to the simplified model diagram of soil side soil pressure or soil resistance force removed, determine the anchor preload concentration force formed by the anchor along the vertical row distance and the action position to design the equivalent simplified diagram of the anchor preload concentration force; then press The retaining structure is designed with vertical foundation beams and slabs.

Further, the one-way load-bearing preloaded bolt spring support described in step 1 includes a support point, a support rod and a spring; one end of the support rod is fixed by the support point, and the other end of the support rod is connected to one end of the spring, and the spring The other end of the anchor rod is connected to the anchor rod, and the preload is applied to the retaining structure by the anchor rod.

The present invention has the following beneficial effects:

Under the action of the uniformly distributed load on the ground and the self-weight of the soil, the distribution of earth pressure on one side of the retaining structure on the side wall of the deep foundation pit is shown in Figure 1, but the bolt support node on the other side corresponding to Figure 1 in the present invention has two differences. The support of the model sketch used in the past: 1. The anchor rod in the soil layer is accompanied by preload when it is tensioned and anchored and bears the load. The spring support in the sketch is attached with a preload Npi, which acts on the retaining structure. 2. Under the action of pre-pressure, the retaining structure moves to the side of the soil body, and the anchor rod support will follow up and move without pulling, which is shown as disengagement on the schematic diagram. When it is connected under the action of earth pressure to generate displacement, it can support (pull). This one-way support (pull), and the bearing that can preload is called again: one-way bearing preloading anchor rod spring bearing.

At the same time, the present invention has been considered at the beginning of the design, the beneficial effect of the soil resistance behind the retaining structure on the retaining structure, the precompression stress introduced into the soil body at the same time, and the generation of three stresses on the limit equilibrium slip surface of the soil wedge increment. The preload uniform force of the spring support in the design of the present invention is one-third of the original soil side active earth pressure uniform force P, and it also has a theoretical basis after demonstration. Like this makes according to the present invention design foundation pit side wall soil retaining structure, can greatly save the soil retaining structure material consumption on the basis of guaranteeing the soil retaining ability of design requirement, just it is aimed at the bolt consumption item, utilizes the present invention just can The amount of bolts is reduced by more than 50%.

Description of drawings

Fig. 1 is a schematic diagram of the soil retaining model of the side wall of the foundation pit; in the figure: 1 is the soil retaining structure; 2 is the spring support of the pre-stressed anchor rod (one-way bearing); 3 is the elevation of the bottom of the foundation pit;

Fig. 2 is a schematic diagram of the soil retaining model of the side wall of the foundation pit after the bolt is removed to apply preload to the soil retaining structure;

Fig. 3 is the model diagram of removing soil side soil pressure or soil resistance;

Figure 4 is the equivalent schematic diagram of the preloaded concentrated force of the designed anchor:

Figure 5 is a schematic diagram of the anchor support node.

detailed description

Specific Embodiment 1: This embodiment is described in conjunction with FIG. 1 to FIG. 4 ,

The method for designing the retaining structure of the side wall of the foundation pit includes the following steps:

Step 1, calculate the active earth pressure value and draw the mark, establish the model diagram, as shown in Figure 1; in the model diagram, one side of the soil retaining structure 1 is the soil side, and the other side of the soil retaining structure 1 (Fig. The left side of the soil retaining structure in 1) is provided with a number of unidirectional bearing preloaded anchor rod spring bearings 2 and anchor rods, and the unidirectional load bearing preloaded anchor rod spring bearings 2 are connected to the anchor rods, and the anchor rods apply pressure to the soil retaining structure 1. Prepressure Npi1 (Npi shown in Figure 1); Note: The active earth pressure value in Figure 1 is the earth pressure distribution diagram when the initial zero preload is present;

Step 2: Mirror the pressure value of active earth pressure P reduced by 3:1 in the model diagram to the side of the bolt spring support, remove the pre-pressure Npi1, as shown in Figure 2, and then remove the soil side (retaining structure The earth pressure or soil resistance on the right side), and the simplified model diagram of the soil side soil pressure or soil resistance is obtained, as shown in Figure 3.

Step 3. It is known that the preload value that can be applied by the bolt is equal to the trapezoidal line load of the model diagram shown in Figure 3, and the concentrated force Npi2 (Npi shown in Figure 4) is collected according to the sharing interval; and then the trapezoidal line is determined The centroid or center point of the load can be used to obtain the vertical row distance of the bolt;

Step 4. According to the model diagram 3 with the side soil pressure or soil resistance removed, determine the anchor preload concentration formed by the anchor along the vertical row distance and the action position to design the equivalent simplified diagram of the anchor preload concentration, as shown in As shown in Figure 4; then design the retaining structure according to the vertical foundation beam slab.

The one-way load-bearing preload anchor rod spring support 2 described in step 1 includes a support point 2-1, a support rod 2-2 and a spring 2-3; one end of the support rod 2-2 passes through the support point 2-1 Fixed, the other end of the support rod 2-2 is connected to one end of the spring 2-3, and the other end of the spring 2-3 is connected to the anchor rod, and the anchor rod applies preload to the soil retaining structure 1, when the soil retaining structure 1 is facing the soil side When moving, the anchor rod does not pull the load. When the retaining structure 1 moves to the side of the support, the anchor rod pulls the load, which is called one-way load.

Demonstration to the design method of the present invention:

1. From the geotechnical test, the geometric relationship between the envelope of Coulomb shear strength and the tangent point of the Mohr stress circle is τ= _τf ; the stress formula (1) and (2) under the limit equilibrium state of the soil can be written:

Simultaneous formula (1), (2) can be derived:

Under the condition of limit equilibrium state, the relationship between soil shear strength and principal stress is a linear function, and the differential and increment are:

dτ _f = Δτ _f ; dσ = Δσ (5)

Formulas (3), (4) are derived and differentiated from formula (5a) to σ ₁ and σ ₃ respectively to obtain the incremental formula:

Equations (6) and (7) can be written in component form according to the principal compressive stress increment.

2. The horizontal angle and normal stress formula of the limit equilibrium surface of the soil mass:

From formula (8), (9) get formula:

3. Assume that the soil on the side wall of the foundation pit is subjected to a horizontal compressive stress increment Δσ ₃ ;

From formula (10):

Equation (11) is derived for τ _f :

Write the component formula of differential to get increment, from the formula: Δτ _f ＝ Δτ _f1 ＝ Δτ _f3 :

From formula (7), (13) get relational formula:

By the formula: have to:

Already have:

Equations (11), (14) are derived for σ ₃ :

Write the fractional expression of the differential to get the increment

Equation (13a), (16) and vector increment effect get:

Δσ ₁ = Δσ _1τ + Δσ ₁₃ = 3·Δσ ₁₃

Suppose: Δσ ₁ ＝σ ₁ ; σ ₃ ＝p; from formula (17):

P: earth pressure; q: uniform ground load; σ ₃ : small principal compressive stress; σ ₁ : large principal compressive stress.

Δσ ₁ : vertical compressive stress increment of soil unit (large principal compressive stress increment);

Δσ ₃ : horizontal compressive stress increment of soil unit (small principal compressive stress increment);

Δτ _f : shear strength increment on the limit equilibrium plane of the soil wedge;

Under the action of uniform ground load and soil self-weight, the distribution of earth pressure on one side of the retaining structure on the side wall of the deep foundation pit is shown in Figure 1, and the schematic and detailed diagram of the anchor support node 2 on the other side of Figure 1 is shown in Figure 5 As shown, there are two points different from the support of the model sketch used in the past in two points: 1. The anchor in the soil layer is accompanied by preload when it is tensioned and anchored and bears the load. On the spring support of the sketch Attached with preload Npi, acting on the retaining structure. 2. Under the action of pre-pressure, the retaining structure moves to the side of the soil body, and the anchor rod support will follow up and move without pulling, which is shown as disengagement on the schematic diagram. When it is connected under the action of earth pressure to generate displacement, it can support (pull). This one-way support (pull), and the bearing that can preload is called again: one-way bearing preloading anchor rod spring bearing.

Claims (2)

1. foundation pit side-wall soil-baffling structure design method, it is characterised in that comprise the following steps：

Step 1: calculating active earth pressure numerical value and mark of drawing, establishing model sketch；In model sketch, soil-baffling structure (1) Side be soil body side, soil-baffling structure (1) opposite side provided with some unidirectional carrying precompression anchor pole spring fastenings (2) and anchor pole, Unidirectional carrying precompression anchor pole spring fastening (2) connection anchor pole, anchor pole applies precompression Npi1 to soil-baffling structure (1)；

Step 2: active earth pressure P in model sketch is pressed into 3:The pressure value mirror image of 1 reduction is gone to anchor pole spring fastening side Fall precompression Npi1, then remove the soil pressure or earth resistance of soil body side, obtain removing the model of soil body lateral earth pressure or earth resistance Sketch；

Step 3: the precompressed force that known anchor pole can apply is equal to the trapezoidal line load of model sketch, collect by interval is shared Into concentrated force Npi2；The ladder track lotus centre of form or central point are determined again, draw anchor pole vertically array pitch；

Step 4: determining the anchor pole anchor pole that vertically array pitch is formed according to the model sketch for removing soil body lateral earth pressure or earth resistance Precompressed concentrated force and the active position design equivalent sketch of anchor pole precompressed concentrated force；Again soil-baffling structure is designed by vertical ground beam slab.

2. foundation pit side-wall soil-baffling structure design method according to claim 1, it is characterised in that unidirectional described in step one Carrying precompression anchor pole spring fastening (2) includes the strong point (2-1), pole (2-2) and spring (2-3)；Described pole (2-2) One end it is fixed by the strong point (2-1), one end of the other end connecting spring (2-3) of pole (2-2), spring (2-3) it is another One end connects anchor pole, and precompression is applied to soil-baffling structure (1) by anchor pole.